JP2002296225A - Heater-integrated type oxygen sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater-integrated type oxygen sensor element capable of rapidly raising temperature, having a ceramic porous layer with high adherence, and having an electrode prevented from being poisoned by an exhaust gas. SOLUTION: This heater-integrated type oxygen sensor element is provided with a cylindrical tube 2 formed of a ceramic solid electrolyte and having one end sealed, a reference electrode 3 and a measurement electrode 4 formed at opposite positions of the inside surface and the outside surface of the cylindrical tube 2, respectively, a ceramic insulation layer 5 having an opening 6 formed so as to expose part or the whole part of the measurement electrode 4 with a heating element 7 embedded around the opening 6, a dense ceramic solid electrolyte layer 8 formed on the surface of the insulation layer 5, and the ceramic porous layer 11 overlaid so as to cover at least the opening 6 and the electrolyte layer 8 around it. A ceramic intermediate layer 12 having a thickness of 5-100 μm and a surface roughness Ra of 1.5-4 μm is formed between the electrolyte layer 8 and the porous layer 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater-integrated oxygen sensor element for controlling the ratio of air to fuel in an internal combustion engine of an automobile or the like, and more particularly, to an integrated heating element and a sensor section. The present invention relates to a heater-integrated oxygen sensor element having electrodes having excellent durability.

[0002]

2. Description of the Related Art At present, in internal combustion engines such as automobiles,
By detecting the oxygen concentration in the exhaust gas and controlling the amount of air and fuel supplied to the internal combustion engine based on the detected value, harmful substances such as CO, H
A method of reducing C and NOx has been adopted.

As the detection element, a solid electrolyte mainly composed of a solid electrolyte mainly composed of zirconia having oxygen ion conductivity and having a pair of electrode layers formed on an outer surface and an inner surface of a cylindrical tube having one end sealed. Type oxygen sensors are used. As a typical example of this oxygen sensor, as shown in FIG. 5, a reference electrode made of platinum and in contact with a reference gas such as air is formed on the inner surface of a cylindrical tube 31 made of a ZrO2 solid electrolyte and having a sealed end. In addition, there is known a cylindrical tube 31 in which a measurement electrode 33 is formed on the outer surface of a cylindrical tube 31 so as to be in contact with a gas to be measured such as exhaust gas.
Various ceramic porous layers 34 are formed on the surface of the measurement electrode 33.

In such an oxygen sensor, generally,
As a so-called stoichiometric air-fuel ratio sensor (λ sensor) used for controlling the ratio of air to fuel near 1, a porous layer 34 serving as a protective layer is provided on the surface of a measurement electrode 33. The air-fuel ratio of the engine intake system is controlled by detecting the difference in oxygen concentration generated on both sides of the cylindrical tube at the temperature.

On the other hand, a so-called wide-range air-fuel ratio sensor (A / F sensor) used to control a wide range of air-fuel ratio is a gas diffusion-controlling layer having fine pores on the surface of a measurement electrode 33. A ceramic porous layer 34 is provided, an applied voltage is applied to a cylindrical tube 31 made of a solid electrolyte through a pair of electrodes 32, 33, and a limit current value obtained at that time is measured to control an air-fuel ratio in a lean burn region. is there. In both the stoichiometric air-fuel ratio sensor and the wide area air-fuel ratio sensor, it is necessary to heat the sensing unit to an operating temperature of about 700 ° C. Therefore, a rod-shaped heater is provided inside the cylindrical tube to heat the sensing unit to the operating temperature. 35 are inserted.

[0006]

However, in recent years, the exhaust gas regulations have been strengthened, and it has become necessary to detect CO, HC and NOx immediately after the engine is started. In response to such a request, as described above, in the cylindrical oxygen sensor of the indirect heating type in which the heater 35 is inserted into the cylindrical tube 31, the time required for the sensing unit to reach the activation temperature (activation time) Time) is too slow to meet exhaust gas regulations. As a method of avoiding the problem, a reference electrode and a measurement electrode are provided on the inner surface and the outer surface of a cylindrical tube made of a solid electrolyte, and a gas-permeable porous insulating layer is provided on the surface of the measurement electrode, and further, A cylindrical heater-integrated oxygen sensor element provided with a platinum heating element in a gas non-permeable layer having low gas permeability is disclosed in
No. 206380.

On the other hand, the present applicant has disclosed a sensor element in which a reference electrode and a measurement electrode are formed on the inner surface and the outer surface of a cylindrical tube made of a ceramic solid electrolyte and one end of which is sealed, and the measurement electrode is exposed. A ceramic insulating layer provided with an opening in a measurement electrode forming portion is formed on the outer surface of the cylindrical tube so that the measurement electrode is exposed from the opening, and at least the ceramic insulation layer around the exposed measurement electrode is formed. We have proposed a heater-integrated oxygen sensor element in which a heating element is buried inside and a porous ceramic layer is formed on the surface of the measurement electrode to protect the electrode from exhaust gas. However, unlike the conventional indirect heating method, the heater-integrated oxygen sensor is a direct heating method and thus can rapidly raise the temperature. However, the adhesion of the ceramic porous layer is weak, so that the ceramic porous layer cannot be used. It is easy to peel off, and as a result, there is a disadvantage that the electrode is poisoned and the life of the electrode is short.

That is, on the surface of the ceramic insulating layer,
Normally, a dense ceramic solid made of zirconia is used to reduce the stress caused by the difference in thermal expansion and firing shrinkage between the cylindrical tube, which is a solid electrolyte, and the ceramic insulating layer, and to minimize the thermal stress as much as possible. An electrolyte layer is provided.
On the other hand, the ceramic porous layer is often formed on the entire peripheral surface of the element including the measurement electrode surface in consideration of productivity and the like, but the adhesion between the ceramic porous layer and the ceramic solid electrolyte layer is weak. This causes a problem that the ceramic porous layer peels off. Accordingly, an object of the present invention is to provide a heater-integrated oxygen sensor element capable of rapidly raising the temperature, having a strong adhesion of the ceramic porous layer, and preventing the electrodes from being poisoned by the exhaust gas. .

[0009]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that an intermediate layer having a specific thickness and a specific surface roughness is provided between a ceramic porous layer and a ceramic solid electrolyte layer. The present invention has found a new fact that the electrode can be effectively protected from poisoning by exhaust gas since the adhesive force of the ceramic porous layer is improved by intervening, and the electrode is not easily peeled off. Was completed.

That is, the heater-integrated oxygen sensor element of the present invention comprises a cylindrical tube made of a ceramic solid electrolyte having oxygen ion conductivity and one end of which is sealed, and an inner surface and an outer surface of the cylindrical tube which are opposed to each other. A reference electrode and a measurement electrode formed, a ceramic insulating layer having an opening formed so as to expose a part or the entirety of the measurement electrode, and a heating element buried around the opening; A dense ceramic solid electrolyte layer formed on the surface of the substrate, and a porous ceramic porous layer formed so as to cover at least the opening and the surrounding ceramic solid electrolyte layer. Between the ceramic solid electrolyte layer and the ceramic porous layer,
The thickness is 5 to 100 μm and the surface roughness Ra is 1.5 to 4 μm
Wherein the ceramic intermediate layer is provided. Specifically, the ceramic intermediate layer is preferably a porous layer made of zirconia.

In the heater-integrated oxygen sensor element of the present invention, a heater element in which a heating element is embedded in a ceramic insulating layer is wound around the surface of a sensor element having a cylindrical tube made of a solid electrolyte. Since the heater element and the sensor element can be manufactured by simultaneous firing, the oxygen sensor is manufactured by separately manufacturing the oxygen sensor and the heater and then fitting the heater in the oxygen sensor. The manufacturing cost is extremely low as compared with the element, and it is excellent from the viewpoint of economy.

[0012]

FIG. 1A is a schematic perspective view showing one example of a heater-integrated wide-range air-fuel ratio sensor element according to the present invention.
This will be described with reference to FIG. 2B, which is a cross-sectional view taken along the line X ₁ -X _1, and an enlarged view of a main part of FIG. The heater-integrated oxygen sensor element 1 shown in FIG. 1 is made of a ceramic solid electrolyte having oxygen ion conductivity, and has a tip sealed, that is, as a first electrode on the inner surface of a cylindrical tube 2 having a U-shaped cross section. A reference electrode 3 which is in contact with a reference gas such as air is formed on the outer surface of the cylindrical tube 2 which faces the reference electrode 3 and which, as a second electrode, comes into contact with a gas to be measured such as exhaust gas. A measurement electrode 4 is formed.

A ceramic insulating layer 5 is formed on the outer surface of the cylindrical tube 2 having a sealed end. An opening 6 is formed in the ceramic insulating layer 5 so that the measurement electrode 4 is exposed, and a heating element 7 (a heating resistor such as a platinum heater) is provided in the ceramic insulating layer 5 around the opening 6. Body) is buried. The heating element 7 is connected to the terminal electrodes 10 via the lead electrodes 9, and the heating element 7 is heated by passing an electric current through the heating element 7 through the lead electrodes 9. The electrode 4 is heated by the dense ceramic insulating layer 5 in which the heating element 7 is embedded.

On the surface of the ceramic insulating layer 5, a ceramic solid electrolyte layer 8 is formed as a heat insulating layer in order to increase the heating efficiency of the heating element 7. A ceramic porous layer 11 is formed on the surface of the opening 6 by thermal spraying or the like so as to cover the opening 6. The porous layer 11 is formed on the entire peripheral surface including the opening 6 and the solid electrolyte layer 8.

As shown in FIGS. 1B and 2, a zirconia layer having a surface roughness Ra of 1.5 to 3 μm and a thickness of 5 to 100 μm is provided between the ceramic porous layer 11 and the solid electrolyte layer 8. Is provided. Thereby, the adhesive force of the ceramic porous layer 11 formed on the surface is increased. Ceramic intermediate layer 12
Has a surface roughness Ra smaller than 1.5 μm or 4
If it is larger than μm, the adhesion of the ceramic porous layer 11 is weak. Also, if the thickness of the ceramic intermediate layer 12 is smaller than 10 μm or larger than 100 μm, the adhesive force of the ceramic porous layer 11 similarly becomes weak. In particular, the surface roughness Ra of the ceramic intermediate layer 12 is 2 to 3 μm,
The thickness is preferably 20 to 50 μm.

The thickness of the ceramic porous layer 11 covering the measurement electrode 4 in the opening 6 is preferably 40 to 600 μm in the entire area of the measurement electrode 4 in order to enhance the detection accuracy by the measurement electrode 4. desirable. By setting the outer diameter of the entire element to 3 to 6 mm, particularly 3 to 4 mm, the power consumption can be reduced and the sensing performance can be improved. Hereinafter, each component of the present invention will be described.

(Solid Electrolyte Material) Cylindrical tube in the present invention
2 and a cell used to form the solid electrolyte layer 8.
Examples of the lamic solid electrolyte include ZrO_TwoContains
Ceramics, specifically, Y_TwoO_Threeand
Yb_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
Or partially stabilized ZrO containing 3 to 15 mol%_TwoThere
Is stabilized ZrO_TwoEtc. are used. In addition, ZrO_TwoDuring ~
In which 1 to 20 atomic% of Zr is substituted with Ce_TwoFor
By increasing the oxygen ion conductivity, the response
There is an effect that the property is further improved. In addition,
In order to improve the binding properties, the above ZrO_TwoFor Al_TwoO
_ThreeAnd SiO_TwoCan be added and contained.
The creep characteristics at high temperature
From Al_TwoO_ThreeAnd SiO_Two5 weight in total
%, Particularly preferably 2% by weight or less.

(Ceramic Intermediate Layer 12) As the material of the ceramic layer of the present invention, the same material as the above-mentioned solid electrolyte can be used. Among them, Y ₂ O ₃ and Yb ₂
O ₃ -stabilized zirconia is preferred.

(Ceramic Insulating Layer 5) As the ceramic insulating layer 5 in which the heating element 7 is embedded, for example, a ceramic material such as alumina, spinel, forsterite, zirconia, or glass is preferably used. At this time, when zirconia is used as the ceramic insulating layer 5, the zirconia itself is a solid electrolyte, so that the leakage current from the heating element 7 does not affect the detection of oxygen concentration. In between, it is desirable to form an intermediate layer of alumina, spinel, forsterite, or the like. Further, glass can be used for the glass insulating layer as the ceramic insulating layer 5, but in this case, from the viewpoint of heat resistance, Ba is used.
A glass containing at least one of O, PbO, SrO, CaO, and CdO in an amount of 5% by weight or more, particularly, a crystallized glass is desirable. The ceramic insulating layer 5 is desirably made of dense ceramics 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 5 increases the strength of the insulating layer, thereby increasing the mechanical strength of the wide-range air-fuel ratio sensor element itself.

(Heating Element 7) The heating element 7 embedded in the ceramic insulating layer 5 is made of one kind of metal selected from the group consisting of platinum, rhodium, palladium and ruthenium, or two or more kinds of alloys. In particular, it is desirable to select a metal or an alloy having a melting point higher than the firing temperature of the ceramic insulating layer 5 in terms of co-sintering with the ceramic insulating layer 5. In addition to the above metals, alumina, spinel, a compound of alumina / silica,
Forsterite or zirconia, which can be the above-mentioned electrolyte, is 10 to 80% by volume, especially 30 to 50%.
It is desirable to mix within the range.

(Heater Structure) FIG. 1 shows the structure of a heater in which a heating element 7 is embedded in a ceramic insulating layer 5.
As shown in the sectional view of (b), a ceramic insulating layer 5 in which a heating element 7 is embedded inside is laminated on the surface of a cylindrical tube 2 made of a solid electrolyte. The heating element 7 needs to be provided via the ceramic insulating layer 5 having no solid electrolyte performance such as alumina without directly contacting the cylindrical tube 2 and the electrodes 3 and 4, The thickness of the ceramic insulating layer 5 between the cylindrical tube 2 and the heating element 7 is at least 2 μm.
m or more.

(Electrode) Each of the reference electrode 3 and the measurement electrode 4 formed on the surface of the cylindrical tube 2 is at least one selected from the group consisting of platinum, rhodium, palladium, ruthenium and gold. An alloy is used. In addition, during the operation of the sensor, the above-mentioned ceramic solid electrolyte component is used for the purpose of preventing grain growth of the metal in the electrode and for increasing the contact point at the so-called three-phase interface between the metal particles, the solid electrolyte and the gas related to the response. 1 to 50% by volume, especially 10 to 30% by volume
May be mixed in the above electrode. The opening 6
FIG. 1 (a) shows the shape of the measurement electrode 4 exposed to
It is desirable to be formed in a vertically long rectangular shape or an elliptical shape as shown in FIG. On the other hand, the reference electrode 3 formed on the inner surface of the cylindrical tube 2 made of a solid electrolyte only needs to be formed at least on the inner surface portion facing the portion of the measurement electrode 4 exposed from the opening 6. It may be formed over an area larger than the exposed area, for example, over the entire inner surface of the cylindrical tube 2.

(Opening 6) The shape of the opening 6 may be rectangular or elliptical as described above.
Is rectangular, it is preferable that the corners of the opening have a gentle curve or have a c-shaped structure from the viewpoint of reducing the concentration of thermal stress on the corners of the opening 6.

(Ceramic porous layer 11) The porosity of the ceramic porous layer 11 is 5 to 30%, particularly 10 to 20%.
It is desirable to form by at least one kind selected from zirconia, alumina, spinel, magnesia and γ-alumina having fine pores. Among these, spinel is particularly desirable in terms of thermal stability. From the viewpoint of further preventing exhaust gas poisoning, zirconia, alumina,
It is desirable to provide a ceramic protective layer made of at least one selected from spinel, magnesia and γ-alumina. The ceramic porous layer 11 is formed on the surface of the measurement electrode 4 exposed in the opening 7 as shown in FIG. 1B, and the ceramic protective layer 13 serves 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) element. In this case, the ceramic porous layer 11 is preferably made of a porous material having an open porosity of 10 to 40%. 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 porous layer 11 serving as such a gas diffusion controlling layer, a porous body having an open porosity of 5 to 30% is desirable. The ceramic protective layer made of alumina or spinel described above may be provided on the surface of the ceramic porous layer 11 serving as the gas diffusion control layer, from the viewpoint of further preventing poisoning of exhaust gas. Such a heater-embedded oxygen sensor can be applied as a wide-range air-fuel ratio sensor (A / F sensor) described later.

(Manufacturing Method) Next, a method of manufacturing the oxygen sensor element of the present invention will be described with reference to FIG. 3 by taking the manufacturing method of the heater-integrated oxygen sensor element of FIG. 1 as an example. (1) First, a hollow cylindrical tube 12 whose one end is sealed as shown in FIG. This cylindrical tube 12 is formed by adding an organic binder for molding to a ceramic solid electrolyte powder having oxygen ion conductivity such as zirconia, etc., as appropriate, for example, extrusion molding, isostatic pressing (rubber pressing), or press forming. It is produced by the method described above. As the solid electrolyte powder to be used, Y ₂ O ₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , and Sm are used as stabilizers with respect to zirconia powder.
A mixed powder obtained by adding a rare earth oxide powder such as ₂ O ₃ , Nd ₂ O ₃ , Dy ₂ O ₃ in an amount of 1 to 30 mol%, preferably 3 to 15 mol% in terms of oxide, or zirconia and the above-mentioned stable powder. Coprecipitated raw material powder with an agent is used. In addition, ZrO ₂
ZrO ₂ powder in which 1 to 20 atomic% of Zr is substituted by Ce, or a coprecipitated raw material can also be used. Further, for the purpose of improving sinterability, Al ₂ O 3 is added to the solid electrolyte powder.
It is also possible to add O ₃ or SiO ₂ at a ratio of 5% by weight or less, particularly 2% by weight or less.

(2) Patterns 13 and 14 serving as a reference electrode and a measurement electrode are formed on opposing inner and outer surfaces of the cylindrical tube 12 made of the solid electrolyte by using, for example, a conductive paste containing platinum. Slurry dip method,
Alternatively, it is formed by screen printing, pad printing, or roll transfer. At this time, it is efficient that the reference electrode is printed on the inner surface of the cylindrical tube 12 by filling the conductive paste, discharging the paste, and applying the conductive paste to the entire inner surface. Thus, the sensor body X is manufactured.

(3) Next, a heater element Y as shown in FIG. 3B is formed. The heater element Y is prepared by first preparing a slurry by using the zirconia powder described above and appropriately adding an organic binder for molding to the slurry, and using this slurry by a doctor blade method, an extrusion molding method, a pressing method, or the like. A green sheet 15 for forming a ceramic solid electrolyte layer having a thickness is prepared. The thickness of one green sheet is 50 to 500 μm from the viewpoint of sheet handling.
m, particularly preferably in the range of 100 to 300 μm. A slurry is prepared on the surface of the green sheet 15 by using a ceramic powder such as alumina, spinel, forsterite, zirconia, or glass and appropriately adding an organic binder for molding, and using this slurry, a doctor blade method and extrusion molding are performed. Sheet 18 for forming the ceramic insulating layer 5 having a predetermined thickness by a pressing method, a pressing method or the like.
Is prepared. The thickness of one green sheet is 50 to 500 μm, particularly 100 to 30 μm, from the viewpoint of sheet handling.
A range of 0 μm is particularly preferred. Thereafter, a conductive paste containing platinum powder is printed on the surface of the formed green sheet 18 by a screen printing method, a pad printing method, a roll transfer method, or the like, and a heating element pattern 16 including a lead pattern is applied. Another green sheet 19 is laminated or a slurry of ceramic powder is applied by a printing method or a transfer method to obtain a sheet-like laminated body in which a heating element is embedded. Then, the heating element pattern 16
A ceramic intermediate layer 20 composed of zirconia to which a pore-forming agent is added or zirconia mixed with a powder having a crystal particle diameter of 0.5 to 10 μm as appropriate is screen-printed on the opposite surface where Printing is performed to a predetermined thickness by a pad printing method, a roll transfer method, or the like. Thereafter, the opening 17 is appropriately formed by punching or the like.

(4) Next, as shown in FIG. 3 (c), a heater element Y is wound around the surface of the cylindrical sensor element X to form a cylindrical laminate. In order to wind the heater element Y around the sensor element X, the heater element Y and the sensor element X are bonded together with an adhesive such as an acrylic resin or an organic solvent interposed therebetween, or a pressure is applied by a roller or the like. In addition, it can be mechanically bonded. At this time, the seam of the wound heater element Y takes into account shrinkage during firing,
The sheet ends may be overlapped or bonded at a predetermined interval.

(5) The cylindrical tube 12 made of the solid electrolyte and the green sheets 18 and 19 forming the ceramic insulating layer of the heater element Y constituting the sensor element X are fired simultaneously at a temperature at which firing is possible. , Sensor element X
And the sensor element Y can be integrated. For example,
In the case where zirconia is used as the solid electrolyte, 1300 to 1 in an inert atmosphere such as argon gas or the atmosphere.
By firing at 700 ° C. for about 1 to 10 hours, the heater element Y and the sensor element X can be simultaneously fired.

(Other Manufacturing Methods) Other manufacturing methods include:
After winding the heater element Y formed by the above (3) on the surface of the cylindrical tube 12 having no electrodes to form a cylindrical laminate, an electrode paste is screen-printed, putt-printed on the cylindrical laminate, After being applied to the inner surface of the cylindrical tube 12 and the surface of the cylindrical tube in the opening 17 of the heater element Y by a roll transfer method or a dipping method, simultaneous firing can be performed as described in (5) above. Further, as still another method, (3)
Is wound around the heater element Y formed by the above-described process to produce a cylindrical laminated body, and then the electrode paste is printed on the inner surface of the cylindrical tube 12 and the opening 17 in the heater element Y to be baked or sputtered. It can also be formed by a method or a plating method.

(Method for Forming Ceramic Porous Layer) Next, a ceramic porous layer is formed on the sensor element manufactured as described above. The method for forming the porous layer is as follows. No. (1) 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. In particular, spinel is excellent in improving the thermal shock resistance. (2) The ceramic is coated by a sputtering method or a plasma spraying method to form a ceramic porous layer.
In particular, the plasma spraying method is desirable in terms of ease of forming the ceramic porous layer. In these methods, the sensor element is formed so as to cover at least the opening 6 of the cylindrical sensor element and its periphery. However, in consideration of productivity, the diffusion resistance is formed on the entire peripheral surface including the opening 6 of the cylindrical sensor element. It is desirable to form a layer in order to make the thickness of the ceramic porous layer 11 on the measurement electrode surface constant. According to the slurry dipping method, the sensor element is immersed in a slurry, pulled up, and then baked. In addition, the thickness of the measurement electrode surface of the ceramic porous layer can be easily controlled by the viscosity of the slurry. Further, according to the sputtering method, sputtering is performed while the sensor element is rotated at a low speed about the longitudinal axis of the cylindrical tube so that the side surface of the cylindrical tube faces the evaporation source. The thickness of the diffusion resistance layer can be easily controlled by the sputtering time. Further, according to the thermal spraying method, FIG.
As shown in (1), the sensor element 21 can be formed by plasma spraying ceramic particles on the surface of the sensor element 21 while rotating the sensor element 21 around the longitudinal axis A of the cylindrical tube at a high speed. The thickness of the ceramic porous layer 11 can be easily controlled by the spraying time.

(Other Element Structure) The present invention can be applied to an air-fuel ratio sensor element. As another application example of the present invention, an air-fuel ratio sensor element will be described with reference to a schematic perspective view (a) of FIG. 4 and an enlarged view (b) of a main part in a X2-X2 section thereof. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Air-fuel ratio sensor element 25 of FIG.
According to the above, the first electrode pair for constituting the sensor element is provided in the cylindrical tube 2 having a sealed U-shaped vertical section made of a ceramic solid electrolyte having oxygen ion conductivity. Is formed. Specifically, a reference electrode 3 that is in contact with a reference gas such as air is formed on an inner surface of the cylindrical tube 2, and a measurement target gas such as exhaust gas is formed on an outer surface of the cylindrical tube 2 that faces the reference electrode 3. A measuring electrode 4 to be in contact is formed.

A space 26 is formed on the outer surface of the cylindrical tube 2 so that a part or the whole of the measuring electrode 4 is exposed, and the heating element 7 (platinum heater) is formed around the space 26. ) Are provided. On the upper surface of the space 26, a ceramic solid electrolyte layer 28 having oxygen ion conductivity is formed so as to close the space 26.
The inner surface on the side of the space 26 and the outer surface of the solid electrolyte layer 28 facing the inner surface have a second
Are formed. The solid electrolyte layer 28 and the second pair of electrodes 29 and 30 function as a pump cell for controlling the oxygen concentration in the space 26 to a predetermined concentration.

The solid electrolyte layer 28 having the second pair of electrodes 29 and 30 is formed with a small diffusion hole 31 for taking in the exhaust gas to be measured. In the space 26, a ceramic porous body 27 is provided to control the diffusion. Further, the heating element 7 disposed in the ceramic insulating layer 5 is connected to the terminal electrode 33 via the lead electrode 32, and the heating element 7 is heated by passing a current to the heating element 7 through these. ,
The structure is such that the cylindrical tube 2 made of the solid electrolyte having the reference electrode 3 and the measuring electrode 4 and the sensing part made up of the solid electrolyte layer 28 having the second electrode pair 29 and 30 are heated.

In this embodiment, a ceramic porous layer 34 similar to the above is provided on the surface of the dense ceramic solid electrolyte layer 28. Then, the solid electrolyte layer 28
A ceramic intermediate layer 35 made of zirconia having a thickness of 5 to 100 μm and a surface roughness Ra of 1.5 to 4 μm is formed between the ceramic intermediate layer 35 and the porous layer 34 to improve the adhesion of the ceramic porous layer 34. Let me.

As described above, an example of the present invention has been described.
The present invention relates to all heater-integrated oxygen sensors including at least a sensing unit having a pair of porous platinum electrodes facing inside and outside, and a heating element (platinum heater) embedded in a ceramic insulating layer. Needless to say, the present invention can be similarly applied to an element having a built-in heating element in the gas sensor.

[0037]

The present invention will now be described in detail with reference to examples.
However, the present invention is not limited to the following examples.
No. (Example) Commercially available alumina powder and 5 mol% Y_TwoO_ThreeContained
Zirconia powder and 8 mol% Y _TwoO_ThreeContaining zirconia
Powder and platinum powder were prepared respectively. First, 5 mol% Y
_TwoO_ThreeZirconia powder containing polyvinyl alcohol solution
To form a kneaded clay, and after sintering by extrusion molding, the outer diameter becomes
One end sealed so that about 4 mm, inner diameter is 1 mm
Create a cylindrical molded body, on the surface of the position opposed to the
A rectangular measuring electrode pattern made of platinum paste and
And lead pattern are printed and applied.
Apply platinum paste to the entire surface to form a reference electrode
Was. The thickness of the measurement electrode and the reference electrode is about
It was adjusted to be 5 μm. Also, 5 mol% Y_TwoO_ThreeIncluding
Add polyvinyl alcohol solution to zirconia powder
A solid electrolyte with a thickness of about 200 μm
A green sheet for forming a layer was prepared. After this, the heating element
8 mol% Y on the opposite side to print_TwoO_ThreeContaining zirconia
As shown in Table 1, powder was added at a rate of 20 to 50% by volume.
Add a pore-forming agent (polyethylene beads with a particle size of 5 μm)
To make a slurry, and the thickness after firing is about 2 to 160 μm
The ceramic intermediate layer was printed as shown in FIG.
Nos. 2 to 15). The shape of the measuring electrode is
Punch a rectangular opening with a size that matches the shape
Opened by the ring. After that, the parts other than the opening
Mina powder is applied to a thickness of about 10μm after firing.
And then apply a conductive paste containing platinum powder around the opening.
Adjust so that the thickness of the heat pattern is about 10 μm after firing.
Clean print, and further alumina powder on it, as well
After sintering, apply so that the thickness becomes about 10 μm and bury the heating element
A heater element Y having the structure shown in FIG. Next
Then, an adhesive is applied to the surface of the cylindrical sensor body as an adhesive.
Wrap the heater element using a cryl resin,
A laminate was prepared. Then, the cylindrical laminate is placed in the atmosphere.
Baking at 1400-1500 ° C for a predetermined time in
An integrated cylindrical heater-integrated sensor element was fabricated.
Was. Then, use a surface roughness meter to measure the surface roughness of the ceramic intermediate layer.
After measuring the height, move the sensor element around the center axis of the cylindrical tube.
While rotating at a speed of 1000 rpm, the sensor element
The thickness is reduced by plasma spraying on the entire peripheral surface including the opening.
Sera consisting of spinel with a porosity of about 30% at 100 μm
A mic porous layer was formed. After this, it is 1
It is said that the temperature is raised to 000 ° C in 15 seconds and air-cooled to room temperature
The temperature cycle is one cycle, and this is repeated 5000 times
The peeling of the ceramic porous layer on the electrode surface when turned over
Examined. Table 1 shows the results. The ceramic intermediate layer
The thickness is measured with a scanning electron microscope, and the surface roughness is measured with a surface roughness meter.
Was measured respectively.

[Table 1] From Table 1, it can be seen that Sample No. 1 in which the thickness of the ceramic intermediate layer is less than 5 μm. 2. Sample No. 2 in which the thickness of the ceramic intermediate layer exceeds 100 μm. In No. 8, the ceramic porous layer was peeled off by the temperature cycle. Sample No. having a surface roughness smaller than 1.5 μm. Sample No. 9 and Sample No. having a surface roughness of more than 4 μm. Even in No. 15, peeling of the ceramic porous layer occurred. On the other hand, no peeling of the ceramic porous layer was observed in all of the samples of the present invention. In particular, the thickness of the ceramic intermediate layer is about 10 to 50 μm, and the surface roughness is about 2 to 50 μm.
In the case of 3 μm, the ceramic porous layer did not peel off even when the temperature cycle was further repeated 5000 cycles.

[0038]

According to the present invention, the adhesion of the ceramic porous layer is improved by interposing an intermediate layer having a specific surface roughness and thickness between the ceramic porous layer and the ceramic solid electrolyte layer. Since the electrode is not easily peeled off, the electrode can be effectively protected from poisoning by exhaust gas.

[Brief description of the drawings]

FIG. 1A is a schematic perspective view showing a heater-integrated oxygen sensor element according to a first embodiment of the present invention, and FIG.
Is a sectional view taken along the line X1-X1.

FIG. 2 is an explanatory diagram showing the concept of the present invention.

FIG. 3 is an explanatory view showing a method of manufacturing the heater-integrated oxygen sensor element shown in FIG.

FIG. 4A is a cross-sectional view showing another heater-integrated oxygen sensor element according to the present invention, and FIG. 4B is a partially enlarged view of a X2-X2 cross section thereof.

FIG. 5 is a sectional view showing a conventional heater-integrated oxygen sensor element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Oxygen sensor element integrated with a heater, 2 ... Cylindrical tube, 3 ... Reference electrode, 4 ... Measurement electrode, 5 ... Ceramic insulating layer, 6 ... Opening, 7 ... Platinum heater, 8 ... Solid electrolyte layer, 11 ... Ceramic porous Layer, 12 ceramic intermediate layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G004 BB07 BC02 BD04 BE04 BE10 BE12 BE13 BE15 BE16 BE22 BE23 BE25 BF03 BF09 BJ02 BL08 BM04 BM10 4G031 AA08 AA12 AA29 BA03 BA07 CA07 CA09 GA06 GA18

Claims (4)

[Claims] 1. A cylindrical tube made of a ceramic solid electrolyte having oxygen ion conductivity, one end of which is sealed, a reference electrode and a measurement electrode formed at opposing positions on an inner surface and an outer surface of the cylindrical tube, respectively. An opening is formed so that part or all of the measurement electrode is exposed, and a ceramic insulating layer in which a heating element is buried around the opening, and a dense material formed on the surface of the ceramic insulating layer. A heater-integrated oxygen sensor comprising: a ceramic solid electrolyte layer; and a ceramic porous layer adhered and formed so as to cover at least the opening and the ceramic solid electrolyte layer around the opening. And a ceramic porous layer having a thickness of 5 to 100 μm and a surface roughness Ra of 1.5 to
A heater-integrated oxygen sensor element comprising a 4 μm ceramic intermediate layer. 2. A heater-integrated oxygen sensor element according to claim 1, wherein said ceramic intermediate layer is a porous layer made of zirconia. 3. The heater-integrated oxygen sensor element according to claim 1, wherein the ceramic porous layer is formed by a thermal spraying method. 4. The heater-integrated oxygen sensor element according to claim 1, wherein said ceramic porous layer is made of spinel.