Gas sensor

Abstract

To provide a gas sensor that is capable of electrically connecting terminal metal fittings and an electrode pad of a sensor element in a reliable manner.SOLUTION: A gas sensor comprises: a tabular sensor element 21 having an electrode pad 24; terminal metal fittings 75, each having a body part and a folded part 75b extending in an axial direction, and each provided with a contact part C1 electrically connected to the electrode pad; and a cylindrical separator 91 holding a rear end side of the terminal metal fittings. The contact parts are accommodated inside the separator. The terminal metal fittings have an extension part 75c that is further folded from an open end of the folded part, extends in a direction orthogonal to the axial direction and is provided with the contact part. Further, in the gas sensor, AX>DX is satisfied, when viewing along a width direction of the sensor element, and when an end of the electrode pad nearest one inner surface 91si of the separator is a pad end, and when the extension part extends in a direction of separating from the pad end in the width direction, and DX denotes a maximum width of the folded part and AX denotes a length of projection in the width direction of the extension part.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas sensor including a sensor element for detecting the concentration of a target gas and a terminal fitting. [Background technology]

[0002] Oxygen and NO in exhaust gases from automobiles, etc. x 2. Description of the Related Art As a gas sensor for detecting the concentration of a gas, there is known one having a plate-shaped sensor element using a solid electrolyte. A widely used gas sensor of this type has multiple electrode pads (electrode terminal portions) provided on the rear end sides of the opposing main surfaces of a plate-shaped sensor element, and each of the electrode pads is electrically contacted with a rod-shaped (wire-shaped) terminal metal fitting to extract a sensor output signal from the sensor element to the outside or to supply power to a heater stacked on the sensor element (Patent Document 1). This terminal metal fitting has a spring contact portion that comes into contact with an electrode pad, and a spring holding portion that is folded back from the spring contact portion, and the spring holding portion is held by a separator (insulator). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-116273 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when viewed in the width direction of the sensor element, the spring contact portion of the rod-shaped terminal metal fitting in particular is in almost point contact with the electrode pad, and therefore if the spring contact portion swings in the width direction due to vibrations during assembly or use of the gas sensor, the connection with the electrode pad may be cut off, and the reliability of the electrical connection may decrease.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a gas sensor that can reliably electrically connect the terminal metal fittings to the electrode pads of the sensor element even if the terminal metal fittings are misaligned in the width direction of the sensor element. [Means for solving the problem]

[0006] In order to solve the above problems, the gas sensor of the present invention includes a plate-shaped sensor element extending in an axial direction and having an electrode pad on an outer surface near a rear end thereof, a terminal fitting having a main body extending in the axial direction and a folded portion folded back from a front end of the main body to a rear end thereof, the terminal fitting being provided with a contact portion electrically connected to the electrode pad, and a cylindrical separator extending in the axial direction and holding the rear end of the terminal fitting, the contact portion being accommodated inside the separator, the terminal fitting further having an extension portion folded back from an open end of the folded portion to extend in a direction intersecting the axial direction, the contact portion being provided therein, and when viewed along the width direction of the sensor element, an end of the electrode pad closest to one inner surface of the separator is defined as a pad end, the extension portion extends in a direction away from the pad end in the width direction, and when a maximum width of the folded portion is defined as DX and a length of the extension portion projected in the width direction is defined as AX, a relationship AX>DX is satisfied.

[0007] In this way, even if the terminal metal fitting (folded portion) is displaced in the width direction due to vibration during assembly of the gas sensor or during use, the length AX of the extension portion is longer than the maximum width DX of the folded portion, so that any part of the extension portion overlaps with the electrode pad to maintain contact, thereby ensuring electrical connection between the terminal metal fitting and the electrode pad.

[0008] In the gas sensor of the present invention, the electrode pads may be arranged in a plurality of rows along the width direction, and a region of the extension portion excluding the contact portion may not overlap with other electrode pads. This can prevent the extended portion from accidentally coming into contact with another electrode pad, causing an unintended current to flow or preventing the sensor output from being obtained.

[0009] In the gas sensor of the present invention, when the distance between an end of an electrode pad and the one inner surface of the separator is defined as BX, the relationship AX>BX may be satisfied. When the terminal fitting (folded portion) is displaced in the width direction due to vibration during installation or use of the gas sensor, and when the displacement (vibration) reaches its maximum, the folded portion abuts against the inner surface of the separator. The maximum vibration at this time is BX. Therefore, by making AX>BX, even if the deflection of the folded portion reaches its maximum and abuts against the inner surface of the separator, some part of the extension portion will still overlap with the electrode pad to maintain contact, thereby enabling a more reliable electrical connection between the terminal fitting and the electrode pad.

[0010] In addition, in the gas sensor of the present invention, a plurality of electrode pads may be arranged along the width direction, and the tips of the extension portions of two terminal fittings each connected to two electrode pads adjacent to each other in the width direction may be arranged at different positions in the axial direction. This can prevent the tips of the extension portions from accidentally coming into contact with each other, causing an unintended current to flow or preventing the sensor output from being obtained.

[0011] In the gas sensor of the present invention, the terminal metal fitting may be rod-shaped. The present invention is particularly effective for rod-shaped terminal fittings, since the contact area with the electrode pads is small and the connection with the electrode pads is easily cut off by vibration in the width direction. Effect of the Invention

[0012] According to the present invention, a gas sensor can be obtained in which the terminal metal fittings and the electrode pads of the sensor element can be reliably electrically connected to each other even if the terminal metal fittings are misaligned in the width direction of the sensor element. [Brief description of the drawings]

[0013] [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 cross-sectional view taken along line AA in FIG. [Diagram 3] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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 taken along line AA in Fig. 1, and Fig. 3 is a perspective view of a terminal fitting 75.

[0015] In FIG. 1, the gas sensor (NOx 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 housing 11 surrounding the ceramic holder 30 radially, and a separator 91. The portion of the sensor element 21 where the detection portion 22 is formed protrudes toward the tip from the ceramic holder 30 . A filling hole 30h communicating with the through hole 32 is formed at the rear end side of the through hole 32 of the ceramic holder 30, and the sensor element 21 is hermetically held within the through hole 32 of the ceramic holder 30 by filling the filling hole 30h with a sealing material (talc in this example) 41. A separator 91 that holds a plurality of terminal fittings 75, 76 is disposed on the rear end side of the ceramic holder 30. The separator 91 has a cylindrical shape with a bottom, and the rear end side forms a bottom 91e.

[0016] As shown in FIG. 2, a plurality of holding grooves 91r for holding the terminal fittings 75, 76 are formed along the axis O on the inner side of a side wall 91s of the separator 91 (see also FIG. 1). The terminal fitting 75 has a bent portion 75s that extends radially outward, and an opposing wall 91p that faces obliquely is formed on the inner side of a side wall 91s of the separator 91 for engaging with the bent portion 75s. The terminal metal fittings 75 are disposed on both ends of the sensor element 21 in the width direction, one at a time, and the terminal metal fitting 76 is disposed in the center of the sensor element 21 in the width direction.

[0017] A central hole 91h in which the sensor element 21 is disposed is formed in the central portion of the separator 91, and the plurality of holding grooves 91r communicate with the central hole 91h. The terminal fittings 75, 76 contact the electrode pads 24 (FIG. 1) of the sensor element 21 via the holding grooves 91r and the central hole 91h. The separator 91 has a bottom portion 91e formed with insertion holes (not shown) for the terminal fittings 75, 76. As shown in FIG.

[0018] Returning to FIG. 1, a portion of the sensor element 21 near the rear end protrudes rearward from the ceramic holder 30 and the housing 11, and terminal fittings 75, 76 are pressure-welded to each of the electrode pads 24 formed in the portion near the rear end, thereby electrically connecting them. The terminal metal fitting 76 is disposed closer to the tip than the terminal metal fitting 75. The electrode pad 24 electrically connected to the terminal metal fitting 76 via the contact portion C2 is also disposed closer to the tip than the electrode pad 24 electrically connected to the terminal metal fitting 75 via the contact portion C1. On the other hand, the rear ends of the terminal fittings 75 and 76 are connected to a lead wire 71 , and the lead wire 71 is led out through a sealing material 85 . Further, the portion of the sensor element 21 near the rear end, including the electrode pads 24, is covered with an outer cylinder 81. This will be explained in further detail below.

[0019] 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 a detection electrode or the like (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 constant 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 known in the art, and a pair of detection electrodes forming a detection section 22 are arranged 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 and formed at a portion connected to the detection electrodes near the rear end.

[0020] In this example, a heater (not shown) is provided inside the portion of the sensor element 21 near the front end of the ceramic material formed in a laminated shape on the solid electrolyte (component), and an electrode pad 24 for connecting a lead wire 71 for applying a voltage to the heater is formed and exposed near the rear end. Although not shown, these electrode pads 24 are formed in a vertically long rectangle, and for example, three or two electrode terminals are arranged horizontally on the wide surfaces (both surfaces) of the strip plate near the rear end of the sensor element 21. The detection portion 22 of the sensor element 21 is covered with a porous protective layer (not shown) made of alumina, spinel, or the like.

[0021] The housing 11 is cylindrical with different diameters at the front and rear, with a small diameter at the front end and a cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 12 for fitting and fixing protectors 51, 61 (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 housing 11 for fixing the sensor 1 to an exhaust pipe of an engine. Behind the polygonal portion 14, a polygonal portion 14 is provided for screwing the sensor 1 with the screw 13. Behind the polygonal portion 14, a cylindrical portion 15 is provided for fitting and welding a protective tube (outer tube) 81 that covers the rear of the gas sensor 1, and behind the polygonal portion 14, a cylindrical portion 15 is provided for welding the protective tube (outer tube) 81 thereto. In addition, in FIG. 1, the caulking cylindrical portion 16 is bent inward for after caulking.

[0022] On the other hand, the housing 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.

[0023] A ceramic holder 30 made of insulating ceramic (e.g., alumina) and formed into a roughly short cylindrical shape is disposed inside the housing 11. The ceramic holder 30 has a flange 31, and while the front-facing surface of the flange 31 is engaged with the step 17, the ceramic holder 30 is pressed from the rear end side by the caulking cylindrical portion 16 via a seal material 42, a sleeve 43, etc. As a result, the ceramic holder 30 is positioned within the housing 11 and is gap-fitted.

[0024] On the other hand, in this embodiment, the tip portion of the sensor element 21 has a two-layer structure and is covered with cylindrical protectors (protective covers) 51, 61 each having a bottom and an air hole (hole). The rear ends of the protectors 51, 61 are fitted onto the cylindrical portion 12 of the housing 11 and welded thereto.

[0025] 1, terminal fittings 75, 76 provided at the ends of lead wires 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 of the sensor element 21 by their spring properties. In the gas sensor 1 of this embodiment, the terminal fittings 75, 76 including the pressure-contact portions are provided in holding grooves 91r (FIG. 2) provided in an insulating separator 91 arranged in an outer cylinder 81. The separator 91 is engaged with a disc spring 82 arranged in the outer cylinder 81.

[0026] On the other hand, a protective outer cylinder 83 is fitted onto the outer surface of the rear end side of the outer cylinder 81, and a seal material (e.g., rubber) 85 is disposed inside the protective outer cylinder 83. Furthermore, a water-repellent ventilation filter 95 is interposed between the outer cylinder 81 and the protective outer cylinder 83. In addition, the lead wire 71 is passed through a seal material 85 arranged inside the rear end of the outer tube 81 and led out to the outside, and the protective outer tube 83 is crimped to reduce the diameter and compress this seal material 85, thereby maintaining airtightness of this area.

[0027] Next, the terminal fitting 75 will be described with reference to FIGS. In this example, the terminal fitting 75 is a rod-shaped terminal (having a circular cross section in this example) and is made of a metal wire. The terminal fitting 75 integrally includes a main body 75a extending in the direction of the axis O, a folded-back portion 75b formed by folding back the tip of the main body 75a toward the sensor element 21, and an extended portion 75c. The extended portion 75c is folded back from an open end of the folded-back portion 75b (an end portion on the rear end side of the folded-back portion 75b in this example) and extends in a direction intersecting with the direction of the axis O.

[0028] Furthermore, as the folded portion 75b elastically bends radially relative to the main body portion 75a, the contact portion C1 located at any location on the folded portion 75b and the extension portion 75c connected thereto is electrically connected to the electrode pad 24. Note that "any part on the folded portion 75b and the extended portion 75c connected thereto" includes the part bent from the open end of the folded portion 75b and the extended portion 75c. The "part bent from the open end of the folded portion 75b" usually includes a part of the outer surface of the folded portion 75b that is flush with the outer surface of the extended portion 75c. This is because the part that is flush with the extended portion 75c is likely to come into contact with the electrode pad 24. On the other hand, the rear end side of the main body portion 75a is connected to the lead wire 71 via a crimp terminal.

[0029] 2 and 3, the extension portion 75c extends in a direction intersecting the axis O (in FIG. 2, the direction is along the main surface of the sensor element 21). In addition, as shown in FIG. 1, the contact portion C1 and the extension portion 75c are housed inside the separator 91. As shown in FIG. 2, when viewed along the width direction of the sensor element 21, the end of the electrode pad 241 closest to one inner surface (the inner surface on the left side in FIG. 2) 91si of the separator 91 is defined as the pad end. In this case, the extension 75c of the upper left terminal fitting 751 extends in a widthwise direction away from the pad end. In addition, when the maximum width of the folded-back portion 75b is DX and the length of the extension 75c projected in the widthwise direction is AX, the relationship AX>DX is satisfied.

[0030] In this way, even if the folded portion 75b of the terminal fitting 75 (751) is displaced in the width direction due to vibration during assembly of the gas sensor 1 or during use, the length AX of the extension portion 75c is longer than the maximum width DX of the folded portion 75b, so that some portion of the extension portion 75c overlaps with the electrode pad 24 (241), maintaining the contact portion C1, and ensuring electrical connection between the terminal fitting 75 and the electrode pad 24.

[0031] For example, in FIG. 2, if the upper left terminal fitting 751 (its folded portion 75b) is shifted to the outside of the sensor element 21 (the left side of FIG. 2), unless the extension portion 75c is provided, the contact portion C1 may also shift to the left and fail to pass beyond the end of the pad for electrical continuity. On the other hand, by providing the extension portion 75c, a new contact portion C10 can be maintained on the right side portion of the extension portion 75c (in the direction moving away from the pad end in the width direction), and electrical continuity can be ensured.

[0032] Furthermore, as shown in FIG. 2, in this example, when the distance between the pad end and one inner surface (the inner surface on the left side in FIG. 2) 91si of the separator 91 is BX, AX>BX is satisfied. When the folded portion 75b of the terminal fitting 75 shifts in the width direction due to vibration during assembly or use of the gas sensor 1, and the shift width (vibration) reaches a maximum, the folded portion 75b abuts against the inner surface 91si of the separator 91, and the maximum vibration width at this time is BX. Therefore, by making AX>BX, even if the deflection of the folded-back portion 75b reaches its maximum and abuts against the inner surface 91si of the separator 91, some portion of the extension portion 75c will still overlap with the electrode pad 24 to maintain the contact portion C1, thereby enabling an even more reliable electrical connection between the terminal fitting 75 and the electrode pad 24.

[0033] When the contact portion C1 is in almost point contact with the electrode pad 24, the contact portion C1 is determined to be one point. On the other hand, since the extension portion 75c extends in the width direction, the contact portion C1 may have a certain range of area in the direction along the main surface of the sensor element 21 (width direction). The contact portion C1 is determined by obtaining a CT image of the gas sensor 1 from the direction of the axis O and observing an image of the vicinity of the contact point between the extension portion 75c and the electrode pad 24 from a cross-sectional view such as that shown in FIG.

[0034] In the present invention, a plurality of electrode pads 24 are arranged in the width direction, and the region of the extension portion 75c excluding the contact portion C1 does not have to overlap with the other electrode pads 24. This can prevent the extended portion 75c from accidentally coming into contact with another electrode pad 24, causing an unintended current to flow, or preventing the sensor output from being obtained.

[0035] In addition, in the present invention, a plurality of electrode pads 24 are arranged along the width direction, and of the two terminal fittings 75 each connected to two adjacent electrode pads 24 in the width direction, the tips of the extension portions 75c may be positioned at different positions in the direction of the axis O. This can prevent the tips of the extension portions 75c from accidentally coming into contact with each other, causing an unintended current to flow and preventing the sensor output from being obtained.

[0036] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be embodied in various forms without departing from the gist of the present invention. The gas sensor to which the present invention is applied is not limited to an oxygen sensor, but may be any gas sensor that detects other types of gas, such as a NOx sensor or a hydrogen sensor, as long as it has a terminal fitting. In addition, in this example, the extension portion is integral with the terminal fitting and is formed by bending the folded portion, but it may also be in a form in which a separate plate-shaped extension portion is joined to the open end side of the folded portion by welding or the like. The terminal fittings are not limited to being rod-shaped, and may be shaped by processing a metal plate. Examples of rod-shaped terminal fittings include those having a circular cross section or a polygonal cross section with an aspect ratio of 1:1.0 to 1:1.2. [Explanation of symbols]

[0037] 1 Gas sensor 21 Sensor element 24, 241 Electrode pads 75,751 Terminal fittings 75a Main body 75b Folded part 75c extension part 91 Separator 91si Separator inner surface C1, C10 contact part O axis

Claims

1. a plate-shaped sensor element extending in the axial direction and having an electrode pad on an outer surface of a rear end side; a terminal fitting including a main body portion extending in the axial direction and a folded portion folded back from a front end of the main body portion to a rear end side, the terminal fitting being provided with a contact portion electrically connected to the electrode pad; a cylindrical separator extending in the axial direction and holding a rear end side of the terminal fitting; A gas sensor comprising: The contact portion is housed inside the separator, The terminal fitting further has an extension portion that is folded back from an open end of the folded back portion, extends in a direction intersecting the axial direction, and is provided with the contact portion, When viewed along the width direction of the sensor element, an end of the electrode pad closest to one inner surface of the separator is defined as a pad end. The extension portion extends in a direction away from the pad end in the width direction, The gas sensor is characterized in that, when the maximum width of the folded portion is DX and the length of the extended portion projected in the width direction is AX, AX>DX is satisfied.

2. A plurality of the electrode pads are arranged along the width direction, 2. The gas sensor according to claim 1, wherein a region of the extension portion excluding the contact portion does not overlap with other electrode pads.

3. When the distance between the end of the pad and the inner surface of one of the separators is BX, 3. The gas sensor according to claim 1, wherein AX>BX is satisfied.

4. A plurality of the electrode pads are arranged along the width direction, 3. The gas sensor according to claim 1, wherein the terminal fittings are connected to two electrode pads adjacent to each other in the width direction, and the tips of the extension portions of the terminal fittings are disposed at different positions in the axial direction.

5. 3. The gas sensor according to claim 1, wherein the terminal metal fitting is rod-shaped.

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