JP2015075367A - Exhaust gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a heat crack of a sensor element.SOLUTION: An exhaust gas sensor 1 projects from a wall surface of an exhaust passage, and includes a sensor element and a cover 5 for covering the sensor element. The cover 5 includes: a cylindrical circumferential wall section 73 having a plurality of gas continuity holes 71a-71d, and 72a-72d; and an end wall section 75 of a tip of the cylindrical circumferential wall section 73. The gas continuity holes 71a-71d, and 72a-72d are formed on the upstream side and downstream side, and on the side flow side of the exhaust gas flow direction in the cylindrical circumferential wall section 73, respectively. The inner diameter d1 of the gas continuity holes 71a and 72a on the upstream side of the exhaust gas flow direction is set shorter than the inner diameter d2 of the gas continuity holes 71b and 72b on the side flow side of the exhaust gas flow direction.

Description

  The present invention relates to an exhaust gas sensor that is installed in an exhaust passage and includes a sensor element and a cover that covers the sensor element.

  An exhaust gas sensor is provided in the exhaust passage of the engine, the state of the exhaust gas is detected by the exhaust gas sensor, and this detection information is used for engine control and the like. Such exhaust gas sensors include a NOx sensor, an air-fuel ratio sensor, an oxygen sensor, and the like. Usually, exhaust gas is caused to flow into a sensor element made of a ceramic material or the like, and NOx, oxygen, etc. in the exhaust gas are exhausted by this sensor element. The component of is detected.

In general, the exhaust gas sensor has a structure in which the sensor element is covered and protected by a cover having a gas conduction hole. For example, Patent Document 1 discloses a cover having a double structure including an inner cover and an outer cover.
Further, since the sensor element operates at a high temperature, the sensor element has a built-in heater (see, for example, Patent Document 2).

JP 2004-19512 A JP 2009-287939 A

  By the way, the sensor element is heated from several hundreds of degrees Celsius to nearly 1000 degrees Celsius for gas detection, whereas the exhaust gas has a temperature much lower than this, so the exhaust gas flowing into the sensor element generates heat from the sensor element. I will take away. In particular, if the flow rate of the exhaust gas flowing into the sensor element is large, heat removal due to the exhaust gas becomes large, causing heat cracks in the sensor element, leading to failure of the exhaust gas sensor. As a measure for avoiding this, it is conceivable to install the exhaust gas sensor avoiding a place where the flow rate of the exhaust gas is large.

  On the other hand, some exhaust gas sensors detect a typical state of the exhaust gas downstream of the exhaust gas purification device. In this case, the exhaust gas sensor is installed at a location where the exhaust gas is sufficiently mixed and the exhaust gas state is not biased. It is preferable to install. From this point of view, the location where the state of the exhaust gas can be properly detected is limited, but the location where this thoroughly mixed exhaust gas circulates may coincide with the location where the flow rate of the exhaust gas is high, Preventing the occurrence of heat cracks is an issue.

  The present invention has been devised in view of such problems, and an object thereof is to provide an exhaust gas sensor capable of preventing the occurrence of heat cracks. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

  (1) The exhaust gas sensor disclosed herein is an exhaust gas sensor that protrudes from the wall surface of the exhaust passage and has a sensor element and a cover that covers the sensor element, and the cover has a plurality of gas conduction holes. A cylindrical peripheral wall portion, and an end wall portion of a tip end portion of the cylindrical peripheral wall portion, and the gas conduction hole includes an upstream side, a downstream side, and a side flow side in the exhaust gas flow direction of the cylindrical peripheral wall portion. And the inner diameter of the gas conduction hole on the upstream side in the exhaust gas flow direction is set smaller than the inner diameter of the gas conduction hole on the upstream side in the exhaust gas flow direction.

(2) The cover preferably includes an inner cover and an outer cover each having a gas conduction hole, and the plurality of gas conduction holes are preferably formed in the cylindrical peripheral wall portion of the outer cover.
(3) Further, the cylindrical peripheral wall portion of the outer cover is disposed on a small-diameter distal-end-side cylindrical peripheral wall portion disposed on the outer periphery on the distal end side of the inner cover and an outer periphery on the proximal end side of the inner cover. The distal end side cylindrical peripheral wall portion and the proximal end side cylindrical peripheral wall portion are connected by a stepped wall portion, and the plurality of gas conduction holes are It is preferable that both the distal end side cylindrical peripheral wall portion and the proximal end side cylindrical peripheral wall portion are formed.

  According to the disclosed exhaust gas sensor, the inner diameter of the gas conduction hole on the upstream side in the exhaust gas flow direction is the inner diameter of the gas conduction hole on the upstream side in the exhaust gas flow direction among the plurality of gas conduction holes formed in the cover that covers the sensor element. Therefore, the flow rate of the exhaust gas flowing into the sensor element from the gas conduction hole on the upstream side in the exhaust gas flow direction can be reduced. Thereby, since heat removal due to the exhaust gas can be reduced, heat cracks can be prevented from occurring in the sensor element.

It is a typical perspective view of the exhaust gas sensor concerning one embodiment. It is a typical longitudinal section of an exhaust gas sensor concerning one embodiment. It is A arrow directional view of FIG. 2 which shows typically the arrangement | positioning location of the gas conduction | electrical_connection hole of the exhaust gas sensor which concerns on one Embodiment, (a) shows an outer cover, (b) shows an inner cover. It is a typical figure showing composition of an exhaust passage concerning one embodiment. It is a typical contour figure which shows the result of having simulated the flow volume of the exhaust gas in one cross section of the exhaust passage which concerns on one Embodiment. It is a typical contour figure which shows the result of having simulated the flow of exhaust gas in two sections inside an exhaust gas sensor, (a) shows the exhaust gas sensor concerning one embodiment, and (b) shows the exhaust gas sensor concerning a comparative example. ing. It is sectional drawing which shows typically the exhaust gas flow in the exhaust gas sensor which concerns on one Embodiment, (a) shows a surface parallel to the longitudinal direction of an exhaust passage, (b) shows a surface perpendicular | vertical to the longitudinal direction of an exhaust passage. Show.

  Embodiments of the present invention will be described below with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.

[1. Constitution]
[1-1. overall structure]
In this embodiment, the NOx sensor 1 shown in FIG. 4 is illustrated as an exhaust gas sensor of the present invention. The NOx sensor 1 shown here is installed in an exhaust passage 8 of a vehicle using a diesel engine as a drive source. The exhaust passage 8 is for exhausting exhaust gas discharged from an engine (not shown) to the outside of the vehicle body, and the upstream side of the SCR device (exhaust gas purification device) 9 in the exhaust passage 8 is upstream of the catalyst. A downstream portion is distinguished as a catalyst downstream flow path 82.

  The SCR device 9 is interposed between the catalyst upper flow path 81 and the catalyst lower flow path 82 in the exhaust passage 8 to remove NOx contained in the exhaust gas. An SCR catalyst (selective reduction catalyst) 92 is built in the casing 91 of the SCR device 9. The SCR catalyst 92 causes NOx in the exhaust gas to react with urea (ammonia) injected from the inlet side of the casing 91. NOx is reduced to nitrogen and water.

  The casing 91 includes a cylindrical portion 91a formed in a cylindrical shape, an upstream end portion 91b provided at an upstream end portion of the cylindrical portion 91a, and a tapered downstream end portion 91c provided at a downstream end portion of the cylindrical portion 91a. Including. The upstream end 91 b of the casing 91 is connected to the downstream end of the catalyst upper flow path 81, and the downstream end 91 c of the casing 91 is connected to the upstream end of the catalyst lower flow path 82.

The catalyst lower flow path 82 connects the downstream end portion of the SCR device 9 and the outside of the vehicle body, and is formed in a bent cylindrical shape here. The first bent portion 82a, the straight portion 82c, and the second bent portion are formed from the upstream side. Part 82b. The 1st bending part 82a is a part connected to the downstream end part 91c of the casing 91, and is the shape bent at substantially right angle. The second bent portion 82b is a portion connected to the outside of the vehicle body, and has a shape bent in a direction away from the downstream end portion 91c. The straight portion 82c is a portion extending between the first bent portion 82a and the second bent portion 82b and has a linear shape.
The NOx sensor 1 is installed in the straight part 82c. The NOx sensor 1 has a straight portion 82c (that is, the exhaust passage 8) such that its axial center is oriented in a direction orthogonal to the longitudinal direction of the straight portion 82c and its tip is located near the radial center of the straight portion 82c. ) Protruding from the wall surface.

[1-2. Configuration of NOx sensor (exhaust gas sensor)]
As shown in FIGS. 1 and 2, the NOx sensor 1 has a mounting portion 4 and a sensor portion 2 formed on the same axis. The mounting portion 4 includes a screw portion 41 that is fixed to an exhaust pipe (not shown) that forms the exhaust passage 8, and a metal fitting 42 that is used for fixing the screw portion 41.
As shown in FIG. 2, the sensor unit 2 includes a sensor element 3 extending on the center line O of the NOx sensor 1 and a cover 5 covering the sensor element 3. The sensor element 3 is made of a ceramic material or the like and has a long and narrow plate shape, and a heater (not shown) is built in the sensor element 3.

  Here, the cover 5 has a double structure including an inner cover 6 and an outer cover 7. The inner cover 6 includes a cylindrical inner peripheral wall portion 61 and a conical inner end wall portion 62 that closes the tip of the inner peripheral wall portion 61. The inner peripheral wall portion 61 forms a proximal end side portion of the inner cover 6, and the inner end wall portion 62 forms a distal end side portion of the inner cover 6. The length of the inner peripheral wall 61 is substantially the same as the length of the sensor element 3, and the inner diameter of the inner peripheral wall 61 is set larger than the width and thickness of the sensor element 3. Thereby, a space for the exhaust gas to flow is secured between the inner peripheral surface of the inner cover 6 and the outer peripheral surface of the sensor element 3. The inner peripheral wall portion 61 is formed with a hook-shaped portion 65 that protrudes outward in the radial direction and whose front end faces the front end side of the inner peripheral wall portion 61.

  The outer cover 7 includes a large-diameter large-diameter peripheral wall portion (base-end-side cylindrical peripheral wall portion) 71 disposed on the outer periphery of the inner peripheral wall portion 61 and a small-diameter small-diameter peripheral wall portion disposed on the outer periphery of the inner end wall portion 62 ( A distal-end-side cylindrical peripheral wall portion) 72. The large-diameter peripheral wall 71 and the small-diameter peripheral wall 72 are connected by a stepped wall 74 having a surface perpendicular to the sensor center line O. The connecting portion between the large-diameter peripheral wall portion 71 and the stepped wall portion 74 and the connecting portion between the small-diameter peripheral wall portion 72 and the stepped wall portion 74 are all formed into a smooth curved surface. Further, the outer peripheral wall portion (cylindrical peripheral wall portion) 73 of the outer cover 7 is formed by the large diameter peripheral wall portion 71 and the small diameter peripheral wall portion 72.

The inner diameter of the large-diameter peripheral wall portion 71 is larger than the outer diameter of the inner peripheral wall portion 61, and there is a space for exhaust gas to flow between the inner peripheral surface of the large-diameter peripheral wall portion 71 and the outer peripheral surface of the inner peripheral wall portion 61. It is secured. Further, the inner diameter of the small-diameter peripheral wall portion 72 is substantially the same as the maximum outer diameter of the inner end wall portion 62, and the length dimension of the small-diameter peripheral wall portion 72 is set larger than the length dimension of the inner end wall portion 62. Yes. Thereby, a space for flowing exhaust gas is secured between the inner peripheral surface of the small-diameter peripheral wall portion 72 and the outer peripheral surface of the inner end wall portion 62.
The distal end of the small-diameter peripheral wall portion 72 (that is, the distal end of the outer peripheral wall portion 73) is closed by an outer end wall portion (end wall portion) 75 having a surface perpendicular to the sensor center line O. The connection portion between the small-diameter peripheral wall portion 72 and the end wall portion 75 is formed in a smooth curved surface.

[1-3. Gas conduction hole]
As shown in FIGS. 1 to 3, four gas conduction holes 71 a to 71 d and 72 a to 72 d are formed in both the large diameter peripheral wall portion 71 and the small diameter peripheral wall portion 72. In addition, six gas conduction holes 61 a to 61 f are formed in the inner peripheral wall portion 61, and a gas conduction hole 62 a is also formed in the top portion of the inner end wall portion 62.

  First, the gas conduction holes 71a to 71d and 72a to 72d of the outer peripheral wall portion 73 will be described. These gas conduction holes 71 a to 71 d and 72 a to 72 d are substantially circular in shape when viewed from the front, and are formed through the large-diameter peripheral wall 71 and the small-diameter peripheral wall 72 toward the sensor center line O, respectively. Yes. The gas conduction holes 71 a to 71 d are formed on the distal end side of the large-diameter peripheral wall portion 71 and are located on the distal end side with respect to the flange-shaped portion 65 of the inner peripheral wall portion 61. The gas conduction holes 72 a to 72 d are formed on the distal end side of the small-diameter peripheral wall portion 72, and are located on the distal end side with respect to the top portion of the inner end wall portion 62.

  FIG. 3A shows an end face of the outer cover 7 schematically showing the arrangement positions of the gas conduction holes 71a to 71d and 72a to 72d with large and small “o” marks so as to indicate the shape and size of the front view. It is a figure (A arrow line view in FIG. 2). Hereinafter, as shown in FIG. 3A, the outer peripheral wall 73 is divided into four regions having a central angle of 90 ° equally along the circumferential direction, and among these, the side facing the exhaust gas flow direction (that is, the side) The region of 45 ° both ends centered on the most upstream point) is the side facing the upstream side 73A and the upstream side 73A along the exhaust gas flow direction (that is, 45 ° both ends centering on the most downstream point). A range region) is sandwiched between the downstream side 73C, the upstream side 73A, and the downstream side 73C, and a pair of sides (regions) facing each other are defined as side flow sides 73B and 73D. The exhaust gas flow direction is assumed to be along the longitudinal direction of the straight portion 82 c of the exhaust passage 8.

  The gas conduction holes 71a to 71d of the large-diameter peripheral wall portion 71 and the gas conduction holes 72a to 72d of the small-diameter peripheral wall portion 72 are respectively provided on the upstream side 73A, the side flow sides 73B and 73D, and the downstream side 73C of the outer peripheral wall portion 73. Is formed. In the present embodiment, the gas conduction holes 71a and 72a on the upstream side 73A are opposed to the exhaust gas flow direction. In other words, the gas conduction holes 71a and 72a on the upstream side 73A are formed through the outer peripheral wall portion 73 in parallel with the exhaust gas flow direction at the most upstream points of the large-diameter peripheral wall portion 71 and the small-diameter peripheral wall portion 72, respectively. .

  The gas conduction holes 71 a to 71 d and 72 a to 72 d are arranged at constant intervals along the circumferential direction of the outer peripheral wall portion 73 (that is, here at a rotation angle of 90 ° with respect to the sensor center line O). Accordingly, the gas conduction holes 71c and 72c on the downstream side 73C are disposed at positions facing the gas conduction holes 71a and 72a on the upstream side 73A and the sensor center line O therebetween. In other words, the gas conduction holes 71c and 72c on the downstream side 73C are formed through the outer peripheral wall portion 73 in parallel with the exhaust gas flow direction at the most downstream points of the large diameter peripheral wall portion 71 and the small diameter peripheral wall portion 72, respectively. .

  As shown in FIG. 1, the inner diameters of the gas conduction holes 71a and 72a on the upstream side 73A and the inner diameters of the gas conduction holes 71c and 72c on the downstream side 73C are both the gas conduction holes 71b on the side flow sides 73B and 73D. 72b, 71d, 72d are set smaller than the inner diameter. Here, the gas conduction holes 71a, 72a on the upstream side 73A and the gas conduction holes 71c, 72c on the downstream side 73C have the same inner diameter d1, whereas the gas conduction holes 71b, 72b on the side flow sides 73B, 73D, 71d and 72d have twice the inner diameter d2 (d2 = 2d1).

  Next, the gas conduction holes 61a to 61f of the inner peripheral wall portion 61 will be described. Each of these gas conduction holes 61a to 61f is a substantially rectangular shape having a uniform plan view, and is formed through the base of the inner peripheral wall 61 toward the sensor center line O as shown in FIG. ing. Note that these gas conduction holes 61a to 61f are located on the base side (exhaust passage) from the flange 65 so that the flange 65 is positioned between the gas conduction holes 71a to 71d of the large-diameter end wall 71. On the wall side). Further, the gas conduction hole 62 a of the inner end wall portion 62 has a substantially circular shape in plan view, and is formed through the inner end wall portion 62 on the sensor center line O.

  FIG. 3 (b) is an end view of the inner cover 6 schematically showing the arrangement positions of the gas conduction holes 61a to 61f, 62a by marks “□” and “◯”, respectively, in order to show the shapes of the front views. It is (A arrow line view in FIG. 2). As shown in FIG. 3 (b), here, the gas conduction holes 61 a to 61 f are arranged at a constant interval along the circumferential direction of the inner peripheral wall portion 61 (that is, here, every 60 ° rotation with respect to the sensor center line O). Corners).

  Comparing the arrangement of the gas conduction holes 61a to 61f in the inner peripheral wall portion 61 with the arrangement of the gas conduction holes 71a to 71d and 72a to 72d in the outer peripheral wall portion 73 described above, the gas conduction on the upstream side 73A of the outer peripheral wall portion 73 will be described. The gas conduction hole 61a of the inner peripheral wall portion 61 is disposed at a position corresponding to the holes 71a and 72a, and the gas conduction hole of the inner peripheral wall portion 61 is located at a position corresponding to the gas conduction holes 71c and 72c on the downstream side 73C of the outer peripheral wall portion 73. 61d is arranged. In addition, gas conduction holes 61b and 61c of the inner peripheral wall portion 61 are arranged at a position corresponding to the one side flow side 73B of the outer peripheral wall portion 73, and an inner position at a position corresponding to the other side flow side 73D of the outer peripheral wall portion 73. Gas conduction holes 61e and 61f in the peripheral wall portion 61 are arranged.

[2. Action and Effect]
(1) According to the NOx sensor 1 described above, of the gas conduction holes 71a to 71d and 72a to 72d formed in the outer cover 7 that covers the sensor element 3, the gas conduction holes 71a and 72a on the upstream side 73A in the exhaust gas flow direction. Since the inner diameter d1 is set smaller than the inner diameter d \ -2 of the gas conduction holes 71b, 72b, 71d, 72d on the exhaust gas flow direction side flow sides 73B, 73D, the gas conduction holes 71a, 72a on the upstream side 73A The flow rate (flow rate per unit time) of the exhaust gas flowing into the sensor element 3 can be reduced. Since this point has been confirmed by simulation, it will be described below. Thereby, since heat removal due to the exhaust gas can be reduced, it is possible to prevent the sensor element 3 from being rapidly cooled by the exhaust gas and causing heat cracks.

  (2) Further, according to the NOx sensor 1 described above, since the cover 5 is composed of the inner cover 6 and the outer cover 7, the exhaust gas flows through the gas conduction holes 71 a to 71 d and 72 a to 72 d of the outer cover 7 and the inner cover 6. It flows into the sensor element 3 after passing through both of the holes 61a to 61d and 62a. This point is also confirmed by performing simulations, and will be described below. Thus, since the exhaust gas flowing through the exhaust passage 8 is suppressed from flowing into the sensor element 3 vigorously and directly, the sensor element 3 can be prevented from being rapidly cooled by the exhaust gas and causing heat cracks.

  (3) According to the NOx sensor 1 described above, since the gas conduction holes 71a to 71d and 72a to 72d are formed in both the large diameter peripheral wall portion 71 and the small diameter peripheral wall portion 72 of the outer cover 7, the sensor element 3 can ensure the flow rate of the exhaust gas flowing into the NO. 3, and can ensure the responsiveness of the NOx sensor 1.

[3. simulation result]
5 and 6 are obtained by simulation and are schematic contour diagrams showing the flow rate of exhaust gas. In this simulation, an exhaust gas flow in the catalyst lower flow path 82 shown in FIG. 4 is assumed, exhaust gas having a predetermined flow rate and temperature is given as a boundary condition from the catalyst upper flow path 81 side, and the flow rate of the exhaust gas in the catalyst lower flow path 82 is calculated. In order to show the deviation of the flow rate of the exhaust gas confirmed from this result, in FIGS. 5 and 6, the calculated flow rate is stepped into a plurality of levels, and these are shown separately in lightness. Here, for the sake of convenience of the drawing, the flow rate is roughly shown.

  FIG. 5 shows a cross section including the radial center of the catalyst downstream flow path 82 and the sensor center line O of the NOx sensor 1 according to the above embodiment. FIG. 6A shows the inside of the modeled NOx sensor 1 according to the embodiment, and FIG. 6B shows the inside of the NOx sensor 11 according to the comparative example. FIG. 6 shows two cross sections including a sensor center line O and a cross section parallel to the exhaust gas flow direction and a cross section perpendicular to the exhaust gas flow direction. Show.

  In the NOx sensor 11 shown in FIG. 6B, the gas conduction holes 71a to 71d and 72a to 72d formed in the outer cover 7 have the same inner diameter d2 as compared with the NOx sensor 1 according to the above embodiment. Is different. That is, in the NOx sensor 11 according to the comparative example, the outer cover 17 corresponding to the outer cover 7 according to the above embodiment has a large diameter peripheral wall portion 171 and a large diameter peripheral wall portion 171 corresponding to the large diameter peripheral wall portion 71 and the small diameter peripheral wall portion 72 according to the above embodiment, respectively. The small-diameter peripheral wall portion 172 has gas conduction holes 171a to 171d and 172a to 172d each having an inner diameter d2. The NOx sensor 11 according to the comparative example is common to the NOx sensor 1 according to the above embodiment except for the outer cover 17 described above. In FIG. 6B, the same reference numerals are given to these common members. It is attached.

  As shown in FIG. 5, in the first bent portion 82a of the catalyst downstream flow path 82, the exhaust gas flow direction is bent in accordance with the bent shape, and in this way, the exhaust gas is concentrated near the tip of the NOx sensor 1 in the straight portion 82c. I understand that That is, the location where the NOx sensor 1 is installed is a location where the flow rate of the exhaust gas is large. Usually, in such a location, heat removal due to the exhaust gas becomes large, and thus there is a possibility that a heat crack may occur in the sensor element 3. is there. However, since this location coincides with a location where exhaust gas with sufficient mixing flows, it is preferable to install the NOx sensor 1 at this location in order to properly detect the state of the exhaust gas.

  On the other hand, when attention is paid to the flow rate inside the NOx sensor 1, as shown in FIG. 6B, in the NOx sensor 11 according to the comparative example, the space between the sensor element 3 and the inner cover 6 is partially colored. It can be seen that the flow rate of the exhaust gas flowing into the sensor element 3 is partially high. In particular, in the vicinity of the base portion of the sensor element 3, there is a portion where the flow rate of exhaust gas is considerably large. Further, in the space between the inner cover 6 and the outer cover 17, the color is dark over substantially the entire area, so that the flow rate of exhaust gas that enters the outer cover 17 from the exhaust passage 8 through the gas conduction holes 171 a to 171 d and 172 a to 172 d. It can be seen that there are many.

  On the other hand, as shown in FIG. 6A, in the NOx sensor 1 according to the above embodiment, the space between the sensor element 3 and the inner cover 6 is entirely white, and the base of the sensor element 3 is There is no part where the flow rate of the exhaust gas as seen by the NOx sensor 11 is considerably large in the vicinity, and it can be seen that the flow rate of the exhaust gas flowing into the sensor element 3 is reduced. Further, in the space between the inner cover 6 and the outer cover 7, there are many lighter colored portions than the NOx sensor 11, and the exhaust gas that enters the inner side of the outer cover 7 from the exhaust passage 8 through the gas conduction holes 71 a to 71 d and 72 a to 72 d. It can be seen that the flow rate is also reduced. In particular, the flow rate of the exhaust gas is reduced on the base side of the space between the large-diameter peripheral wall portion 71 and the inner peripheral wall portion 61.

  FIG. 7 is a schematic diagram showing the exhaust gas flow direction corresponding to FIG. 6A, obtained by simulation, and FIG. 7A shows a cross section parallel to the longitudinal direction of the exhaust passage 8. FIG. 7B shows a cross section perpendicular to the longitudinal direction of the exhaust passage 8. The white arrow shown in FIG. 7 indicates the main exhaust gas flow direction inside the NOx sensor 1, and the exhaust gas flow direction is not limited to this, and there is a fine flow directed in various directions.

  As shown in FIG. 7, the exhaust gas mainly flows into the outer cover 7 from the gas conduction holes 71 a and 72 a on the upstream side 73 </ b> A and the gas conduction holes 71 c on the downstream side 73 </ b> C of the large diameter peripheral wall portion 71. It can be seen that the gas flows out of the outer cover 7 from the gas conduction hole 72c on the downstream side 73C and the gas conduction holes 71b, 72b, 71d, 72d on the side flow sides 73B and 73D.

  Among these, the exhaust gas flowing in from the gas conduction hole 71a on the upstream side 73A of the large-diameter peripheral wall portion 71 collides with the bowl-shaped portion 65 as shown in FIG. 7A, and the large-diameter peripheral wall portion 71 and the inner peripheral wall portion 61. It can be seen that the gas flows from the gas conduction hole 61d on the downstream side 73C of the inner peripheral wall portion 61 to the inside of the inner cover 6 and flows to the sensor element 3 side. The exhaust gas flows into the inside of the large-diameter peripheral wall portion 71 from the gas conduction hole 71c on the downstream side 73C of the large-diameter peripheral wall portion 71 against the flow direction, as described above, on the downstream side 73C of the inner peripheral wall portion 61. This is probably because the exhaust gas flows into the inner cover 6 from the gas conduction hole 61d, whereby the pressure decreases on the downstream side 73C of the space between the large-diameter peripheral wall portion 71 and the inner peripheral wall portion 61.

  Further, as indicated by broken line arrows in FIG. 7B, the exhaust gas is also directed toward the sensor element 3 from the gas conduction holes 61b, 61c, 61e, 61f on the side flow sides 73B, 73D of the inner peripheral wall 61. It is thought to flow. Furthermore, although it is not a main flow, it is considered that there is also a flow of exhaust gas flowing from the gas conduction hole 62a of the inner end wall portion 62 toward the inner side of the inner cover 6.

  The exhaust gas flowing into the inner cover 6 in this way flows around the sensor element 3 toward the inner end wall portion 62 side, and mainly passes through the gas conduction hole 62a of the inner end wall portion 62 to become the inner cover 6. It can be seen that it flows out of. Further, as shown in FIG. 7A, a part of the exhaust gas flowing into the inner cover 6 is a space on the base side of the upstream side 73A that is relatively low pressure from the gas conduction hole 61a on the upstream side 73A. Also flows out. Since the exhaust gas can flow into the sensor element 3 when flowing inside the inner cover 6 in this way, if the flow rate of the exhaust gas inside the inner cover 6 is large, the flow rate of the exhaust gas flowing into the sensor element 3 also increases. Can be guessed.

  In the NOx sensor 1 according to the above embodiment, as described above, the inner diameter d1 of the gas conduction holes 71a, 72a on the upstream side 73A is the inner diameter d2 of the gas conduction holes 71b, 72b, 71d, 72d on the side flow sides 73B, 73D. Therefore, the flow rate of exhaust gas flowing into the inner side of the outer cover 7 through the gas conduction holes 71a and 72a on the upstream side 73A can be reduced, whereby the flow rate of exhaust gas flowing into the inner side of the inner cover 6 is reduced. Therefore, the flow rate of the exhaust gas flowing into the sensor element 3 can be reduced.

  As described above, according to the NOx sensor 1 according to the above embodiment, the flow rate of the exhaust gas flowing into the sensor element 3 can be reduced. Therefore, as shown in FIG. Even if the location where the flow rate of the exhaust gas is large coincides, it is possible to prevent heat cracks from occurring in the sensor element 3 while properly detecting the state of the exhaust gas.

  In addition, the NOx sensor 1 according to the above embodiment and the NOx sensor 11 according to the comparative example have no difference in the main exhaust gas flow direction inside the sensor. For this reason, compared with the NOx sensor 11, the NOx sensor 1 reliably emits exhaust gas to the sensor element 3 in the same manner as the NOx sensor 11 while reducing the flow rate of the exhaust gas flowing into the sensor element 3 as described above. It can be made to flow. Therefore, according to the NOx sensor 1 according to the above embodiment, the same detectability as that of the NOx sensor 11 can be obtained.

[4. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
The shape, number, and arrangement of the gas conduction holes shown above are examples, and are not limited to the above. For example, the arrangement intervals of the gas conduction holes 71a to 71d and 72a to 72d formed in the outer peripheral wall portion 73 and the gas conduction holes 61a to 61f formed in the inner peripheral wall portion 61 are not uniform along the circumferential direction. May be. Further, the positions where the gas conduction holes 71a and 72a on the upstream side 73A and the gas conduction holes 71c and 72c on the downstream side 73C are formed are not the most upstream point and the most downstream point of the outer circumferential wall part 73, respectively. May be. Further, the specific number of the gas conduction holes 71a to 71d and 72a to 72d formed in the outer peripheral wall portion 73 is arbitrary.

  Moreover, the magnitude | size of each gas conduction | electrical_connection hole 71a-71d, 72a-72d, 61a-61f, 62a is not limited to said thing. As long as the inner diameter d1 of the gas conduction holes 71a and 72a on the upstream side 73A is set smaller than the inner diameter d2 of the gas conduction holes 71b, 72b, 71d and 72d on the side flow sides 73B and 73D, as described above. Since the flow rate of the exhaust gas flowing from the gas conduction holes 71a and 72a on the upstream side 73A can be reduced, the occurrence of heat cracks can be prevented.

  Further, the inner diameters of the gas conduction holes 71c, 72c on the downstream side 73C of the outer peripheral wall 73 may not be set smaller than the inner diameter d2 of the gas conduction holes 71b, 72b, 71d, 72d on the side flow sides 73B, 73D. However, if it is set to be small as described above, the flow rate of the exhaust gas flowing into the sensor element 3 can be further reduced, which is more effective in preventing heat cracks in the sensor element 3.

  Moreover, the structure of the cover 5 shown above is an example. For example, in the case where the sensor element 3 is heated to a relatively low temperature, the inner cover 6 may be omitted, or the above-described hook-shaped portion 65 may be provided. Omitted, the exhaust gas that has flowed into the large-diameter peripheral wall 71 from the gas communication hole 71 a on the upstream side 73 </ b> A may flow directly toward the gas communication hole 61 a of the inner peripheral wall 61. Further, the shapes of the outer cover 7 and the inner cover 6 are not limited to those described above. For example, the outer cover 7 is not formed in a step shape by the large-diameter peripheral wall portion 71 and the small-diameter peripheral wall portion 72 described above, but a cylindrical peripheral wall portion having a uniform diameter, and an end wall portion of the tip portion, It may be formed by.

  Since the structure of the cover 5 and the flow direction of the exhaust gas inside the sensor (the inner part of the cover 5) are considered to be related, the gas conduction hole is provided in the sensor element 3 according to the structure of the cover 5. It is preferable to set the arrangement so that the gas can surely flow in. When the cover 5 has a double structure as exemplified in the above embodiment, a gas conduction hole is formed not only in the outer cover 7 but also in the inner cover 6 to secure a flow path for allowing exhaust gas to flow into the sensor element 3. There is a need to.

Moreover, the structure of the exhaust passage 8 shown above is an example, and the exhaust passage 8 may include, for example, a plurality of exhaust gas purification devices, or may include other exhaust gas purification devices instead of the SCR device 9. Also good. Moreover, although the exhaust passage of the vehicle which uses a diesel engine as a drive source was illustrated above, the object in which this exhaust gas sensor is installed is not limited to this.
Moreover, the shape of the catalyst downstream flow path 82 and the casing 91 is arbitrary. For example, the catalyst downstream flow path 82 does not have to be bent as described above.

  Further, the installation position of the exhaust gas sensor is not limited to the above, and the exhaust gas sensor may be installed, for example, in the first bent portion 82a in the catalyst lower flow path 82 described above. In the above embodiment, the exhaust gas sensor is installed downstream of the exhaust gas purification device. However, the exhaust gas sensor may be installed upstream of the exhaust gas purification device.

  For example, the NOx sensor 1 is installed in the upstream catalyst flow path 81 upstream of the SCR device 9 to detect the NOx amount of the exhaust gas before flowing into the SCR device 9, and the urea injection amount is determined based on this detection information. You may control. Also in this case, it is preferable to install the NOx sensor 1 at a location where the exhaust gas is sufficiently mixed so that the exhaust gas state is not biased, but the sufficiently mixed exhaust gas circulates in the catalyst upper flow path 81. Even if the location coincides with a location where the flow rate of exhaust gas is large, the above-described NOx sensor 1 can prevent the occurrence of heat cracks while properly detecting the state of exhaust gas as described above.

  In the above, a NOx sensor is exemplified as the exhaust gas sensor, but the exhaust gas sensor may be another exhaust gas sensor such as an oxygen sensor. In this case as well, heat removal due to the exhaust gas can be reduced by reducing the flow rate of the exhaust gas flowing into the sensor element from the gas conduction hole upstream in the exhaust gas flow direction as described above. It can prevent that a crack arises.

1 NOx sensor (exhaust gas sensor)
3 Sensor element 5 Cover 6 Inner cover 61 Inner peripheral wall
61a-61f Gas conduction hole
62 Inner end wall
62a Gas conduction hole
7 Outer cover 71 Large-diameter peripheral wall (tip-side cylindrical peripheral wall)
71a-71d Gas conduction hole 72 Small-diameter peripheral wall part (base end side cylindrical peripheral wall part)
72a-72d Gas conduction hole 73 Outer peripheral wall part (cylindrical peripheral wall part)
73A Upstream side 73B, 73D Side flow side 73C Downstream side 75 Outer end wall (end wall)
8 Exhaust passage 9 SCR device (exhaust gas purification device)

Claims (1)

An exhaust gas sensor that protrudes from the wall surface of the exhaust passage and has a sensor element and a cover that covers the sensor element,
The cover has a cylindrical peripheral wall portion in which a plurality of gas conduction holes are formed, and an end wall portion at a tip portion of the cylindrical peripheral wall portion,
The gas conduction holes are respectively formed on the upstream and downstream sides of the cylindrical peripheral wall portion in the exhaust gas flow direction and on the side flow side,
An exhaust gas sensor, wherein an inner diameter of the gas conduction hole on the upstream side in the exhaust gas flow direction is set smaller than an inner diameter of the gas conduction hole on the upstream side in the exhaust gas flow direction.