Gas sensor

Abstract

To provide a gas sensor capable of further improving water resistance and responsiveness by using a protector.SOLUTION: A gas sensor 1 includes: a sensor element 21 extending in an axis O direction and having a detection portion formed at a tip side; a main metal fitting 11; and a closed-end cylindrical protector 51 fixed to the periphery of a tip side of the main metal fitting and surrounding the tip side of the sensor element. The protector has a gas introduction hole 56 disposed on a side surface and a gas discharge hole 53 disposed closer to the tip side than the gas introduction hole, and also surrounds the tip side of the sensor element and has an inner cylinder 60 disposed inside the protector. A tip 60a of the inner cylinder extends closer to the tip side than the gas introduction hole. An effective length L1 of the inner cylinder in an axial direction at the tip closer to the tip of the main metal fitting is a half or less of an effective length L2 of the protector in an axial direction, and the tip of the inner cylinder and an inner surface of the protector are not in contact with each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor equipped with a protector. [Background technology]

[0002] Conventionally, gas sensors have been known in which a sensor element is held in a cylindrical metal shell and the tip end of the sensor element, which is exposed to exhaust gas, is protected by a single or double protector. This protector has a gas inlet hole, but is required to be water-resistant to prevent condensed water mixed in the exhaust gas from reaching the sensor element, and to have responsiveness to quickly introduce exhaust gas into the detection section of the sensor element. Here, the sensor element is heated by its own heater or by high-temperature exhaust gas, and if condensed water comes into contact with the sensor element, thermal shock may occur, which may cause the element to crack.

[0003] Therefore, a technology has been developed in which the protector is made single-layered to improve responsiveness, and a gas inlet hole is provided in a horizontal step in the protector, bringing the gas inlet hole close to the tip side of the metal shell (Patent Document 1). According to this technology, exhaust gas first flows from the gas inlet hole toward the metallic shell on the rear end side, then changes direction in the internal space between the gas inlet hole and the metallic shell, and flows toward the front end side inside the protector. At this time, condensed water hits the front-facing surface of the metallic shell and breaks down into fine droplets, improving water resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-72458 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the gas introduction hole is provided in the horizontal step portion of the protector, there is a limit to improving the response. The present invention has been made in view of the above circumstances, and has as its object to provide a gas sensor that can further improve water resistance and responsiveness by using a protector. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the gas sensor of the present invention is a gas sensor including: a sensor element extending in an axial direction and having a detection portion formed on a tip side thereof; a cylindrical metal shell surrounding and holding the radial periphery of the sensor element; and a cylindrical protector fixed to the periphery of the tip side of the metal shell and surrounding the tip side of the sensor element, wherein the protector has a gas inlet hole arranged on a side surface thereof and a gas outlet hole arranged tipward of the gas inlet hole, and further has an inner tube surrounding the tip side of the sensor element and arranged inside the protector, wherein the tip of the inner tube extends tipward beyond the gas inlet hole, and an effective length L1 of the inner tube in the axial direction further tip than the tip of the metal shell is not more than half of an effective length L2 of the protector in the axial direction, and the tip of the inner tube and the inner surface of the protector are not in contact with each other.

[0007] In this gas sensor, the gas inlet is located on the side (side surface) of the protector, which allows the measurement gas, such as exhaust gas, to flow into the protector from the gas inlet more easily than when the gas inlet is located on the horizontal step of the protector, thereby improving responsiveness. However, in this case, condensed water contained in the measurement gas directly hits the sensor element inside the protector, reducing water resistance. Therefore, by arranging an inner cylinder inside the protector and surrounding the tip side of the sensor element, the inner cylinder prevents condensed water from coming into contact with the sensor element, thereby improving water resistance. As a result, it is possible to further improve (achieve) both water resistance and responsiveness by using a protector.

[0008] Here, by extending the tip of the inner cylinder further forward than the gas introduction hole, the side surface of the inner cylinder overlaps with the gas introduction hole, thereby reliably preventing condensed water from coming into contact with the sensor element from the gas introduction hole. Furthermore, since the effective axial length L1 of the inner tube is less than half the effective axial length L2 of the protector, the actual internal space of the protector without the inner tube increases, and the discharge of the measured gas from the gas inlet to the gas outlet is not hindered, thereby reliably improving responsiveness. Furthermore, since the tip of the inner tube and the inner surface of the protector are not in contact with each other, the measured gas can be more easily discharged from the space between the inner tube and the protector to the gas discharge hole, further improving responsiveness.

[0009] In the gas sensor of the present invention, an opening may be provided on a side surface of the inner cylinder, and the opening may not overlap with the gas introduction hole in a radial direction from the center of the inner cylinder to the outside. This gas sensor allows the measurement gas, such as exhaust gas, to easily flow into the sensor element through the opening, improving response. Furthermore, because the opening does not overlap with the gas inlet, the side of the inner cylinder does not lose its function of preventing condensed water from contacting the sensor element through the gas inlet, maintaining water resistance. The "radial direction from the center of the inner cylinder to the outside" also refers to the direction perpendicular to the axis of the gas inlet.

[0010] In the gas sensor of the present invention, the opening may be located closer to the rear end than the gas introduction hole. Condensed water that flows into the protector (the space between the protector and the inner cylinder) from the gas inlet hole falls toward the tip due to gravity. Therefore, if the opening is positioned toward the rear end of the gas inlet hole, condensed water can be prevented from entering the opening, improving water resistance.

[0011] In the gas sensor of the present invention, the sensor element may have an element introduction hole at a tip end thereof for introducing the gas to be detected into the detection portion, and the element introduction hole may overlap with the opening in the axial direction. According to this gas sensor, the measurement gas that has flowed into the inner cylinder from the opening can easily reach the detection section via the element introduction hole, thereby further improving the response. It should be noted that "the element introduction hole overlaps with the opening in the axial direction" means that the element introduction hole and the opening only partially overlap in the axial direction.

[0012] In the gas sensor of the present invention, the tip of the inner cylinder may be located further forward than the tip of the sensor element. According to this gas sensor, the inner cylinder covers the tip end side of the sensor element, thereby further improving water resistance.

[0013] In the gas sensor of the present invention, the protector may be the outermost layer. This gas sensor can further improve response compared to a double or more protector excluding the inner cylinder.

[0014] In the gas sensor of the present invention, the inner cylinder may have no bottom surface, and the tip of the inner cylinder may extend in the axial direction. With this gas sensor, the measurement gas inside the inner cylinder that comes into contact with the sensor element can be more easily exchanged than when the inner cylinder has a bottom surface, thereby further improving responsiveness. [Effects of the Invention]

[0015] According to the present invention, a gas sensor can be obtained that can further improve water resistance and responsiveness by using a protector. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a partially enlarged view of the protector and its vicinity in FIG. [Figure 3] FIG. 10 is a partial cross-sectional view showing a modified example of the gas sensor according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described in detail with reference to Figures 1 and 2. Figure 1 is a cross-sectional view of a gas sensor 1 according to an embodiment of the present invention, and Figure 2 is an enlarged view of a portion near a protector in Figure 1.

[0018] In FIG. 1, the gas sensor (wide-range air-fuel ratio gas sensor) 1 includes a sensor element 21, a holder (ceramic holder) 30 having a through hole 32 penetrating in the axial direction O and through which the sensor element 21 is inserted, a metal shell 11 surrounding the ceramic holder 30 radially, a protector 51, and an inner cylinder 60. The front end side of the sensor element 21, where the detection portion 22 is formed, protrudes further forward than the ceramic holder 30 and the metal shell 11. The sensor element 21 thus passed through the through hole 32 is fixed inside the metal shell 11 while maintaining airtightness in the front-to-rear direction by compressing a seal material (talc in this example) 41 arranged on the rear end face side (upper side in the figure) of the ceramic holder 30 in the front-to-rear direction via a sleeve 43 and a ring washer 45 made of an insulating material.

[0019] The rear end side 29 of the sensor element 21 protrudes rearward beyond the sleeve 43 and the metallic shell 11, and the electrode terminals 24 formed on the rear end side 29 are electrically connected by pressure contact with the terminal fittings 75 provided at the ends of the lead wires 71 that are drawn to the outside through a sealing material 85. The rear end side 29 of the sensor element 21, including the electrode terminals 24, is covered with an outer cylinder 81. This will be explained in more detail below.

[0020] The sensor element 21 extends in the direction of the axis O and is in the form of a strip (plate) with a detection section 22, consisting of detection electrodes (not shown) and adapted to detect a specific gas component in a gas to be detected, at its tip (lower side in the figure) facing the object to be measured. The cross section of the sensor element 21 is rectangular (rectangular) of a fixed size at both the front and rear ends, and is formed as an elongated structure made primarily of ceramic (solid electrolyte, etc.). The sensor element 21 itself is the same as a conventionally known sensor element, with a pair of detection electrodes forming the detection section 22 disposed at the tip end of the solid electrolyte (member), and an electrode terminal 24 connected to the detection electrodes and exposed at the rear end for connection to a lead wire 71 for extracting detection output.

[0021] In this example, a heater (not shown) is provided inside the front end of the ceramic material formed in a laminated state on the solid electrolyte (member) of the sensor element 21, and electrode terminals 24 for connecting lead wires 71 for applying voltage to the heater are formed and exposed on the rear end. Although not shown, these electrode terminals 24 are formed in a vertically elongated rectangular shape, and for example, at the rear end side 29 of the sensor element 21, three or two electrode terminals are lined up horizontally on the wide surfaces (both sides) of the strip plate. The detection section 22 of the sensor element 21 is covered with a porous protective layer 23 made of alumina, spinel, or the like. The sensor element 21 is also provided with an element introduction hole 25 that communicates with the detection section 22 and introduces the gas to be detected into the detection section 22, and a porous diffusion resistance layer (not shown) is disposed in the element introduction hole 25.

[0022] The metal shell 11 has a cylindrical shape with concentric front and rear ends but different diameters, and has a small-diameter cylindrical annular portion (hereinafter also referred to as the cylindrical portion) 12 at the front end for fitting and fixing a protector 51 (described later) thereto, and a larger-diameter screw 13 for fixing to an engine exhaust pipe is provided on the outer peripheral surface at the rear (upper part in the figure).Furthermore, behind this, there is a polygonal tool engaging portion 14 for screwing the sensor 1 with this screw 13.Furthermore, behind this tool engaging portion 14, there is a cylindrical portion 15 connected to which a protective tube (outer tube) 81 that covers the rear of the gas sensor 1 is fitted and welded, and behind this, there is a thin-walled cylindrical portion 16 for crimping that has a smaller outer diameter than the cylindrical portion 12.

[0023] 1, the crimping cylindrical portion 16 is bent inward for the purpose of post-crimping. A gasket 19 is attached to the underside of the tool engaging portion 14 for sealing when screwed in. On the other hand, the metallic shell 11 has an inner hole 18 penetrating therethrough 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 to the front end side.

[0024] A ceramic holder 30 made of insulating ceramic (e.g., alumina) and formed in a roughly short cylindrical shape is disposed inside the metal shell 11. The ceramic holder 30 has a front-facing surface 30a formed in a tapered shape that narrows toward the front end. A portion of the front-facing surface 30a near the outer periphery is engaged with the step portion 17, and the ceramic holder 30 is pressed from the rear end side by a sealing material 41, thereby positioning the ceramic holder 30 within the metal shell 11 and providing a clearance fit. On the other hand, the through hole 32 is provided in the center of the ceramic holder 30 and is a rectangular opening having substantially the same dimensions as the cross section of the sensor element 21 so that the sensor element 21 can pass through with almost no gap.

[0025] The sensor element 21 is inserted into the through-hole 32 of the ceramic holder 30 , and the tip 21 a of the sensor element 21 protrudes forward beyond the ceramic holder 30 and the tip 12 a of the metallic shell 11 .

[0026] On the other hand, the tip of the sensor element 21 is covered with a single-layered, bottomed, cylindrical protector (protective cover) 51. A step 51d is formed in the radial direction (perpendicular to the direction of the axis O) at a location near the rear end of the protector 51, and the diameter of the tip side of the step 51d is smaller. Gas introduction holes 56 are opened in the side surface (side surface along the axis O) of the protector 51 on the tip side of the step portion 51d. In this example, a plurality of gas introduction holes 56 (12 holes) are provided at equal intervals along the circumferential direction of the side surface of the protector 51.

[0027] Further, a horizontal step 60d is formed in a portion near the rear end of the inner cylinder 60 along the radial direction (direction perpendicular to the direction of the axis O), and the diameter of the portion on the tip side of the horizontal step 60d is smaller. The rear end of the inner cylinder 60 is fitted onto the cylindrical portion 12 of the metallic shell 11. Furthermore, the rear end of the protector 51 is fitted onto the rear end of the inner cylinder 60, and the rear ends of the inner cylinder 60 and the protector 51 are both welded to the cylindrical portion 12. In this way, the inner cylinder 60 is disposed inside the protector 51 with a radial gap therebetween.

[0028] Meanwhile, a gas exhaust hole 53 (one in this example) is provided in the center of the bottom 51a at the tip of the protector 51. The gas exhaust hole 53 is located closer to the tip than the gas inlet hole 56, and the gas inside the protector 51 is sucked out through the gas exhaust hole 53 by the flow of the detection target gas that flows through the attachment object (exhaust pipe, etc.) to which the gas sensor 1 is attached, and the detection target gas is introduced into the protector 51 through the gas inlet hole 56 due to the negative pressure. 1, the center of bottom 51a at the tip of protector 51 is cut and raised toward the rear end along two parallel slits to form cover 51f, and gas discharge hole 53 is formed facing radially in the gap between bottom 51a of protector 51 and cover 51f. In this case, when protector 51 is viewed from the tip side in the direction of axis O, gas discharge hole 53 is not directly visible, so that water droplets such as condensed water can be prevented from entering inside protector 51 through gas discharge hole 53.

[0029] As shown in FIG. 1, each electrode terminal 24 formed on the rear end side 29 of the sensor element 21 is electrically connected to each terminal fitting 75 provided at the tip of each lead wire 71 drawn to the outside through a sealing material 85 by being pressed against it by its spring property. In the gas sensor 1 of this embodiment, the terminal fittings 75 including the pressure-contact portions are disposed opposite each other in respective housing portions provided in an insulating separator 91 disposed in the outer cylinder 81.

[0030] The separator 91 is restricted from moving radially and toward the tip end via a holding member 82 that is fixed by crimping inside the outer cylinder 81. The tip end of the outer cylinder 81 is fitted onto and welded to the cylindrical portion 15 on the rear end side of the metallic shell 11, thereby covering the rear of the gas sensor 1 in an airtight manner. The lead wire 71 is passed through a sealing material (e.g., rubber) 85 arranged inside the rear end of the outer tube 81 and is pulled out to the outside, and the small diameter tube portion 83 is crimped to reduce the diameter and compress the sealing material 85, thereby maintaining airtightness in this area.

[0031] Incidentally, a step 81d having a larger diameter at the front end is formed slightly rearward from the center of the outer cylinder 81 in the direction of the axis O, and the inner surface of this step 81d supports and pushes the rear end of the separator 91 forward. Meanwhile, a flange 93 formed on the outer periphery 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 the axis O by the step 81d and the holding member 82.

[0032] Next, the characteristic features of the present invention will be described. As shown in FIGS. 1 and 2, in this embodiment, a gas introduction hole 56 is arranged on the side surface (side face) of the protector 51. This allows the measurement gas, such as exhaust gas, to flow more easily into the protector 51 through the gas inlet 56 than when the gas inlet is provided in the horizontal step of the protector, improving responsiveness. However, in this case, condensed water contained in the measurement gas directly hits the sensor element 21 inside the protector 51, reducing water resistance. Therefore, by placing an inner cylinder 60 inside the protector 51 and surrounding the tip side of the sensor element 21, the inner cylinder 60 prevents condensed water from coming into contact with the sensor element 21, thereby improving water resistance. As described above, the use of the protector 51 can further improve (achieve) both water resistance and responsiveness.

[0033] Here, since the tip 60a of the inner tube 60 extends further forward than the gas introduction hole 56, the side surface of the inner tube 60 overlaps with the gas introduction hole 56, thereby reliably preventing condensed water from coming into contact with the sensor element 21 from the gas introduction hole 56. Furthermore, since the effective length L1 of the inner tube 60 in the axial direction O at the point further forward than the tip 12a of the metallic shell 11 is equal to or less than half the effective length L2 of the protector 51 in the axial direction O, the actual internal space of the protector 51 without the inner tube 60 increases, and the discharge of the gas to be measured from the gas inlet hole 56 to the gas outlet hole 53 is not hindered, thereby reliably improving responsiveness. Furthermore, since the tip 60a of the inner tube 60 and the inner surface of the protector 51 are not in contact with each other, the gas to be measured can be more easily discharged from the space between the inner tube 60 and the protector 51 to the gas discharge hole 53, thereby further improving responsiveness.

[0034] The effective lengths L1 and L2 refer to the lengths of the inner spaces of the inner cylinder 60 and the protector 51, respectively, in the direction of the axis O, at points further forward than the front end 12a of the metal shell 11. Here, an inner hole 18 is formed on the rear end side of the front end 12a of the metallic shell 11, and the inner hole 18 also forms a kind of space. However, since the atmosphere and the gas to be measured remain near the inner hole 18 and the degree of gas exchange is low, the rear end side of the front end 12a of the metallic shell 11 is excluded from the calculation of the effective lengths L1 and L2.

[0035] Specifically, in FIG. 1, the internal space of the inner cylinder 60 is defined by the region from the front end 12 a of the metal shell 11 to the front end of the inner cylinder 60 . 1, the horizontal step 60d of the inner cylinder 60 overlaps the front end 12a of the metal shell 11, so the internal space of the protector 51 is defined by the region from the horizontal step 60d to the inner surface of the front end of the protector 51.

[0036] For example, as shown in FIG. 3 , when the inner cylinder 68 is press-fitted into the annular portion 12 of the metallic shell 11, the horizontal step portion of the inner cylinder does not overlap the tip 12 a of the metallic shell 11, and therefore the internal space of the protector 58, and therefore the effective length L2, is defined on the tip side of the tip 12 a of the metallic shell 11.

[0037] As shown in FIG. 2, in this embodiment, an opening 60h may be provided on the side surface of the inner cylinder 60 (the side surface along the axis O), and the opening 60h may not overlap with the gas introduction hole . This allows the measurement gas, such as exhaust gas, to easily flow into the sensor element 21 through the opening 60h, improving responsiveness. In addition, since the opening 60h does not overlap with the gas inlet hole 56, the function of the side surface of the inner cylinder 60 to prevent condensed water from coming into contact with the sensor element 21 from the gas inlet hole 56 is not impaired, and water resistance can be maintained.

[0038] Note that "the opening 60h does not overlap with the gas introduction hole 56" means that it does not overlap in the circumferential direction of the inner tube 60 and the protector 51, does not overlap in the axial direction O of the inner tube 60 and the protector 51, or does not overlap in both the circumferential direction and the axial direction O. In this example, a plurality of (12) openings 60h are provided at equal intervals along the circumferential direction of the side surface of the inner cylinder 60.

[0039] As shown in FIG. 2, in this embodiment, the opening 60h may be located closer to the rear end than the gas introduction hole 56. Condensed water that flows into the inside of the protector 51 (the space between the protector 51 and the inner cylinder 60) from the gas introduction hole 56 falls toward the tip side due to gravity. Therefore, if the opening 60h is positioned closer to the rear end than the gas introduction hole 56, it is possible to prevent the condensed water from entering the opening 60h, thereby improving water resistance.

[0040] As shown in FIG. 2, in this embodiment, the element introduction hole 25 of the sensor element 21 may overlap with the opening 60h in the axis O direction. In this way, the measurement gas that has flowed into the inner cylinder 60 from the opening 60h can more easily reach the detection section 22 via the element introduction hole 25, thereby further improving the response.

[0041] As shown in FIG. 2, in this embodiment, the tip 60a of the inner cylinder 60 may be located closer to the tip side than the tip 21a of the sensor element 21. In this way, the inner cylinder 60 covers the tip end side of the sensor element 21, thereby further improving water resistance.

[0042] In this embodiment, the protector 51 may be the outermost layer, in other words, the protector 51 may be a single-layer protector. In this way, the response can be further improved compared to a double or more protector excluding the inner cylinder 60.

[0043] In this embodiment, the inner cylinder 60 may not have a bottom surface, and the tip 60a of the inner cylinder 60 may extend in the direction of the axis O (straight). In this way, the measurement gas inside the inner cylinder 60 that comes into contact with the sensor element 21 can be more easily exchanged than when the inner cylinder 60 has a bottom surface, thereby further improving responsiveness.

[0044] It is preferable that the minimum radial clearance between the protector 51 and the inner cylinder 60 is 0.5 mm or more. If the minimum clearance is less than 0.5 mm, gas exchange between the protector 51 and the inner cylinder 60 may become difficult.

[0045] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and can be embodied in various forms without departing from the spirit of the present invention. For example, when cutting the metal material that will become the metallic shell, the inner cylinder may also be machined out, and the inner cylinder may be formed integrally with the metallic shell. The sensor element is not limited to one that measures the concentration of oxygen, but may be one that measures the concentration of nitrogen oxides (NOx) or hydrocarbons (HC), etc. The sensor element may be cylindrical. The shape and number of the gas introduction holes and openings are not limited, and may be, for example, elliptical. The shape of the front end-facing surface of the metallic shell is also not limited to the above. The protector and the inner cylinder are not limited to being cylindrical, but may be, for example, an elliptical cylinder. [Explanation of symbols]

[0046] 1 Gas sensor 11 Metal body 21 Sensor element 21a Tip of sensor element 22 Detection unit 25 Element introduction hole 51,58 Protector 53 Gas exhaust hole 56, 562 Gas inlet 60,68 Inner cylinder 60a Tip of inner cylinder 60h opening O axis

Claims

1. a sensor element extending in an axial direction and having a detection portion formed at a tip end thereof; a cylindrical metallic shell that surrounds and holds the sensor element in a radial direction; a cylindrical protector with a bottom that is fixed to the periphery of the tip end of the metallic shell and surrounds the tip end of the sensor element; A gas sensor comprising: the protector has a gas inlet hole disposed on a side surface and a gas outlet hole disposed on a tip side of the gas inlet hole, The sensor element further includes an inner cylinder that surrounds the tip end side of the sensor element and is disposed inside the protector, the tip of the inner cylinder extends further to the tip side than the gas introduction hole, an effective length L1 of the inner cylinder in the axial direction at a point further forward than the tip of the metallic shell is equal to or less than half an effective length L2 of the protector in the axial direction, and wherein the tip of the inner cylinder and the inner surface of the protector are not in contact with each other.

2. An opening is provided on a side surface of the inner cylinder, 2. The gas sensor according to claim 1, wherein the opening does not overlap with the gas introduction hole in a radial direction from the center of the inner cylinder to the outside.

3. 3. The gas sensor according to claim 2, wherein the opening is located rearward of the gas inlet hole.

4. the sensor element has an element introduction hole at a tip end thereof for introducing a gas to be detected into the detection portion; 3. The gas sensor according to claim 1, wherein the element introduction hole overlaps with the opening in the axial direction.

5. 3. The gas sensor according to claim 1, wherein the tip of the inner cylinder is located closer to the tip of the sensor element.

6. 3. The gas sensor according to claim 1, wherein the protector is an outermost layer.

7. 3. The gas sensor according to claim 1, wherein the inner cylinder has no bottom surface, and the tip of the inner cylinder extends in the axial direction.

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