Gas sensor

Abstract

To provide a gas sensor which can effectively suppress the quantity of water received by the gas sensor.SOLUTION: A gas sensor 1 comprises a sensor element 2, a housing 3, and an element cover 4. The element cover 4 has: an inner cover 5 which is arranged covering a tip side of the sensor element 2; and an outer cover 6 which is arranged outside of the inner cover 5. A lateral wall 51 of the inner cover 5 is provided with an inner lateral wall hole 511. A bottom wall 52 of the inner cover 5 is provided with an inner bottom wall hole 521. A lateral wall 61 of the outer cover 6 is provided with an outer lateral wall hole 611. The outer lateral wall hole 611 is provided at a tip side of the inner cover 5. When a total area of the inner lateral wall hole 511 is S1s, a total area of the inner bottom wall hole 521 is S1b, and a total area of the outer lateral wall hole 611 is S2s, 0.09≤S1b / S2s≤0.34 and 0.49≤S1s / S2s≤0.90 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] Gas sensors are known that are installed in the exhaust system of an internal combustion engine of an automobile or the like and measure the concentration of a specific gas, such as oxygen or nitrogen oxides, in exhaust gas to be measured. For example, some gas sensors include a sensor element that detects the concentration of the specific gas in the measured gas, a housing into which the sensor element is inserted, and an element cover disposed at the tip of the housing.

[0003] Patent Document 1 discloses a gas sensor having an inner cover (hereinafter also referred to as the inner cover) and an outer cover (hereinafter also referred to as the outer cover) as element covers. The gas sensor described in Patent Document 1 specifies the relationship between the outer diameter of the inner cover and the inner diameter of the outer cover in order to sufficiently increase the responsiveness of the sensor output and sufficiently prevent water from adhering to the sensor element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5851479 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the gas sensor described in Patent Document 1 does not specifically mention the size of the gas holes formed in the inner cover and the outer cover. Furthermore, depending on the environment in which the gas sensor is used, there is a concern that water may seep inside the inner cover and accumulate inside the inner cover. If water accumulates inside the inner cover, there is a concern that the accumulated water may come into contact with the sensor element, which may result in a large amount of water exposure to the sensor element. If the amount of water exposure is large, it becomes difficult to prevent element cracking, so measures to prevent this may be required.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a gas sensor that can effectively suppress the amount of water exposure to the sensor element. [Means for solving the problem]

[0007] One aspect of the present invention is a gas analyzer including a sensor element (2) for detecting a concentration of a specific gas in a measurement gas (G); a housing (3) into which the sensor element is inserted and held; an element cover (4) disposed on the tip side of the housing, The element cover includes a cylindrical inner cover (5) with a bottom that is disposed so as to cover the tip end side of the sensor element, and a cylindrical outer cover (6) with a bottom that is disposed so as to cover the outer side of the inner cover with a space (41) therebetween, The side wall (51) of the inner cover is provided with an inner side wall hole (511) through which the measurement gas passes. The bottom wall (52) of the inner cover is provided with an inner bottom wall hole (521) through which the measurement gas passes. The side wall (61) of the outer cover is provided with an outer side wall hole (611) through which the measurement gas passes. The outer side wall hole is provided closer to the tip end than the inner cover, When the total area of ​​the inner side wall holes is S1s, the total area of ​​the inner bottom wall holes is S1b, and the total area of ​​the outer side wall holes is S2s, The gas sensor (1) satisfies 0.09≦S1b / S2s≦0.34 and 0.49≦S1s / S2s≦0.90. [Effects of the Invention]

[0008] In the gas sensor, the total area S1s of the inner side-wall holes, the total area S1b of the inner bottom-wall holes, and the total area S2s of the outer side-wall holes satisfy 0.09≦S1b / S2s≦0.34 and 0.49≦S1s / S2s≦0.90, thereby effectively suppressing the amount of water exposure to the sensor element.

[0009] As described above, according to the above aspect, it is possible to provide a gas sensor that can effectively suppress the amount of water that the sensor element is exposed to. In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view taken along the axial direction of a gas sensor according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a tip end portion of the gas sensor according to the first embodiment. [Figure 3] FIG. 2 is an explanatory diagram of an example of mounting a gas sensor to an exhaust system in the first embodiment. [Figure 4] FIG. 3 is a plan view of the inner cover as viewed from the tip side in the first embodiment. [Figure 5] 3 is a cross-sectional view taken along line VV in FIG. 2. [Figure 6] 6 is a cross-sectional view taken along line VI-VI in FIG. 2. [Figure 7] FIG. 3 is a plan view of the outer cover as viewed from the tip side in the first embodiment. [Figure 8] 8 is a cross-sectional view taken along the axial direction of the sensor element in the first embodiment, taken along the line VIII-VIII in FIG. 9. [Figure 9] 9 is a cross-sectional view taken along line IX-IX in FIG. 8. [Figure 10] FIG. 3 is an explanatory diagram showing the main gas flow of the measurement gas inside the element cover in the first embodiment. [Figure 11] FIG. 4 is an explanatory diagram showing how water in the exhaust pipe comes into contact with the gas sensor; [Figure 12] FIG. 10 is an explanatory diagram showing water entering the outer cover. [Figure 13] FIG. 10 is an explanatory diagram showing water entering the inner cover. [Figure 14] FIG. 10 is an explanatory diagram showing how water begins to accumulate inside the inner cover. [Figure 15] FIG. 10 is an explanatory diagram showing how water accumulated in the inner cover comes into contact with the sensor element. [Figure 16] 1 is an explanatory diagram of a water exposure test in Experimental Examples 1 and 2. [Figure 17] FIG. 17 is an explanatory diagram of a water exposure test corresponding to the cross section XVII-XVII in FIG. 16. [Figure 18] 10 is an explanatory diagram of a response test of a gas sensor in Experimental Examples 3 and 4. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Embodiment 1) An embodiment of the gas sensor will be described with reference to FIGS. As shown in Fig. 1, the gas sensor 1 of this embodiment includes a sensor element 2, a housing 3, and an element cover 4. The sensor element 2 detects the concentration of a specific gas in a measurement gas G. The housing 3 holds the sensor element 2 by inserting it therein. The element cover 4 is disposed on the tip side of the housing 3.

[0012] 2, the element cover 4 has a cylindrical inner cover 5 with a bottom and a cylindrical outer cover 6 with a bottom. The inner cover 5 is disposed so as to cover the tip side of the sensor element 2. The outer cover 6 is disposed so as to cover the outside of the inner cover 5 with a space 41 left therebetween.

[0013] An inner side wall hole 511 through which the measurement gas flows is provided in the side wall 51 of the inner cover 5. An inner bottom wall hole 521 through which the measurement gas flows is provided in the bottom wall 52 of the inner cover 5. An outer side wall hole 611 through which the measurement gas flows is provided in the side wall 61 of the outer cover 6. The outer side wall hole 611 is provided closer to the tip than the inner cover 5. In particular, in this embodiment, the entire outer side wall hole 611 is located closer to the tip than the bottom wall 52 of the inner cover 5.

[0014] In this specification, the side of the gas sensor 1 in the axial direction Z that is exposed to the gas to be measured is referred to as the tip side, and the opposite side is referred to as the base side.

[0015] When the total area of ​​the inner side wall holes 511 is S1s, the total area of ​​the inner bottom wall holes 521 is S1b, and the total area of ​​the outer side wall holes 611 is S2s, these satisfy the following relationship. 0.09≦S1b / S2s≦0.34 (Formula 1) 0.49≦S1s / S2s≦0.90 (Formula 2)

[0016] The total area S1s is the sum of the opening areas of all inner side wall holes 511, the total area S1b is the sum of the opening areas of all inner bottom wall holes 521, and the total area S2s is the sum of the opening areas of all outer side wall holes 611.

[0017] The gas sensor 1 of this embodiment is a sensor that is attached to the exhaust system of an internal combustion engine of an automobile or the like and detects the oxygen concentration, etc., in exhaust gas. In this case, the measurement gas is exhaust gas, and the specific gas is oxygen. In this embodiment, the gas sensor 1 can be an A / F sensor (i.e., an air-fuel ratio sensor). In this case, the gas sensor 1 detects the oxygen concentration based on the current that flows through the sensor cell 23 of the sensor element 2, which depends on the oxygen concentration, etc., in the exhaust gas, and can detect the air-fuel ratio in the air-fuel mixture.

[0018] As shown in FIG. 3, the gas sensor 1 of this embodiment can be installed in an exhaust pipe 72 downstream of a catalytic converter 71 provided at the most downstream position in the exhaust system of an automobile.

[0019] 1, the sensor element 2 is held inside the housing 3 via an insulator 11. A base end cover 12 is attached to the base end side of the housing 3.

[0020] The inner cover 5 and the outer cover 6 are fixed to the housing 3. The inner cover 5 and the outer cover 6 are fixed to the housing 3 so that a portion of each of their base ends overlaps. The inner cover 5 and the outer cover 6 are provided so as to protrude from the housing 3 toward the tip end, and are provided so as to cover the sensor element 2 from the tip end side.

[0021] 2 and 4, the inner cover 5 has a first side wall portion 501 and a second side wall portion 502. The first side wall portion 501 is provided with an inner side wall hole 511. The second side wall portion 502 is provided closer to the tip side than the first side wall portion 501 and has a smaller diameter as viewed in the axial direction Z than the first side wall portion 501. As shown in FIGS. 2 and 5, annular spaces are formed between the outer peripheral surface of the first side wall portion 501 and the inner peripheral surface of the outer cover 6, and between the outer peripheral surface of the second side wall portion 502 and the inner peripheral surface of the outer cover 6.

[0022] As shown in FIG. 2 , the first side wall portion 501 and the second side wall portion 502 each have a cylindrical shape parallel to the axial direction Z. The inner cover 5 has a tapered portion 504 connecting the first side wall portion 501 and the second side wall portion 502. A bottom wall 52 is provided on the tip side of the second side wall portion 502. A third side wall portion 503 having a diameter larger than that of the first side wall portion 501 is provided on the base end side of the first side wall portion 501. At the third side wall portion 503, the inner cover 5 overlaps with the outer cover 6. The tip end of the sensor element 2 is disposed inside the first side wall portion 501. In this embodiment, the side wall 61 of the outer cover 6 is formed in a cylindrical shape with approximately the same diameter from the portion overlapping with the third side wall portion 503 of the inner cover 5 to the tip end. An outer bottom wall hole 621 is formed in the bottom wall 62 of the outer cover 6.

[0023] As shown in FIG. 4, a plurality of inner bottom wall holes 521 are formed. Furthermore, as shown in FIGS. 5 to 7, a plurality of inner side wall holes 511, outer side wall holes 611, and outer bottom wall holes 621 are each formed. As shown in FIG. 2, a plurality of outer side wall holes 611 are formed at the same position in the axial direction Z. A plurality of inner side wall holes 511 are formed at the same position in the axial direction Z. The inner side wall holes 511, outer side wall holes 611, and outer bottom wall holes 621 are all arranged at equal intervals in the circumferential direction. The inner side wall holes 511 and the outer side wall holes 611 are arranged so as not to overlap with each other when viewed from the radial direction of the gas sensor 1. Furthermore, the inner bottom wall holes 521 and the outer bottom wall holes 621 are arranged so as not to overlap with each other when viewed from the axial direction Z.

[0024] In this embodiment, the sensor element 2 is a laminated element in which a plurality of ceramic layers are laminated, as shown in Figures 8 and 9. The sensor element 2 has a solid electrolyte body 22 having oxygen ion conductivity and ceramic layers 261, 262, and 263 laminated on the solid electrolyte body 22. The solid electrolyte body 22 is mainly composed of zirconia, for example. The other ceramic layers 261, 262, and 263 are mainly composed of alumina.

[0025] The sensor cell 23 is formed by the solid electrolyte body 22, and the measurement electrode 231 and reference electrode 232 provided on the solid electrolyte body 22. A chamber 271 into which a measurement gas is introduced is formed facing the measurement electrode 231. An inlet 264 for the measurement gas into the chamber 271 is provided on the tip side of the chamber 271 (i.e., at the tip of the element). In addition, a duct 272 into which a reference gas (here, the atmosphere) is introduced is formed facing the reference electrode 232. In addition, a heater 25 for heating the sensor cell 23 is built into the sensor element 2.

[0026] The sensor element 2 has a porous protective layer 24 provided on its surface. The protective layer 24 is formed so as to cover the entire periphery of the sensor element 2, at least at the position in the axial direction Z where the sensor cell 23 is formed. In this embodiment, the protective layer 24 is formed so as to cover the entire surface of the sensor element 2 that faces the inner space of the inner cover 5. The protective layer 24 is mainly composed of alumina, for example.

[0027] When the gas sensor 1 configured as described above is installed in an exhaust pipe 72 as shown in FIG. 3, the measurement gas flows toward the element cover 4 of the gas sensor 1 in a direction substantially perpendicular to the axial direction Z. Therefore, as shown in FIG. 10, the measurement gas G is mainly introduced into the outer cover 6 through the outer side wall holes 611. A portion of the measurement gas G introduced into the outer cover 6 is introduced into the inner cover 5 through the inner side wall holes 511. This allows the measurement gas G to reach the sensor element 2. The measurement gas G in the inner cover 5 is mainly discharged to the outside of the inner cover 5 through the inner bottom wall holes 521.

[0028] Since the outer side wall hole 611 is provided closer to the tip than the inner cover 5, a gas flow with a relatively high flow rate is generated in the space on the tip side of the inner bottom wall hole 521. Therefore, a Venturi effect is generated in this portion, promoting the discharge of the measurement gas G from the inner bottom wall hole 521. Therefore, in the inner cover 5, a gas flow is formed in which the measurement gas G is mainly introduced through the inner side wall hole 511 and discharged from the inner bottom wall hole 521.

[0029] As described above, in the gas sensor 1 of this embodiment, the total area S1s of the inner side wall holes 511, the total area S1b of the inner bottom wall holes 521, and the total area S2s of the outer side wall holes 611 satisfy both of the above (Equation 1) and (Equation 2).

[0030] In this embodiment, the diameter φ1s of the inner side wall hole 511, the diameter φ1b of the inner bottom wall hole 521, and the diameter φ2s of the outer side wall hole 611 satisfy both of the following (Equation 3) and (Equation 4). 0.5≦φ1b / φ2s≦0.95 (Formula 3) 0.7≦φ1s / φ2s≦0.95 (Formula 4)

[0031] Furthermore, the total area S2b of the outer bottom wall holes 621 can be set to satisfy the following (Equation 5) relative to the total area S2s of the outer side wall holes 611, for example. 0.19≦S2b / S2s≦0.80 (Formula 5)

[0032] Furthermore, the diameter φ2b of the outer bottom wall hole 621 can be set to satisfy the following (Equation 6) with respect to the diameter φ2s of the outer side wall hole 611, for example. 0.43≦φ2b / φ2s≦0.90 (Formula 6)

[0033] Also, S1s is, for example, 12.3 to 20.4 mm 2 It can be said that: S1b is, for example, 3.9 to 6.1 mm 2 It can be said that: S2s is, for example, 20.3 to 30.4 mm 2 It can be said that: S2b is, for example, 6.2 to 12.4 mm 2 It can be said that: φ1s can be set to, for example, 1.4 to 1.8 mm. φ1b can be set to, for example, 1.3 to 1.6 mm. φ2s can be set to, for example, 1.8 to 2.2 mm. φ2b can be set to, for example, 1.0 to 1.4 mm.

[0034] Next, the effects of this embodiment will be described. In the gas sensor 1, the total area S1s of the inner side-wall holes 511, the total area S1b of the inner bottom-wall holes 521, and the total area S2s of the outer side-wall holes 611 satisfy the relationships of the above-mentioned (Equation 1) and (Equation 2). This effectively prevents the sensor element 2 from being exposed to water. This point has been confirmed by Experimental Example 1, which will be described later.

[0035] As described above, when the gas sensor 1 is installed in the exhaust system of an automobile, it is conceivable that water W accumulated in the exhaust pipe 72 will flow into the element cover 4, as shown in Fig. 11 . That is, it is conceivable that the water W accumulated in the exhaust pipe 72 will move upstream and flow into the gas sensor 1 due to rocking or tilting of the vehicle, wind from the outside air, etc. In particular, in a gas sensor 1 installed in an exhaust pipe 72 downstream of a catalytic converter 71, there is a concern that water W will infiltrate into the element cover 4. That is, it is particularly conceivable that water W will accumulate in the exhaust pipe 72 close to the outside air, and it is fully conceivable that water W in the exhaust pipe 72 will flow into the gas sensor 1 due to rocking or tilting of the vehicle, wind from the outside air, etc.

[0036] If the amount of water W that enters the inner cover 5 is large and the amount that is discharged is small, the water W will accumulate inside the inner cover 5. In this case, there is a concern that the sensor element 2 will be submerged in the water W that has accumulated inside the inner cover 5. In this case, there is a concern that the sensor element 2 may crack.

[0037] In the first place, if the amount of water W heading toward the gas sensor 1 is not particularly large, the above-mentioned concerns do not arise. However, depending on the usage environment, it is possible that a large amount of water W will head toward the gas sensor 1. If the amount of water W heading toward the gas sensor 1 is not particularly large, as shown in FIG. 12 , the water W that has entered through the outer side wall hole 611 is discharged through the other outer side wall holes 611 and the outer bottom wall hole 621, and is prevented from entering the inner cover 5.

[0038] When the amount of water W flowing toward the gas sensor 1 increases, it is conceivable that the water may enter the inner cover 5 from the outer cover 6 through the inner side wall holes 511, etc., as shown in Figs. 13 to 15. When the water W accumulates in the inner cover 5 as shown in Fig. 15, the sensor element 2 may come into contact with the accumulated water W. In this case, as described above, even if the sensor element 2 has the protective layer 24, there is a concern that the element may crack.

[0039] On the other hand, even if water W does enter the inner cover 5, the above situation can be avoided if the water W does not accumulate inside the inner cover 5, as shown in Figure 13. If the amount of water W discharged from the inner cover 5 exceeds the amount of water W entering the inner cover 5, the water W can be prevented from accumulating inside the inner cover 5.

[0040] From this perspective, the inventors of the present application have conducted extensive research into the sizes of the inner side-wall holes 511, the inner bottom-wall holes 521, and the outer side-wall holes 611. Based on this research, as described above, in the gas sensor 1 of this embodiment, the total area S1s of the inner side-wall holes 511, the total area S1b of the inner bottom-wall holes 521, and the total area S2s of the outer side-wall holes 611 satisfy the relationships of the above (Equation 1) and (Equation 2). This effectively prevents water from accumulating inside the inner cover 5, and effectively prevents the sensor element 2 from being wet.

[0041] In this embodiment, the diameter φ1s of the inner side wall hole 511, the diameter φ1b of the inner bottom wall hole 521, and the diameter φ2s of the outer side wall hole 611 satisfy the relationships of the above (Equation 3) and (Equation 4). This makes it possible to more effectively prevent the sensor element 2 from being wetted. This point has been confirmed by Experimental Example 2, which will be described later.

[0042] The inner cover 5 also has a first side wall portion 501 and a second side wall portion 502. This facilitates smooth gas flow within the inner cover 5. Specifically, the smaller inner diameter of the space within the inner cover 5 at the tip end side facilitates airflow from the base end side to the tip end side due to the Venturi effect in the inner bottom wall holes 521. As a result, the output responsiveness of the gas sensor 1 is improved. On the other hand, if water infiltrates the inner cover 5, the water level is likely to rise within the second side wall portion 502, which has a smaller inner diameter. Therefore, by defining the total area S1s of the inner side wall holes 511, the total area S1b of the inner bottom wall holes 521, and the total area S2s of the outer side wall holes 611 as described above, water is less likely to accumulate within the inner cover 5, effectively preventing the sensor element 2 from becoming wet.

[0043] In addition, a plurality of inner bottom wall holes 521 are formed, which makes it easier to discharge water W that has entered the inner cover 5.

[0044] The sensor element 2 is a laminated element in which multiple ceramic layers are stacked. In the case of such a laminated sensor element 2, the element is relatively susceptible to cracking due to stress caused by exposure to water. In other words, the problem of exposure to water is likely to occur. Therefore, by specifying the total area S1s of the inner side wall holes 511, the total area S1b of the inner bottom wall holes 521, and the total area S2s of the outer side wall holes 611 as in this embodiment, element cracking can be effectively prevented.

[0045] The sensor element 2 has a porous protective layer 24 on its surface. Therefore, even if water droplets or the like adhere to the sensor element 2, stress on the body of the sensor element 2 can be suppressed, preventing cracking of the sensor element. That is, the presence of the protective layer 24 can prevent cracking due to water exposure, even for small amounts of water. However, if the sensor element 2 comes into contact with water accumulated inside the inner cover 5, it may be difficult to prevent cracking due to water exposure, even with the protective layer 24. Therefore, in this embodiment, the inner side wall hole 511, the inner bottom wall hole 521, and the outer side wall hole 611 are defined to prevent water from accumulating inside the inner cover 5, thereby preventing the sensor element 2 from coming into contact with water. This effectively prevents cracking due to water exposure.

[0046] As described above, according to this embodiment, it is possible to provide a gas sensor that can effectively suppress the amount of water that the sensor element is exposed to.

[0047] (Experimental Example 1) In this example, the relationship between S1b / S2s and S1s / S2s and the water exposure of the gas sensor was investigated.

[0048] Gas sensors having the same basic configuration as the gas sensor 1 shown in Embodiment 1 were prepared as samples. However, the relationships S1s / S2s and S1b / S2s among the total area S1s of the inner side-wall holes 511, the total area S1b of the inner bottom-wall holes 521, and the total area S2s of the outer side-wall holes 611 were variously changed to prepare multiple types of samples, as shown in Table 1 below. That is, multiple types of samples were prepared by changing S1s / S2s in the range of 0.36 to 1.10 and changing S1b / S2s in the range of 0.08 to 0.38.

[0049] Here, in each sample, three inner bottom wall holes 521 (see FIG. 4), eight inner side wall holes 511 (see FIG. 5), eight outer side wall holes 611 (see FIG. 6), and eight outer bottom wall holes 621 (see FIG. 7) are formed. In addition, in each sample, no particular holes are provided in the inner cover 5 and the outer cover 6 other than the three inner bottom wall holes 521, eight inner side wall holes 511, eight outer side wall holes 611, and eight outer bottom wall holes 621.

[0050] Furthermore, the diameter φ1s of the inner side wall hole 511 was set to 1.6 mm, and the diameter φ1b of the inner bottom wall hole 521 was set to 1.5 mm. Furthermore, the diameter φ2b of the outer bottom wall hole 621 was set to 1.2 mm.

[0051] 16 and 17, the test was performed by causing flowing water W to impinge on the gas sensor, which was positioned with its tip facing vertically downward. Specifically, the water W was sprayed from the nozzle 73 toward the outer side wall hole 611 of the element cover 4 in a direction perpendicular to the axial direction Z, i.e., horizontally. The inner diameter of the nozzle 73 was 5 mm, the flow rate of the water W sprayed from the nozzle 73 per unit time was 100 ml / s, and the spray time of the water W was 100 seconds. The distance between the nozzle outlet of the nozzle 73 and the outer side wall hole 611 was approximately 15 mm.

[0052] After the water exposure test for each sample, the sensor element 2 was removed from each sample and the water exposure status was confirmed. The water exposure in question here is water exposure to the extent that the sensor element 2 is submerged in water W accumulated inside the inner cover 5 (this will be referred to as flowing water exposure). Therefore, to make the flowing water exposure visible, carbon powder was applied to the surface of the sample in advance to make it black. When the sample is exposed to flowing water, the carbon powder peels off from the exposed area, causing the exposed area to turn white. When this whitening was observed visually, it was evaluated as having been exposed to flowing water. However, localized whitening in very small areas due to the adhesion of water droplets was determined not to be due to flowing water exposure. The evaluation results are shown in Table 1 below. In Table 1, "〇" indicates that the sensor element 2 was not exposed to flowing water, and "×" indicates that the sensor element 2 was exposed to flowing water.

[0053] [Table 1]

[0054] As can be seen from Table 1, no water was spilled on any of the items that met the conditions 0.49≦S1b / S2s≦0.90 and 0.09≦S1s / S2s≦0.34.

[0055] (Experimental Example 2) In this example, the relationship between φ1s / φ2s and φ1b / φ2s and the water exposure of the gas sensor was investigated.

[0056] Gas sensors having the same basic configuration as gas sensor 1 shown in Embodiment 1 were prepared as samples. However, the relationships between diameter φ1s of inner side-wall hole 511, diameter φ1b of inner bottom-wall hole 521, and diameter φ2s of outer side-wall hole 611, i.e., φ1s / φ2s and φ1b / φ2s, were variously changed as shown in Table 2 below to prepare multiple types of samples. That is, multiple types of samples were prepared by changing φ1s / φ2s in the range of 0.60 to 1.05 and changing φ1b / φ2s in the range of 0.45 to 1.00.

[0057] The other configurations of the sample used in this example were the same as those of the sample used in Experimental Example 1. The test method and evaluation method were also the same as those of Experimental Example 1. The evaluation results are shown in Table 2 below. In Table 2, "◯" indicates that the sample was not exposed to running water, and "×" indicates that the sample was exposed to running water.

[0058] [Table 2]

[0059] As can be seen from Table 2, no flooding occurred in any of the cases where 0.5≦φ1b / φ2s≦0.95 and 0.7≦φ1s / φ2s≦0.95 were satisfied.

[0060] (Experimental Example 3) In this example, the relationship between S1b / S2s and the response of the gas sensor was investigated. As in Experimental Example 1, gas sensors having the same basic structure as gas sensor 1 shown in Embodiment 1 were prepared as samples. Then, a response test was conducted on each sample with S1b / S2s varied from 0.06 to 0.41. The other structures of the samples were the same as those of the sample used in Experimental Example 1.

[0061] Specifically, first, the gas sensor 1 was attached to an exhaust pipe 72 as shown in FIG. 18 . In this state, an internal combustion engine (not shown) connected to the exhaust pipe 72 was operated, causing exhaust gas G to flow through the exhaust pipe 72 at a gas flow rate of 20 m / s. Then, measurements were performed using the gas sensor 1 with the element temperature heated to an activation temperature (700°C). The output of the gas sensor 1 was measured over time by an external computer (not shown) connected via a detection circuit. The internal combustion engine was operated while varying the air-fuel ratio (i.e., A / F) between 14 and 15. The output of the gas sensor 1 changed with this change in the air-fuel ratio, but there was a delay in the change in the gas sensor output relative to the actual change in the air-fuel ratio. The degree of this delay is referred to as responsiveness.

[0062] Therefore, after changing the A / F ratio from 14 to 15, the time from when the output of the gas sensor 1 changed by 5% to when it changed by 68% was measured. This time was referred to as the "63% response time." The responsiveness was judged based on whether the 63% response time was 180 ms or less. The results are shown in Table 3. In Table 3, "◯" indicates a 63% response time of 180 ms or less, and "×" indicates a 63% response time of more than 180 ms.

[0063] [Table 3]

[0064] As can be seen from Table 3, sufficient responsiveness can be ensured for sensors that satisfy at least 0.06≦S1b / S2s≦0.34. Therefore, it is believed that sufficient sensor responsiveness can be ensured if the above (Equation 1) is satisfied.

[0065] (Experimental Example 4) In this example, the relationship between φ1b / φ2s and the response of the gas sensor was investigated. As in Experimental Example 1, gas sensors having the same basic configuration as gas sensor 1 shown in Embodiment 1 were prepared as samples. Then, a response test was conducted on each sample with φ1b / φ2s varied from 0.40 to 1.05. Other configurations of the samples were the same as those of the sample used in Experimental Example 1.

[0066] The test and evaluation methods were the same as in Experimental Example 3. The evaluation results are shown in Table 4. In Table 4, "◯" indicates a 63% response time of 180 ms or less, and "×" indicates a 63% response time of more than 180 ms.

[0067] [Table 4]

[0068] As can be seen from Table 4, sufficient responsiveness can be ensured for sensors that satisfy at least 0.40≦φ1b / φ2s≦0.95. Therefore, it is believed that sufficient sensor responsiveness can be ensured if the above (Equation 3) is satisfied.

[0069] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention.

[0070] The features of the present invention are as follows. [1] A sensor element (2) for detecting the concentration of a specific gas in a measurement gas (G); a housing (3) into which the sensor element is inserted and held; an element cover (4) disposed on the tip side of the housing, The element cover includes a cylindrical inner cover (5) with a bottom that is disposed so as to cover the tip end side of the sensor element, and a cylindrical outer cover (6) with a bottom that is disposed so as to cover the outer side of the inner cover with a space (41) therebetween, The side wall (51) of the inner cover is provided with an inner side wall hole (511) through which the measurement gas passes. The bottom wall (52) of the inner cover is provided with an inner bottom wall hole (521) through which the measurement gas passes. The side wall (61) of the outer cover is provided with an outer side wall hole (611) through which the measurement gas passes. The outer side wall hole is provided closer to the tip end than the inner cover, When the total area of ​​the inner side wall holes is S1s, the total area of ​​the inner bottom wall holes is S1b, and the total area of ​​the outer side wall holes is S2s, A gas sensor (1) that satisfies 0.09≦S1b / S2s≦0.34 and 0.49≦S1s / S2s≦0.90. [2] The gas sensor described in [1], wherein the inner cover has a first side wall portion in which the inner side wall hole is provided, and a second side wall portion that is provided further forward than the first side wall portion and has a smaller diameter than the first side wall portion when viewed in the axial direction. [3] The gas sensor according to [1] or [2], wherein a plurality of the inner bottom wall holes are formed. [4] When the diameter of the inner side wall hole is φ1s, the diameter of the inner bottom wall hole is φ1b, and the diameter of the outer side wall hole is φ2s, 0.5≦φ1b / φ2s≦0.95 and 0.7≦φ1s / φ2s≦0.95, The gas sensor according to any one of [1] to [3], which satisfies the above. [5] The gas sensor according to any one of [1] to [4], wherein the sensor element is a laminated element in which a plurality of ceramic layers are laminated. [6] The gas sensor according to any one of [1] to [5], wherein the sensor element has a porous protective layer on the surface. [Explanation of symbols]

[0071] 1 gas sensor, 2 sensor element, 3 housing, 4 element cover, 5 inner cover, 51 side wall (of inner cover), 511 inner side wall hole, 52 bottom wall (of inner cover), 521 inner bottom wall hole, 6 outer cover, 61 (side wall of outer cover), 611 outer side wall hole, S1s total area of ​​inner side wall holes, S1b total area of ​​inner bottom wall holes, S2s total area of ​​outer side wall holes

Claims

1. A sensor element (2) for detecting the concentration of a specific gas in the gas to be measured (G), A housing (3) that holds the sensor element by inserting it inside, The housing comprises an element cover (4) disposed on the tip side, The element cover comprises a bottomed cylindrical inner cover (5) disposed to cover the tip side of the sensor element, and a bottomed cylindrical outer cover (6) disposed to cover the inner cover with a space (41) left on the outside. The inner cover's side wall (51) is provided with an inner side wall hole (511) through which the gas to be measured flows. The bottom wall (52) of the inner cover is provided with an inner bottom wall hole (521) through which the gas to be measured flows. The outer cover's side wall (61) is provided with an outer side wall hole (611) through which the gas to be measured flows. The outer side wall hole is located on the tip side of the inner cover. When the total area of ​​the inner side wall holes is S1s, the total area of ​​the inner bottom wall holes is S1b, and the total area of ​​the outer side wall holes is S2s, Satisfying 0.09 ≤ S1b / S2s ≤ 0.34 and 0.49 ≤ S1s / S2s ≤ 0.90, Furthermore, when the diameter of the inner side wall hole is φ1s, the diameter of the inner bottom wall hole is φ1b, and the diameter of the outer side wall hole is φ2s, 0.5 ≤ φ1b / φ2s ≤ 0.95, and 0.7 ≤ φ1s / φ2s ≤ 0.95, A gas sensor (1) that satisfies the following conditions.

2. The gas sensor according to claim 1, wherein the inner cover has a first side wall portion provided with the inner side wall hole, and a second side wall portion provided on the tip side of the first side wall portion and having a diameter smaller in the axial direction than the first side wall portion.

3. The gas sensor according to claim 1 or 2, wherein a plurality of inner bottom wall holes are formed.

4. When the diameter of the inner side wall hole is φ1s, the diameter of the inner bottom wall hole is φ1b, and the diameter of the outer side wall hole is φ2s, 0.5 ≤ φ1b / φ2s ≤ 0.95, and 0.7 ≤ φ1s / φ2s ≤ 0.95, A gas sensor according to claim 1 or 2, satisfying the requirements.

5. The gas sensor according to claim 1 or 2, wherein the sensor element is a stacked element in which a plurality of ceramic layers are stacked.

6. The gas sensor according to claim 1 or 2, wherein the sensor element is provided with a porous protective layer on its surface.

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