JP3898603B2 - Oxygen sensor element - Google Patents

Description

【００８１】
表１より、本発明のセラミック絶縁層の周囲に多孔質の固体電解質層を配置した試料Ｎｏ．２〜試料Ｎｏ．１７は素子の破損率が低いことがわかる。その中で,気孔率が３〜１９％の試料および多孔質の固体電解質層の厚みが１０〜３００μｍの試料については特に破損率が低かった。
【００８２】
【発明の効果】
以上詳述した通り、本発明によれば、ヒータ部におけるジルコニア固体電解質層と前記セラミック絶縁層の間に、多孔質のジルコニア固体電解質層を形成することによって、長時間運転に対してもクラックの発生や破壊することのない優れた安定性を有する平板状の酸素センサ素子を提供することができる。
【図面の簡単な説明】
【図１】本発明の酸素センサ素子の一例を説明するための概略断面図である。
【図２】本発明における酸素センサ素子の概略平面図である。
【図３】図２の酸素センサ素子の発熱体パターンの構造を説明するための概略斜視図である。
【図４】図２の酸素センサ素子の発熱体パターンの他の構造を説明するための概略斜視図である。
【図５】図３（ｃ）の酸素センサ素子の応用例を説明するための概略斜視図である。
【図６】本発明の酸素センサ素子のさらに他の例を説明するために概略断面図である。
【図７】図１の酸素センサ素子の製造方法を説明するための分解斜視図である。
【図８】従来のヒータ一体型酸素センサ素子の構造を説明するための概略断面図である。
【図９】従来の他のヒータ一体型酸素センサ素子の構造を説明するための概略断面図である。
【符号の説明】
１ センサ部
２ ヒータ部
３ 基板
４ 基準電極
５ 測定電極
６ セラミック多孔質層
７ セラミック絶縁層
８ 発熱体
９ ジルコニア固体電解質層
１０ 多孔質ジルコニア固体電解質層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen sensor element, and more particularly to an oxygen sensor element for controlling a ratio of air and fuel in an internal combustion engine such as an automobile.
[0002]
[Prior art]
Currently, in an internal combustion engine such as an automobile, 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 from the internal combustion engine, For example, a method of reducing CO, HC, and NOx is adopted.
[0003]
As this detection element, a solid electrolyte type oxygen mainly composed of a solid electrolyte mainly composed of zirconia having oxygen ion conductivity and having a pair of electrode layers formed on the outer surface and the inner surface of a cylindrical tube sealed at one end. A sensor is used. As a representative example of this oxygen sensor, as shown in the schematic sectional view of FIG. ₂ A reference electrode 42 made of platinum as a sensor part and in contact with a reference gas such as air is formed on the inner surface of the cylindrical tube 41 made of a solid electrolyte and sealed at the tip, and an exhaust gas or the like is formed on the outer surface of the cylindrical tube 41. A measurement electrode 43 that is in contact with the gas to be measured is formed.
[0004]
In such an oxygen sensor, as a so-called theoretical air-fuel ratio sensor (λ sensor), which is generally used for controlling the ratio of air to fuel near 1, a ceramic porous as a protective layer is formed on the surface of the measurement electrode 43. A layer 44 is provided, and an oxygen concentration difference generated on both sides of the cylindrical tube 41 at a predetermined temperature is detected to control the air-fuel ratio of the engine intake system. At this time, the theoretical air-fuel ratio sensor needs to be heated to an operating temperature of about 700 ° C. For this reason, a rod heater 45 is inserted inside the cylindrical tube 41 to heat the sensor unit to the operating temperature. Yes.
[0005]
However, in recent years, 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, in the indirect heating type cylindrical oxygen sensor in which the rod heater 45 is inserted into the cylindrical tube 41 as described above, the time required for the sensor unit to reach the activation temperature (hereinafter, referred to as the following) The activation time) is slow, and there is a problem that exhaust gas regulations cannot be fully met.
[0006]
In recent years, as a method for avoiding this problem, as shown in the schematic cross-sectional view of FIG. 9, a reference electrode 48 and a measurement electrode 47 are provided on the outer surface and the inner surface of a flat substrate 46 made of a zirconia solid electrolyte, and at the same time, alumina A heater-integrated oxygen sensor element in which a platinum or tungsten heater 50 is embedded inside a ceramic insulating layer 49 made of ceramics has been proposed.
[0007]
[Problems to be solved by the invention]
However, the flat heater integrated oxygen sensor as shown in FIG. 9 is a direct heating method, unlike the indirect heating method of FIG. Since the shape is a flat plate and the thermal expansion coefficients of the zirconia solid electrolyte substrate 46 and the alumina ceramic insulating layer 49 are different, the zirconia solid electrolyte substrate 46 and the alumina ceramic insulating layer 49 are repeatedly subjected to such rapid temperature increase. There was a problem that a crack was generated at the interface of this, and that the crack could eventually lead to breakage due to the progress of this crack.
[0008]
In addition, since the absolute strength of the zirconia solid electrolyte substrate 46 and the alumina ceramic insulating layer 49 is reduced due to the miniaturization of the element, the occurrence of cracks and breakage is becoming very prominent. It has become a major factor to inhibit.
[0009]
Accordingly, the present invention provides a flat plate oxygen sensor element having a flat plate shape, excellent in durability and heat resistance, and having excellent stability that does not generate or break even when operated for a long time. It is intended to do.
[0010]
[Means for Solving the Problems]
As a result of studying the above problems, the present inventor has found that a long plate-like zirconia solid electrolyte substrate having an air introduction hole is present. When, A sensor part having a pair of electrodes on the inner wall surface of the air introduction hole and the outer surface facing the inner wall surface, and a ceramic insulating layer And the ceramic insulating layer Within Buried Heating element And is located below the sensor unit Oxygen sensor element having a heater Because The heater section On the top and bottom sides of Porous zirconia solid electrolyte layer having a porosity of 3 to 20% Formed Has been The periphery of the porous zirconia solid electrolyte layer excluding the heater portion is all covered with the zirconia solid electrolyte substrate. By improving the bonding strength between the ceramic insulating layer and the solid electrolyte, it is possible to provide an element with excellent heat resistance and durability while preventing the element from being destroyed at the time of rapid temperature rise, which is a problem with flat plate sensor elements. I found it.
[0014]
In order to reduce the size, a pair of electrodes of the sensor unit is formed near the tip of the element, and an electrode pad for connecting a terminal is provided near the rear end of the element. Direction perpendicular to the longitudinal direction Elements It is desirable that the width of is larger than the width of the element tip.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of the basic structure of the oxygen sensor element of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a schematic cross-sectional view for explaining an example of the oxygen sensor element of the present invention. These are generally referred to as theoretical air-twist ratio sensor elements, and each includes a sensor unit 1 and a heater unit 2 in the example of FIG.
[0017]
In the oxygen sensor element of FIG. 1, a base 3 having an oxygen ion conductivity made of a zirconia solid electrolyte and having an air introduction hole 3 a with a sealed tip inside, and an air introduction hole 3 a in the base 3. A reference electrode 4 that comes into contact with air and a measurement electrode 5 that comes into contact with exhaust gas are formed on opposite surfaces of the inner wall of the substrate 3 and the substrate 3 to form a sensor unit 1 having a function of detecting the oxygen concentration. .
[0018]
Further, from the viewpoint of preventing electrode poisoning by exhaust gas, a ceramic porous layer 6 may be formed on the surface of the measurement electrode 5 as an electrode protective layer.
[0019]
On the other hand, the heater section 2 has a heating element 8 made of platinum or the like embedded in a ceramic insulating layer 7. In the oxygen sensor element of FIG. 1, the heater section 2 is a part of the zirconia solid electrolyte substrate 3. The periphery is covered with the zirconia solid electrolyte layer 9 to be.
[0020]
In the present invention, in the structure of the heater section described above, a porous zirconia solid electrolyte layer (hereinafter referred to as a porous layer) having a porosity of 3 to 20% at the interface between the alumina ceramic insulating layer 7 and the zirconia solid electrolyte layer 9. .)) 10 is formed.
[0021]
By providing such a porous layer 10, thermal stress due to the thermal expansion coefficient between the zirconia solid electrolyte layer 9 and the alumina ceramic insulating layer 7 can be relaxed. As the porosity of the porous layer 10, 3 to 20%, particularly 5 to 15% is excellent. This is because if the porosity is less than 3%, the stress relaxation effect is not sufficient, and cracking or breakage tends to occur. If the porosity is more than 20%, the strength of the porous layer itself is increased. It is because it will fall. This porosity is defined as the area occupied by the pores in the longitudinal section of the porous layer.
[0022]
Further, the thickness of the porous layer 10 is effective in the range of 10 to 300 μm, particularly 20 to 50 μm, and the pore size is effective in the range of 3 to 10 μm, particularly 3 to 5 μm. .
[0023]
Even if the thickness of the porous layer 10 is smaller than 10 μm or exceeds 300 μm, the bonding strength between the alumina ceramic insulating layer 7 and the solid electrolyte layer 9 tends to be lowered.
[0024]
The porous layer is formed by applying a slurry in which a pore forming agent such as resin beads is blended at a ratio of 5 to 30% by volume to the zirconia powder composition, or by forming the slurry into a sheet by a doctor blade method or the like. It can be formed by disposing and firing between the ceramic insulating layer and the zirconia solid electrolyte layer 9. The porosity and pore diameter can be easily controlled by the particle diameter and blending amount of the pore forming agent.
[0025]
The zirconia solid electrolyte in the zirconia solid electrolyte substrate 3 and the zirconia solid electrolyte layers 9, 9 ′ and the zirconia solid electrolyte layer 10 containing alumina in the oxygen sensor element of the present invention is ZrO. ₂ Y as a stabilizer ₂ O _Three And Yb ₂ O _Three , Sc ₂ O _Three , Sm ₂ O _Three , Nd ₂ O _Three , Dy ₂ O _Three Partially stabilized ZrO containing 1 to 30 mol%, preferably 3 to 15 mol% of at least one selected from the group of ₂ Or stabilized ZrO ₂ Is used. Furthermore, for the purpose of improving the sinterability, the above ZrO ₂ In contrast to SiO ₂ However, if a large amount is added, the creep properties at high temperatures are deteriorated. ₂ The total amount of is preferably 5% by mass or less, and particularly preferably 2% by mass or less.
[0026]
Furthermore, in the present invention, it is desirable that the minimum thickness S of the zirconia solid electrolyte layer 9 covering the heater portion 2 is 20 μm or more, particularly 50 μm or more, more preferably 100 μm or more. This is formed for the purpose of strengthening the bonding force between the solid electrolytes at the same time as preventing water vapor from entering through the pores in some cases when pores exist inside the zirconia solid electrolyte layer 9.
[0027]
The zirconia solid electrolyte layer 9 is preferably made of the same material as the zirconia solid electrolyte constituting the substrate 3 on which the sensor unit 1 is formed, and is made of a dense body having a relative density of 90% or more, particularly 95% or more. It is desirable.
[0028]
In the oxygen sensor element of FIG. 1, the heater unit 2 is built in the lower part of the substrate 3 having the sensor unit 1, so that it is covered with a zirconia solid electrolyte and integrated with the sensor unit 1 by firing. It consists of
[0029]
In the present invention, the ceramic insulating layer 7 forming the heater portion 2 includes a) a sintered body mainly composed of alumina, b) a sintered body mainly composed of a composite oxide containing at least Al and Mg, c ) It is desirable that it is composed of at least one sintered body selected from the group of sintered bodies mainly composed of a composite oxide of Al and at least one selected from the group consisting of Y and rare earth elements.
[0030]
a) The sintered body mainly composed of alumina contains 90% by mass or more of alumina, and for the purpose of improving the sinterability, as a component other than the main component, alkaline earth such as Mg and Ca Metal oxide and SiO ₂ It is desirable to contain at least one selected from the group of 1 to 10% by mass in total.
[0031]
Further, b) a sintered body mainly composed of a composite oxide of Al and Mg is based on a two-component standard based on oxide conversion of Al and Mg, and Al is converted to 20 to 90 mol% in terms of oxide, and Mg It is desirable to contain in the ratio of 10-80 mol% in conversion of an oxide.
[0032]
In this case, although depending on the composition used and the firing temperature, the crystal phase in the obtained ceramic insulating layer 4 is Al. ₂ O _Three Phase, MgO / Al ₂ O _Three It is composed of two or three kinds of crystals of (spinel) phase and MgO phase. Among the above composition ranges, the range in which the Al amount is 50 to 80 mol% in terms of oxide and the Mg amount is 20 to 50 mol% in terms of oxide is particularly preferable.
[0033]
Further, c) As a composite oxide of Al and at least one selected from the group of Y and rare earth elements, Al is an oxide based on a two-component standard in terms of oxides of Y and rare earth elements and Al. It is desirable that it is 20 to 90 mol% in terms of conversion and Y and rare earth elements are in the range of 10 to 80 mol%. Within the above range, it is desirable that the amount of Al is 50 to 80 mol%, and at least one selected from the group of Y and rare earth elements is 20 to 50 mol%. Specifically, La, Yb, Nd, Dy, Sc, Sm, and Sc are suitably used as the rare earth element.
[0034]
The crystal phase at this time is Al. ₂ O _Three And a composite oxide of Al and Y or a rare earth element, or Y or a rare earth element oxide. For example, as a complex oxide, for example, Al ₂ O _Three And Y ₂ O _Three 3Y is used ₂ O _Three ・ 5Al ₂ O _Three 2Y ₂ O _Three ・ Al ₂ O _Three And Y ₂ O _Three It consists of a crystal phase combining crystals such as.
[0035]
The sintered body constituting the ceramic insulating layer 7 in which the heating element 8 is embedded has a relative density of 80% or more, particularly 90% or more, more preferably 95% or more, and an open porosity of 5% or less, particularly 3%. By comprising the following dense sintered body, the strength of the heater section 2 through the ceramic insulating layer 7 can be increased, and the strength of the entire element can be increased.
[0036]
Further, in this ceramic insulating layer 7, alkali metals such as Na, K, etc. are desirably controlled to a total amount of 50 ppm or less in terms of oxide in order to migrate and deteriorate the electrical insulation of the heater section 2.
The reference electrode 4 and the measurement electrode 5 deposited on the surface of the substrate 3 are both platinum or an alloy of platinum and one selected from the group of rhodium, palladium, ruthenium and gold. In addition, for the purpose of preventing the grain growth of the metal in the electrode during the operation of the sensor and the purpose of increasing the contact at the so-called three-phase interface between platinum particles, solid electrolyte and gas related to responsiveness, The components may be mixed in the electrode in a proportion of 1 to 50% by volume, particularly 10 to 30% by volume. Further, the electrode shape may be a quadrangle or an ellipse. The thickness of the electrode is preferably 3 to 20 μm, particularly preferably 5 to 10 μm.
[0037]
The heater 8 and the leads 8a1 and 8a2 embedded in the alumina ceramic insulating layer 7 in the heater part 2 are made of platinum as a metal, or an alloy of platinum and one kind selected from the group of rhodium, palladium and ruthenium, or W A single substance or an alloy selected from the group consisting of W, Mo, and Re can be used.
[0038]
In the case of using a platinum heater as the heater, from the viewpoint of preventing platinum grain growth during firing, in addition to alumina, the same ceramic powder forming the ceramic insulating layer is 10 to 40% by volume, particularly 20 to 20%, based on the total amount. It is preferable to add 30% by volume. In this case, the resistance ratio between the heater 8 and the leads 8a1 and 8a2 is preferably controlled in the range of 9: 1 to 7: 3 at any room temperature.
[0039]
Further, the ceramic porous layer 6 formed on the surface of the measurement electrode 5 has a thickness of 10 to 800 μm, particularly 100 to 500 μm, and a porosity of 10 to 50% from a group of zirconia, alumina, γ-alumina and spinel. It is desirable that it is formed by at least one selected.
[0040]
The oxygen sensor element of the present invention is most suitably used for a small-sized oxygen sensor element. Specifically, the electrode area of the measurement electrode 5 is 8 to 18 mm in order to achieve excellent gas responsiveness with the miniaturization of the element. ² It is desirable that the width in the direction perpendicular to the longitudinal direction at a portion of 5 mm or more, particularly 10 mm or more from the tip of the element is 2.0 to 3.5 mm. According to the present invention, by controlling the area of the measurement electrode 5 and the width of the tip in the above range, it is possible to improve the rapid temperature rise of the measurement electrode 5 by the heater and improve the gas responsiveness by the sensor. .
[0041]
The oxygen sensor element of the present invention includes a pair of electrodes 5 of the sensor unit 1 near the tip of the element, and includes an electrode pad 11 for connecting a terminal near the rear end of the element. In setting the area and width within the above ranges, the width L1 in the direction orthogonal to the longitudinal direction of the rear end of the element is larger than the width L2 of the front end of the element, or the width of the sensor element is It is desirable that the element increases continuously or discontinuously from the front end to the rear end. In particular, it is appropriate that the maximum width at the rear end portion where the electrode pad 11 is formed is 3.7 to 5 mm, particularly 4.0 to 4.5 mm.
[0042]
In this case, as a specific structure of the oxygen sensor element, specifically, as shown in FIG. 2A, in other words, the width continuously increases from the front end to the rear end of the element. As shown in FIG. 2 (b), the width of the element increases between the front end portion and the rear end portion at the stepped portion v, as shown in FIG. 2 (c). As shown, a taper portion p is provided between the front end portion and the rear end portion, and the width becomes partially continuous continuously.
[0043]
As described above, the width of the portion where the electrode pad 11 is provided is widened, and the width L1 of the portion where the electrode pad 11 is formed is larger than the width L2 of the tip portion of the element. A connector, a metal pin, etc. can be attached to the electrode pad 11 easily and firmly.
[0044]
In addition, as the arrangement of the heating elements 8 in the heater unit 2, the pair of heating elements in the cross section may be usually formed in the same plane. Since the shape is very limited, as shown in FIG. 1, when the pair of heating elements 8 in the cross section perpendicular to the longitudinal direction of the heater portion 2 is formed via the ceramic insulating layer 7a, the heater portion Can be miniaturized.
[0045]
More specifically, as shown in the schematic transmission diagram for explaining the structure of the heating element pattern in FIG. 3, the lead 8 a 1 extends in the longitudinal direction from one end side in the long ceramic insulating layer 7, and the ceramic insulating layer 7 is formed in a portion facing the electrode forming portion of the sensor portion 1 near the other end portion of the sensor 7, and after being folded at the other end portion of the element, connected to the lead 8a2 via the heat generating portion 8b2. Yes. In the present invention, at least the heat generating portions 8b1 and 8b2 are formed above and below via the ceramic insulating layer 7a, and the heat generating portions 8b1 and 8b2 are formed of vias 8c penetrating the ceramic insulating layer 7a at the other end. It is electrically connected by a connection body.
[0046]
The heating element pattern of FIG. 3 is composed of a meander structure (waveform) pattern. When the width of the heating element is x, in the meander structure of FIG. 3, the width x of the heating element 8 has the maximum amplitude of the waveform. Equivalent to. When the heat generating portions 8b1 and 8b2 each have a predetermined width x, generally, when they are formed in the same plane, the width w of the entire element is a margin for embedding the heat generating portions 8b1 and 8b2 in the insulating layer 7. In order to prevent a short circuit between the portions and the heating elements 8b1 and 8b2, the width w of the entire element needs to be about w ≧ 3x.
[0047]
On the other hand, when the heat generating portions 8b1 and 8b2 are formed between different layers, the insulating property is maintained by the ceramic insulating layer 7a even when the heat generating portions 8b1 and 8b2 are overlapped in plan view. The width w can be smaller than 3x. In particular, in order to reduce the size, it is desirable to satisfy w ≦ 2.5x, and further w ≦ 2x.
[0048]
The thickness of the ceramic insulating layer 7a between the upper and lower heat generating portions 8a1 and 8b2 is preferably 1 to 300 μm, particularly 5 to 100 μm, and more preferably 5 to 50 μm from the viewpoint of electrical insulation.
[0049]
In the example of FIG. 3, the heating element 8 has a meandering (waveform) pattern that is folded in a direction orthogonal to the longitudinal direction of the element. However, the heating element pattern is limited to this. For example, as shown in the pattern diagram of the heating element in FIG. 4, a meander pattern having a folding in the longitudinal direction of the element may be used.
[0050]
Furthermore, according to the present invention, using the oxygen sensor element of FIG. 2 (c), for example, as shown in FIG. Can be attached to.
[0051]
In addition, the oxygen sensor element of the present invention has an element thickness of 0.8 to 3 mm, particularly 1 to 2 mm, and an element length of 45 to 55 mm, particularly 45 to 50 mm, from the viewpoint of element strength. It is preferable from the relationship between the rapid temperature rise property and how the element is mounted in the engine.
[0052]
The oxygen sensor element of the present invention is also applied to a wide range sensor element as shown in FIG. FIG. 6 is a schematic sectional view for explaining a typical structure thereof. According to the oxygen sensor element of FIG. 6, the electrode pair of the reference electrode 4 and the measurement electrode 5 is formed on the opposing surface of the base 3, and the space portion 14 is formed on the upper side of the measurement electrode 5 by the substrate 13. The substrate 13 is provided with a diffusion hole 15 having a size of 0.1 to 0.5 mm for taking in the exhaust gas.
[0053]
In such an oxygen sensor, a pumping cell is formed by a pair of electrodes 4 and 5 sandwiching the base 3, and the current flowing between the electrode pairs is controlled in accordance with the oxygen concentration in the exhaust gas to control the oxygen in the exhaust gas. Control the air / fuel ratio.
[0054]
The space 14 can be filled with porous ceramics to give the element strength. Further, the diffusion hole 15 can be formed on the side surface or the tip in addition to the upper surface of the element. Furthermore, the diffusion hole 15 functions as a hole for taking in a certain exhaust gas into the space. Therefore, the diffusion hole 15 may be formed by a large number of holes, or may be formed by a ceramic porous layer.
[0055]
The reference electrode 4 formed on the lower surface of the base 3 is formed on the inner wall of the air introduction hole 3a. An alumina ceramic insulating layer 7 in which a heating element 8 made of W or Pt is embedded is covered with a zirconia solid electrolyte layer 9 immediately below the air introduction hole 3a. By heating the heating element 8, the base 3 and the electrode pairs 4, 5 are heated. In the oxygen sensor of the present invention, as another example, pumping electrodes can be formed on both surfaces of the substrate 11.
[0056]
Also in such an oxygen sensor element, the zirconia solid electrolyte layer 10 containing 5 to 10% by mass of alumina is formed between the alumina ceramic insulating layer 7 and the zirconia solid electrolyte layer 9.
[0057]
Next, the manufacturing method of the oxygen sensor element according to the present invention will be described with reference to the manufacturing method of the oxygen sensor element shown in FIG. 1, using Pt as the heating element and alumina as the ceramic insulating layer. This will be described with reference to an exploded perspective view.
[0058]
First, a solid electrolyte green sheet 21 is prepared. For example, the green sheet 21 may be formed by appropriately adding a forming organic binder to a zirconia ceramic solid electrolyte powder having oxygen ion conductivity to form a doctor blade method, extrusion molding, or isostatic pressing (rubber press). Or it produces by well-known methods, such as press formation.
[0059]
Next, a conductive paste containing platinum, for example, is used to form the pattern 22, the lead pattern 23, and the through hole (not shown) that become the measurement electrode 5 and the reference electrode 4 on both surfaces of the green sheet 21. After the slurry dip method, or screen printing, pad printing, or roll transfer is used for printing, the green sheet 25 and the green sheet 26 in which the air introduction hole 24 is formed are interposed with an adhesive such as an acrylic resin or an organic solvent, or a roller or the like The laminated body A for the sensor part is produced by mechanically adhering while applying pressure.
Furthermore, the conductive paste containing platinum used at this time is one containing an organic resin component such as ethyl cellulose in platinum particles containing zirconia in a proportion of 1 to 50% by volume, particularly 10 to 30% by volume. By using it, the sensitivity of the electrode can be increased. At this time, a porous slurry for forming the ceramic porous layer 6 may be formed by printing on the surface of the pattern serving as the measurement electrode 5.
[0060]
Next, 5 to 30 pore forming agents such as resin beads and carbon powder having an average particle diameter of 5 to 50 μm are added to the zirconia powder composition forming the green sheet 21 on the surface of the zirconia green sheet 27 as shown in FIG. The porous layer 28a is formed by printing by a slurry dip method, or screen printing, pad printing, or roll transfer, using a paste added and mixed by volume%. Next, Al ₂ O _Three An insulating paste in which an organic resin and a solvent are added to the powder and mixed is printed by a slurry dip method, or screen printing, pad printing, or roll transfer to form the ceramic insulating layer 29a.
[0061]
Next, as shown in FIG. 2, the heater pattern 30 and the lead pattern 31 are printed and applied to the surface of the ceramic insulating layer 29a. Then, the insulating paste 29 is applied to form the ceramic insulating layer 29b. Thereafter, the porous zirconia solid electrolyte layer 28b is formed again using the porous layer forming paste.
[0062]
Thereafter, in order to coat the porous zirconia solid electrolyte layers 28a, 28b with the solid electrolyte, the ceramic insulating layers 28a, 28b and the porous zirconia solid electrolyte layers 28a, 28b are surrounded by a paste made of zirconia powder. The zirconia solid electrolyte layer 32 is printed and formed at substantially the same height. And the zirconia green sheet 33 is laminated | stacked again, and the laminated body B of the heater part 2 is produced.
[0063]
In producing the laminated body of the heater section 2, the ceramic insulating layers 28a, 28b, 29a, and 29b are formed by printing and applying an insulating paste as described above. It can also be formed into a sheet and laminated by a sheet forming method such as.
[0064]
When the platinum heater is formed on different surfaces as in the oxygen sensor element of FIG. 2, the upper heater pattern and lead pattern are separated from the upper heater pattern and lead pattern, and the lower heater pattern is separated. After the formation of the lead pattern and the ceramic insulating layer, the upper heater pattern and the lead pattern may be formed. The lower heater pattern and the upper heater pattern may be formed by forming a through hole in the intervening ceramic insulating layer and filling the through hole with a conductive paste when the upper heater pattern is formed. Or the front-end | tip part of the intervening ceramic insulating layer is notched, a conductive paste is apply | coated and connected to the notch part, and the platinum heater connected to one is formed.
[0065]
Further, in the present invention, a solid electrolyte green sheet containing a pore forming agent can be laminated on the ceramic insulator surface.
[0066]
Thereafter, the laminated body A of the sensor unit 1 and the laminated body B of the heater unit 2 are either bonded with an adhesive such as an acrylic resin or an organic solvent, or mechanically bonded to each other while applying pressure with a roller or the like. After bonding and integration, these are fired. Firing is performed in the air or in an inert gas atmosphere at a temperature range of 1300 ° C. to 1700 ° C. for 1 to 10 hours. At the time of firing, in order to suppress warping of the sensor part A at the time of firing, the amount of warpage can be reduced by placing a smooth substrate such as alumina on the laminate as a weight.
[0067]
Thereafter, if necessary, the surface of the measurement electrode after firing is formed by at least one ceramic selected from the group consisting of alumina, zirconia, and spinel by plasma spraying or the like, and the oxygen is integrated with the heater portion. A sensor element can be formed.
[0068]
In the above method, the heater part 1 is formed by simultaneous firing with the sensor part 2. However, after the sensor part 1 and the heater part 2 are fired separately from each other, an appropriate inorganic material such as glass is used. It is also possible to integrate by bonding with a bonding material.
[0069]
When the heater is formed of W, the laminate is manufactured in the same manner as in the case of using the above-described platinum heater, but firing is performed in a reducing atmosphere or an inert gas atmosphere at a temperature range of 1300 ° C to 1700 ° C. It is necessary to bake for 1 to 10 hours.
[0070]
【Example】
The theoretical air-fuel ratio sensor element shown in FIG. 1 was manufactured as follows according to FIG.
[0071]
First, 5 mol% Y containing 0.1% by weight of alumina and silica, respectively. ₂ O _Three A polyvinyl alcohol solution was added to the contained zirconia powder to produce a slurry, and a zirconia green sheet 21 having a thickness after sintering of 0.4 mm was produced by extrusion molding.
[0072]
Thereafter, a conductive paste containing platinum powder containing 30% by volume of zirconia having an average particle size of 0.1 μm and 8 mol% of yttria in the crystal is screen-printed on both surfaces of the zirconia green sheet 21 and measured. After the electrode 22 and the reference electrode pattern 22 and the lead pattern 23 are printed and formed, the zirconia green sheet 25 and the zirconia green sheet 26 in which the air introduction holes 24 are formed are laminated with an acrylic resin adhesive to form the sensor unit laminate A. Obtained.
[0073]
Next, 5 mol% Y containing 5 to 40 vol% of pore forming agent (flow beads; average particle diameter of about 4 μm) on the surface of the zirconia green sheet 27. ₂ O _Three After forming the slurry of contained zirconia powder to be 5 to 400 μm after firing to form the porous zirconia layer 28a, an insulating paste made of alumina powder is prepared, and the thickness is 20 μm after firing. The ceramic insulating layer 29a was formed by printing. And the heater pattern 30 and the lead pattern 31 were screen-printed using the paste of the platinum powder containing 10 volume% of alumina on the surface.
[0074]
Further, a ceramic insulating layer 29b is formed on the surfaces of the heater pattern 30 and the lead pattern 31 by screen printing so that the alumina insulating paste is 20 μm after firing, and again a zirconia slurry containing the pore forming agent. After being fired, a porous zirconia layer 28b was formed by stacking to a thickness of 5 to 400 μm.
[0075]
And around this laminated body, 5 mol% Y ₂ O _Three A zirconia solid electrolyte layer 32 was formed by applying a paste made of the contained zirconia powder to the same height as the laminate by screen printing. And the zirconia sheet | seat 33 was laminated | stacked further and the laminated body for heater parts which embed | buried the heater pattern 30 between ceramic insulating layers 29a and 29b was produced.
[0076]
Then, the sensor part laminated body and the heater part laminated body were laminated | stacked, and it baked at 1500 degreeC for 1 hour, and produced the sensor element which integrated the heater.
[0077]
In addition, all the produced oxygen sensor elements had a measurement electrode area of 12 mm based on FIG. ² The length of the element was 50 mm, the width of the portion from the tip of the element to 20 mm was 3 mm, the width of the electrode pad forming portion was 4.5 mm, and the length was 10 mm. The element thickness was 1.5 mm.
[0078]
A temperature at which 20 sensor elements having different porosities and thicknesses of porous bodies are produced by the above-described method, the temperature is raised from room temperature to 1000 ° C. in about 20 seconds, and then forcibly cooled to room temperature with a fan. The cycle was regarded as one cycle, and the damage rate after performing this about 200,000 times was determined. At this time, the mirror-polished surface of the porous solid electrolyte layer in contact with the ceramic insulating layer was measured at 10 points on a scanning electron micrograph of 2000 times, and the area ratio of pores was measured and the average value was measured. Was defined as the porosity. Similarly, the thickness of the porous solid electrolyte layer was measured by a scanning electron micrograph.
[0079]
The results are shown in Table 1. The table also shows a sensor element (sample No. 1) integrated with a heater that does not form a porous solid electrolyte layer for comparison.
[0080]
[Table 1]

[0081]
From Table 1, sample No. 1 in which a porous solid electrolyte layer was arranged around the ceramic insulating layer of the present invention was obtained. 2-Sample No. 2 No. 17 shows that the damage rate of the element is low. Among them, the damage rate was particularly low for samples with a porosity of 3 to 19% and samples with a porous solid electrolyte layer thickness of 10 to 300 μm.
[0082]
【The invention's effect】
As described above in detail, according to the present invention, by forming a porous zirconia solid electrolyte layer between the zirconia solid electrolyte layer and the ceramic insulating layer in the heater section, cracks can be generated even for a long time operation. It is possible to provide a flat plate oxygen sensor element having excellent stability that does not occur or break.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view for explaining an example of an oxygen sensor element of the present invention.
FIG. 2 is a schematic plan view of an oxygen sensor element according to the present invention.
3 is a schematic perspective view for explaining the structure of a heating element pattern of the oxygen sensor element of FIG. 2. FIG.
4 is a schematic perspective view for explaining another structure of the heating element pattern of the oxygen sensor element of FIG. 2. FIG.
FIG. 5 is a schematic perspective view for explaining an application example of the oxygen sensor element of FIG.
FIG. 6 is a schematic sectional view for explaining still another example of the oxygen sensor element of the present invention.
7 is an exploded perspective view for explaining a method of manufacturing the oxygen sensor element of FIG. 1. FIG.
FIG. 8 is a schematic cross-sectional view for explaining the structure of a conventional heater-integrated oxygen sensor element.
FIG. 9 is a schematic cross-sectional view for explaining the structure of another conventional oxygen sensor element integrated with a heater.
[Explanation of symbols]
1 Sensor part
2 Heater part
3 Substrate
4 Reference electrode
5 Measuring electrode
6 Ceramic porous layer
7 Ceramic insulation layer
8 Heating element
9 Zirconia solid electrolyte layer
10 Porous zirconia solid electrolyte layer

Claims (5)

A long plate-like zirconia solid electrolyte substrate having an air introduction hole ;
A sensor unit having a pair of electrodes on the inner wall surface of the air introduction hole and the outer surface facing it;
An oxygen sensor element comprising a ceramic insulating layer and a heating element embedded in the ceramic insulating layer , and comprising a heater portion located below the sensor portion ,
A porous zirconia solid electrolyte layer having a porosity of 3 to 20% is formed on the upper surface side and the bottom surface side of the heater part,
The oxygen sensor element, wherein the porous zirconia solid electrolyte layer is entirely covered with the zirconia solid electrolyte substrate except for the heater side . The heating element in the heater unit includes a first heating unit and a second heating unit having different heights in the vertical direction in a cross section in a direction perpendicular to the longitudinal direction of the heater unit,
The oxygen sensor element according to claim 1, wherein the first heat generating part and the second heat generating part are connected in the heater part . 3. The oxygen sensor element according to claim 1, wherein a side surface of the ceramic insulating layer in the heater portion is in contact with a zirconia solid electrolyte substrate. Of the pair of electrode pairs in the sensor section, the area of the electrode in contact with the measurement gas is 8～18Mm ^2, and the width direction of the element perpendicular to the longitudinal direction of the element is at least 5mm from the device tip The oxygen sensor element according to any one of claims 1 to 3, wherein the above is 2.0 to 3.5 mm. The pair of electrode pairs in the vicinity of the tip of the element is formed, and an electrode pad for connecting a terminal to the vicinity of the rear end of the element,
5. The oxygen sensor element according to claim 1, wherein the width of the element in a direction orthogonal to the longitudinal direction in the electrode pad forming portion is larger than the width of the tip of the element.

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