JP2006038496A - Gas sensor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor capable of reducing a shift in a λ point, and capable of controlling combustion finely, while preventing a catalyst metal particle from being poisoned. <P>SOLUTION: An outer electrode layer 26 and an inner electrode layer 27 are formed in a solid electrolyte 28, in a sensor element 2 of this gas sensor 1. The outer electrode layer 26 is coated with an electrode protection layer 100. The electrode protection layer 100 is a porous body carried with the catalyst metal particle such as platinum. A porous poisoning preventive layer 110 is provided to cover the electrode protection layer 100. The poisoning preventive layer 110 prevents the catalyst metal particle in the electrode protection layer 100 from being poisoned. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas sensor used for combustion control or the like of an internal combustion engine and a manufacturing method thereof.

  Conventionally, the following configuration is known as a gas sensor that is installed in an exhaust system of an internal combustion engine and detects oxygen concentration in exhaust gas and is used for combustion control of the internal combustion engine. That is, the gas sensor element provided in the gas sensor includes a solid electrolyte body made of a ceramic such as zirconia having oxygen ion conductivity, and a detection electrode made of platinum or the like provided on one surface of the solid electrolyte body and in contact with the gas to be measured. And a reference electrode made of platinum or the like provided on the other surface of the solid electrolyte body and in contact with the reference gas. A porous electrode protective layer made of alumina magnesia spinel or the like for preventing poisoning of the detection electrode is formed on the surface of the detection electrode.

  This gas sensor can extract the electromotive force generated in the solid electrolyte body according to the oxygen concentration in the gas to be measured from the reference electrode and the detection electrode, and can detect the oxygen concentration using the value of this electromotive force. This is a so-called oxygen concentration electromotive force type gas sensor.

  By the way, in recent years, there is a demand for a gas sensor that can effectively control combustion of an internal combustion engine and is effective for strengthening exhaust gas regulations. As a gas sensor element for this purpose, it is necessary that the shift of the λ point is small and the oxygen concentration can be measured accurately. However, in the conventional gas sensor, the measurement accuracy of the oxygen concentration may decrease depending on the type of exhaust gas. For example, hydrogen in the exhaust gas has a higher diffusion rate (a rate at which the exhaust gas reaches the detection electrode via the electrode protective layer), and therefore, it is easier to reach the detection electrode than other exhaust gases. Then, the reached hydrogen reacts with the detection electrode, so that the detection electrode makes a misjudgment, and the λ point that should be detected is shifted, so that precise combustion control may be difficult.

  Therefore, in order to obtain a gas sensor with a small displacement of λ point and capable of precise combustion control of an internal combustion engine, a catalyst layer containing catalytic metal particles such as platinum that has excellent catalytic performance such as platinum in a form of covering an electrode protective layer is provided. A gas sensor provided has been proposed (see Patent Document 1). As a result, by reacting hydrogen in the exhaust gas with the catalyst layer and suppressing the arrival of hydrogen to the detection electrode, it is possible to obtain a gas sensor that reduces the shift of the λ point and enables precise combustion control of the internal combustion engine. it can.

Further, a gas sensor is known in which not only a catalyst layer containing catalyst metal particles is provided so as to cover the electrode protection layer, but also the catalyst metal particles are supported on the electrode protection layer (see Patent Document 2). . In this gas sensor, more catalyst metal particles are supported on the catalyst layer than the electrode protective layer, and in the same manner as in Patent Document 1, the catalyst layer reacts with hydrogen in the exhaust gas to make it difficult for hydrogen to reach the detection electrode. Thus, it is possible to obtain a gas sensor that reduces the shift of the λ point and enables precise combustion control of the internal combustion engine.
Japanese Patent Laid-Open No. 11-237361 Japanese Patent Publication No.8-7177

  However, the catalyst layer of Patent Document 1 is generally formed by preparing a slurry containing a material for forming the catalyst layer and applying the slurry so as to cover the electrode protection layer. There is a possibility that the catalyst layer is not chemically bonded to the electrode protective layer and the catalyst layer is peeled off from the electrode protective layer. Then, the electrode protective layer is directly exposed to the exhaust gas containing hydrogen. Therefore, the detection electrode may erroneously determine from hydrogen that easily reaches the detection electrode more than other exhaust gas, and the λ point that should be detected may be shifted, making precise combustion control difficult.

  On the other hand, in Patent Document 2, similarly to Patent Document 1, even if the catalyst layer is peeled off from the electrode protective layer, the catalyst metal particles in the electrode protective layer are contained in the electrode protective layer itself because the electrode protective layer itself contains the catalyst metal particles. It can react with hydrogen and suppress the arrival of hydrogen at the detection electrode. In addition, since an electrode protective layer is generally formed so that a detection electrode may be covered using plasma spraying etc., it is better than the adhesiveness of an electrode protective layer and a catalyst layer.

  However, the electrode protective layer is directly exposed to the exhaust gas, and the catalytic metal particles carried on the electrode protective layer may be poisoned by poisoning substances such as lead, phosphorus, and silicon in the exhaust gas. As a result, the catalytic metal particles are deteriorated, the reaction with the hydrogen in the exhaust gas hardly occurs, and there is a possibility that the hydrogen reaches the detection electrode. Therefore, the detection electrode may misjudgment from hydrogen, and the λ point that should be detected may be shifted, making precise combustion control difficult.

  The present invention has been made in view of such conventional problems, and provides a gas sensor and a manufacturing method thereof capable of precise combustion control by reducing the shift of the λ point while preventing poisoning of catalytic metal particles. It is to provide.

  The gas sensor of the present invention is provided on one surface of the solid electrolyte body having oxygen ion conductivity, a detection electrode in contact with the gas to be measured, and on the other surface of the solid electrolyte body, A reference electrode in contact with a reference gas; a porous electrode protective layer provided to cover the detection electrode; and supporting the catalytic metal particles; and the catalytic metal particles provided to cover the electrode protective layer. And a sensor element having a porous poisoning prevention layer for preventing poisoning of the porous body.

  As described above, by supporting the catalyst metal particles on the electrode protective layer, the electrode protective layer itself can be directly exposed to hydrogen in the exhaust gas without providing a separate catalyst layer. In other words, by obtaining catalyst gas particles capable of precise combustion control of an internal combustion engine by suppressing the arrival of hydrogen to the detection electrode and reducing the shift of the λ point with the catalyst metal particles lamented by the electrode protective layer. Can do.

  Furthermore, the gas sensor of the present invention includes a porous poisoning prevention layer which is provided so as to cover the electrode protection layer and prevents the catalytic metal particles from being poisoned. As a result, even if the electrode protective layer is directly exposed to the exhaust gas, the catalytic metal particles carried on the electrode protective layer are prevented from being poisoned by poisonous substances such as lead, phosphorus, silicon, etc. in the exhaust gas. And the catalyst metal particles are less likely to deteriorate. Therefore, the reaction between hydrogen in the exhaust gas and the catalytic metal particles is maintained, and hydrogen is prevented from reaching the detection electrode. Therefore, it is possible to obtain a gas sensor that reduces the shift of the λ point and enables precise combustion control of the internal combustion engine.

  The gas sensor of the present invention can be applied to a gas sensor composed of a bottomed cylindrical solid electrolyte body, and can also be applied to a laminated gas sensor in which a reference electrode, a detection electrode, etc. are formed on a plate-shaped solid electrolyte body.

  The electrode protective layer is provided so as to cover at least the detection electrode. Or it can also provide so that the whole surface of the solid electrolyte body containing a detection electrode may be covered. Furthermore, the poisoning prevention layer may be provided so as to cover at least the electrode protective layer, or may be provided so as to cover the entire surface of the solid electrolyte body.

  Furthermore, the poisoning prevention layer of the present invention comprises titania powder and ceramic powder other than titania. This titania has an excellent effect of adsorbing poisonous substances, and the poisoning prevention layer containing this titania effectively reacts with poisonous substances such as phosphorus in the exhaust gas, and the catalyst in the detection electrode and electrode protective layer. It can prevent poisoning of metal particles. On the other hand, ceramic powders other than titania are preferably ceramic powders such as spinel, mullite and the like that hardly undergo heat shrinkage. By using such a ceramic powder, peeling from the electrode protective layer due to heat shrinkage can be suppressed, and an excellent durable poisoning prevention layer can be obtained.

  Further, the particle size distribution of the primary particles of the titania powder has a peak at 1 μm or less, and the particle size distribution of the primary particles of the ceramic powder other than the titania powder has a peak at 10 μm or more. By adjusting the particle size distribution of the primary particles of the titania powder and the particle size distribution of the primary particles of the ceramic powder other than titania in this way, the air permeability of the poisoning prevention layer is sufficiently maintained, and the poisonous material is Adsorbed reliably.

  Moreover, the load in the electrode protective layer of this invention is 10-200 micrograms. When the supported amount is less than 10 μg, there is little reaction between the electrode protective layer and hydrogen, a difference in the diffusion rate of the exhaust gas occurs, the λ point shifts, and precise combustion control may be difficult. On the other hand, when the loaded amount is larger than 200 μg, the exhaust gas diffusion rate is generally slowed down, and the responsiveness as a gas sensor may be lowered. Therefore, when the loading amount in the electrode protective layer is 10 to 200 μg, it is possible to effectively obtain a gas sensor capable of reducing the shift of the λ point and performing precise combustion control.

  Further, the electrode protective layer of the present invention has a porosity of 5 to 50%. When the porosity is less than 5%, the exhaust gas diffusion rate is generally slow, and the responsiveness as a gas sensor may be reduced. On the other hand, when the porosity is higher than 50%, the reaction between the electrode protective layer and hydrogen is small, the difference in the diffusion rate of the exhaust gas occurs, the λ point shifts, and precise combustion control becomes difficult. There is. Furthermore, electrode deterioration is likely to occur and durability may be reduced. Therefore, when the porosity is 5 to 50%, it is possible to effectively obtain a gas sensor capable of reducing the shift of the λ point and performing precise combustion control.

  Moreover, the electrode protective layer of this invention is 50-500 micrometers in thickness. When the thickness of the electrode protective layer is less than 50 μm, the catalytic metal particles in the electrode protective layer are reduced, the reaction between the electrode protective layer and hydrogen is small, the difference in the exhaust gas diffusion rate occurs, and the λ point is It may shift, and precise combustion control may be difficult. On the other hand, when the thickness is larger than 500 μm, the exhaust gas diffusion rate is generally slowed down, and the responsiveness as a gas sensor may be lowered. Therefore, when the thickness is 50 to 500 μm, it is possible to effectively obtain a gas sensor capable of reducing the shift of the λ point and performing precise combustion control.

  Moreover, the electrode protective layer of the present invention preferably contains at least one selected from alumina, alumina magnesia spinel, and zirconia. Since these materials are thermally and chemically stable, it is possible to obtain an electrode protective layer that is not easily deteriorated.

  Further, the catalytic metal particles of the present invention are composed of at least one selected from Pt, Pd, Rh, and Ru. Since these materials are excellent in catalyst performance, the effects of the present invention can be obtained with certainty.

  Hereinafter, a gas sensor as an embodiment to which the present invention is applied will be described with reference to the drawings. In the present embodiment, a gas sensor (oxygen sensor) that is mounted on an exhaust pipe of an automobile (particularly on the downstream side of the catalyst or the like) and detects the concentration of oxygen in the exhaust gas will be described. FIG. 1 is a cross-sectional view showing the overall configuration of the gas sensor 1 of the present embodiment.

  As shown in FIG. 1, the gas sensor 1 includes a sensor element 2 having a bottomed cylindrical shape with a closed end, a ceramic heater 3 inserted into a bottomed hole 25 of the sensor element 2, and the sensor element 2 inside thereof. The metal shell 5 is held. In the present embodiment, among the directions along the axis of the sensor element 2 shown in FIG. 1, the side (closed side, lower side in the drawing) toward the tip exposed to the measurement target gas (exhaust gas) is used. In the following description, the “front end side” is referred to as the “rear end side” and the side facing the opposite direction (upper side in the drawing) is referred to.

  This oxygen sensor element 2 includes a solid electrolyte body 28 having oxygen ion conductivity mainly composed of partially stabilized zirconia in which yttria is solid-solved as a stabilizer, and an inner surface of a bottomed hole 25 of the solid electrolyte body 28. In addition, the internal electrode layer 27 formed in a porous shape by Pt or a Pt alloy so as to cover almost the entire surface, and the external surface formed in a porous shape on the outer surface of the solid electrolyte body 28 in the same manner as the internal electrode layer 27. An electrode layer 26 is provided. Further, an engagement flange portion 92 that protrudes radially outward is provided at a substantially intermediate position in the axial direction of the sensor element 2. The ceramic heater 3 is formed in a rod shape and includes a heat generating portion 42 having a heat generating resistor therein. When the ceramic heater 3 is energized through heater lead wires 19 and 22 (described later), the heat generating portion 42 generates heat, and has a function of heating the sensor element 2 to activate the sensor element 2. Fulfill.

The metal shell 5 has a screw portion 66 for attaching the gas sensor 1 to the attachment portion of the exhaust pipe, and a hexagonal portion 93 to which an attachment tool is applied when attaching the gas sensor 1 to the attachment portion of the exhaust pipe. The metal shell 5 includes an alumina support member 51 that supports the sensor element 2 from the front end side, a filling member 52 made of talc powder that fills the rear end side of the support member 51, and the filling member 52 at the rear end. An alumina sleeve 53 that presses from the side toward the tip side is configured to be housed inside.

The metal shell 5 is provided with a metal-side stepped portion 54 projecting radially inward on the inner periphery of the front end side, and the support member 51 is locked to the metal-side stepped portion 54 via a packing 55. Yes. The sensor element 2 is supported by the metal shell 5 when the engagement flange portion 92 is supported on the support member 51 via the packing 94. A filling member 52 is disposed between the inner surface of the metal shell 5 on the rear end side of the support member 51 and the outer surface of the sensor element 2, and a sleeve 53 and an annular ring 15 are provided on the rear end side of the filling member 52. It arrange | positions in the state inserted sequentially coaxially.

A front end side of the inner cylinder member 14 made of SUS304L is inserted inside the rear end side of the metal shell 5. The inner cylinder member 14 has the metal-side rear end 60 of the metal shell 5 in the direction of the inner tip, with the opening end (tip opening end 59) having an enlarged diameter on the tip side in contact with the annular ring 15. The metal shell 5 is fixed by caulking. The gas sensor 1 has a structure in which the filling member 52 is compressed and filled through the sleeve 53 by crimping the metal-side rear end portion 60 of the metal shell 5, whereby the sensor element 2 has a cylindrical shape. The metallic shell 5 is held in an airtight manner.

The inner cylinder member 14 is formed with an inner cylinder stepped portion 83 at a substantially intermediate position in the axial direction, the tip side of the inner cylinder stepped portion 83 is formed as an inner cylinder tip side body portion 61, and the inner cylinder stepped portion is formed. The rear end side of the portion 83 is formed as the inner cylinder rear end side body portion 62. The inner cylinder rear end side body part 62 is formed to have both an inner diameter and an outer diameter smaller than the inner cylinder front end side body part 61, and the inner diameter is slightly larger than the outer diameter of a separator body 85 of the separator 7 described later. ing. In addition, a plurality of air introduction holes 67 are formed in the inner cylinder rear end side body portion 62 at predetermined intervals along the circumferential direction.

The outer cylinder member 16 is formed into a cylindrical shape by deep-drawing a SUS304L plate material, and includes an outer cylinder rear end side portion 63 including an opening communicating from the outside to the rear end side, and an inner cylinder member on the front end side. 14, an outer cylinder front end side portion 64 that is coaxially connected from the rear end side, and an outer cylinder step portion 35 that connects the outer cylinder rear end side portion 63 and the outer cylinder front end side portion 64 are formed. The outer cylinder rear end side portion 63 is formed with a caulking portion 88 for fixing the elastic seal member 11 in an airtight manner.

Further, a metal double protector 81, 82 having a plurality of gas intake holes is welded to the outer periphery on the front end side of the metal shell 5 so as to cover the tip portion protruding from the tip of the metal shell 5 of the sensor element 2. It is attached.

Further, a cylindrical filter 68 for preventing water from entering through the air introduction hole 67 is disposed outside the inner cylinder rear end side body portion 62 of the inner cylinder member 14. The filter 68 is, for example, a porous fiber structure of polytetrafluoroethylene (trade name: Gore-Tex (Japan Coretex Co., Ltd.), while preventing permeation of liquid mainly composed of water, etc. This is configured as a water repellent filter that allows permeation of gas.

The outer cylinder front end side portion 64 of the outer cylinder member 16 is formed in a shape that covers the inner cylinder member 14 (specifically, the inner cylinder rear end side body portion 62) where the filter 68 is disposed from the outside, and the outer cylinder front end portion. A plurality of air introduction holes 84 are formed at predetermined intervals along the circumferential direction at positions corresponding to the filter 68 in the side portion 64.

The outer cylinder member 16 and the inner cylinder member 14 are configured such that at least a part of the outer cylinder front end side portion 64 of the outer cylinder member 16 on the rear end side of the atmosphere introduction hole 84 is radially passed through the filter 68. First caulking portion 56 formed by caulking inward, and second caulking formed by caulking at least a part on the tip side from air introduction hole 84 inward in the radial direction, also through filter 68 It is fixed by the part 57. At this time, the filter 68 is held in an airtight manner between the outer cylinder member 16 and the inner cylinder member 14. Moreover, the outer cylinder front end side portion 64 of the outer cylinder member 16 is disposed so as to overlap from the outer side with respect to the inner cylinder front end side body portion 61, and at least a part of the overlapping portion faces the inner side in the circumferential direction. The connection crimping part 75 is formed by crimping.

Thereby, the atmosphere as the reference gas is introduced into the atmosphere introduction hole 84, the filter 68 and the atmosphere introduction hole 67, and the inner cylinder member 14, and is introduced into the bottomed hole 25 of the sensor element 2. On the other hand, since water droplets cannot pass through the filter 68, entry into the inner cylinder member 14 is prevented.

The elastic seal member 11 disposed inside the rear end of the outer cylinder member 16 (outer cylinder rear end side portion 63) includes two element lead wires 20 and 21 electrically connected to the sensor element 2, and ceramic. Four lead wire insertion holes 17 for inserting two heater lead wires 19 and 22 electrically connected to the heater 3 are formed so as to penetrate from the front end side to the rear end side.

Further, the separator 7 in which the front end side of the inner cylinder member 14 is inserted and arranged in the inner cylinder rear end side body portion 62 is for inserting the element lead wires 20 and 21 and the heater lead wires 19 and 22. The separator lead wire insertion hole 71 is formed so as to penetrate from the front end side to the rear end side. Further, the separator 7 is formed with a bottomed holding hole 95 opened in the front end surface in the axial direction. The rear end portion of the ceramic heater 3 is inserted into the holding hole 95, and the ceramic heater 3 is positioned in the axial direction with respect to the separator 7 by abutting the rear end surface of the ceramic heater 3 against the bottom surface of the holding hole 95. .

The separator 7 includes a separator main body 85 that is inserted inside the rear end of the inner cylinder member 14, and a separator flange 86 that extends from the rear end of the separator main body 85 to the outer side in the circumferential direction. Yes. That is, in the separator 7, the separator body 85 is inserted into the inner cylinder member 14, and the separator flange 86 is supported on the rear end surface of the inner cylinder member 14 via the annular seal member 40 made of fluoro rubber. The inner cylinder member 16 is disposed inside.

The element lead wires 20 and 21 and the heater lead wires 19 and 22 are passed through the separator lead wire insertion hole 71 of the separator 7 and the lead wire insertion hole 11 of the elastic seal member 11, and the inner cylinder member 14 and the outer cylinder member 16. It is drawn from the inside to the outside. These four lead wires 19, 20, 21, and 22 are externally connected to a connector (not shown). The external signals such as the ECU and the lead wires 19, 20, 21, and 22 are input / output via the connector.

Further, although not shown in detail, each lead wire 19, 20, 21, 22 has a structure in which the conducting wire is covered with an insulating film made of resin, and the rear end side of the conducting wire is a connector terminal provided in the connector. Connected. And the front end side of the conducting wire of the element lead wire 20 is crimped with the rear end portion of the terminal fitting 43 fitted on the outer surface of the sensor element 2, and the leading end side of the conducting wire of the element lead wire 21 is It is crimped to the rear end portion of the terminal fitting 44 that is press-fitted into the inner surface of the sensor element 2. Thereby, the element lead wire 20 is electrically connected to the external electrode layer 26 of the sensor element 2, and the element lead wire 21 is electrically connected to the internal electrode layer 27. On the other hand, the leading ends of the lead wires 19 and 22 for the heater are respectively connected to a pair of heater terminal fittings joined to the heating resistor of the ceramic heater 3.

  Then, on the rear end side of the separator 7, an elastic sealing material 11 made of fluorine rubber or the like having excellent heat resistance is fixed to the outer cylinder member 16 by caulking the outer cylinder member 16 and forming a caulking portion 88. Has been. The elastic seal member 11 includes a main body 31 and a seal member flange 32 that extends radially outward from a side peripheral surface 72 on the distal end side of the main body 31. Four lead wire insertion holes 17 are formed so as to penetrate the main body portion 31 and the small diameter portion 33 in the axial direction.

Next, the sensor element 2 which is a main part of the present invention will be described in detail.
As shown in FIG. 2, the sensor element 2 is provided with a porous electrode protection layer 100 that covers the outer electrode layer 26.

  The electrode protective layer 100 is made of a heat-resistant ceramic such as alumina magnesia spinel and carries catalytic metal particles. The electrode protective layer 100 has a thickness of 200 μm and a porosity of 40%. The supported catalytic metal particles are made of platinum and have an average particle size of 0.01 to 50 μm. The catalytic metal particles are supported on the electrode protective layer 100 at a loading amount of 60 μg.

  As described above, by supporting the catalytic metal particles on the electrode protective layer 100, the electrode protective layer 100 itself can be directly exposed to the exhaust gas without providing a separate catalyst layer. That is, the gas sensor 1 that enables precise combustion control of the internal combustion engine by suppressing the arrival of hydrogen to the outer electrode layer 26 and reducing the shift of the λ point with the catalyst metal particles supported on the electrode protective layer 100. Can be obtained.

  Furthermore, the sensor element 2 of the present invention includes a porous poisoning prevention layer 101 that is provided so as to cover the electrode protective layer 100 and prevents the catalytic metal particles from being poisoned. As a result, even if the electrode protective layer 100 is directly exposed to the exhaust gas, the catalytic metal particles supported on the electrode protective layer 100 are poisoned by poisonous substances such as lead, phosphorus and silicon in the exhaust gas. The catalyst metal particles are less likely to deteriorate. Therefore, the reaction between the hydrogen in the exhaust gas and the catalytic metal particles is maintained, and the arrival of hydrogen at the outer electrode layer 26 is suppressed. Therefore, it is possible to obtain the gas sensor 1 that can reduce the shift of the λ point and enables precise combustion control of the internal combustion engine.

  In addition, the poisoning prevention layer 101 is composed of titania powder and ceramic powder other than titania. This titania has an excellent effect of adsorbing poisonous substances, and the poisoning prevention layer 101 containing this titania effectively reacts with poisonous substances such as phosphorus in the exhaust gas, and the outer electrode layer 26 and the electrode protective layer. The poisoning of catalyst metal particles in 100 can be prevented. On the other hand, spinel or the like is used as a ceramic powder other than titania. By using such a ceramic powder, peeling from the electrode protective layer 100 due to heat shrinkage can be suppressed, and the poisoning prevention layer 101 having excellent durability can be obtained.

  Further, the particle size distribution of the primary particles of the titania powder has a peak at 0.003 to 0.5 μm, and the particle size distribution of the primary particles of the ceramic powder other than the titania powder has a peak at 15 to 65 μm. Thus, by adjusting the particle size distribution of the primary particles of the titania powder and the particle size distribution of the primary particles of the ceramic powder other than the titania, the air permeability is sufficiently maintained, and the poisonous material is reliably adsorbed. Thus, an appropriate porous poisoning prevention layer 101 is obtained.

  The poisoning prevention layer 101 preferably has a thickness of 50 μm to 300 μm. If the thickness is less than 50 μm, it is difficult to sufficiently capture the poisonous substance, and it is difficult to obtain the effect of sufficiently suppressing the peeling of the electrode protective layer 100. on the other hand. When the thickness exceeds 300 μm, the poisoning prevention layer 101 itself easily peels from the electrode protective layer 100.

  The solid electrolyte body 28 in the present embodiment corresponds to the solid electrolyte body in the claims, the outer electrode layer 26 in the present embodiment corresponds to the detection electrode in the claims, and the inner electrode in the present embodiment. The layer 27 corresponds to the reference electrode in the claims.

  Next, the manufacturing method of the gas sensor 1 of this embodiment is demonstrated in detail. First, after adding 5 mol% of yttria to zirconia and granulating it, it is formed into a bottomed cylindrical shape with a closed tip as shown in FIG. 1 and fired at a temperature of 1400 to 1600 ° C. in an electric furnace. A solid electrolyte body 28 was obtained. Next, the outer electrode layer 26 made of platinum is provided on the outer peripheral surface of the solid electrolyte body 28 by vapor deposition, chemical plating, or the like. On the other hand, the inner electrode layer 27 is similarly provided on the inner surface of the gas sensor element using vapor deposition, chemical plating, or the like.

Next, the electrode protective layer 100 is formed by plasma spraying alumina magnesia spinel on the surface of the outer electrode layer 26. Then, the solid electrolyte body 28 with the outer electrode layer 26 on which the electrode protection layer 100 is formed is immersed in an aqueous solution of H ₂ PtCl ₆ , and the atmosphere is evacuated to form platinum that is a catalyst metal particle in the electrode protection layer 100. Is supported. The time for the solid electrolyte body 28 to be immersed in the aqueous solution of H ₂ PtCl ₆ is 5 minutes to 20 minutes. Then, it is made to dry, and after baking, it bakes at 200 to 800 degreeC for 5 to 30 minutes with an electric furnace.

  As described above, the electrode protective layer 100 is formed by impregnating a solution containing the catalyst metal particles in a vacuum state after plasma spraying and then evacuating the electrode. Thereby, since the catalyst metal particles can be supported on the electrode protective layer 100, the electrode protective layer 100 itself can be directly exposed to the exhaust gas. Therefore, the catalyst metal particles supported on the electrode protective layer 100 can suppress the arrival of hydrogen to the outer electrode layer 26, reduce the shift of the λ point, and enable precise combustion control of the internal combustion engine. Can be obtained.

  Next, a predetermined amount of titania powder and ceramic powder other than titania, alumina sol, and nylon cobblestone are used and mixed by a pot mill to prepare a slurry. When the slurry is 100% by weight, the titania powder and ceramic powder other than titania are 70% by weight, and the alumina sol is 7% by weight. And the solid electrolyte body 28 in which the electrode protective layer 100 was formed was immersed in this slurry, a coating film was formed in the outer surface of the electrode protective layer 100, and it dried at 700-730 degreeC, and the poisoning prevention layer 101 was formed. The sensor element 2 according to the present embodiment was obtained.

  The poisoning prevention layer 101 formed by the above method is provided so as to cover the electrode protective layer 100. As a result, even if the electrode protective layer 100 is directly exposed to the exhaust gas, the catalytic metal particles supported on the electrode protective layer 100 are poisoned by poisonous substances such as lead, phosphorus and silicon in the exhaust gas. The catalyst metal particles are less likely to deteriorate. Therefore, the reaction between the hydrogen in the exhaust gas and the catalytic metal particles is maintained, and the hydrogen is prevented from reaching the outer electrode layer 26. Therefore, it is possible to obtain the gas sensor 1 that can reduce the shift of the λ point and enables precise combustion control of the internal combustion engine.

  Next, a manufacturing method for assembling the sensor element 2 to produce a gas sensor will be described. The element lead wires 20 and 21 are bonded to the terminal fittings 43 and 44, respectively, and the heater lead wires 19 and 22 are bonded to the heater terminal fitting of the ceramic heater 3 in advance. Then, the lead wires 19, 20, 21, 22 are inserted into the separator lead wire insertion holes 71 of the separator 7 with the ceramic heater 3 positioned inside the terminal fitting 44. Next, in a state where the lead wires 19, 20, 21, 22 are inserted through the lead wire insertion holes 17 of the elastic seal member 11, the lead wires 19, 20, 21, 22 are moved until the front end surface of the elastic seal member 11 contacts the rear end surface of the separator 7. . In this way, the sensor upper intermediate is produced. An annular seal member 40 is attached to the outer periphery of the separator main body 85 in advance.

  Next, as shown in FIG. 3, the sensor element 2 is held by the metal shell 5, and the protectors 81 and 82 are welded to the front end side of the metal shell 5, and the front end side of the inner cylinder member 14 is connected to the rear end side. Prepare the lower sensor intermediate. A cylindrical filter 68 is set around the inner cylinder rear end side body portion 62 of the inner cylinder member 14. Then, the separator body 85 of the sensor upper intermediate separator 7 is positioned in the inner cylinder rear end side body 62 of the inner cylinder member 14 of the sensor lower intermediate. Thereby, the terminal metal fitting 44 is inserted into the bottomed hole 25 of the sensor element 2 together with the ceramic heater 3, and is electrically connected to the inner electrode layer 27. Further, the terminal fitting 43 is fitted on the outer surface of the sensor element 2 and is electrically connected to the outer electrode layer 26.

  Then, the outer cylinder member 16 is moved from the rear end side of the elastic seal member 11 in a state where the lead wires 19, 20, 21, 22 are passed through the inner side of the outer cylinder member 16. Move it until it overlaps the outside. Next, while pressing the outer cylinder step portion 35 toward the distal end side in the axial direction, the overlapping portion of the outer cylinder member 16 and the inner cylinder distal end body portion 62 is crimped inward in the radial direction, and the connection crimped portion 75 is joined. And the outer cylinder member 16 and the inner cylinder member 14 are fixed. The caulking was performed by Happomaru caulking.

  Next, as shown in FIG. 4, a portion of the outer cylinder member 16 (outer cylinder rear end side portion 63) located outside the side peripheral surface of the elastic seal member 11 (specifically, the outer cylinder rear end side portion 63). ) Is crimped inward in the radial direction using a crimping jig CL to form a crimped portion 88, and the elastic seal member 11 is compressed and deformed. Thereby, the elastic seal member 11 is fixed to the outer cylinder member 16 in an airtight manner. This caulking was also performed by Happomaru caulking. And the gas sensor 1 is completed by forming the 1st crimping part 56 and the 2nd crimping part 57 with respect to the outer cylinder member 16 and the inner cylinder member 14 which were fixed by the connection crimping part 75. FIG.

The embodiment of the present invention has been described above. However, the present invention is not limited to the embodiment, and various design changes can be made within a range in which the object of the present invention can be achieved.
For example, in the present embodiment, the concentration electromotive force type oxygen concentration sensor is taken as an example, but the present invention is not limited to this, and can be applied to a limiting current type sensor.

It is sectional drawing of the gas sensor 1 of this embodiment. It is an expanded sectional view of the sensor element 2 arrange | positioned at the gas sensor 1 of this embodiment. It is an assembly drawing of the gas sensor 1 of this embodiment. It is an assembly drawing of the gas sensor 1 of this embodiment following FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas sensor 2 ... Gas sensor element 3 ... Heater 5 ... Main metal fitting 26 ... Outer electrode layer 27 ... Inner electrode layer 100 ... Electrode protective layer 101 ... Prevention of poisoning layer

Claims (8)

A solid electrolyte body having oxygen ion conductivity;
A detection electrode provided on one surface of the solid electrolyte body and in contact with the gas to be measured;
A reference electrode provided on the other surface of the solid electrolyte body and in contact with a reference gas;
A porous electrode protection layer provided to cover the detection electrode and carrying catalytic metal particles;
A porous poisoning prevention layer provided to cover the electrode protection layer and preventing the catalytic metal particles from being poisoned;
A gas sensor, comprising: a sensor element having:   The gas sensor according to claim 1, wherein the poisoning prevention layer is made of titania powder and ceramic powder other than titania.   In the poisoning prevention layer, the primary particle size distribution of the titania powder has a peak at 1 μm or less, and the primary particle size distribution of the ceramic powder other than the titania powder has a peak at 10 μm or more. The gas sensor according to claim 2.   The gas sensor according to any one of claims 1 to 3, wherein an amount of the catalyst metal particles supported on the electrode protective layer is 10 to 200 µg.   The gas sensor according to any one of claims 1 to 4, wherein the electrode protective layer has a porosity of 5 to 50%.   The gas sensor according to claim 1, wherein the electrode protective layer has a thickness of 50 to 500 μm.   The gas sensor according to claim 1, wherein the electrode protective layer includes at least one selected from alumina, alumina magnesia spinel, and zirconia. The gas sensor according to any one of claims 1 to 7, wherein the catalyst metal particles are made of at least one selected from Pt, Pd, Rh, and Ru.