Gas Sensors

Abstract

To provide a gas sensor in which damage of a separator is suppressed and generation of metal powder due to vibration of the separator is suppressed, so that reliability of electric connection between an electrode pad and a terminal metal fitting is secured.SOLUTION: A gas sensor 1 includes a sensor element 21 with an electrode pad 24, a main body metal fitting 11, an external cylinder 81 made of metal and having a tubular shape, and a separator 91 housed in the external cylinder and holding a terminal metal fitting 75 connected to an electrode pad of the sensor element. The external cylinder includes, in the order from a front end side, a large-diameter part 81a, a step part 81d extending from a rear end of the large-diameter part to the inside in a radial direction and perpendicular to an axial line O direction, a diameter-reducing part 81b reducing in a diameter while extending from the step part to the rear end side, and a small-diameter part 81c continuing to the diameter-reducing part. A rear end facing surface of the separator is engaged by a front end facing surface of the step part. A gap G between the external cylinder and the separator in the radial direction is 1 mm or more. An inner diameter D1 of the small-diameter part and an inner diameter D2 in a region where the gap of the large-diameter part is formed satisfy a relation of 0.5≤D1 / D2≤0.8.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas sensor having an outer cylinder that houses a sensor element. [Background technology]

[0002] Conventionally, there has been known a gas sensor in which a sensor element for detecting a specific gas in a gas to be measured is held by a metal shell, and the rear end side of the sensor element is housed in a metal outer tube. Here, the front end side of the outer tube is connected to the rear end side of the metal shell, and the rear end side of the outer tube is an unfixed free end. The front end side of the outer tube is a large diameter portion, and a small diameter portion is formed on the rear end side of the large diameter portion via a step portion (rising portion). The rear end side of the separator is engaged with the inside of this step portion (the surface facing the front end). However, when this gas sensor is mounted on a vehicle or the like and used, the rear end of the outer cylinder, which is the free end, vibrates due to vibrations caused by the vehicle traveling, and stress is concentrated near the rising portion of the outer cylinder close to the connection portion with the metal shell, causing cracks. In view of this, a technology has been reported in which a tapered portion narrowing from the rising portion of the outer cylinder toward the rear end is provided to relieve the stress concentration near the rising portion (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6778125 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a problem that shocks or vibrations such as those caused by flying stones hitting the gas sensor can deform the outer cylinder, damaging the separator inside, or vibrating the separator, which is a heavy object inside the outer cylinder, causing wear on the outer cylinder adjacent to the separator and the metal fittings holding the separator, generating metal powder. This metal powder can get between the electrode pads of the sensor element and the terminal fittings held by the separator, reducing the reliability of the electrical connection between the electrode pads and the terminal fittings.

[0005] The present invention has been made in consideration of the current situation, and aims to provide a gas sensor which suppresses damage to the separator and also suppresses the generation of metal powder due to vibration of the separator, thereby ensuring the reliability of the electrical connection between the electrode pads and the terminal fittings. [Means for solving the problem]

[0006] A gas sensor according to the present invention is a gas sensor including a sensor element extending in an axial direction and having an electrode pad on a rear end side thereof, a metal shell surrounding and holding the sensor element, a cylindrical metallic outer cylinder attached to the rear end side of the metal shell and housing the rear end side of the sensor element, and a separator housed in the outer cylinder and holding terminal fittings connected to the electrode pads of the sensor element, wherein the outer cylinder has, in order from a front end side, a large diameter portion, a step portion extending radially inward from a rear end of the large diameter portion and perpendicular to the axial direction, a reduced diameter portion extending from the step portion toward the rear end side and reducing in diameter, and a small diameter portion connected to the reduced diameter portion, a rear end facing surface of the separator is engaged with a front end facing surface of the step portion, the radial gap between the outer cylinder and the separator is 1 mm or more, and an inner diameter D1 of the small diameter portion and an inner diameter D2 of a region of the large diameter portion where the gap is formed satisfy a relationship of 0.5≦D1 / D2≦0.8. The terminal metal fitting protrudes toward the rear end side beyond the separator, and the reduced diameter portion extends toward the rear end side beyond the terminal metal fitting. It is characterized by:

[0007] According to this gas sensor, by making the gap 1 mm or more, it is possible to prevent the separator from coming into contact with the inner surface of the outer cylinder due to impact or vibration caused by a flying stone colliding with the gas sensor, which could result in damage to the separator or generation of metal powder from metal components such as the outer cylinder. Also, by setting D1 / D2 ≤ 0.8, the radial length of the stepped portion becomes longer, so that even if the separator is miniaturized (reduced in diameter), it can be surely locked and fixed to the stepped portion. As a result, the vibration of the separator, which is a heavy object inside the outer cylinder, can be reduced, and the wear of metal members such as the outer cylinder and the generation of metal powder can be suppressed. Also, by setting 0.5 ≤ D1 / D2, the small-diameter portion is not overly reduced in diameter, and internal components (sealing materials, lead wires, etc.) of the gas sensor can be surely accommodated inside the small-diameter portion. And by providing a reduced-diameter portion between the stepped portion and the small-diameter portion of the outer cylinder, it is possible to suppress stress concentration near the stepped portion and the occurrence of cracks.

[0008] As described above, it is possible to suppress damage to the outer cylinder due to vibration, suppress the generation of metal powder due to vibration of the separator, and ensure the reliability of the electrical connection between the electrode pad and the terminal fitting. Furthermore, according to this gas sensor, the terminal fitting is disposed inside the reduced diameter portion, which is larger in diameter than the small diameter portion. Therefore, even if the terminal fitting vibrates due to vibration, it is unlikely to come into contact with the inner surface of the outer tube, thereby suppressing damage to or displacement of the terminal fitting.

[0009] In the gas sensor of the present invention, the axial length LT of the reduced-diameter portion may be longer than the radial length LD of the reduced-diameter portion. According to this gas sensor, compared with the case where LT < LD, the inner diameter of the reduced-diameter portion can be increased, and a space can be secured so that internal components (terminal fittings, etc.) do not contact the inner surface of the reduced-diameter portion.

[0011] In the gas sensor of the present invention, the reduced-diameter portion may be frustoconical. That the reduced-diameter portion is frustoconical means, in other words, when looking at a cross-section along the axial direction, the reduced-diameter portion is a linear taper. When the reduced-diameter portion is a linear taper in this way, the internal space of the reduced-diameter portion becomes larger than that of a curved (concave inward) taper, so that even if the internal components (terminal fittings, etc.) of the reduced-diameter portion vibrate due to vibration, it is difficult to contact the inner surface of the outer cylinder.

[0012] In the gas sensor of the present invention, the small-diameter portion may have a diameter difference between the inner diameter of the rear end portion and the inner diameter of the front end portion of itself within 5%. According to this gas sensor, the small diameter portion can be formed into a straight cylindrical shape having a contour extending substantially along the axial direction. Effect of the Invention

[0013] According to the present invention, a gas sensor can be obtained which suppresses breakage of the separator and also suppresses the generation of metal powder due to vibration of the separator, thereby ensuring the reliability of the electrical connection between the electrode pads and the terminal fittings. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a partially enlarged view of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention will be described in detail with reference to Fig. 1 and Fig. 2. Fig. 1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention, and Fig. 2 is a partially enlarged view of Fig. 1.

[0016] 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 direction O for inserting the sensor element 21 therethrough, a metal shell 11 surrounding the radial periphery of the ceramic holder 30, and an outer cylinder 81. A portion of the sensor element 21 near the front end where the detection portion 22 is formed protrudes toward the front end from the ceramic holder 30. The sensor element 21 thus passed through the through hole 32 is fixed inside the metallic 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. The portion of the sensor element 21 close to the rear end 29, including the rear end 29, protrudes rearward from the sleeve 43 and the metallic shell 11, and the terminal fittings 75 provided at the ends of the lead wires 71 drawn to the outside through a sealing material 85 are pressed and electrically connected to the electrode pads 24 formed in the portion close to the rear end 29. The portion of the sensor element 21 close to the rear end 29, including the electrode pads 24, is covered by an outer tube 81. This will be described in more detail below.

[0017] The sensor element 21 extends in the direction of the axis O and is in the form of a strip (plate) 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 (rectangle) 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 forming the detection section 22 are disposed at a portion near the tip of the solid electrolyte (member), and an electrode pad 24 for connecting a lead wire 71 for extracting detection output is exposed at a portion connected to the detection electrodes and near the rear end.

[0018] In this example, a heater (not shown) is provided inside a portion of the sensor element 21 near the front end of the ceramic material formed in a laminated shape on the solid electrolyte (member), and electrode pads 24 for connecting lead wires 71 for applying voltage to the heater are formed and exposed near the rear end. Although not shown, these electrode pads 24 are formed in a vertically elongated rectangular shape, and for example, three or two electrode pads are arranged horizontally on the wide surfaces (both sides) of the strip plate near the rear end 29 of the sensor element 21. The detection portion 22 of the sensor element 21 is covered with a porous protective layer 23 made of alumina, spinel, or the like.

[0019] 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 a cylindrical portion) 12 with a small diameter at the front end for fitting and fixing a protector 60 (described later), and a screw 13 with a larger diameter for fixing to an exhaust pipe of an engine is provided on the outer circumferential surface at the rear (upper part in the figure). A polygonal portion 14 is provided at the rear of the metal shell 11 for screwing the sensor 1 with the screw 13. A cylindrical portion 15 is provided at the rear of the polygonal portion 14, and a protective tube (outer tube) 81 that covers the rear of the gas sensor 1 is fitted and welded to the cylindrical portion 15. A thin-walled crimping cylindrical portion 16 with a smaller outer diameter is provided at the rear of the polygonal portion 14. In FIG. 1, the crimping cylindrical portion 16 is bent inward for crimping. A gasket 19 for sealing when screwed is attached to the lower surface of the polygonal portion 14. 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 the tip of the sensor element 21 protrudes beyond the tips of the ceramic holder 30 and the metallic shell 11 . Meanwhile, in this embodiment, the tip portion of the sensor element 21 has a single structure and is covered with a cylindrical protector (protective cover) 60 with a bottom having vent holes (holes) 61, 63. The rear end of the protector 60 is fitted onto the cylindrical portion 12 of the metal shell 11 and welded. Note that a plurality of vent holes 61 are provided at a step portion near the center of the protector 60 in the direction of the axis O, spaced apart in the circumferential direction. Meanwhile, one vent hole 63 serving as a discharge hole is provided at the tip side of the protector 60.

[0022] 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 pads 24 formed near the rear end 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 held in opposing positions in respective housing portions provided in an insulating separator 91 arranged in an outer cylinder 81. The separator 91 is restricted from moving radially and toward the tip side via a retaining metal fitting 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 near the rear end 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 pulled out to the outside. The small-diameter second crimping portion 81r (described later) is crimped to reduce the diameter and compress the sealing material 85, thereby maintaining the airtightness of this portion.

[0023] Next, the outer cylinder 81 will be described in detail. The outer tube 81 has, in order from the tip side, a large diameter portion 81a, a step portion 81d extending radially inward from the rear end of the large diameter portion 81a and perpendicular to the direction of the axis O, a reduced diameter portion 81b extending from the step portion 81d toward the rear end side and reducing in diameter, and a small diameter portion 81c connected to the reduced diameter portion 81b. The step 81d is formed slightly rearward from the center of the outer cylinder 81 in the direction of the axis O, and the front-facing surface of this step 81d is engaged with the rear-facing surface of the separator 91. Meanwhile, the separator 91 has a flange 93 formed on its outer periphery supported on a retaining metal fitting 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 retaining metal fitting 82. The retaining metal fitting 82 is fixed to the inside of the outer tube 81 by a first crimping portion 81p, which is formed by crimping the large diameter portion 81a radially inward. Also, the sealing material 85 is fixed to the inside of the outer tube 81 by a second crimping portion 81r, which is formed by crimping the rear end side of the small diameter portion 81c radially inward. Additionally, "the front-facing surface of step 81d engages with the rear-facing surface of separator 91" means that a portion of the rear-facing surface of separator 91 may be in partial contact with a portion of the front-facing surface of step 81d.

[0024] Next, the characteristic features of the present invention will be described with reference to FIG. As shown in FIG. 2, a radial gap G between (the inner peripheral surface of) the outer cylinder 81 and the separator 91 is 1 mm or more. Furthermore, the inner diameter D1 of the small diameter portion 81c and the inner diameter D2 of the area where the gap G is formed of the large diameter portion 81a satisfy the relationship 0.5≦D1 / D2≦0.8.

[0025] Here, the gap G is the minimum gap value in any cross section obtained by cutting the gas sensor 1 in the radial direction. This cross section is obtained, for example, from an X-ray image. The inner diameter D1 is the minimum value of the inner diameter at a portion where the inner surface of the small diameter portion 81c is not in contact with other members (for example, excluding the second crimped portion 81r etc. which is in contact with the seal material 85 in FIG. 2). Moreover, the inner diameter D2 is the minimum value of the inner diameter in the above-mentioned region, and is calculated using the cross section used to calculate the gap G described above.

[0026] In this way, by making the gap G 1 mm or more, it is possible to prevent the separator 91 from vibrating due to an impact or vibration, such as a flying stone hitting the gas sensor 1, and coming into contact with metal components (such as the outer tube 81 or the retaining bracket 82) that are close to (or in contact with) the separator 91, which could result in damage to the separator 91 or the generation of metal powder from these metal components. Furthermore, by making D1 / D2≦0.8, the radial length of the step 81d is increased, so that even if the separator 91 is made smaller (reduced in diameter), it can be reliably engaged and fixed to the step 81d. As a result, the vibration of the separator 91, which is a heavy object inside the outer tube 81, is reduced, and the generation of metal powder due to wear of the retaining metal fittings 82 of the separator 91 can be suppressed. Furthermore, by making D1 / D2 0.5≦D1, the small diameter portion 81c does not become too small, and the internal components of the gas sensor 1 (sealing material 85, lead wire 71, etc.) can be reliably accommodated inside the small diameter portion 81c. Furthermore, by providing the reduced diameter portion 81b between the step portion 81d and the small diameter portion 81c of the outer cylinder 81, it is possible to suppress the occurrence of cracks due to stress concentration near the step portion 81d. As a result, damage to the outer tube 81 due to vibration can be suppressed, and the generation of metal powder due to vibration of the separator 91 can be suppressed, thereby ensuring the reliability of the electrical connection between the electrode pads 24 and the terminal fittings 75.

[0027] If D1 / D2>0.8, it becomes difficult to reduce the diameter of separator 91, and it also becomes difficult to reduce the vibration of the separator due to vibration. If 0.5>D1 / D2, it becomes difficult to accommodate internal parts in small diameter portion 81c, and the drawing process near step portion 81d becomes severe when molding outer tube 81, which increases the residual stress near step portion 81d and makes it difficult to suppress damage to the outer tube due to vibration. In order for separator 91 to be engaged with step 81d, the outer diameter of the surface of separator 91 facing the tip needs to be larger than the inner diameter of reduced diameter portion 81b at the connection with step 81d (ie, the tip of reduced diameter portion 81b). Furthermore, D2 is, for example, 13 to 15 mm.

[0028] In this example, as shown in FIG. 2, the axial length LT of the reduced-diameter portion 81b is longer than the radial length LD. By doing so, compared with the case where LT < LD, the inner diameter of the reduced-diameter portion 81b can be increased, and a space can be secured so that internal components (such as the terminal fitting 75) do not contact the inner surface of the reduced-diameter portion 81b. The ratio of LT / LD is preferably 1.85 or more. Note that LT and LD are the dimensions of the inner surface of the reduced-diameter portion 81b.

[0029] Also, in this example, as shown in FIG. 2, the rear end 75e of the terminal fitting 75 protrudes to the rear end side of the separator 91, and the reduced-diameter portion 81b extends to the rear end side of the rear end 75e of the terminal fitting 75. By doing so, since the terminal fitting 75 is disposed inside the reduced-diameter portion 81b having a diameter larger than that of the small-diameter portion 81c, even if the terminal fitting 75 swings due to vibration, it is difficult to contact the inner surface of the outer cylinder 81, and breakage or misalignment of the terminal fitting 75 can be suppressed.

[0030] Also, in this example, as shown in FIG. 2, the reduced-diameter portion 81b has a frustum shape. In other words, when looking at the cross-section along the axis O direction in FIG. 2, the reduced-diameter portion 81b has a linear taper. When the reduced-diameter portion 81b has a linear taper in this way, the internal space of the reduced-diameter portion 81b becomes larger than that of a curved (concave inward) taper. Therefore, even if the internal components (such as the terminal fitting 75) in the reduced-diameter portion 81b swing due to vibration, it is difficult to contact the inner surface of the outer cylinder 81.

[0031] The gas sensor of the present invention can be embodied by appropriately changing the design of its structure and configuration without departing from the gist of the present invention. The sensor element is not limited to one that measures the concentration of oxygen, and one that measures the concentration of nitrogen oxides (NOx), hydrocarbons (HC), or the like may be used. The shape of the small-diameter portion 81c is not limited. For example, the diameter difference between the rear end portion and the front end portion of itself with respect to the inner diameter of the front end portion of itself is within 5%, that is, it can be a straight cylindrical shape having a contour substantially along the axis O direction. There are various metal members that may be in the vicinity of (or in contact with) the separator 91 and generate metal powder depending on the structure of the gas sensor, and are not limited to the outer cylinder 81 and the metal holder 82. [Explanation of symbols]

[0032] 1 Gas sensor 11 Metal fitting 21 Sensor element 24 Electrode Pads 75 Terminal fittings 81 Outer cylinder 81a Large diameter section 81b Reduced diameter part 81c Small diameter section 81d Step 91 Separator O axis G Gap

Claims

1. A sensor element extending in an axial direction and having an electrode pad on a rear end side thereof; a metal shell surrounding and holding the sensor element; a cylindrical outer cylinder made of metal and attached to a rear end side of the metallic shell and housing a rear end side of the sensor element; a separator that is housed in the outer cylinder and holds terminal fittings that are connected to the electrode pads of the sensor element; A gas sensor comprising: The outer cylinder has, in order from the tip side, a large diameter portion, a step portion extending radially inward from a rear end of the large diameter portion and perpendicular to the axial direction, a reduced diameter portion extending from the step portion toward the rear end side and reducing in diameter, and a small diameter portion connected to the reduced diameter portion, The rear end facing surface of the separator is engaged with the front end facing surface of the step portion, The radial gap between the outer cylinder and the separator is 1 mm or more, and an inner diameter D1 of the small diameter portion and an inner diameter D2 of the large diameter portion in a region where the gap is formed satisfy a relationship of 0.5≦D1 / D2≦0.8, The terminal metal fitting protrudes toward the rear end side beyond the separator, The gas sensor is characterized in that the reduced diameter portion extends to a rear end side beyond the terminal fitting.

2. 2. The gas sensor according to claim 1, wherein a length LT of the reduced diameter portion in the axial direction is longer than a length LD of the reduced diameter portion in the radial direction.

3. A gas sensor as described in claim 1 or 2, characterized in that the reduced diameter portion is truncated cone shaped.

4. A gas sensor as described in any one of claims 1 to 3, wherein the small diameter portion has an inner diameter at its rear end that is within 5% of the inner diameter at its front end.

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