JPH09170999A - Manufacture of oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an oxygen sensor whereby a porous layer can be formed on the surface of an element main body of the sensor easily without a gap. SOLUTION: A platinum paste is printed at both faces of a solid electrolytic sheet 12 thereby forming an atmospheric electrode and an exhaust gas electrode 19. After the solid electrolytic sheet 12, a frame body 16, a bottom sheet 15 and a protecting sheet 20 are sequentially laminated, the laminate is pressed and bonded with a predetermined pressure into one body. A slurry P for forming a porous layer is stirred under predetermined conditions to adjust a viscosity. A front end part of an element main body 13 is dipped in the slurry P, and then raised up, so that the slurry P is adhered to the front end part. A porous layer 21 is thus formed. An unnecessary part of the porous layer 21 is cut and removed by a scraper B. The element main body 13 is, after being degreased, baked in a predetermined temperature pattern. A spray layer and a trap layer are formed on the porous layer 21. Then, a heater is bonded to the bottom sheet 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxygen sensor for detecting the oxygen concentration in exhaust gas discharged from an internal combustion engine or the like.

[0002]

2. Description of the Related Art Conventionally, oxygen sensors have been used to detect the oxygen concentration in exhaust gas from internal combustion engines. For example, as shown in FIGS. 6 (a) and 7 (a), the oxygen sensor 40 includes an element body 13 including a solid electrolyte sheet 12 through which oxygen ions can permeate, and the element body 13 at a predetermined temperature or higher. And a heater 14 for heating.

More specifically, the element body 13 will be described.
Is the solid electrolyte sheet 12, the protective sheet 20, the frame 1
6 and the base sheet 15 and the like. The base sheet 15 and the frame body 16 are sequentially stacked on the upper surface of the heater 14, and the solid electrolyte sheet 12 is further stacked on the upper surface of the frame body 16. And these base sheets 1
An atmosphere introducing space 17 is defined by the inner wall surfaces of the frame 5, the frame body 16 and the solid electrolyte sheet 12. The atmosphere having a known oxygen concentration is introduced into the atmosphere introducing space 17.

The solid electrolyte sheet 12 is made of platinum (Pt).
And has a pair of electrodes 18 and 19. One electrode (hereinafter, referred to as “atmosphere side electrode”) 18 is provided on the inner surface of the solid electrolyte sheet 12 (the lower surface in FIG. 6A), and the inside of the atmosphere introducing space 17 is provided on the inner surface thereof. The atmosphere introduced into the air comes into contact with it. On the other hand, the other electrode (hereinafter referred to as “exhaust gas side electrode”) 19
Is disposed on the outer surface (the upper surface in FIG. 6A) of the solid electrolyte sheet 12. The exhaust gas side electrode 19 is covered with a protective sheet 20 laminated on the outer surface of the solid electrolyte sheet 12 except for the tip side (the left end side in FIG. 6A), so that exhaust gas does not come into contact with it. There is.

The tip side of the solid electrolyte sheet 12 (see FIG. 6)
On the outer surface (on the left end side of (a)), a porous layer 41 made of a material obtained by molding a ceramic powder into a sheet shape so as to cover the exhaust gas side electrode 19, and a thermal spray layer 42 formed by thermal spraying of a ceramic material. And are sequentially stacked. Further, a trap layer 43 for suppressing invasion of poisoning components such as lead contained in the exhaust gas into the thermal spray layer 42 is laminated on the thermal spray layer 42.

When the exhaust gas comes into contact with the outer surface of the solid electrolyte sheet 12 through the layers 41 to 43, and the atmosphere of the atmosphere introducing space 17 comes into contact with the inner surface of the sheet 12, the space between the inner and outer surfaces of the sheet 12 is increased. An electromotive force is generated according to the difference in oxygen concentration between the atmosphere and the exhaust gas, and the electromotive force is taken out to the outside through the electrodes 18 and 19. Therefore,
According to the oxygen sensor 40, the oxygen concentration of exhaust gas can be detected based on the magnitude of the electromotive force.

The sprayed layer 42 has a function of controlling the diffusion rate of the exhaust gas contacting the exhaust gas side electrode 19 to stabilize the gas atmosphere.
2 is laminated on the porous layer 41 as described above.

The conventional oxygen sensor 11 adopts such a structure because the surface roughness of the surface of the solid electrolyte sheet 12 is relatively small (ten-point average roughness: about 12.
5z), when the thermal spray layer 42 is formed directly on this surface, it is difficult to secure the adhesion between the thermal spray layer 42 and the solid electrolyte sheet 12. That is, a porous layer 41 having a large surface roughness (10-point average surface roughness: about 50 z) is laminated on the surfaces of the solid electrolyte sheet 12 and the exhaust gas side electrode 19, and the thermal spray layer 42 is formed on the porous layer 41. By forming the sprayed layer 42 on the porous layer 41
It is possible to improve the adhesiveness and prevent the thermal sprayed layer 42 from peeling off. (For example, the oxygen sensor described in JP-A-2-141653)

[0009]

The porous layer 41 is composed of
The porosity is set to be large so as not to hinder the movement of the exhaust gas from the sprayed layer 42 to the outer surface of the solid electrolyte sheet 12, and has almost no function of regulating the movement of the exhaust gas. Therefore, as shown in FIG.
Exhaust gas entering the inside of the porous layer 41 through the side portions S1 to S3 of the porous layer 41 and the gap G1 between the sprayed layer 42 and the protective sheet 20 shown in FIG.
Reach easily. When the exhaust gas enters the porous layer 41 without passing through the trap layer 43 in this way, there arises a problem that platinum forming the exhaust gas side electrode 19 is deteriorated by poisoning components such as lead contained in the exhaust gas.

To solve the above problems, for example,
As shown in FIGS. 6 (b) and 7 (b), the sprayed layer 42 is formed so as to cover the respective side surfaces S4 to S6 of the solid electrolyte sheet 12 and the step portion K1 between the solid electrolyte sheet 12 and the porous layer 41. It is possible to suppress the exhaust gas from reaching the exhaust gas side electrode 19 by forming it. However, since the surface of the solid electrolyte sheet 12 or the protective sheet 20 has a small surface roughness, these surfaces and the sprayed layer 42 do not come into close contact with each other.
Alternatively, there is a possibility that a minute gap serving as an entry path of the exhaust gas may be formed between the surface of the protective sheet 20 and the thermal spray layer 42. In particular, the step portion K1 is shown in FIG.
A gap G2 as shown in (3) is likely to be formed.

Therefore, the porous layer 41 is formed not only on the upper surface of the solid electrolyte sheet 12 but also on the side surfaces S4 to S6 thereof and on the upper and side surfaces of the protective sheet 20, and the porous layer 41 is formed.
It is necessary to form the sprayed layer 42 on the surface of the.

Conventionally, when the porous layer 41 is formed on each surface such as the upper surface and the side surface of the solid electrolyte sheet 12 and the protective sheet 20, as shown in FIG. 8, the porous layer 41 is divided into a plurality of regions. The method of adhering the porous sheets A1 to A6 for forming the porous layer 41 in each region has been adopted. However, in such a method, not only the process is extremely complicated, but also it is difficult to bring the respective porous sheets A1 to A6 into close contact with each other, and in particular, there is no gap in the step portion K1 between the solid electrolyte sheet 12 and the protective sheet 20. It was extremely difficult to adhere the porous sheets A1 to A6.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an oxygen sensor in which a porous layer can be easily formed on the surface of an element body without a gap. It is to provide a manufacturing method.

[0014]

In order to achieve the above object, the present invention provides an element body having a solid electrolyte sheet having electrodes formed on both surfaces thereof, and a sheet shape for heating the element body. A method for manufacturing an oxygen sensor comprising a heater and a laminate, wherein in the element body, a predetermined portion including at least a part of an electrode on an exhaust gas side is immersed in a slurry for forming a porous layer to form the same portion. A step of forming a porous layer by adhering the slurry to the surface of the porous layer, a step of removing an unnecessary portion of the porous layer, and a step of forming a sprayed layer on the porous layer from which the unnecessary portion is removed. That is the point.

(Operation) In the method of manufacturing an oxygen sensor according to the present invention, a predetermined portion of the element body including at least a part of the electrode on the exhaust gas side is immersed in the slurry for forming the porous layer, and the surface of the portion is immersed. A porous layer is formed by depositing the slurry. After that, the unnecessary portion of the porous layer, for example, the porous layer formed on the surface of the portion where the heater is joined in the element body is removed. Further, a sprayed layer is formed by a spraying method on the porous layer from which the unnecessary portion has been removed. At this time, since the surface roughness of the porous layer is large, the sprayed layer is in a state of being in close contact with the porous layer.

As described above, in the method of manufacturing an oxygen sensor according to the present invention, a predetermined portion of the element body is immersed in the slurry, and the porous layer is formed by the slurry adhering to the surface of the portion. Therefore, unlike the method of adhering a plurality of porous sheets to the surface of the element body, a continuous porous layer without gaps can be easily formed on the surface of a predetermined portion of the element body. Therefore, for example, even when there is a stepped portion on the surface of the element body, the porous layer can be formed without a gap. Since the sprayed layer is formed on the porous layer thus formed without any gap, the predetermined portion is covered with the sprayed layer without any gap.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described below with reference to FIGS. Since the oxygen sensor according to the present embodiment has substantially the same configuration as that of the above-described related art, the difference between the two will be mainly described below, and the same structure as the oxygen sensor according to the related art will be described below. The same reference numerals are given to the members.

FIG. 1 shows an oxygen sensor 1 according to this embodiment.
FIG. In FIG. 1, the porous layer 21 and the sprayed layer 22 are not shown. As shown in the figure, the oxygen sensor 11 according to the present embodiment has an elongated shape as a whole, and the base sheet 1 is provided on the upper surface of the heater 14.
5, the frame body 16, the solid electrolyte sheet 12, and the protective sheet 20 are sequentially laminated. The heater 14 and the element body 13 are fixed inside a housing (not shown) of the oxygen sensor 11.

FIG. 2 is a vertical sectional view of the oxygen sensor 11.
As shown in FIG. 2, an exhaust gas side electrode 19 is formed on the upper surface of the solid electrolyte sheet 12, and an atmosphere side electrode 18 is formed on the lower surface thereof along the longitudinal direction of the solid electrolyte sheet 12. The both electrodes 18, 19 are electrode reaction parts 18a, 19a formed on the tip side (the left side in FIG. 1) of the oxygen sensor 11.
And a terminal 19c (only the terminal 19c of the exhaust gas side electrode is shown) formed on the base end side and electrically connected to a lead wire (not shown) of the oxygen sensor 11, and an electrode reaction part 18
electrode lead portion 18 for connecting the terminals a, 19a and the terminal 19c
b, 19b.

The electromotive force corresponding to the exhaust gas oxygen concentration generated between the inner and outer surfaces of the solid electrolyte sheet 12 is the electrode reaction parts 18a, 19a, the electrode lead parts 18b, 19b, and the terminal 1.
9c, taken out through the lead wire. Further, the protective sheet 2 is provided on the electrode lead portion 19b of the exhaust gas side electrode 19.
0 is laminated so that exhaust gas does not come into contact with the lead portion 19b.

The heater 14 is made of a ceramic material such as alumina, and a heating portion (not shown) is embedded inside the heater 14. Further, on the lower surface of the heater 14, a pair of terminals (not shown) electrically connected to the heat generating portion are formed. When a predetermined current is supplied to the heat generating portion through these terminals, the heat generating portion generates heat and maintains the element body 13 at a predetermined temperature (for example, 400 ° C.) or higher.

FIG. 3 is a sectional view taken along line III-III in FIG. As shown in FIGS. 2 and 3, a porous layer 21 is formed on the surface of the tip side portion of the element body 13 except for the lower surface which is in contact with the heater 14. The thermal sprayed layer 2 is formed on the porous layer 21.
2 is formed, and the trap layer 2 is formed on the sprayed layer 22.
3 are formed. As a result, the electrode reaction portion 19a of the exhaust gas side electrode 19, or the solid electrolyte sheet 12, the upper surface and side surfaces of the protective sheet 20, and the solid electrolyte sheet 12
The stepped portion K1 and the like formed by the protective sheet 20 are covered with these layers 21-23.

Next, the oxygen sensor 11 having the above structure
The manufacturing method will be described with reference to FIGS. 4 and 5. [1] (Mixing step) Zirconia (ZrO2) powder obtained by adding yttria (Y2 O3) in a predetermined weight ratio, a solvent (ion-exchanged water), a binder (methyl cellulose),
And the mixture to which the active material (glycerin) has been added is mixed by a mixer. Then, this mixture is stirred and mixed by a kneader.

[2] (Molded Sheet Drying Step) The kneaded product is extrusion-molded by a molding machine, and the molded sheet is dried by a dryer. [3] (Punching Step) The molded sheet is punched by a punching machine to obtain a solid electrolyte sheet 12, a frame body 16, and a base sheet 1.
5. Form a material (green sheet) to be the protective sheet 20.

[4] (Electrode printing step) Platinum paste is printed on both surfaces of the material of the solid electrolyte sheet 12,
The atmosphere side electrode 18 and the exhaust gas side electrode 19 are formed respectively. After forming the electrodes 18 and 19, the materials for the solid electrolyte sheet 12, the frame body 16, the base sheet 15, and the protective sheet 20 are dried.

[5] (Laminating step) Solid electrolyte sheet 1
2. After drying the materials for the frame body 16, the base sheet 15, and the protective sheet 20, these are laminated in order as shown in FIG. Then, the respective materials are pressure-bonded at a predetermined pressure to be integrated.

[6] (Slurry mixing step) Zirconia powder, polyvinyl butyral resin (PVB), peptizer,
Dioctyl phthalate, trichlene, and alcohol are mixed in the weight distribution shown in Table 1 below to form a slurry P for forming a porous layer.

[0028]

[Table 1] The polyvinyl butyral resin is a binder for binding the zirconia powder to bring the viscosity of the slurry P to a predetermined value. The deflocculant has the function of dispersing zirconia particles into a colloidal state, and is mixed in the range of 1 to 3% by weight as shown in Table 1. The action of this deflocculant hardly changes even when added in an amount of 3% by weight or more.

Dioctyl phthalate is a plasticity improver for improving the plasticity of the slurry P, but it is not preferable to add dioctyl phthalate in an amount of 5% by weight or more because it adversely affects the slurry P. Further, trichlene is an organic solvent for the slurry P, and for example, an organic solvent such as toluene or xylene can be substituted. The alcohol is a viscosity adjusting agent for adjusting the viscosity adjusting time of the slurry P described later, and is appropriately selected from the viscosity adjusting agents such as ethanol, propanol, butanol, and hexanol.

A weight mixing ratio of zirconia powder as a main agent and polyvinyl butyral resin (binder), peptizer, dioctyl phthalate (plasticity improver), trichlene (organic solvent), alcohol (viscosity modifier) as an additive. Is adjusted based on the weight distribution shown in Table 1 according to the required properties such as viscosity, plasticity, and tackiness of the slurry P.

[7] (Slurry Stirring Step) 200 g of the slurry P was placed in a rotary container (volume: 1 liter) of a stirrer, and nylon balls (diameter: 10 to 15 mm, weight: 8 to 10) were used to shorten the stirring time. 12 g) is put in a predetermined quantity (40 to 50 pieces).

Then, the rotary container is rotated at a rotation speed of 30 to 60 rpm, and the slurry P in the container is stirred for a predetermined time. If this stirring time is too long, the zirconia powder is uniformly dispersed and the slurry P does not become porous.
0-40 minutes is suitable.

[8] (Slurry viscosity adjusting step) The stirred slurry P is degassed in vacuum to adjust its viscosity to a predetermined value. Here, if the viscosity of the slurry P is larger than 7 Pa · s, the thickness of the porous layer 21 will be increased more than necessary when forming the porous layer 21 described later, and the viscosity is smaller than 1 Pa · s. Therefore, the porous layer 21 does not have a predetermined thickness. In the present embodiment, the slurry P has a viscosity of 1 to 7
By adjusting the pressure to be Pa · s, the porous layer 21
Is 0.1 to 0.2 mm thick.

[0034]

[9] (Dip Step) As shown in FIG. 4A, the tip of the element body 13 is dipped in the slurry P prepared in the above step. At this time, as shown in the figure, part of the protective sheet 20 is also immersed in the slurry P. When the tip portion of the element body 13 in the slurry P is pulled up after a predetermined time, the porous layer 21 having a thickness of 0.1 to 0.2 mm is formed on the portion by the attached slurry P. Since the thickness of the porous layer 21 is substantially determined by the viscosity of the slurry P, the element body 13
It is not necessary to strictly control the time for immersing the tip portion of the in the slurry P.

[10] (Drying Step) The porous layer 21 formed on the tip of the element body 13 is dried for a predetermined time. [11] (Removal Step) As shown in FIG. 4B, the porous layer 21 formed on the lower surface (the right side surface in the figure) of the base sheet 15 is scraped by the scraper B to remove it. As a result, the element body 13 is brought into the state shown in FIG.

[12] (Firing Step) The element body 13 having the porous layer 21 formed in the above step is degreased and then fired in a predetermined temperature pattern. The tenth-point average surface roughness of the porous layer 21 after firing is about 50 z.

[13] (Spraying Step) The porous layer 21
Thermally spray a ceramic material such as spinel (magnesium aluminate) on top. As a result, FIG.
As shown in (c), the sprayed layer 22 is formed. At this time, since the sprayed layer 22 is in close contact with the porous layer 21 having a high surface roughness, no gap is formed between the layers 21 and 22.

[14] (Trap Layer Forming Step) A slurry for forming a trap layer containing alumina powder is applied onto the sprayed layer 22 and dried for a predetermined time. As a result, as shown in FIG. 5D, a trap layer 23 is formed on the sprayed layer 22.

[15] (Heater Bonding Step) In the step [11], the heater 14 that has been fired in advance is bonded to the lower surface of the base sheet 15 from which the porous layer 21 has been removed.
Alternatively, the heater 14 is superposed on the lower surface of the oxygen sensor 1
The element main body 13 and the heater 14 are held in close contact with each other by one holding member (not shown).

In the present embodiment, the above steps [1] to
Oxygen sensor 11 as shown in FIGS. 2 and 3 via [15]
Is manufactured. The embodiment described above has the following (a)
It has the characteristics of (c).

(A) According to this embodiment, a gap is formed in the upper surface or the side surface of the element body 13 including the electrode reaction portion 19a of the exhaust gas side electrode 19, or in the step portion K1 between the solid electrolyte sheet 12 and the protective sheet. It is possible to form a continuous porous layer 21 without a gap, and to form the sprayed layer 22 and the trap layer 23 on the porous layer 21 without a gap. Therefore, these layers 21 to 23 increase the invasion route to the exhaust gas side electrode 19 to suppress the invasion of the exhaust gas, and prevent the exhaust gas side electrode 19 from being deteriorated by the poisoning component contained in the exhaust gas. You can

(B) In the present embodiment, the tip side portion of the element body 13 is immersed in the slurry P for forming the porous layer 21 adjusted to have a predetermined viscosity, and the slurry P is attached to the portion. Thus, the porous layer 21 is formed. Therefore, the porous layer 21 can be easily formed as compared with the conventional method in which a plurality of porous sheets are adhered to the surface of the element body 13 to form the porous layer.

(C) According to the present embodiment, the thickness of the porous layer 21 can be appropriately adjusted by adjusting the viscosity of the slurry P. Another embodiment in which some of the steps in the above embodiment are modified will be described below.

(1) The removal of the porous layer 21 in the step [11] may be performed before the layer 21 is dried. Further, regardless of the removal method using the scraper B, for example, a resin tape is attached to the lower surface of the base sheet 15 and masked in advance to form the porous layer 21, and then the tape is peeled off. Base sheet 1
Alternatively, the porous layer 21 formed on the lower surface of 5 may be removed.

(2) In the step [5], the solid electrolyte sheet 12, the frame body 16, the base sheet 15, and the material for the protective sheet 20 are sequentially laminated, and the base sheet 15 is formed.
In this case, a material (green sheet) for the heater 14 is laminated. Then, in the step [13], degreasing and firing are performed on the element body 13 and the heater 14, and the step [1
The oxygen sensor 11 is manufactured through steps 2] to [14]. According to such a method, it is not necessary to remove the porous layer 21 formed on the lower surface of the base sheet 15 in the step [11], and the manufacturing process can be shortened.

The technical idea grasped from each of the above-mentioned embodiments will be described below together with its effects. (A) A method for manufacturing an oxygen sensor, comprising: stacking an element body having a solid electrolyte sheet having electrodes formed on both sides thereof, and a sheet-shaped heater for heating the element body, the element body comprising: In the heater, a predetermined portion including at least a part of the exhaust gas side electrode, after forming a porous layer by attaching the slurry to the surface of the predetermined portion by immersing in a slurry for forming a porous layer,
A method for manufacturing an oxygen sensor, comprising forming a sprayed layer on the porous layer.

According to the above (a), a continuous porous layer having no gap can be easily formed on the surface of the element body and the heater by covering at least a part of the electrode on the exhaust gas side. Therefore, the sprayed layer can be formed on the porous layer without any gaps to suppress the invasion of the exhaust gas, and the deterioration of the electrode on the exhaust gas side due to the exhaust gas can be prevented.

(B) The method for producing an oxygen sensor according to claim 1, wherein the slurry for forming the porous layer is adjusted to have a predetermined viscosity. According to the above (b), the porous layer can be controlled to have a predetermined thickness by adjusting the viscosity of the slurry for forming the porous layer to a predetermined viscosity.

[0049]

As described above in detail, according to the method for manufacturing an oxygen sensor of the present invention, it is possible to form a continuous porous layer on the surface of the element body without a gap. Therefore, since the sprayed layer is formed on the porous layer without any gap, it is possible to prevent the trouble caused by the poisoning component contained in the exhaust gas coming into contact with the electrode of the element body.

In addition, the same layer can be easily formed as compared with the conventional method in which a plurality of porous sheets are adhered to the surface of the element body to form the porous layer.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an oxygen sensor according to an embodiment.

FIG. 2 is a vertical sectional view of an oxygen sensor.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

FIG. 4 is an explanatory view for explaining a manufacturing process of the oxygen sensor.

FIG. 5 is a cross-sectional view for explaining the manufacturing process of the oxygen sensor.

FIG. 6A and FIG. 6B are longitudinal sectional views of the oxygen sensor.

7A is a sectional view taken along line VIIA-VIIA of FIG. 6A,
6B is a sectional view taken along line VIIB-VIIB of FIG.

FIG. 8 is a perspective view for explaining a method of forming a porous layer according to a conventional technique.

[Explanation of symbols]

11 ... Oxygen sensor, 12 ... Solid electrolyte sheet, 13 ... Element body, 14 ... Heater, 18 ... Atmosphere side electrode, 19 ... Exhaust gas side electrode, 21 ... Porous layer, 22 ... Spraying layer.

Claims (1)

[Claims] 1. A method of manufacturing an oxygen sensor, comprising: stacking an element body having a solid electrolyte sheet having electrodes formed on both sides thereof, and a sheet-shaped heater for heating the element body. In the element body, a step of forming a porous layer by depositing a predetermined portion including at least a part of the electrode on the exhaust gas side into a slurry for forming a porous layer to attach the slurry to the surface of the same portion, A method of manufacturing an oxygen sensor, comprising: a step of removing an unnecessary portion of the porous layer; and a step of forming a sprayed layer on the porous layer from which the unnecessary portion is removed.