Gas sensor

Abstract

Gas sensor (100; 300), which includes: a sensor element (110) having a gas inlet (111) through which a gas of the object being measured is introduced, and which is suitable for detecting a concentration of a predetermined gas in the gas of the object being measured which flows through the gas inlet (111) into the sensor element (110); an inner protective cover (130; 330) having a sensor element chamber (124) inside it and in which one or more element chamber inlets (127; 227; 327) and one or more element chamber outlets (138a) are arranged, wherein a front end of the sensor element (110) and the gas inlet (111) are housed in the sensor element chamber (124), the element chamber inlet (127; 227; 327) is an inlet to the sensor element chamber (124) and the element chamber outlet (138a) is an outlet from the sensor element chamber (124); and an outer protective cover (140) arranged outside the inner protective cover (130; 330) and comprising a body section (143) having a cylindrical shape and in which one or more outer inlets (144a) are arranged, and a front end section (146) having a cylindrical shape with a bottom and an inner diameter smaller than the inner diameter of the body section (143), and in which one or more outer outlets (147a) are arranged, wherein the outer inlet (144a) is an inlet for the gas of the object being measured from the outside and the outer outlet (147a) is an outlet for the gas of the object being measured to the outside, wherein the outer protective cover (140) and the inner protective cover (130; 330) form a first gas chamber (122) as a space between the body section (143) of the outer protective cover (140) and the inner protective cover (130; 330) and a second gas chamber (126) as a space between the front end section (146) of the outer protective cover (140) and the inner protective cover (130; 330), the first gas chamber (122) being at least a section of a flow channel for the gas of the object being measured between the outer inlet (144a) and the element chamber inlet (127; 227; 327) and the second gas chamber (126) being at least a section of a flow channel for the gas of the object being measured between the outer outlet (147a) and the element chamber outlet (138a) and not directly connected to the first gas chamber (122), the element chamber inlet (127; 227; 327) is formed in the inner protective cover (130; 330) such that an element-side opening (129; 329) of the element chamber inlet (127; 227; 327), which is located next to the sensor element chamber (124), is open in a forward direction, which is a direction from a rear end to the front end of the sensor element (110), the outer inlet (144a) comprises a horizontal hole (144b) which is arranged in a lateral section of the body section (143) of the outer protective cover (140), the outer outlet (147a) is not located in a lateral section of the front end section (146) of the outer protective cover (140), wherein a cross-sectional area ratio S1 / S2, which is a ratio of a total cross-sectional area S1 [mm²] 2 ] of the outer inlet (144a) to a total cross-sectional area S2 [mm² 2] of the external outlet (147a) is 3 or more and 5.0 or less.

Description

Technical area

[0001] The present invention relates to a gas sensor. Technical background

[0002] An example of a known gas sensor detects the concentration of a specified gas, such as NOx or oxygen, in a sample gas, such as the exhaust gas from a car. PTL 1 describes, for example, a gas sensor comprising an outer and an inner protective cover. The inner protective cover has a cylindrical shape with a bottom and is positioned between the outer protective cover and a sensor element such that it covers the front end of the sensor element. The outer protective cover described in PTL 1 has several first outer gas holes through which the sample gas enters and second outer gas holes through which the sample gas flows out. Furthermore, according to PTL 1, the inner protective cover is designed in a specified shape such that the sensor element exhibits a fast response time in detecting gas concentrations while simultaneously maintaining high heat retention properties.

[0003] Document PTL 2 discloses a gas sensor with a protective element whose gas discharge performance is enhanced to improve the sensor's responsiveness and which effectively protects a sensing element from water adhesion. For this purpose, in a gas sensor, a base end portion of a second outer wall of an outer protective element is hermetically connected to a front end portion of a first inner wall of an inner protective element, satisfying the relationships A ≤ B < C < D and (0.6 × B) ≤ A. Here, A represents the total opening area of ​​a second outer hole of the outer protective element, B the total opening area of ​​a second inner hole of the inner protective element, C the total opening area of ​​a first inner hole, and D the total opening area of ​​a first outer hole.

[0004] Document PTL 3 discloses gas sensors designed to increase the flow across the sensor element. This ensures good measurement dynamics even when these gas sensors are exposed to exhaust gases with low flow velocities.

[0005] Document PTL 4 discloses a sensor device for detecting at least one property of a fluid medium, in particular the exhaust gas of an internal combustion engine. The sensor device comprises at least one protective housing for receiving at least one sensor element, wherein at least one flow path through which the fluid medium flows is provided within the protective housing. The flow path has at least three deflection points at which the fluid medium undergoes a change of direction by an angle of at least 90°. The sensor device exhibits high resistance to thermal shock combined with high dynamics of the sensor element. List of prior art documents Patent literature PTL 1: WO 2014 / 192 945 A1 PTL 2: DE 10 2014 221 027 A1 PTL 3: WO 2014 / 001 049 A1 PTL 4: DE 10 2013 221 255 A1 Disclosure of the invention

[0006] The response behavior of the gas sensor described above in detecting gas concentrations can vary depending on the orientation in which the gas sensor is mounted on a pipe or similar object. In other words, the response behavior can decrease depending on the orientation in which the gas sensor is mounted.

[0007] The present invention was made to solve the problem described above, and the main objective of the present invention is to reduce the influence of the orientation in which the gas sensor is mounted on the response behavior.

[0008] To solve the problem described above, the present invention uses the following configuration.

[0009] A gas sensor according to the present invention comprises: a sensor element having a gas inlet through which the gas of the object being measured is introduced, and which is suitable for detecting a concentration of a predetermined gas in the gas of the object being measured, which flows through the gas inlet into the sensor element; an inner protective cover having a sensor element chamber inside it, in which one or more element chamber inlets and one or more element chamber outlets are arranged, wherein a front end of the sensor element and the gas inlet are housed in the sensor element chamber, the element chamber inlet is an inlet to the sensor element chamber, and the element chamber outlet is an outlet from the sensor element chamber; and an outer protective cover arranged outside the inner protective cover and comprising a body section having a cylindrical shape and in which one or more outer inlets are arranged, and a front end section having a cylindrical shape with a bottom and an inner diameter smaller than the inner diameter of the body section, and in which one or more outer outlets are arranged, wherein the outer inlet is an inlet for the gas of the object being measured from the outside and the outer outlet is an outlet for the gas of the object being measured to the outside, wherein the outer protective cover and the inner protective cover form a first gas chamber as a space between the body section of the outer protective cover and the inner protective cover and a second gas chamber as a space between the front end section of the outer protective cover and the inner protective cover, the first gas chamber being at least a section of a flow channel for the gas of the object being measured between the outer inlet and the element chamber inlet, and the second gas chamber being at least a section of a flow channel for the gas of the object being measured between the outer outlet and the element chamber outlet and not directly connected to the first gas chamber, The element chamber inlet is designed in the inner protective cover such that an element-side opening of the element chamber inlet, located next to the sensor element chamber, is open in a forward direction, which is a direction from a rear end to the front end of the sensor element. the outer inlet comprises a horizontal hole located in a lateral section of the body section of the outer protective cover, and the outer outlet is not located in a lateral section of the front end section of the outer protective cover.

[0010] The gas flowing around the gas sensor enters the sensor through the outer inlet in the outer protective cover, passes through the first gas chamber and the element chamber inlet, and reaches the gas inlet in the sensor element chamber. The gas flowing through the element chamber outlet and the second gas chamber then exits through the outer outlet in the outer protective cover. Because the outer outlet in this gas sensor is not located in the lateral section of the front end of the outer protective cover, the influence of the sensor's orientation on its response is reduced. The reason for this is as follows.If an external outlet is formed in the lateral section of the front end of the outer protective cover, the response behavior can vary depending on the relationship between the position of the external outlet in the lateral section and the direction in which the gas under test flows around the external outlet. For example, if the external outlet in the lateral section is open parallel to and parallel with the upstream side of the direction in which the gas under test flows, the flow of the gas under test, which tends to escape from the space in the outer protective cover through the external outlet in the lateral section, is obstructed by the gas under test flowing around the external outlet, and the response behavior tends to decrease as a result.If the response behavior varies significantly depending on the relationship between the position of the external outlet in the lateral section and the direction in which the gas flows, the response behavior can, for example, decrease depending on the orientation in which the gas sensor is mounted. Since the external outlet of the gas sensor according to the invention is not located in the lateral section, the influence of the orientation of the gas sensor on the response behavior can be reduced. Furthermore, the external inlet of the gas sensor according to the present invention includes the horizontal hole formed in the lateral section of the body portion of the outer protective cover. Accordingly, the gas enters more easily through the external inlet than in the case where the external inlet does not include a horizontal hole, for example, where the external inlet includes only a vertical hole.This improves the response time. Furthermore, in the gas sensor according to the present invention, the element chamber inlet is designed within the inner protective cover such that its element-side opening, located next to the sensor element chamber, is open in the forward direction. Therefore, the gas of the sample, which has flowed out through the element-side opening, is neither blown against a surface of the sensor element (a surface other than the gas inlet) in a direction perpendicular to the surface of the sensor element, nor does it flow over a long distance along the surface of the sensor element before reaching the gas inlet. Accordingly, cooling of the sensor element can be reduced.Cooling of the sensor element is reduced by adjusting the direction in which the element-side opening is open, rather than by decreasing the flow rate and velocity of the gas being measured inside the inner protective cover. Therefore, the degree of slowdown in response time when detecting gas concentrations can be reduced. As a result, the sensor element exhibits both a fast response time and high heat retention properties.

[0011] Here, the expression "the element-side opening is open in the forward direction" encompasses a case in which the element-side opening is open parallel to the forward direction and a case in which the element-side opening is open obliquely to the forward direction of the sensor element, such that it is located closer to the sensor element with increasing distance in the forward direction of the sensor element. In the gas sensor according to the present invention, the external outlet can be formed in at least either a lower section of the front end section or a corner section between the side section and the lower section of the front end section. The external outlet can only be formed in either the lower section or the corner section.

[0012] In the gas sensor according to the present invention, the minimum path length P from the outer inlet to the gas inlet can be 5.0 mm or more and 11.0 mm or less. If the minimum path length P from the outer inlet to the gas inlet is 11.0 mm or less, the gas sample entering through the outer inlet reaches the gas inlet in a relatively short time. Accordingly, the response time for detecting gas concentrations is improved. If the minimum path length P is 5.0 mm or more, the occurrence of problems due to an insufficient minimum path length P can be reduced. Such problems include, for example, the risk of external toxins and water entering through the outer inlet easily reaching the sensor element, and the risk of the sensor element being easily cooled by the gas sample.

[0013] In the gas sensor according to the present invention, the minimum displacement P is preferably 10.5 mm or less, more preferably 10.0 mm or less, even more preferably less than 10.0 mm, even more preferably 9.5 mm or less, and even more preferably 9.0 mm or less. Reducing the minimum displacement P improves the response time in detecting gas concentrations. The minimum displacement P can be 7.0 mm or more or 8.0 mm or more.

[0014] In the gas sensor according to the present invention, the cross-sectional area ratio S1 / S2 is a ratio of a total cross-sectional area S1 [mm²]. 2 ] of the outer inlet to a total cross-sectional area S2 [mm² 2The cross-sectional area ratio of the outer outlet must be greater than 2.0 and less than 5.0. If the cross-sectional area ratio S1 / S2 is greater than 2.0, the total cross-sectional area S1 is relatively large, so the flow rate at which the gas enters through the outer inlet tends to increase. Furthermore, the total cross-sectional area S2 is relatively small, so the flow rate at which the gas tends to flow back out through the outer outlet tends to decrease. Consequently, the gas in the space around the gas inlet is easily replaced by the gas that has entered. This improves the response in detecting gas concentrations. If the total cross-sectional area S2 is too small, the flow rate at which the gas exits through the outer outlet decreases, and the response may correspondingly deteriorate.However, if the cross-sectional area ratio S1 / S2 is 5.0 or less, the decrease in response behavior can be suppressed.

[0015] In the gas sensor according to the present invention, the cross-sectional area ratio S1 / S2 is 3.0 or more, and preferably 3.4 or more. As the cross-sectional area ratio S1 / S2 increases, the response in detecting gas concentrations tends to improve.

[0016] In the gas sensor according to the present invention, the total cross-sectional area S1 can be 10 mm². 2 or more. The total cross-sectional area S1 can also be 30 mm². 2 or less. The total cross-sectional area S2 can be 2 mm². 2 or more. The total cross-sectional area S2 can also be 10 mm². 2 or less.

[0017] In the gas sensor according to the present invention, the inner protective cover can comprise a first element and a second element, and the element chamber inlet can be configured as a gap between the first element and the second element. Likewise, the first element can comprise a first cylindrical section surrounding the sensor element, and the second element can comprise a second cylindrical section with a diameter larger than the diameter of the first cylindrical section. The element chamber inlet can be a tubular gap between an outer circumferential surface of the first cylindrical section and an inner circumferential surface of the second cylindrical section. Brief description of the drawings Fig. Figure 1 is a schematic diagram showing how a gas sensor 100 is attached to a pipe 20. Fig. 2 is a sectional view along line AA according to Fig. 1. Fig. Figure 3 is a sectional view along line BB according to Fig. 2. Fig. 4 is a section view along line CC according to Fig. 3. Fig. 5 is a sectional view of an outer protective cover 140 along line CC according to Fig. 3. Fig. 6 is a view in the direction of arrow D according to Fig. 3. Fig. Figure 7 is an enlarged partial section view along line EE according to Fig. 4. Fig. Figure 8 is a sectional view showing the case in which external outlets 147a include several horizontal holes 147b. Fig. Figure 9 is a perspective view showing the case in which the outer outlets 147a include several horizontal holes 147b. Fig. Figure 10 is a sectional view showing the case in which the outer outlets 147a include corner holes 147d. Fig. Figure 11 is a sectional view showing element chamber inlets 227 according to a modification. Fig. Figure 12 is a vertical sectional view of a Gas Sensor 300 according to a modification. Fig. Figure 13 is a sectional view of an outer protective cover 140 according to experimental example 4. Fig. Figure 14 is an enlarged partial sectional view of a gas sensor 100 according to experimental example 5. Fig. Figure 15 is a graph showing the angular dependence of the reaction time of gas sensors according to experimental examples 1 to 5. Fig. Figure 16 is a graph showing the relationship between the flow velocity V and the reaction time in experimental examples 1 to 5. Description of embodiments

[0018] With reference to the drawings, embodiments of the present invention will now be described. Fig. Figure 1 is a schematic diagram showing how a gas sensor 100 is attached to a pipe 20. Fig. 2 is a sectional view along line AA according to Fig. 1. Fig. Figure 3 is a sectional view along line BB according to Fig. 2. Fig. 4 is a section view along line CC according to Fig. 3. Fig. 5 is a sectional view of an outer protective cover 140 along line CC according to Fig. 3. Fig. Figure 5 shows the structure, wherein a first cylindrical section 134, a second cylindrical section 136, a front end section 138 and a sensor element 110 are separated from the one shown in Fig. The structure shown in section 4 has been removed. Fig. 6 is a view in the direction of arrow D according to Fig. 3. Fig. Figure 7 is an enlarged partial section view along line EE according to Fig. 4.

[0019] As in Fig. As shown in Figure 1, the gas sensor 100 is attached to the pipe 20, which is an exhaust gas path from a combustion engine of a vehicle. The gas sensor 100 detects the concentration of at least one of the gas components, such as NOx and O2, of the exhaust gas emitted from the combustion engine as the test gas. As shown in Figure 1, the gas sensor 100 is attached to the pipe 20, which is an exhaust gas path from a combustion engine. Fig. As shown in Figure 2, the gas sensor 100 is attached to the tube 20 such that its central axis is perpendicular to the flow of the gas in the tube 20. It should be noted that the gas sensor 100 can be attached to the tube 20 such that its central axis is perpendicular to the flow of the gas in the tube 20 and has a predetermined angle (for example, 45°) with respect to the vertical direction.

[0020] As in Fig. As shown in Figure 3, the gas sensor 100 comprises a sensor element 110 for detecting the concentration of a predefined gas in the gas being measured, and a protective cover 120 for protecting the sensor element 110. The gas sensor 100 also includes a metal housing 102 and a metal nut 103 with an external thread on its outer circumferential surface. The housing 102 is inserted by a mounting element 22, which is welded to the tube 20 and has an internal thread on its inner circumferential surface. The nut 103 is screwed into the mounting element 22, thus securing the housing 102 to the mounting element 22. This secures the gas sensor 100 to the tube 20. The direction in which the gas being measured flows through the tube 20 is determined according to Figure 3. Fig. 3 the direction from left to right.

[0021] The sensor element 110 is a thin, elongated, plate-shaped element with a multilayered structure comprising several layers of an oxygen-ion-conducting solid electrolyte such as zirconium oxide (ZrO2). The sensor element 110 has a gas inlet 111 through which the gas to be measured is introduced and which is suitable for detecting the concentration of the specified gas (for example, NOx or O2) in the gas flowing into the sensor element 110 through the gas inlet 111. In the present embodiment, the gas inlet 111 is located at the front end face of the sensor element 110 (according to Fig. 3 of the base surface of the sensor element 110) is open. The sensor element 110 has a heating element arranged therein, the heating element having the function of heating the sensor element 110 in order to adjust its temperature. The structure of the sensor element 110 and the principle of detecting gas concentrations are generally known and are described, for example, in the unexamined Japanese patent application with publication number 2008-164411. The front end (according to Fig. 3 the lower end) and the gas inlet 111 of the sensor element 110 are arranged in a sensor element chamber 124. The direction from the rear end to the front end of the sensor element 110 (according to Fig. 3 the downward direction) is referred to as a forward direction.

[0022] The sensor element 110 comprises a porous protective layer 110a that at least partially covers its surface. In the present embodiment, the porous protective layer 110a is formed on five of the six side faces of the sensor element 110 and covers substantially the entire surface of a section of the sensor element 110 that is exposed in the sensor element chamber 124. More precisely, the porous protective layer 110a covers the entire front end face (according to Fig. 3 the underside) of the sensor element 110, in which the gas inlet 111 is formed. In addition, the porous protective layer 110a covers four side surfaces (according to Fig. 4. Top, bottom, left and right side surfaces) of the sensor element 110, which are connected to the front end surface of the sensor element 110 via areas near the front end surface of the sensor element 110. The porous protective layer 110a, for example, has the function of suppressing the formation of cracks in the sensor element 110 due to the adhesion of water or the like contained in the gas of the object being measured. The porous protective layer 110a also has the function of suppressing the adhesion of an oil component or the like contained in the gas of the object being measured to electrodes (not shown) on the surface of the sensor element 110. The porous protective layer 110a can be formed from a porous material such as a porous aluminum oxide material, a porous zirconium oxide material, a porous spinel material, a porous cordierite material, a porous titania material, or a porous magnesia material.The porous protective layer 110a can be produced, for example, by plasma spraying, screen printing, or dipping. Although the gas inlet 111 is also covered with the porous protective layer 110a, the gas in the test object can flow through the porous protective layer 110a and reach the gas inlet 111 because the porous protective layer 110a is made of a porous material. The porous protective layer 110a can have a thickness of, for example, 100 µm to 700 µm; however, the thickness is not limited to this range.

[0023] The protective cover 120 is arranged to surround the sensor element 110. The protective cover 120 comprises an inner protective cover 130, which has a cylindrical shape with a bottom and covers the front end of the sensor element 110, and an outer protective cover 140, which has a cylindrical shape with a bottom and covers the inner protective cover 130. A first gas chamber 122 and a second gas chamber 126 are formed as cavities defined between 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. The gas sensor 100, the sensor element 110, the inner protective cover 130, and the outer protective cover 140 have the same central axis. The protective cover 120 is made of a metal (for example, stainless steel).

[0024] The inner protective cover 130 comprises a first element 131 and a second element 135. The first element 131 includes a large-diameter section 132 with a cylindrical shape, a first cylindrical section 134 with a diameter smaller than that of the large-diameter section 132, and a stepped section 133 connecting the large-diameter section 132 to the first cylindrical section 134. The first cylindrical section 134 surrounds the sensor element 110. The second element 135 includes a second cylindrical section 136 with a diameter larger than that of the first cylindrical section 134; a front end section 138 with an inverted, truncated, conical shape extending in the forward direction (according to Fig. 3 of the downward direction) of the sensor element 110 is arranged in front of the second cylindrical section 136; and a connecting section 137 connects the second cylindrical section 136 to the front end section 138. A single element chamber outlet 138a (also referred to as the inner gas hole) is formed in a circular shape in the center of the lower surface of the front end section 138. The element chamber outlet 138a is connected to the sensor element chamber 124 and the second gas chamber 126 and serves as the outlet for the gas of the object being measured in the sensor element chamber 124. There are no particular restrictions regarding the diameter of the element chamber outlet 138a, and it can, for example, be from 0.5 mm to 2.6 mm. The element chamber outlet 138a is arranged in the forward direction of the sensor element 110 (according to the downward direction) of the sensor element 110 (according to the downward direction) of the sensor element 110; and a connecting section 137 connects the second cylindrical section 136 to the front end section 138. Fig. 3 of the downward direction) is arranged in front of the gas inlet 111. In other words, the element chamber outlet 138a (according to Fig. 3 below the gas inlet 111) further from the rear end of the sensor element 110 (the (not shown) according to Fig. 3 upper end of the sensor element 110) away from the gas inlet 111.

[0025] The large-diameter section 132, the first cylindrical section 134, the second cylindrical section 136, and the front end section 138 all share the same central axis. The inner circumferential surface of the large-diameter section 132 is in contact with the housing 102 such that the first element 131 is attached to the housing 102. The outer circumferential surface of the connecting section 137 of the second element 135 is in contact with the inner circumferential surface of the outer protective cover 140 and is attached to it, for example, by welding. Alternatively, the second element 135 can be attached by designing the front end section 138 such that its outer diameter is slightly larger than the inner diameter of a front end section 146 of the outer protective cover 140, and by press-fitting the front end section 138 into the front end section 146.

[0026] Several projecting sections 136a are formed on the inner circumferential surface of the second cylindrical section 136 such that they project towards and are in contact with the outer circumferential surface of the first cylindrical section 134. As shown in Fig. As shown in Figure 4, three projecting sections 136a are arranged at equal intervals in the circumferential direction of the inner circumferential surface of the second cylindrical section 136. The projecting sections 136a are essentially hemispherical. Because the projecting sections 136a are provided, the positional relationship between the first cylindrical section 134 and the second cylindrical section 136 can be easily determined by the projecting sections 136a. The projecting sections 136a preferably press the outer circumferential surface of the first cylindrical section 134 radially inward. In such a case, the positional relationship between the first cylindrical section 134 and the second cylindrical section 136 can be more reliably determined by the projecting sections 136a. The number of projecting sections 136a is not limited to three and can instead be two, four, or more.Preferably, three or more protruding sections 136a are provided such that the first cylindrical section 134 and the second cylindrical section 136 can be stably fixed.

[0027] An element chamber inlet 127 (see Fig. 3, Fig. 4 and Fig. 7) is formed in the inner protective cover 130. The element chamber inlet 127 is a gap between the first element 131 and the second element 135 and serves as an inlet for the gas of the object being measured into the sensor element chamber 124. More precisely, the element chamber inlet 127 is a tubular gap (gas flow channel) between the outer circumferential surface of the first cylindrical section 134 and the inner circumferential surface of the second cylindrical section 136. The element chamber inlet 127 comprises an outer opening 128 and an element-side opening 129. The outer opening 128 is an opening adjacent to the first gas chamber 122, which is a space in which the outer inlets 144a are arranged. The element-side opening 129 is an opening adjacent to the sensor element chamber 124, which is a space in which the gas inlet 111 is arranged. The outer opening 128 is located closer to the rear end of the sensor element 110 (according to Fig. 3 the upper end) as the element-side opening 129. Therefore, the element chamber inlet 127 serves as a flow channel on the path of the object gas from the outer inlets 144a to the gas inlet 111, extending from the side of the rear end (according to Fig. 3 of the upper side) to the side of the front end (according to Fig. 3 of the lower side) of the sensor element 110. Likewise, the element chamber inlet 127 is a flow channel that runs parallel to the direction of the sensor element 110 from front to back (according to Fig. 3 a vertical flow channel).

[0028] The element-side opening 129 is preferably positioned such that the distance A1 to the gas inlet 111 (see Fig. 7) -1.5 mm or more. The distance A1 can be 0 mm or more or more than 1.5 mm. The distance A1 is the distance in the direction of the sensor element 110 from front to back (according to Fig. 3 of the vertical direction), and the direction from front to back (according to Fig. 3 the upward direction) is defined as positive. More precisely, the distance A1 is the distance between a section of the edge of the opening of the gas inlet 111 that is closest to the element-side opening 129, and a section of the edge of the element-side opening 129 that is closest to the gas inlet 111 in the direction of the sensor element 110 from front to back. If the gas inlet according to Fig. 3. A horizontal hole is open to a side face of the sensor element 110, and if the element-side opening 129 is located between the upper and lower ends of the gas inlet opening, the distance A1 is defined as 0 mm. The upper limit of the distance A1 is determined by the shapes of the inner protective cover 130 and the sensor element chamber 124. Although there are no specific limitations, the distance A1 may be 7.5 mm or less, 5 mm or less, or 2 mm or less.

[0029] The element-side opening 129 is at a distance A2 (see Fig. 7) from the sensor element 110. The distance A2 is the distance in a direction perpendicular to the front-to-back direction of the sensor element 110. More precisely, the distance A2 is the distance between a section of the sensor element 110 that is closest to the element-side opening 129 and a section of the edge of the element-side opening 129 that is closest to the sensor element 110 in a direction perpendicular to the front-to-back direction of the sensor element 110. As the distance A2 increases, the element-side opening 129 moves further away from the sensor element 110, thus further reducing the cooling of the sensor element 110. The distance A2 is not subject to any particular limitations and can, for example, be from 0.6 mm to 3.0 mm. The element-side opening 129 is open parallel to the front-to-back direction of the sensor element 110 and in the back-to-front direction of the sensor element 110.In other words, the element-side opening 129 is according to the . Fig. 3 and Fig. 7 downwards (towards the area directly below). Therefore, the sensor element 110 is outside the area of ​​a virtual extension of the element chamber inlet 127 from the element-side opening 129 (according to the Fig. 3 and Fig. 7 of the area directly below the element-side opening 129). Accordingly, the gas of the object being measured, which flows out through the element-side opening 129, is not blown directly against the surface of the sensor element 110, and cooling of the sensor element 110 can be reduced.

[0030] The outer opening 128 is arranged at a distance A3 from the outer inlet 144a (see Fig. 7) The distance A3 is the distance in the direction of sensor element 110 from front to back (according to the Fig. 3 and Fig. 7 of the vertical direction). Similar to distance A1, the front-to-back direction is defined as positive. More precisely, distance A3 is the distance between a section of the edge of the opening of the outer inlet 144a that is closest to the outer opening 128 and a section of the edge of the outer opening 128 that is closest to the outer inlet 144a in the front-to-back direction of the sensor element 110. In the present embodiment, several outer inlets 144a are provided, comprising horizontal holes 144b and vertical holes 144c, and the upper ends of the horizontal holes 144b are located in the direction shown. Fig. 3 vertical direction closest to the outer opening 128. Therefore, the distance A3 to Fig. 7 the distance between the upper end of the horizontal hole 144b and the outer opening 128. If the outer opening 128 is, for example, in the position shown in the diagram Fig. Since the distance A3 lies in the vertical direction below the lower end of the vertical hole 144c, the distance A3 is the distance between the lower end of the vertical hole 144c and the outer opening 128 in the vertical direction. The outer opening 128 can be positioned such that the distance A3 is 0 or more (positive). Alternatively, the outer opening 128 can be positioned such that the distance A3 is 0 or less (negative). The distance A3 is not subject to any particular restrictions and can, for example, be -3 mm or more and 3 mm or less. Alternatively, the distance A3 can be -2 mm or more, -1 mm or more, 2 mm or less, or 1 mm or less.

[0031] The outer opening 128 is arranged at a distance A6 from the outer inlet 144a (see Fig. 7) The distance A6 is the distance in the direction perpendicular to the direction of the sensor element 110 from front to back (according to the Fig. 3 and Fig. 7 in the vertical direction). The distance A6 is the distance between the outer inlet 144a, which is closest to the outer opening 128 in the front-to-back direction of the sensor element 110, and the outer opening 128. In the present embodiment, the distance A6 is equal to half the difference between the inner diameter of a lateral section 143a and the inner diameter of the second cylindrical section 136. The distance A6 is not subject to any particular limitations and can, for example, be greater than 0 mm and 2.5 mm or less. Alternatively, the distance A6 can be 0.5 mm or more, 1 mm or more, 2.0 mm or less, or 1.5 mm or less.

[0032] The outer circumferential surface of the first cylindrical section 134 and the inner circumferential surface of the second cylindrical section 136 are separated in the radial direction of the first and second cylindrical sections 134 and 136 by a distance A4 at the element-side opening 129 and by a distance A5 at the outer opening 128. The outer circumferential surface of the first cylindrical section 134 and the inner circumferential surface of the second cylindrical section 136 are connected at a point where the protruding sections 136a are in contact with the first cylindrical section 134 (the point in the sectional view according to Fig. 4) by a distance A7 from each other. There are no particular restrictions regarding the distances A4, A5, and A7, and they can, for example, be from 0.3 mm to 2.4 mm. The opening ranges of the element-side opening 129 and the outer opening 128 can be adjusted by setting the distances A4 and A5. In the present embodiment, the distances A4, A5, and A7 are the same, and the element-side opening 129 and the outer opening 128 have the same opening range. In the present embodiment, the distance A4 (the distances A5 and A7) corresponds to half the difference between the outer diameter of the first cylindrical section 134 and the inner diameter of the second cylindrical section 136. The distance between the element-side opening 129 and the outer opening 128 in the vertical direction, i.e.,The length L of the element chamber inlet 127 in the vertical direction (which corresponds to the path length of the element chamber inlet 127) is not subject to any special restrictions and can, for example, be more than 0 mm and 6.6 mm or less. Alternatively, the length L can be 3 mm or more or 5 mm or less.

[0033] As in Fig. As shown in Figure 3, the outer protective cover 140 comprises a large-diameter section 142 having a cylindrical shape; a body section 143 having a cylindrical shape, connected to the large-diameter section 142 and having a smaller diameter than the large-diameter section 142; and the front end section 146, which has a cylindrical shape with a bottom surface and whose inner diameter is smaller than that of the body section 143. The body section 143 comprises the side section 143a, which has a side surface extending in the direction of the central axis of the outer protective cover 140 (as shown in Figure 3). Fig. 3 in the vertical direction), and a stepped section 143b, which defines the underside of the body section 143 and connects the lateral section 143a and the front end section 146. The central axes of the large-diameter section 142, the body section 143, and the front end section 146 coincide with the central axis of the inner protective cover 130. The inner circumferential surface of the large-diameter section 142 is in contact with the housing 102 and the large-diameter section 132 such that the outer protective cover 140 is attached to the housing 102. The body section 143 is arranged to cover the outer circumferences of the first cylindrical section 134 and the second cylindrical section 136. The front end section 146 is arranged such that it covers the front end section 138, and its inner circumferential surface is in contact with the outer circumferential surface of the connecting section 137.The front end section 146 comprises a lateral section 146a which has a side surface extending in the direction of the central axis of the outer protective cover 140 (according to . Fig. The outer protective cover 140 extends in the vertical direction (3) and has an outer diameter smaller than the inner diameter of the lateral section 143a, and a lower section 146b, which defines the underside of the outer protective cover 140. The front end section 146 is arranged in the forward direction in front of the body section 143. The outer protective cover 140 has several outer inlets 144a formed in the body section 143 (twelve outer inlets 144a in the present embodiment) and several outer outlets 147a formed in the front end section 146 (six outer outlets 147a in the present embodiment). The outer inlets 144a are inlets for the gas of the object being measured from the outside, and the outer outlets 147a are outlets for the gas of the object being measured to the outside.

[0034] The outer inlets 144a (also referred to as first outer gas holes) are holes that connect the area outside the outer protective cover 140 (the outside) with the first gas chamber 122. The outer inlets 144a comprise several horizontal holes 144b (six horizontal holes 144b in the present embodiment) formed at regular intervals in the lateral section 143a and several vertical holes 144c (six vertical holes 144c in the present embodiment) formed at regular intervals in the stepped section 143b (see Fig. 3, Fig. 4, Fig. 5 to Fig. 6) The outer inlets 144a (the horizontal holes 144b and the vertical holes 144c) are circular (perfectly circular) holes. There are no particular restrictions regarding the diameters of the twelve outer inlets 144a, and they may, for example, be from 0.5 mm to 2 mm. Alternatively, the diameters of the outer inlets 144a may be 1.5 mm or less. In the present embodiment, the horizontal holes 144b have identical diameters, and the vertical holes 144c have identical diameters. The diameter of the horizontal holes 144b is larger than that of the vertical holes 144c. As shown in the Fig. 4 and Fig. As shown in Figure 5, the outer inlets 144a are designed such that the horizontal holes 144b and the vertical holes 144c are arranged alternately at regular intervals in the circumferential direction of the outer protective cover 140. In other words, according to the Fig. 4 and Fig. 5 the line connecting the central axis of the outer protective cover 140 and the center of each horizontal hole 144b, and the line connecting the central axis of the outer protective cover 140 and the center of one of the vertical holes 144c that is next to this horizontal hole 144b, at an angle of 30° (360° / 12).

[0035] The outer outlets 147a (also referred to as second outer gas holes) are holes that connect the area outside the outer protective cover 140 (the exterior) with the second gas chamber 126. The outer outlets 147a comprise several vertical holes 147c (six vertical holes 147c in the present embodiment) formed at regular intervals in the circumferential direction of the outer protective cover 140 in the lower section 146b of the front end section 146 (see Fig. 3, Fig. 5 and Fig. 6) Unlike the outer inlets 144a, none of the outer outlets 147a are located in a lateral section of the outer protective cover 140 (in this case, a lateral section 146a of the front end section 146). The outer outlets 147a (in this example, the vertical holes 147c) are circular (perfectly circular) holes. There are no particular restrictions regarding the diameters of the six outer outlets 147a, and they may, for example, be from 0.5 mm to 2.0 mm. Alternatively, the diameters of the outer outlets 147a may be 1.5 mm or less. In the present embodiment, the outer outlets 147a have identical diameters. The diameter of the vertical holes 147c is smaller than the diameter of the horizontal holes 144b.

[0036] The outer protective cover 140 and the inner protective cover 130 form the first gas chamber 122, the space between the body section 143 and the inner protective cover 130. More precisely, the first gas chamber 122 is a space surrounded by the step section 133, the first cylindrical section 134, the second cylindrical section 136, the large-diameter section 142, the side section 143a, and the step section 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 also form the second gas chamber 126, the space between the front end section 146 and the inner protective cover 130. More precisely, the second gas chamber 126 is a space surrounded by the front end section 138 and the front end section 146.Since the inner circumferential surface of the front end section 146 is in contact with the outer circumferential surface of the connecting section 137, the first gas chamber 122 and the second gas chamber 126 are not directly connected to each other.

[0037] The manner in which the gas being measured flows inside the protective cover 120 when the gas sensor 100 detects the concentration of the specified gas is now described. First, the gas being measured, flowing through the tube 20, enters the first gas chamber 122 through at least one of the outer inlets 144a (one of the horizontal holes 144b and one of the vertical holes 144c). Next, the gas being measured exits the first gas chamber 122 through the outer opening 128 into the element chamber inlet 127, flows through the element chamber inlet 127, and enters the sensor element chamber 124 through the element-side opening 129. At least a portion of the gas being measured, which enters the sensor element chamber 124 through the element-side opening 129, reaches the gas inlet 111 of the sensor element 110.When the gas being measured reaches the gas inlet 111 and enters the sensor element 110, the sensor element 110 generates an electrical signal (a voltage or a current) corresponding to the concentration of the specified gas (e.g., NOx or O2) in the gas being measured. The gas concentration is determined based on this electrical signal. The gas being measured in the sensor element chamber 124 enters the second gas chamber 126 through the element chamber outlet 138a and flows out through at least one of the outer outlets 147a. The power of the heating element arranged in the sensor element 110 is controlled, for example, by a control unit (not shown) so that the temperature of the sensor element 110 is maintained at a specified temperature.

[0038] The protective cover 120 is preferably designed such that a minimum path length P from the outer inlets 144a to the gas inlet 111 is 5.0 mm or more and 11.0 mm or less when the gas of the object being measured flows inside the protective cover 120 in the manner described above. In the present embodiment, the minimum path length P is the length of the dashed line PL, i.e., the bold dot-dash line in Fig. 7. The minimum path length P is the length of the shortest path for the gas of the sample from the outer opening of the outer inlet 144a to the outer opening of the gas inlet 111. If several outer inlets 144a are present, the minimum path length P is the shortest of the minimum path lengths from the outer inlets 144a to the gas inlet 111. In the present embodiment, the outer protective cover 140 has the horizontal holes 144b and the vertical holes 144c as outer inlets 144a. As shown in Fig. As shown in Figure 3, the horizontal holes 144b are arranged above the vertical holes 144c and are closer to the outer opening 128 than the vertical holes 144c. Furthermore, in the present embodiment, the gas inlet 111, as shown in Figure 3, has a horizontal opening 144b. Fig. 4 shows a rectangular opening and is according to Fig. 4 is shifted upwards from the central axis of the inner protective cover 130 and the outer protective cover 140. Accordingly, in the present embodiment, the minimum path length from one of the six horizontal holes 144b, which according to Fig. The minimum path P of the protective cover 120 is located at the upper left, to the gas inlet 111. The minimum path from the horizontal hole 144b at the upper right is... Fig. The distance to gas inlet 111 is also the same (= minimum distance P). Fig. Figure 7 is an enlarged partial sectional view of an area around the horizontal hole 144b in the upper left. Fig. 4 along line EE. That in Fig. The horizontal hole 144b shown in point 7 is the horizontal hole 144b in the upper left corner. Fig. 4. According to Fig. 7 is the minimum path distance P, the length of the shortest path (the dashed line PL) from a terminal segment C1 (according to Fig. 7 the upper end section) of the outer opening of the horizontal hole 144b, wherein the end section C1 is closest to the outer opening 128, to an end section C2 (according to Fig. 7 the left end section) of the outer opening of the gas inlet 111. The minimum path length P is determined without taking the porous protective layer 110a into account. In Fig. For example, a section of the path represented by the dashed line PL from the element-side opening 129 to the gas inlet 111, without considering the porous protective layer 110a, is defined as a combination of the straight line connecting the element-side opening 129 to the lower left corner of the sensor element 110 and the straight line connecting the lower left corner of the sensor element 110 to the left end of the opening of the gas inlet 111. In the embodiment described above, the shape, position, etc., of the gas inlet 111 are such that the minimum path lengths from the four horizontal holes 144b, with the exception of the horizontal holes 144b at the top left and top right, are Fig. 4 to the gas inlet 111 are slightly larger than the minimum path length P. If the horizontal holes 144b, as in this case, have different minimum path lengths, the minimum path lengths of as many horizontal holes 144b as possible are preferably 5.0 mm or more and 11.0 mm or less. In the present embodiment, not only the minimum path length P of the horizontal holes 144b at the top left and top right in Fig. 4, but also the minimum path lengths of the other horizontal holes 144b 5.0 mm or more and 11.0 mm or less. In addition to the horizontal holes 144b, the minimum path length of at least one of the vertical holes 144c to the gas inlet 111 can also be 5.0 mm or more and 11.0 mm or less. Moreover, the minimum path lengths from the vertical holes 144c to the gas inlet 111 can all be 5.0 mm or more and 11.0 mm or less. Furthermore, the minimum path lengths from the outer inlets 144a (in this case the horizontal holes 144b and the vertical holes 144c) to the gas inlet 111 can all be 5.0 mm or more and 11.0 mm or less.

[0039] The sensor element 110 contained in the gas sensor 100 is preferably suitable for rapidly detecting changes in the concentration of the specified gas in the gas being measured. In other words, the sensor element 110 preferably exhibits a fast response time when detecting gas concentrations. If the minimum path length P, determined as described above, is short, at 11.0 mm or less, the gas entering through the external inlets 144a reaches the gas inlet 111 relatively quickly, and the response time improves accordingly. If the minimum path length P is 5.0 mm or more, the occurrence of problems due to an insufficient minimum path length P can be reduced.Such problems include, for example, the risk that external toxins and water, which have entered through the external inlets 144a, may easily reach the sensor element 110, and the risk that the sensor element 110 may be easily cooled by the gas of the object being measured, or that the power required of the heating element to prevent cooling of the sensor element 110 may increase. The minimum path length P is preferably 10.5 mm or less, more preferably 10.0 mm or less, even more preferably less than 10.0 mm, even more preferably 9.5 mm or less, and even more preferably 9.0 mm or less. A reduction in the minimum path length P improves the response time in detecting gas concentrations. The minimum path length P can be reduced, for example, by adjusting at least one of the distances A1 to A7 and the length L according to [reference missing]. Fig. 7 or by adjusting the diameters of the outer inlets 144a. The minimum travel distance P can be 7.0 mm or more or 8.0 mm or more.

[0040] The outer protective cover 140 is preferably structured such that a cross-sectional area ratio S1 / S2, which is a ratio of the total cross-sectional area S1 [mm²] 2 ] of the outer inlets 144a to the total cross-sectional area S2 [mm² 2The cross-sectional area ratio of the outer outlets 147a is greater than 2.0 and 5.0 or less. If the cross-sectional area ratio S1 / S2 is greater than 2.0, the total cross-sectional area S1 is relatively large, so the flow rate at which the gas under test enters through the outer inlets 144a tends to increase. Furthermore, the total cross-sectional area S2 is relatively small, so the flow rate at which the gas under test attempts to enter through the outer outlets 147a (the backflow) tends to decrease. Consequently, the gas under test in the space around the gas inlet 111 is easily replaced by the gas that has entered. This improves the response time in the detection of gas concentrations. If the total cross-sectional area S2 is too small, the flow rate at which the gas under test flows out through the outer outlets 147a decreases, and the response may correspondingly deteriorate.However, if the cross-sectional area ratio S1 / S2 is 5.0 or less, the decrease in response time can be suppressed. The cross-sectional area ratio S1 / S2 can be adjusted, for example, by setting the number of outer inlets 144a and outer outlets 147a, or by setting the cross-sectional areas of the outer inlets 144a and the outer outlets 147a.

[0041] In the present embodiment, the total cross-sectional area S1 is the sum of the total cross-sectional area of ​​the six horizontal holes 144b and the total cross-sectional area of ​​the six vertical holes 144c. The total cross-sectional area S2 is the sum of the cross-sectional areas of the six vertical holes 147c. The cross-sectional area of ​​each outer inlet 144a is the area of ​​the outer inlet 144a along a plane perpendicular to the direction in which the gas of the sample flows through the outer inlet 144a. In the present embodiment, the outer inlets 144a are circular holes, and the areas of the circular shapes serve as their cross-sectional areas. This also applies to the outer outlets 147a.If, for example, one of the outer inlets 144a is shaped such that its cross-sectional area is not regular, for example, such that its cross-sectional area differs on the inlet side (the outer surface of the outer protective cover 140) and the outlet side (the inner surface of the outer protective cover 140), the minimum value of the cross-sectional area is defined as the cross-sectional area of ​​this outer inlet 144a. This also applies to the outer outlets 147a.

[0042] The cross-sectional area ratio S1 / S2 is preferably 2.5 or more, more preferably 3.0 or more, and even more preferably 3.4 or more. As the cross-sectional area ratio S1 / S2 increases, the response time in detecting gas concentrations tends to improve. The total cross-sectional area S1 can be 10 mm². 2 or more. The total cross-sectional area S1 can also be 30 mm². 2or less. The total cross-sectional area S2 can be 2 mm². 2 or more. The total cross-sectional area S2 can also be 10 mm². 2 or less.

[0043] In the present embodiment, the outer protective cover 140 comprises the front end section 146, which has a cylindrical shape with a bottom and includes the side section 146a and the lower section 146b. The outer outlets 147a are not formed in the side section 146a of the outer protective cover 140. If the outer outlets 147a were formed in the side section 146a of the outer protective cover 140, the response behavior could vary depending on the relationship between the positions of the outer outlets 147a in the side section 146a and the direction in which the gas of the sample flows around the outer outlets 147a. Fig. 8 and Fig. Figures 9 and 9 are a sectional view and a perspective view, respectively, illustrating the case in which the outer outlets 147a include several horizontal holes 147b (in this example, three horizontal holes 147b) formed in the lateral section 146a. The figures shown in the Fig. 8 and Fig. The outer protective cover 140 shown in Figure 9 has outer outlets 147a comprising three horizontal holes 147b and three vertical holes 147c. The horizontal holes 147b and the vertical holes 147c are arranged alternately at equal intervals around the circumference of the outer protective cover 140. When the Fig. 8 and Fig. 9 shown outer protective cover 140, for example, the direction in which the gas of the object being measured flows is from left to right, as in Fig. 8, represented by arrow D1, is one of the horizontal holes 147b (according to Fig. 8 the leftmost horizontal hole 147b) parallel to the upstream side of the direction in which the gas of the object flows (according to Fig. 8 to the left), and opened to this. In this case, the flow of the object gas, which tends to flow through this horizontal hole 147b from the space inside the outer protective cover 140, is obstructed by the object gas flowing around this horizontal hole 147b, and the response tends to decrease as a result. In contrast, it is assumed that the direction in which the object gas flows, which in Fig. 8. The direction shown by arrow D2 is the direction shown. The direction of arrow D2 is that achieved by rotating the direction of arrow D1 according to Fig. 8 obtained by 60° clockwise direction and points to the midpoint between the left horizontal hole 147b and the upper right horizontal hole 147b in the lateral section 146a of the outer protective cover 140 according to Fig. 8. In this case, the horizontal holes 147b are arranged only at positions relatively far from the area around the location where the gas being measured is blown against the lateral section 146a in a direction perpendicular to it. Accordingly, the flow of the gas being measured, which tends to flow out through the horizontal holes 147b, is not significantly impeded, and the probability of a decrease in response is lower. If the response varies considerably depending on the relationship between the positions of the external outlets 147a in the lateral section 146a (in this example, the horizontal holes 147b) and the direction in which the gas being measured flows, the response may decrease depending on the orientation in which the gas sensor 100 is mounted (the angle of the outer protective cover 140 about the central axis in the direction of rotation).If, for example, the gas sensor 100 is mounted on the tube 20 in such a way that the gas being measured flows in the direction of arrow D1, the response time tends to decrease. However, since the outer outlets 147a of the gas sensor 100 according to the present embodiment are not formed in the lateral section 146a, the influence of the orientation in which the gas sensor 100 is mounted on the response time can be reduced. The influence of the orientation in which the gas sensor 100 is mounted on the response time is referred to as angular dependence. In the gas sensor 100 according to the present embodiment, the angular dependence can be reduced because the outer outlets 147a are not formed in the lateral section 146a.

[0044] The outer inlets 144a include the horizontal holes 144b formed in the lateral section 143a of the cylindrical body section 143 of the outer protective cover 140. Accordingly, the gas under test enters more readily through the outer inlets 144a than in the case where the outer inlets 144a do not include horizontal holes 144b, for example, in the case where the outer inlets 144a include only the vertical holes 144c. This improves the response time. The precise reason for this is as follows. The direction in which the gas under test enters through the vertical holes 144c (according to Fig. 3 the vertical direction) is perpendicular to the direction in which the gas of the object being measured flows (according to Fig. 3 the direction from left to right). Therefore, the gas under test is caused by a suction force (a negative pressure) generated when the gas under test flows out through the outer outlets 147a, causing it to enter through the vertical holes 144c. In contrast, the direction in which the gas under test enters through the horizontal holes 144b is quite close to the direction in which the gas under test flows. Therefore, due to its dynamic pressure, the gas under test readily enters through the horizontal holes 144b. Accordingly, the gas under test enters more readily through the horizontal holes 144b than through the vertical holes 144c, and the response can be improved if the outer inlets 144a encompass the horizontal holes 144b.

[0045] Furthermore, the element chamber inlet 127 of the gas sensor 100 is configured in the inner protective cover 130 such that the element-side opening 129 is open in the forward direction. Therefore, the gas of the sensor element that has flowed out of the element-side opening 129 is neither blown against a surface of the sensor element 110 (a surface other than the gas inlet 111) in a direction 110 perpendicular to the surface of the sensor element, nor does it flow a long distance along the surface of the sensor element 110 before reaching the gas inlet 111. Accordingly, cooling of the sensor element 110 can be reduced. Cooling of the sensor element 110 is reduced by adjusting the direction in which the element-side opening 129 is open, and not by reducing the flow rate and velocity of the gas of the sensor element inside the inner protective cover 130.Therefore, the extent of the decrease in response time when detecting gas concentrations can be reduced. As a result, the sensor element 110 exhibits a fast response time and simultaneously high heat retention properties.

[0046] Since the gas sensor 100 described in detail above, according to the present embodiment, has no external outlets 147a in the lateral section 146a of the front end section 146, the influence of the orientation in which the gas sensor 100 is mounted on its response behavior can be reduced. Furthermore, since the external inlets 144a comprise the horizontal holes 144b formed in the lateral section 143a of the body section 143, the response behavior is improved. Moreover, since the inner protective cover 130 has the element chamber inlet 127, which is configured such that the opening 129 is open in the forward direction, the sensor element 110 exhibits both a fast response behavior and high heat retention properties.

[0047] Since the minimum path length P from the outer inlets 144a to the gas inlet 111 is 11.0 mm or less, the response time for detecting gas concentrations is improved. Furthermore, since the minimum path length P is 5.0 mm or more, the occurrence of problems due to an insufficient minimum path length P can be reduced. Additionally, since the cross-sectional area ratio S1 / S2 is greater than 2.0 and 5.0 or less, the response time for detecting gas concentrations is further improved.

[0048] The present invention is in no way limited to the embodiment described above and can be implemented in different forms within the technical scope of the present invention.

[0049] The shape of the protective cover 120 is not limited, for example, to that described above. The shape of the protective cover 120 and the shapes, number, arrangement, etc., of the element chamber inlet 127, the element chamber outlet 138a, the outer inlets 144a, and the outer outlets 147a can be suitably modified, provided that no outer outlets 147a are formed in the lateral section 146a of the front end section 146, the outer inlets 144a include the horizontal holes 144b formed in the lateral section 143a of the body section 143, and the element-side opening 129 of the element chamber inlet 127 is open in the forward direction.Although, for example, the element chamber inlet 127 is configured as a gap between the first element 131 and the second element 135, the element chamber inlet is not limited to this and can be configured in any shape, as long as the element chamber inlet serves as an entrance to the sensor element chamber 124. The element chamber inlet can, for example, be a through-hole formed in the inner protective cover 130. If the element chamber inlet is a through-hole, it can be a vertical hole or a [missing information] according to [missing information]. Fig. The opening 129 on the element side is angled in the vertical direction, so that it opens in the forward direction. The element chamber inlet 127 is not limited to one and may instead be provided multiple times. The element chamber outlet 138a, the outer inlets 144a, and the outer outlets 147a are not limited to holes and may instead be gaps between elements forming the protective cover 120. These components may be provided in any number, as long as they are provided. Although the outer inlets 144a include the horizontal holes 144b and the vertical holes 144c, the vertical holes 144c may be omitted as long as the horizontal holes 144b are formed. Likewise, instead of or in addition to the vertical holes 144c, corner holes may be formed in the corner between the lateral section 143a and the stepped section 143b.There is no particular restriction regarding the outer outlets 147a, as long as they are not formed in the lateral section 146a of the front end section 146, i.e., as long as they do not include horizontal holes. The outer outlets 147a may include corner holes in the corner between the lateral section 146a and the lower section 146b, instead of or in addition to the vertical holes 147c. The element chamber inlet 127 and the element chamber outlet 138a may include one or more below a horizontal hole, a vertical hole, and a corner hole.

[0050] Now, examples of corner holes will be described. Fig. Figure 10 is a sectional view showing the case where the outer outlets 147a encompass several corner holes 147d. As in Fig. As shown in Figure 10, the outer outlets 147a formed in the front end section 146 comprise the corner holes 147d instead of the vertical holes 147c. These corner holes are formed in the corner between the side section 146a and the lower section 146b. Six corner holes 147d (in Fig. (Only four corner holes 147d are shown in Figure 10) are arranged at regular intervals in the circumferential direction of the outer protective cover 140. The corner holes 147d can be designed such that the angle 0 between the outer openings of the corner holes 147d (according to the enlarged view at the bottom left in Figure 10) is 0. Fig. 10 of a straight line a) and the floor area (lower surface) of the lower section 146b (according to the enlarged view below left in Fig. 10 a straight line b) lies in the range of 10° to 80°. In Fig. In the embodiment described above, the angle θ is 45°. Even if corner holes are formed in the corner between the lateral section 143a and the stepped section 143b, the angles θ between the outer openings of the corner holes and the bottom surface (the lower surface) of the lower section 146b can be in the range of 10° to 80°.

[0051] In the embodiment described above, the protruding sections 136a are formed on the inner circumferential surface of the second cylindrical section 136. However, the protruding sections 136a are not limited to this, as long as at least one protruding section is formed on either the outer circumferential surface of the first cylindrical section 134 or on the inner circumferential surface of the second cylindrical section 136 such that it projects towards and is in contact with each other. Furthermore, in the embodiment described above, the outer circumferential surface of the second cylindrical section 136 is, as in the Fig. 3 and Fig. Figure 4 shows the sections 136a formed inwards at the points where they are formed. However, it is not necessary for the outer circumferential surface of the second cylindrical section 136 to be recessed. The shape of the sections 136a is not limited to a hemispherical shape and can be any shape. It should be noted that it is not necessary for the sections 136a to be formed on the outer circumferential surface of the first cylindrical section 134 or on the inner circumferential surface of the second cylindrical section 136.

[0052] In the embodiment described above, the element chamber inlet 127 is a tubular gap between the outer circumferential surface of the first cylindrical section 134 and the inner circumferential surface of the second cylindrical section 136. However, the element chamber inlet 127 is not limited to this. For example, a recess (groove) can be formed in at least either the outer circumferential surface of the first cylindrical section or the inner circumferential surface of the second cylindrical section, and the element chamber inlet can be formed as a gap defined by the recess between the first cylindrical section and the second cylindrical section. Fig. Figure 11 is a sectional view showing element chamber inlets 227 according to a modification. Fig. 11 the outer circumferential surface of a first cylindrical section 234 and the inner circumferential surface of a second cylindrical section 236 are in contact with each other, and several recesses 234a (according to Fig. 11 Four recesses 234a) are formed at regular intervals in the outer circumferential surface of the first cylindrical section 234. The gaps between the inner circumferential surface of the second cylindrical section 236 and the recesses 234a serve as element chamber inlets 227.

[0053] In the embodiment described above, the element chamber inlet 127 is a flow channel that runs parallel to the direction of the sensor element 110 from front to back (according to Fig. 3 of the vertical direction). However, the element chamber inlet is not limited to this. The element chamber inlet can instead be designed, for example, as a flow channel that is oblique to the front-to-back direction, so that the flow channel gets closer to the sensor element 110 from back to front as the distance increases in the direction of the sensor element 110. Fig. Figure 12 is a vertical sectional view of a Gas Sensor 300 according to a modification in this case. Fig. 12 are components that correspond to those of gas sensor 100, are designated by the same reference symbols, and their exact description is omitted. As in Fig. As shown in Figure 12, the gas sensor 300 comprises an inner protective cover 330 instead of the inner protective cover 130. The inner protective cover 330 comprises a first element 331 and a second element 335. Instead of the first cylindrical section 134 that the first element 131 comprises, the first element 331 comprises a body section 334a with a cylindrical shape and a first cylindrical section 334b ​​with a diameter that decreases with increasing distance from the sensor element 110 from back to front. The end section of the first cylindrical section 334b ​​in the front-to-back direction of the sensor element 110 is connected to the body section 334a.Instead of the second cylindrical section 136 and the connecting section 137 comprising the second element 135, the second element 335 comprises a second cylindrical section 336 with a diameter that decreases with increasing distance from the sensor element 110 from back to front. The second cylindrical section 336 is connected to the front end section 138. The outer circumferential surface of the first cylindrical section 334b ​​and the inner circumferential surface of the second cylindrical section 336 are not in contact with each other, and the gap formed between them serves as the element chamber inlet 327. The element chamber inlet 327 has an outer opening 328, which is located adjacent to the first gas chamber 122, and an element-side opening 329, which is located adjacent to the sensor element chamber 124.The first cylindrical section 334b ​​and the second cylindrical section 336 are shaped such that the element chamber inlet 327 serves as a flow channel running obliquely from front to back, so that with increasing distance in the direction of the sensor element 110, the flow channel moves closer to the sensor element 110 (closer to the central axis of the inner protective cover 330). Similarly, the element-side opening 329 opens obliquely in the direction of front to back, so that with increasing distance in the direction of the sensor element 110, it moves closer to the sensor element 110 (see the enlarged view in Figure 1). Fig. 12) If the element chamber inlet 327 is an inclined flow channel, or if the element-side opening 329 is inclined as described above, the gas of the object being measured flows in the sensor element chamber 124 through the element-side opening 329 in a direction inclined from front to back relative to the direction of the sensor element 110. Accordingly, a similar result can be achieved as with the element chamber inlet 127 and the element-side opening 129 according to the embodiment described above. In other words, the gas of the object being measured is neither blown against the surface of the sensor element 110 (a surface other than the gas inlet 111) in a direction perpendicular to the surface of the sensor element 110, nor does it flow a long distance along the surface of the sensor element 110 before reaching the gas inlet 111. Accordingly, cooling of the sensor element 110 can be reduced. Fig. 12 The element chamber inlet 327 has a width that decreases with increasing distance from the sensor element 110 from back to front. Therefore, the opening area of ​​the element-side opening 329 is smaller than that of the outer opening 328. In other words, the element chamber inlet 327 is designed such that the above with reference to Fig. The distance A4 described in section 7 is smaller than the distance A5. When the gas under test enters through the outer opening 328 and flows out through the element-side opening 329, the gas under test accordingly flows out at a flow velocity that is higher than the velocity at which the gas under test enters. Therefore, the response time in the detection of gas concentrations can be improved. Although the opening range of the element-side opening 329 according to Fig. If the outer opening is 328 mm smaller than the opening, this feature is optional. For the gas sensor 300, according to the [document / reference]... Fig. In the modification shown in Figure 12, the distance A1 is the distance from the gas inlet 111 to the lower end of the element-side opening 329 in the vertical direction.

[0054] In the embodiment described above, the first gas chamber 122 is the only flow channel for the gas of the object being measured between the element chamber inlet 127 and the outer inlets 144a. However, the first gas chamber 122 is not limited to this, as long as it constitutes at least a section of the flow channel for the gas of the object being measured between the element chamber inlet 127 and the outer inlets 144a. For example, the protective cover 120 can, in addition to the inner protective cover 130 and the outer protective cover 140, include an intermediate protective cover arranged between the inner protective cover 130 and the outer protective cover 140, and the flow channel for the gas of the object being measured between the element chamber inlet 127 and the outer inlets 144a can comprise several gas chambers.Similarly, in the embodiment described above, the second gas chamber 126 is the only flow channel for the gas of the object being measured between the element chamber outlet 138a and the outer outlets 147a. However, the second gas chamber 126 is not limited to this, as long as the second gas chamber 126 is at least a section of the flow channel for the gas of the object being measured between the element chamber outlet 138a and the outer outlets 147a.

[0055] In the embodiment described above, the gas inlet 111 is located in the front end face of the sensor element 110 (according to Fig. 3 of the lower surface of the sensor element 110). However, the gas inlet 111 is not limited to this. The gas inlet 111 can, for example, be located in a side surface of the sensor element 110 (according to Fig. 4 of the upper, lower, left or right surface of the sensor element 110) must be open.

[0056] In the embodiment described above, the sensor element 110 comprises the porous protective layer 110a. However, it is not necessary for the sensor element 110 to comprise the porous protective layer 110a. Examples

[0057] Examples of gas sensors that have actually been manufactured are now described. Experimental examples 3 to 5 correspond to examples of the present invention, and experimental examples 1 and 2 correspond to comparative examples. The present invention is not limited to the following examples. [Experimental Example 1]

[0058] A gas sensor 100 according to experimental example 1 resembled the one in the Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. 7 Gas sensor 100 shown, with the exception that the outer outlets 147a, as in the Fig. 8 and Fig. Figure 9 shows the three horizontal holes 147b formed in the lateral section 146a and the three vertical holes 147c. The first element 131 of the inner protective cover 130 had a thickness of 0.3 mm and an axial length of 10.2 mm. The large-diameter section 132 had an axial length of 1.8 mm and an outer diameter of 14.4 mm, and the first cylindrical section 134 had an axial length of 8.4 mm and an outer diameter of 7.7 mm. The second element 135 had a thickness of 0.3 mm and an axial length of 11.5 mm. The second cylindrical section 136 had an axial length of 4.5 mm and an inner diameter of 9.7 mm, and the front end section 138 had an axial length of 4.9 mm. The base surface of the front end section 138 had a diameter of 3.0 mm.Regarding the element chamber inlet 127, the distance A1 was 0.59 mm, the distance A2 was 1.7 mm, the distance A3 was 3.1 mm, the distances A4, A5, and A7 were 1.0 mm, the distance A6 was 2.05 mm, and the length L was 4 mm. The element chamber outlet 138a had a diameter of 1.5 mm. The outer protective cover 140 had a thickness of 0.4 mm and an axial length of 24.35 mm. The large-diameter section 142 had an axial length of 5.85 mm and an outer diameter of 15.2 mm. The body section 143 had an axial length of 8.9 mm (an axial length from the upper end of body section 143 to the upper surface of step section 143b was 8.5 mm). The body section 143 had an outer diameter of 14.6 mm. The front end section 146 had an axial length of 9.6 mm and an outer diameter of 8.7 mm.The outer inlets 144a comprised six horizontal holes 144b with a diameter of 1 mm and six vertical holes 144c with a diameter of 1 mm. The horizontal holes 144b and the vertical holes 144c were arranged alternately at equal intervals (adjacent holes form an angle of 30°). The outer outlets 147a comprised three horizontal holes 147b with a diameter of 1 mm and three vertical holes 147c with a diameter of 1 mm. The horizontal holes 147b and the vertical holes 147c were arranged alternately at equal intervals (adjacent holes form an angle of 60°). The material of the protective cover 120 was SUS301S. The sensor element 110 of the gas sensor 100 had a width (according to ). Fig. 4 a length in the direction from left to right) of 4 mm and a thickness (according to Fig. 4 (a length in the vertical direction) of 1.5 mm. The porous protective layer 110a was a porous aluminum oxide body with a thickness of 400 µm. The minimum path length P was 11.4 mm. The total cross-sectional area S1 was 9.42 mm². 2 The total cross-sectional area S2 was 4.71 mm². 2 The cross-sectional area ratio S1 / S2 was 2.00. [Experimental Example 2]

[0059] A gas sensor 100 according to experimental example 2 was similar to the gas sensor 100 according to experimental example 1, except that the inner diameter of the first cylindrical section 134 of the first element 131 was 7.88 mm, which was larger than in experimental example 1. In experimental example 2, the distances A4, A5, and A7 were 0.61 mm, the distance A2 was 2.1 mm, the minimum path length P was 11.7 mm, and the total cross-sectional area S1 was 9.42 mm². 2 , the total cross-sectional area S2 4.71 mm 2and the cross-sectional area ratio S1 / S2 2.00. [Experimental Example 3]

[0060] A gas sensor 100 according to experimental example 3 was the one in the Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. Figure 7 shows a gas sensor 100. In experimental example 3, the outer outlets 147a did not include horizontal holes 147b, and the diameter of the vertical holes 147c was 1 mm, as in experimental example 1. The horizontal holes 144b had a diameter of 1.5 mm and were set back, so that the distance A3 was 0.84 mm. The remaining dimensions were the same as in experimental example 2. The minimum path length P was 10.0 mm, and the total cross-sectional area S1 was 15.32 mm². 2 , the total cross-sectional area S2 4.71 mm 2 and the cross-sectional area ratio S1 / S2 3.25. [Experimental Example 4]

[0061] A gas sensor 100 according to experimental example 4 was identical to the gas sensor 100 according to experimental example 3, except that the cross-sectional area of ​​the vertical holes 144c and the cross-sectional area of ​​the three vertical holes 147c were increased. More precisely, the vertical holes 144c and the vertical holes 147c were as shown in Fig. Figure 13 shows the outer protective cover 140 as having an arc shape extending in the circumferential direction, thus increasing its cross-sectional area. The vertical holes 144c and 147c were formed in an arc shape with a width of 1 mm. The six vertical holes 144c had a cross-sectional area of ​​2.4 mm². 2 The three vertical holes 147c also had a cross-sectional area of ​​2.4 mm². 2 The minimum path length P was 10.0 mm, the total cross-sectional area S1 was 25.03 mm². 2, the total cross-sectional area S2 7.21 mm 2 and the cross-sectional area ratio S1 / S2 is 3.47. [Experimental Example 5]

[0062] A gas sensor 100 according to experimental example 5 was correct with the exception that the horizontal holes 144b, as in Fig. Figure 14 shows that the sensors were located closer to the rear end than the outer opening 128, and the distance A3 was -0.16 mm, corresponding to the gas sensor 100 according to experimental example 3. The minimum path length P was 9.9 mm. Fig. 14. The minimum path length P for gas sensor 100 according to experimental example 5 was the length of the shortest path (the dashed line PL) from an end section Cl (according to Fig. 14 the lower end section) of the outer opening of the horizontal hole 144b, wherein the end section C1 was closest to the outer opening 128, to an end section C2 (according to Fig. 14 the left end section) of the outer opening of the gas inlet 111. The total cross-sectional area S1 was 15.32 mm² 2 , the total cross-sectional area S2 4.71 mm 2 and the cross-sectional area ratio S1 / S2 3.25. [Assessment of angle dependency]

[0063] The influence of the orientation of each gas sensor mounting, as shown in experimental examples 1 to 5, on the response behavior (the angular dependence) was evaluated. First, the gas sensor shown in experimental example 1 was mounted on a surface that was... Fig. 1 and Fig. 2. The gas sensor was attached to a pipe in the manner shown. The orientation of the attachment according to experimental example 1 was such that the gas under test flowed in the direction of arrow D1 according to Fig. The gas flowed through the tube at a velocity of V = 8 m / s. The gas used for measurement was obtained by mixing oxygen with ambient air to adjust the oxygen concentration. The gas was then forced to flow through the tube at a velocity of V = 8 m / s. The oxygen concentration of the gas flowing through the tube was varied from 22.9% to 20.2%, and the change in the sensor output over time was measured. The sensor output immediately before the change in oxygen concentration was defined as 0%, and the output at the point when it stabilized after the change in oxygen concentration was defined as 100%. The time interval from when the output exceeded 10% until it exceeded 90% was defined as the response time (in seconds) for gas concentration detection.The shorter the reaction time, the higher the sensitivity to changes in gas concentrations. The orientation of the gas sensor mounting, as shown in experimental example 1, was changed in several orientations, and the reaction time was measured in each orientation. More precisely, the reaction time was measured after the mounting orientation was changed to cause the gas being measured to flow in the direction of arrow D1, as shown in [reference missing]. Fig. With 8 defined as 0°, the orientation of the gas sensor mounting was changed from 0° to 360° by rotating the gas sensor around the central axis of the outer protective cover 140 in 30° increments, and the response time was measured in each mounting orientation. The orientation of the gas sensor mounting is the same at 0° and 360°. Each of the gas sensors according to experimental examples 2 to 5 was also mounted in different orientations, and the response time was measured in each mounting orientation. For the gas sensor according to experimental example 2, similar to experimental example 1, the mounting orientation was adjusted to cause the gas under test to flow in the direction of arrow D1 according to Fig. 8 is defined as 0°. In experimental examples 3 to 5, the orientation of the mounting to cause the gas under test to flow from top left to bottom right was determined according to Fig. 4 in a direction towards which the upper left horizontal hole 144b points Fig. 4 is open, parallel direction defined as 0°.

[0064] Fig. Figure 15 is a graph showing the angular dependence of the reaction time of each of the gas sensors according to experimental examples 1 to 5. As shown from Fig. As is clearly evident from Figure 15, the reaction time in experimental examples 1 and 2 varied considerably depending on the orientation of the gas sensor mounting. Therefore, the reaction time exhibited a high angular dependence. More precisely, in experimental examples 1 and 2, the reaction time increased periodically in intervals of essentially 120°. In experimental examples 1 and 2, the outer outlets 147a comprised three horizontal holes 147b formed in the lateral section 146a, and the horizontal holes 147b were arranged at equal intervals (of 120°) around the central axis of the outer protective cover 140. Therefore, when the mounting orientation was 0°, 120°, 240°, or 360°, one of the horizontal holes 147b was open parallel to and facing the upstream side of the direction in which the gas under test was flowing.Accordingly, in experimental examples 1 and 2, when the mounting was oriented at 0°, 120°, 240°, or 360°, the flow of the gas under test, which tended to flow out of the outer protective cover 140 through this horizontal hole 147b, was impeded by the gas under test flowing around this horizontal hole 147b, and the response behavior therefore tended to decrease. As shown in... Fig. As is clearly evident in Figure 15, the fluctuations in reaction time dependent on the orientation of the installation were considerably lower in experimental examples 3 to 5 than in experimental examples 1 and 2. Therefore, the angular dependence was low. This is presumably due to the fact that experimental examples 3 to 5 did not have external outlets 147a in the lateral section 146a. [Assessment of response behavior]

[0065] For each of the gas sensors according to experimental examples 1 to 5, the flow velocity V of the sample gas flowing through the tube was set to 1, 2, 4, 6, 8, and 10 m / s, and the response time [sec] was measured at each flow velocity V. The response time was measured in a similar manner to the response time measurement used to evaluate the angular dependence described above. When the flow velocity V = 8 m / s, as in the case described above for evaluating the angular dependence, the orientation of the mounting was varied from 0° to 360°, and the response time was measured multiple times at each mounting orientation. In addition, the oxygen concentration in the sample gas flowing through the tube was varied from 20.2% to 22.9% (a change reversed to that used in the evaluation of the angular dependence).In this case as well, the orientation of the mounting was varied similarly from 0° to 360°, and the reaction time was measured multiple times in each orientation. The average of all reaction times was defined as the reaction time for a flow velocity of V = 8 m / s. In the other cases (flow velocities V = 1, 2, 4, 6, and 10 m / s), the mounting orientation was not changed. The reaction time was measured after decreasing (from 22.9% to 20.2%) and increasing (from 20.2% to 22.9%) the oxygen concentration in the sample gas flowing through the tube, and the average of the reaction times was determined as the reaction time for each flow velocity V. The mounting orientation was set to 0° for experimental examples 1 and 2 and to 180° for experimental examples 3 to 5.

[0066] Table 1 shows the diameters and number of external inlets and outlets in the outer protective cover, the minimum path length P, the total cross-sectional areas S1 and S2, the cross-sectional area ratio S1 / S2 and the reaction time at each flow velocity V for experimental examples 1 to 5. Fig. Figure 16 is a graph showing the relationship between the flow velocity V and the reaction time in experimental examples 1 to 5. [Table 1] 1 Äußere Schutzschicht MinimaleWegstrecke P[mm] Total cross-sectional area S1 [mm 2 ] Total cross-sectional area S2 [mm 2 ] Querschnittsbereichsverhältnis S1 / S2 Reaktionszeit (Strömungsgeschwindigkeit 1 m / s)[sek] Reaktionszeit (Strömungsgeschwindigkeit 2 m / s)[sek] Reaktionszeit (Strömungsgeschwindigkeit 4 m / s)[sek] Reaktionszeit (Strömungsgeschwindigkeit 6 m / s)[sek] Reaction time (flow velocity 8 m / s) [sec] Reaction time (flow velocity 10 m / s) [sec] Outer entrance Outer outlet Experimental Example 1 Diameter 1 mm · 6 (horizontal hole) Diameter 1 mm · 6 (vertical hole) Diameter 1 mm · 3 (horizontal hole) Diameter 1 mm · 3 (vertical hole) 11,4 9,42 4,71 2,00 6,1 3,7 1,8 1 0,6 0,4 Experimental Example 2 Diameter 1 mm · 6 (horizontal hole) Diameter 1 mm · 6 (vertical hole) Diameter 1 mm · 3 (horizontal hole) Diameter 1 mm · 3 (vertical hole) 11,7 9,42 4,71 2,00 9,6 6,5 2,8 1,6 1 0,45 Experimental Example 3 Diameter 1.5 mm · 6 (horizontal hole) Diameter 1 mm · 6 (vertical hole) Diameter 1 mm · 6 (vertical hole) 10,0 15,32 4,71 3,25 5,7 3 1,2 0,5 0,3 0,2 Experimental Example 4 Diameter 1.5 mm - 6 (horizontal hole) 2.4 mm 2 6 (vertical hole) 2.4 mm 2 · 3 (vertical hole) 10,0 25,03 7,21 3,47 5,2 2,6 1,1 0,4 0,3 0,2 Experimental Example 5 Diameter 1.5 mm · 6 (horizontal hole) Diameter 1 mm · 6 (vertical hole) Diameter 1 mm · 6 (vertical hole) 9,9 15,32 4,71 3,25 5,3 2,6 1,1 0,5 0,3 0,2

[0067] Table 1 and Fig.Figure 16 shows that the reaction time for each of experimental examples 1 to 5 increased with a decrease in flow velocity V. At each flow velocity V, the reaction times for experimental examples 3 to 5 were shorter than those for experimental examples 1 and 2. More precisely, the reaction times for experimental examples 3 to 5, where the minimum path length P was 11.0 mm or less and the cross-sectional area ratio S1 / S2 was greater than 2.0, were shorter than those for experimental examples 1 and 2, where the minimum path length P was greater than 11.0 mm and the cross-sectional area ratio S1 / S2 was 2.0 or less. For experimental examples 1 to 5, the reaction time decreased as the minimum path length P decreased.A comparison between experimental examples 3 and 5, which had the same cross-sectional area ratio S1 / S2 and different minimum path lengths P, shows that the minimum path length P is preferably less than 10.0 mm. In experimental examples 1 to 5, the reaction time decreased as the cross-sectional area ratio S1 / S2 increased. A comparison between experimental examples 3 and 4, which had the same minimum path length P and different cross-sectional area ratios S1 / S2, shows that the cross-sectional area ratio S1 / S2 is preferably 3.4 or higher.A comparison between experimental examples 2 to 5, in which the first cylindrical sections 134 of the first elements 131 had the same inner diameter and in which the protective covers 120 had relatively similar shapes, shows that the differences between the reaction time of experimental example 2 and the reaction times of experimental examples 3 to 5 increased with a decrease in the flow velocity V. This indicates that, particularly at a low flow velocity V (of 4 m / s or less), the reaction time-reducing effect achieved by setting the minimum displacement P to 11.0 mm or less or by setting the cross-sectional area ratio S1 / S2 to more than 2.0 is likely enhanced.

[0068] The present application claims priority over Japanese patent application No. 2016-121008, filed on June 17, 2016, the entire contents of which are incorporated herein by reference. Industrial applicability

[0069] The present invention is applicable to gas sensors that detect the concentration of a specific gas such as NOx in a measurement gas such as the exhaust gas of an automobile.

Claims

Gas sensor (100; 300) comprising: a sensor element (110) having a gas inlet (111) through which a gas to be measured is introduced, and which is suitable for detecting a concentration of a predetermined gas in the gas to be measured flowing into the sensor element (110) through the gas inlet (111); an inner protective cover (130; 330) having a sensor element chamber (124) inside it, in which one or more element chamber inlets (127; 227; 327) and one or more element chamber outlets (138a) are arranged, wherein a front end of the sensor element (110) and the gas inlet (111) are housed in the sensor element chamber (124), the element chamber inlet (127; 227; 327) is an inlet to the sensor element chamber (124), and the element chamber outlet (138a) is a The outlet is from the sensor element chamber (124); and an outer protective cover (140) that is outside the inner protective cover (130;330) and comprises a body section (143) having a cylindrical shape and in which one or more external inlets (144a) are arranged, and a front end section (146) having a cylindrical shape with a bottom and an inner diameter smaller than the inner diameter of the body section (143), and in which one or more external outlets (147a) are arranged, wherein the external inlet (144a) is an inlet for the gas of the object being measured from the outside and the external outlet (147a) is an outlet for the gas of the object being measured to the outside, wherein the outer protective cover (140) and the inner protective cover (130; 330) comprise a first gas chamber (122) as the space between the body section (143) of the outer protective cover (140) and the inner protective cover (130; 330) and a second gas chamber (126) as the space between the front end section (146) of the outer protective cover (140) and the inner protective cover (130;330), the first gas chamber (122) is at least a section of a flow channel for the gas of the object being measured between the outer inlet (144a) and the element chamber inlet (127; 227; 327), and the second gas chamber (126) is at least a section of a flow channel for the gas of the object being measured between the outer outlet (147a) and the element chamber outlet (138a) and is not directly connected to the first gas chamber (122), the element chamber inlet (127; 227; 327) is formed in the inner protective cover (130; 330) such that an element-side opening (129; 329) of the element chamber inlet (127; 227;327), which is located next to the sensor element chamber (124), is open in a forward direction, which is a direction from a rear end to the front end of the sensor element (110), the outer inlet (144a) comprises a horizontal hole (144b) which is arranged in a lateral section of the body section (143) of the outer protective cover (140), the outer outlet (147a) is not arranged in a lateral section of the front end section (146) of the outer protective cover (140), wherein a cross-sectional area ratio S1 / S2, which is a ratio of a total cross-sectional area S1 [mm2] of the outer inlet (144a) to a total cross-sectional area S2 [mm2] of the outer outlet (147a), is 3 or more and 5.0 or less.; Gas sensor (100; 300) according to claim 1, wherein a minimum path distance P from the outer inlet (144a) to the gas inlet (111) is 5.0 mm or more and 11.0 mm or less. Gas sensor (100; 300) according to claim 2, wherein the minimum path distance P is 10.0 mm or less. Gas sensor (100; 300) according to one of claims 1 to 3, wherein the total cross-sectional area S1 is 10 mm2 or more and 30 mm2 or less. Gas sensor (100; 300) according to one of claims 1 to 4, wherein the total cross-sectional area S2 is 2 mm2 or more and 10 mm2 or less. Gas sensor (100; 300) according to one of claims 1 to 5, wherein the inner protective cover (130; 330) comprises a first element (131; 331) and a second element (135; 335), wherein the element chamber inlet (127; 227; 327) is formed as a gap between the first element (131; 331) and the second element (135; 335). Gas sensor (100; 300) according to claim 6, wherein the first element (131; 331) comprises a first cylindrical section (134; 234; 334b) surrounding the sensor element (110), wherein the second element (135; 335) comprises a second cylindrical section (136; 236; 336) having a diameter larger than the diameter of the first cylindrical section (134; 234; 334b), and the element chamber inlet (127; 227; 327) is a tubular gap between an outer circumferential surface of the first cylindrical section (134; 234; 334b) and an inner circumferential surface of the second cylindrical section (136; 236; 336).

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