gas sensor

Abstract

To provide a gas sensor that is low-cost and offers excellent reliability in electrical connection between terminal fittings and sensor elements at high temperatures. [Solution] A gas sensor 1 comprises a sensor element 21 extending in the axial direction O and having an electrode pad 24 on the surface of its rear end, a terminal fitting 75 that elastically contacts the electrode pad, and a separator 91 that holds the terminal fitting, wherein the terminal fitting is mainly composed of Fe, and by mass%, consists of Ni: 9.75~10.25%, Cr: 23.00~23.90%, Mn: 5.80~6.20%, N: 0.47~0.53%, with the remainder being Fe and unavoidable impurities.

Description

Technical Field

[0001] The present invention relates to a gas sensor including a terminal fitting electrically connected to a sensor element.

Background Art

[0002] As a gas sensor for detecting the concentration of oxygen and NO in exhaust gas of automobiles and the like, there is known one having a plate-shaped sensor element using a solid electrolyte. As this type of gas sensor, an electrode pad is provided on the surface of the rear end side of a plate-shaped sensor element, and a terminal fitting is electrically contacted with this electrode pad to extract a sensor output signal from the sensor element to the outside, which is widely used. And as the material of the terminal fitting, a Ni-based alloy (for example, Inconel (registered trademark)) having excellent heat resistance and little creep deformation even when exposed to high temperatures such as exhaust gas is generally used (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, Ni-based alloys are expensive, leading to cost increases. On the other hand, when using an Fe-based alloy with a low Ni content or the like for the terminal fitting, the heat resistance becomes insufficient.

[0005] The present invention has been made in view of such a situation, and an object thereof is to provide a gas sensor having low cost and excellent reliability in electrical connectivity between a terminal fitting and a sensor element at high temperatures.

Means for Solving the Problems

[0006] ​The gas sensor of the present invention comprises a sensor element extending in the axial direction and having an electrode pad on its rear end surface, a terminal fitting that elastically contacts the electrode pad, and a separator that holds the terminal fitting. A gas sensor comprising the terminal fittings, wherein the terminal fittings are mainly composed of Fe, and by mass%, consist of Ni: 9.75~10.25%, Cr: 23.00~23.90%, Mn: 5.80~6.20%, N: 0.47~0.53%, with the remainder being Fe and unavoidable impurities.

[0007] According to this gas sensor, the alloy with the above composition has high heat resistance despite being an Fe-based alloy, which is less expensive than Ni-based alloys. Therefore, by using the above composition for the terminal fittings, a gas sensor can be obtained that is low-cost and has excellent reliability in the electrical connection between the terminal fittings and the sensor element at high temperatures.

[0008] In the gas sensor of the present invention, the terminal fitting has a main body portion that extends in the axial direction and is held by the separator in a state in which it is inserted into the terminal insertion hole of the separator, a contact portion that extends toward the electrode pad and contacts the electrode pad, and a folded portion that connects the main body portion and the contact portion, and at least the contact portion and the folded portion are made of a single plate having a plate surface, and the folded portion has a projection that extends along the plate surface, and when viewed from the direction normal to the plate surface in the region where the projection is provided, the projection may constitute the outer edge of the folded portion.

[0009] When the sensor element is heated by the gas being measured, such as exhaust gas, the terminal fittings in contact with the electrode pads of the sensor element also become very hot. Therefore, if the projection forms the outer edge of the folded portion when viewed from the normal direction close to the axial direction, the outer shape of the folded portion will be larger when viewed from the axial direction, and the projected area of ​​the folded portion will also increase by the amount of the projection. As a result, a protrusion is interposed in the gap between the terminal insertion hole and the folded portion of the separator when viewed from the axial direction. This makes it easier to dissipate heat from the terminal fitting axially through the protrusion, suppressing overheating of the terminal fitting and further improving the reliability of the electrical connection between the terminal fitting and the sensor element at high temperatures. Furthermore, since the temperature inside the sensor tends to gradient along the axial direction, the air inside the sensor tends to move along the axial direction. For this reason, heat near the terminal fitting tends to dissipate easily in the axial direction in which the terminal insertion hole extends. Consequently, in the case of a protrusion that does not form an outer edge of the folded portion and does not increase the projected area of ​​the folded portion in the axial direction (a protrusion that rises along the axial direction), the surface area of ​​the terminal fitting increases due to the protrusion itself, but heat does not escape easily in the axial direction, making heat dissipation difficult.

[0010] In the gas sensor of the present invention, the separator has an element insertion hole surrounding the rear end of the sensor element, and the projection may extend toward the element insertion hole. According to this gas sensor, the protrusion is positioned to block (part of) the element insertion hole, thereby suppressing the transfer of radiant heat from the sensor element located at the tip of the terminal fitting to the component at the rear end of the terminal fitting. This allows for heat shielding of a component located further back than the separator and having low heat resistance (for example, a rubber grommet).

[0011] In the gas sensor of the present invention, the projection may be positioned at a location offset in the width direction of the terminal fitting relative to the contact portion. This gas sensor prevents the protrusion from coming into contact with the contact area, thereby suppressing a decrease in the reliability of the electrical connection between the contact area and the electrode pad.

[0012] In the gas sensor of the present invention, the initial spring force of the terminal fitting when assembled to the gas sensor may be 3.0 N or more. According to this gas sensor, even though the terminal fittings are made of a low-cost Fe-based alloy, they have high heat resistance, so even if heat is applied to the terminal fittings, the decrease in contact pressure can be suppressed. [Effects of the Invention]

[0013] According to the present invention, a gas sensor with low cost and excellent reliability in electrical connectivity between a terminal fitting and a sensor element at high temperatures can be obtained.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view of a gas sensor according to an embodiment of the present invention. [Figure 2] It is a schematic plan view of a separator in which a terminal fitting is held and a sensor element is inserted, as viewed from the tip side. [Figure 3] It is a perspective view of a terminal fitting. [Figure 4] It is a plan view of the terminal fitting as viewed from the tip side. [Figure 5] It is a perspective view showing a state in which a protrusion of a terminal fitting according to an embodiment of the present invention constitutes an outer edge of a folded-back portion. [Figure 6] It is a perspective view showing a state in which a protrusion of a terminal fitting does not constitute an outer edge of a folded-back portion.

Mode for Carrying Out the Invention

[0015] Embodiments of the present invention will be described in detail based on FIGS. 1 to 4. FIG. 1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention, FIG. 2 is a schematic plan view of a separator 91 that holds a terminal fitting 75 and into which a sensor element 21 is inserted, as viewed from the tip side, FIG. 3 is a perspective view of the terminal fitting 75, and FIG. 4 is a plan view of the terminal fitting 75 as viewed from the tip side. [[ID=3​​​​​Among the sensor elements 21, the tip - side portion where the detection unit 22 is formed protrudes beyond the tip of the ceramic holder 30. The sensor element 21 passed through the through - hole 32 in this way compresses the sealing material (in this example, talc) 41 arranged on the rear - end face side (upper side in the drawing) of the ceramic holder 30 in the front - rear direction through the sleeve 43 made of an insulating material and the ring washer 45, so as to maintain airtightness and be fixed in the front - rear direction inside the main body fitting 11.

[0018] Note that the portion near the rear end 29 including the rear end 29 of the sensor element 21 protrudes rearward from the sleeve 43 and the main body fitting 11. Terminals 75 and 76 provided at the tips of the lead wires 71 drawn out to the outside through the rubber grommets 85 are press - connected to the electrode pads 24 formed in the portion near the rear end 29, and are electrically connected. Also, the portion near the rear end 29 of the sensor element 21 including this electrode pad 24 is covered by the outer cylinder 81. This will be described in more detail below.

[0019] The sensor element 21 extends in the direction of the axis O and has a strip - like (plate - like) shape with a detection unit 22 composed of a detection electrode etc. (not shown) provided on the tip - side (lower side in the drawing) facing the measurement object to detect a specific gas component in the detected gas. The cross - section of the sensor element 21 is a rectangle with a constant size in the front - rear direction, and is formed as an elongated shape mainly made of ceramic (such as a solid electrolyte). The sensor element 21 itself is the same as those known in the prior art. A pair of detection electrodes forming the detection unit 22 are arranged at the tip - side portion of the solid electrolyte (member), and electrode pads 24 for connecting the lead wires 71 for taking out the detection output are formed and exposed at the portion near the rear end.

[0020] Also, in this example, a heater (not shown) is provided inside the tip - side portion of the ceramic material formed in a laminated state on the solid electrolyte (member) of the sensor element 21, and electrode pads 24 for connecting the lead wires 71 for applying voltage to this heater are formed and exposed at the portion near the rear end. Although not shown in the diagram, these electrode pads 24 are formed in a vertically elongated rectangular shape, and for example, near the rear end 29 of the sensor element 21, three or two electrode pads are arranged horizontally on the wide surface (both sides) of the strip. Furthermore, the detection portion 22 of the sensor element 21 is covered with a porous protective layer 23 made of alumina or spinel.

[0021] The main fitting 11 is cylindrical with concentrically different diameters at its front and rear, with the front end having a smaller diameter and a cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 12 for fitting and fixing the protector 60, which will be described later, to the outside. On the outer surface of the rear (upper part in the figure) there is a screw 13 with a larger diameter for fixing to the engine's exhaust pipe. Behind it, there is a polygonal section 14 into which the gas sensor 1 is screwed in using the screw 13. Behind this polygonal section 14, there is a cylindrical section 15 into which a protective cylinder (outer cylinder) 81 that covers the rear of the gas sensor 1 is fitted and welded, and behind that there is a cylindrical section 16 for crimping that has a smaller outer diameter and thinner wall. Note that in Figure 1, the crimping cylindrical portion 16 is bent inward for use after crimping. A gasket 19 for sealing during screwing is attached to the lower surface of the polygonal portion 14. On the other hand, the main fitting 11 has an inner hole 18 that penetrates in the direction of the axis O. The inner circumferential surface of the inner hole 18 has a tapered step portion 17 that narrows radially inward from the rear end to the front end.

[0022] Inside the main fitting 11 is a ceramic holder 30 made of insulating ceramic (e.g., alumina) and formed in a generally short cylindrical shape. The ceramic holder 30 has a tip-facing surface 30a that is tapered towards the tip. Then, the ceramic holder 30 is positioned and fitted into the main fitting 11 by the sealing material 41 pressing the ceramic holder 30 from the rear end side while the outer circumference portion of the tip-facing surface 30a is locked to the stepped portion 17. On the other hand, the through-hole 32 is located in the center of the ceramic holder 30 and is a rectangular opening with dimensions approximately the same as the cross-section of the sensor element 21, so that the sensor element 21 can pass through with virtually no gaps.

[0023] The sensor element 21 is passed through the through hole 32 of the ceramic holder 30, and the tip of the sensor element 21 protrudes further than the tips of the ceramic holder 30 and the main body fitting 11. On the other hand, in this embodiment, the tip portion of the sensor element 21 has a single-layer structure and is covered with a bottomed cylindrical protector (protective cover) 60 having ventilation holes 61 and 63. The rear end of the protector 60 is fitted onto the cylindrical portion 15 of the main fitting 11 and welded. The ventilation holes 61, which serve as introduction holes, are provided in multiple locations circumferentially spaced apart on a stepped portion near the center in the axial direction O of the protector 60. On the other hand, one ventilation hole 63, which serves as an discharge hole, is provided on the tip side of the protector 60.

[0024] Furthermore, as shown in Figure 1, each electrode pad 24 formed near the rear end 29 of the sensor element 21 is electrically connected to the terminal fittings 75 and 76 provided at the ends of each lead wire 71 that are pulled out to the outside through a grommet 85, by being pressed against them by their spring properties. In this example, each terminal fitting 75 and 76, including the pressure-contact portion, is held in a facing position within each terminal insertion hole 91h provided in an insulating separator 91 located inside the outer cylinder 81 of the gas sensor 1.

[0025] Furthermore, an element insertion hole 91s surrounding the rear end 29 of the sensor element 21 is formed around the axis of the separator 91, and each terminal insertion hole 91h is arranged to surround the element insertion hole 91s (Figure 2). Furthermore, at the tip of the separator 91, the element insertion hole 91s is in communication with each terminal insertion hole 91h.

[0026] Furthermore, the separator 91's movement in the radial direction and toward the tip is restricted via a retaining fitting 82 that is crimped and fixed inside the outer cylinder 81. The tip of this outer cylinder 81 is then fitted onto the cylindrical portion 15 near the rear end of the main fitting 11 and welded, thereby providing an airtight cover to the rear of the gas sensor 1. The lead wire 71 is pulled out to the outside through a sealing material (e.g., rubber) 85 located inside the rear end of the outer cylinder 81, and the airtightness of this part is maintained by reducing the diameter of this small-diameter second crimping portion 81r (described later) and compressing this grommet 85.

[0027] The outer cylinder 81 has a large diameter section at the front and a small diameter section at the rear, and has a stepped section 81d extending radially inward between the large and small diameter sections. The rear end surface of the separator 91 is locked to the front-facing surface of the stepped section 81d. On the other hand, the flange 93 formed on the outer circumference of the separator 91 is supported on a retaining bracket 82 fixed to the inside of the outer cylinder 81, and the separator 91 is held in the axial direction O by the stepped section 81d and the retaining bracket 82. Furthermore, the rear end of the outer cylinder 81 is crimped radially inward, and the grommet 85 is fixed to the inside of the outer cylinder 81.

[0028] Next, we will explain the terminal fitting 75. In this embodiment, the gas sensor 1 has four terminal fittings 75 and one terminal fitting 76 located at the rear end of the terminal fittings 75. However, terminal fitting 76 is an output terminal and is therefore excluded from the scope of "terminal fittings" in the claims in this embodiment. However, terminal fitting 76 may also be included in the scope of "terminal fittings" of the present invention. Furthermore, the number of terminal fittings 76 is not limited to one; it may be zero or two or more. As shown in Figure 2, these four terminal fittings 751 to 754 are all line-symmetrical or point-symmetrical with respect to each other. Therefore, in Figure 3, terminal fitting 751 in Figure 2 is described as "terminal fitting 75," but the configurations of the other terminal fittings 752 to 754 are substantially the same.

[0029] First, terminal fitting 75 is mainly composed of Fe, and by mass%, consists of Ni: 9.75~10.25%, Cr: 23.00~23.90%, Mn: 5.80~6.20%, N: 0.47~0.53%, with the remainder being Fe and unavoidable impurities. The alloy with the above composition has high heat resistance despite being an Fe-based alloy, which is less expensive than Ni-based alloys. Therefore, by using the above composition for the terminal fitting 75, a gas sensor can be obtained that is low-cost and has excellent reliability in the electrical connection between the terminal fitting 75 and the sensor element 21 at high temperatures. Furthermore, "mainly composed of Fe" means that the Fe content exceeds 50% by mass.

[0030] Furthermore, as shown in Figure 3, the terminal fitting 75 integrally comprises a roughly plate-shaped main body portion 75a extending in the direction of axis O, a contact portion 75b folded back from the tip to the rear end of the main body portion 75a, a crimp terminal portion 75c connected to the rear end of the main body portion 75a, and a folded portion 75d connecting the main body portion 75a and the contact portion 75b.

[0031] The main body portion 75a is held by the separator 91 while inserted into the terminal insertion hole 91h of the separator 91. The contact portion 75b extends toward the sensor element 21 (and its electrode pad 24) and makes electrical contact with the electrode pad 24. Furthermore, the folded portion 75d is elastically deformable, and as the folded portion 75d bends elastically, the contact portion 75b connected to the folded portion 75d is pressed against the electrode pad 24, ensuring reliable contact with the electrode pad 24. On the other hand, the crimp terminal portion 75c has a known cylindrical shape, and the lead wire 71 (see Figure 1) is electrically connected by inserting the stripped insulation from the lead wire 71 into this cylinder and crimping it.

[0032] The terminal fitting 75 can be manufactured, for example, by punching out a single metal sheet of the above composition and then bending the contact portion 75b and the folded portion 75d, but is not limited to this. However, at least the contact portion 75b and the folded portion 75d consist of a single plate having a plate surface.

[0033] Furthermore, as shown in Figure 3, in this example, the folded portion 75d has a projection 75p that extends along the plate surface 75s. As shown in Figure 4, when viewed from the normal direction n of the plate surface 75s in the region where the protrusion 75p is provided (hatched area in Figure 4), the protrusion 75p constitutes the outer edge 75e of the folded portion.

[0034] Here, the reason why the normal direction n is based on the "plate surface 75s in the region where the protrusion 75p is provided (hatched area in Figure 4)" is as follows. In other words, as shown in Figure 3, the folded portion 75d is curved rather than flat because it is made by folding the plate, and the direction of the normal changes depending on the position of the folded portion 75d. Therefore, the normal of the plate surface 75s in the "region where the protrusion 75p is provided" is adopted. Furthermore, the normal vector is defined as the normal vector at the centroid of the "region where projection 75p is provided". The "region where protrusion 75p is provided" is described below.

[0035] The "region where projection 75p is provided" is determined as follows: First, as shown in Figure 4, determine the sign of the radius of curvature of each part that constitutes the contour (outer edge 75e) of the folded portion 75d. For example, at position P0 in Figure 4, following the direction of the arrow, the line first moves from top to bottom, and from the point where the radius of curvature = 0 (straight line), it curves counterclockwise at P0 (radius of curvature > 0), changes direction horizontally, and connects back to a point where the radius of curvature = 0 (straight line). In other words, near position P0, the radius of curvature is either positive or negative (positive). On the other hand, at position P1 (projection 75p) in Figure 4, following the direction of the arrow, it first curves clockwise from right to left horizontally (radius of curvature < 0), then curves counterclockwise towards the left at the apex of projection 75p (radius of curvature > 0), and then curves clockwise towards the left (radius of curvature < 0). In other words, near position P1, between two positions where the radius of curvature is one of the positive and negative (negative), there exists the other (positive) of the positive and negative radii. This case is considered to be "projection 75p".

[0036] Furthermore, the "region where the projection 75p is provided" is the hatched region enclosed between the line segment L connecting two positions where the radius of curvature is one positive or one negative, and the other positive or negative point that forms the tip t of the projection 75p. Furthermore, between two positions where the radius of curvature is one of two (negative), there may be two or more positions where the other (positive) radius of curvature exists.

[0037] In this example, the main body 75a includes a pair of retaining portions 75f1 that bend in an L-shape from both ends near the center of its axis O toward the sensor element 21, and a single retaining portion 75f2 that extends radially from one end of the main body 75a toward the tip in the axis O direction. These retaining parts 75f1 and 75f2 abut against predetermined parts of the wall surface of the terminal insertion hole 91h, thereby locking the terminal fitting 75 inside the terminal insertion hole 91h. Furthermore, a flat-shaped locking portion 75g is formed from the tip of each retaining portion 75f1, extending radially outward and toward the tip. This pair of locking portions 75g expands within the terminal insertion hole 91h and contacts the wall surface of the terminal insertion hole 91h, thereby securely locking the terminal fitting 75 within the terminal insertion hole 91h.

[0038] Next, referring to Figures 5 and 6, we will explain the effect of the projection 75p forming the outer edge 75e of the folded portion 75d when viewed from the normal direction n. As shown in Figures 1 and 5, the sensor element 21 is heated by the gas G being measured, such as exhaust gas, and the terminal fittings 75 in contact with the electrode pads 24 of the sensor element 21 also become very hot.

[0039] Therefore, as shown in Figure 5, if the projection 75p forms the outer edge 75e of the folded portion 75d when viewed from the normal direction n, which is close to the axis O direction, the outer shape of the folded portion 75d will be larger when viewed from the axis O direction, and the projected area of ​​the folded portion 75d will also increase by the amount of the projection 75p. As a result, when viewed from the direction of axis O, the projection 75p is interposed in the gap between the terminal insertion hole 91h of the separator 91 and the folded portion 75d, making it easier to dissipate the heat H of the terminal fitting 75 in the direction of axis O via the projection 75p, thereby suppressing overheating of the terminal fitting 75 and further improving the reliability of the electrical connection between the terminal fitting 75 and the sensor element 21 at high temperatures.

[0040] Furthermore, the heat H of the terminal fitting 75 tends to dissipate more easily in the direction of the axis O along which the terminal insertion hole 91h extends. Now, consider the case where a projection 750p is provided on the folded portion 750d of the terminal fitting, extending in the thickness direction of the plate surface of the folded portion 750d, as shown in Figure 6. Since this projection 750p does not constitute the outer edge 750e of the folded portion 750d, the outer shape of the folded portion 750d does not increase when viewed from the direction of axis O, and the projected area of ​​the folded portion 750d does not increase. In this case, although the surface area of ​​the terminal fitting increases due to the protrusion 750p itself, heat H is difficult to dissipate in the axial direction O, making heat dissipation difficult. As a result, the terminal fitting 75 overheats, making it difficult to improve the reliability of the electrical connection between the terminal fitting 75 and the sensor element 21 at high temperatures. Furthermore, if the projection 750p protrudes in the thickness direction of the plate surface of the folded portion 750d, the projection 750p may function as a rib, making it difficult for the folded portion 750d to bend, and potentially reducing the pressing force applied when the contact portion connected to the folded portion 750d is pressed against the electrode pad.

[0041] Furthermore, as shown in Figure 2, in this example, the projection 75p extends toward the element insertion hole 91s (arrow in Figure 2). In this way, the projection 75p is positioned to block (part of) the element insertion hole 91s, thereby suppressing the transfer of radiant heat from the sensor element 21 located on the tip side of the terminal fitting 75 to the member on the rear end side of the terminal fitting 75, and enabling heat shielding for a member located further rear than the separator 91 and having low heat resistance (for example, a rubber grommet 85).

[0042] Furthermore, as shown in Figures 3 and 4, in this example, the projection 75p is positioned offset in the width direction of the terminal fitting 75 relative to the contact portion 75b. In this way, the projection 75p comes into contact with the contact portion 75b, which helps to suppress a decrease in the reliability of the electrical connection between the contact portion 75b and the electrode pad 24.

[0043] The gas sensor of the present invention can be implemented by appropriately modifying its structure and configuration, without departing from the spirit of the invention. The sensor element is not limited to one that measures oxygen concentration; one that measures the concentration of nitrogen oxides (NOx) or hydrocarbons (HC), etc., may also be used. The shape, position, and number of protrusions provided on the folded portion 75d are not limited. For example, as shown in Figure 5, in addition to the protrusion 75p facing the sensor element 21 (or instead of the protrusion 75p), a second protrusion 75p2 facing radially may be provided. The shape of the terminal fitting is not limited to the shape shown in Figure 3. For example, it may be a shape in which the main body portion 75a is directly connected to the contact portion 75b without going through the folded portion 75d. [Examples]

[0044] By changing the dimensions of the contact portion 75b and the folded portion 75d of the terminal fitting, various spring forces were obtained to produce terminal fittings for each of the embodiments 1 to 3 and comparative example 1 (shape shown in Figure 3), and these were assembled into the gas sensor shown in Figure 1. The composition of the terminal fittings is as follows: Examples 1-3 are as follows (by mass%): Ni: 9.75-10.25%, Cr: 23.00-23.90%, Mn: 5.80-6.20%, N: 0.47-0.53%, with the remainder being Fe and unavoidable impurities; Comparative Example 1 is as follows (by mass%): Ni: 4.00-4.60%, Cr: 16.50-17.35%, Mn: 14.00-15.00%, N: 0.30-0.35%, with the remainder being Fe and unavoidable impurities.

[0045] The deformation amount D0 of the terminal fitting 75 was measured when it was assembled to a new (heat-free) gas sensor 1. Next, the terminal fitting 75 was removed from the gas sensor 1, and the deformation amount D1 of the terminal fitting 75 was measured. Here, as shown in Figure 4, D0 and D1 are the maximum distance (spring height) from the back surface of the main body portion 75a of the terminal fitting 75 to the contact portion 75b.

[0046] Furthermore, the load applied to the removed terminal fitting 75 when a displacement of (D1-D0) was applied was measured using a load cell, and this load was defined as the "initial spring force of the terminal fitting." Next, the terminal fitting 75 was heated in an atmospheric environment at 540°C for 75 hours, allowed to cool to room temperature, and then the load was measured when a displacement of (D1-D0) was applied in the same manner. This load was defined as the "heat-resistant spring force." Then, the heat-resistant terminal fittings 75 were assembled to the sensor, and the contact state with the sensor element (electrode pad 24) was determined. The determination criteria were defined as follows. ◎: Heat-resistant spring force of 4.5N or more ○: Heat-resistant spring force of 2.5N or more, less than 4.5N ×: Heat-resistant spring force less than 2.5N The results obtained are shown in Table 1.

[0047] [Table 1]

[0048] In Examples 1-3, where the initial spring force of the terminal fitting was 3.0 (N) or higher, the decrease in spring force was minimal even after heat resistance, and the contact condition with the sensor element (electrode pad 24) was good. In Comparative Example 1, where the initial spring force of the terminal fitting was less than 3.0 (N), the decrease in spring force after heat resistance was significant, and the contact condition with the sensor element (electrode pad 24) deteriorated. [Explanation of Symbols]

[0049] 1. Gas sensor 11 Main fittings 21 Sensor element 24 electrode pads 75, 751~754 Terminal fittings 75a Main body 75b Contact area 75d Folded section 75p, 75p2 protrusion 75e Outer edge of the folded portion 91 Separator 91h Terminal insertion hole 91s Element insertion hole O axis n normal direction H terminal fitting heat

Claims

1. A sensor element extending in the axial direction and having electrode pads on the surface of its rear end, A terminal fitting that elastically contacts the electrode pad, A separator that holds the terminal fittings, A gas sensor comprising, The aforementioned terminal fitting is a gas sensor characterized by being mainly composed of Fe, with mass percent consisting of Ni: 9.75 to 10.25%, Cr: 23.00 to 23.90%, Mn: 5.80 to 6.20%, N: 0.47 to 0.53%, and the remainder being Fe and unavoidable impurities.

2. The terminal fitting has a main body portion that extends in the axial direction and is held by the separator in a state where it is inserted into the terminal insertion hole of the separator, a contact portion that extends toward the electrode pad and contacts the electrode pad, and a folded portion that connects the main body portion and the contact portion. At least the contact portion and the folded portion consist of a single plate having a plate surface, The folded portion has a projection that extends along the surface of the plate, The gas sensor according to claim 1, characterized in that, when viewed from the direction normal to the plate surface in the region where the projection is provided, the projection constitutes the outer edge of the folded portion.

3. The separator has an element insertion hole surrounding the rear end of the sensor element, The gas sensor according to claim 2, characterized in that the projection extends toward the element insertion hole.

4. The gas sensor according to claim 2 or 3, wherein the projection is positioned at a location offset in the width direction of the terminal fitting with respect to the contact portion.

5. The gas sensor according to claim 1 or 2, characterized in that the initial spring force of the terminal fitting when assembled to the gas sensor is 3.0 N or more.

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