Gas sensor and gas sensor mounting structure

Abstract

The present application provides a kind of gas sensor capable of improving moisture resistance and responsiveness simultaneously using a layer of protection.The gas sensor (1) is provided with a detection part formed at the front end side to detect the detected gas (G), a main metal shell (11) and a one-layer cylindrical protection member (51) fixed to the periphery of the front end side of the main metal shell, the protection member has a gas inlet hole (56) and a gas outlet hole (53) arranged at a position closer to the front end side than the gas inlet hole, the main metal shell has a fixed part (13) whose outer surface is directly or indirectly fixed to the pipe (100) for the flow of the detected gas, and a tool engaging part (14) which is a tool engaging part with a large diameter located at the rear end side of the fixed part for mounting the gas sensor, the distance (L1) between the gas inlet hole and the gas outlet hole in the axial direction (O) is greater than the distance (L2) between the tool engaging part and the gas inlet hole in the axial direction, and the front end (21a) of the sensor element is located at a position closer to the front end side than the gas inlet hole.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas sensor provided with a one-layer protector and a gas sensor mounting structure. BACKGROUND

[0002] Conventionally, a gas sensor is known which holds a sensor element inside a cylindrical main body metal case and protects the front end side of the sensor element exposed to exhaust gas with a one-layer or two-layer protector. A gas introduction hole is provided on the protector, but it is required to have moisture resistance, that is, to suppress condensed water mixed in the exhaust gas from reaching the sensor element, and it is also required to have responsiveness, that is, to rapidly introduce the exhaust gas to the detection portion of the sensor element.

[0003] Therefore, a technology has been developed which improves responsiveness by providing the protector as a one-layer (Patent Literature 1). In this technology, the sensor element is held inside a cylindrical insulator, and a porous filter is disposed at a gas introduction port provided at the front end of the insulator. By this, condensed water flying to the gas introduction port is captured by the porous filter, and the moisture of the sensor element is suppressed.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2017-67734 Figure 1 ) SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, in the case of the above technology, the sensor element is housed inside the insulator, and the flow of the exhaust gas to the sensor element is performed via the porous filter, so even if the protector is provided as a one-layer, there is a tendency for the responsiveness to decrease.

[0009] The present application was completed in view of the above circumstances, and aims to provide a gas sensor and a gas sensor mounting structure which can simultaneously improve moisture resistance and responsiveness using a one-layer protector.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] A gas sensor according to the present application is characterized by comprising: a sensor element extending in an axial direction, a detection portion that detects a detected gas being formed at a front end side; a main body metal case that is cylindrical, that surrounds a periphery of the sensor element in a radial direction, and that holds the sensor element; and a protector that is a single cylindrical layer, that is fixed to a periphery of the front end side of the main body metal case, and that surrounds the front end side of the sensor element, the protector having a gas introduction hole and a gas discharge hole that is disposed at a position further toward the front end side than the gas introduction hole, the main body metal case having a fixed portion whose outer surface is directly or indirectly fixed to a pipe through which the detected gas flows, and a tool engagement portion that is a tool engagement portion having a diameter larger than a diameter of the fixed portion, that is located at a rear end side of the fixed portion, and that is used for mounting the gas sensor, a distance L1 in the axial direction between the gas introduction hole and the gas discharge hole being larger than a distance L2 in the axial direction between the tool engagement portion and the gas introduction hole, and a front end of the sensor element being located at a position further toward the front end side than the gas introduction hole.

[0012] According to the gas sensor, in a case where the front end side of the gas sensor is made to face an inside of the pipe, the fixed portion is fixed to the pipe, and a front end of the tool engagement portion is made to contact an outer surface of the pipe to be mounted, it is easy to make a portion of the protector where L1 is relatively long (the front end side of the gas sensor) protrude toward the inside of the pipe.

[0013] As a result, the gas discharge hole located at the front end side of the gas sensor is made to be close to a center of the pipe where a flow rate of the detected gas is the highest, and it is possible to reliably suck the detected gas inside the protector from the gas discharge hole to the outside using negative pressure, and thus responsiveness is improved.

[0014] Further, by making L2 < L1, it is easy to dispose the gas introduction hole at a radial outer side of the pipe. Thus, it is possible to suppress the gas introduction hole from being directly exposed to the detected gas having a high flow rate inside the pipe, and further suppress water droplets contained in the detected gas from directly entering the protector from the gas introduction hole, and thus moisture resistance is improved.

[0015] Further, compared to a vicinity of the gas discharge hole where a flow rate of the detected gas is the highest and negative pressure is generated, a pressure of the gas introduction hole located at an outer side of the pipe becomes high, and a pressure difference between the gas discharge hole and the gas introduction hole becomes large. Thus, replacement of gas inside the protector is further promoted, and responsiveness is further improved.

[0016] For the gas sensor according to the present application, it is also possible that a maximum inner diameter DA at the distance L1 of the protector is 1 / 2 or less of the distance L1.

[0017] According to the gas sensor, the portion of the protector in which the front end of the gas introduction hole is located is made slender in the axial direction. Therefore, the pressure in the vicinity of the gas discharge hole becomes further negative pressure due to the Venturi effect, the gas in the protector is further drawn to the outside from the gas discharge hole, and thus the responsiveness is further improved.

[0018] For the gas sensor of the present application, the total opening area S1 of the gas discharge holes can also be 50% or less of the area S2 of the bottom of the protector.

[0019] According to the gas sensor, the pressure in the vicinity of the gas discharge hole becomes further negative pressure, the gas in the protector is further drawn to the outside from the gas discharge hole, and thus the responsiveness is further improved.

[0020] A gas sensor mounting structure according to the present application is characterized by comprising: a gas sensor; and a pipe through which a gas to be detected flows, wherein the gas sensor mounting structure is formed by mounting the gas sensor to the pipe, the gas sensor is the gas sensor according to any one of the technical solutions 1 to 3, in a state in which the front end side of the gas sensor faces the inside of the pipe from the mounting hole surface of the pipe, the fixing portion is directly or indirectly fixed to the pipe, and the front end of the tool engagement portion is mounted in a state in which the front end facing surface directly or indirectly contacts the outer surface of the pipe, the gas introduction hole is disposed at a position that is radially outward of the imaginary inner surface of the mounting hole, and the gas discharge hole is disposed on the inside of the pipe.

[0021] According to the gas sensor mounting structure, since the front end side of the gas sensor faces the inside of the pipe from the mounting hole surface of the pipe, the fixing portion is fixed to the pipe, and the front end of the tool engagement portion contacts the outer surface of the pipe to be mounted, it is easy to make the portion of the protector in which L1 is relatively long (the front end side of the gas sensor) protrude to the inside of the pipe.

[0022] As a result, the gas discharge hole located at the front end side of the gas sensor is made to be close to the center of the pipe where the flow rate of the gas to be detected is the highest, the gas to be detected in the protector is more reliably drawn to the outside from the gas discharge hole by the negative pressure, and thus the responsiveness is improved.

[0023] In addition, by making L2 < L1, it is easy to dispose the gas introduction hole at a position that is radially outward of the imaginary inner surface of the mounting hole. Thus, the gas introduction hole is inhibited from being directly exposed to the gas to be detected flowing at a high flow rate in the inside of the pipe, and further, water droplets contained in the gas to be detected are also inhibited from being directly immersed into the protector from the gas introduction hole, and the moisture resistance is improved.

[0024] In addition, compared with the vicinity of the gas discharge hole in which the flow rate of the detected gas is the highest and in which a negative pressure is generated, the pressure of the gas introduction hole located at a position further outward than the imaginary inner surface of the pipe becomes higher, and the pressure difference between the gas discharge hole and the gas introduction hole becomes larger. Therefore, the replacement of the gas in the protector is further promoted, and the responsiveness is further improved.

[0025] Effects of the Invention

[0026] According to the present application, a gas sensor and a gas sensor mounting structure capable of simultaneously improving the moisture resistance and the responsiveness using one layer of a protector can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a sectional view of a gas sensor according to an embodiment of the present application.

[0028] Figure 2 is a sectional view of a gas sensor mounting structure in which the gas sensor is mounted to a pipe.

[0029] Figure 3 is a plan view of the protector as viewed from the front end side toward the rear end side. DETAILED DESCRIPTION

[0030] Based on Figures 1-3 An embodiment of the present application will be described in detail. Figure 1 is a sectional view of a gas sensor 1 according to an embodiment of the present application, Figure 2 is a sectional view of a gas sensor mounting structure 200 in which the gas sensor 1 is mounted to a pipe 100, Figure 3 is a plan view of the protector 51 as viewed from the front end side toward the rear end side.

[0031] In Figure 1 In the embodiment, the gas sensor (a full-area air-fuel ratio gas sensor) 1 includes a sensor element 21, a holder (a ceramic holder) 30 having a through-hole 32 that penetrates in the direction of the axis O and through which the sensor element 21 is inserted, a main body metal case 11 that surrounds the periphery of the ceramic holder 30 in the radial direction, and a protector 51.

[0032] The front end side in which the detection portion 22 is formed in the sensor element 21 protrudes toward the front end than the ceramic holder 30 and the main body metal case 11. The sensor element 21 that passes through the through-hole 32 compresses the seal (in this case, talc) 41 disposed on the rear end surface side (the upper side in the drawing) of the ceramic holder 30 in the front-rear direction with the aid of the sleeve 43 and the annular gasket 45 that are made of an insulating material, and thus the sensor element 21 is hermetically fixed to the inside of the main body metal case 11 in the front-rear direction.

[0033] Further, the rear end side 29 of the sensor element 21 protrudes rearward of the sleeve 43 and the main body metal case 11, and the electrode terminals 24 formed at the rear end side 29 are crimped and electrically connected to the terminal metal pieces 75 provided at the front ends of the lead wires 71 drawn to the outside through the seal 85. In addition, the rear end side 29 of the sensor element 21 including the electrode terminals 24 is covered by the outer tube 81. Hereinafter, a more detailed description will be given.

[0034] The sensor element 21 extends in the direction of the axis O and has a band plate shape (plate shape), and includes a detection portion 22 for detecting a specific gas component in a detected gas, which is composed of a detection electrode and the like (not shown) at the front end side (lower side in the drawing) facing the measurement object. The cross section of the sensor element 21 has a certain size in the front-rear direction and has an elongated structure mainly composed of a ceramic (solid electrolyte or the like). The sensor element 21 itself is the same as the element known in the art, and a pair of detection electrodes constituting the detection portion 22 is disposed at the front end side of the solid electrolyte (member), and electrode terminals 24 for connecting lead wires 71 for detection output are exposed at the rear end side connected thereto.

[0035] In addition, in the present example, a heater (not shown) is provided inside the front end side of the ceramic material of the solid electrolyte (member) in the sensor element 21 in a stacked manner, and electrode terminals 24 for connecting lead wires 71 for applying a voltage to the heater are exposed at the rear end side. Further, these electrode terminals 24 are formed in a vertically long rectangular shape, and for example, three or two electrode terminals are arranged in the lateral direction on the wide surface (both surfaces) of the band plate at the rear end side 29 of the sensor element 21, which is not shown.

[0036] Further, the detection portion 22 of the sensor element 21 is covered with a porous protective layer 23 composed of alumina or spinel or the like. In addition, the sensor element 21 is provided with an element introduction hole 25 communicating with the detection portion 22 to introduce a detected gas to the detection portion 22, and a porous diffusion resistance layer not shown is disposed at the element introduction hole 25.

[0037] The main body metal case 11 is a cylindrical shape with a concentrically different diameter in the front-rear direction, has a circular ring-shaped portion (hereinafter, also referred to as a cylindrical portion) 12 of a cylindrical shape with a small diameter at the front end side for externally fitting and fixing a protector 51 described later, and a screw thread (fixing portion) 13 with a larger diameter than the circular ring-shaped portion 12 is provided on the outer peripheral surface at the rear (upper side in the drawing) thereof, and the screw thread 13 is formed as an external screw thread for fixing to an exhaust pipe of an engine. Further, a polygonal tool engagement portion 14 is provided at the rear of the screw thread 13, and the tool engagement portion 14 is a tool engagement portion with a large diameter for screwing into the sensor 1 by the screw thread 13. In addition, a cylindrical portion 15 for externally fitting and welding a protective cylinder (outer cylinder) 81 covering the rear of the gas sensor 1 is continuously provided at the rear of the tool engagement portion 14, and a pressing cylindrical portion 16 with an outer diameter smaller than the cylindrical portion 15 and a thin wall is provided at the rear of the cylindrical portion 15.

[0038] Further, the tool engagement portion 14 has a larger diameter than the screw thread 13, and a stepped portion is formed between the front end facing surface 14a of the tool engagement portion 14 and the rear end side of the screw thread 13.

[0039] Further, the pressing cylindrical portion 16 is bent inwardly in the main body metal case 11 since it has been pressed. Figure 1 Further, a gasket 19 for sealing at the time of screwing is attached to the lower surface of the tool engagement portion 14.

[0040] On the other hand, the main body metal case 11 has an inner hole 18 that penetrates in the direction of the axis O. The inner peripheral surface of the inner hole 18 has a tapered stepped portion 17 that becomes thinner toward the radial inner side as it goes from the rear end side toward the front end side.

[0041] A ceramic holder 30 that is made of an insulating ceramic (for example, alumina) and is formed in a substantially short cylindrical shape is disposed inside the main body metal case 11. The ceramic holder 30 has a front end facing surface 30a that is formed in a tapered shape that becomes thinner as it goes toward the front end. Further, the outer peripheral portion of the front end facing surface 30a is latched to the stepped portion 17, and the ceramic holder 30 is pressed from the rear end side by a seal member 41, so that the ceramic holder 30 is positioned inside the main body metal case 11 and is clearance-fitted to the main body metal case 11.

[0042] On the other hand, a through hole 32 is provided at the center of the ceramic holder 30, and is formed as a rectangular opening with substantially the same size as the cross section of the sensor element 21 so that the sensor element 21 passes through substantially without clearance.

[0043] The sensor element 21 passes through the through hole 32 of the ceramic holder 30 so that the front end 21a of the sensor element 21 protrudes forward of the front end 12a of the ceramic holder 30 and the main body metal case 11.

[0044] On the other hand, the front end portion of the sensor element 21 is covered with a bottomed cylindrical protective member (protective cover) 51. The rear end of the protective member 51 is fitted and welded to the cylindrical portion 12 of the main body metal case 11. Further, a stepped portion 51d in the radial direction (direction perpendicular to the axis O direction) is formed at the portion of the protective member 51 at the rear end, and the diameter of the front end side of the protective member 51 is smaller than the diameter of the stepped portion 51d.

[0045] Further, a gas introduction hole 56 is opened at the stepped portion 51d. As shown in Figure 3 In this example, a plurality of (12) gas introduction holes 56 are provided at equal intervals in the circumferential direction of the stepped portion 51d.

[0046] Further, in the peripheral edge of the gas introduction hole 56, the perpendicular line to the radial direction from the plane 56e of the inner peripheral edge of the protective member 51 forms an angle (not parallel to the radial direction), and when the peripheral edge of the protective member 51 on the inner side of the gas introduction hole 56 is located at the rearmost side (in other words, the peripheral edge of the protective member 51 on the inner side of the gas introduction hole 56 is located at the rearmost side than the peripheral edge on the outer side of the protective member 51), it is difficult for water droplets in the detected gas to intrude from the gas introduction hole 56 into the inside of the protective member 51, and thus is preferable.

[0047] On the other hand, a gas discharge hole 53 (one in this example) is provided at the center of the bottom portion 51a of the front end of the protective member 51. The gas discharge hole 53 is disposed at a position on the front end side than the gas introduction hole 56, and by the flow of the detected gas flowing in the pipe in which the gas sensor 1 is installed, the gas in the inside of the protective member 51 is sucked out from the gas discharge hole 53 to the outside, and due to the negative pressure thereof, the detected gas is introduced from the gas introduction hole 56 into the inside of the protective member 51.

[0048] Further, in the Figure 1 example, the center of the bottom portion 51a of the front end of the protective member 51 is cut to the rear end side with two parallel slits to form a cover 51f, and the gas discharge hole 53 is formed toward the radial direction in the gap between the bottom portion 51a of the protective member 51 and the cover 51f. In this case, when the protective member 51 is viewed from the front end side in the axis O direction, the gas discharge hole 53 cannot be directly seen, and thus it is possible to suppress the intrusion of water droplets such as condensed water from the gas discharge hole 53 into the inside of the protective member 51.

[0049] Further, as shown in Figure 1As shown, each terminal metal piece 75 is elastically pressed and electrically connected to each electrode terminal 24 formed on the rear end side 29 of the sensor element 21. Each terminal metal piece 75 is disposed at the front end of each lead wire 71 that is pulled out to the outside by the sealing member 85. Furthermore, in the gas sensor 1 of this example, each terminal metal piece 75 including the pressing portion is disposed in a receiving portion in a relatively opposite manner, and each receiving portion is disposed within an insulating partition 91 disposed within the outer cylinder 81. In addition, the movement of the partition 91 radially and at the front end is restricted by a retaining member 82 that is riveted and fixed within the outer cylinder 81. Furthermore, by inserting and welding the front end of the outer cylinder 81 to the cylindrical portion 15 at the rear end side of the main metal housing 11, the rear of the gas sensor 1 is covered in an airtight manner.

[0050] Furthermore, the lead wire 71 is pulled outward through a seal (e.g., rubber) 85 located inside the rear end of the outer cylinder 81, and the seal 85 is compressed by riveting the small-diameter cylinder portion 83 to maintain the airtightness of this part.

[0051] Incidentally, a stepped portion 81d with a larger diameter at the front end is formed on the outer cylinder 81 at a position slightly towards the rear end from the center in the direction of the axis O. The inner surface of the stepped portion 81d supports the partition 91 by pressing it forward against the rear end of the partition 91. On the other hand, the flange 93 formed on the outer periphery of the partition 91 is supported on the retaining member 82, which is fixed to the inner side of the outer cylinder 81. The partition 91 is held in the direction of the axis O by the stepped portion 81d and the retaining member 82.

[0052] Next, the characteristic features of the present invention will be described.

[0053] like Figure 1 As shown, in this embodiment, the distance L1 between the gas inlet hole 56 and the gas outlet hole 53 in the direction of axis O is greater than the distance L2 between the tool engaging part 14 and the gas inlet hole 56 in the direction of axis O, and the front end 21a of the sensor element 21 is located at a position closer to the front end than the gas inlet hole 56.

[0054] Thus, as Figure 2 As shown, when the front end of the gas sensor 1 faces the inside of the piping 100 (exhaust pipe, etc.) through the mounting hole 100h of the piping 100 through which the gas G is to be detected to be flowed, and the thread 13 is directly or indirectly fixed to the piping 100, and the front end of the tool engaging part 14 is directly or indirectly in contact with the outer surface 100e of the piping 100 with the surface 14a, it is easy to make the part of the protective member 51 that is longer than L2 (the front end of the gas sensor 1) protrude into the inside of the piping 100.

[0055] As a result, the gas discharge hole 53 located at the front end side of the gas sensor is brought close to the center of the highest flow rate of the detected gas G of the pipe 100, and the detected gas G in the protector 51 is reliably drawn to the outside from the gas discharge hole 53 by the negative pressure, so the responsiveness is improved.

[0056] In addition, by being set to L2 < Ll, it is easy to arrange the gas introduction hole 56 at a position that is radially outward of the imaginary inner surface 100a2 of the mounting hole 100h. Thereby, the gas introduction hole 56 is suppressed from being directly exposed to the detected gas G of high flow rate inside the pipe 100, and further, the water droplets contained in the detected gas G are also suppressed from being directly immersed into the protector 51 from the gas introduction hole 56, so the moisture resistance is improved.

[0057] In addition, the pressure of the gas introduction hole 56 located at a position that is radially outward of the imaginary inner surface 100a2 of the pipe 100 becomes higher than the vicinity of the gas discharge hole 53 of the highest flow rate of the detected gas G and becomes the negative pressure, and the pressure difference between the gas discharge hole 53 and the gas introduction hole 56 becomes large. Therefore, as shown by the flow (arrow) of the detected gas G, it is easy to further draw the detected gas G in the protector 51 to the outside from the gas discharge hole 53, and it is easy to introduce the gas into the protector 51 from the gas introduction hole 56 at a position that is radially outward of the imaginary inner surface 100a2, the replacement of the gas in the protector 51 is further promoted, and the responsiveness is further improved. Figure 2

[0058] On the contrary, in the case of L2 ≥ Ll, the distance L2 of the tool engagement portion 14 from the gas introduction hole 56 is relatively long. As a result, even if the tool engagement portion 14 is made to be distanced radially outward from the mounting hole 100h of the pipe 100, the gas introduction hole 56 itself enters the inside of the mounting hole 100h (radially inward of the imaginary inner surface 100a2), the gas introduction hole 56 is directly exposed to the detected gas G of high flow rate inside the pipe 100, and the moisture resistance is reduced.

[0059] In addition, in the case of L2 ≥ Ll, the portion of Ll of the protector 51 (front end side of the gas sensor) is relatively shortened, and it is difficult to protrude further inside the pipe 100 from the mounting hole 100h. As a result, it is difficult to bring the gas discharge hole 53 close to the center of the pipe 100, it is difficult to maintain the gas discharge hole 53 at the negative pressure, and the responsiveness is reduced.

[0060] Further, Ll is the distance of the gas introduction hole 56 and the gas discharge hole 53 in the direction of the axis O, and indicates the distance between the front end of the gas introduction hole 56 and the rear end of the gas discharge hole 53.

[0061] ​Likewise, L2 is the distance of the tool engaging portion 14 from the gas introduction hole 56 in the direction of the axis O, and indicates the distance between the front end of the tool engaging portion 14 toward the surface 14a and the rear end of the gas introduction hole 56.

[0062] In addition, in the case where there are a plurality of gas introduction holes 56 and a plurality of gas discharge holes 53, L1 indicates the distance between the foremost gas introduction hole of the plurality of gas introduction holes 56 and the rearmost gas discharge hole of the plurality of gas discharge holes 53. Likewise, L2 indicates the distance between the front end of the tool engaging portion 14 toward the surface 14a and the foremost gas introduction hole of the plurality of gas introduction holes 56.

[0063] In addition, the reason why the front end 21a of the sensor element 21 needs to be located at a position further forward than the gas introduction hole 56 is as follows. That is, the detected gas G introduced from the gas introduction hole 56 is directed toward the front end side inside the protector 51. Therefore, by locating the front end 21a of the sensor element 21 at a position further forward than the gas introduction hole 56, it is easy to reliably bring the detected gas G into contact with the detection portion 22 (located near the front end 21a) of the sensor element 21, and the detection accuracy is improved.

[0064] Here, "the screw 13 is directly or indirectly fixed to the pipe 100" means that, in the present example, a cylindrical cylinder 102 is fixed outside the pipe 100 in a manner of surrounding the mounting hole 100h of the pipe 100, and the gas sensor 1 is fixed by threadably fixing the fixing portion (external thread) of the main body metal case 11 side to the pipe side fixing portion (for example, internal thread) of the inner surface of the cylinder 102. Such a state is set as a state in which the screw 13 is "indirectly" fixed to the pipe 100.

[0065] On the other hand, for example, in the case where the mounting hole 100h of the pipe 100 integrally projects to the radial outside near the mounting hole 100h without using the cylinder 102 or the thickness of the pipe 100 itself is thick, the screw 13 is "directly" fixed to the pipe side fixing portion (for example, internal thread) of the inner surface of the pipe 100.

[0066] Similarly, "installation where the front end facing surface 14a of the tool engagement portion 14 directly or indirectly contacts the outer surface 100e of the piping 100" means, in this example, with the screw 13 fixed to the cylinder 102, the front end facing surface 14a of the tool engagement portion 14 contacts the outer surface (rear end facing surface) of the cylinder 102. Furthermore, specifically, by attaching a tool such as a wrench to the tool engagement portion 14, the thread (external thread) 13 on the side of the main metal housing 11 is screwed into the internal thread on the inner surface of the cylinder 102, thereby causing the front end facing surface 14a of the tool engagement portion 14 to abut against the outer surface of the cylinder 102 via the washer 19. This state is defined as the installation where the front end facing surface 14a of the tool engagement portion 14 "indirectly" contacts the outer surface 100e of the piping 100.

[0067] On the other hand, if, as described above, the mounting hole 100h of the piping 100 is not used and the piping 100 protrudes radially outward in an integral manner, or if the piping 100 itself is thick, then with the thread 13 fixed to the piping 100 itself, the front end of the tool engagement part 14 is positioned facing the surface 14a and is "directly" contacted with the outer surface 100e of the piping 100 via the gasket 19.

[0068] Additionally, the "imaginary inner surface 100a2" of mounting hole 100h refers to the surface along... Figure 2 In the radial cross-section of the pipe 100 shown, the inner surface is obtained by externally inserting the contour of the inner surface 100a of the pipe 100 at the position of the mounting hole 100h. This external insertion can, for example, be forming an approximate curve through a point by marking multiple points on the inner surface 100a of the pipe 100.

[0069] The radially inner side of the imaginary inner surface 100a2 can be considered as the interior of the piping 100 through which the gas G being detected flows. On the other hand, the radially outer side of the imaginary inner surface 100a2 can be considered as the exterior of the piping 100, and it is assumed that there is almost no flow of the gas G being detected.

[0070] When the maximum inner diameter DA of the protective element at a distance L1 is less than half of the distance L1, the portion of the protective element 51 at L1, which is closer to the front end than the gas inlet hole 56, becomes elongated in the axial direction O. Therefore, the pressure near the gas outlet hole 53 becomes negative due to the Venturi effect, and the gas inside the protective element 51 is further drawn outward from the gas outlet hole 53, thus further improving the responsiveness.

[0071] In addition, such as Figure 3As shown, when the total opening area S1 of the gas discharge holes 53 is 50% or less of the area S2 of the bottom 51a of the protector 51, the pressure in the vicinity of the gas discharge holes 53 further becomes a negative pressure, and the gas in the protector 51 is further drawn to the outside from the gas discharge holes 53, so the responsiveness is further improved.

[0072] Further, in order to reliably reduce the pressure in the vicinity of the gas discharge holes 53, it is preferable that the gas discharge holes 53 be located at the foremost end of the protector 51, that is, be provided to the bottom 51a.

[0073] The gas sensor of the present application can be embodied by appropriately changing the configuration and structure thereof without departing from the gist of the present application.

[0074] For example, in the above embodiment, the stepped portion 51d of the protector 51 is formed along the radial direction (parallelly), and the perpendicular line to the plane of the periphery of the inside of the protector 51 by the gas introduction hole 56 provided to the stepped portion 51d is perpendicular to the radial direction, but the stepped portion of the protector 51 can also be formed to have an angle with respect to the radial direction.

[0075] Therefore, it is preferable that the inside of the protector not be observed when the gas introduction hole is observed from the outside of the radial direction. However, even if the stepped portion 51d of the protector 51 is formed to be tapered so as to descend toward the front end side as it goes toward the inside of the radial direction, it is sufficient as long as the inside of the protector 51 is not observed when the gas introduction hole 56 is observed from the outside of the radial direction.

[0076] In addition, as the sensor element, it is not limited to an element that measures the concentration of oxygen, and an element that measures the concentration of nitrogen oxide (NOx) or hydrocarbon (HC) or the like can also be used.

[0077] As the sensor element, a cylindrical sensor element can also be used.

[0078] The shape or number of the gas introduction holes or the gas discharge holes are not limited, and can be, for example, elliptical. The shape of the tool engagement portion is also not limited to the above shape.

[0079] Explanation of Reference Numerals

[0080] 1, gas sensor; 11, main body metal case; 13, fixed portion (external thread); 14, tool engagement portion; 14a, front end facing surface of tool engagement portion; 21, sensor element; 21a, front end of sensor element; 22, detection portion; 51, protector; 53, gas discharge hole; 56, gas introduction hole; 100, pipe; 100a2, imaginary inner surface; 100e, outer surface of pipe; 100h, mounting hole; O, axis; G, gas to be detected.

Claims

1. A gas sensor, characterized by, Having: a sensor element extending in an axial direction, a detection portion that detects a detected gas being formed at a front end side; a main body metal case that is cylindrical, that surrounds a periphery of the sensor element in a radial direction, and that holds the sensor element; and a protector that is a single cylindrical layer, that is fixed to a periphery of the front end side of the main body metal case, and that surrounds the front end side of the sensor element, the protector having a gas introduction hole and a gas discharge hole disposed at a position further toward the front end side than the gas introduction hole, the main body metal case having a fixed portion whose outer surface is directly or indirectly fixed to a pipe through which the detected gas flows, and a tool engagement portion that is a tool engagement portion having a larger diameter than the fixed portion, which is located at a rear end side of the fixed portion and which is used for mounting the gas sensor, a distance (L1) in the axial direction between the gas introduction hole and the gas discharge hole being larger than a distance (L2) in the axial direction between the tool engagement portion and the gas introduction hole, a front end of the sensor element being located at a position further toward the front end side than the gas introduction hole.

2. The gas sensor according to claim 1, wherein a maximum inner diameter (DA) of the protector at the distance (L1) is 1 / 2 or less of the distance (L1).

3. The gas sensor according to claim 1 or 2, wherein a total opening area (S1) of the gas discharge hole is 50% or less of an area (S2) of a bottom of the protector. Having:

4. A gas sensor mounting structure characterized by comprising: a gas sensor; and a pipe through which a detected gas flows, the gas sensor mounting structure being formed by mounting the gas sensor to the pipe, the gas sensor being the gas sensor according to any one of claims 1 to 3, in a state in which a front end side of the gas sensor faces an inside of the pipe from a mounting hole of the pipe, the fixed portion is directly or indirectly fixed to the pipe, and a front end of the tool engagement portion directly or indirectly contacts an outer surface of the pipe to be mounted, the gas introduction hole is disposed at a position further radially outward than an imaginary inner surface of the mounting hole, the gas discharge hole is disposed at an inside of the pipe. ​

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