JP2006208165A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor that is easily removable from an exhaust pipe, even after a prolonged use. <P>SOLUTION: This gas sensor 101 comprises a gas detection element 103 of which tip side is exposed to gas to be measured, and a cylindrical subject metal fitting 121 for fixing the gas detection element 103, by projecting the tip side of the gas detection element 103 rather than its own tip, the subject metal fitting 121 having a fixing screw part 129 for attaching to the exhaust pipe 401, the surface of a fixing screw part 120 having a coated layer 301 with a Vickers hardness of 300 HV or larger. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas sensor having a gas detection element and a metal shell.

  Conventionally, as a gas sensor having a gas detection element, for example, an oxygen sensor for measuring the oxygen concentration of exhaust gas discharged from an internal combustion engine has been proposed. Such a gas sensor typically has a structure including a gas detection element and a cylindrical metal shell that fixes the gas detection element by projecting the distal end side of the gas detection element from its own distal end. Thus, in such a gas sensor, a screw portion provided in the metal shell is screwed into a screw portion of a gas sensor mounting hole provided in, for example, an exhaust pipe of an internal combustion engine, and the distal end side of the gas detection element is placed in the exhaust pipe. It is attached to the exhaust pipe so that it is exposed.

  By the way, when an internal combustion engine or the like is used, the exhaust pipe receives a heat load from the internal combustion engine or the like, and this heat is also conducted to a gas sensor attached to the exhaust pipe. Specifically, heat is transmitted to the gas sensor by conducting from the screw portion of the sensor mounting hole to the screw portion of the metal shell. At this time, if excessive heat is conducted through both screw parts, the screw part of the sensor mounting hole and the screw part of the metal shell may be joined, and the exhaust pipe and the metal shell may be seized. It may be difficult to remove.

Therefore, conventionally, by providing an anti-seizure layer for preventing seizure with the exhaust pipe on the surface of the threaded portion of the metal shell, the exhaust pipe and the metal shell are not even if excessive heat is conducted through both screw parts. The seizure was prevented and the gas sensor was easily removed from the exhaust pipe.
Japanese translation of PCT publication No. 2004-503058

  However, in recent years, the heat load applied to the exhaust pipe and the metal shell has been increased due to further enhancement of the performance of the internal combustion engine. Furthermore, the use of the gas sensor for a long time is increasing due to the improvement in durability of the gas sensor itself. Then, the seizure prevention layer as in Patent Document 1 may not sufficiently prevent seizure between the metal shell and the exhaust pipe. In other words, after using the gas sensor for a long time, the seizure prevention layer cannot fully exhibit the effect of seizure, and it may be difficult to remove the gas sensor from the exhaust pipe.

  The present invention has been made in view of the present situation, and an object of the present invention is to provide a gas sensor in which the gas sensor can be easily detached from the exhaust pipe even after the gas sensor has been used for a long time.

As a solution, the gas sensor of the present invention includes a gas detection element that is exposed to the gas to be measured and a cylindrical shape that fixes the gas detection element by projecting the front end side of the gas detection element beyond its own end. A gas sensor having a threaded portion to be attached to the exhaust pipe.
A coating layer having a Vickers hardness of 300 HV or more is provided on the surface of the threaded portion.

  Thus, in the present invention, a coating layer having a Vickers hardness of 300 HV or more is formed on the surface of the thread portion. Thereby, even if the heat load applied to the exhaust pipe or the metal shell is increased due to further enhancement of the performance of the internal combustion engine, it is possible to prevent seizure between the exhaust pipe and the metal shell. Moreover, even if the use of the gas sensor increases for a long time due to improvement in durability of the gas sensor itself, seizure between the metal shell and the exhaust pipe can be prevented.

  In addition, when the Vickers hardness of the coating layer is less than 300 HV, sufficient hardness cannot be obtained, and thus seizure may not be prevented. On the other hand, when the Vickers hardness of the coating layer exceeds 600 HV, the coating layer itself may be too hard to be formed on the surface of the threaded portion.

  And in this invention, it is preferable that 10 wt% or less of phosphorus is contained in the coating layer. By containing phosphorus in the coating layer, the coating layer can easily have a Vickers hardness of 300 HV or more. In addition, when it exceeds 10 wt%, the coating layer itself becomes brittle and it is difficult to obtain the effects of the present invention.

  By the way, the inventors have found that when the metal shell and the exhaust pipe are made of the same metal material, the phenomenon of seizure occurs. Therefore, as in the present invention, by providing a coating layer having a Vickers hardness of 300 HV or more on the surface of the threaded portion of the metal shell, even if the metal shell and the exhaust pipe are made of the same metal material, the seizure can be effectively prevented. it can. The same kind of metal material refers to a metal material whose main component is the same kind.

  Further, the metal shell of the gas sensor is generally formed of stainless steel. At this time, when the exhaust pipe to which the gas sensor is attached is stainless steel of the same system, the inventors have found that a phenomenon of seizure occurs particularly. Therefore, as in the present invention, seizing can be effectively prevented by providing a coating layer having a Vickers hardness of 300 HV or more on the surface of the threaded portion.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A cross-sectional view of the gas sensor 101 according to the present embodiment is shown in FIG. In FIG. 1, the lower side is the front end side and the upper side is the rear end side. The gas sensor 101 is an oxygen sensor that detects an oxygen concentration in exhaust gas that is a gas to be measured. As shown in FIG. 1, the gas sensor 101 includes a gas detection element 103 that extends in the direction of the axis C, and a cylindrical metal shell 121 that surrounds the periphery of the gas detection element 103.

  Among these, the gas detection element 103 has a bottomed cylindrical shape with a closed end portion 105, and is mainly formed of partially stabilized zirconia in which yttria is solid-solved as a stabilizer. An internal electrode layer 108 formed in a porous shape with Pt or a Pt alloy is formed on the inner peripheral surface of the gas detection element 103 so as to cover almost the entire surface, and a similar porous external layer is formed on the outer peripheral surface. An electrode layer 106 is provided. Further, an engagement flange portion 111 that protrudes radially outward is provided at a substantially intermediate position in the axial direction of the gas detection element 103. The engagement flange portion 111 is used to hold the gas detection element 103 on the metal shell 121 as will be described later. A ceramic heater 109 having a heating resistor is inserted inside the gas detection element 103 and is formed in a rod shape.

  The metal shell 121 has a cylindrical shape made of SUS430 and has a distal end portion 123 that is inserted into the protector 151. In addition, a shelf (support surface) 125 for holding the gas detection element 103 in the axial direction is provided on the inner periphery of the metal shell 121 at a position on the rear end side from the front end portion 123. On the other hand, an attachment screw portion 129 for attaching the gas sensor 101 to the exhaust gas pipe is provided on the outer periphery of the metal shell 121 at a position on the rear end side of the front end portion 123. The details of the mounting screw portion 129 will be described. Further, a hexagonal flange portion 131 (tool engaging portion) used when the gas sensor 101 is attached to the exhaust gas pipe is provided on the rear end side of the attachment screw portion 129.

  The metal shell 121 holds the gas detection element 103 coaxially in a state where the front end portion 105 of the gas detection element 103 protrudes from the front end surface of the metal shell 121. Specifically, as shown in FIG. 1, a first plate packing 133 is disposed on the shelf 125 of the metal shell 121. Furthermore, a cylindrical first fixing member 135 (made of alumina) having a stepped portion 136 on the inner periphery is disposed thereon. The gas detection element 103 is inserted into the first fixing member 135, and the engagement flange portion 111 of the gas detection element 103 is engaged with the stepped portion 136 of the first fixing member 135 via the second plate packing 137. is doing. On the rear end side of the first fixing member 135, a filling sealing layer 139 in which talc is compressed and filled is disposed in a gap formed by the outer peripheral surface of the gas detection element 103 and the inner peripheral surface of the metal shell 121. Yes.

Further, on the rear end side of the filling sealing layer 139, a cylindrical second fixing member 141 (made of alumina) through which the gas detection element 103 passes is disposed. A caulking ring 145 is disposed on the rear end side of the second fixing member 141, and the rear end portion 132 of the metal shell 121 is caulked inward in the radial direction, so that the gas detection element 103 is hermetically sealed in the metal shell 121. Held in a state.

  The protector 151 is inserted into the front end 123 of the metal shell 121 and fixed. The protector 151 includes a cylindrical inner cover portion 153 made of SUS310S that covers the front end portion 105 of the gas detection element 103 through a gap, and a cylindrical outer cover made of SUS310S disposed on the outer periphery of the inner cover portion 153. A double structure having a portion 173 and a gas introduction hole 176 are provided for each.

  And the rear-end side of the hexagon flange part 131 among the metal shells 121 is fixed to the front end part 201S of the cylindrical metal outer cylinder 201 from the outside by full-circle laser welding. Further, a grommet 203 made of fluoro rubber is inserted into the rear end side opening 201K of the metal outer cylinder 201, and the metal outer cylinder 201 is caulked toward the inner side in the radial direction. It is fixed in an airtight state. A through hole is provided in the central portion of the grommet 203, and a filter member 205 that prevents air from entering while the atmosphere is introduced inside the metal outer tube 201 is disposed in the through hole. Further, a separator 207 made of insulating alumina is disposed on the front end side of the grommet 203. Sensor output lead wires 211 and 212 and heater lead wires 213 and 214 (not shown) are disposed through the grommet 203 and the separator 207. In the separator 207, connector portions 215B and 216B of the first and second sensor terminal fittings 215 and 216 and heater terminal fittings 217 and 218 (not shown) are arranged while being insulated from each other, and the ceramic heater 109 is arranged. The rear end side is accommodated.

The first sensor terminal fitting 215 has a connector portion 215B that grips and electrically connects the sensor output lead wire 211 by caulking, and an insertion portion 215C is inserted into the bottomed hole of the gas detection element 103. The internal electrode layer 108 is electrically connected. The second sensor terminal fitting 216 has a connector portion 216B.
Grips and electrically connects the sensor output lead wire 121 by crimping, and the gripper 216C grips the outer periphery near the rear end of the gas detection element 103 and electrically connects to the external electrode layer 106. is doing. The two heater terminal fittings 217 and 218 are electrically connected to the heater lead wires 213 and 214, respectively, and are also electrically connected to each other by being joined to the pair of electrode pad portions 109B of the ceramic heater 109. ing.

  The separator 207 is formed with a flange portion 207C protruding outward in the radial direction, while the metal outer cylinder 201 is formed with four inner convex portions 201C at equal intervals along the circumferential direction. ing. Then, in a state where the rear end surface of the flange portion 207C is brought into contact with the inner convex portion 201C, the separator 207 is energized rearward by using the biasing member 219, whereby the separator 207 is disposed inside the metal outer cylinder 201. Is held in. The urging member 219 has a cylindrical shape and is held by the separator 207 by its own elastic force, and is deformed by crimping the metal outer cylinder 201 positioned on the radially outer side thereof to the radially inner side. It is comprised so that the collar part 207C of 207 may be urged | biased to the back side.

  Next, the mounting screw part 129 of the metal shell 121 which is a main part of the present invention will be described. A coating layer 301 is formed on the surface of the mounting screw portion 129 of the metal shell 121. In this embodiment, the coating layer 301 contains 5 wt% phosphorus. The coating layer 301 has a Vickers hardness of 300 HV or higher. Thus, the phosphorus 301 is contained in an amount of 10 wt% or less, so that the multi-layered layer 301 having a Vickers hardness of 300 or more can be formed, and when attached to the exhaust pipe 401 described later, The seizure with the metal shell 121 can be prevented.

  In this embodiment, the coating layer 301 has a thickness of 5 μm. This thickness is preferably 1 to 10 μm. When the thickness is less than 1 μm, it is difficult to obtain a sufficient effect of forming the coating layer 301. On the other hand, even if the thickness is larger than 10 μm, the production time and cost are increased without changing the effect of preventing seizure.

  As shown in FIG. 2, the gas sensor 101 is fixed to a gas sensor mounting hole 402 provided with an exhaust pipe 401 (in this embodiment, SUS409L stainless steel) of an internal combustion engine or the like. Specifically, the attachment fitting portion 129 of the metal shell 121 is attached by screwing into the attachment hole screw portion 403 provided in the gas sensor attachment hole 402. Then, the exhaust gas passing through the exhaust pipe 401 is exposed to the gas detection element 103 to measure the gas concentration. At this time, since the gas sensor 101 is attached to the exhaust pipe 401 for a long time, the metal shell 121 and the exhaust pipe 401 are affected by the thermal load. However, in the present invention, by having the coating layer 301, the influence of this heat load can be suppressed and seizure between the exhaust pipe 401 and the metal shell 121 can be prevented. In this embodiment, the metal shell 121 is made of SUS430, and the exhaust pipe 401 is made of SUS409L. Both are made of stainless steel and are of the same system. By having the coating layer 301, seizure between the exhaust pipe 401 and the metallic shell 121 can be prevented.

The gas sensor 101 is manufactured as follows.
First, plastic working and cutting are performed on the steel material of SUS430 to form a cylindrical metal shell 121 having a hexagonal flange portion 131, a mounting screw portion 129, a shelf portion 133, a tip portion 123, and the like. At this time, in the present embodiment, the distal end portion 123 corresponds to a portion where an overlapping portion 301 is expected to occur between the protector 151 (outer cover portion 173), and the distal end portion 123 includes a large diameter portion 303, The metal shell 121 is formed so that a small diameter portion 305 having an outer diameter smaller than that of the large diameter portion 303 is formed on the rear end side of the large diameter portion 303.

  On the other hand, an outer cover portion 173 and an inner cover portion 153 having a bottomed cylindrical shape made of SUS310S that are preliminarily molded to a predetermined size are prepared. Then, by performing spot welding at four locations, the inner cover portion 153 and the outer cover portion 173 are fixed coaxially to obtain the protector 151. Further, by moving the protector 151 from the front end side of the metal shell 123 and moving the protector 151 until the rear end of the outer cover portion 173 contacts the front end surface of the mounting screw portion 129, the rear end of the outer cover portion 173 is reached. The portion 180 is attached to the outside of the distal end portion 123 of the metal shell 121. At this time, the outer cover portion 173 is press-fitted into the large-diameter portion 303 of the distal end portion 123 of the metal shell 121. Then, laser light is irradiated from the outer peripheral surface of the outer cover portion 173 located on the radially outer side of the small-diameter portion 305 of the metal shell 121 to form the welded portion W over the entire circumference, and the laser between the protector 151 and the metal shell 121. Weld. Thereby, the protector 151 and the metal shell 121 are firmly fixed by press-fitting and laser welding.

  In the metal shell 121 to which the protector 151 is fixed, the first plate packing 133, the first fixing member 135, the second plate packing 137, the gas detection element 103, the talc ring that serves as the filling sealing layer 139, the second The fixing member 141 and the caulking ring 145 are sequentially inserted. Thereafter, the rear end portion 132 of the metal shell 121 is caulked inward in the radial direction, and the talc ring is compressed and filled to form the filling sealing layer 139, while the gas detecting element 103 is held in the metal shell 121 and the lower portion An assembly 401 (see FIG. 3) is produced.

Next, the sensor output lead wires 211 and 212 and the heater lead wire 213 are connected to the first and second sensor terminal fittings 215 and 216 and the two heater terminal fittings 217, respectively, and the ceramic heater 109 is connected to the first sensor terminal fitting 215. The lead wires 211, 212, and 213 (the remaining one is not shown) are inserted into the separator 207 while being positioned inside. Note that the flange 207C of the separator 207
A biasing member 219 is attached in advance around the tip side. Thus, the separator 207 having the lead wires 211, 212, and 213 inserted therein is inserted into the metal outer tube 201. Next, the lead wires 211, 212, and 213 are inserted into lead wire insertion holes formed in the grommet 203, and the grommet 203 is fitted into the rear end side opening 201 </ b> K of the metal outer cylinder 201. Thereby, the upper assembly 402 (refer FIG. 3) is produced.

Then, the upper assembly 402 is moved toward the lower assembly 401, and the upper assembly 402 is moved until the distal end portion 201 </ b> S of the metal outer cylinder 201 contacts the hexagonal flange portion 131 of the metal shell 121. At this time, the heater 15 is inserted into the gas detection element 103. Thereafter, the distal end portion 201S of the metal outer cylinder 201 and the metal shell 121 located inside the metal outer cylinder 201 are temporarily connected by crimping with a caulking jig while pressing the metal outer cylinder 201 toward the distal end side.

Next, in the metal outer cylinder 201, a portion located on the radially outer side of the biasing member 219 is crimped toward the radially inner side to deform the biasing member 219, and the biasing member 219 and the inner convex portion. The flange portion 207C of the separator 207 is sandwiched between 201C. As a result, the separator 207 is held in the metal outer cylinder 201. Thereafter, a portion of the metal outer cylinder 201 that is located on the radially outer side of the grommet 203 is crimped toward the radially inner side to fix the grommet 203 to the metal outer cylinder 201 in an airtight state. And the front-end | tip part 201S of the metal outer cylinder 201 already temporarily connected and the metal shell 121 are all-around laser welded.

  Next, the gas sensor 101 is completed by applying a coating layer 301 material containing 5 wt% phosphorus to the mounting screw portion 129. Examples of the application method include a method using a brush or brush, a method of spraying with a spray, and the like.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, the gas sensor 101 of the embodiment is provided with only the covering layer 301, but the present invention is not limited to this, and a conventional anti-seize layer is further provided between the covering layer 301 and the mounting screw portion 129 of the metal shell 121. May be. Thereby, the seizure between the metal shell 121 and the gas sensor mounting hole 402 provided with the exhaust pipe 401 can be prevented more effectively.

The fragmentary sectional view of gas sensor 101 concerning an embodiment. Explanatory drawing in which the gas sensor 101 of embodiment is attached to the exhaust pipe 401. FIG. The assembly drawing of the gas sensor 101 of embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Gas sensor 103 Gas detection element 121 Main metal fitting 129 Mounting screw part 201 Metal outer cylinder 203 Grommet 207 Separator 301 Covering layer 401 Exhaust pipe

Claims (4)

A gas detection element whose tip is exposed to the gas to be measured;
A cylindrical metal shell for fixing the gas detection element by projecting the front end side of the gas detection element from the front end of the gas detection element;
In the metal shell, in the gas sensor having a screw part for attaching to the exhaust pipe,
A gas sensor comprising a coating layer having a Vickers hardness of 300 HV or more on a surface of the thread portion.   The gas sensor according to claim 1, wherein the coating layer contains 10 wt% or less of phosphorus.   The gas sensor according to claim 1 or 2, wherein the metal shell and the exhaust pipe are made of the same metal material. The metal shell and the exhaust pipe are made of stainless steel,
The gas sensor according to claim 1 or 2, wherein the stainless steel forming the metal shell and the stainless steel forming the exhaust pipe are of the same system.