JP2014228313A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a length of an element smaller and shorter by improving a fitting structure of a tip end side of the element without reducing a projection length of the tip end side of the element in a gas sensor wherein the inside of a cylindrical fitting body is disposed with a holder formed with a penetration hole penetrating a front and a rear end, and a band-plate like sensor element provided with a porous protection layer covering a detection part of the tip end side is inserted into the penetration hole, and the tip end including the porous protection layer is projected from a tip of the tip end of the holder.SOLUTION: A recessed part 35 recessed toward a rear side is provided for a region surrounding a penetration hole 38 inside a tip end facing surface of a holder 31, and a space is formed so as to be held between an inner peripheral surface 36 of the recessed part 35 and an outer peripheral surface of a porous protection layer 25. A sensor element 21 makes a rear end 26 of the porous protection layer 25 penetrate into the recessed part 35. Because of the penetration of the rear end 26 into the recessed part 35, even if a length of a front and a rear end is the same, the shortening of the projection length of a tip end side of the sensor element 21 can be achieved, and thus, a full length of the sensor element 21 can be shortened.

Description

  The present invention relates to a gas sensor such as an oxygen gas sensor, a NOx gas sensor, or an HC gas sensor for detecting a specific gas concentration in a gas to be measured such as exhaust gas.

  In such a gas sensor (for example, an oxygen sensor), a sensor having a strip shape or a rod shape made of a solid electrolyte having oxygen ion conductivity in which a pair of electrodes (detection electrodes) are provided on the tip side forming the detection portion. Some elements (hereinafter also simply referred to as elements) are used. Such a gas sensor (hereinafter also referred to simply as a sensor) has an insulating material (inside) inside a metal fitting body (main metal fitting) formed in a cylindrical shape with a screw portion attached to an exhaust gas pipe of an engine, for example. A holder made of ceramic (for example, alumina), that is, a member for positioning the element is disposed. Then, the sensor element is made to project forward from the tip of the holder to the through hole provided in the holder so as to penetrate through the tip, and the projecting part including the sensor is measured. It has the structure exposed to object gas (for example, refer patent document 1 (FIG. 1)). Such a gas sensor is fixed to the exhaust pipe through a screw portion of the metal fitting body by screwing, and the tip end side of the element protrudes into the exhaust pipe to be exposed to the exhaust gas, and is generated based on the gas concentration difference. It is used for air-fuel ratio control by outputting an electric signal to an ECU (Engine Control Unit) provided outside via an electric lead connected to an electrode terminal provided near the rear end of the element. The

  In this type of gas sensor, a protector (with a vent hole at an appropriate position at the tip of the metal fitting body) is provided to protect the tip portion (detection portion) of the element exposed to the exhaust gas and make the detection portion difficult to get wet. In addition to that, a spinel, alumina, etc. are provided on the surface of the element (self) in order to prevent deterioration of detection performance due to foreign matter at the tip part and prevention of cracking due to water adhesion. Usually, a protective layer (porous protective layer) made of a porous film is coated and formed. In particular, the element may be provided with a heater for shortening the time to the temperature for activating the solid electrolyte forming the element, and in such an element, as a countermeasure against damage due to thermal shock caused by water contained in the gas. In addition, the porous protective layer is coated and formed in a predetermined range (region) from the tip to the rear.

  By the way, about the sensor element which comprises this kind of gas sensor, noble metals, such as platinum, are used for conductors (conductive layer), such as an electrode provided inside and outside and an electrode for energizing a heater. For this reason, as the front and rear length of the element increases, the amount of use increases and the cost increases. Therefore, there is a demand for shortening the length of the head in order to reduce costs. In addition to the reduction of the amount of precious metals used, not only the demand for energy saving such as the reduction of power consumption, but also the recent shortening or miniaturization has been demanded. As for the shortening of the sensor element, for example, it is conceivable to shorten the protruding amount (protruding length) of the rear end portion protruding behind the holder provided in the metal fitting body, but this naturally has a limit. This is because the rear end portion of this element is formed with an electrode terminal that forms a contact point with a terminal (terminal fitting) provided at the leading end of a lead wire drawn out to the outside. In order to improve reliability, a predetermined front and rear length (dimension) is required on the formation surface. Further, at the contact, it is necessary to avoid the thermal influence received from the tip side of the element. For this purpose, the position of the electrode terminal is desired to be as far as possible from the tip of the element that is at a high temperature. For these reasons, there is a limit to shortening the length dimension of the element on the rear end side of the holder.

JP 2012-189579 A

  Therefore, how to reduce the tip side that protrudes forward from the tip of the holder, that is, the side opposite to the rear end of the sensor element, that is, the tip that is exposed to the gas to be measured. Is an issue. However, in order to improve the detection performance, the detection electrode needs to be easily exposed to the gas to be measured, and in this sense, it is not preferable to reduce the protrusion length on the tip side.

  On the other hand, this element is arranged through a through-hole provided through the front and rear in the holder. The cross-section of this through-hole is filled and compressed on the rear end side of the holder inside the metal fitting body. In order to hold the sealing material (talc), to position the element, and to ensure the stability of the holding, the cross-section (shape and size) through which the element passes almost without any gap. On the other hand, as described above, the porous protective layer is coated and formed on the surface of the portion near the tip protruding from the tip of the holder in a predetermined range from the tip to the rear, including the detection electrode forming portion. Is done. And the thickness is as thick as about 0.2-0.3 mm. For this reason, in order to assemble it through the through hole of the holder, the rear end of the element is passed through the through hole from the front end side of the holder. Further, in order to protect the element, this porous protective layer should be provided in a predetermined front and rear region from the front to the rear, and it is not preferable to shorten the formation region. Therefore, including these circumstances, there is a problem that it is not easy to shorten the length of the tip portion of the element protruding from the tip of the holder.

  The present invention has been made in view of such a problem, and for the porous protective layer formed in the portion near the tip of the element, a necessary front-and-rear length is ensured and the tip of the element protrudes from the tip of the holder. It is an object of the present invention to provide a gas sensor structure capable of realizing a shortening of an element by improving the mounting structure on the tip side of the element without causing a decrease in length and a decrease in detection performance due to the decrease. .

According to the first aspect of the present invention, a holder in which a through-hole penetrating through is formed inside a metal fitting body having a cylindrical shape, and a detector is provided on the tip side of the through-hole. A sensor element in the form of a strip or a rod having a porous protective layer coated in a predetermined range from the tip to the rear is passed through, and the sensor element projects the tip forward from the tip of the holder, and In the gas sensor provided by positioning the rear end of the porous protective layer at the tip of the through hole or ahead of the tip,
The holder has a concave portion that is recessed rearward with respect to a region surrounding the through hole when viewed from the tip-facing surface;
The sensor element is provided such that the rear end of the porous protective layer enters the recess and is positioned behind the front end of the holder;
The recess is formed such that a space can be maintained between the inner peripheral surface of the recess and the outer peripheral surface of the porous protective layer.

According to a second aspect of the present invention, in the holder, the outer peripheral surface is circular when viewed from the front end side, and the inner peripheral surface of the concave portion is cylindrical. It is a gas sensor of description.
According to a third aspect of the present invention, the front end side of the metal fitting main body is provided with a vent hole having a cylindrical wall that surrounds and surrounds the front end portion of the sensor element protruding forward from the front end of the holder. The protector is attached with a multi-layer structure,
Among the multi-layered protectors, the cylindrical wall of the innermost protector has the vent hole provided at a portion corresponding to the porous protective layer provided on the front end side of the sensor element in the front-rear direction. On the other hand, the protector outside the protector on the inside is provided so that the cylindrical wall covers the vent hole,
In addition, when the inner diameter of a portion of the cylindrical wall of the inner protector corresponding to the porous protective layer is D1, and the inner diameter of the recess is D2, the relation of D1> D2 is established. The gas sensor according to claim 2.

According to a fourth aspect of the present invention, an annular portion having an inner diameter smaller than the outer diameter of the holder is provided on the distal end side of the metal fitting body, and the holder has an inner portion of the annular portion at the distal end surface. It is placed on an annular shelf provided at the rear of the peripheral surface and is arranged inside the metal fitting body,
When the inner diameter of the annular portion is D3, D3 and the inner diameter D2 are
The gas sensor according to claim 3, wherein a relationship of D3> D2 is satisfied.
In the present invention according to claim 5, the front end of the sensor element protrudes ahead of the front end of the metal fitting body, the protrusion dimension is L5, and the rear end of the porous protective layer in the sensor element is the When the dimension that is inserted into the recess and positioned behind the tip of the holder is L3,
The gas sensor according to any one of claims 1 to 4, wherein a relationship of L5> L3 is satisfied.

  In the present invention, since it has the above configuration, even if the range of the front and rear length of the porous protective layer of the sensor element is the same as that of the conventional sensor element, the rear end of the porous protective layer enters the recess. Therefore, the protrusion length protruding from the tip of the holder on the tip side of the element can be shortened. As a result, according to the present invention, the total length of the element can be shortened corresponding to the shortening, so that the amount of noble metals such as Pt used for forming the element can be reduced, and power saving can be achieved. Figured. Moreover, of the tip portion of the element, the portion protruding toward the front from the bottom surface of the recess (tip of the through hole) is in a state where it can be exposed to gas even if it is in the recess. In other words, the protrusion length protruding from the tip of the holder among the portions near the tip of the element can be regarded as the protrusion length protruding from the bottom surface of the recess in the present invention. Therefore, by ensuring the bottom surface (transverse section) of the recess as large as possible and securing the protruding length as in the conventional case, the extent to which the detection unit provided on the tip side of the element is exposed to gas is the same as in the conventional case. Degree or close to it. As a result, the length of the element can be shortened while suppressing a decrease in detection performance.

  As described above, according to the present invention, the porous protective layer formed in the portion near the tip of the element has a necessary front-and-rear length (front-and-rear length), and does not deteriorate the detection performance. By improving the mounting structure, the overall length of the element can be shortened. According to the present invention, the rear end of the porous protective layer may be brought into contact with the tip of the through hole, that is, the bottom surface of the concave portion. It is preferable for preventing interference or collision when assembling through the hole.

  In general, the through hole provided in the holder has the same shape and size as the cross section of the element so that there is almost no gap (a minute gap) when passing through the through hole. . In other words, if the element is in the shape of a long strip (or square bar), and the cross-sectional shape of the element is rectangular, the through hole provided in the holder for passing the element fits the element with a small gap. If the element has a round bar shape, the through hole is a circular through hole having the same diameter. On the other hand, the holder itself is usually made of ceramic because of the requirement of ensuring electrical insulation and heat resistance, and the outer shape of the holder is circular when viewed from the tip side, except for the through hole. For example, a cylindrical shape. Therefore, in order to ensure uniform thickness and eliminate the occurrence of ceramic firing strain and stress concentration, the holder is preferably configured as described in claim 2. However, in the present invention, the inner peripheral surface of the concave portion of the holder may be a polygon as viewed from the front end side (as viewed from the axial direction), but in that case, a polygon that is as close to a circle as possible with as many corners as possible. It is good to do.

  In the present invention, in order to shorten the sensor element, the concave portion provided on the front end surface of the holder is deepened (the depth of the concave recessed toward the rear), and the rear end of the porous protective layer is as much as possible. It can be said that it is better to be located in the back (behind the recess). On the other hand, in this type of gas sensor, as described above, a protector is attached to protect the tip portion of the element. Moreover, in recent years, the protector is attached in a multi-layer structure (usually a two-layer structure) in order to improve the protection performance. Further, in the gas sensor of the present invention, the gas to be measured does not stay inside the protector, but smoothly flows in the entire area inside the protector and protrudes from the tip of the through hole of the holder. It is preferable in view of gas concentration detection performance to come in contact with the gas. On the other hand, when the holder of the present invention has a cylindrical inner peripheral surface as described in claim 2, the inner peripheral surface of the protector is also cylindrical, and the inner diameter D2 of the concave portion is If it is larger than the inner diameter D1 of the protector, the space inside the protector becomes wider (backward). As a result, the gas entering the concave portion tends to stay in the depth, and therefore the detection accuracy of the concentration of the gas flowing in the exhaust pipe to be measured is lowered. For this reason, even if the inner diameter D2 of the recess is preferably as large as possible, the inner diameter D1 of the cylindrical wall of the inner protector is made larger than the inner diameter D2 of the recess as in the invention described in claim 3. Should. In addition, in the outside protector, the vent hole provided in the portion corresponding to the porous protective layer of the inside protector is covered in order to make the detection part difficult to get wet. In order to secure the thickness of the concave portion in the radial direction in the holder and increase the strength thereof, it is preferable that the invention according to claim 4 is used. Further, as in the fifth aspect of the invention, it is preferable to relatively increase the dimension for projecting the tip of the element ahead of the tip of the metal fitting body in order to improve the gas concentration detection (measurement) responsiveness. .

The front longitudinal cross-sectional view and principal part enlarged view of embodiment which actualized the gas sensor of this invention. The further enlarged view of the principal part enlarged view of FIG. FIG. 3 is a cross-sectional view taken along line S1-S1 in FIG. FIG. 3 is a cross-sectional view taken along line S2-S2 of FIG. The expanded half sectional view explaining the part which has passed the element through the through-hole of the holder. The figure which looked at FIG. 5 from the bottom (tip side). FIG. 6 is a cross-sectional view taken along line S3-S3 in FIG. Explanatory drawing of the process of fixing a sensor element to a metal fitting body. The figure explaining the last process of manufacture of the gas sensor of FIG. 1, and an assembly. Sectional drawing equivalent to the S3-S3 arrow directional cross-sectional view of FIG. 5 explaining another example of a holder.

  The form for implementing the gas sensor of this invention is demonstrated in detail based on FIGS. However, this embodiment is embodied in an all-range air-fuel ratio gas sensor that detects the oxygen concentration in the exhaust gas. Therefore, first, the overall configuration of the gas sensor will be outlined first, and then the configuration of each gas sensor will be further described together with each part. This will be described in detail. In the figure, reference numeral 1 denotes an all-range air-fuel ratio gas sensor, in which a holder 31 having a through-hole 38 penetrating through the inside is disposed inside a cylindrical metal fitting body 11 (hereinafter also simply referred to as the main body 11). The sensor element 21 having a band plate shape or a rod shape is passed through the through hole 38 of the holder 31, and a portion closer to the distal end where the detection unit 22 is formed projects forward from the distal end surface (tip) 32 of the holder 31. I am letting. The sensor element 21 passed through the through hole 38 in this way has a sealing material (talc in this example) 41 disposed on the rear end surface 39 side (the upper side in the drawing) of the holder 31 as a press ring (sleeve) made of an insulating material. By compressing in the front-rear direction via 43 or the like, the inner side of the metal fitting body 11 is fixed while being kept airtight in the front-rear direction. The portion near the rear end 29 including the rear end 29 of the element 21 protrudes rearward from the presser ring 43 and the metal fitting body 11, and is connected to each electrode terminal (not shown) formed near the rear end 29. A terminal fitting 75 provided at the tip of each lead wire 71 drawn out through the sealing material 85 is pressed and electrically connected. Further, the portion near the rear end 29 of the element 21 including this electrode terminal is covered with a protective cylinder 81. This will be described in more detail below.

  The sensor element 21 is in the form of a strip (plate) having a detection unit 22 made of a detection electrode or the like (not shown) on the distal end side (lower side in the drawing) directed toward the measurement object, and has a transverse section. The rectangular shape (rectangular shape) of a certain size is formed before and after (see FIG. 3 and FIG. 4), and it is formed as an elongated body mainly composed of a solid electrolyte and ceramic. However, a porous protective layer 25 made of alumina, spinel, or the like is coated and formed in a predetermined range L1 extending rearward from the tip 23 of the element 21 near the tip. The cross section is increased by the thickness of the layer 25 (for example, 0.2 to 0.3 mm) (the thickness is exaggerated). The sensor element 21 itself is the same as a conventionally known one, and is arranged at a portion near the front end of the solid electrolyte (member) to form a detection unit 22 and a pair of detection electrodes that are connected to this and located near the rear end. The electrode terminal (not shown) for connecting the lead wire 71 for taking out the detection output is exposed. In this example, a heater (not shown) is provided inside the element 21 near the tip of the ceramic material formed in a laminated form on the solid electrolyte (member). An electrode terminal (not shown) for connecting a lead wire 71 for applying a voltage to the heater is exposed. Although not shown in the figure, these electrode terminals are formed in a vertically long rectangle such that three or two of the electrode terminals are arranged side by side on the wide surface (both sides) of the band plate, for example, at a portion near the rear end 29 of the element 21. .

  The metal fitting body 11 constituting the sensor 1 of the present example has a cylindrical shape with concentric and different diameters in the front and rear, a small diameter at the tip side, and a cylindrical annular portion (hereinafter referred to as a cylinder) for externally fitting and fixing a protector described later. A screw 13 for fixing to an engine exhaust pipe having a larger diameter is provided on the outer peripheral surface behind (in the drawing). In addition, a polygonal portion 14 for screwing the sensor 1 with the screw 13 is provided behind it. Further, behind the polygonal portion 14, a cylindrical portion 15 for externally fitting and welding a protective cylinder (outer cylinder) 81 that covers the back of the gas sensor 1 is provided, and the outer diameter is provided behind it. A small and thin caulking cylindrical portion 16 is provided. The caulking cylindrical portion 16 is bent inward in FIG. 1 after caulking. On the other hand, the inner peripheral surface of the small-diameter annular portion (cylindrical portion) 12 on the distal end side of the annular shelf 17 having a tapered taper is formed at the rear (upper side in the drawing) following the inner peripheral surface 12b near the distal end 12a. And is formed on a cylindrical surface 18 having the same inner diameter. A gasket 19 for sealing at the time of screwing is attached to the lower surface of the polygonal portion 14.

  In this example, a holder 31 formed in an approximately short cylindrical shape from an insulating material (for example, alumina) is disposed inside the main body 11 and is placed on the annular shelf 17. Yes. However, the holder 31 is formed such that the outer peripheral portion 32b of the tip end surface 32 is tapered and is placed and positioned on the annular shelf 17 (see FIG. 2). Further, the holder 31 is formed so that the outer peripheral surface 34 is in a gap-fitting state with respect to the cylindrical surface 18 inside the main body 11. The holder 31 is provided with a through-hole 38 that passes through the holder 31 at the center corresponding to the axis G of the metal fitting body 11. However, the through-hole 38 is a rectangular opening having substantially the same size as the transverse section so that a portion of the element 21 that is not covered or formed by the porous protective layer 25 passes through with almost no gap. ing. In addition, a concave portion 35 that is recessed backward with a predetermined depth L2 is provided in a region surrounding the through hole 38 in the tip-facing surface of the holder 31.

  In this example, the concave portion 35 has a circular shape that is concentric with the outer peripheral surface 34 when viewed from the distal end surface 32 (see FIGS. 5 to 7). The portion close to the tip (the porous protective layer 25) is set to a size that allows the space K to enter the space (see FIGS. 2, 5, and 6). However, the diameter (inner diameter) D2 of the recess 35 is made smaller than the inner diameter D1 of a protector (cylindrical wall of the inner protector) described later, and this D2 is a holder at the tip of the metal fitting body 11. It is smaller than the inner diameter D3 of the cylindrical portion 12 that is smaller than the outer diameter of 31. However, the inner diameter D2 is smaller than the inner diameter D1 of the protector, which will be described later, and the inner diameter D3 of the cylindrical portion 12 at the tip of the metal fitting body 11, but is close to them (see FIGS. 1 to 7). The bottom surface 37 (the tip of the through hole 38) 37 in the back of the recess 35 is a flat surface. In this example, the sensor element 21 having a belt-like shape is passed through the through hole 38 of the holder 31, and the tip 23 of the element 21 is ahead of the tip surface 32 of the holder 31 and the tip 12 a of the metal fitting body 11. Protruding. In addition, the part near the rear end 26 of the porous protective layer 25 is inserted into the recess 35, and the rear end 26 is located behind the front end (front end surface 32) of the holder 31 by an appropriate amount L 3.

  Since the gas sensor 1 of this example has such a configuration, the details will be described later. Even though the front and rear length L1 of the porous protective layer 25 of the sensor element 21 is the same as that of the conventional sensor element 21, the holder 31 The protrusion length L4 on the front end side of the sensor element 21 protruding from the front end 32 can be reduced. That is, since the rear end 26 of the porous protective layer 25 enters the concave portion 35, the projecting length L4 can be shortened, so that the total length of the element 21 can be shortened. Note that the closer the rear end 26 of the porous protective layer 25 is to the bottom surface 37 (the front end of the through hole 38) 37 of the recess 35, the more effective the shortening of the porous protective layer 25 is. May be at the same position as the bottom surface 37 of the recess 35. In addition, the tip 23 of the element 21 protrudes further forward than the tip 12a of the metal fitting body 11. The protruding dimension L5 is relatively larger than the dimension L3 to detect the gas concentration (measurement). ) It is preferable for improving responsiveness.

  In the gas sensor 1 of the present example, as described above, the seal material (talc in this example) 41 is arranged in a filled state on the rear end surface 39 side (the upper side in the drawing) of the holder 31 provided in the metal fitting body 11. A presser ring 43 is disposed behind the sealing material 41, and a thin caulking cylindrical portion 16 connected to the cylindrical portion 15 near the rear end of the main body 11 is bent inward through a ring washer 45 and the tip is bent. Compressed on the side. And by this compression, the internal sealing material 32 grade | etc., Is compressed, and the element 21 is being fixed to the inner side of the metal fitting main body 11 airtightly.

  The element 21 is fixed in such a manner that the rear end 29 of the element 21 is connected to each of the through holes provided in the holder 31, the sealing material 41, and the presser ring 43 as shown in the upper left diagram of FIG. 8. As shown in the lower part of the left figure of FIG. 8, this assembled work product is inserted (arranged) inside the metal fitting body 11. Then, a ring washer 45 is disposed at the rear end of the presser ring 43 and inside the caulking cylindrical portion 16 at the rear end of the main body 11, and the tip 23 of the element 21 is projected by an appropriate amount. Next, the tip 12a of the metal fitting body 11 in this state is positioned and supported by a jig 201 as shown in the right figure of FIG. In this support, the lower surface of the polygonal portion 14 of the metal fitting body 11 is brought into contact with the positioning portion 205 of the jig 201. Thereafter, the crimping cylindrical portion 16 is compressed to the tip side and bent inward with a crimping die 210 as illustrated in FIG. As a result, the parts including the element 21 and the holder 31 are fixed to the inside of the metal fitting body 11, and the protrusion length L4 is obtained from the tip of the holder 31 at the tip 23 of the element 21. In addition, in the center of the seal material (talc molding) 41 before compression and the presser ring 43, a rectangular hole whose cross section corresponds to the cross section of the element 21 when viewed from the direction of the axis G is provided, like the holder 31. Is provided.

  On the other hand, returning to FIG. 1, the tip portion of the element 21 is covered with bottomed cylindrical protectors (protective covers) 51 and 61 each having a two-layer structure and both having vent holes (holes). Yes. Among these, the inner protector 51 has a cylindrical shape with a different diameter that expands from the tip to the rear in three stages, and a large-diameter cylindrical portion 55 at the upper end thereof is an annular portion (cylindrical portion) 12 at the tip of the metal fitting body 11. And is welded (see FIG. 2). Note that the intermediate medium-diameter cylindrical portion 54 has a long cylindrical wall 54a having the same diameter with respect to the small-diameter cylindrical portion 53 at the front end, and is provided on the front end side of the element 21 in a portion closer to the rear end. For example, eight vent holes 56 are provided in the circumferential direction at portions corresponding to the porous protective layer 25. The inner diameter D1 of the cylindrical wall 54a forming the medium diameter cylindrical portion 54 is set to be the same as or smaller than the inner diameter D3 of the cylindrical portion 12 at the tip of the metal fitting body 11, but as described above, It is larger than the inner diameter D2 of the recess 35. Further, for example, four vent holes 56 are provided in the circumferential direction in the small diameter cylindrical portion 53 at the tip.

  Further, the outer protector 61 has a cylindrical shape with a different diameter that expands in two steps from the front end side, and a large-diameter cylindrical portion 65 at the upper end thereof is externally fitted to the large-diameter cylindrical portion 55 of the inner protector 51, At the same time, it is welded to the cylindrical portion 12 at the tip of the metal fitting body 11. The inner diameter of the large diameter cylindrical portion 65 of the outer protector 65 is the same as the outer diameter of the large diameter cylindrical portion 55 of the inner protector 51. The tip of the inner protector 51 has a front-rear length located at a portion closer to the tip of the medium-diameter cylindrical portion 54, and the cylindrical wall 65 a corresponds to the porous protective layer 25 in the inner protector 51. The vent hole 56 is covered. The vent holes 67 of the outer protector 61 are provided, for example, at eight positions in the circumferential direction near the tip of the large-diameter cylindrical portion 65, and are also provided at the center of the bottom of the small-diameter cylindrical portion 63 at the tip. . The small-diameter cylindrical portion 63 at the tip of the outer protector 61 has its rear end fitted to the tip of the medium-diameter cylindrical portion 54 of the inner protector 51. Thus, when the gas sensor 1 is attached to the exhaust pipe and the gas flows through the exhaust pipe, the gas flowing from the upstream to the downstream passes through the vent hole 67 of the outer protector 61 and is located between the inner and outer protectors 51 and 61. It enters and flows through the vent hole 56 of the inner protector 51 so as to come into contact with the tip portion of the element 21. Then, the air enters the space between the inner and outer protectors 51 and 61 through the vent hole 56 of the inner protector 51 and flows downstream through the vent hole 67 of the outer protector 61.

  In the gas sensor 1 according to the present embodiment, as described above (see FIG. 1), each lead wire that is led to the outside through the sealing material 85 is connected to each electrode terminal formed near the rear end 29 of the element 21. Each terminal fitting 75 provided at the tip of 71 is pressed by its spring property and is electrically connected. In the gas sensor 1, each terminal fitting 75 including the pressure contact portion is provided in a terminal fitting holding member 91 made of an insulating material disposed in a protective cylinder (metal cylinder) 81 having a different diameter cylindrical shape. In each accommodating part, it is provided in opposing arrangement, respectively. The terminal fitting holding member 91 is restricted from moving in the radial direction and the distal end side via an annular support member 80 fixed in a protective cylinder (metal cylinder) 81. Then, the rear end of the gas sensor 1 is covered in an airtight manner by fitting the front end portion (large diameter cylindrical portion) 82 of the protective cylinder 81 to the cylindrical portion 15 near the rear end of the metal fitting body 11 and welding it. ing. The lead wire 71 is drawn out through a sealing material (for example, rubber) 85 disposed inside the small-diameter cylindrical portion 83 at the rear end of the protective cylinder 81, and the small-diameter cylindrical portion 83 is reduced in diameter. By crimping and compressing the sealing material 85, the airtightness of this part is maintained. Incidentally, this sealing material 85 is arranged in such a manner that the rear end of the terminal fitting holding member 91 is pushed forward, whereby the mounting stability of the terminal fitting holding member 91 and the terminal fitting 75 provided therein is improved. It has been. The terminal fitting holding member 91 has a flange 93 formed on the outer periphery thereof supported on an annular support member 80 fixed to the inside of the protective cylinder 81, and receives the compressive force of the sealing material 85. ing.

  Now, in the gas sensor 1 of this example configured as described above, as described above, the holder 31 has the concave portion 35 that is recessed backward with respect to the region surrounding the through hole 38 in the tip-facing surface. Moreover, the recess 35 is formed so that the space K can be held between the inner peripheral surface 36 and the outer peripheral surface of the porous protective layer 25 in the sensor element 21 (FIGS. 2 and 2). 5, see FIG. The element 21 is provided behind the front end 32 of the holder 31 with the rear end 26 of the porous protective layer 25 entering the recess 35. For this reason, in this example gas sensor 1, even if the front and rear length L1 of the porous protective layer 25 of the sensor element 21 is the same as that of the conventional sensor element 21, the rear end 26 of the porous protective layer 25 is formed in the recess 35. The protrusion length L4 on the front end side of the sensor element 21 protruding from the front end 32 of the holder 31 can be shortened by the amount of penetration. Thereby, since the full length of the element 21 can be shortened, the cost reduction and power saving of an element are achieved.

  Moreover, among the portions near the tip of the element 21, the portion protruding toward the front from the bottom surface 37 (tip of the through hole 38) of the recess 35 can be exposed to gas even if it is in the recess 35. It is in. That is, in the conventional sensor, the protrusion length protruding from the tip of the holder among the portions near the tip of the element can be regarded as the protrusion length protruding from the bottom surface 37 of the recess 35 in the above embodiment. For this reason, the bottom surface (cross section) 37 of the concave portion 35 is secured as large as possible, and the protrusion 22 is secured in the same manner as in the past, so that the detection unit 22 provided on the tip side of the element 21 is exposed to gas. Can be similar to or close to conventional. Thereby, the length of the element 21 can be shortened while suppressing a decrease in detection performance.

  In the present embodiment, the protectors 51 and 61 as described above are attached, and the protector 51 on the inside surrounds the tip portion of the element 21 with its cylindrical wall 54a holding the space. The vent hole 56 is provided in a portion corresponding to the porous protective layer 25 provided on the front end side of the sensor element 21 in the front-rear direction, but the cylindrical wall 65a of the outer protector 61 is provided in the through-hole direction. The pores 56 are covered. Therefore, it is possible to suppress the gas and water contained in the gas from entering the detection unit 22 of the element 21. Moreover, since the inner protector 51 is provided with a vent hole 56 at a portion corresponding to the porous protective layer 25, the gas that has entered the inner side of the outer protector 61 is smoothly blown to the detection unit 22. Or you can touch. For this reason, the effect of preventing damage to the element 21 due to thermal shock is high, and it is also effective in preventing deterioration in detection performance. The dimensional relationship between the inner diameter D2 of the inner peripheral surface 36 of the recess 35 and the inner diameter D1 of the portion corresponding to the detection electrode in the cylindrical wall 54a of the inner protector 51 is such that D1> D2. Therefore, it is effective in preventing the gas from staying in the recess 35 in the back of the protector 51, which is preferable in terms of detection performance.

  Incidentally, for example, as shown in FIG. 9, the gas sensor 1 of the above example is manufactured and assembled as described above with the tip-side subassembly 101 including the element 21, while the other part is the above-described It is manufactured by separately manufacturing and assembling the end side part as a semi-assembled body (in-process product) 102 and assembling both of them. That is, as shown in FIG. 9, both of them are arranged coaxially, and the part near the rear end 29 of the element 21 protruding in the lower half assembly 101 is opposed to the terminal fitting holding member 91. The terminal fittings 75 are inserted relative to each other, and the terminal fittings 75 are brought into pressure contact with the electrode terminals provided near the rear end 29 of the element 21 by spring characteristics. 1 is manufactured as the gas sensor 1 of FIG. 1 by fitting the large-diameter cylindrical portion 82 at the front end of the protective cylinder 81 to the cylindrical portion 15 near the rear end of the metal fitting body 11 and laser welding the entire circumference at the same portion. The

  The gas sensor of the present invention can be embodied by appropriately changing the structure and configuration without departing from the gist of the present invention. In the above example, the outer appearance of the holder 31 is circular when viewed from the front end side, and the inner peripheral surface 36 of the recess 35 is also circular. Figured. Therefore, it is possible to suppress the occurrence of firing strain due to the thickness difference when the ceramic is made. However, in the present invention, as seen from the front end side, the holder may have a polygonal (rectangular) inner peripheral surface 36 as shown in FIG. 10, for example. However, in this case, it is preferable to make the thickness as uniform as possible in terms of improving the strength and preventing the occurrence of firing strain.

  Further, in the above embodiment, the element is in the form of a strip having a rectangular (rectangular) cross section. However, the element used in the sensor of the present invention may have a square cross section. It may be a thing. Furthermore, in the above description, the full-range air-fuel ratio gas sensor is embodied, but the gas sensor according to the present invention can be embodied in other gas sensors.

1 gas sensor 11 metal fitting body 12 annular part (cylindrical part)
12a Front end 12b of metal fitting body Inner peripheral surface 17 of annular portion 21 annular shelf 21 sensor element 22 detection portion 23 tip 25 of element 25 porous protective layer 26 rear end of porous protective layer 29 rear end of element 31 holder 32 of holder Tip surface (tip)
34 The outer peripheral surface 35 of the holder Recess 36 The inner peripheral surface 37 of the recess The bottom surface of the recess (tip of the through hole)
38 Through-hole 51, 61 Protector 54a, 65a Cylindrical walls 56, 67 of the protector Vent D1 Inner diameter D2 of the part corresponding to the detection electrode in the cylindrical wall of the protector D3 Inner diameter D3 Inner diameter L3 of the annular protective layer Dimension L5 positioned rearward of tip of holder at rear end L5 Projection dimension from tip of metal fitting body tip of element K Space between inner peripheral surface of recess and outer peripheral surface of porous protective layer

Claims (5)

A holder in which a through-hole penetrating through is formed inside the metal fitting body having a cylindrical shape. The through-hole is provided with a detection portion on the tip side and is porous in a predetermined range from the tip to the rear. A sensor element in the form of a strip or rod covered with a protective layer is passed through, the sensor element has its tip protruding forward from the tip of the holder, and the rear end of the porous protective layer is In the gas sensor provided at the tip of the through hole or ahead of the tip,
The holder has a concave portion that is recessed rearward with respect to a region surrounding the through hole when viewed from the tip-facing surface;
The sensor element is provided such that the rear end of the porous protective layer enters the recess and is positioned behind the front end of the holder;
The gas sensor is characterized in that the recess is formed so that a space can be maintained between an inner peripheral surface of the recess and an outer peripheral surface of the porous protective layer.   2. The gas sensor according to claim 1, wherein the holder has a circular outer peripheral surface when viewed from the front end side, and an inner peripheral surface of the recess has a cylindrical shape. At the front end side of the metal fitting body, a protector with a ventilation hole having a cylindrical wall that holds and surrounds the front end portion of the sensor element protruding forward from the front end of the holder is attached in a multi-layer structure. ,
Among the multi-layered protectors, the cylindrical wall of the innermost protector has the vent hole provided at a portion corresponding to the porous protective layer provided on the front end side of the sensor element in the front-rear direction. On the other hand, the protector outside the protector on the inside is provided so that the cylindrical wall covers the vent hole,
In addition, when the inner diameter of a portion of the cylindrical wall of the inner protector corresponding to the porous protective layer is D1, and the inner diameter of the recess is D2, the relation of D1> D2 is established. The gas sensor according to claim 2. An annular portion having an inner diameter smaller than the outer diameter of the holder is provided on the distal end side of the metal fitting main body, and the holder has an annular shape provided behind the inner peripheral surface of the annular portion at the distal end surface. Placed on the shelf and placed inside the metal fitting body,
When the inner diameter of the annular portion is D3, D3 and the inner diameter D2 are
The gas sensor according to claim 3, wherein a relationship of D3> D2 is established. The front end of the sensor element protrudes forward from the front end of the metal fitting body, the projecting dimension is L5, and the rear end of the porous protective layer of the sensor element is inserted into the recess so as to extend from the front end of the holder. When the dimension located at the rear is L3,
The gas sensor according to any one of claims 1 to 4, wherein a relationship of L5> L3 is established.

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