JP4698041B2 - Air-fuel ratio sensor element - Google Patents

Description

【００６４】
表１より、ポンピング部の内側電極面積と測定電極面積の比率が０．８より大きな従来の試料Ｎｏ．１および測定電極面積が内側電極面積よりも大きなＮｏ．１４は良品率が低いことがわかる。また、測定電極面積が０．３倍より小さな試料Ｎｏ．７ではセンシングが認められなかった。
【００６５】
これに対して、本発明に従い、測定電極面積が内側電極面積より０．８倍より小さいと良品率が向上することがわかる。特に、実験より、内側電極面積が１０ｍｍ²より小さな試料Ｎｏ．８では測定中に固体電解質層にクラックが入るものが多かった。また、内側電極面積が２０ｍｍ²を越える試料Ｎｏ．３では、素子は作製できたものの８００℃まで昇温できないものが多かった。
【００６６】
従って、本発明のポンピング部の内側電極面積が１０〜２０ｍｍ²で、測定電極の面積比率が内側電極の０．３〜０．８倍とすることによって良品率が高いことがわかる。
【００６７】
【発明の効果】
以上詳述した通り、本発明の空燃比センサ素子によれば、センシング部の測定電極の面積と、ポンピング部の内側電極との面積比率を制御することにより、急速昇温などの熱衝撃性に優れた空燃比センサ素子が歩留まりよく提供できる。したがって、製造コストが極めて安価になり、経済性の観点からも優れている。
【図面の簡単な説明】
【図１】 本発明の空燃比センサ素子の一例を説明するための概略斜視図である。
【図２】 図１の空燃比センサ素子におけるＸ−Ｘ縦断面図である。
【図３】 本発明の空燃比センサ素子の製造方法を説明するための図であって、センサ素体を作製する工程を示す図である。
【符号の説明】
１は空燃比センサ素子、２は円筒管、３は基準電極、４は測定電極、５は空間部６は発熱体、７はセラミック絶縁層、８は固体電解質層、９は内側電極、１０は外側電極、１１はガス拡散孔、１２はリード電極、１３は端子電極、１４は多孔質体、１６は拡散律速体をそれぞれ示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio sensor element for controlling the ratio of air and fuel in an internal combustion engine such as an automobile. Specifically, the heating element and the sensor unit are integrated to generate heat with a high manufacturing yield. The present invention relates to an air-fuel ratio sensor element integrated with a body.
[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]
This detection element is made of a solid electrolyte mainly composed of zirconia having oxygen ion conductivity, and a solid electrolyte type in which a pair of electrode layers are respectively formed on the outer surface and the inner surface of a cylindrical base body sealed at one end. An oxygen sensor element is used.
[0004]
In such an oxygen sensor, in general, in a so-called theoretical air-fuel ratio sensor element (λ sensor) used for controlling the ratio of air to fuel near 1, a porous layer serving as a protective layer is formed on the surface of the outer measurement electrode. An air-fuel ratio of the engine intake system is controlled by detecting a difference in oxygen concentration generated on both sides of the cylindrical base body at a predetermined temperature.
[0005]
On the other hand, a so-called wide-range air-fuel ratio sensor element (A / F sensor) used to control a wide range of air-fuel ratio is a ceramic porous material that becomes a gas diffusion-controlling layer having fine pores on the surface of a measurement electrode. A layer is provided, an applied voltage is applied to a cylindrical base body made of a solid electrolyte through a pair of electrodes, and a limit current value obtained at that time is measured to directly control the air-fuel ratio.
[0006]
In both the theoretical air-fuel ratio sensor element and the wide-range air-fuel ratio sensor element, it is necessary to heat the sensing part to an operating temperature of about 700 ° C. For this reason, the sensing part is provided inside the oxygen sensor element made of a cylindrical base. A rod-shaped ceramic heater is inserted to heat up to the operating temperature.
[0007]
[Problems to be solved by the invention]
However, in recent years, there has been a tendency to tighten exhaust gas regulations, and it has become necessary to detect CO, HC, and NOx immediately after the engine is started. In response to such a demand, as described above, in the indirect heating type cylindrical oxygen sensor element in which the ceramic heater is inserted into the cylindrical base body, the time required for the sensing unit to reach the activation temperature (hereinafter referred to as the temperature) The activation time) is slow, and there is a problem that exhaust gas regulations cannot be fully met.
[0008]
On the other hand, the present inventors previously provided a sensing part by forming a reference electrode and a measurement electrode on the inner and outer surfaces of the cylindrical substrate facing each other, and provided a narrow space on the upper surface of the measurement electrode of the sensing part. Heating efficiency is achieved by providing a pumping part formed by forming a solid electrolyte layer with a pair of electrodes on both sides, and a heater part made of a ceramic insulating layer with a heating element embedded around the space part We proposed an air-fuel ratio sensor element that can improve activation and shorten activation time. This air-fuel ratio sensor element is formed by simultaneously firing the sensing part, the pumping part and the heater part.
[0009]
However, as described above, the measurement electrode of the sensing unit and the inner electrode of the pumping unit are opposed to each other through a narrow space of 10 to 40 μm. There was a major manufacturing problem that the peripheral part was in contact with the short circuit during firing, resulting in a defective product.
[0010]
Accordingly, the present invention provides an air-fuel ratio sensor element having a structure in which the sensing part and the pumping part are opposed to each other through a narrow space. It is intended to provide.
[0011]
[Means for Solving the Problems]
As a result of studying the above problems, the present inventors have determined that the inner electrode of the pumping unit facing the measurement electrode of the sensing unit through the space with a specific area smaller than that of the measurement electrode in the cylindrical air-fuel ratio sensor element. As a result of the formation, the above-mentioned problems were solved, and it was found that the target device could be manufactured with a high yield, and the present invention was achieved.
[0012]
That is, the air-fuel ratio sensor element of the present invention, a solid electrolyte cylindrical substrate to form a first electrode pair consisting of a reference electrode and the measuring electrode so as to be opposite to each other of the inner and outer surfaces of said solid electrolyte cylindrical body a sensing unit comprising, as through a space between the measuring electrode provided on the outer surface of the solid electrolyte cylindrical body, and a solid electrolyte layer provided on the outer surface of the solid electrolyte cylindrical body, the in the air-fuel ratio sensor element formed by and a pumping part made by forming a second electrode pair consisting of an inner electrode and the outer electrode so as to be opposite to each other of the inner and outer surfaces of the space portion side of the solid electrolyte layer, wherein with the area of the inner electrode of the pumping unit is 10 to 20 mm ^2, the area of the measuring electrode of the sensing portion is 0.3 to 0.8 times the area of said inner electrode of said pumping unit Characterized in that there.
[0013]
Also, located around the space, between the solid electrolyte layer and the solid electrolyte cylindrical body, set embedded a heating element for heating the first electrode pair and said second pair of electrodes By disposing the ceramic insulating layer, the heating efficiency of the air-fuel ratio sensor element can be improved and the activation time can be shortened.
[0014]
The gas diffusion holes for introducing the measurement gas from the outside into the space is preferably formed on the solid electrolyte layer. Incidentally, the solid electrolyte layer having a second pair of electrodes, wherein said at first that the electrode pairs are formed wound around the surface of the cylindrical substrate, comprising.
[0015]
The air-fuel ratio sensor element of the present invention, as described later, in the production, on the surface of the sensor body having a cylindrical substrates composed of solid electrolytes, winding the solid electrolyte layer having a pre-Symbol second electrode pair Te, in order to be able to prepare and co-firing, in comparison to the oxygen sensor element past, the assembly process is small and the manufacturing cost becomes very expensive, is superior in terms of economy.
[0016]
However, a disadvantage of the above manufacturing method is that the measurement electrode and the inner electrode of the pumping part formed at a position facing each other through the space are both made of the same size, so the end portions of both However, the yield was poor because of the short circuit due to contact during firing.
[0017]
On the other hand, in the present invention, the size of the inner electrode formed on the solid electrolyte layer in the pumping part is 10 to 20 mm ² and the area of the measurement electrode is 0.3 to 0.8 times larger. Even in the case of forming by simultaneous firing, a short circuit between the measurement electrode of the sensing unit and the inner electrode of the pumping unit is effectively prevented, and the air-fuel ratio sensor element can be manufactured with high yield.
[0018]
Further, according to the air-fuel ratio sensor element of the present invention, since the sensing part, the pumping part, and the heater part are integrated as a cylindrical body, thermal stress is evenly distributed over the entire element. Concentration of thermal stress is prevented, and excellent thermal shock properties that cannot be obtained with a flat plate element can be obtained. In addition, according to the air-fuel ratio sensor element of the present invention, the heater portion in which the heating element is embedded in the ceramic insulating layer provided between the solid electrolyte cylindrical substrate and the solid electrolyte layer, which is located around the space portion, is provided. As a result, the first electrode pair and the second electrode pair formed in the vicinity of the space on the outer surface of the cylindrical base body made of the solid electrolyte can be efficiently heated. The activation time of the sensor, that is, the arrival time to a predetermined temperature can be shortened.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter will be described a basic structure example of the air-fuel ratio sensor element of the present invention schematic perspective view of FIG. 1, based on the X-X cross-sectional view of the air-fuel ratio sensor element of Figure 1 shown in FIG.
[0020]
The air-fuel ratio sensor element 1 of FIGS. 1 and 2 includes a solid electrolyte cylindrical base 2 (hereinafter referred to as a cylindrical tube 2) made of ceramics having oxygen ion conductivity, and the inner and outer surfaces thereof. The first electrode pair for constituting the sensor element is formed at a position facing each other. Specifically, a reference electrode 3 that is in contact with a reference gas such as air is formed on the inner surface of the cylindrical tube 2, and a measured gas such as exhaust gas is formed on the outer surface of the cylindrical tube 2 that faces the reference electrode 3. Measuring electrode 4 is formed in contact with each other, forming a sensing part.
[0021]
A solid electrolyte layer 8 having oxygen ion conductivity is formed on the upper surface of the measurement electrode 4 via the space 5, and the inner surface of the solid electrolyte layer 8 on the space 5 side is opposed to it. A second electrode pair consisting of an inner electrode 9 and an outer electrode 10 is formed as a pumping electrode on the outer surface of the solid electrolyte layer 8 to form a pumping portion.
[0022]
The solid electrolyte layer 8 including the second electrode pair 9 and 10 forming the pumping portion is formed with a small gas diffusion hole 11 for taking in the exhaust gas to be measured gas.
[0023]
According to the present invention, the measurement electrode 4 is formed to have a smaller area than the inner electrode 9 of the pumping portion. It is important that the area of the measurement electrode 4 is 0.3 to 0.8 times the area of the inner electrode 9. This is because if the area of the measuring electrode 4 is larger than 0.8 times that of the inner electrode 9, the two electrodes are easily short-circuited and the manufacturing yield is greatly reduced. On the other hand, if it is less than 0.3 times, the sensing function is lowered and the gas responsiveness tends to deteriorate. The size of the measuring electrode 4 is particularly preferably 0.5 to 0.7 times that of the inner electrode 9 of the pumping part.
[0024]
Note that the short circuit due to the contact between both electrodes can be eliminated by making either the measurement electrode 4 or the inner electrode 9 smaller. However, if the inner electrode 9 is made smaller than the measurement electrode 4, the pumping current per unit area is increased. As a result, there is a problem that the outer electrode 10 and the inner electrode 9 of the pumping are likely to be deteriorated. As a result, it is necessary to reduce the measurement electrode 4 side.
[0025]
Further, according to the present invention, the area of the inner electrode 9 in the pumping portion needs to be 10 to 20 mm ² . When the area of the inner electrode 9 is smaller than 10 mm ² , the current density flowing between the electrodes 9 and 10 is increased, and the solid electrolyte layer is easily reduced. On the other hand, when the area exceeds 20 mm ² , the size of the element itself is increased to form this, and it is difficult to rapidly raise the element. As the size of the inner electrode 9, a range of 12 to 18 mm ² is particularly desirable.
[0026]
In addition, a ceramic insulating layer 7 in which a heating element 6 is embedded around the space 5 is disposed between the cylindrical tube 2 and the solid electrolyte layer 8. The heating element 6 disposed in the ceramic insulating layer 7 is connected to the terminal electrode 13 via the lead electrode 12, and the heating element 6 is heated by passing a current through the heating element 6 through the lead electrode 12. The sensing part made of a solid electrolyte having the electrode 3 and the measurement electrode 4 and the pumping part made of the solid electrolyte layer 8 having the second electrode pair 9 and 10 are heated.
[0027]
At this time, as the overall size of the element, by setting the outer diameter to 3 to 6 mm, particularly 3 to 4 mm, the power consumption of the element can be reduced and the sensing performance can be enhanced.
[0028]
The ceramic solid electrolyte used in the present invention is made of a ceramic containing ZrO ₂ , and Y ₂ O ₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , Dy are used as stabilizers. 1 to 30 mol% of rare earth oxides such as ₂ O ₃ in terms of oxide, preferably the partially stabilized ZrO ₂ or stabilized ZrO ₂ containing 3 to 15 mol% are used.
[0029]
Further, by using ZrO ₂ in which 1 to 20 atomic% of Zr in ZrO ₂ is substituted with Ce, there is an effect that electron conductivity is increased and responsiveness is further improved.
[0030]
Furthermore, for the purpose of improving the sinterability, Al ₂ O ₃ and SiO ₂ can be added to the ZrO ₂ , but if it is contained in a large amount, the creep properties at high temperatures are deteriorated. The total amount of Al ₂ O ₃ and SiO ₂ is preferably 5% by weight or less, particularly 2% by weight or less.
[0031]
On the other hand, the ceramic insulating layer 7 for burying a heating element 6, alumina, spinel, forsterite, ceramic material such as zirconia A is preferably used. Furthermore, it is possible to use glass as the ceramic insulating layer 7, glass in this case contains in view of heat resistance, BaO, PbO, SrO, CaO, at least one of CdO 5 wt% or more In particular, crystallized glass is desirable.
[0032]
The ceramic insulating layer 7 is preferably composed of a dense ceramic having a relative density of 80% or more and an open porosity of 5% or less. This is because the mechanical strength of the oxygen sensor element itself can be increased as a result of the strength of the insulating layer being increased because the ceramic insulating layer 7 is dense.
[0033]
The heating element 6 embedded in the ceramic insulating layer 7 is preferably made of one kind of metal selected from the group consisting of platinum, rhodium, palladium and ruthenium, or two or more kinds of alloys. From the viewpoint of simultaneous sintering with the ceramic insulating layer 7, it is desirable to select a metal or alloy having a melting point higher than the firing temperature of the ceramic insulating layer 7.
[0034]
In addition to the above metals, the heating element 6 contains alumina, spinel, an alumina / silica compound, forsterite, or zirconia that can be used as the above electrolyte in a volume from the viewpoint of preventing sintering and increasing the adhesion between the insulating layer and the like. It is desirable to mix in the range of 10 to 80%, particularly 30 to 50% by ratio.
[0035]
The solid electrolyte layer 8 that closes the space portion 5 is formed on the surface of the ceramic insulating layer 7 so as to cover the space portion 5. The solid electrolyte layer 8 is made of the same material as the solid electrolyte constituting the cylindrical tube 2 having oxygen ion conductivity, like the cylindrical tube 2. In particular, the solid electrolyte layer 8 is preferably made of the same material as that of the solid electrolyte constituting the cylindrical tube 2.
[0036]
In addition, the solid electrolyte layer 8 formed on the outer surface of the ceramic insulating layer 7 prevents heat from being emitted from the heating element 6. Further, the same solid electrolyte is formed on the upper and lower surfaces of the ceramic insulating layer 7. As a result, the stress caused by the difference in thermal expansion and firing shrinkage between the cylindrical tube 2 made of the solid electrolyte and the ceramic insulating layer 7 is applied. It also acts to relax and reduce the thermal stress as much as possible.
[0037]
The heating element 6 needs to be embedded in the ceramic insulating layer 7 without being in direct contact with the solid electrolyte layer 8 and the second electrode pair 9, 10 above the cylindrical tube 2 or the space 5. The thickness of the ceramic insulating layer 7 between the heating element 6 and the cylindrical tube 2 and the solid electrolyte layer 8 is desirably at least 2 μm, preferably 5 μm.
[0038]
The shape of the space portion 5 is not particularly limited, but when formed on the outer surface of the cylindrical tube 2, it is preferable that the length in the longitudinal direction of the cylindrical tube 2 is long or elliptical. In the case where the space portion 5 is rectangular, the corner portion is formed by a gently curved surface, thereby reducing the concentration of thermal stress on the corner portion of the space portion 5. Further, the height of the space portion is preferably 10 to 50 μm, particularly 20 to 30 μm.
[0039]
In the air-fuel ratio sensor element of FIGS. 1 and 2, the gas diffusion hole 11 formed in the solid electrolyte layer 8 formed in the upper part of the space portion 5 preferably has a diameter of 100 to 500 μm, and this gas diffusion hole is small. One or two or more gas diffusion holes 11 may be provided.
[0040]
In the air-fuel ratio sensor element of FIGS. 1 to 2, the gas diffusion hole 11 is formed in the solid electrolyte layer 8. The gas diffusion hole 11 can introduce the gas to be measured into the space portion 5. If it exists, it does not matter where it is formed. For example, a gas diffusion hole 11 is formed in the longitudinal direction of the cylindrical tube 2 and a gas to be measured is introduced from the vicinity of the tip of the air-fuel ratio sensor element 1 or a porous body having gas permeability from the space 5 to the tip. The gas to be measured can be introduced into the space portion 5 by using the pores in the porous body as gas diffusion holes.
[0041]
Further, a porous diffusion rate controlling body 16 is provided in the vicinity of the gas diffusion hole 11 in the space portion 5, and the exhaust gas flowing into the space portion 5 is controlled by the gas diffusion hole 11 and the diffusion rate controlling body 16. Is desirable. The diffusion rate controlling body 16 is interposed between the gas diffusion hole 11, the inner electrode 9 and the measurement electrode 4, and is formed of a cylindrical body having a hole aligned with the gas diffusion hole 11 as shown in FIG. . As the material of the diffusion rate controlling body 16, the same material as the above solid electrolyte material is used, and alumina, spinel and the like are used. The diffusion rate controlling body 16 also has a function of protecting the exhaust gas that has passed through the gas diffusion hole 11 from directly touching the measurement electrode 4 and the inner electrode 9.
[0042]
Each electrode forming the first electrode pair 3, 4 and the second electrode pair 9, 10 in the air-fuel ratio sensor element 1 of the present invention is one selected from the group consisting of platinum, rhodium, palladium, ruthenium and gold, Alternatively, two or more alloys, particularly platinum, is preferably used.
[0043]
Further, for the purpose of preventing the grain growth of the metal in the electrode during the sensor operation and for the purpose of increasing the contact of the so-called three-phase interface between the metal particles related to the responsiveness, the solid electrolyte, and the gas, the above-described cylindrical tube 2 is used. Or it is desirable to mix the solid electrolyte component which comprises the solid electrolyte layer 8 in the said electrode in the ratio of 1-50 volume%, especially 10-30 volume%.
[0044]
Of the first electrode pairs 3 and 4, the reference electrode 3 formed on the inner surface of the cylindrical tube 2 is formed on the inner surface portion of the measurement electrode 4 that faces the portion exposed to the space portion 5. Alternatively, it may be formed on an area larger than the exposed area of the measurement electrode 4, for example, on the entire inner surface of the cylindrical tube 2.
[0045]
Further, among the above electrodes, the three electrodes 4, 9, 10 that are in contact with the gas to be measured are appropriately coated with zirconia, alumina, magnesia, and the like on the surface in order to prevent the electrodes from being poisoned. An electrode protective layer having a thickness of 10 to 200 μm, particularly 50 to 150 μm, made of a porous material having an open porosity of 10 to 40% selected from the group of spinels may be formed.
[0046]
Further, the space 5 may be filled with a porous body having a larger porosity than the diffusion rate controlling body 16 in order to protect the electrodes 4 and 9 and to increase the strength of the space 5. Is possible.
[0047]
Next, a method for manufacturing the air-fuel ratio sensor element of the present invention will be described with reference to FIG. 3, taking the method for manufacturing the air-fuel ratio sensor element of FIGS.
(1) First, as shown in FIG. 3, in order to form the cylindrical tube 2, a hollow cylindrical tube body 20 with one end sealed is prepared. The cylindrical tube body 20 may be formed by extrusion molding, isostatic pressing (rubber press), press formation, or the like by appropriately adding a molding organic binder to a ceramic solid electrolyte powder having oxygen ion conductivity such as zirconia. It is produced by the well-known method.
(2) And, as shown in FIG. 3, the electrode pattern 21 to be the reference electrode 3 is formed on the inner surface of the cylindrical tube body 20 made of the solid electrolyte, for example, a conductive paste containing platinum is placed inside the cylindrical tube body 20. Fill and discharge to form coating on the entire inner surface. In this way, the sensor element A is manufactured.
(3) Next, as shown in FIG. 3, a green sheet 22 is formed using a solid electrolyte slurry forming the cylindrical tube 20, and an insulating material such as alumina is formed in a region where the measurement electrode of the green sheet 22 is not formed. After forming the insulating layer 23a by applying the insulating slurry, the heating element pattern 25 including the lead pattern is printed and formed again, and the insulating slurry 23 is applied again to form the insulating layer 23b to insulate the heating element pattern 25. It is embedded in the layers 23a and 23b. Then, the solid electrolyte slurry in which the green sheet 22 is formed is applied to the surface of the insulating layer 23 b including the opening 26 where the insulating layers 23 a and 23 b are not formed, and the solid electrolyte body 27 is filled in the opening 26. Then, the heater element body B is formed on the surface of the solid electrolyte body 27 by forming a measurement electrode pattern 28 and a porous cylindrical body 29 as a diffusion-controlling body as appropriate by slurry application or the like.
[0048]
Further, the pumping element body C is formed by printing and applying the electrode patterns 30 and 31 for pumping on both surfaces of the solid electrolyte green sheet 33 in which the gas introduction holes 32 are formed.
[0049]
Then, the heater element B and the pumping element C are wound around the surface of the sensor element A, and the green sheet 23 side of the laminate produced as described above is wound around the surface of the sensor element A, and then fired simultaneously. Can be formed.
[0050]
For example, when zirconia is used as the solid electrolyte and alumina is used as the ceramic insulating layer, the baking may be performed at 1300 to 1700 ° C. for about 1 to 10 hours in an inert atmosphere such as argon gas or in the air.
[0051]
In the above manufacturing method, the ceramic insulating layers 23a and 23b in which the heating element pattern 25 is embedded by slurry application are formed on the surface of the solid electrolyte green sheet 22. However, the ceramic insulating layer is not used without using the solid electrolyte green sheet 22. It is also possible to form 23a and 23b by a laminate of green sheets.
[0052]
In the above manufacturing method, the surface of the ceramic insulating layer 23b is covered when the solid electrolyte body 27 is filled and formed in the opening 26. However, there is no problem even with the opening 26 alone.
[0053]
The gas diffusion hole 11 may be formed at any stage in the above manufacturing process. For example, as shown in FIG. 3, the through-hole 29 is formed in the solid electrolyte layer green sheet 23 of the laminate B before the winding process, or the solid electrolyte layer after firing is perforated using a micro drill or the like. However, it is preferably formed before firing from the viewpoint of workability and yield.
[0054]
If necessary, a porous slurry can be applied to the surface of the electrode before firing, or a protective layer made of a porous material can be formed by a thermal spraying method after firing.
[0055]
【Example】
First, a slurry was prepared by adding a polyvinyl alcohol solution to zirconia powder containing 5 mol% Y ₂ O ₃ , sintered by extrusion molding, and then sealed at one end so that the outer diameter was about 4 mm and the inner diameter was 1 mm. A cylindrical tube body was manufactured, and a platinum paste was applied to the entire inner surface of the molded body to form a reference electrode, thereby preparing a sensor body A.
[0056]
A slurry was prepared by adding an acrylic binder and a toluene solution to zirconia powder containing 5 mol% Y ₂ O _3, and a zirconia green sheet having a thickness of about 200 μm was prepared by a doctor blade method.
[0057]
Thereafter, a slurry containing alumina powder is applied to the surface of the region where the measurement electrode of the zirconia green sheet is not formed so as to have a thickness of about 10 μm after firing by screen printing, and then the thickness after firing using platinum paste is 10 μm. A heating element pattern was formed by printing, and the alumina slurry was applied again so that the heating element pattern was embedded, thereby forming an alumina insulating layer in which the heating element was embedded on the surface of the zirconia green sheet.
[0058]
Then, after applying and filling a slurry of zirconia powder containing 5 mol% Y ₂ O _{3 on the} electrode forming region of the zirconia green sheet where the alumina insulating layer is not formed, the electrode paste as a measurement electrode is applied to the surface. coating was formed, also formed by printing a diffusion rate control member, to prepare a heater element B.
[0059]
The thicknesses of the measurement electrode and the reference electrode were adjusted to be about 10 μm after firing. The area of the measurement electrode was the size shown in Table 1 after firing.
[0060]
Next, after forming the inner electrode, the pumping electrode pair of the outer electrode, and the lead wire on both surfaces of another zirconia green sheet produced in the same manner as described above, 8 mol% Y that becomes a diffusion-controlling layer on one electrode surface _{A 2} O ₃ -containing zirconia powder was formed to a thickness of 30 μm to prepare a pumping element body C. At this time, the sizes of the inner electrode and the outer electrode were adjusted to the sizes shown in Table 1 after firing. The inner electrode and the outer electrode have substantially the same area.
[0061]
Then, the heater element B and the pumping element C were sequentially wound around the surface of the sensor element A to prepare a cylindrical laminate. Note that an acrylic binder was used as an adhesive for bonding between the element bodies during winding. Thereafter, this cylindrical laminate was baked at 1500 ° C. in the atmosphere for 2 hours to complete 50 sensor elements having different sizes of the measurement electrode and the inner electrode of the pumping part.
[0062]
The air-fuel ratio sensor element produced was evaluated by applying 0.5 V between the electrodes of the pumping unit at 800 ° C. in the atmosphere to pump oxygen in the space to the atmosphere, and the oxygen partial pressure in the space was set to a predetermined value (starting up) The ratio (non-defective product ratio) of the devices showing 400 to 500 mV in electric power was determined as non-defective products.
[0063]
[Table 1]

[0064]
From Table 1, a conventional sample No. in which the ratio of the inner electrode area of the pumping portion to the measurement electrode area is larger than 0.8. No. 1 and No. 1 in which the measurement electrode area is larger than the inner electrode area. 14 shows that the yield rate is low. In addition, the sample no. In 7, no sensing was observed.
[0065]
On the other hand, according to the present invention, it can be seen that when the measurement electrode area is smaller than 0.8 times the inner electrode area, the yield rate is improved. In particular, experiments from a small sample No. inner electrode area than 10 mm ² In No. 8, many solid electrolyte layers cracked during measurement. Sample No. whose inner electrode area exceeded 20 mm ² was used. In No. 3, many devices could be manufactured but the temperature could not be increased to 800 ° C.
[0066]
Therefore, it can be seen that the yield rate is high when the inner electrode area of the pumping portion of the present invention is 10 to 20 mm ² and the area ratio of the measurement electrode is 0.3 to 0.8 times that of the inner electrode.
[0067]
【The invention's effect】
As described above in detail, according to the air-fuel ratio sensor element of the present invention, by controlling the area ratio between the measurement electrode of the sensing unit and the inner electrode of the pumping unit, the thermal shock resistance such as rapid temperature rise can be achieved. An excellent air-fuel ratio sensor element can be provided with high yield. Therefore, the manufacturing cost is extremely low, which is excellent from the viewpoint of economy.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view for explaining an example of an air-fuel ratio sensor element of the present invention.
2 is X-X in the vertical cross-sectional view of the air-fuel ratio sensor element of FIG.
FIG. 3 is a view for explaining the method for manufacturing the air-fuel ratio sensor element of the present invention, and is a view showing a process of manufacturing a sensor element body.
[Explanation of symbols]
1 is an air-fuel ratio sensor element, 2 is a cylindrical tube, 3 is a reference electrode, 4 is a measurement electrode, 5 is a space 6 is a heating element, 7 is a ceramic insulating layer, 8 is a solid electrolyte layer, 9 is an inner electrode, 10 is The outer electrode, 11 is a gas diffusion hole, 12 is a lead electrode, 13 is a terminal electrode, 14 is a porous body, and 16 is a diffusion rate limiting body.

Claims (4)

A solid electrolyte cylindrical substrate; and
A sensing portion formed by forming a first electrode pair consisting of a reference electrode measuring electrode so as to be opposite to each other of the inner and outer surfaces of said solid electrolyte cylindrical body,
A solid electrolyte layer that is to through the space portion, provided on the outer surface of the solid electrolyte cylindrical body between the measurement electrode provided on an outer surface of the solid electrolyte cylindrical body,
In the air-fuel ratio sensor element formed by and a pumping part made by forming a second electrode pair consisting of an inner electrode and the outer electrode so as to be opposite to each other of the inner and outer surfaces of the space portion side of the solid electrolyte layer,
With the area of the inner electrode of the pumping part is 10 to 20 mm ² that the area of the measuring electrode of the sensing portion is 0.3 to 0.8 times the area of said inner electrode of said pumping unit An air-fuel ratio sensor element. Located around the space, ceramic between said solid electrolyte cylindrical substrate the solid electrolyte layer, was set embedded a heating element for heating the first electrode pair and said second pair of electrodes The air-fuel ratio sensor element according to claim 1, further comprising an insulating layer. The air-fuel ratio sensor element according to claim 1 or 2, wherein the solid electrolyte layer includes a gas diffusion hole for introducing a gas to be measured into the space from the outside .   4. The solid electrolyte layer comprising the second electrode pair is formed by wrapping around the surface of the cylindrical substrate comprising the first electrode pair. Or an air-fuel ratio sensor element.

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