JP2003057204A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor having improved temperature increase efficiency in a section, where the inner and outer electrodes of the sensor sheet are formed by increasing the section, where the inner and outer electrodes in the sensor sheet are formed with rapid increase to a temperature at which the oxygen sensor can be operated. SOLUTION: The oxygen sensor comprises a base sheet, that is made of an insulating material where a resistance electrical heating element is embedded in the inside, an air duct sheet that is made of oxygen-ion-conductive solid electrolyte where a cutting for air ducts is formed, and a sensor sheet that is similarly made of the oxygen-ion-conductive electrolyte where electrodes are formed on both the surfaces. On the base sheet, the air duct sheet and the sensor sheet are formed in a layer successively in one piece without the intermediary of an intermediate layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for measuring the oxygen concentration in exhaust gas for automobiles, for example.

[0002]

2. Description of the Related Art In recent years, exhaust gas emitted from an internal combustion engine of an automobile or the like poses a problem that it harms the environment and the human body, and regulations on exhaust gas have been tightened. Therefore, various exhaust gas purification systems have been developed,
The air-fuel ratio feedback control system has been drawing attention from an early stage because it does not require modification of the engine body and does not impair engine performance or fuel consumption. In this air-fuel ratio feedback control system, the oxygen sensor plays an important role, and various types of oxygen sensors have been developed and put into practical use.

As such an oxygen sensor, a so-called laminated oxygen sensor in which a detection element and a heater are laminated and integrated is often manufactured. Such a laminated oxygen sensor is attached to an exhaust gas manifold, and the detection element portion of the laminated oxygen sensor is sealed inside the exhaust gas manifold. Then, the oxygen concentration is detected by this detection element portion, and the control unit which has received the signal sets the air-fuel ratio and the like so as to obtain the most appropriate oxygen concentration (combustion state).

FIG. 2A is an exploded perspective view schematically showing an example of a laminated oxygen sensor, and FIG. 2B is an exploded perspective view.
3 is a vertical sectional view of the oxygen sensor shown in FIG.

As shown in FIG. 2, a conventional oxygen sensor 5 is used.
0 is the intermediate layer 53 and the air duct notch 550 on the base material sheet 51 in which the resistance heating element 52 is embedded.
Air duct sheet 54 having a substantially U shape in plan view,
And the inner electrode 57 and its terminal portion 570 on the upper and lower surfaces thereof,
Outer electrode 59, its terminal portion 590, connection terminal portion 570a
The sensor sheet 56 formed with is laminated in order and integrated. Also, this oxygen sensor 50
Among the members constituting the above, the base material sheet 51 was made of an insulating material, and the intermediate layer 53, the air duct sheet 54 and the sensor sheet 56 were made of an oxygen ion conductive solid electrolyte.

A resistance heating element 5 embedded in a base material sheet 51.
2 is composed of a heating portion 52a and a belt-shaped heating element terminal portion 52b which are sequentially coupled in a U-shape and a left-right inverted U-shape, and the heating element terminal portion 52b has a through hole 520. It is connected to the external terminal 520a formed on the outer side of the base material sheet 51 through. Further, the air duct notch 550 formed in the air duct sheet 54 is
By sandwiching the air duct sheet 54 between the intermediate layer 53 and the sensor sheet 56, a hollow air duct 55 is formed.
Becomes Further, the terminal portion 570 of the inner electrode 57 formed on the sensor sheet 56 and the connection terminal portion 570 a formed on the outer side of the sensor sheet 56 are connected to each other through the through hole 5.
8 are connected.

The inner electrode 57 is adapted to come into contact with the atmosphere in the air duct 55, while the outer electrode 59 is contacted.
Is in contact with the exhaust gas, but the outer electrode 5
9 is covered with a porous electrode protection layer 500 so that it does not come into direct contact with exhaust gas.

The intermediate layer 53 is formed between the base sheet 51 and the air duct sheet 54, and diffuses the flow of heat emitted from the resistance heating element 52 while propagating inside. Sensor sheet 56
It plays a role of making the temperature of the portion (hereinafter, also referred to as a detection portion) where the inner electrode 57 and the outer electrode 59 are formed uniform.

In order to detect the oxygen concentration in the exhaust gas with such an oxygen sensor 50, first, the sensor sheet 56 is used.
The detection part of (1) is heated by the resistance heating element 52 to a temperature at which the oxygen sensor can be used. Between the inner electrode 57 that is in contact with the atmosphere of high oxygen concentration on the lower surface of the sensor sheet 56 (inside the air duct 55) and the outer electrode 59 that is in contact with the exhaust gas of low oxygen concentration on the upper surface of the sensor sheet 56. A dark and light cell is formed on the to generate an electromotive force. Since the oxygen concentration in the atmosphere can be a constant value, the oxygen concentration in the exhaust gas can be detected by using the oxygen sensor 50.

By the way, in the air-fuel ratio feedback control system using such an oxygen sensor, the air-fuel ratio feedback control is performed while the temperature of the detection portion of the sensor sheet is raised to the usable temperature of the oxygen sensor after the engine is started. The control system cannot function, and the air-fuel mixture that greatly deviates from the stoichiometric air-fuel ratio is sucked into the engine, and the exhaust gas discharged during this time contains a large amount of NOx, CO, HC and the like. It will be that. Therefore, it is desirable to be as short as possible from the time when the engine is started until the air-fuel ratio feedback control system functions, and an oxygen sensor that is excellent in the temperature raising efficiency of the detection portion of the sensor sheet is desired. Was there.

[0011]

However, since the conventional oxygen sensor as described above has a structure in which the intermediate layer is interposed between the base sheet and the air duct sheet, it is embedded in the base sheet. Also, in order to heat the detection portion of the sensor sheet with the resistance heating element, it is necessary to heat the intermediate layer as well, and it has not been possible to quickly raise the detection portion to a temperature at which the oxygen sensor can be used. Further, when the intermediate layer is interposed between the base material sheet and the air duct sheet, the space between the resistance heating element and the detection portion of the sensor sheet is inevitably widened, so that the resistance heating element is discharged. It takes a long time for the heat to propagate to the detection portion, which also makes it impossible to quickly raise the detection portion to a temperature at which the oxygen sensor can be used. That is, the conventional oxygen sensor is inferior in the temperature raising efficiency of the detection portion of the sensor sheet.

In view of the above problems, the present invention can quickly raise the temperature of the portion of the sensor sheet where the inner and outer electrodes are formed to the temperature at which the oxygen sensor can be used. Another object of the present invention is to provide an oxygen sensor which is excellent in temperature raising efficiency of a portion where the outer electrode is formed.

[0013]

According to the present invention, a base material sheet made of an insulating material, in which a resistance heating element is embedded, and an oxygen ion conductive solid electrolyte are provided, and a notch for an air duct is formed. And an air duct sheet, which is also composed of an oxygen ion conductive solid electrolyte, and a sensor sheet having electrodes formed on both surfaces thereof, and the air duct sheet and the sensor sheet on the base material sheet. It is an oxygen sensor characterized by being sequentially laminated and integrated without an intermediate layer. Hereinafter, the present invention will be described in detail.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The oxygen sensor of the present invention comprises an insulating material, a base material sheet in which a resistance heating element is embedded, and an oxygen ion conductive solid electrolyte to form a notch for an air duct. Air duct sheet,
Similarly, it is composed of an oxygen ion conductive solid electrolyte, and is composed of a sensor sheet having electrodes formed on both sides thereof,
The air duct sheet and the sensor sheet are sequentially laminated and integrated on the base sheet without an intermediate layer.

In the following description, the oxygen sensor of the present invention will be described as an oxygen sensor for measuring the oxygen concentration in the exhaust gas of an automobile, but the use of the oxygen sensor of the present invention is not limited to this. However, it can be used as various oxygen sensors using oxygen as a medium.

In the oxygen sensor of the present invention, the air duct sheet and the sensor sheet are sequentially laminated and integrated on the base sheet without an intermediate layer. That is, unlike the conventional oxygen sensor described above, the intermediate layer is not heated when the detection portion of the sensor sheet is heated, and the resistance heating element embedded in the base sheet and the detection Since the space between the oxygen sensor and the portion is narrow, the temperature of the detection portion can be quickly raised to the temperature at which the oxygen sensor can be used, as compared with the conventional oxygen sensor.

FIG. 1A is an exploded perspective view schematically showing an embodiment of the oxygen sensor of the present invention, and FIG.
FIG. 4 is a vertical sectional view thereof. As shown in FIG. 1, the oxygen sensor 10 of the present invention is mainly composed of a base sheet 11, an air duct sheet 14 and a sensor sheet 16, and a space between the base sheet 11 and the air duct sheet 14 is provided between the base sheet 11 and the air duct sheet 14. The oxygen sensor 50 has almost the same structure as that of the oxygen sensor 50 described in the above-mentioned conventional technique except that the intermediate layer is not interposed. Therefore, a detailed description of the structure will be omitted here.

The base material sheet 11 formed at the lowermost part of the oxygen sensor 10 of the present invention is a plate-like body in which the resistance heating element 12 is embedded, and the air duct sheet 14 laminated thereon. And functions as a heater for heating the sensor sheet 16. The size of the base sheet 11 is not particularly limited and may be appropriately determined according to the size of the target oxygen sensor.
Length 50-100mm, width 3-20mm, thickness 0.2-
It is about 0.8 mm.

On the bottom surface of the base material sheet 11, there are provided external terminals 120a which are electrically connected to the ends of the heating element terminal portion 12b of the resistance heating element 12 formed therein and through the through holes 120. External terminal 120a
Through, the resistance heating element 12 is connected to an external control device or the like. The shape of the external terminal 120a is not particularly limited, but is usually rectangular.

The insulating material forming the base sheet 11 is not particularly limited, and examples thereof include alumina, zirconia,
Examples thereof include oxide ceramics such as mullite, nitride ceramics such as silicon nitride and aluminum nitride, ceramics such as carbide ceramics such as silicon carbide, glass materials, and forsterite. Among these,
Alumina ceramics are preferred. In particular, the main component is alumina and the sintering aid is SiO ₂
Is preferably 4% by weight or less, MgO is 0.5% by weight or less, and CaO is 1.2% by weight or less, and the density ratio is 96% or more. If the density rate of the base material sheet 11 is less than 96% or if the amount of the sintering aid is larger than the above range, there is a high possibility that there will be holes.
Further, since the grain boundaries of the alumina ceramics constituting them are deteriorated due to migration or the like and holes are easily formed, the resistance heating element 12 is easily oxidized when the oxygen sensor 10 is used for a long period of time. The above-mentioned density ratio refers to the percentage of the ratio of the actual density of the sintered body to the theoretical density of the ceramic.

Such a base sheet 11 can be obtained by firing a green sheet containing the above-mentioned material as a main component, and the green sheet to be the base sheet 11 and an air duct described later. It is desirable that the surfaces of the green sheets that will be the sheets 14 contact each other be roughened surfaces. This is because the contact area of these green sheets becomes large, and the adhesive strength between the base sheet 11 and the air duct sheet 14 obtained after firing becomes excellent. Further, the base material sheet 11 and the air duct sheet 1
When the surfaces of the green sheets 4 to be in contact with each other are roughened surfaces, a mixed layer of the materials constituting these is easily formed at the interface between the base material sheet 11 and the air duct sheet 14 and in the vicinity thereof. Therefore, it is considered that the adhesive strength between the base material sheet 11 and the air duct sheet 14 becomes excellent. Specifically, the roughened surface is JIS B
Ra according to 0601 is preferably about 10 to 50 μm. Such a roughened surface can be formed, for example, by rubbing the surface of each green sheet with sandpaper, a brush or the like.

The resistance heating elements 12 are embedded in the base sheet 11 and are sequentially connected in a U-shape and a left-right inverted U-shape, and are arranged at substantially equal intervals in the width direction of the base sheet 11. The heating portion 12a has a repeating pattern, and the strip-shaped heating element terminal portion 12b extends from both end portions of the heating portion 12a to the vicinity of the end portion of the base sheet 11. In addition, as described above, the heating element terminal portion 12 of the resistance heating element 12
The end portion of b is the base sheet 1 through the through hole 120.
The electrical connection with the external terminal 120a formed outside 1 is achieved.

The resistance heating element 12 has a thickness of 5 to 20 μm.
m, the line width in the heat generating part 12a is preferably about 0.1 to 0.5 mm, and the line width in the heat generating terminal part 12b is preferably about 0.2 to 1.0 mm. . When the thickness and line width of the resistance heating element 12 are in such ranges, the resistance value of the resistance heating element 12 can be made suitable, and at the same time, the resistance heating element 12 can be obtained.
No wire breakage, migration or short circuit will occur. Further, the length of the vertical component of the repetitive pattern in the heat generating portion 12a is appropriately adjusted according to the size of the oxygen sensor 10 and the like, but is preferably about 6.0 to 15 mm. This is because the temperature stability of the resistance heating element 12 is excellent in this range. The number of turns of the repeating pattern in the heat generating portion 12a is appropriately determined in consideration of the line width and line spacing of the resistance heating element 12, but is preferably 4 to 8 times. This is because the detection portion of the sensor sheet 16 can be heated to a uniform temperature.

Further, the pattern of the heat generating portion 12a of the resistance heating element 12 formed in the region directly below the air duct 15 may be formed relatively denser than the pattern of the heat generating portion 12a outside the region. desirable. Normally, the inside of the air duct 15 (in the air) has a very small thermal conductivity as compared with the material of which the air duct sheet 14 is made, and thus it is difficult for heat to be transferred.
There is a case where the temperature of the portion facing (the portion where the inner electrode 17 of the sensor sheet 16 is formed, that is, the detection portion) is not satisfactorily heated. However, if the pattern of the heat generating portion 12a is set to the above-described pattern, the heat generation amount in the area can be made relatively larger than the heat generation amount outside the area, and as a result, the detection portion of the sensor sheet 16 can be obtained. Can be heated satisfactorily and quickly.

The pattern of the heat generating portion 12a can be appropriately determined according to the size of the oxygen sensor 10 and the line width of the heat generating portion 12a. For example, the turn interval of the heat generating portion 12a near the center of the above area. Is the narrowest, and the pattern may have a pattern in which the turn interval of the heat generating portion 12a gradually increases toward both ends.

The resistance heating element 12 having such a pattern is
It is formed by printing a conductor paste. The conductor paste is preferably a conductor paste containing Pt or W as a main component. This is because Pt is not oxidized by oxygen in the atmosphere and W has the highest melting point among metals. The through holes and the external terminals are preferably made of the same conductor paste. However, when a conductor paste containing W as a main component is used, it is desirable to perform a plating treatment such as nickel plating or gold plating on the portions (external terminals) that come into contact with the atmosphere. This is to prevent the portion that comes into contact with the atmosphere from being oxidized. The remainder of the conductor paste is preferably composed of a ceramic component, and examples of this ceramic component include alumina, silicon nitride, mullite, and the like, or a ceramic composed of a mixture thereof.

Other examples of the above conductor paste include:
For example, those containing a refractory metal such as Ta, Nb, Ti, Mo and Re as a main component can be cited. Also,
Ceramics such as alumina may be added to these refractory metals. Even when these high melting point metals are used in the conductor paste, it is desirable to perform plating treatment on the portion in contact with the atmosphere for the same reason as in the case of W. The Pt and W and the refractory metals thereof may be used alone or in combination of two or more.

The sensor sheet 16 has an inner electrode 17 and its terminal portion 170 formed on its lower surface, and an outer electrode 19 and its terminal portion 190 on its upper surface, and a connection terminal portion 170.
a is formed, and the inner electrode 17 and the outer electrode 1 are formed.
9 is formed at a position that faces the sensor sheet 16. This is to form a density cell between the inner electrode 17 and the outer electrode 19.

Such a sensor sheet 16 is made of an oxygen ion conductive solid electrolyte, and it is desirable that the oxygen ion conductive solid electrolyte contains zirconia ceramic as a main component. In particular, a partially stabilized zirconia containing zirconia as a main component and containing about 8 mol% of yttria is desirable. This is because it has high oxygen ion conductivity and good strength, and is also excellent in thermal shock resistance. The size of the base sheet 11 is not particularly limited.
It is desirable that the thickness be the same as the above, but the thickness is desirably about 0.2 to 0.6 mm.
This is because the range is such that a suitable oxygen ion conductivity can be secured.

The inner electrode 17 formed on the lower surface of the sensor sheet 16 has an air duct sheet 14 which will be described later.
Of the outer electrode 1 formed on the upper surface of the sensor sheet 16 so as to come into contact with the atmosphere in the air duct 15 of
9 is adapted to come into contact with exhaust gas.

Such inner electrode 17 and outer electrode 19
The shape of is not particularly limited, but is usually a rectangular shape as shown in FIG. In addition, the inner electrode 17 and the outer electrode 19
Is preferably a mesh structure. For example,
When the outer electrode 19 has a mesh structure, the sensor sheet 16, the outer electrode 19 and the three phases of the exhaust gas come into contact with each other.
This is because the increase of the phase boundary points improves the diffusibility of the exhaust gas and also improves the catalytic activity of the outer electrode 19. When the inner electrode 17 has a mesh structure, the same effect can be obtained for the three phases of the sensor sheet 16, the inner electrode 17, and the atmosphere.

The inner electrode 17 and the outer electrode 19 are
It is formed by printing a conductor paste on both sides of the sensor sheet 16. The conductor paste is preferably a conductor paste containing platinum as a main component. Usually, a noble metal is used for the conductor paste, but platinum is the most excellent in catalytic activity, chemical stability, electron conductivity and heat resistance. Other examples of the above precious metals include
For example, rhodium, palladium, etc. can be mentioned. Further, the conductor paste may be a ceramic such as alumina added to the noble metal.

The terminal portions 170 and 190 are strip-shaped, and one end portion thereof is connected to the inner electrode 17 and the outer electrode 19, respectively, and the other end portion thereof is connected to a control portion or the like. Since the terminal portion 170 of the inner electrode 17 is formed on the lower surface of the sensor sheet 16, it cannot be directly connected to the control portion or the like. Therefore,
The terminal portion 170 is electrically connected to the connection terminal portion 170a formed on the upper surface of the sensor sheet 16 through the through hole 18, and the connection terminal portion 170a is connected to the control portion and the like. ing. It is desirable that the terminal portions 170 and 190, the connection terminal portion 170a and the through hole 18 are made of the same material as that of the inner electrode 17 and the outer electrode 19 described above.

In general, as shown in FIG. 1B, a porous electrode protection layer 100 is formed on the outer electrode 19. This is to prevent the outer electrode 19 from directly contacting the exhaust gas and attaching dirt or the like. Electrode protection layer 100
There is no particular limitation on the material of, for example, spinel (M
Examples thereof include heat resistant metal oxides such as gO-Al ₂ O ₃ ), alumina and magnesia. It has excellent heat resistance,
This is because the outer electrode 19 can be reliably protected.

The air duct sheet 14 has a groove-shaped notch 150 for the air duct formed in the vicinity of its center, and is substantially U-shaped in a plan view. In addition, the notch 150 for the air duct of the air duct sheet 14 is formed by the base sheet 11
The air duct 15 having a hollow shape is formed by being sandwiched between the sensor sheet 16 and the sensor sheet 16 from above and below.

The shape of the air duct notch 150 may be substantially the same as the inner electrode 17 and the terminal portion 170 as shown in FIG. 1, or may be a rectangular shape. The size of the inner electrode 17 is not particularly limited as long as the inner electrode 17 fits inside the inner electrode 17, and is appropriately determined according to the size and shape of the inner electrode 17.

The air duct sheet 14 is made of the same oxygen ion conductive solid electrolyte as the sensor sheet 16 described above, and its size is preferably the same as that of the base sheet 11 described above. .

Each member constituting the oxygen sensor 10 of the present invention is as described above. The oxygen sensor 10 of the present invention made of such a member is such that the air duct sheet 14 and the sensor sheet 1 are sequentially provided on the base material sheet 11.
Since 6 is laminated and integrated, the inner electrode 17 and the outer electrode 19 which are heated by the resistance heating element 12 embedded in the base material sheet 11 and the sensor sheet 16 sandwiched between them are The difference in oxygen concentration between the exhaust gas and the atmosphere can be satisfactorily measured.

Further, as described above, the oxygen sensor of the present invention is one in which the air duct sheet and the sensor sheet are sequentially laminated and formed on the base material sheet without an intermediate layer. Therefore, when heating the portion where the inner electrode and the outer electrode of the sensor sheet are formed,
The intermediate layer is not heated, and the distance between the resistance heating element embedded in the base sheet and the detection portion of the sensor sheet is narrowed, so the oxygen sensor can be used quickly in the detection portion of the sensor sheet. The temperature can be raised to the temperature. That is, the oxygen sensor of the present invention has excellent temperature raising efficiency.

Further, the air-fuel ratio feedback control system using the oxygen sensor of the present invention has a short time from the start of the engine to the start of operation, and NOx, CO, H
The amount of exhaust gas containing a large amount of C etc. can be reduced.

Next, an example of the method of manufacturing the oxygen sensor of the present invention will be described. The oxygen sensor of the present invention can be manufactured by producing a base sheet, an air duct sheet, and a green sheet to be a sensor sheet, and then laminating and firing them.

(1) Preparation of Green Sheet as Base Material Sheet To prepare a green sheet as a base material sheet, first, a raw material slurry containing ceramic powder, a binder resin and a solvent is prepared. Then, the raw material slurry is extruded, doctor bladed, screen printed, or printed using a mask to prepare a first green sheet. The resistance heating element 12 is located near one end of the first green sheet. A through hole to be the through hole 120 is formed by punching or the like at the position where the conductor paste that will be the end of the heating element terminal portion 12b is printed.

The type of ceramics constituting the above ceramic powder is not particularly limited, and examples thereof include the ceramic powder described in the oxygen sensor of the present invention. Among these, alumina, mullite, and silicon nitride are preferable, and particularly, those containing alumina as a main component and SiO ₂ , MgO, CaO, etc. added as a sintering aid are preferable. Further, in this case, it is desirable that the average particle diameter of the alumina particles is about 1 to 10 μm.

Next, the through hole formed in the first green sheet is filled with a conductive paste to be the through hole 120, and the conductive paste is used to screen the resistance heating element on the first green sheet by a screen printing method or the like. After printing the conductor paste layer to be 12, the first green sheet, the conductor paste layer and the like are dried. The conductor paste layer is printed so that the end portion of the heating element terminal portion 12b of the resistance heating element 12 overlaps with the through hole that is the through hole 120 filled with the conductor paste.

Examples of the conductor paste include the same as the conductor paste described in the resistance heating element of the oxygen sensor of the present invention. For example, when the refractory metal contained in the conductor paste is W. The average particle size of the W particles is preferably 0.5 to 5 μm. The thickness of the conductor paste layer is preferably about 10 to 80 μm.

Next, using the same raw material slurry as that for the first green sheet, extrusion molding method, doctor blade method, screen printing method, printing using a mask, or the like, is used to make the same size as the first green sheet. After producing the second green sheet, the second green sheet is laminated on the surface of the first green sheet on which the conductor paste layer serving as the resistance heating element 12 is printed, and dried to form a green sheet laminate. Create.

Then, the green sheet laminate is turned over and the through holes 120 filled with the conductor paste are formed.
A conductor paste layer to be the external terminals 120a is printed in the region including the through holes to be the conductor paste, and the conductor paste to be the external terminals 120a is dried to produce a green sheet to be the base sheet. To do. By printing the conductor paste in this manner, the conductor paste layer that becomes the end of the heating element terminal portion 12b of the resistance heating element 12 and the conductor paste layer that becomes the external terminal 120a become a through hole that becomes the through hole 120. It is connected through the filled conductor paste.

Further, a roughened surface having Ra according to JIS B 0601 of about 10 to 50 μm is provided on the opposite side of the surface of the dried green sheet, which is the base sheet, on which the conductor paste layer to be the external terminals 120a is printed. It is desirable to apply the roughening treatment. This is because it is possible to improve the adhesive strength between the air duct sheet and the base sheet of the oxygen sensor manufactured through the subsequent steps. The method of forming the roughened surface is not particularly limited, and examples thereof include a method of rubbing the surface of the green sheet serving as the base sheet with sandpaper, a brush or the like.

(2) Preparation of Green Sheet for Air Duct Sheet and Sensor Sheet In order to prepare green sheet for air duct sheet and sensor sheet, first, for solid electrolyte layer containing ceramic powder, binder resin and solvent. Prepare the paste. Then, the solid electrolyte layer paste is extruded, doctor bladed, screen printed, or printed with a mask to prepare an air duct sheet and a green sheet for a sensor sheet.

The type of ceramic constituting the above ceramic powder is not particularly limited, and for example, the zirconia ceramic described in the oxygen sensor of the present invention is desirable. In particular, zirconia is the main component and yttria is the whole. A partially stabilized zirconia content of about 8 mol% (mixed crystal system of cubic crystal and monoclinic crystal) is desirable.

Next, a through hole opening is formed in the sensor sheet green sheet, and the through hole opening is described in the oxygen sensor of the present invention.
Fill with a noble metal paste such as platinum, rhodium or palladium. A ceramic such as alumina may be added to the noble metal paste.

Then, using the above-mentioned precious metal paste, an inner electrode having the shape as described in the oxygen sensor of the present invention and a conductor paste layer to be the terminal portion thereof are screened on one surface of the sensor sheet green sheet. Print by printing method. At this time, printing is performed so that the conductor paste layer near the one end of the terminal portion of the inner electrode and the conductor paste filled in the through hole opening are connected. Then, the sensor sheet green sheet or the like is dried.

Next, the dried green sheet for sensor sheet is turned over to become the outer electrode and its terminal portion at the position opposite to the inner electrode and its terminal portion on the opposite surface on which the conductor paste layer serving as the inner electrode is formed. Conductor paste layer,
Also, a conductor paste layer to be a connection terminal portion is printed by a screen printing method or the like, and these conductor paste layers are dried to produce a green sheet to be a sensor sheet. At this time, the conductor paste layer serving as the connection terminal portion is formed in a region including the through hole opening filled with the conductor paste. By forming the conductor paste layer to be the connection terminal portion in this manner, the conductor paste layer to be the connection terminal portion and the conductor paste layer to be the terminal portion of the inner electrode are connected via the conductor paste to be the through hole. Will be done.

The green sheet to be the air duct sheet is the same as the green sheet for the air duct sheet.
It can be manufactured by performing a processing process using a cutter or the like to form a groove portion serving as a U-shaped notch for an air duct as shown in FIG. In addition, according to JIS B 0601, the surface of the green sheet that serves as the air duct sheet comes into contact with the green sheet that serves as the base sheet.
It is desirable to apply a roughening treatment to obtain a roughened surface having Ra of about 10 to 50 μm. This is because it is possible to improve the adhesive strength between the air duct sheet and the base sheet of the oxygen sensor manufactured through the subsequent steps. The method for forming the roughened surface is not particularly limited, and, for example,
Examples thereof include a method of rubbing the surface of the green sheet which will be the air duct sheet with sandpaper, a brush or the like.

(3) Then, the green sheets produced in the above (1) and (2) are laminated in the order of a green sheet as a base sheet, a green sheet as an air duct sheet and a green sheet as a sensor sheet. The oxygen sensor of the present invention can be manufactured by performing degreasing and baking treatment after pressure bonding.

[0056]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 (1) Preparation of Green Sheet as Base Material Sheet 87 parts by weight of alumina, 1.5 parts by weight of talc, 9.5 parts by weight of kaolin, 2.0 parts by weight of calcium carbonate and 13 parts of water.
5 parts by weight were pulverized in an alumina ball mill for 6 hours, mixed, and then spray-dried to be granulated to prepare a raw material powder for a base sheet.

Next, 100 parts by weight of the raw material powder, 0.5 parts by weight of the dispersant and 53.2 parts by weight of toluene were mixed for 5 hours in an alumina ball mill to prepare a slurry A. In addition, 7.43 parts by weight of xylene and 8.33 of PVB
Parts by weight, ethanol 31.43 parts by weight, n-butyl 3.
Slurry B was prepared by mixing 13 parts by weight and 5.42 parts by weight of DOP in a pot mill for 3 hours.

The slurry A and the slurry B thus prepared were mixed in an alumina ball mill for 16 hours to prepare a raw material slurry. Then, this raw material slurry was filtered using a 400 mesh (25 μm) mesh, and the viscosity of the raw material slurry was adjusted to 5 Pa · s (50
00 cps), and the first and second green sheets were produced by the doctor blade method. Then, a through-hole to be a through-hole was formed in the first green sheet by punching.

Next, 74.8 parts by weight of platinum powder, 2.6 parts by weight of ethyl cellulose and 22.6 of α-terpineol.
The raw material paste is adjusted by mixing parts by weight, and the raw material paste is kneaded for 1 hour with a liquor machine, and then further passed through three rollers 5 times to further knead, and the viscosity is 20 Pa · s.
The platinum paste was prepared by adjusting to.

Using the first green sheet, the second green sheet and the platinum paste thus obtained, a green sheet to be a base sheet was prepared by the method described in the above embodiment. Here, the size of the green sheet serving as the base sheet is 54.5 mm in length, 4.3 mm in width, and 200 μm in thickness.
The pattern of the conductor paste layer to be formed was as shown in FIG.

(2) Preparation of Green Sheet for Air Duct Sheet and Sensor Sheet First, zirconia powder 1 containing 8 mol% of yttria was prepared.
15 parts by weight of methylcellulose, 1 part by weight of benzyl alcohol, and 19 parts by weight of water were mixed with 00 parts by weight to prepare a paste for a solid electrolyte layer, and an air duct sheet and a green sheet for a sensor sheet were produced by a doctor blade method. . The air duct sheet green sheet had a thickness of 0.2 mm, and the sensor sheet green sheet had a thickness of 0.2 mm.

Next, using the air duct sheet and the sensor sheet green sheet, a green sheet to be an air duct sheet and a sensor sheet was produced by the method described in the above embodiment. here,
The composition of the inner electrode and its terminal portion, the outer electrode and its terminal portion, and the conductor paste layer to be the connection terminal portion formed on the upper and lower surfaces of the green sheet that serves as the sensor sheet is Pt powder (particle size 0.5 to 1 μm). Was 62% by weight, organic Pt (platinum salt of fatty acid) was 10% by weight (Pt 1% by weight), co-material was 8% by weight, binder (polyvinyl butyral) and solvent (α-terpineol) were 20% by weight. . The through holes for establishing electrical connection between the terminal portion of the inner electrode and the connection terminal portion were filled with a conductor paste having the same component as that of the conductor paste layer serving as the inner electrode. Also,
By using a cutter to form a notch for the air duct in the shape that the inner electrode formed on the sensor sheet fits inside the green sheet for the air duct sheet,
A green sheet to be an air duct sheet was produced.

Each of the green sheets prepared in (1) and (2) above is laminated in the order of a green sheet to be a base sheet, a green sheet to be an air duct sheet and a green sheet to be a sensor sheet at 50 ° C. and 10 MPa.
(100 kg / cm ² ), thermocompression bonding was performed for 60 seconds to prepare an oxygen sensor laminate.

Then, this oxygen sensor laminated body is used for 500
Degreasing was carried out at 1 ° C for 1 hour, followed by baking at 1500 ° C for 4 hours. The degreasing and firing were performed in an oxidizing atmosphere. Further, spinel (MgO.Al ₂ O ₃ ) is plasma-sprayed so as to cover the outer electrode of the obtained sintered body to form an electrode protective layer having a thickness of 5 μm. An oxygen sensor of the present invention was manufactured by laminating a duct sheet and a sensor sheet in this order.

Example 2 Similar to Example 1 except that the pattern of the heat generating portion of the resistance heating element formed in the region directly below the air duct is formed more densely than the pattern of the heat generating portion outside the region. Manufactured an oxygen sensor. Specifically, the pattern of the heat generating portion has a minimum turn interval of 150 μm in the central part of the heat generating part, and the pattern is such that the turn interval gradually increases from the central part toward the outside, and the maximum turn The spacing was 300 μm.

Example 3 First, a green sheet to be a base sheet and an air duct sheet was prepared in the same manner as in Example 1, and the surfaces of these green sheets that contact each other were rubbed with sandpaper (# 800). As a result, a roughened surface having Ra of 20 μm according to JIS B 0601 was formed. Then, an oxygen sensor was manufactured in the same manner as in Example 1.

Comparative Example 1 The same as Example 1 except that an intermediate layer having a thickness of 0.2 mm made of the same components as the air duct sheet and the sensor sheet was formed between the base sheet and the air duct sheet. Manufactured an oxygen sensor.

Thermocouples were embedded in the detection portions of the sensor sheets of the oxygen sensors manufactured in Examples 1 to 3 and Comparative Example 1, each was connected to a DC power source of 12 V, and a current was passed to heat the resistance heating element to 800 ° C. Then, the temperature of the detection portion was measured with the thermocouple, and the time until the temperature of the detection portion was raised to 800 ° C. was measured. The results are shown in Table 1.

[0070]

[Table 1]

As is clear from the results shown in Table 1, in the oxygen sensors according to Examples 1 to 3, the time until the temperature of the detection portion of the sensor sheet was raised to 800 ° C. was 14 to 18.
Seconds, and the oxygen sensor according to Example 2 was able to raise the temperature of the above-mentioned detection portion as quickly as 14 seconds. on the other hand,
In the oxygen sensor according to Comparative Example 1, 25 seconds and Examples 1 to 3
It took more time to raise the temperature of the above-mentioned detection portion than that of the oxygen sensor according to the above. That is, the oxygen sensors according to Examples 1 to 3 were superior in heating efficiency to the oxygen sensors according to Comparative Example 1. Further, the oxygen sensor according to Example 3 had very excellent adhesive strength between the base sheet and the air duct sheet.

[0072]

As described above, the oxygen sensor of the present invention is one in which the air duct sheet and the sensor sheet are sequentially laminated and integrated on the substrate sheet without an intermediate layer. Therefore, when the inner electrode and the outer electrode of the sensor sheet are heated, the intermediate layer is not heated, and the resistance heating element embedded in the base sheet and the inner side of the sensor sheet are not heated. The interval between the electrode and the portion where the outer electrode is formed is narrowed, so that the portion of the sensor sheet where the inner electrode and the outer electrode are formed can be quickly raised to the temperature at which the oxygen sensor can be used. That is, the oxygen sensor of the present invention has excellent temperature raising efficiency.

[Brief description of drawings]

FIG. 1A is an exploded perspective view schematically showing an embodiment of an oxygen sensor of the present invention, and FIG. 1B is a vertical sectional view thereof.

FIG. 2A is an exploded perspective view schematically showing an embodiment of a conventional oxygen sensor, and FIG. 2B is a vertical sectional view thereof.

[Explanation of symbols]

10 oxygen sensor 11 Base sheet 12 Resistance heating element 14 Air duct sheet 15 air ducts 16 sensor sheet 17 Inner electrode 18 through holes 19 outer electrode 100 Electrode protection layer 110 heater part Notch for 150 air ducts 160 sensor 170, 190 Terminal part 170a connection terminal part

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G004 BB04 BD04 BE04 BE13 BE22                       BF03 BF05 BF09 BH15 BJ03                       BK03 BL08 BL09 BL18 BL19                       BM04 BM06 BM07

Claims (2)

[Claims] 1. A base material sheet made of an insulating material, in which a resistance heating element is embedded, and an air duct sheet made of an oxygen ion conductive solid electrolyte, in which notches for an air duct are formed, Consisting of an oxygen ion conductive solid electrolyte and a sensor sheet having electrodes formed on both surfaces thereof, on the base material sheet, the air duct sheet and the sensor sheet without an intermediate layer, sequentially. An oxygen sensor, which is formed by stacking and is integrated. 2. The pattern of the heating portion of the resistance heating element formed in the region directly below the air duct is formed relatively denser than the pattern of the heating portion outside the region. Oxygen sensor.