Gas sensor

Abstract

To provide a gas sensor improved in reliability of electric connections by suppressing a short circuit between terminal metal fittings arranged on a main surface of a sensor element.SOLUTION: A gas sensor 200 includes: a sensor element 10 having electrode pads 11 on main surfaces 10f1, 10f2; terminal metal fittings 21-25; a separator 166; and a lead wire 146. The terminal metal fitting includes: a main body part 21a; an extension part 21b connected to a tip end side of the main body part and electrically connected to the electrode pads; and an ended annular caulking part 21c connected to a rear end side of the main body part and grasping a core wire 146c of the lead wire. The caulking part includes two or more pawl parts 21c1, 21c2 arranged spaced from each other in an axis O direction and grasping the core wires, respectively. In the at least one terminal metal fitting of the plurality of terminal metal fittings, when a maximum width of an outermost tip end of the pawl part 21c2 in the axis line direction is defined as L, and a minimum interval of radial intervals between the extension parts of the terminal metal fitting adjacent to the one main surface is defined as B, L<B is satisfied.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Gas sensors for detecting the concentrations of oxygen and NOx in exhaust gases from automobiles and the like are known to have a sensor element using a solid electrolyte. One such gas sensor uses an electrode pad provided at the rear end of a plate-shaped sensor element, a separator (insulating member) arranged to surround the radially outer side of the rear end of the sensor element, and a terminal fitting held in an insertion hole of the separator (see Patent Document 1). The terminal fitting is electrically connected to the electrode pad of the sensor element, and the rear end of the terminal fitting is crimped to a lead wire so that a sensor output signal from the sensor element is taken out via the lead wire. The lead wire is inserted into a rubber grommet arranged at the rear end of the gas sensor and taken out.

[0003] As described in Patent Document 1, terminal fittings generally include a plate-shaped main body portion held by the separator, an extension portion connected to the front end of the main body portion and electrically connected to the electrode pad, and a crimping portion (crimp terminal portion) connected to the rear end of the main body portion and crimping the lead wire. The crimping portion has a plurality of claw portions arranged with gaps in the axial direction. A plurality of electrode pads and terminal fittings connected thereto are arranged on at least one of the main surfaces of the sensor element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-63716 A (Fig. 3) Summary of the Invention [Problem to be solved by the invention]

[0005] 7, consider a case where the crimping portion 320 of the terminal fitting 300 has three claws 321 to 323 arranged in axial order from top to bottom. When the core wire 146c of the lead wire 146 is gripped and crimped by the crimping portion 320, the core wire 146c may break between the claws 321 to 323 due to excessive crimping force, etc. 7(a), if the breakage occurs at P1 between the lead wire 146 and the claw 321, the broken core wire 146c is unlikely to fall off because it is still held by at least one of the claws 321 to 323. The same applies when the breakage occurs at P2 between the claws 321 and 322.

[0006] On the other hand, as shown in Figure 7(b), when the breaking position is P3 between the claw portions 322 and 323, the broken core wire scrap 146s is held only by the claw portion 323, and therefore, if the claw portion 323 is not tightened sufficiently, the core wire scrap 146s may fall off to the extension portion 330 below. Since the extension portion 330 is generally folded back from the tip of the main body portion 310, the fallen core wire scraps 146s are likely to get caught on the extension portion 330. However, if multiple terminal fittings 300, 400 are arranged on one main surface of the sensor element, the core wire residue 146s may become caught between the extension portions 330, 430 of adjacent terminal fittings 300, 400, acting as a bridge, which may cause a short circuit between the terminal fittings 300, 400. The tip of the core wire 146c rarely protrudes far beyond the claw portion 323, and the length T2 of the core wire scrap 146s can be approximated by the width T1 of the claw portion 323 in the axial direction O.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas sensor that suppresses short circuits between a plurality of terminal fittings arranged on at least one main surface of a sensor element, thereby improving the reliability of electrical connections. [Means for solving the problem]

[0008] In order to solve the above problems, the gas sensor of the present invention includes a sensor element having a plate shape extending in the axial direction and having a plurality of electrode pads along the width direction on at least one main surface on the rear end side, a plurality of terminal fittings extending in the axial direction and electrically connected to the electrode pads respectively, a cylindrical separator having an insertion hole for holding the terminal fittings and surrounding the rear end side of the sensor element, and a lead wire connected to the rear end side of the terminal fittings and extending to the outside. The terminal fitting has a main body portion held by the separator, an extension portion connected to the front end side of the main body portion and extending toward the sensor element to be electrically connected to the electrode pad, and an end-ring-shaped caulking portion connected to the rear end side of the main body portion for gripping and caulking the core wire at the front end side of the lead wire. The caulking portion has two or more claw portions arranged with a gap in the axial direction for gripping the core wire respectively. Among the plurality of terminal fittings, in at least one terminal fitting, when the maximum width in the axial direction of the foremost claw portion among the claw portions is L, and the minimum interval in the radial direction of the extension portion of the terminal fitting adjacent to the one main surface is B, it is characterized in that L < B is satisfied.

[0009] [[ID=​​​​​​​​​​​​In the gas sensor of the present invention, among the maximum widths in the axial direction of each of the claw portions, L may be the smallest. According to this gas sensor, the maximum width of the foremost claw portion where the core wire residue is most likely to drop off toward the extension portion side can be made the minimum L, and L < B can be surely realized to further suppress a short circuit between adjacent terminal fittings.

[0012] In the gas sensor of the present invention, when the total length in the axial direction of the caulking portion is M, the maximum distance between opposing surfaces is D when the insertion hole is rectangular, and the equivalent circle diameter is D when the insertion hole is circular or elliptical, M > D may be satisfied. When caulking the caulking portion, if the core wire breaks and drops off between the lead wire and the rearmost claw portion, the length of the core wire residue can be approximated by the total length M. And when the core wire residue rotates and lies down during dropping off, if the maximum distance between opposing surfaces or the equivalent circle diameter D of the insertion hole satisfies M > D, the lying-down core wire residue will be caught in the insertion hole, so that it is possible to further suppress reaching the extension portion on the tip side and causing a short circuit.

Effect of the Invention

[0013] According to this invention, a gas sensor that suppresses a short circuit between a plurality of terminal fittings arranged on at least one main surface of a sensor element and improves the reliability of electrical connection can be obtained.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view along the longitudinal direction of the gas sensor according to an embodiment of the present invention. [Figure 2] It is a perspective view of a sensor element. [Figure 3] It is a perspective view of a terminal fitting. [Figure 4] It is a perspective view of the terminal fitting after caulking the caulking portion. [Figure 5] It is a bottom view of a separator and a terminal fitting as viewed from the tip side. [Figure 6] It is a schematic diagram showing the total length M of the caulking portion and the maximum distance D of the insertion hole of the separator. [Figure 7] FIG. 10 is a schematic diagram showing a state in which adjacent terminal fittings are short-circuited in a conventional gas sensor. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described. FIG. 1 is an overall cross-sectional view along the longitudinal direction of a gas sensor (oxygen sensor) 200 according to an embodiment of the present invention, FIG. 2 is a perspective view of a sensor element 10, FIG. 3 is a perspective view of a terminal fitting 21, FIG. 4 is a perspective view of the terminal fitting 21 after the crimping portion 21c has been crimped, and FIG. 5 is a bottom view of a separator 166 and terminal fittings 21 to 25 as viewed from the tip side. This gas sensor 200 is an oxygen sensor that detects the oxygen concentration in the exhaust gas of an automobile or various internal combustion engines.

[0016] In FIG. 1, the gas sensor 200 includes a cylindrical metal shell 138 having a threaded portion 139 formed on its outer surface for fixing to an exhaust pipe, a plate-shaped sensor element 10 extending in the direction of axis O (the longitudinal direction of the gas sensor 200: the up-down direction in the figure), a cylindrical ceramic sleeve 106 arranged to surround the radial periphery of the sensor element 10, a cylindrical ceramic separator 166 arranged inside the tip side of an insertion hole 166h that penetrates in the axial direction so as to surround the periphery of the rear end of the sensor element 10, and five terminal fittings 21 to 25 (only two are shown in FIG. 1) arranged between the sensor element 10 and the separator 166. The gas detection portion 10a at the tip of the sensor element 10 is covered with a porous protective layer 20 made of alumina or the like (see FIG. 2).

[0017] The metal shell 138 is made of stainless steel, has a through hole 154 penetrating in the axial direction, and is configured in a generally cylindrical shape having a shelf portion 152 protruding radially inward from the through hole 154. The sensor element 10 is disposed in this through hole 154 so that the tip portion of the sensor element 10 protrudes beyond the tip of the sensor element 10. Furthermore, the shelf portion 152 is formed as an inward tapered surface that is inclined with respect to a plane perpendicular to the axial direction.

[0018] Inside the through hole 154 of the metal shell 138, an annular alumina ceramic holder 151, a powder-filled layer 156 (hereinafter also referred to as a talc ring), and the above-mentioned ceramic sleeve 106 are layered in this order from the front end to the rear end, surrounding the radial periphery of the sensor element 10. A crimping packing 157 is disposed between the ceramic sleeve 106 and the rear end portion 140 of the metallic shell 138. The rear end portion 140 of the metallic shell 138 is crimped so as to press the ceramic sleeve 106 toward the front end side via the crimping packing 157.

[0019] On the other hand, as shown in FIG. 1, a single-layer protector 143 made of metal (e.g., stainless steel) having a plurality of holes is attached by welding or the like to the outer periphery of the tip side (lower side in FIG. 1) of the metal shell 138, covering the protruding portion of the sensor element 10.

[0020] An outer cylinder 144 is fixed to the outer periphery on the rear end side of the metallic shell 138. A rubber grommet 170 is disposed in an opening on the rear end side (upper side in FIG. 1) of the outer cylinder 144. The rubber grommet 170 has lead wire insertion holes (not shown) through which five lead wires 146 (only two are shown in FIG. 1) electrically connected to the five terminal metal fittings 21 of the sensor element 10 (only two are shown in FIG. 1) are inserted. The grommet 170 is held inside the outer tube 144 by crimping it from the outside of the outer tube 144 .

[0021] A separator 166 is disposed on the rear end side (upper side in FIG. 1) of the sensor element 10 protruding from the rear end portion 140 of the metallic shell 138. The separator 166 is disposed around a total of five electrode pads 11 (only two are shown in FIG. 1) formed on the main surface of the rear end side of the sensor element 10. The separator 166 is formed in a cylindrical shape having an insertion hole 166h penetrating in the axial direction, and is provided with a flange portion 167 protruding radially outward from the outer surface. The separator 166 is held inside the outer cylinder 144 by the flange portion 167 abutting against the outer cylinder 144 via a holding member 169.

[0022] 2, the sensor element 10 has a plate shape extending in the direction of the axis O, and a tip portion 10s serves as a gas detection portion 10a that detects the oxygen concentration, and the gas detection portion 10a is covered with a porous protective layer 20. The sensor element 10 itself has a known configuration, and although not shown, it includes a gas detection portion having an oxygen ion-permeable solid electrolyte body and a pair of electrodes, and a heater portion that heats the gas detection portion and maintains it at a constant temperature. Three electrode pads 11 are arranged in the width W direction on the rear end side of one main surface 10f1 of the sensor element 10, and a sensor output signal from the gas detection unit 10a is output from these electrode pads 11 via lead portions (not shown). Two electrode pads 11 are also arranged in the width W direction on the rear end side of the other main surface 10f2 provided opposite the main surface, and power is supplied to the heater portion via lead portions (not shown). Each electrode pad 11 has a rectangular shape that is long in the direction of the axis O, and can be formed as a sintered body mainly made of Pt, for example.

[0023] Fig. 3 shows a perspective view of the terminal fitting 21. In this embodiment, as shown in Fig. 5, the gas sensor 200 has five terminal fittings 21 to 25, of which four terminal fittings 21, 23 to 25 are arranged at the vertices (corners) of a rectangle within the separator 166, with adjacent terminal fittings being line-symmetrical and terminal fittings on diagonal lines having the same shape. That is, there are two types of terminal fittings: the terminal fitting 21 in Fig. 3 and a terminal fitting line-symmetrical to it to the right of Fig. 3, and the components of each terminal fitting are substantially the same, so only the terminal fitting 21 in Fig. 3 will be described. Although the shape of the single terminal fitting 22 is slightly different from that of the terminal fitting 21, the configuration is essentially the same in that it has a main body portion, an extension portion, and a crimping portion, which will be described later, so a description thereof will be omitted. The terminal fitting 22 is disposed between (in the center of) the two terminal fittings 21 and 23 inside the separator 166 (FIG. 5).

[0024] As shown in Figure 3, the terminal fitting 21 has a main body portion 21a that is approximately plate-shaped and extends in the direction of the axis O and is held by the separator 166, an extension portion 21b that is connected to the tip side of the main body portion 21a and extends toward the sensor element 10, and a crimping portion (crimp terminal portion) 21c that is connected to the rear end of the main body portion 21a. The terminal fitting 21 also has various locking portions for holding and fixing itself within the separator 166 . The extension portion 21b is electrically connected to the electrode pad 11, and in this example is folded back from the leading edge of the main body portion 21a toward the rear end, but is not limited to this. The crimping portion 21c is formed in a closed annular shape that grips and crimps the core wire 146c at the tip side of the lead wire 146.

[0025] In this example, the main body portion 21a, the extension portion 21b, and the tightening portion 21c are integrally formed by pressing a single metal plate, but this is not limited to this, and for example, some of these may be separate bodies that are connected together. Furthermore, the terminal fitting 21 can be manufactured by punching out a single metal plate (such as Inconel (registered trademark)) and then bending each portion, but the manufacturing method is not limited to this.

[0026] Then, the core wire 146c facing the covering on the tip side of the lead wire 146 is inserted into and crimped to the open-ended annular crimping portion 21c before crimping, so that, as shown in FIG. 4, the lead wire 146 is electrically connected. Further, as shown in FIG. 3, the crimping portion 21c has two or more (two in this example) claw portions 21c1, 21c2 that are arranged with a gap in the direction of the axis O and grip the core wire 146c respectively. <00001`39> Let the maximum width in the direction of the axis O of the foremost claw portion 21c2 among the claw portions 21c1, 21c2 be L. Here, the maximum width L of the claw portion 21c2 is the maximum width among the line segments parallel to the axis O in the region from the free end of the claw portion 21c2 to the gap G (FIG. 3) with the adjacent claw portion 21c1 in the direction of the axis O.

[0028] Next, referring to FIG. 5, the minimum radial distance B between the extending portions 21b, 22b of the adjacent terminal fittings 21, 22 will be described. First, as shown in FIG. 3, in the extending portion 21b, the region from its free end 21bs toward the main body portion 21a to the position (base portion) 21be where the tangent of the outer surface becomes parallel to the axis O direction is set as the measurement target region for the minimum distance B. The same applies to the extending portion 22b. Then, the minimum distance B in the radial direction (direction perpendicular to the axis O direction) is obtained within the measurement target regions of the respective extending portions 21b, 22b. Note that the reference in the direction of the axis O when measuring the maximum width L and the minimum distance B is the direction in which the sensor element 10 extends.

[0029] And, on at least one main surface 10f1, when the minimum distance between the extending portions 21b, 22b of the adjacent terminal fittings 21, 22 is B, it is necessary to satisfy L < B. As described with reference to FIG. 6, the length of the core wire scraps broken between the claw portions 21c1, 21c2 can be approximated by the maximum width L in the direction of the axis O of the claw portion 21c2. Therefore, if L < B, even if this core wire scrap falls off to the extending portions 21b, 22b, it will not be caught so as to bridge between the extending portions 21b, 22b and will fall, suppressing a short circuit between the adjacent terminal fittings 21, 22.

[0030] In addition, the maximum width of the claw portions at the leading ends of the caulking portions of the terminal fittings 21 and 22 must both be L or less. Also, when the minimum interval C between another adjacent terminal fittings 22 and 23 is smaller than B, it is necessary to satisfy L < C with respect to the maximum width L of the claw portions at the leading ends of the caulking portions of the terminal fittings 21 and 22. Furthermore, in this example, on the other main surface 10f2 of the sensor element 10, since there are two terminal fittings, the minimum interval E between the adjacent terminal fittings 24 and 25 is wide, and even without special design, the maximum width L of the claw portions at the leading ends satisfies L < E. However, if L < B is satisfied on one main surface 10f1 of the sensor element 10, it is not necessary to satisfy L < E on the other main surface 10f2. Of course, it is preferable to satisfy L < B and L < E on both main surfaces 10f1 and 10f2.

[0031] Of the maximum widths in the direction of the axis O of the respective claw portions 21c1 and 21c2 of the terminal fitting 21, L (of the leading claw portion 21c2) may be the smallest. By doing so, the maximum width of the leading claw portion 21c2, where the core wire scraps are most likely to fall off toward the extending portion side, can be made the minimum L, and it is possible to surely realize L < B and further suppress a short circuit between the adjacent terminal fittings 21 and 22.

[0032] As shown in FIG. 6, when the total length in the direction of the axis O of the caulking portion 21c is M and the maximum interval of the insertion holes 166h is D, it is preferable to satisfy M > D. As already described, when the break position of the core wire 146c is P1 between the lead wire 146 and the rearmost claw portion 21c1, the possibility that the broken core wire scraps 146s fall off is low, but there is still a risk of falling off. In this case, the length of the core wire scraps 146s can be approximated by the total length M in the direction of the axis O of the caulking portion 21c.

[0033] If the core wire scraps 146s fall off with the axis O direction as the longitudinal direction as it is, they reach the extending portion 21b on the tip side through the insertion hole 166h, which may cause a short circuit. On the other hand, if the core wire scrap 146s rotates and falls over while falling off, if the maximum spacing D of the insertion holes 166h satisfies M>D, the fallen core wire scrap 146s will get caught inside the insertion holes 166h, thereby further preventing it from reaching the extension portion 21b on the tip side and causing a short circuit. In this example, since the insertion hole 166h is rectangular, the maximum distance between the opposing surfaces of the insertion hole 166h (there are two opposing surfaces, and the larger distance between them) is defined as D. If the insertion hole is circular or elliptical, the equivalent diameter of the circle is defined as D.

[0034] It goes without saying that the present invention is not limited to the above-described embodiments, but covers various modifications and equivalents that fall within the spirit and scope of the present invention. For example, the shape and number of the terminal fittings are not limited to those in the above embodiment, and the shape of the separator and the shape of the separator insertion holes are also not limited to those in the above embodiment. Further, types of gas sensors include oxygen sensors, full-range air-fuel ratio sensors, NOx sensors, and the like. [Explanation of symbols]

[0035] 10 Sensor element 10f1, 10f2 main surface 11 Electrode pads 21~25 Terminal fittings 21a Main body 21b Extension part 21c Crimping part 21c1, 21c2 Claw part 21c2 Cutting edge of the claw 146 Lead Wire 146c core wire 166 Separator 166h Insertion hole 200 Gas Sensor O axis

Claims

1. a plate-shaped sensor element extending in the axial direction and having a plurality of electrode pads on at least one main surface on the rear end side along the width direction; a plurality of terminal fittings extending in the axial direction and electrically connected to the electrode pads, respectively; a cylindrical separator having an insertion hole for holding the terminal metal fitting and surrounding a rear end side of the sensor element; a lead wire connected to a rear end of the terminal fitting and extending to the outside; A gas sensor comprising: the terminal fitting has a main body portion held by the separator, an extension portion connected to a front end side of the main body portion and extending toward the sensor element to electrically connect to the electrode pad, and an annular crimp portion having an end connected to a rear end side of the main body portion and gripping and crimping a core wire at a front end side of the lead wire, the crimping portion has two or more claw portions that are arranged with a gap in the axial direction and each grip the core wire, In at least one of the plurality of terminal fittings, a maximum width of a tip end of the claw portion in the axial direction is defined as L, When the minimum radial distance between the extension portions of the terminal fittings adjacent to the one main surface is B, A gas sensor characterized in that L<B is satisfied.

2. 2. The gas sensor according to claim 1, wherein all of the terminal fittings satisfy L<B.

3. 3. The gas sensor according to claim 1, wherein L is the smallest of the maximum widths of the claws in the axial direction.

4. The total length of the crimped portion in the axial direction is defined as M, When the insertion hole is rectangular, the maximum distance between the opposing surfaces is D, and when the insertion hole is circular or elliptical, the equivalent diameter of the circle is D, 3. The gas sensor according to claim 1, wherein M>D is satisfied.

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