Gas sensor

Abstract

To provide a gas sensor inhibiting damage from occurring when a sensor element is assembled.SOLUTION: A gas sensor 200 comprises: a sensor element 10; a main metal fitting 138; a cylindrical holder 151 including a first rectangular element hole 151h through which the sensor element is inserted; a sleeve 106 including a second rectangular element hole 106h through which the sensor element is inserted on a rear end side from the holder; and filling powder 156 filling a gap between the main metal fitting and the sensor element. At least one of the holder and the sleeve is formed with flat surfaces 106f, 151f in contact with the filling powder and protrusions 106p, 151p protruding from the flat surface toward the filling powder and surrounding the first element hole or the second element hole. The protrusions are tapered toward the filling powder when viewed in a direction D perpendicular to the principal surface of the sensor element. A boundary BR where a corner part 10e parallel to an axis o direction of the sensor element faces the protrusion is positioned between apexes 106t, 151t and skirt parts 106b, 151b of the protrusion.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 plate-shaped sensor element. This type of gas sensor has been used in which the sensor element is held by a cylindrical metal shell, an annular holder and a sleeve are arranged in the inner hole of the metal shell, the holder and sleeve have an element hole through which the sensor element is inserted, and a filler powder such as a talc ring is arranged between the holder and the sleeve to fill the gap between the metal shell and the sensor element (Patent Document 1). Here, by crimping the sleeve so as to press it against the holder, the filler powder is compressed and enters into the gap between the metallic shell and the sensor element, forming a seal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-138679 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of a conventional gas sensor, the periphery of the element hole 1100h of the holder 1100 or the sleeve 1200 is flat, as shown in Fig. 8. Therefore, when the filling powder 1300 is compressed through the sleeve 1200, pressure is concentrated on the corner 1000e of the sensor element 1000, which has low strength, and there is a risk that the sensor element 1000 may be damaged. The reason for this is thought to be as follows: For example, if the periphery of the element hole 1100h of the holder 1100 is a flat surface, when the filling powder 1300 is compressed, the pressing force F of the filling powder 1300 is evenly applied to the sensor element 1000 around the element hole 1100h. However, this results in the pressing force F being applied to the corner 1000e, which has low strength, in the same way as other parts, which leads to damage to the corner 1000e. On the other hand, since the filling powder 1300 fills (seals) the gap between the metallic shell and the sensor element 1000, it is difficult to weaken the pressing force F as a whole.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas sensor in which damage to the sensor element during assembly is suppressed. [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 a detection portion formed on a tip end side for detecting a gas to be detected, a cylindrical metal shell surrounding and holding the sensor element in a radial direction, a cylindrical holder held in an inner hole of the metal shell and having a rectangular first element hole through which the sensor element is inserted, a cylindrical sleeve held in the inner hole of the metal shell on the rear end side of the holder and having a rectangular second element hole through which the sensor element is inserted, and a cylindrical sleeve disposed in the inner hole of the metal shell between the holder and the sleeve and having a detection portion formed on a tip end side of the metal shell and a detection portion formed on a tip end side of the metal shell. and filling powder filling a gap with the sensor element. In this gas sensor, at least one of the holder and the sleeve is formed with a flat surface in contact with the filling powder and a protrusion that protrudes from the flat surface toward the filling powder and surrounds the first element hole or the second element hole, and the protrusion tapers toward the filling powder when viewed from a direction perpendicular to the main surface of the sensor element, and the boundary where a corner of the sensor element parallel to the axial direction faces the protrusion is located between the top of the protrusion and the bottom where the protrusion connects to the flat surface.

[0007] According to this gas sensor, when the filled powder is compressed, the pressing force of the filled powder applied to the sensor element near the boundary portion becomes the highest pressing force on the side closer to the top, becomes a lower pressing force at the boundary portion, further decreases from the boundary portion toward the bottom portion, and becomes the lowest pressing force at the bottom portion and the flat surface. And thereby, since the pressing force of the filled powder gradually weakens along the axial direction of the corner portion, it is possible to suppress the application of a high pressing force to the corner portion with low strength in the same manner as other portions (for example, the portion where the sensor element faces the top), and it is possible to suppress breakage during the assembly of the sensor element. On the other hand, near the top portion, the distance between the sleeve and the holder becomes close and the pressing force becomes high, so that the gap between the main fitting and the sensor element can be surely filled (sealed) with the filled powder.

[0008] In the gas sensor of the present invention, when viewed from a direction perpendicular to the main surface of the sensor element, the relationship c < a < b may be satisfied with respect to the width c of the top of the protrusion, the width b of the bottom portion where the protrusion is connected to the flat surface, and the width a of the sensor element. According to this gas sensor, the boundary portion can be surely positioned between the top portion and the bottom portion.

[0009] In the gas sensor of the present invention, the top of the protrusion may be flat. According to this gas sensor, compared with the case where the top has a steep mountain shape, the filled powder in the region around the sensor element can be compressed as a surface. Thereby, the region around the sensor element can be stably filled with the filled powder, and the gap between the main fitting and the sensor element can be more surely filled (sealed).

[0010] In the gas sensor of the present invention, the protrusion may reach the end of the flat surface. According to this gas sensor, the area where the filled powder in the region around the sensor element can be compressed with a high pressing force increases by the amount that the protrusion reaches the end of the flat surface. Thereby, the gap between the main fitting and the sensor element can be more surely filled (sealed).

[0011] In the gas sensor of the present invention, the gas sensor may be an oxygen sensor or a NOx sensor. [Effects of the Invention]

[0012] According to the present invention, a gas sensor can be obtained in which damage to the sensor element during assembly is suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view taken along the longitudinal direction of a gas sensor according to an embodiment of the present invention. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] 10 is a front view showing the positional relationship between the sensor element, the holder, and the sleeve when viewed from a direction perpendicular to the main surface of the sensor element. FIG. [Figure 6] FIG. 4 is a diagram showing the dimensions of a protrusion and a sensor element when viewed from a direction perpendicular to a main surface of the sensor element. [Figure 7] FIG. 10 is a perspective view showing a modified example of the sleeve. [Figure 8] FIG. 10 is a diagram showing a compressed state of a filling powder in a conventional gas sensor. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 holder 151, and FIG. 4 is a perspective view of a sleeve 106. 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.

[0015] 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 axial direction O (the longitudinal direction of the gas sensor 200: the up-down direction in the figure), a ceramic cylindrical sleeve 106 arranged to surround the radial periphery of the sensor element 10, a ceramic (alumina) cylindrical holder 151, a ceramic cylindrical 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 four terminal fittings 21 (only two are shown in FIG. 1) arranged between the sensor element 10 and the separator 166. Furthermore, the 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).

[0016] 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.

[0017] Inside the through hole 154 of the metal shell 138, a holder 151, a filling powder 156 (hereinafter also referred to as a talc ring), and the above-mentioned 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 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 sleeve 106 toward the front end side via the crimping packing 157.

[0018] On the other hand, as shown in FIG. 1, a single-layer protector 142 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.

[0019] 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 four lead wires 146 (only two are shown in FIG. 1) electrically connected to the four terminal metal fittings 21 (only two are shown in FIG. 1) of the sensor element 10 are inserted. The grommet 170 is held inside the outer tube 144 by crimping it from the outside of the outer tube 144 .

[0020] 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 four 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.

[0021] 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 detection portion 10a that detects the oxygen concentration, and the 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. Furthermore, four corners 10e are formed parallel to the axis O of the sensor element 10.

[0022] Two electrode pads 11 are arranged in the width W direction at the rear end of one main surface 10m1 of the sensor element 10, and a sensor output signal from the 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 at the rear end of the other main surface 10m2 provided opposite the main surface, and power is supplied to the heater unit 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 holder 151. The holder 151 is cylindrical and has a rectangular first element hole 151h through which the sensor element 10 is inserted. The holder 151 is formed with a flat surface 151f that contacts the filling powder 156 (upper side of Figure 3) and a protrusion 151p that protrudes from the flat surface 151f toward the filling powder 156 (upper side of Figure 3) and surrounds the first element hole 151h.

[0024] When viewed from a direction D perpendicular to the main surface 10m1 of the sensor element 10, the protrusion 151p has a generally trapezoidal shape tapering toward the filler powder 156 (upper side in FIG. 3). The flat surface 151f is formed on the radially outer side of the first element hole 151h, and the protrusion 151p is formed from the flat surface 151f toward the radially inner side to surround the first element hole 151h.

[0025] The protrusion 151p has a top 151t and a bottom 151b where the protrusion 151p is connected to the flat surface 151f. In this example, a sloped inclined surface 151s is formed between the top 151t and the bottom 151b. However, the shape of the protrusion 151p between the top 151t and the bottom 151b is not limited to this and may be, for example, stepped. In this example, the top portion 151t is flat (surface).

[0026] Furthermore, the peripheral edge 151hm where the first element hole 151h intersects with the protrusion 151p extends parallel to the main surface 10m1 at the top 151t, then extends along the inclined surface 151s toward the tip side in the direction of the axis O, and has a contour that extends along the direction D midway along the inclined surface 151s. Therefore, when the sensor element 10 is inserted into the first element hole 151h, the boundary BR (BR is also the periphery 151hm) where the four corners 10e (only three are shown in FIG. 3) of the sensor element 10 face the protrusion 151p is located midway along the slope 151s, that is, between the top 151t and the bottom 151b. The reason for this will be described later.

[0027] 4 shows a perspective view of the sleeve 106. The sleeve 106 has a similar structure to that of the holder 151, so an outline thereof will be explained. Specifically, the sleeve 106 is cylindrical and has a rectangular second element hole 106h through which the sensor element 10 is inserted. The sleeve 106 is formed with a flat surface 106f that contacts the filling powder 156 (upper side of Figure 4) and a protrusion 106p that protrudes from the flat surface 106f toward the filling powder 156 (upper side of Figure 4) and surrounds the second element hole 106h.

[0028] When viewed from a direction D perpendicular to the main surface 10m1 of the sensor element 10, the protrusion 106p has a generally trapezoidal shape tapering toward the filler powder 156 (upper side in FIG. 4). The flat surface 106f is formed radially outward from the second element hole 106h, and the protrusion 106p is formed radially inward from the flat surface 106f to surround the second element hole 106h.

[0029] The protrusion 106p has a top 106t and a bottom 106b where the protrusion 106p is connected to the flat surface 106f. In this example, a sloped surface 106s is formed between the top 106t and the bottom 106b. The peripheral edge 106hm where the second element hole 106h intersects with the protrusion 106p also has a contour similar to that of the peripheral edge 151hm of the holder 151, and similarly, the boundary BR (BR is also the peripheral edge 106hm) where the four corners 10e (not shown) of the sensor element 10 face the protrusion 106p is located midway along the slope 106s, that is, between the top 106t and the bottom 106b.

[0030] Next, with reference to FIG. 5, the reason why the boundary portion BR is located between the top portions 151t, 106t and the bottom portions 151b, 106b will be described. FIG. 5 is a front view showing the positional relationship between the sensor element 10, the holder 151, and the sleeve 106 when viewed from a direction D perpendicular to the main surface 10m1 of the sensor element 10. As shown in FIG.

[0031] Focusing on the sensor element 10 and the holder 151, the four corners 10e of the sensor element 10 face (are close to) the protrusion 151p at the boundary BR (BR is also the periphery 151hm). The boundary BR is located midway along the slope 151s (between the top 151t and the bottom 151b). Therefore, when the filling powder 156 is compressed through the sleeve 106, the pressing force of the filling powder 156 applied to the sensor element 10 near the boundary portion BR is the highest pressing force F1 on the side closer to the top 151t, and is a pressing force F2 lower than F1 at the boundary portion BR, and becomes even lower from the boundary portion BR toward the bottom portion 151b, becoming the lowest pressing force F3 at the bottom portion 151b and the flat surface 151f. This is because the top 151t is closest to the sleeve 106 and therefore the compressive load of the filler powder 156 is the highest.

[0032] As a result, the pressing force of the filling powder 156 gradually weakens as shown by F1 to F3 along the axis O of the corner 10e, preventing the corner 10e, which has low strength, from being subjected to a high pressing force F in the same way as other areas (for example, the area where the sensor element 10 faces the top 151t), thereby preventing damage to the sensor element 10 during assembly. On one hand, near the top 151t, the distance to the sleeve 106 becomes shorter and the pressing force becomes higher, so that the filling powder 156 can surely fill (seal) the gap between the main fitting 138 and the sensor element 10. Similarly, regarding the sleeve 106 as well, it is possible to suppress breakage during the assembly of the sensor element 10.

[0033] As shown in FIG. 6, in order to surely position the boundary portion BR between the top 151t and the bottom portion 151b, when viewed from the direction D, it is preferable to satisfy the relationship of c < a < b with respect to the width c of the top 151t, the width b of the bottom portion 151b, and the width a of the sensor element 10. Similarly, in order to surely position the boundary portion BR between the top 106t and the bottom portion 106b, when viewed from the direction D, it is preferable to satisfy the relationship of c2 < a < b2 with respect to the width c2 of the top 106t, the width b2 of the bottom portion 106b, and the width a of the sensor element 10.

[0034] As shown in FIGS. 3 and 4, in this example, the tops 151t and 106t are flat (plane). By doing so, compared with the case where the tops 151t and 106t are in a steep mountain shape, the filling powder 156 in the region around the sensor element 10 can be compressed as a plane. Thereby, the periphery of the sensor element 10 can be stably filled with the filling powder 156, and the gap between the main fitting 138 and the sensor element 10 can be more surely filled (sealed).

[0035] Also, as shown in FIG. 4, in this example, the protrusion 106p reaches the end portion 106G of the flat surface 106f. Here, in the example of FIG. 4, the flat surface 106f extends to the outer peripheral surface of the sleeve 106 (excluding the chamfer of the corner of the sleeve 106), and the outer peripheral surface corresponds to the end portion 106G. On the other hand, as shown in the sleeve 116 of the modification example in FIG. 7, for example, the protrusion 116p (the end face 116e) of the sleeve 116 may be located radially inward of the end portion (the outer peripheral surface of the sleeve 116) 116G of the flat surface 116f. However, the area in which the filling powder 156 in the region around the sensor element 10 can be compressed with a high pressing force increases by the amount that the protrusion 106p reaches the end 106G of the flat surface 106f. This allows the gap between the metallic shell 138 and the sensor element 10 to be filled (sealed) more reliably.

[0036] 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 of the protrusion is not limited to the above embodiment. The boundary may be located anywhere between the top and bottom of the protrusion. The protrusion may be formed on at least one of the holder and the sleeve, but it is more preferable that the protrusion be formed on both the holder and the sleeve. Further, types of gas sensors include oxygen sensors, full-range air-fuel ratio sensors, NOx sensors, and the like. [Explanation of symbols]

[0037] 10 Sensor element 10a Detection unit 10e Corner 10m1, 10m2 Main surface of sensor element 106, 116 sleeves 106h Second element hole 106f, 151f flat surface 106p, 151p protrusion 106b, 151b hem 106t, 151t top 106G, 116G Flat surface edge 138 Metal body 151 Holder 151h First element hole 156 Filled powder 200 Gas Sensor O axis D: Direction perpendicular to the main surface of the sensor element BR boundary

Claims

1. a plate-shaped sensor element extending in the axial direction and having a detection portion formed at its tip end for detecting a target gas; a cylindrical metallic shell that surrounds and holds the sensor element in a radial direction; a cylindrical holder that is held in the inner hole of the metallic shell and has a rectangular first element hole through which the sensor element is inserted; a cylindrical sleeve that is held in the inner hole of the metallic shell at a position rearward of the holder and has a rectangular second element hole through which the sensor element is inserted; a filler powder disposed in an inner hole of the metallic shell between the holder and the sleeve, the filler powder filling a gap between the metallic shell and the sensor element; In a gas sensor comprising: a flat surface in contact with the filling powder and a protrusion protruding from the flat surface toward the filling powder and surrounding the first element hole or the second element hole are formed on at least one of the holder and the sleeve; the protrusions are tapered toward the filler powder when viewed from a direction perpendicular to the main surface of the sensor element, A gas sensor characterized in that a boundary portion where a corner portion of the sensor element parallel to the axial direction faces the protrusion is located between the top of the protrusion and a bottom portion where the protrusion connects to the flat surface.

2. When viewed from a direction perpendicular to the main surface of the sensor element, Where c is the width of the top of the protrusion, b is the width of the base where the protrusion connects to the flat surface, and a is the width of the sensor element, 2. The gas sensor according to claim 1, wherein the relationship c<a<b is satisfied.

3. 3. The gas sensor according to claim 1, wherein the top of the protrusion is flat.

4. 3. The gas sensor according to claim 1, wherein the protrusion reaches an end of the flat surface.

5. 3. The gas sensor according to claim 1, wherein the gas sensor is an oxygen sensor or a NOx sensor.

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