JP2002174619A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor having a sealing structure exhibiting a highly hermetic sealing characteristic when being installed to a metallic case while securing excellent durability even in a severe environment. SOLUTION: This gas sensor formed into a cylindrical shape is provided with a detection part constructed of a pair of electrodes 3 and 4, which are formed on both of the outside and inside main faces in the vicinity of the front end of a cylindrical solid electrolyte base body 2, for detecting an environmental condition, a heating part constructed of a heating resistor 8, which is buried inside a ceramic insulating layer 6 formed on the outside surface of the base body 2, for heating the detection part, and terminal parts 11 and 18 arranged in the vicinities of the rear end of the base body 1. Between the detection part and the terminal parts 11 and 18, a ceramic member 21 for hermetically sealing a clearance with respect to a case body housing the gas sensor 1 is formed integrally by simultaneous burning with the detection part and the heating part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxygen sensor element for detecting an oxygen concentration in an exhaust gas of an automobile, or a nitrogen oxide concentration, for example, comprising a detection unit having a zirconia solid electrolyte and a pair of electrodes. The present invention relates to a gas sensor in which a NOx sensor element to be detected is housed in a metal case body, and particularly to an improvement in a gas-tight sealing structure for a gas that requires heat resistance and high reliability.

[0002]

2. Description of the Related Art The structure of a conventional gas sensor will be described with reference to FIG. FIG. 4A is a schematic cross-sectional view of a flat-plate type heater-integrated sensor element 41 for detecting oxygen concentration. An oxygen ion conductive plate-shaped solid electrolyte 42a is formed so as to surround the air introduction hole 43.
A measuring electrode 44 made of Pt is formed on the outer surface of a, and a reference electrode 45 made of Pt is formed on the side of the air introduction hole 43, and these portions form a detecting portion for detecting the oxygen concentration in the surrounding atmosphere. I have. These electrodes 44, 45 are hermetically isolated from each other by a solid electrolyte 42a, and the electrodes 44, 45
An electromotive force is generated according to the ratio of oxygen concentration between the two. An insulating layer 46 made of aluminum oxide is provided on the solid electrolyte 42b opposed to the air introducing hole 43.
A heating resistor 47 sandwiched between is built in, thereby heating the detection unit.

In addition, such a flat sensor element 41
Is housed in a metal case 48 and mounted on an automobile or the like. At this time, since the measurement electrode 44 formed on the outer surface of the solid electrolyte 42a needs to be completely shut off from the atmosphere, the sensor element 41 is sealed in the metal case 48 so as not to contact the atmosphere. Is being done.

For example, according to Japanese Patent Publication No. 2000-511645, as shown in FIG.
There has been proposed a structure in which a sealing material 50 made of ceramic powder is filled between two ceramic members 49a and 49b to be penetrated, and the ceramic members 49a and 49b are pressurized to secure gas tightness.

As another sealing structure, Al ₂ O ₃
It is known that a sealing member made of ceramics such as is bonded to the sensor element using silicate glass and the like, and the sealing member is interposed between the sensor element and a metal case.
No. 9823 and the like.

[0006]

However, FIG.
In the gas seal structure using the ceramic powder as shown in FIG.
The sealing material 50 made of the pressurized ceramic powder leaks from the gap between the ceramic members 49a and 49b, and as a result, the sensor element mixes the reference atmosphere and the gas to be measured. There was a fatal problem.

In the method of joining with glass,
There is a problem that a joining process using glass is separately required, and a joining technique with high accuracy is required to enhance joining reliability.

Accordingly, an object of the present invention is to provide a gas sensor having excellent durability even in a severe environment and capable of forming a sealing structure having high hermetic sealing when attached to a case body. Is what you do.

[0009]

A gas sensor according to the present invention comprises:
A detection unit for detecting an environmental condition by forming a pair of electrodes on both the inner and outer main surfaces near the tip of the cylindrical solid electrolyte substrate, and the detection unit in a ceramic insulating layer formed on the outer surface of the substrate. In a cylindrical gas sensor comprising a heating portion having a heating resistor embedded therein for heating and a terminal portion provided near a rear end of the base, the gas sensor is provided between the detection portion and the terminal portion. A ceramic member for hermetically sealing a gap with a case body for storing the ceramic member is integrally formed by simultaneous firing with the detection portion and the heating portion.

It is desirable that the ceramic member be made of ceramics containing ZrO ₂ as a main component from the viewpoint of simultaneous sintering. Further, the sealing property can be further enhanced by interposing a sealing material at a contact portion between the ceramic member and the case body.

Furthermore, the durability of the sensor element can be enhanced by coating the entire outer surface on the tip side of the joint with the ceramic member with a ceramic porous layer.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings showing an example of the gas sensor of the present invention. FIG. 1 is a schematic perspective view (a) showing an example of a gas sensor, and a cross-sectional view (A) of FIG. However, in (a), the ceramic protective layer 13 is omitted for convenience of explanation.

The sensor element 1 shown in FIG. 1 is made of a zirconia ceramic solid electrolyte having oxygen ion conductivity, and a first electrode is formed on the inner surface of a cylindrical tube 2 having a sealed end.
A reference electrode 3 which is in contact with a reference gas such as air is formed and adhered to a measurement gas such as exhaust gas as a second electrode at a position facing the reference electrode 3 with the cylindrical tube 2 interposed therebetween. The measuring electrode 4 is formed by adhesion. The detection part is formed by the reference electrode 3, the cylindrical tube 2 made of a zirconia solid electrolyte, and the measurement electrode 4.

A ceramic insulating layer 6 of Al ₂ O ₃ or the like is formed on the outer surface of the cylindrical tube 2 having a sealed end. The opening 7 is formed so that a part or the whole is exposed.

A heating resistor 8 made of Pt or the like for heating the detecting portion is buried in the ceramic insulating layer 6 around the opening 7. On the surface of the ceramic insulating layer 6, a ceramic heat insulating layer 9 made of Al ₂ O ₃ or the like is formed in order to increase the heating efficiency of the heating resistor 8.

Reference electrode 3 formed on the inner surface of cylindrical tube 2
Is connected to the sensor terminal 11a provided on the outer surface of the cylindrical tube 2 via the open end surface of the cylindrical tube 2. on the other hand,
The measurement electrode 4 formed on the outer surface of the cylindrical tube 2 is connected to a lead portion 10 formed on the surface of the ceramic heat insulating layer 9 via the end face of the opening 7 formed in the ceramic insulating layer 6, and is connected to the ceramic heat insulating layer 9. Terminal portion 11 formed on the surface of layer 9
b. In addition, the edge part which exists in the said end surface in the cylindrical pipe 2 is chamfered C, and the defect of the electrical connection which arises in an edge part is avoided.

A protective layer 12 made of ZrO ₂ or the like is further formed on the surface of the lead portion 10 formed on the surface of the ceramic heat insulating layer 9. The protective layer 12 can protect the lead portion 10 from physical destruction such as scratching when assembling the element or collision with foreign matter when the element falls. The ceramic protective layer 12 is preferably made of the same ZrO ₂ as the solid electrolyte in order to prevent stress from being generated due to a difference in thermal expansion with the solid electrolyte. Further, at least the surface of the detecting section is covered with a porous ceramic protective layer 13.

A metal member 14 for connection to an external circuit is brazed and fixed to the sensor terminals 11a and 11b by a brazing material 15, respectively. As a result, the detection data generated in the detection unit is transferred to the read unit 1.
0, sensor terminals 11a, 11b and metal member 14
And is connected to an external circuit via.

On the other hand, the heating resistor 8 formed in the ceramic insulating layer 6 is formed so as to penetrate the lead portion 16 also formed in the ceramic insulating layer 6 and the ceramic insulating layer 6 and the ceramic heat insulating layer 9. The through conductors (not shown) are electrically connected to the heater terminal portions 18 formed on the outer surface of the ceramic heat insulating layer 9. A metal member 19 for connecting to an external heat-generating power source is fixed on the terminal portion 18 with a brazing material 20, and a current flows through the heat-generating resistor 8 through the metal member 19, whereby the heat-generating resistor 8 is heated and measured. The temperature of the detecting portion including the electrode 4, the cylindrical tube 2, and the reference electrode 3 is rapidly raised to a predetermined temperature.

Further, according to the present invention, the sensor element 1 is sealed and fixed to a metal case, which will be described later, at a substantially central portion between the detection portion of the sensor element 1 and the terminal portions 11 and 18. A ceramic member 21 is mounted. Note that this ceramic member 21 is
It is important to form the sensor element 1 and the ceramic member 21 firmly and without gaps between the ceramic member 21 and the sensor element 1.

FIG. 2 is a schematic cross-sectional view of the sensor element 1 with the metal case cut away for explaining the structure when the sensor element 1 is fixed to the metal case. According to FIG. 2, the sensor element 1 is inserted into the metal case 22, the sensor element 1 is pressed by a press, and the corner of the ceramic member 21 is formed with respect to the inner wall 23 a of the flange portion 23 formed on the metal case 22. In addition, the metal case 22a is caulked and fixed by the groove 25 formed in the flange member 23 while the parts 24 are in contact with each other, so that gas tightness can be secured at a low cost, and the manufacturing cost of the measurement sensor is greatly reduced. It is possible to reduce it.

In addition, a known sealing material 26 such as asbestos packing or Ni-coated copper packing is interposed between the ceramic member 21 and the inner wall 23a of the flange member 23 at this time to improve hermetic sealing. it can.
Further, it is desirable that the corners 24 of the ceramic member 21 be chamfered such as a C surface in order to prevent chipping or the like from occurring during handling. Form and abut them,
By performing pressure bonding, stress concentration can be avoided, and breakage of the ceramic member 21 can be prevented.

Further, according to the sensor element 1 of the present invention,
A ceramic protective layer 13 is formed on the outer surface of the detection unit. As is apparent from the mounting structure of the sensor element 1, the tip side of the ceramic member 21 is exposed to the gas to be measured. It is desirable to form the ceramic protective layer 13 on the entire surface of the sensor element 1 on the tip side of the ceramic member 21. Thereby, the durability of the portion of the sensor element 1 exposed to the gas to be measured can be increased.

According to the present invention, since the ceramic member 21 is formed by integrally sintering the main body of the sensor element 1, the material of the ceramic member 21 is made of a ceramic material that can be co-fired with the sensor main body. It is necessary to become. ZrO ₂ , S
iO ₂ , MgO, Y ₂ O ₃ and rare earth oxides, Ca
One or more of metal oxide-based ceramics of O and Al ₂ O ₃ may be mentioned. Particularly, it is made of ceramics mainly composed of ZrO ₂ , and 3 to 15 mol% of rare earth element oxide, MgO or CaO. ZrO ₂ ceramics stabilized by is preferably used.

In the present invention, when forming the cylindrical tube 2,
The ceramic solid electrolyte used is ZrO_TwoContains
Ceramics, specifically, Y_TwoO_ThreeAnd Y
b_TwoO _Three, Sc_TwoO_Three, Sm_TwoO_Three, Nd_TwoO_Three, Dy_TwoO_ThreeEtc.
1 to 30 mol% of rare earth oxide in terms of oxide, preferably
Is a partially stabilized ZrO containing 3 to 15 mol%._TwoOr
Stabilized ZrO_TwoIs used.

Further, the content of Zr in ZrO ₂ is 1 to 20 atomic%.
The use of ZrO _{2 in} which is substituted by Ce has the effect of increasing the electron conductivity and further improving the responsiveness.

Further, for the purpose of improving sinterability, the above Z
Al ₂ O ₃ or SiO ₂ can be added to and contained in rO ₂ , but if it is contained in a large amount, the creep characteristics at high temperatures deteriorate, so that Al ₂ O ₃ and SiO ₂
Is preferably 5% by weight or less, particularly 3% by weight or less in total.

The content of Na in the solid electrolyte is 200 ppm or less, particularly 100 ppm, from the viewpoint of preventing diffusion from the solid electrolyte into the ceramic insulating layer.
Is desirable.

On the other hand, as the ceramic insulating layer 6 in which the heating resistor 8 is embedded, an oxide containing alumina and / or magnesia, particularly, an alumina material, a spinel material, or a composite compound material of alumina and spinel is preferably used. Used. At this time, in order to improve the sinterability of the ceramic insulating layer, it is desirable to add a small amount of a Si component, but the content is 0.1% by weight in terms of oxide.
The effect can be seen from the above, but when the content of Si exceeds 5% by weight, diffusion and segregation of Na in the ceramic insulating layer are promoted, and the life of the heating resistor made of platinum or the like is easily reduced. The Si content is desirably in the range of 0.1 to 5% by weight. The Si content is desirably 0.5 to 3% by weight. In particular, 0.5 to 2% by weight is desirable from the viewpoint of preventing the diffusion of Na.

The ceramic insulating layer 6 is desirably made of a dense ceramic having a relative density of 80% or more and an open porosity of 5% or less. This is because the denseness of the ceramic insulating layer 6 increases the strength of the insulating layer, thereby increasing the mechanical strength of the oxygen sensor itself. Further, the content of Na in the ceramic insulating layer 6 is 50 ppm, particularly 30 ppm.
It is desirable that the content be not more than ppm in order to extend the life of the heater.

The heating resistor 8 embedded in the ceramic insulating layer 6 may be made of one kind of metal selected from the group consisting of platinum, rhodium, palladium and ruthenium, or two or more kinds of alloys. Desirably, it is desirable to select a metal or an alloy having a melting point higher than the firing temperature of the ceramic insulating layer 6 in terms of simultaneous sintering with the ceramic insulating layer 6.

In addition to the above-mentioned metals, the heating resistor 8 may be alumina, spinel, a compound of alumina / silica, forsterite, or the above-mentioned electrolyte, from the viewpoint of preventing sintering and enhancing the adhesion to the insulating layer. It is desirable to mix zirconia and the like in a volume ratio of 10 to 80%, particularly 30 to 50%.

The ceramic heat insulating layer 9 formed on the surface of the ceramic insulating layer 6 in which the heating resistor 8 is embedded is preferably made of zirconia ceramics. The ceramic heat insulating layer 9 made of zirconia can alleviate the stress caused by the difference in thermal expansion and the difference in firing shrinkage between the solid electrolyte and the ceramic insulating layer 6 so that the thermal stress can be minimized. At this time, the distance between the cylindrical tube 2 and the heating resistor 8 and the distance between the ceramic heat insulating layer 9 and the heating resistor 8 are each 2 μm.
It is desirable that this is the case.

Each of the reference electrode 3 and the measuring electrode 4 formed on the inner and outer surfaces of the cylindrical tube 2 is made of one or more alloys selected from the group consisting of platinum, rhodium, palladium, ruthenium and gold. Is used. The ceramic solid electrolyte described above is used for the purpose of preventing grain growth of the metal in the electrode during operation of the sensor and to increase the so-called three-phase interface contact between the metal particles, the solid electrolyte, and the gas related to the response. The components may be mixed in the electrode at a ratio of 1 to 50% by volume, particularly 10 to 30% by volume.

In the present invention, the shape of the measurement electrode 4 exposed in the opening 7 is not particularly limited, and the opening 7 is provided at two positions which are opposite positions in the cylindrical tube 2. , The thermal shock resistance can be improved. The expansion of the opening 7 is set in the range of 30 to 90 degrees with respect to the center of the cross section of the cylindrical tube 2, thereby suppressing the generation of thermal stress around the opening 7 and the heating resistor 8. Heating efficiency can be increased. This opening 7
Is particularly excellent in the range of 40 to 80 degrees.

On the other hand, the reference electrode 3 formed on the inner surface of the cylindrical tube 2 made of a solid electrolyte is connected to the opening 7 of the measuring electrode 4.
It may be formed on the inner surface portion facing the more exposed portion, and may be formed on an area larger than the exposed portion area of the measurement electrode 4, for example, on the entire inner surface of the cylindrical tube 2.

In the oxygen sensor of the present invention, FIG.
As shown in (b), a porous ceramic protective layer 13 is formed on the surface of the measurement electrode 4 exposed in the opening 7, and the ceramic protective layer 13 has the following two purposes. Is formed. First, it is provided for the purpose of preventing the measurement electrode 4 from being poisoned by the exhaust gas and lowering the output voltage. The surface of the measurement electrode 4 which is exposed is made of zirconia, alumina, magnesia or spinel. It is formed as a porous protective layer. An oxygen sensor provided with such a protective layer can be generally used as a stoichiometric air-fuel ratio sensor (λ sensor). In this case, the ceramic protective layer 13 has an open porosity of 10 to 10.
Desirably, it is made of a 40% porous body.

Second, it functions as at least one kind of gas diffusion-controlling layer selected from the group consisting of zirconia, alumina, spinel, magnesia and γ-alumina having fine pores on the exposed surface of the measurement electrode 4. As the ceramic protective layer 13 serving as such a gas diffusion controlling layer, a porous body having an open porosity of 5 to 30% is desirable.

On the surface of the ceramic protective layer 13 serving as the gas diffusion-controlling layer, the above-mentioned ceramic protective layer made of alumina or spinel can be provided from the viewpoint of further preventing poisoning of exhaust gas. Such a heater-type oxygen sensor can be applied as a wide-range air-fuel ratio sensor element (A / F sensor) described later.

Next, a method for manufacturing the oxygen sensor according to the present invention will be described with reference to the method for manufacturing the gas sensor shown in FIG. 1 as an example. (1) First, a hollow cylindrical tube 32 having one end sealed as shown in FIG. The cylindrical tube 32 is formed by adding an appropriate organic binder to a ceramic solid electrolyte powder having oxygen ion conductivity, such as zirconia, as appropriate, for example, by extrusion, isostatic pressing (rubber pressing), or press forming. It is produced by the method described above.

At this time, the solid electrolyte powder used was zirconia powder, Y ₂ O ₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ and Dy as stabilizers. _Two
A mixed powder obtained by adding a rare earth oxide powder such as O ₃ at a ratio of 1 to 30 mol%, preferably 3 to 15 mol% in terms of oxide, or a coprecipitated raw material powder of zirconia and the above stabilizer is used. . It is also possible to use ZrO ₂ powder or coprecipitated material, a 1-20 atomic% of Zr in ZrO ₂ was replaced by Ce. Further, for the purpose of improving the sinterability, it is possible to add Al ₂ O ₃ or SiO ₂ to the solid electrolyte powder in an amount of 5% by weight or less, particularly 3% by weight or less.

(2) Patterns 33 and 34 serving as reference and measurement electrodes are formed on the inner and outer surfaces of the cylindrical tube 32 made of the solid electrolyte by, for example, a slurry dipping method using a conductive paste containing platinum, or Formed by screen printing, pad printing, and roll transfer. At this time, it is efficient to print the reference electrode 33 on the inner surface of the cylindrical tube 32 by filling and discharging the conductive paste and applying the conductive paste to the entire inner surface. Thus, the sensor body A is manufactured.

(3) Next, a heater element B as shown in FIG. 3B is formed. The heater element B is prepared by first preparing a slurry by using zirconia powder and appropriately adding an organic binder for molding, and using the slurry to form a ceramic having a predetermined thickness by a doctor blade method, an extrusion molding method, a pressing method, or the like. A green sheet for forming the insulating layer 35 is manufactured. The thickness of one green sheet is from 50 to 500 μm, particularly from 100 to 3 from the viewpoint of sheet handling.
A range of 00 μm is particularly preferred.

Then, on the surface of the formed green sheet,
Alumina, spinel or composite oxide powder of alumina and spinel is printed by a screen printing method, a pat printing method, a roll transfer method, etc., and thereafter, a conductive paste containing platinum powder is printed by a screen printing method, a pat printing method, a roll transfer method. After applying a platinum heater pattern including a lead portion by printing by a method or the like, the above-described powder for forming a ceramic insulating layer is further applied thereon again to form a ceramic insulating layer 3.
A sheet-like heater laminated body in which the heating resistor 36 is embedded in 5 is obtained. Thereafter, an opening 37 is formed in the heater laminate by punching or the like.

(4) Next, as shown in FIG. 3 (c), a heater element B is wound around the surface of the cylindrical sensor element A to form a cylindrical laminate. At this time, the heater element B
Is wound around the sensor body A by bonding an adhesive such as an acrylic resin or an organic solvent between the heater body B and the sensor body A, or by mechanically applying pressure with a roller or the like. Can be adhered to. At this time, the seams of the wound heater element B may be overlapped with each other at the sheet ends or bonded at a predetermined interval in consideration of shrinkage during firing.

(5) Thereafter, as shown in FIG.
The molded body obtained by winding the heater body B around the sensor body A is formed in advance by pressing a ceramic composition such as ZrO ₂ into a cylindrical molded body 38 for the ceramic member 21.
To a predetermined position into the opening 39, and the gap formed between the two is filled with slurry.

At this time, as the slurry to be filled in the gap between the two, in addition to the same raw material as that of the ceramic member 21, a Y ₂ O ₃ —SiO ₂ —Al ₂ O ₃ composite oxide is preferably used. You. For example, if the composition range is _{20 to} 53% by weight of Y ₂ O _3, 10 to 34% by weight of Al ₂ O _{3, and} 24 to 60% by weight of SiO ₂ , it is easy to form a glassy ceramic having a melting point of 1500 ° C. or less. Produces a gas-tight joint. Further, as other ceramic materials for filling, 3 to
ZrO stabilized with 15 mol% rare earth oxide
To ₂ total weight 100 parts by _{weight, Y 2 O 3, Yb 2} O 3, Sc 2
When 0 to 50 parts by weight of at least one of rare earth oxides such as O ₃ , Sm ₂ O ₃ , Gd ₂ O ₃ , and CeO ₂ or CaO is added, the ceramic member 21 and the main body of the sensor element 1 are added. It is desirable that the joining property is further improved. Further, based on 100 parts by weight of the total weight of ZrO ₂ , SiO ₂
Can be obtained even if 0 to 10 parts by weight is added.

(6) The above-mentioned cylindrical laminate can be integrated by firing at a temperature at which each component can be fired simultaneously. The sintering is performed, for example, in an inert atmosphere such as argon gas or in the air 1300.
By firing at about 1700 ° C. for about 1 to 10 hours, the heater element B and the sensor element A can be simultaneously fired.

In the above manufacturing method, the reference electrode 33
And the measurement electrode 34 was applied when the cylindrical tube 32 was formed.
These electrodes are formed by winding a heater element B around the surface of a cylindrical tube 32 having no electrodes to form a cylindrical laminate, and then screen-printing, pad-printing an electrode paste on the cylindrical laminate. It can be applied to the inner surface of the cylindrical tube 32 and the surface of the cylindrical tube 32 in the opening 37 in the heater element B by a roll transfer method or a dipping method, or can be formed by a sputtering method or a plating method.

Further, in order to form the ceramic protective layer 13 shown in FIG. 1, after firing, a powder of alumina, spinel, zirconia, or the like is printed and applied by a sol-gel method, a slurry dipping method, a printing method, or the like, and is baked. It is also possible to form by coating the above ceramics by a sputtering method or a plasma spraying method, or to apply a slurry for forming a ceramic protective layer 13 in advance when producing a cylindrical laminated body and then sinter it at the same time. It is.

According to the above-described manufacturing method, a sensor, a heater, and a ceramic member can be integrally formed in a single firing step, and a separate bonding step is not required, thereby reducing manufacturing yield and manufacturing cost. This is very preferable because

[0052]

EXAMPLE Here, the gas sealing property of the gas sensor of the present invention installed in a metal case was examined. First, the following materials were prepared for producing evaluation samples. a) ZrO containing 5 mol% Y ₂ O ₃ prepared by a coprecipitation method
₂ powder b) Pt paste d) 5 mol% Y ₂ O ₃ containing 30% by volume of ZrO ₂ powder containing the MgO content containing the following fine Al ₂ O ₃ powder c) Al ₂ O ₃ 10ppm 10 vol% E) Pt paste containing 40 vol% of ZrO ₂ powder containing 5 mol% Y ₂ O ₃ The particle diameter of the ZrO ₂ powder used in the Pt paste of the above e) is an average secondary particle diameter. (D50) was set to 2 μm.

First, a polyvinyl alcohol solution was added to the ZrO ₂ powder of a) to prepare a kneaded material, and a cylindrical tube having an outer diameter of about 4 mm and an inner diameter of 2.3 mm was formed by extrusion molding.
Further, a cylindrical tube 2 having one end sealed was prepared by filling the tip with a clay of ZrO ₂ .

Further, a predetermined amount of an acrylic binder was added to the ZrO ₂ powder of a) to prepare a slurry, and then a green sheet for the ZrO ₂ ceramic protective layer 9 having a thickness of 200 μm was prepared by a doctor blade method.

On the surface of the green sheet for the ceramic protective layer 9, the slurry composed of the Al ₂ O ₃ powder of b) was applied so as to have a thickness of about 10 to 15 μm after firing.
The heating resistor 8 and the lead 16 for the resistor were formed on the surface of the ceramic insulating layer 6 made of Al ₂ O ₃ by screen printing using the Pt paste of the above c). Further, a through hole was opened at a predetermined position of the lead portion 16 by punching, and the Pt paste of d) was filled.

Next, the green sheet for the ceramic protective layer 9 is turned over, and the lead 1 connected to the measuring electrode 4 is turned over.
0, the terminal portion 11b connected to the measurement electrode 4 and the heater terminal portion 18 were respectively formed at predetermined positions by screen printing using the Pt paste of d) or e).
On the lead portion 10 connected to the measurement electrode 4, as the ceramic protective layer 12, the same slurry as the above-mentioned ZrO ₂ slurry for forming a green sheet, which is formed into a green sheet, is fired, and has a thickness of about 15 to 20 μm. Screen printed so that

After that, the green sheet is again turned over,
Wherein such heating resistor 8 is enclosed in the ceramic insulating layer 6 of Al ₂ O _3, after firing the slurry of Al ₂ O ₃ powder of the c), was applied to be about 10 to 15 [mu] m.

As described above, in the green sheet (hereinafter, referred to as a sheet-like laminate) in which the respective prints are laminated, a region where the measurement electrode 4 is to be formed is opened by punching to form an opening 7. , On the surface of the cylindrical tube 2,
The adhesive layer was wound using an adhesion liquid in which the above-mentioned ZrO ₂ powder containing 5 mol% of Y ₂ O ₃ was dispersed in an acrylic resin to produce a cylindrical laminate.

Further, a ZrO ₂ ceramic powder stabilized by 5 mol% of a rare earth element oxide is press-formed into a substantially cylindrical shape to produce a formed body for the ceramic member 21.
The cylindrical laminated body was inserted to a predetermined position along the inner wall of the molded body, and a gap formed between the two was filled with a slurry made of the same raw material as the ceramic member molded body.

Thereafter, in the atmosphere, 1400 to 1500
It was baked at 2 ° C. for 2 hours and integrated.

After firing, a metal member made of a Ni wire of φ0.6 mm made of Au-Cu brazing material is placed on the sensor terminal portion and the heater terminal portion at a predetermined temperature in an inert atmosphere at a predetermined temperature. It was fixed to be 6 mm.

Then, a ceramic protective layer made of spinel and having a porosity of about 30% is coated on the entire surface of the sensor element on the tip side of the ceramic member by plasma spraying so as to have a thickness of about 100 μm. Thus, the gas sensor of the present invention was manufactured. After firing, the outer diameter of the sensor element is 3.0 to 3.1 mm, and the inner diameter is 1.7 to 1.8 mm.
Met.

The gas sensor thus obtained was housed in a metal case via an asbestos packing with a structure as shown in FIG. 2, and was fixed by caulking while being pressed in, to obtain a gas sensor for evaluation.

The gas sensor for evaluation is set on a predetermined gas pressurizing jig, and He gas is supplied from the detecting portion side of the metal case at 2 k.
Pressure was applied at a pressure of gf / cm ² for 30 minutes, and the amount of gas leak to the terminal portion side was measured. As a result, excellent airtightness with a maximum gas leak amount of 0.1 cc / min or less was exhibited.

[0065]

As described above in detail, the gas sensor of the present invention is formed by integrally forming a ceramic member for hermetically sealing the case with a sensor element having a heater by simultaneous firing. The member and the sensor element can be joined and formed with high airtightness. In addition, since the step of joining the ceramic members is not required, the manufacturing process of the gas sensor can be simplified and the cost can be reduced.

[Brief description of the drawings]

1A and 1B are a schematic perspective view and a cross-sectional view taken along the line AA for explaining one embodiment of the gas sensor of the present invention.

FIG. 2 is a schematic sectional view when the gas sensor of FIG. 1 is housed in a metal case.

FIG. 3 is a process chart illustrating an example of a method for manufacturing a gas sensor according to the present invention.

4A is a schematic cross-sectional view of a conventional flat sensor element, and FIG. 4B is a schematic cross-sectional view for explaining a structure when the sensor element is housed in a metal case.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor element 2 Cylindrical tube (solid electrolyte base) 3 Reference electrode 4 Measurement electrode 6 Ceramic insulating layer 7 Opening 8 Heating resistor 9 Ceramic heat insulating layer 13 Ceramic protective layer 21 Ceramic member

Claims (4)

[Claims] 1. A detecting portion for detecting an environmental condition, comprising a pair of electrodes formed on both inner and outer main surfaces near a front end of a cylindrical solid electrolyte substrate, and a ceramic insulating layer formed on an outer surface of the substrate. In a cylindrical gas sensor comprising a heating unit having a heating resistor for heating the detection unit embedded therein, and a terminal unit provided near the rear end of the base, the detection unit and the terminal unit A gas sensor, wherein a ceramic member for hermetically sealing a gap with a case body accommodating the gas sensor is integrally formed by simultaneous firing of the detection unit and the heating unit. 2. The ceramic member according to claim 1, wherein said ceramic member is made of a ceramic containing ZrO ₂ as a main component.
A gas sensor as described. 3. The gas sensor according to claim 1, wherein a sealing material is interposed at a contact portion between the ceramic member and the case body. 4. The gas sensor according to claim 1, wherein a ceramic porous layer is coated on the entire outer surface of the gas sensor on the side closer to the tip than the joint with the ceramic member.