Gas sensor

Abstract

[Problem] To provide a gas sensor that achieves an improvement in the strength of a protector therein. [Solution] A gas sensor 10 comprises a sensor element 100 extending in an axial direction O and a cylindrical protector 51 covering a tip portion of the sensor element. The gas sensor 10 further comprises a reinforcement part 55 having: two or more recessed portions 55a recessed inward in the radial direction from the outer surface of the protector and arranged in the circumferential direction; and peak portions 55b disposed between the adjacent recessed portions, having a diameter larger than that of the recessed portions, and extending in the axial direction.

Description

Gas sensor

[0001] The present invention relates to a gas sensor provided with a protector covering a sensor element.

[0002] Conventionally, as a gas sensor used in an internal combustion engine such as an automobile, an oxygen sensor provided with a sensor element extending in the axial direction is known. This oxygen sensor further has a cylindrical protector covering the tip of the sensor element (Patent Document 1). This protector is provided to prevent moisture in the exhaust pipe from directly hitting the sensor element and to protect the sensor element from impacts from the outside or the like.

[0003] Japanese Patent Application Laid-Open No. 2022-64554

[0004] By the way, since the protector is generally in the shape of a straight cylinder, when a strong impact is applied to the protector from the side, the protector may deform and collapse inward and hit the internal sensor element, possibly damaging the sensor element. Also, as a method of fixing the protector to the main fitting, generally, the rear end portion of the protector is externally fitted to the front end portion of the main fitting, and the fitting portion is welded all around. However, if an unreasonable force is applied to the rear end of the protector, such as fitting the inner protector obliquely to the main fitting, the rear end of the protector may deform and the fitting may become impossible.

[0005] The present invention has been made in view of such a situation, and an object thereof is to provide a gas sensor capable of improving the strength of the protector.

[0006] In order to solve the above problems, the gas sensor of the present invention is a gas sensor comprising a sensor element extending in the axial direction and a cylindrical protector covering the tip of the sensor element, wherein the protector has recesses recessed radially inward from the outer surface of the protector and arranged in the circumferential direction, and a reinforcing portion having two or more recesses, and a top portion arranged between adjacent recesses, having a larger diameter than the recesses and extending in the axial direction.

[0007] According to this gas sensor, by providing a reinforcement portion with a recess and a top on the protector, the strength of the protector can be improved and deformation can be suppressed even if a strong impact is applied to the protector from the side. In turn, the sensor element inside the protector can be reliably protected. On the other hand, if only a recess is provided as a reinforcement portion connected in the circumferential direction on the protector (Figure 4 described later), when an impact is received from the side and a force acts to bend it in a V-shape in the axial direction, the reinforcement portion cannot resist this force and deforms by collapsing inward as shown by the dashed line. In contrast, by providing a top portion that extends in the axial direction, the top portion acts as a rib (reinforcement portion) that suppresses the V-shape deformation in the axial direction, thereby suppressing the deformation of the protector.

[0008] The gas sensor of the present invention further comprises a main fitting positioned on the rear end side of the protector, and the protector is fixed to the main fitting in a state where the rear end of the protector is fitted onto the tip of the main fitting to form a fitting portion, and the reinforcing portion may be formed on the tip side of the fitting portion. With this gas sensor, the part of the protector that is on the tip side of the fitting portion and is prone to being crushed by impacts from the side, etc., can be reinforced with the reinforcing portion.

[0009] In the gas sensor of the present invention, the protector comprises a gas inlet and a gas outlet located at the tip of the gas inlet, and the top portion may overlap the gas inlet or gas outlet with at least one of them in the axial direction. With this gas sensor, the gas inlet and gas outlet of the inner protector, which have low strength, can be reinforced at the top portion, and deformation of the inner protector near the gas inlet and gas outlet can be suppressed.

[0010] In the gas sensor of the present invention, the reinforcing portion may be located in a region that overlaps with the sensor element in the axial direction. With this gas sensor, by providing the reinforcing portion in a region that overlaps with the sensor element in the axial direction, deformation of the inner protector can be suppressed in the region that overlaps with the sensor element, thus making it easier to protect the sensor element.

[0011] The gas sensor of the present invention may have multiple tops spaced apart in the circumferential direction. With this gas sensor, the tops can resist impacts from different directions in the circumferential direction, thereby improving the strength of the protector.

[0012] The gas sensor of the present invention further comprises a main fitting positioned on the rear end side of the protector, and the protector is fixed to the main fitting in a state in which the rear end of the protector is fitted onto the tip of the main fitting to form a fitting portion, and the reinforcing portion may be formed on the fitting portion. With this gas sensor, even if excessive force is applied to the rear end of the inner protector, such as by fitting the inner protector diagonally to the main fitting, the reinforcing portion can improve the strength of the rear end of the inner protector and suppress deformation of the inner protector.

[0013] This invention provides a gas sensor with improved protector strength.

[0014] This is a cross-sectional view of a gas sensor according to the first embodiment of the present invention. This is an external view of the inner protector. This is a cross-sectional view along the line A-A in Figure 2. This is a schematic diagram showing the deformation of the protector when the top is not formed on the reinforcing portion. This is an external view of the inner protector in the second embodiment of the present invention. This is a modified example of the reinforcing portion and is a cross-sectional view corresponding to Figure 3.

[0015] A first embodiment of the present invention will be described in detail with reference to Figures 1 to 3. Figure 1 is a cross-sectional view of a gas sensor 10 according to the first embodiment of the present invention, Figure 2 is an external view of the inner protector 51, and Figure 3 is a cross-sectional view along the line A-A in Figure 2.

[0016] In Figure 1, the gas sensor (oxygen sensor) 10 comprises a sensor element 100, a holder (ceramic holder) 15 having a through hole that penetrates in the axial direction O and through which the sensor element 100 is inserted, a cylindrical protector 51 that covers the tip of the sensor element, and a main metal fitting 11 that surrounds the radial circumference of the ceramic holder 15. In this example, the protector has a two-layer (double) structure consisting of a bottomed cylindrical outer protector 61 and an inner protector 51, but the inner protector 51 corresponds to the "protector" in the claims.

[0017] Of the sensor element 100, the tip portion where the detection part is formed protrudes from the ceramic holder 15 and the main body fitting 11. The sensor element 100, which has passed through the through hole in this manner, is fixed inside the main body fitting 11 by compressing the sealing material (talc in this example) 16A and 16B, which are placed in the inner hole 11A of the main body fitting 11, in the front-to-back direction via a sleeve 17 and ring washer 23 made of insulating material, at the rear end surface side (upper side in the figure) of the ceramic holder 15, thereby maintaining airtightness in the front-to-back direction.

[0018] The rear end portion of the sensor element 100 protrudes behind the sleeve 17 and the main body fitting 11. Terminal fittings 19 provided at the ends of each lead wire 20, which are pulled out to the outside through the grommet 21, are pressed against each electrode pad portion 100B formed at the rear end portion, thereby electrically connecting them. Furthermore, the rear end portion of the sensor element 100, including the electrode pad portion 100B, is covered by the outer cylinder 14. A further detailed explanation follows.

[0019] The sensor element 100 extends in the direction of axis O and has a strip-like (plate-like) shape with a detection section at the tip end (lower side in the figure) facing the object to be measured, which detects a specific gas component in the gas to be detected. The cross-section of the sensor element 100 is a rectangle of a certain size from front to back and is formed as an elongated shape mainly of ceramic (solid electrolyte, etc.). Here, the tip end of the sensor element 100 is provided with a gas to be measured introduction section 100A, which is made of, for example, a porous layer and communicates with the outside, and the gas to be measured is introduced into the detection section inside the sensor element 100 through the gas to be measured introduction section 100A. In addition, an electrode pad section 100B is exposed near the rear end of the sensor element 100. Furthermore, the tip end of the sensor element 100 may be covered with a porous protective layer made of alumina or spinel, etc.

[0020] The main fitting 11 is cylindrical with concentrically different diameters at its front and rear, with a smaller diameter at the front end and a cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 11B for fitting and fixing the protector 50, which will be described later, to the outside. On the outer surface of the rear (upper part in the figure) there is a screw 11C, which has a larger diameter, for fixing to the engine's exhaust pipe. Behind that, there is a polygonal portion 11D for screwing in the sensor 1 with this screw 11C.

[0021] Furthermore, a second cylindrical section 11E is attached to the rear of the polygonal section 11D, onto which a protective cylinder (outer cylinder) 14 covering the rear of the gas sensor 10 is fitted and welded. Behind this second cylindrical section 11E is a crimping cylindrical section 11F with a smaller outer diameter and thinner wall. In Figure 1, this crimping cylindrical section 11F is bent inward for use after crimping. A gasket (not shown) for sealing during screwing is attached to the lower surface of the polygonal section 11D. On the other hand, the main fitting 11 has an inner hole 11A that penetrates in the direction of the axis O. The inner circumferential surface of the inner hole 11A is tapered, narrowing radially inward from the rear end to the front end, and the front-facing surface of the ceramic holder 15 is locked into this tapered section.

[0022] Inside the main fitting 11 is a ceramic holder 15 made of insulating ceramic (e.g., alumina) and formed in a roughly short cylindrical shape. As described above, the tip-facing surface of the ceramic holder 15 is locked into the tapered portion of the inner hole 11A, and the ceramic holder 15 is pressed from the rear end by sealing materials 16A and 16B, thereby positioning and fitting the ceramic holder 15 within the main fitting 11. On the other hand, the through hole of the ceramic holder 15 is provided in the center of the ceramic holder 15 and is a rectangular opening with dimensions approximately the same as the cross-section of the sensor element 100 so that the sensor element 100 passes through with almost no gap. The sensor element 100 is passed through the through hole of the ceramic holder 15, and the tip of the sensor element 100 protrudes beyond the ceramic holder 15 and the main fitting 11.

[0023] On the other hand, in this embodiment, the tip portion of the sensor element 100 is covered by bottomed cylindrical protectors (protective covers) 51 and 61, which have a two-layer (double) structure as described above. The inner protector 51 faces the sensor element 100, and the outer protector 61 is fitted onto the inner protector 51. The rear ends of the inner protector 51 and the outer protector 61 overlap and become one, and the rear end 51e of the inner protector 51 is fitted onto the cylindrical portion 11B of the main fitting 11 to form a fitting portion F. This fitting portion F is then welded, and the protectors 51 and 61 are fixed to the main fitting 11.

[0024] The inner protector 51 has one or more gas inlet holes 56 (e.g., eight in this example, spaced equally in the circumferential direction) on its rear end side wall. The inner protector 51 also has one or more gas outlet holes 53 (e.g., four in this example, spaced equally in the circumferential direction) on its side wall, closer to the tip than the gas inlet holes 56. On the other hand, the outer protector 61 has, for example, eight outer gas inlet holes 67 spaced equally in the circumferential direction on its side wall, and one outer gas outlet hole 69 is provided at the center of the bottom of the tip of the outer protector 61.

[0025] The outer gas inlet 67 is located closer to the front than the gas inlet 56 and closer to the rear than the gas outlet 53. Furthermore, the inner protector 51 is provided with a reinforcing portion 55 that tapers radially inward between the gas inlet 56 and the gas outlet 53 in the axial direction O. Details of the reinforcing portion 55 will be described later.

[0026] Then, as shown in Figure 1, the gas G to be measured, introduced into the inner protector 51 through the gas inlet hole 56, comes into contact with the gas inlet part 100A located at the tip of the sensor element 100 and is detected, and then discharged to the outside (outer protector 61) through the gas discharge hole 53.

[0027] Furthermore, as shown in Figure 1, each electrode pad portion 100B formed near the rear end of the sensor element 100 is electrically connected to each terminal fitting 19 provided at the tip of each lead wire 20 that is pulled out to the outside through a grommet 21, by the spring action of the terminal fittings 19. In this gas sensor 10, each terminal fitting 19, including the contact portion, is provided in a facing arrangement within each housing portion 18A located within an insulating separator 18 arranged inside the outer cylinder 14.

[0028] Furthermore, the separator 18's movement in the radial direction and toward the tip is restricted via a retaining member 25 that is crimped and fixed inside the outer cylinder 14. The tip of the outer cylinder 14 is then fitted onto the second cylindrical portion 11E near the rear end of the main fitting 11 and welded, thereby providing an airtight cover to the rear of the gas sensor 10. The lead wire 20 is pulled out to the outside through a grommet (for example, rubber) 21 located inside the rear end of the outer cylinder 14, and the airtightness of this portion is maintained by crimping the rear end of the outer cylinder 14 to reduce its diameter and compress the grommet 21.

[0029] Next, the reinforcing portion 55 of the inner protector 51 will be described with reference to Figures 2 and 3. Figure 2 is an external view of the inner protector 51, and Figure 3 is a cross-sectional view along the line A-A in Figure 2. As shown in Figure 2, the reinforcing portion 55 has two or more recesses 55a that are recessed radially inward from the outer surface 51L of the inner protector 51 and arranged in the circumferential direction, and a top portion 55b positioned between adjacent recesses 55a. Also, as shown in Figure 3, the top portion 55b is larger in diameter than the recesses 55a and extends in the direction of the axis O. In this example, both the top portion 55b and the recesses 55a of the reinforcing portion 55 are smaller in diameter than the other outer surfaces of the inner protector 51, but this is not limited to this, and for example, the top portion 55b may be larger in diameter than the other outer surfaces of the inner protector 51.

[0030] In this way, by providing the protector 51 with a reinforcing portion 55 having a recess 55a and a top portion 55b, the strength of the protector 51 can be improved and deformation can be suppressed even if a strong impact is applied to the protector 51 from the side. Consequently, the sensor element 100 inside the protector 51 can be reliably protected. On the other hand, as shown in Figure 4, for example, if the protector is provided only with a recess 550 that is connected in the circumferential direction, when it receives an impact IM from the side and a force acts to bend it in a V-shape in the direction of the axis O, it cannot resist this force and the recess 550 deforms so as to collapse inward as shown by the dashed line.

[0031] In response to this, by providing a top portion 55b extending in the direction of axis O, the top portion 55b acts as a rib (reinforcement part) that suppresses the L-shaped deformation in the direction of axis O, thereby suppressing deformation of the protector 51. It should be noted that the impact applied to the protector is not limited to external impacts, but can also include fatigue failure due to vibrations during use.

[0032] In this example, the inner protector 51 is provided with a reinforcing portion 55, compared to the outer protector 61. Even with the reinforcing portion 55 on the inner protector 51, when the outer protector 61 is subjected to impact and deforms inward, pressing against the inner protector 51, the deformation of the inner protector 51 is suppressed, thereby protecting the sensor element 100. Of course, the reinforcing portion may also be provided on the outer protector 61.

[0033] Furthermore, in this example, the reinforcing portion 55 is formed on the tip side of the fitting portion F. This allows the part of the protector 51 that is on the tip side of the fitting portion F and is prone to being crushed by impacts from the side, etc., to be reinforced by the reinforcing portion.

[0034] In this example, the reinforcing portion 55 is formed by crimping the outer surface 51L of the inner protector 51 to reduce its diameter using an eight-way crimping method. As shown in Figure 3, the eight-way crimping method consists of eight identical dies 500 (only two are shown in Figure 3) that form roughly fan-shaped blocks when viewed from above, and their holders, etc. These eight dies 500 are arranged concentrically adjacent to each other around the outer surface 51L of the inner protector 51, and each die 500 is pressed radially inward simultaneously. This forms eight arc-shaped recesses 55a when viewed from the direction of axis O. Note that, as shown in Figure 2, when viewed radially, each recess 55a is rectangular in shape.

[0035] At this time, because adjacent dies 500 are crimped (pressed) with a gap in the circumferential direction, eight top portions 55b are formed between adjacent recesses 55a, which remain the same diameter as the outer surface 51L without being reduced in diameter. Therefore, as shown in Figure 3, the radius D1 on the outer surface side of the top portion 55b is larger than the radius D2 on the outer surface side of the recess 55a, and D1 is approximately the same as the radius of the outer surface 51L. Note that Figure 3 shows the outer edge of the reinforcing portion 55 as viewed from the direction of axis O, and the symbol C in the figure indicates the axis of the inner protector 51.

[0036] Furthermore, as shown in Figure 2, in the inner protector 51, the top portion 55b1 overlaps with at least one of the gas inlet hole 56 or the gas outlet hole 53 in the direction of axis O. This allows the gas inlet hole 56 and the gas outlet hole 53, which have lower strength, to be reinforced at the top portion 55b1 (55b), thereby suppressing deformation of the inner protector 51 near the gas inlet hole 56 and the gas outlet hole 53.

[0037] In this example, the gas inlet holes 56 and each of the top portions 55b are provided at eight equally spaced locations in the circumferential direction. Therefore, all of the gas inlet holes 56 overlap with one of the top portions 55b in the direction of axis O. On the other hand, the gas outlet holes 53 are provided at four equally spaced locations in the circumferential direction. Therefore, all four of the gas outlet holes 53 overlap with one of the top portions 55b in the direction of axis O.

[0038] Furthermore, as shown in Figure 1, the reinforcing portion 55 is located in a region that overlaps with the sensor element 100 in the direction of axis O. By providing the reinforcing portion 55 in a region that overlaps with the sensor element 100 in the direction of axis O, deformation of the inner protector 51 can be suppressed in the region that overlaps with the sensor element 100, making it easier to protect the sensor element 100. In other words, the reinforcing portion 55 has increased strength in a rib-like manner, so the protective effect on the sensor element 100 is improved in this portion. As shown in Figure 2, the protector 51 has a large-diameter outer surface (outermost surface) 51L and a small-diameter surface 51S that is smaller in diameter towards the tip from the outer surface (outermost surface) 51L.

[0039] Next, a second embodiment of the present invention will be described with reference to Figure 5. Figure 5 is an external view of the inner protector 151 in the second embodiment of the present invention. Note that the gas sensor according to the second embodiment is the same as the first embodiment except for the configuration of the inner protector 151, so the same reference numerals are used for components other than the inner protector 151, or their illustration and description are omitted.

[0040] As shown in Figure 5, in the second embodiment, a reinforcing portion 155 is formed in the portion corresponding to the fitting portion F at the rear end of the inner protector 151. This reinforcing portion 155 is also formed by eight-sided crimping, and eight recesses 155a and eight top portions 155b are formed, similar to those in the first embodiment.

[0041] Here, a reinforcing portion 155 is formed in advance at the rear end of the inner protector 151, and then the rear end of the inner protector 151 is fitted to the tip of the main fitting 11. As a result, even if excessive force is applied to the rear end of the inner protector 151, such as by fitting the inner protector 151 to the main fitting 11 at an angle, the reinforcing portion 155 improves the strength of the rear end of the inner protector 151 and suppresses deformation of the inner protector 151. Furthermore, after fitting, the fitting portion F is welded all around at the position of the reinforcing portion 155 to form a welded portion W, thereby fixing the inner protector 51 to the main fitting 11.

[0042] The present invention is not limited to the above-described embodiments, and it goes without saying that it extends to various modifications and equivalents included in the spirit and scope of the present invention. As the sensor element, not only a plate-like element but also a cylindrical element may be used. The protector is not limited to a double protector, and may have two or more layers, or may have a single layer.

[0043] The shape of the top is not limited to the above, and may be in any form other than a linearly extending form. For example, as the shape of the top, a curved form or a tapered spreading form is also included. The shape of the reinforcing part is also not limited to the above. For example, as shown in FIG. 6, when viewed from the direction of the axis O, the reinforcing part 255 may show a polygon (a regular hexagon in FIG. 6), and the vertices of this polygon may form the top 255b. On the other hand, the concave part 255a corresponds to each side of this polygon (excluding the top 255b which is a vertex). In this case, the radius D3 of the top 255b is larger than the radius D3 at any position of the concave part 255a. Also, in FIG. 6, the top 255b is a "point" and extends in the direction of the axis O to form an "edge (line segment)".

[0044] The reinforcing part 255 is formed by a caulking device composed of six dice 600 of the same shape that form trapezoidal blocks when viewed from above (only two are shown in FIG. 6), and caulking (pressing) the outer surface 51L of the inner protector 51 to reduce the diameter. Then, these six dice 500 are arranged concentrically adjacent to the periphery of the outer surface 51L of the inner protector 51, and each die 600 is simultaneously pressed radially inward. As a result, six linearly-shaped concave parts 255a are formed when viewed from the direction of the axis O.

[0045] At this time, in order to caulk (press) the adjacent dice 600 in contact with each other in the circumferential direction, the diameter between the adjacent concave parts 255a is also reduced to be smaller than the outer surface 51L (D3 < D1 in FIG. 3), and six tops 255b forming hexagonal vertices are formed. Therefore, as shown in FIG. 6, the radius D3 on the outer surface side of the top 255b is larger than any radius D4 on the outer surface side of the concave part 255a, and D3 is smaller than the radius of the outer surface 51L (D1). As already described, the top 255b may have a diameter larger than the outer surface 51L of the inner protector 51 (protruding outside the outer surface 51L).

[0046] 10 Gas sensor 11 Main frame 51, 151 Protector (inner protector) 51L Outermost surface of protector 53 Gas discharge hole 55, 155, 255 Reinforcement part 55a, 155a, 255a Recess 55b, 155b, 255b Top 56 Gas introduction hole 100 Sensor element O Axis F Fitting part

Claims

1. A gas sensor comprising: a sensor element extending in the axial direction; and a cylindrical protector covering the tip of the sensor element, wherein the gas sensor further comprises a reinforcing portion having two or more recesses that are recessed radially inward from the outer surface of the protector and arranged in the circumferential direction, and a top portion that is disposed between adjacent recesses, has a larger diameter than the recesses and extends in the axial direction.

2. The gas sensor according to claim 1, further comprising a main body fitting disposed on the rear end side of the protector, wherein the protector is fixed to the main body fitting in a state in which the rear end of the protector is fitted onto the tip of the main body fitting to form a fitting portion, and the reinforcing portion is formed on the tip side of the fitting portion.

3. The gas sensor according to claim 2, wherein the protector comprises a gas inlet and a gas outlet located at the tip of the gas inlet, and the top portion of the protector overlaps with at least one of the gas inlet or the gas outlet in the axial direction.

4. The gas sensor according to claim 1 or 2, characterized in that the reinforcing portion is located in a region that overlaps with the sensor element in the axial direction.

5. The gas sensor according to claim 1 or 2, characterized in that it has a plurality of top portions spaced apart in the circumferential direction.

6. The gas sensor according to claim 1, further comprising a main body fitting disposed on the rear end side of the protector, wherein the protector is fixed to the main body fitting in a state in which the rear end of the protector is fitted onto the tip of the main body fitting to form a fitting portion, and the reinforcing portion is formed in the fitting portion.

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