Gas Sensors

Abstract

The present invention provides a gas sensor capable of simultaneously improving moisture resistance and responsiveness using a single-layer protective member. The gas sensor (1) comprises: a sensor element (21) having a detection portion (22) formed on the front end side thereof for detecting a gas to be detected via an element introduction hole (25); a main metal shell (11); and a single-layer cylindrical protective member (51) fixed around the front end side of the main metal shell, the protective member having a gas introduction hole (56) facing the rear end side and a gas discharge hole (53) arranged on the front end side relative to the gas introduction hole, a gap (G) being provided between the gas introduction hole and the front end facing surface (12a) of the main metal shell in the direction of the axis (O), an area (Sh) facing the front end facing surface of the main metal shell when the gas introduction hole is viewed toward the rear end side along the axis direction, being more than 1 / 2 of an opening area (Sg) of the gas introduction hole, all the element introduction holes being located on the front end side relative to the front end (12f) of the front end facing surface of the main metal shell, and a distance (L1) of the gap (G) being smaller than a diameter (D) of the gas introduction hole.

Description

Technical Field

[0001] The present invention relates to a gas sensor provided with a single-layer protective member. Background Art

[0002] Conventional gas sensors hold a sensor element within a cylindrical metal housing. A single- or double-layered protective member protects the front end of the sensor element, which is exposed to the exhaust gas. This protective member is provided with a gas inlet port. However, these sensors must be water-resistant to prevent condensed water from entering the exhaust gas from reaching the sensor element, while also ensuring responsiveness to quickly introduce exhaust gas into the sensor element's detection section. This poses the risk of the sensor element being heated by its own heater or by high-temperature exhaust gas, resulting in thermal shock and potentially cracking the sensor element when condensed water contacts it.

[0003] Therefore, a technology has been developed that improves responsiveness by making the protective member a single layer. Furthermore, a gas inlet hole is provided on a horizontal step provided on the protective member, with the gas inlet hole facing the front end of the main metal shell (Patent Document 1). With this technology, the exhaust gas is temporarily directed from the gas inlet hole toward the main metal shell. Afterwards, the gas inlet hole changes direction within the internal space between the gas inlet hole and the main metal shell, and then flows toward the front end inside the protective member. This facilitates the separation of condensed water from the exhaust gas due to its own weight.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-70601 ( Figure 1 ). Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, if condensed water that has changed its direction from the main metal housing side directly reaches the detection portion of the sensor element, there is a risk of the element being cracked, and the moisture resistance becomes insufficient.

[0009] The present invention has been made in view of this situation, and an object of the present invention is to provide a gas sensor capable of improving both moisture resistance and responsiveness using a single-layer protective member.

[0010] Solutions for solving problems

[0011] To solve the above-mentioned problems, a gas sensor according to a first aspect of the present technical solution comprises: a sensor element extending in an axial direction and having a detection portion formed on a front end side thereof for detecting a target gas via an element introduction hole; a cylindrical metal shell body that surrounds the sensor element in a radial direction and holds the sensor element; and a single-layer cylindrical protector member fixed to the periphery of the front end side of the metal shell body and surrounds the front end side of the sensor element. The protector member is characterized in that the protector member has a gas introduction hole facing the rear end side and a gas discharge hole located on the front end side of the gas introduction hole. A gap G is defined between the gas introduction hole and a front end-facing surface of the metal shell body in the axial direction. When the gas introduction hole is viewed in the axial direction toward the rear end side, an area Sh facing the front end-facing surface of the metal shell body is at least ½ of an opening area Sg of the gas introduction hole. All of the element introduction holes are located on the front end side of the most forward end of the front end-facing surface of the metal shell body. A distance L1 of the gap G is smaller than a diameter D of the gas introduction hole.

[0012] In this gas sensor, by setting L1 < D, when a water droplet, along with the detected gas, flows from the gas inlet port toward the metal housing, it reliably collides with the front-facing surface of the metal housing, breaking into fine droplets. Consequently, the water droplet changes direction and moves toward the front end within the protective member. Even if it contacts the front end of the sensor element, the thermal shock to the sensor element is reduced, making it less susceptible to cracking, compared to a case where a large-diameter water droplet directly contacts the sensor element, thereby improving moisture resistance.

[0013] Here, by setting Sh>1 / 2×Sg, more than 1 / 2 of the opening area of ​​the gas inlet hole is opposite to the front end facing surface of the main metal shell, so the proportion of water droplets colliding with the front end facing surface from the gas inlet hole toward the main metal shell is increased, which enables the water droplets to collide with the front end facing surface more reliably and be broken into fine water droplets.

[0014] Furthermore, since the protective member is a single layer, the gas to be detected flows more easily into the protective member than a double layer protective member, and the responsiveness is also improved.

[0015] In addition, the reason for setting L1<D is because the maximum diameter of the water droplets introduced into the protective member from the gas inlet hole is D. Assuming L1≥D, when a water droplet of diameter D enters the gap G from the gas inlet hole, it is possible that it does not hit the front end facing surface and moves inside the protective member, and directly contacts the sensor element in the form of large particles.

[0016] A second aspect of the present invention provides a gas sensor comprising: a sensor element extending in an axial direction and having a detection portion formed on its front end for detecting a target gas via an element introduction hole; a cylindrical metal shell body surrounding the sensor element in a radial direction to retain the sensor element; and a single-layer cylindrical protector secured to the periphery of the front end of the metal shell body and surrounding the front end of the sensor element. The protector is characterized in that the protector has a gas introduction hole facing the rear end and a gas discharge hole located further forward than the gas introduction hole. A gap G is defined between the gas introduction hole and a front end-facing surface of the metal shell body in the axial direction. When the gas introduction hole is viewed in the axial direction toward the rear end, an area Sh covered by the front end-facing surface of the metal shell body is at least ½ of an opening area Sg of the gas introduction hole. The element introduction holes are all located further forward than the extreme front end of the front end-facing surface of the metal shell body. A distance L1 of the gap G is smaller than a radial distance L2 between the sensor element and the gas introduction hole.

[0017] In this gas sensor, by setting L1 < L2, when a water droplet, along with the gas being detected, flows from the gas inlet port toward the metal housing, it reliably collides with the front-facing surface of the metal housing, breaking into fine droplets. Consequently, the water droplet changes direction and moves toward the front end within the protective member. Even if it contacts the front end of the sensor element, the thermal shock to the sensor element is reduced, making it less susceptible to cracking, compared to direct contact with a large-diameter water droplet, thereby improving moisture resistance.

[0018] Here, by setting Sh>1 / 2×Sg, more than 1 / 2 of the area of ​​the front end facing surface of the main metal shell is opposite to the gas inlet hole, so the proportion of water droplets colliding with the front end facing surface from the gas inlet hole toward the main metal shell is increased, and the water droplets can more reliably collide with the front end facing surface to be broken into fine water droplets.

[0019] Furthermore, since the protective member is a single layer, the gas to be detected flows more easily into the protective member than a double layer protective member, and the responsiveness is also improved.

[0020] Furthermore, assuming that a water droplet enters the gap G from the gas inlet hole and moves within the protective member without striking the tip-facing surface, the maximum diameter of the water droplet is L1. Here, if L1 < L2, even a water droplet with a maximum diameter of L1 will stay away from the sensor element, reducing the likelihood of contact with the sensor element.

[0021] In the gas sensor of the present technical solution, the front end facing surface of the main metal shell may constitute a horizontal plane parallel to the radial direction and / or a tapered surface that narrows toward the front end and faces radially outward.

[0022] With this sensor, water droplets that collide with the horizontal surface or conical surface from the gas inlet hole bounce downward (horizontal surface) or radially outward (conical surface), that is, not radially inward, so the water droplets are unlikely to come into contact with the sensor element.

[0023] In contrast, if the front-facing surface of the metal housing has a radially inward tapered surface that narrows toward the front end, water droplets colliding with this tapered surface will rebound radially inward and approach the sensor element. Consequently, water droplets are more likely to contact the sensor element and wet it, potentially reducing its water resistance.

[0024] In the gas sensor of this aspect, the interior of the protective member may not be visible when the gas introduction hole is viewed from the radially outer side.

[0025] This gas sensor can suppress water droplets from directly contacting the inside of the protector and even the sensor element from the radial direction.

[0026] Effects of the Invention

[0027] According to the present invention, a gas sensor can be obtained in which both moisture resistance and responsiveness are improved using a single-layer protective member. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a cross-sectional view of a gas sensor according to a first embodiment of the present invention.

[0029] Figure 2 This is a plan view of the protector (gas introduction hole) viewed from the front end side toward the rear end side.

[0030] Figure 3 yes Figure 1 A partial enlarged view of the area near the protective part.

[0031] Figure 4 It is a cross-sectional view of a gas sensor 1 according to a second embodiment of the present invention.

[0032] Figure 5 It is a cross-sectional view showing an embodiment in which the orientation of the gas introduction hole is different.

[0033] Figure 6 This is a cross-sectional view showing a state in which the interior of the protective member can be seen when the gas introduction hole is viewed from the outside in the radial direction. DETAILED DESCRIPTION

[0034] based on Figures 1 to 3 An embodiment of the first aspect of the present invention will be described in detail. Figure 1 is a cross-sectional view of a gas sensor 1 according to a first embodiment of the present invention. Figure 2 This is a top view of the protective member 51 (gas introduction hole 56) viewed from the front end toward the rear end. Figure 3 yes Figure 1 A partial enlarged view of the area near the protective part.

[0035] exist Figure 1 In the figure, the gas sensor (full-range air-fuel ratio gas sensor) 1 includes a sensor element 21, a holder (ceramic holder) 30 having a through hole 32 that penetrates along the axis O and for the sensor element 21 to be inserted, a main metal shell 11 surrounding the radial periphery of the ceramic holder 30, and a protective member 51.

[0036] The front end of the sensor element 21, where the detection portion 22 is formed, protrudes further forward than the ceramic holder 30 and the main metal housing 11. Having thus passed through the through-hole 32, the sensor element 21 is compressed in the front-to-back direction by a sealant (talc in this example) 41 disposed on the rear end face side (upper side in the figure) of the ceramic holder 30 via a sleeve 43 made of an insulating material and an annular gasket 45, thereby being fixed to the inside of the main metal housing 11 in an airtight manner in the front-to-back direction.

[0037] Furthermore, the rear end 29 of the sensor element 21 protrudes rearward from the sleeve 43 and the main metal housing 11. Terminal metal fittings 75 are crimped and electrically connected to the electrode terminals 24 formed on the rear end 29. These terminal metal fittings 75 are provided at the front ends of the leads 71, which are drawn to the outside through the sealing material 85. Furthermore, the rear end 29 of the sensor element 21, including the electrode terminals 24, is covered by the outer cylinder 81. This will be described in more detail below.

[0038] The sensor element 21 extends along the axis O and is formed into a strip (plate) shape, with a detection portion 22 composed of detection electrodes (not shown) on the front end side facing the measurement object (the lower side in the figure) and detecting a specific gas component in the gas being measured. The cross-section of the sensor element 21 is a rectangular (rectangular) shape of a certain size in the front-to-back direction. It is formed as a slender member mainly composed of ceramic (solid electrolyte, etc.). The sensor element 21 itself is similar to conventionally known elements. A pair of detection electrodes constituting the detection portion 22 are arranged on the front end side of the solid electrolyte (member), and electrode terminals 24 for connecting to leads 71 ​​for extracting the detection output are exposed on the rear end side connected to them.

[0039] In this example, a heater (not shown) is provided within the front end of the ceramic material layered on the solid electrolyte (member) in the sensor element 21. Electrode terminals 24 are exposed on the rear end for connection to leads 71 ​​for applying voltage to the heater. These electrode terminals 24 are formed in a vertically long rectangular shape. For example, three or two electrode terminals are arranged horizontally on the wide sides (both sides) of the strip at the rear end 29 of the sensor element 21, though this is not shown.

[0040] The detection portion 22 of the sensor element 21 is covered with a porous protective layer 23 made of alumina, spinel, or the like. Furthermore, the sensor element 21 is provided with an element introduction hole 25 that communicates with the detection portion 22 and introduces the gas to be detected into the detection portion 22. A porous diffusion resistor layer (not shown) is disposed in the element introduction hole 25.

[0041] The main metal shell 11 is cylindrical with concentric and varying diameters in the front-to-back direction. It has a small-diameter cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 12 on the front end for externally fitting and fixing a protective member 51, described later. On the outer circumferential surface of the rear portion (shown above), a thread 13 having a larger diameter than the cylindrical portion is provided, which is used to fix to the exhaust pipe of the engine. Furthermore, a polygonal tool engagement portion 14 is provided at the rear portion for screwing the sensor 1 in using the thread 13. Furthermore, a cylindrical portion 15 is provided in series with the rear portion of the tool engagement portion 14. The protective cylinder (outer cylinder) 81 covering the rear of the gas sensor 1 is externally fitted and welded to the cylindrical portion 15. A thin-walled rivet cylindrical portion 16 having a smaller outer diameter than the cylindrical portion 15 is provided at the rear portion of the cylindrical portion 15.

[0042] In addition, the rivet cylindrical portion 16 has been rivet so that Figure 1 In addition, a gasket 19 for sealing when screwing is installed on the lower surface of the tool engaging portion 14.

[0043] On the other hand, the main metal shell 11 has an inner hole 18 penetrating in the direction of the axis O. The inner peripheral surface of the inner hole 18 has a tapered step portion 17 that tapers radially inward from the rear end side toward the front end side.

[0044] A ceramic holder 30, made of insulating ceramic (e.g., alumina) and formed into a roughly short cylindrical shape, is located inside the metal housing 11. The ceramic holder 30 has a front-facing surface 30a that tapers toward the front end. The outer periphery of the front-facing surface 30a is engaged with the step 17, and the ceramic holder 30 is pressed from the rear end by a seal 41, thereby securing the ceramic holder 30 in place and allowing it to fit loosely within the metal housing 11.

[0045] On the other hand, the through hole 32 is provided at the center of the ceramic holder 30 and is formed as a rectangular opening having substantially the same size as the cross section of the sensor element 21 so that the sensor element 21 can pass therethrough substantially without a gap.

[0046] The sensor element 21 passes through the through hole 32 of the ceramic holder 30 , with the front end 21 a of the sensor element 21 protruding forward from the ceramic holder 30 and the front end 12 a of the metal housing 11 .

[0047] Meanwhile, the front end of the sensor element 21 is covered by a single-layer, bottomed, cylindrical protector (protective cover) 51. The rear end of the protector 51 is externally fitted and welded to the cylindrical portion 12 of the main metal housing 11. Furthermore, a radially (perpendicular to the axis O) stepped portion 51d is formed near the rear end of the protector 51. The diameter of the portion near the front end of the stepped portion 51d is smaller than that of the portion near the front end.

[0048] Furthermore, a gas introduction hole 56 is opened toward the rear end side in the step portion 51d. Figure 2 As shown, in this example, a plurality (12) of gas inlet holes 56 are provided at equal intervals in the circumferential direction of the step portion 51d. Furthermore, "toward the rear end side" means that a perpendicular line passing through a plane 56e on the inner peripheral edge of the protective member 51 forms an angle with the radial direction (is not parallel to the radial direction), and that the peripheral edge of the gas inlet hole 56 on the inner side of the protective member 51 is located at the rear end side (in other words, the inner peripheral edge of the gas inlet hole 56 is located at the rear end side compared to the peripheral edge on the outer side of the protective member 51).

[0049] On the other hand, a gas discharge hole 53 (one in this example) is provided at the center of the bottom portion 51a at the front end of the protective member 51. The gas discharge hole 53 is located closer to the front end than the gas inlet hole 56. As the detected gas flows through the installation object (exhaust pipe, etc.) on which the gas sensor 1 is installed, the gas within the protective member 51 is sucked out through the gas discharge hole 53. The negative pressure from this suction draws the detected gas into the protective member 51 through the gas inlet hole 56.

[0050] In addition, Figure 1 In the example shown, the bottom 51a at the front end of the protective member 51 is cut upward toward the rear end with two parallel slits in the center to form a cover 51f. Gas discharge holes 53 are radially formed in the gap between the bottom 51a and the cover 51f of the protective member 51. In this case, the gas discharge holes 53 are not directly visible when the protective member 51 is viewed from the front end in the direction of the axis O. This prevents water droplets such as condensed water from entering the protective member 51 through the gas discharge holes 53.

[0051] In addition, if Figure 1As shown, each terminal metal fitting 75 utilizes its elasticity to press-fit and electrically connect to each electrode terminal 24 formed on the rear end 29 of the sensor element 21. Each terminal metal fitting 75 is provided at the distal end of each lead 71, which is drawn to the outside via a seal 85. Furthermore, in the gas sensor 1 of this example, each terminal metal fitting 75, including the press-fit portion, is disposed oppositely within each housing portion. Each housing portion is provided within an insulating partition 91 disposed within the outer cylinder 81. Furthermore, radial and distal movement of the partition 91 is restricted by a retaining member 82 riveted to the outer cylinder 81. Furthermore, by fitting and welding the distal end of the outer cylinder 81 to the cylindrical portion 15 on the rear end of the main metal housing 11, the rear of the gas sensor 1 is hermetically sealed.

[0052] The lead wire 71 is pulled outward through a seal (eg, rubber) 85 disposed inside the rear end portion of the outer tube 81 , and the seal 85 is compressed by reducing and caulking the small-diameter cylindrical portion 83 , thereby maintaining airtightness in this portion.

[0053] Incidentally, a stepped portion 81d having a larger diameter at the front end is formed slightly toward the rear end of the outer cylinder 81 relative to the center in the direction of the axis O. The inner surface of this stepped portion 81d supports the partition plate 91 by pressing the rear end of the partition plate 91 forward. Meanwhile, a flange 93 formed on the outer periphery of the partition plate 91 is supported by a retaining member 82 fixed to the inner side of the outer cylinder 81. The partition plate 91 is retained in the direction of the axis O by the stepped portion 81d and the retaining member 82.

[0054] Next, the characteristic features of the first aspect of the present invention will be described.

[0055] like Figure 1 、 Figure 3 As shown in FIG. 1 , in this embodiment, a gap G is provided between the gas introduction hole 56 and the front end facing surface 12a of the main metal shell 11, which are opposite to each other in the direction of the axis O. Figure 2 As shown, when the gas introduction hole 56 is viewed from the axis O toward the rear end, the area Sh facing the front end facing surface 12a of the metal shell body 11 is at least 1 / 2 of the opening area Sg of the gas introduction hole 56. Sh and Sg are each a total area; for example, Sg is obtained by adding the opening areas of the twelve individual gas introduction holes 56.

[0056] In the present embodiment, the area Sh1 of each of the individual gas introduction holes 56 is also equal to or greater than ½ of the opening area Sg1 . Sh1 and Sg1 represent the areas corresponding to the individual gas introduction holes 56 .

[0057] Moreover, all the element introduction holes 25 are located further forward than the front end 12f of the front end facing surface 12a of the main metal shell 11, and the distance L1 of the gap G (the distance between the front end 12f and the flat surface 56e) is smaller than the diameter D of the gas introduction hole 56.

[0058] By setting L1 < D, when water droplets W, such as condensed water, flow from the gas inlet 56 toward the metal housing 11 along with the gas being detected, these water droplets W reliably collide with the front-facing surface 12a of the metal housing 11, breaking into fine droplets. Consequently, these water droplets change direction and move toward the front end within the protective member 51. Even if they contact the front end of the sensor element 21, compared to a case where a large-diameter water droplet W directly contacts the sensor element 21, the thermal shock to the sensor element 21 is reduced, making it less likely to break, and improving its moisture resistance.

[0059] Here, by setting Sh>1 / 2×Sg, more than 1 / 2 of the opening area of ​​the gas inlet hole 56 is opposite to the front end facing surface 12a of the main metal shell 11, so the proportion of water droplets W from the gas inlet hole 56 toward the main metal shell 11 colliding with the front end facing surface 12a is increased, and the water droplets W can be more reliably collided with the front end facing surface 12a to be broken into fine water droplets.

[0060] Furthermore, since the protective member 51 is a single layer, the gas to be detected flows more easily into the protective member than a double layer protective member, and the responsiveness is also improved.

[0061] In addition, L1 only needs to be larger than 0. When L1>0.5 mm, the gas can be easily introduced into the protective member 51, which is preferred.

[0062] In addition, the reason for setting L1<D is because the maximum diameter of the water droplets W introduced into the protective member 51 from the gas inlet hole 56 is D. Assuming L1≥D, when the water droplets W with a diameter of D enter the gap G from the gas inlet hole 56, there is a possibility that they will not hit the front end toward the surface 12a and move inside the protective member 51, and directly contact the sensor element 21 in the form of large particles.

[0063] Furthermore, the reason why all element introduction holes 25 need to be located further forward than the foremost end 12f is as follows. Specifically, the detected gas introduced through gas introduction hole 56 changes direction from the front end toward the foremost end 12f of surface 12a, and then flows toward the foremost end within protective member 51. Therefore, by positioning all element introduction holes 25 further forward than the foremost end 12f, the detected gas can reliably contact the detection portion 22 of sensor element 21 for detection, thereby improving detection accuracy.

[0064] When at least a portion of the element introduction hole 25 is located closer to the front end than the plane 56 e of the gas introduction hole 56 , the gas to be detected can be more reliably brought into contact with the detection portion 22 of the sensor element 21 for detection, further improving detection accuracy.

[0065] In addition, if Figure 2 As shown, when there are multiple gas inlet holes 56, it is optimal if each gas inlet hole 56 and the front end 12f of the front-facing surface 12a of the metal shell 11 that faces the gas inlet hole 56 satisfy the relationship L1 < D. However, if at least one of the multiple gas inlet holes 56 satisfies the relationship L1 < D, the amount of water droplets that reach the sensor element 21 in the form of large particles can be reduced.

[0066] In addition, as described below, Figure 5 、 Figure 6 When the plane 56 e is inclined, L1 of each gas introduction hole 56 is the shortest distance between the front end 12 f and the peripheral edge of the gas introduction hole 56 on the plane 56 e .

[0067] Then, based on Figure 4 An embodiment of the second aspect of the present invention will be described in detail. Figure 4 It is a partial enlarged view of the vicinity of the protector 151 of the gas sensor according to the second embodiment of the present invention.

[0068] The gas sensor of the second embodiment has the same structure as that of the gas sensor of the first embodiment except for the front end facing surfaces 120a1 and 120a2 of the main metal shell 11 and the protector 151 , and therefore description and illustration of the same parts are omitted.

[0069] like Figure 4 As shown, in this embodiment, a gap G is also provided between the gas introduction hole 156 and the front end facing surfaces 120a1 and 120a2 of the metal shell body 11 in the direction of the axis O. Furthermore, when the gas introduction hole 156 is viewed from the axis O toward the rear end, the area Sh facing the front end facing surfaces 120a1 and 120a2 of the metal shell body 11 is equal to or greater than 1 / 2 of the opening area Sg of the gas introduction hole 156, although this is not shown.

[0070] Furthermore, all the element introduction holes 25 are located further forward than the most forward ends 120 f of the front-facing surfaces 120 a 1 and 120 a 2 of the metal shell 11 , and the distance L1 of the gap G is smaller than the radial distance L2 between the sensor element 21 and the gas introduction hole 156 .

[0071] By setting L1 < L2, when a water droplet W, along with the gas being detected, flows from the gas inlet hole 156 toward the metal housing 11, the water droplet W reliably collides with the front-facing surfaces 120a1 and 120a2 of the metal housing 11, breaking into fine droplets. Therefore, in the second embodiment, compared to a case where a large-diameter water droplet W directly contacts the sensor element 21, the thermal shock to the sensor element 21 is reduced, making it less susceptible to cracking, thereby improving moisture resistance.

[0072] In addition, L1 only needs to be larger than 0. When L1>0.5 mm, the gas can be easily introduced into the protective member 51, which is preferred.

[0073] The second embodiment differs from the first embodiment in that L1 < L2 is specified. The reason for L1 < L2 is as follows. Specifically, if a water droplet W enters gap G from gas inlet hole 156 and moves within protective member 151 without striking tip-facing surfaces 120a1 and 120a2, its maximum diameter is L1. Therefore, if L1 < L2, even a water droplet W with a maximum diameter of L1 will stay away from sensor element 21, reducing the likelihood of contact with sensor element 21.

[0074] In addition, Figure 4 In the example, the front end facing surface of the main metal shell 11 is composed of a horizontal surface 120a1 parallel to the radial direction and a tapered surface 120a2 connected to the radial outside of the horizontal surface 120a1 and narrowed toward the front end and facing the radial outside.

[0075] In this way, if the front end facing surface of the main metal shell 11 does not have a structure of "a tapered surface narrowing toward the front end side and toward the radial inside", the water droplets W that collide with the horizontal surface 120a1 or the tapered surface 120a2 from the gas inlet hole 156 will rebound downward (horizontal surface 120a1) or toward the radial outside (tapered surface 120a2), that is, in a direction not close to the radial inside, so it is difficult for the water droplets W to contact the sensor element 21.

[0076] In contrast, Figure 4 As shown by the dotted line, if the front end-facing surface of the main metal shell 11 facing the gas inlet hole 156 has a "tapered surface 120t that narrows toward the front end and faces radially inward," a water droplet W that collides with the tapered surface 120t will rebound radially inward and approach the sensor element 21. Therefore, compared with a horizontal surface or a tapered surface facing radially outward, the water droplet W may be more likely to contact and wet the sensor element 21, thereby reducing the water resistance.

[0077] Therefore, it is preferable that a horizontal surface or a radially outward tapered surface face the gas introduction hole 156 rather than a radially inward tapered surface. It is preferable that at least 1 / 2 of the opening area of ​​the gas introduction hole 156 face the horizontal surface or the radially outward tapered surface. However, the front end facing surface of the metal shell 11 may include an inward tapered surface as long as moisture resistance is not reduced.

[0078] In addition, Figure 4 In the example of FIG. 1 , the horizontal surface 120 a 1 corresponds to “the front end 12 f of the front end-facing surface of the metal shell body 11 ” between the horizontal surface 120 a 1 and the tapered surface 120 a 1 .

[0079] In addition, Figure 4 In the example, the gas discharge hole 153 opens directly at the center of the bottom 151 a at the front end of the protection member 151 .

[0080] In addition, in the second form, when there are multiple gas inlet holes 156, for each gas inlet hole 156 and the front end 12f of the front end facing surface 12a of the main metal shell 11 to which the gas inlet hole 56 is respectively opposite, and the sensor element 21, no matter which gas inlet hole 156 there is, it is necessary to be in the relationship of L1<L2.

[0081] Furthermore, L2 of each gas introduction hole 156 is the shortest distance between (the periphery of) the gas introduction hole 156 and the sensor element 21 facing the gas introduction hole 156 .

[0082] The gas sensor of the present invention can be embodied with appropriate design changes to its structure and configuration without departing from the gist of the present invention.

[0083] For example, in the above embodiment, the step portion 51d of the protective member 51 is formed along the radial direction (parallel), and the perpendicular line of the plane of the periphery of the gas inlet hole 56 provided on the step portion 51d close to the inner side of the protective member 51 is perpendicular to the radial direction, but the step portion of the protective member 51 can also be formed to have an angle that is not perpendicular to the radial direction.

[0084] Specifically, if Figure 5 As shown, the step 51d2 of the protector 51 (on the outer surface of the protector 51) can also have a tapered shape that tapers radially outward. In this case, a perpendicular line passing through the plane of the gas inlet hole 56 provided in the step 51d2, near the inner periphery of the protector 51 (this perpendicular line represents the flow direction of water droplets W entering the protector 51 from the gas inlet hole 56) also tapers radially outward as it moves toward the rear end. In other words, water droplets W entering the protector 51 from the gas inlet hole 56 flow away from the sensor element 21, reducing the likelihood of water droplets W contacting the sensor element 21.

[0085] In addition, Figure 5 Examples and the above Figure 3 、 Figure 4 In the example shown in FIG. 5 , when the gas introduction hole 56 ( 156 ) is viewed from the radial outside, the interior of the protective member 51 ( 151 ) cannot be viewed. This prevents the water droplets W from directly contacting the interior of the protective member and even the sensor element 21 from the radial direction.

[0086] In contrast, Figure 6 As shown, consider the following case: the step portion 51d3 of the protector 51 has a tapered shape that descends toward the front end as it goes radially inward, and the interior of the protector 51 can be seen when the gas introduction hole 56 is viewed from the radial outside. In this case, a gap CL is formed when the gas introduction hole 56 is viewed from the radial outside, and there is a possibility that water droplets W may directly contact the interior of the protector and even the sensor element 21 through this gap CL, thereby reducing the moisture resistance.

[0087] Therefore, it is preferable that the inside of the protective member cannot be seen when the gas inlet hole is viewed from the radially outer side. Figure 6 As shown, the step portion 51d3 of the protective member 51 is tapered so as to descend toward the front end as it moves radially inward. Any structure is sufficient so that the interior of the protective member 51 cannot be seen when the gas introduction hole 56 is viewed from the radial outside. To achieve a structure in which the interior of the protective member 51 cannot be seen, for example, the angle of the step portion 51d3, the thickness of the protective member 51, or the diameter of the gas introduction hole 56 can be adjusted.

[0088] Furthermore, the sensor element is not limited to an element that measures the concentration of oxygen, and an element that measures the concentration of nitrogen oxides (NOx) or hydrocarbons (HC) may also be used.

[0089] As the sensor element, a cylindrical sensor element may also be used.

[0090] The shape and number of the gas inlet and outlet holes are not limited, and they may be, for example, elliptical. The shape of the front end surface of the main metal shell is also not limited to the above-described shape.

[0091] Description of Reference Numerals

[0092] 1. Gas sensor; 11. Main metal shell; 11e. Rear end facing surface of the main metal shell; 12a, 120a1, 120a2. Front end facing surface of the main metal shell; 12f, 120f, the front end of the front end facing surface; 21. Sensor element; 22. Detection part; 25. Element introduction hole; 51, 151. Protective part; 53, 153. Gas exhaust hole; 56, 156. Gas introduction hole; O, axis.

Claims

1. A gas sensor, characterized in that: have: a sensor element extending in the axial direction and having a detection portion formed on the front end side thereof for detecting a gas to be detected via the element introduction hole; a cylindrical main metal housing, the main metal housing surrounding the radial circumference of the sensor element to hold the sensor element; as well as A single-layer cylindrical protective member is fixed to the periphery of the front end side of the main metal shell and surrounds the front end side of the sensor element. The protective member has a gas inlet hole facing the rear end side and a gas exhaust hole arranged on the front end side relative to the gas inlet hole. In the axial direction, a gap (G) is provided between the gas inlet hole and the front end facing surface of the main metal shell. When the gas inlet hole is viewed toward the rear end along the axial direction, the area (Sh) facing the front end facing surface of the main metal shell is at least 1 / 2 of the opening area (Sg) of the gas inlet hole. All of the component introduction holes are located closer to the front end side than the front end of the front end facing surface of the main metal shell. The distance (L1) of the gap (G) is smaller than the diameter (D) of the gas introduction hole.

2. A gas sensor, characterized in that: have: a sensor element extending in the axial direction and having a detection portion formed on the front end side thereof for detecting a gas to be detected via the element introduction hole; a cylindrical main metal housing, the main metal housing surrounding the radial circumference of the sensor element to hold the sensor element; as well as A single-layer cylindrical protective member is fixed to the periphery of the front end side of the main metal shell and surrounds the front end side of the sensor element. The protective member has a gas inlet hole facing the rear end side and a gas exhaust hole arranged on the front end side relative to the gas inlet hole. In the axial direction, a gap (G) is provided between the gas inlet hole and the front end facing surface of the main metal shell. When the gas inlet hole is viewed toward the rear end along the axial direction, the area (Sh) facing the front end facing surface of the main metal shell is at least 1 / 2 of the opening area (Sg) of the gas inlet hole. All of the component introduction holes are located closer to the front end side than the front end of the front end facing surface of the main metal shell. A distance (L1) of the gap (G) is smaller than a distance (L2) in a radial direction between the sensor element and the gas introduction hole.

3. The gas sensor according to claim 1 or 2, characterized in that The front end facing surface of the main metal shell is configured as a horizontal surface parallel to the radial direction and / or a tapered surface that narrows toward the front end side and faces radially outward.

4. The gas sensor according to claim 1 or 2, characterized in that When the gas introduction hole is viewed from the radially outer side, the interior of the protective member cannot be viewed.

5. The gas sensor according to claim 3, characterized in that When the gas introduction hole is viewed from the radially outer side, the interior of the protective member cannot be viewed.

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