Sensor mounting structure
The sensor mounting structure addresses the issue of thermal cycling-induced cracking and peeling by using a screw engagement and flange sandwiching mechanism, ensuring long-term protector retention and material flexibility.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- NITERRA CO LTD
- Filing Date
- 2023-01-10
- Publication Date
- 2026-07-29
AI Technical Summary
The existing gas sensor mounting structures are prone to cracking and peeling due to thermal cycling from high-temperature exhaust gases, leading to displacement or detachment of the protector, necessitating a reliable mounting solution.
A sensor mounting structure that uses a male screw on the outer surface of the main fitting engaging with a female screw on the gas pipe's mounting boss, with a flange portion of the protector sandwiched between the shelf and the main fitting, eliminating the need for welding and preventing cracks and peeling.
The structure reliably maintains the gas sensor protector over a long period, allowing the use of less weldable materials like stainless steel and preventing detachment during thermal cycles.
Smart Images
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Figure 0007897159000002
Abstract
Description
Technical Field
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[0001] The present invention relates to a mounting structure of a sensor in which a gas sensor is attached to a gas pipe.
Background Art
[0002] Gas sensors for detecting the concentration of specific gas components such as oxygen and NOx in exhaust gas or intake air of automobiles and the like are known (Patent Document 1). A sensor element for detecting gas is provided at the tip of the gas sensor, and the sensor element is held by a main body fitting. Further, the sensor element is covered with a cylindrical protector, and the rear end of the protector is welded to the main body fitting. This gas sensor is screwed to the exhaust pipe so as to penetrate the exhaust pipe, and the measured gas such as exhaust gas flowing through the exhaust pipe contacts the sensor element at the tip of the gas sensor, thereby detecting the gas.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] By the way, high-temperature exhaust gas flows intermittently through the exhaust pipe, and the gas sensor is repeatedly subjected to a thermal cycle from a high temperature (for example, 650 ° C or higher) to room temperature. Then, the welded portion of the protector is also subjected to a thermal cycle and expands and contracts, and cracks or peeling may occur. As a result, there is a risk that the protector may be displaced from its initial position or fall off.
[0005] Therefore, an object of the present invention is to provide a mounting structure of a sensor that can reliably hold the protector of the gas sensor over a long period of time.
Means for Solving the Problems
[0006] To solve the above problems, the sensor mounting structure of the present invention comprises a gas sensor comprising: a sensor element extending in the axial direction and having a detection portion at its tip; a main fitting surrounding the sensor element while allowing the detection portion of the sensor element to protrude; a cylindrical protector covering the detection portion; and a gas pipe through which the gas to be measured flows, to which the gas sensor is attached via the main fitting, wherein the outer surface of the main fitting is provided with a male screw; the gas pipe is provided with a cylindrical mounting boss that penetrates the pipe wall and has a female screw on its inner surface that engages with the male screw; and the rear end of the protector has a flange portion extending radially outward. as one The mounting boss is provided with an annular shelf portion extending radially inward, and the flange portion is sandwiched between the outer surface of the shelf portion and the tip-facing surface of the main fitting.
[0007] This sensor mounting structure holds the gas sensor protector by sandwiching each flange portion between the outer surface of the shelf and the tip-facing surface of the main fitting. This eliminates the need to weld the protector to the main fitting, preventing cracks and peeling that can occur due to thermal cycling at the welded area. As a result, the gas sensor protector can be reliably maintained over a long period of time. Furthermore, it is not necessary to select a material with excellent weldability for the protector; for example, inexpensive stainless steel can be used as the protector.
[0008] In the sensor mounting structure of the present invention, the flange portion may be compressed in the thickness direction by the outer surface of the shelf portion and the tip-facing surface of the main fitting. With this sensor mounting structure, the flange portion is fixed between the outer surface and the tip-facing surface without wobbling.
[0009] In the sensor mounting structure of the present invention, the maximum outer diameter of the flange portion may be smaller than the minimum inner diameter of the mounting boss excluding the shelf portion. This allows the flange portion to be inserted smoothly into the mounting boss from above without interfering with the female threads.
[0010] In the sensor mounting structure of the present invention, the protector comprises an inner protector and an outer protector disposed spaced apart outside the inner protector, and both the inner protector and the outer protector may have the flange portion. This sensor mounting structure allows the inner and outer protectors to be securely held to the gas sensor via their respective flange portions. [Effects of the Invention]
[0011] According to this invention, the protector of the gas sensor can be reliably maintained over a long period of time. [Brief explanation of the drawing]
[0012] [Figure 1] This is a cross-sectional view of a sensor mounting structure according to an embodiment of the present invention. [Figure 2] This is a partial cross-sectional view of a modified example of a sensor mounting structure according to an embodiment of the present invention. [Modes for carrying out the invention]
[0013] Embodiments of the present invention will be described below. Figure 1 is a cross-sectional view of a sensor mounting structure 200 according to an embodiment of the present invention. Figure 1 shows a cross-sectional view of the sensor mounting structure 200 along the axis O direction of the gas sensor 1A (along the axial direction of the gas pipe 100). In Figure 1, the sensor mounting structure 200 comprises a gas sensor 1A, a protector 60A, and a gas pipe (engine exhaust pipe) 100 through which the gas to be measured flows and to which the gas sensor 1A is attached. In this example, the protector 60A is pre-fixed (welded, etc.) to the gas sensor 1A side (main fitting 11). However, it is also possible to pre-fix the protector 60A to the gas pipe 100 side, and then later attach the gas sensor 1A (main fitting 11) to the protector 60A on the gas pipe 100 side.
[0014] The gas sensor (all-range air-fuel ratio gas sensor) 1A comprises a sensor element 21, a holder (ceramic holder) 30A having a through hole 32 that penetrates in the axial direction O and through which the sensor element 21 is inserted, a main fitting 11 that surrounds the radial periphery of the holder 30A, and a protector 60A. Furthermore, the tip portion of the sensor element 21, where the detection section 22 is formed, protrudes beyond the tip of the holder 30A. The sensor element 21, which has passed through the through hole 32 in this manner, is fixed inside the main fitting 11 while maintaining airtightness in the front-to-back direction by compressing the sealing member 41, which is located on the rear end face side (upper side in the figure), via an insulating (ceramic) sleeve 43 and a ring washer 45.
[0015] Furthermore, the rear end portion of the sensor element 21, including the rear end 29, protrudes rearward from the sleeve 43 and the main body fitting 11. Terminal fittings 75 provided at the ends of each lead wire 71, which are pulled out to the outside through a rubber grommet 85, are pressed against each electrode terminal 24 formed in the rear end portion, thereby electrically connecting them. In addition, the rear end portion of the sensor element 21, including these electrode terminals 24, is covered by the outer cylinder 81. Further details will be explained below.
[0016] The sensor element 21 extends in the direction of the axis O and has a strip shape (plate shape) with a detection unit 22 at the tip side (lower side in the figure) facing the measurement target, which consists of a detection electrode or the like (not shown) and detects a specific gas component in the detected gas. The cross-section of the sensor element 21 forms a rectangle (square) of a constant size successively, and is formed as an elongated one mainly made of ceramic (such as solid electrolyte). The sensor element 21 itself is the same as the conventionally known one, and a pair of detection electrodes forming the detection unit 22 are arranged at a position closer to the tip of the solid electrolyte (member), and following this, an electrode terminal 24 for connecting the lead wire 71 for taking out the detection output is formed and exposed at a position closer to the rear end.
[0017] Also, in this example, inside the sensor element 21, a heater (not shown) is provided inside a position closer to the tip of the ceramic material formed in a laminated state on the solid electrolyte (member), and at a position closer to the rear end, an electrode terminal 24 for connecting the lead wire 71 for applying voltage to this heater is formed and exposed. Although not shown in the figure, these electrode terminals 24 are formed in a vertically long rectangle, and for example, at a position closer to the rear end of the sensor element 21, three or two electrode terminals are arranged side by side on the wide surface (both surfaces) of the strip. Note that the detection unit 22 of the sensor element 21 is covered with a porous protective layer 23 made of alumina or spinel or the like.
[0018] The main body fitting 11 has a through-hole penetrating in the direction of the axis O and has a concentric and different-diameter cylindrical shape successively. Also, the main body fitting 11 has an annular part (hereinafter also referred to as a cylindrical part) 18 with a small diameter and a cylindrical shape at the tip side, and on the outer peripheral surface at its rear (upper side in the figure), a male screw 13 for fixing to the exhaust pipe 100 with a larger diameter than that is provided. And behind this, a polygonal part 14 for screwing the sensor 1 with this male screw 13 is provided. Also, behind this polygonal portion 14, a cylindrical portion 15 is continuously provided, onto which a protective cylinder (outer cylinder) 81 that covers the rear of the gas sensor 1A is externally fitted and welded. Behind the cylindrical portion 15, there is a caulking cylindrical portion 16 with a smaller outer diameter and thinner wall. In FIG. 1, this caulking cylindrical portion 16 is bent inward for caulking. A gasket 19 for sealing during screwing is attached to the lower surface of the polygonal portion 14. Furthermore, on the inner peripheral surface near the annular portion 18 of the main fitting 11, there is a tapered stepped portion 17 that tapers inward in the radial direction from the rear end side toward the front end side.
[0019] Inside the main fitting 11 (inside the through-hole), a holder 30A made of insulating ceramic (e.g., alumina) and formed in a generally short cylindrical shape is arranged. The holder 30A has a tip-facing surface 30f formed in a tapered shape that tapers toward the tip. While the portion near the outer periphery of the tip-facing surface 30f is locked to the stepped portion 17, the holder 30A is positioned and clearance-fitted inside the main fitting 11 by being pressed by the seal member 41 from the rear end side. On the other hand, the through-hole 32 is provided at the center of the holder 30A and is a rectangular opening with substantially the same dimensions as the cross-section of the sensor element 21 so that the sensor element 21 passes through it with substantially no gap.
[0020] The sensor element 21 is passed through the through-hole 32 of the holder 30A, and the tip of the sensor element 21 protrudes beyond the tips of the holder 30A and the main fitting 11. On the other hand, the tip portion of the sensor element 21 is covered with a protector 60A having a cylindrical shape and capable of introducing or discharging the measured gas. In this embodiment, the protector 60A is composed of a double protector in which a bottomed cylindrical inner protector 51 having ventilation holes 56 and discharge holes 53 and a bottomed cylindrical outer protector 61 having ventilation holes 67 and discharge holes 69 are arranged separately.
[0021] The rear ends of the inner protector 51 and the outer protector 61 are fitted onto the outer surface of the annular portion 18. Furthermore, flange portions 51f and 61f extending radially outward are provided at the rear edges of the inner protector 51 and the outer protector 61, respectively. Furthermore, the flange portion 51f is located further back than the flange portion 61f, and both extend so that the flange portion 51f overlaps the rear end of the flange portion 61f.
[0022] On the other hand, as shown in Figure 1, each electrode terminal 24 formed near the rear end of the sensor element 21 is electrically connected to each terminal fitting 75 provided at the end of each lead wire 71 that is pulled out to the outside through a grommet 85, by the spring action of the fitting. In this example of gas sensor 1A, each terminal fitting 75, including the contact portion, is provided in a facing arrangement within each housing portion provided within an insulating separator 91 located inside the outer cylinder 81. The movement of the separator 91 in the radial direction and toward the tip is restricted via a retaining member 82 that is crimped and fixed inside the outer cylinder 81. The tip of the outer cylinder 81 is 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 1A. The lead wire 71 is routed to the outside through a grommet 85 located inside the rear end of the outer cylinder 81. By crimping the small-diameter cylindrical portion 83 to reduce its diameter and compressing the grommet 85, airtightness in this area is maintained.
[0023] Incidentally, a stepped portion 81d is formed slightly towards the rear end of the outer cylinder 81, with a larger diameter at the tip, and the inner surface of this stepped portion 81d supports the rear end of the separator 91 by pushing it forward. On the other hand, the flange 93 formed on the outer circumference of the separator 91 is supported on a holding member 82 fixed to the inside of the outer cylinder 81, and the separator 91 is held in the direction of axis O by the stepped portion 81d and the holding member 82.
[0024] On the other hand, the exhaust pipe 100 has a cylindrical mounting boss 103 on its inner surface through which the gas to be measured flows, and which penetrates the pipe wall 101 and has a female thread 103M on its inner surface that engages with the male thread 13. The mounting boss 103 is welded to the pipe wall 101. Furthermore, an annular shelf portion 105 extending radially inward is provided on the exhaust pipe 100 side (lower side in Figure 1) of the mounting boss 103.
[0025] Each flange portion 51f and 61f is sandwiched between the outer surface 105e of the shelf portion 105 (the surface facing away from the exhaust pipe 100 (the upper surface in Figure 1)) and the tip-facing surface 11s of the main fitting 11. As a result, the protector 60A of the gas sensor 1A is held in place by sandwiching its respective flange portions 51f and 61f between the outer surface 105e of the shelf portion 105 and the tip-facing surface 11s of the main fitting 11. Therefore, there is no need to weld the protector 60A to the main fitting 11, and it is possible to prevent cracks or peeling that may occur due to thermal cycles at the welded area. As a result, the protector 60A of the gas sensor 1A can be reliably held in place over a long period of time. Furthermore, it is not necessary to select a material with excellent weldability for Protector 60A; for example, inexpensive stainless steel can be used for Protector 60A.
[0026] The flange portions 51f and 61f may be compressed in the thickness direction by the outer surface 105e of the shelf portion 105 and the tip-facing surface 11s of the main fitting 11. In this way, the flange portions 51f and 61f are fixed between the outer surface 105e and the tip-facing surface 11s without wobbling.
[0027] The maximum outer diameter of the flange portions 51f and 61f may be smaller than the minimum inner diameter of the mounting boss 103 excluding the shelf portion 105 (i.e., the maximum diameter of the threads of the female screw 103M). This allows the flange portions 51f and 61f to be inserted into the mounting boss 103 from above without interfering with the female thread 103M, enabling smooth insertion. Note that the maximum outer diameter of flange portions 51f and 61f refers to the outer diameter of the flange portion 51f or 61f that protrudes radially.
[0028] The present invention is not limited to the embodiments described above, and it goes without saying that it extends to various modifications and equivalents that fall within the spirit and scope of the present invention. For protection, a single layer of protection is also acceptable, not just a double layer.
[0029] In the case of a double protector, as shown in Figure 2, the rear ends of the inner protector 51 and the outer protector 61 may be welded together to provide a welded section W that reaches the main fitting 11. While providing a welded joint W increases the amount of welding work, it prevents the protector 60A from falling off the gas sensor 1A when screwing the gas sensor 1A to the mounting boss 103. Furthermore, even if a thermal cycle occurs during the use of the gas sensor, causing cracks or peeling in the welded joint W, the protector 60A itself remains sandwiched between the outer surface 105e and the tip-facing surface 11s via the flange portions 51f and 61f.
[0030] In addition to NOx sensors, other gas sensors include oxygen sensors and all-range gas sensors. Sensor elements are not limited to plate shapes; cylindrical elements can also be used. The gas pipe is not limited to exhaust pipes, nor is the shape of the mounting boss limited. [Explanation of Symbols]
[0031] 1A Gas Sensor 11 Main fittings 11s Main fitting tip facing surface 13 Male screw 21 Sensor element 22 Detection unit 60A Protector 51 Inner protector 61 Outer protector 51f, 61f flange section 100 Gas pipe (exhaust pipe) 101 Pipe wall 103 Mounting boss 103M Female Thread 105 Shelf 105e Shelf section exterior 200 Sensor mounting structure O axis
Claims
1. A gas sensor comprising a sensor element extending in the axial direction and having a detection portion at its tip, and a main body fitting surrounding the sensor element while allowing the detection portion of the sensor element to protrude, A cylindrical protector covering the detection unit, The gas sensor is attached via the main fitting, and a gas pipe through which the gas to be measured flows, A sensor mounting structure comprising: The outer surface of the main fitting is provided with a male thread, and the gas pipe is provided with a cylindrical mounting boss that penetrates the pipe wall and has a female thread on its inner surface that engages with the male thread. The rear end of the protector is integrally provided with a flange portion extending radially outward, and the mounting boss is provided with an annular shelf portion extending radially inward. The sensor mounting structure is characterized in that the flange portion is sandwiched between the outer surface of the shelf portion and the tip-facing surface of the main fitting.
2. The mounting structure for a sensor according to claim 1, characterized in that the flange portion is compressed in the thickness direction by the outer surface of the shelf portion and the tip-facing surface of the main fitting.
3. The sensor mounting structure according to claim 1, characterized in that the maximum outer diameter of the flange portion is smaller than the minimum inner diameter of the mounting boss excluding the shelf portion.
4. The sensor mounting structure according to claim 1, wherein the protector comprises an inner protector and an outer protector disposed spaced apart outside the inner protector, and both the inner protector and the outer protector have the flange portion.