Gas Sensors

Abstract

To provide a gas sensor that suppresses damage to an outer cylinder due to vibration while reducing a diameter of a separator.SOLUTION: A gas sensor 1 includes: a sensor element 21; a main metal fitting 11; a metallic and cylindrical outer cylinder 81 housing a rear end side of the sensor element; and a separator 91 holding a terminal metal fitting 75. The outer cylinder has: a large-diameter portion 81a; a small-diameter portion 81c arranged on a rear end side of the large-diameter portion and extending straight; and a stepped portion 81d connected to the large-diameter portion and the small-diameter portion by a connection line L1 and extending in a radial direction. In addition, the outer cylinder has a plurality of convex reinforcing ribs 81e connected to the small-diameter portion and protruding outside the small-diameter portion, and connected to a part of the stepped portion across the connection line and protruding from the stepped portion to a rear end side. A rear end facing surface of the separator is engaged with a front-end facing surface of the stepped portion. A drawing ratio represented by a ratio D2 / D1 between an inner diameter D1 of the large-diameter portion and an inner diameter D2 of the small-diameter portion on a tip-facing surface of the stepped portion is 0.72 or less. The reinforcing ribs are arranged spaced circumferentially.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 a free end that is not fixed. In addition, the front end side of the outer tube is a large diameter part, and a small diameter part is formed on the rear end side of the large diameter part via a step part. The rear end side of the separator is engaged with the inside of this step part (the surface facing the front end) (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-17278 A Summary of the Invention [Problem to be solved by the invention]

[0004] 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 step of the outer cylinder close to the connection part with the metal shell, causing cracks. As described above, the separator, which is a heavy object, is held inside the step of the outer cylinder, which acts to increase the vibration of the outer cylinder due to vibration, etc. Therefore, a possible measure to reduce the vibration of the outer cylinder is to make the separator lighter (smaller in diameter). However, in order to reduce the diameter of the separator, it is necessary to make the small diameter part thinner than the large diameter part, and it was found that the necking of the step becomes larger, promoting cracks near the step. Furthermore, a rubber grommet is generally attached to the rear end of the outer cylinder, but if the temperature in the environment in which the gas sensor is used rises and exceeds the heat resistance of the grommet, it becomes difficult to ensure airtightness using the grommet. One way to deal with this is to reduce the thickness of the outer cylinder to suppress the conduction of heat from the outer cylinder to the grommet. However, this makes the outer cylinder more susceptible to damage due to vibration, etc.

[0005] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a gas sensor in which the diameter of the separator is reduced and damage to the outer cylinder due to vibration is suppressed. [Means for solving the problem]

[0006] The gas sensor of the present invention is a gas sensor including a sensor element extending in an axial direction, a metal shell surrounding and holding the sensor element, a metallic cylindrical outer cylinder attached to a 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 a terminal metal fitting connected to the sensor element, the outer cylinder having a large diameter portion, a small diameter portion disposed rearward of the large diameter portion and extending straight, and a separator connected to the large diameter portion and connected to the small diameter portion by a connection wire, the separator being axially extending in the direction of the sensor element. the separator further has a plurality of convex reinforcing ribs that are connected to the small diameter portion and protrude outwardly from the small diameter portion, and that straddle the connection line and are connected to a part of the step portion and protrude rearward from the step portion, a rear-end-facing surface of the separator is engaged with a front-end-facing surface of the step portion, a drawing rate represented by a ratio D2 / D1 of an inner diameter D1 of the large diameter portion to an inner diameter D2 of the small diameter portion at the front-end-facing surface of the step portion is 0.72 or less, and the reinforcing ribs are arranged at intervals in the circumferential direction.

[0007] According to this gas sensor, by making D2 / D1≦0.72, the radial length of the step portion is increased, so that even if the separator is made smaller (smaller in diameter), it can be reliably engaged and fixed to the step portion. As a result, the separator, which is a heavy object inside the outer cylinder, can be made smaller in diameter (lighter in weight), and vibration of the outer cylinder due to vibration, etc. can be reduced. Furthermore, by making the separator smaller in diameter, the weight and cost of the entire gas sensor 1 can be reduced. On the other hand, if D2 / D1≦0.72 is set as described above in order to reduce the diameter of the separator, the small diameter portion becomes thinner than the large diameter portion, and the necking of the step portion becomes larger, promoting cracks near the connection line between the step portion and the small diameter portion. Therefore, by providing multiple convex reinforcing ribs across the connecting wire and part of the small diameter portion and step portion, the strength of the step portion, particularly in the vicinity of the connecting wire, can be improved, and damage to the outer tube due to vibration can be suppressed while the diameter of the separator is reduced.

[0008] In the gas sensor of the present invention, the reinforcing rib may have an outer surface that conforms to the outer surfaces of the step portion and the small diameter portion. According to this gas sensor, the amount of deformation of the outer cylinder when the ribs are formed by press working or the like is small, and residual stress is small, so that stress corrosion cracking of the outer cylinder due to vibration can be suppressed.

[0009] In the gas sensor of the present invention, a grommet having an insertion hole for inserting a lead wire connected to the terminal fitting may be held on the rear end side of the outer cylinder, and the maximum thickness of the outer cylinder may be 0.4 mm or less. According to this gas sensor, since the thickness of the outer cylinder is thin, when a grommet is held at the rear end side of the outer cylinder, heat transfer from the outer cylinder to the grommet can be suppressed, which is particularly advantageous when the gas sensor is used in an environment with high temperatures that tend to exceed the heat resistance temperature of the grommet. Furthermore, by providing the reinforcing ribs, damage to the outer cylinder due to vibration or the like can be suppressed even if the thickness of the outer cylinder is reduced. Effect of the Invention

[0010] According to the present invention, a gas sensor can be obtained in which the diameter of the separator is reduced and damage to the outer cylinder due to vibration is suppressed. [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. [Diagram 3] FIG. [Figure 4] FIG. 13 is a perspective view showing a modified example of the outer cylinder. 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 according to an embodiment of the present invention, Fig. 2 is a perspective view of an outer cylinder 81, and Fig. 3 is a top view of the outer cylinder 81.

[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 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 grommets 85 are crimped 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 1, the terminal fittings 75 provided at the tip of each lead wire 71 drawn to the outside through a grommet 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 pressure-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 grommet (e.g., rubber) 85 arranged inside the rear end of the outer tube 81 and pulled out to the outside, and the small diameter tube portion 81c is crimped to reduce the diameter and compress this grommet 85, thereby maintaining airtightness of this portion.

[0020] Next, the outer cylinder 81 will be described in detail with reference to FIGS. The outer tube 81 has a large diameter portion 81a, a small diameter portion 81c that is located rearward of the large diameter portion 81a and extends straight in the direction of the axis O, a step portion 81d that is connected to the large diameter portion 81a and to the small diameter portion 81c by a connection line L1 and extends radially, and a reinforcing rib 81e. The step portion 81d is formed slightly rearward from the center in the direction of the axis O of the outer cylinder 81. The connection line L1 is also the tip of the small diameter portion 81c, and is annular.

[0021] On the other hand, the reinforcing rib 81e is connected to the small diameter portion 81c and is connected to a part of the step portion 81d across the connection line L1. The reinforcing ribs 81e are formed so as to protrude from the small diameter portion 81c and the step portion 81d. That is, the reinforcing ribs 81e are a plurality of convex members that protrude outward from the small diameter portion 81c and protrude toward the rear end side from the step portion 81d. Here, at the position of the reinforcing rib 81e, the boundary between the small diameter portion 81c and the step portion 81d is raised, so the connection line L1 does not exist. Therefore, at the position of the reinforcing rib 81e, a virtual line obtained by extrapolating the connection line L1 between the small diameter portion 81c and the step portion 81d excluding the reinforcing rib 81e is regarded as the connection line L1.

[0022] In this example, the reinforcing rib 81e extends radially outward from the connection line L1 along the step portion 81d, but does not extend to the large diameter portion 81a and terminates near the radial center of the step portion 81d. As shown in FIG. 2, the reinforcing ribs 81e (six in this example) are arranged at intervals in the circumferential direction.

[0023] Here, when viewed from the inside surface side of the outer tube 81, the reinforcing rib 81e is recessed from the step 81d, so that the rearward facing surface 91e of the separator 91 is engaged with the forward facing surface of the step 81d. 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 tube 81, and the separator 91 is held in the axis O direction 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 grommet 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 rear-facing surface of separator 91 engages with the front-facing surface of step 81d" 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] Furthermore, the drawing ratio, which is expressed as the ratio D2 / D1 of the inner diameter D1 of the large diameter portion 81a on the surface of the step 81d facing the tip to the inner diameter D2 of the small diameter portion 81c, is 0.72 or less. In this way, by making D2 / D1≦0.72, 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 separator 91, which is a heavy object inside the outer cylinder 81, can be made smaller in diameter (reduced in weight), and vibration of the outer cylinder due to vibration or the like can be reduced. Furthermore, by reducing the diameter of the separator 91, it is possible to reduce the weight and cost of the entire gas sensor 1.

[0025] On the other hand, it was found that if D2 / D1≦0.72 is set as described above in order to reduce the diameter of separator 91, small diameter portion 81c becomes thinner than large diameter portion 81a, and the narrowing of step portion 81d becomes larger, promoting cracks near connection line L1 between step portion 81d and small diameter portion 81c. Therefore, by providing a plurality of convex reinforcing ribs 81e across the connecting wire L1 and part of the small diameter portion 81c and the step portion 81d, the strength of the step portion 81d, particularly in the vicinity of the connecting wire L1, can be improved, and the diameter of the separator 91 can be reduced while suppressing damage to the outer tube 81 due to vibration.

[0026] It is preferable that D2 / D1 is 0.65 or less, since this allows the separator 91 to have a further smaller diameter. There is no lower limit to D2 / D1, but it is, for example, 0.5.

[0027] In this example, as shown in FIG. 2, the outer surface of the reinforcing rib 81e is shaped to fit the outer surfaces of the step portion 81d and the small diameter portion 81c. In this way, the amount of deformation of the outer cylinder when the ribs are formed by press working or the like is small, and residual stress is reduced, so that stress corrosion cracking of the outer cylinder due to vibration can be suppressed. Note that "the outer surface of the reinforcing rib 81e has a shape that conforms to the outer surfaces of the step portion 81d and the small diameter portion 81c" means that the outer surface of the reinforcing rib 81e is approximately parallel to the outer surfaces of the step portion 81d and the small diameter portion 81c. In this example, when viewed in cross section in Figure 1, the outline of the outer surface of the reinforcing rib 81e is approximately L-shaped along the outline of the outer surfaces of the step portion 81d and the small diameter portion 81c.

[0028] If the maximum thickness of the outer tube 81 is 0.4 mm or less, when the grommet 85 is held on the rear end side of the outer tube 81, it is possible to suppress heat conduction from the outer tube 81 to the grommet 85. Furthermore, by providing the reinforcing rib 81e, it is possible to suppress damage to the outer tube 81 due to vibration or the like even if the thickness of the outer tube 81 is reduced.

[0029] The gas sensor of the present invention can be embodied by appropriately modifying the design of its structure and configuration without departing from the gist of the present invention. For example, as shown in FIG. 4, each reinforcing rib 181e of the outer cylinder 181 may extend radially outward from the connection line L1 along the step portion 181d to the large diameter portion 181a. Alternatively, as shown in FIG. 4, the outer surface of each reinforcing rib 181e may be a flat surface that extends radially outward from the connection line L1 and descends to a tip that is connected to the large diameter portion 181a. The sensor element is not limited to one that measures the concentration of oxygen, and one that measures the concentration of nitrogen oxides (NOx) or hydrocarbons (HC) may also be used. [Explanation of symbols]

[0030] 1 Gas sensor 11 Metal fitting 21 Sensor element 71 Lead Wire 75 Terminal fittings 81, 181 Outer cylinder 81a, 181a Large diameter section 81c, 181c small diameter section 81d, 181d stepped section 81e, 181e Reinforcement rib 85 Grommet 91 Separator O axis L1 connection line

Claims

1. A sensor element extending in an axial direction; 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 a terminal metal fitting that is connected to the sensor element; A gas sensor comprising: the outer cylinder has a large diameter portion, a small diameter portion disposed rearward of the large diameter portion and extending straight, and a step portion connected to the large diameter portion and to the small diameter portion by a connection line and extending in a radial direction, the connecting wire is connected to a part of the step portion and protrudes toward a rear end side of the step portion, and a plurality of convex reinforcing ribs are provided, the reinforcing ribs being connected to the small diameter portion and protruding outward from the small diameter portion, and the connecting wire is connected to a part of the step portion and protruding toward a rear end side of the step portion, The rear end facing surface of the separator is engaged with the front end facing surface of the step portion, a drawing ratio represented by a ratio D2 / D1 of an inner diameter D1 of the large diameter portion to an inner diameter D2 of the small diameter portion at a tip-facing surface of the step portion is 0.72 or less, The gas sensor is characterized in that the reinforcing ribs are arranged at intervals in a circumferential direction.

2. 2. The gas sensor according to claim 1, wherein an outer surface of the reinforcing rib is shaped to conform to the outer surfaces of the step portion and the small diameter portion.

3. A grommet having an insertion hole through which a lead wire connected to the terminal metal fitting is inserted is held on the rear end side of the outer cylinder.

3. The gas sensor according to claim 1, wherein the maximum thickness of the outer cylinder is 0.4 mm or less.

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