Gas sensor

Abstract

To provide a gas sensor for improving wet resistance regardless of a mounting position of a protector.SOLUTION: A gas sensor 1 includes a sensor element 21, a main metal fitting 11, and a protector 51. The protector is in a bottomed cylindrical shape, and includes at least one gas discharge hole 53 formed on a bottom face 51f2 in an end side and at least two gas introduction holes 56 formed in a rear end side of the gas discharge hole. An extension line L1 of a first side S1 that is the closest from a gravity center G of a bottom face is extended from among the sides of a circumscribed rectangle when only one circumscribed rectangle BR that is tangent to the gas discharge hole while including all the gas discharge holes and has the minimum area is determined by viewing the protector from an end side, and half the gas introduction holes or larger are disposed in a first area R1 that does not include any circumscribed rectangles from among two areas divided by the extension line.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Conventionally, there has been known a gas sensor in which a sensor element is held in a cylindrical metal shell and the tip side of the sensor element exposed to exhaust gas is protected by a single or double protector. This protector is provided with a gas inlet and a gas outlet, but is required to be water resistant to prevent condensed water mixed in the exhaust gas from reaching the sensor element. Here, the sensor element is heated by its own heater or by high-temperature exhaust gas, and if condensed water comes into contact with the sensor element, a thermal shock occurs, which may cause the element to crack. Therefore, a technology has been developed in which a gas inlet hole 560 is provided in a horizontal step provided in a protector 500, and the gas inlet hole faces the tip side of the metal shell, as shown in Fig. 5 (Patent Document 1). According to this technology, exhaust gas flows from the gas inlet hole 560 toward the metal shell, and then changes direction in the internal space between the gas inlet hole 560 and the metal shell, and flows toward the tip side inside the protector 500. For this reason, it is said that condensed water is easily separated from the exhaust gas by its own weight. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-72458 A (Figs. 1 and 3) Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, as shown in FIG. 5, when a gas sensor is attached to an exhaust pipe or the like, depending on the attachment position, the axis O of the sensor element 21 may be tilted at an angle of about 10° from the horizontal position. However, as shown in FIG. 6, the protector 500 of Patent Document 1 has a rectangular gas exhaust hole 530 on the bottom surface at the tip side, so there is a problem that the amount of condensed water CW inside the protector 500 drained from the gas exhaust hole 530 varies depending on the circumferential orientation of the gas sensor. For example, as shown in FIG. 6(a), when the short side of the gas exhaust hole 530 is closer to the horizontal plane on which the gas sensor is to be mounted, that is, the side farther from the center of gravity G of the bottom surface of the protector 500 is closer to the horizontal plane, more condensed water CW is drained from the gas exhaust hole 530. It should be noted that the "horizontal surface of the object to be attached" refers to the horizontal surface of the object to which the gas sensor is attached (for example, the automobile when the gas sensor is attached to an automobile).

[0005] On the other hand, as shown in FIG. 6(b), when the long side of the gas exhaust hole 530 is close to the horizontal plane, that is, when the side closest to the center of gravity G of the bottom surface of the protector 500 is close to the horizontal plane, the gas exhaust hole 530 as a whole is farther (higher) than the horizontal plane, so that the amount of condensed water CW drained from the gas exhaust hole 530 decreases and the condensed water CW is more likely to accumulate inside the protector 500.

[0006] When the level of the condensed water CW rises, the condensed water CW reaches the detection section 22 through the element introduction hole 25 of the sensor element 21, which may cause the element to crack, resulting in insufficient water resistance. The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a gas sensor having improved water resistance regardless of the mounting position of a protector. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the gas sensor of the present invention comprises a sensor element extending in an axial direction, a cylindrical metal shell surrounding and holding a radial periphery of the sensor element, and a protector fixed to a front end side of the metal shell and having the sensor element directly disposed inside the protector, the protector being cylindrical with a bottom and having at least one gas exhaust hole formed in a bottom surface at the front end side and two or more gas inlet holes formed on the rear end side of the gas exhaust hole, wherein when a single circumscribing rectangle is defined that includes all of the gas exhaust holes and is in contact with the gas exhaust holes to have a smallest area when viewed from the front end side of the protector, an extension line of a first side of the circumscribing rectangle that is closest to the center of gravity of the bottom surface is extended, and of two regions separated by the extension line, more than half of the gas inlet holes are disposed in the first region that does not include the circumscribing rectangle.

[0008] According to this gas sensor, even if the side of the gas exhaust hole that is closer to the center of gravity approaches the horizontal plane of the object on which the gas sensor is mounted and the amount of condensed water drained from the gas exhaust hole decreases, more than half of the gas inlet holes are positioned in the first region that is closer to the horizontal plane, so that the amount of water drained from the gas inlet holes increases and condensed water is less likely to accumulate inside the protector. As a result, water resistance can be improved regardless of the mounting position of the protector.

[0009] In the gas sensor of the present invention, the gas introduction hole may be present in the wall surface of the protector on the perpendicular bisector of the first side in the first region. Since the position on the perpendicular bisector is close to the horizontal plane of the gas sensor, it is preferable that a gas inlet hole is present at this position, since this will further increase the amount of water discharged from the gas inlet hole. Effect of the Invention

[0010] According to the present invention, a gas sensor having improved water resistance can be obtained regardless of the mounting position of the protector. [Brief description of the drawings]

[0011] [Figure 1]1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a cross-sectional view showing an element introduction hole of the sensor element. [Diagram 3] FIG. 4 is a plan view of the protector as viewed from the tip side. [Figure 4] FIG. 13 is a plan view of a protector according to a modified example, as viewed from the tip side. [Diagram 5] FIG. 1 is a diagram showing a state in which condensed water accumulates when a conventional gas sensor is attached to an exhaust pipe at an angle of 10° from the horizontal position. [Figure 6] 13 is a diagram showing that the amount of condensed water drained from the gas exhaust hole differs depending on the circumferential orientation of the gas sensor when a rectangular gas exhaust hole is provided on the bottom surface of a protector. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An embodiment of the present invention will be described in detail with reference to Fig. 1 to Fig. 3. Fig. 1 is a cross-sectional view of a gas sensor 1 according to an embodiment of the present invention, Fig. 2 is a cross-sectional view showing an element introduction hole 25 of a sensor element 21, and Fig. 3 is a plan view of a protector 51 as viewed from the tip side.

[0013] In FIG. 1, a gas sensor (full range air-fuel ratio gas sensor) 1 includes a sensor element 21, a holder (ceramic holder) 30 having a through hole 32 penetrating in the axial O direction for inserting the sensor element 21 therethrough, a metal shell 11 surrounding the radial periphery of the ceramic holder 30, and a protector 51. The tip side of the sensor element 21 where the detection portion 22 is formed protrudes further forward than the ceramic holder 30 and the metal shell 11. The sensor element 21 thus passed through the through hole 32 is fixed inside the metal shell 11 while maintaining airtightness in the front-to-rear direction by compressing a seal material (talc in this example) 41 arranged on the rear end face side (upper side in the figure) of the ceramic holder 30 in the front-to-rear direction via a sleeve 43 and a ring washer 45 made of an insulating material.

[0014] The rear end side 29 of the sensor element 21 protrudes rearward beyond the sleeve 43 and the metal shell 11, and the electrode terminals 24 formed on the rear end side 29 are electrically connected by pressure welding to the terminal fittings 75 provided at the ends of the lead wires 71 drawn to the outside through a sealing material 85. The rear end side 29 of the sensor element 21 including the electrode terminals 24 is covered by an outer tube 81. A more detailed description will be given below.

[0015] The sensor element 21 extends in the direction of the axis O and is in the form of a strip (plate) equipped with a detection section 22 consisting of detection electrodes (not shown) for detecting a specific gas component in a gas to be detected, at the tip side (lower side in the figure) facing the measurement target. The cross section of the sensor element 21 has a rectangular shape of a certain size at the front and rear, and is formed as an elongated object mainly made of ceramic (solid electrolyte, etc.). The sensor element 21 itself is the same as that of a conventionally known sensor element, and a pair of detection electrodes constituting the detection section 22 are disposed at the tip side of the solid electrolyte (member), and an electrode terminal 24 for connecting a lead wire 71 for extracting a detection output is exposed and formed at the rear end side connected to the detection electrodes.

[0016] In this example, a heater (not shown) is provided inside the front end of the ceramic material formed in a laminated shape on the solid electrolyte (member) of the sensor element 21, and electrode terminals 24 for connecting lead wires 71 for applying voltage to the heater are formed and exposed on the rear end. Although not shown, these electrode terminals 24 are formed in a vertically elongated rectangle, and for example, on the rear end side 29 of the sensor element 21, three or two electrode terminals are arranged horizontally on the wide surfaces (both sides) of the strip. The detection portion 22 of the sensor element 21 is covered with a porous protective layer 23 made of alumina, spinel, or the like.

[0017] 2, element introduction holes 25 are provided on both short sides of the sensor element 21, which are connected to the detection section 22 and introduce the gas to be detected into the detection section 22 (the measurement chamber 27), and a porous diffusion resistance layer is disposed in the element introduction holes 25. A heater 28 is laminated on the detection section 22. In this embodiment, the protective layer 23 is made up of two layers, an inner layer 23a and an outer layer 23b.

[0018] The metal shell 11 has a cylindrical shape with different diameters at the front and rear, and has a cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 12 at the front end for fitting and fixing a protector 51 (described later) thereto, and a screw 13 having a larger diameter is provided on the outer circumferential surface at the rear (upper part in the figure) of the metal shell 11 for fixing the sensor 1 to an exhaust pipe of an engine. And at the rear of the metal shell 11 is provided a polygonal tool engagement portion 14 for screwing the sensor 1 with the screw 13. Also, at the rear of the tool engagement portion 14 is provided a cylindrical portion 15 for fitting and welding a protective tube (outer tube) 81 that covers the rear of the gas sensor 1 thereto, and at the rear of the tool engagement portion 14 is provided a cylindrical portion 15 for welding the protective tube (outer tube) 81 thereto.

[0019] In addition, this crimping cylindrical portion 16 is bent inwardly in Fig. 1 for after crimping. A gasket 19 is attached to the lower surface of the tool engagement portion 14 for sealing when screwed in. On the other hand, the metallic shell 11 has an inner hole 18 penetrating therethrough in the direction of the axis O. The inner peripheral surface of the inner hole 18 has a tapered step portion 17 that tapers radially inward from the rear end side to the front end side.

[0020] A ceramic holder 30 made of insulating ceramic (e.g., alumina) and formed into a roughly short cylindrical shape is disposed inside the metal shell 11. The ceramic holder 30 has a front-facing surface 30a formed in a tapered shape tapering toward the front end. A portion of the front-facing surface 30a near the outer periphery is engaged with the step portion 17, and the ceramic holder 30 is pressed from the rear end side by a seal material 41, whereby the ceramic holder 30 is positioned within the metal shell 11 and is gap-fitted. On the other hand, the through hole 32 is provided in the center of the ceramic holder 30 and is a rectangular opening having substantially the same dimensions as the cross section of the sensor element 21 so that the sensor element 21 can pass through with almost no gap.

[0021] The sensor element 21 is inserted into the through hole 32 of the ceramic holder 30 , and a tip 21 a of the sensor element 21 protrudes forward beyond the ceramic holder 30 and the tip 12 a of the metallic shell 11 . On the other hand, the tip portion of the sensor element 21 is covered with a single-layered, bottomed, cylindrical protector (protective cover) 51. The rear end of the protector 51 is fitted onto the cylindrical portion 12 of the metal shell 11 and welded thereto.

[0022] The protector 51 has a cylindrical first peripheral wall 51s surrounding the tip side (detection unit 22) of the sensor element 21, a large diameter portion 51x having a tip-facing surface 51f1 connected to the tip side, and a small diameter portion 51y protruding from the large diameter portion 51x to the tip side in the direction of the axis L. The small diameter portion 51y has a cylindrical second peripheral wall 51t connected to the tip-facing surface 51f1 and a bottom surface 51f2 connected to the tip side. The outer diameter of the first peripheral wall 51s is larger than the outer diameter of the second peripheral wall 51t. Furthermore, a plurality of (six) gas introduction holes 56 are formed at equal intervals in the circumferential direction on the tip-facing surface 51f1 (FIG. 3).

[0023] Meanwhile, one rectangular gas discharge hole 53 is disposed so as to include the center of gravity G of the bottom surface 51f2. The center of gravity G can be calculated as the geometric center of a plane figure obtained by projecting the bottom surface 51f2 onto a plane. The gas exhaust hole 53 is positioned closer to the tip than the gas inlet hole 56, and the gas inside the protector 51 is sucked out through the gas exhaust hole 53 to the outside by the flow of the detected gas flowing through the mounting object (exhaust pipe, etc.) on which the gas sensor 1 is mounted, and the detected gas is introduced into the protector 51 through the gas inlet hole 56 due to the negative pressure.

[0024] In this example, on the tip-facing surface 51f1, louvers 51L are formed by cutting and raising from a single cut toward the rear end at the position of each gas introduction hole 56, and the inner wall 51i (Figure 1) of the louvers 51L forms the gas introduction hole 56. In addition, the center of bottom surface 51f2 is cut toward the rear end side along two parallel slits to form cover 53c, and gas exhaust hole 53 is formed in the gap between bottom surface 51f2 and cover 53c facing in the radial direction. In this case, when protector 51 is viewed from the tip side in the axis O direction, gas exhaust hole 53 is not directly visible, so that water droplets such as condensed water can be prevented from entering protector 51 through gas exhaust hole 53.

[0025] 1, the terminal fittings 75 provided at the tip of each lead wire 71 drawn to the outside through a sealing material 85 are pressed against and electrically connected to the electrode terminals 24 formed on the rear end side 29 of the sensor element 21 by their spring properties. In the gas sensor 1 of this embodiment, the terminal fittings 75 including the press-contact portions are provided in respective housing portions provided in an insulating separator 91 arranged in an outer cylinder 81, and are arranged to face each other. The separator 91 is restricted from moving in the radial direction and toward the tip side via a holding member 82 fixed by crimping in the outer cylinder 81. The tip portion of the outer cylinder 81 is fitted and welded to the cylindrical portion 15 on the rear end side of the metal shell 11, thereby covering the rear of the gas sensor 1 in an airtight manner. The lead wire 71 is passed through a sealing material (e.g., rubber) 85 arranged inside the rear end of the outer tube 81 and led out to the outside. The small-diameter tube portion 83 is crimped to reduce the diameter and compress the sealing material 85, thereby maintaining the airtightness of this portion.

[0026] Incidentally, a step 81d having a larger diameter at the front end side is formed slightly rearward from the center of the outer cylinder 81 in the direction of the axis O, and the inner surface of this step 81d supports the rear end of the separator 91 so as to push it forward. Meanwhile, a flange 93 formed on the outer periphery of the separator 91 is supported on a holding member 82 fixed to the inside of the outer cylinder 81, and the separator 91 is held in the direction of the axis O by the step 81d and the holding member 82.

[0027] Next, the characteristic features of the present invention will be described. 3, a circumscribing rectangle BR that contains the gas discharge hole 53 and has the smallest area by contacting the gas discharge hole 53 is determined. In other words, the circumscribing rectangle BR forms the outline of the gas discharge hole 53. Then, an extension line L1 of a first side S1, which is the long side closest to the center of gravity G, of each side of the circumscribing rectangle BR is extended. Then, of the two regions R1 and R2 divided by the extension line L1, more than half of the gas introduction holes 56 (in this example, half of the total number of six gas introduction holes 56, or three) are arranged in the first region R1, which does not include the gas exhaust holes 53 (the circumscribing rectangle).

[0028] In this manner, as shown in FIG. 6(b), even if the side of gas exhaust hole 53 closer to center of gravity G approaches the horizontal plane of gas sensor 1 and the amount of condensed water drained from gas exhaust hole 53 decreases, more than half of gas introduction holes 56 are arranged in first region R1, which is the side closer to the horizontal plane, so that the amount of water drained from gas introduction hole 56 increases and condensed water is less likely to accumulate inside protector 51. As a result, water resistance can be improved regardless of the mounting position of the protector 51.

[0029] In this example, there are two long sides closest to the center of gravity G, and if long side S1 and another long side in Fig. 3 are selected, an extension line L2 can be drawn parallel to the extension line L1. Even if the first region is set based on the extension line L2, more than half of the gas introduction holes 56 (in this example, half of the total number of gas introduction holes 56, i.e., three) are arranged in the first region. In addition, the number of gas introduction holes 56 in the first region R1 counts those in which all of the individual gas introduction holes 56 are within the first region R1, and does not count those in which, for example, only a portion of the gas introduction hole 56 is included in the first region R1. The bounding rectangle excludes squares, since in the case of a square, all sides may be equidistant from the center of gravity G.

[0030] As shown in FIG. 3, in this example, in the first region R1, a gas introduction hole 56 is present in a surface (front end facing surface) 51f1 of the protector 51 on the perpendicular bisector M of the first side S1. Since the position on the perpendicular bisector M is close to the horizontal plane, if the gas introduction hole 56 is located at this position, the amount of drainage from the gas introduction hole 56 is preferably further increased.

[0031] The present invention is not limited to the above embodiments. For example, as shown in Fig. 4, the protector 61 may have two or more gas exhaust holes 63a, 63b. Also, in Fig. 4, the shape of the gas exhaust holes 63a, 63b is circular and is not limited to rectangular. Furthermore, the gas exhaust holes 63a, 63b may be arranged to avoid the center of gravity G. In this case, a single circumscribing rectangle BR is determined that includes all the gas exhaust holes 63a, 63b, contacts the gas exhaust holes 63a, 63b, and has the smallest area. Of the sides of the circumscribing rectangle BR, only the long side on the lower side in FIG. 4 becomes the first side closest to the center of gravity G, and only one extension line L1 is determined. In the example of FIG. 4, of the two regions R1, R2 divided by the extension line L1, the number of gas introduction holes 66 in the first region R1 (three) exceeds half of the total number of gas introduction holes 66 (five).

[0032] The sensor element is not limited to one that measures the concentration of oxygen, so long as it is plate-shaped, but one that measures the concentration of nitrogen oxides (NOx) or hydrocarbons (HC) may also be used. The shape and number of the gas inlet holes are not limited, and may be, for example, elliptical. The shape of the gas exhaust hole is also not limited. The position of the element introduction hole 25 is not limited, and in the above embodiment, it was located on both short side surfaces of the sensor element 21, but it may be located, for example, on the long side surface, or a hole that extends axially inside the element and opens at the rear end side, or the like; in short, it is applicable as long as it is a hole that takes in gas into the sensor element.

[0033] The protector to which the present invention applies is a protector in which the sensor element 21 is directly disposed inside the protector itself. For example, in the case of a double protector, the inner protector closest to the sensor element 21 is the subject of the present invention. [Explanation of symbols]

[0034] 1 Gas sensor 11 Metal fitting 21 Sensor element 51, 61 Protector 51f2 Bottom 53, 63 Gas exhaust hole 56, 66 Gas inlet O axis BR circumscribed rectangle G Center of gravity of bottom surface S1 First side L1, L2 extension line R1, R2 area R1 1st area M Perpendicular bisector of the first side

Claims

1. A sensor element extending in an axial direction; a cylindrical metal shell that surrounds and holds the sensor element in a radial direction; a protector fixed to a tip end side of the metallic shell and having the sensor element directly disposed therein; Equipped with the protector is a cylindrical member having a bottom, and has at least one gas exhaust hole formed in a bottom surface at a tip end side, and two or more gas introduction holes formed on a rear end side of the gas exhaust hole, When the protector is viewed from the tip side, a single circumscribing rectangle that includes all of the gas discharge holes and is in contact with the gas discharge holes to have a minimum area is determined, Extending an extension line of a first side of the circumscribed rectangle that is closest to the center of gravity of the base, a first region that does not include the circumscribing rectangle, and a second region that does not include the circumscribing rectangle, and a third region that does not include the circumscribing rectangle.

2. 2. The gas sensor according to claim 1, wherein the gas introduction hole is present in a wall surface of the protector on a perpendicular bisector of the first side in the first region.

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