JP3677480B2 - Oxygen sensor element - Google Patents

Description

【００６３】
本発明の酸素センサ素子は、いずれもなんら支障なく電極パッドに金属ピンを取り付けることが可能であった。また、素子の大きさにおいては、表１の結果より、素子の測定電極の面積が８〜１８ｍｍ^２、および素子の幅が２〜３．５ｍｍの範囲とすることによって、活性化時間を１０秒以下と小型な素子であり且つ優れた特性を有するセンサ素子を得ることができた。
【００６４】
【発明の効果】
以上詳述したとおり、本発明によれば、素子の長手方向に対して直交する方向の幅を後端部から先端部に向かって連続的、または段階的に小さく、且つ前記一対の電極パッドの形成幅を先端部の幅よりも大きくすることによって、酸素センサ素子におけるセンサ部およびヒータ部の小型化が可能となり、ガス応答性を高めることができる。
【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】本発明の酸素センサ素子の他の例を説明するために概略断面図である。
【図３】本発明における酸素センサ素子の概略平面図である。
【図４】本発明における発熱体パターンの構造を説明するための概略透過図である。
【図５】本発明における発熱体パターンの他の構造を説明するための透過図である。
【図６】本発明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７】図３（ｂ）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】活性化時間の測定方法を説明するためのグラフである。
【図９】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１０】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（ａ）概略断面図と、（ｂ）概略平面図である。
【符号の説明】
１ センサ部
２ ヒータ部
３ 固体電解質
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 白金ヒータ[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 typical example of this oxygen sensor, as shown in the schematic cross-sectional view of FIG. 7, the inner surface of a cylindrical tube 31 made of a ZrO ₂ solid electrolyte and sealed at the tip is made of platinum as a sensor part and made of air. A reference electrode 32 that comes into contact with a reference gas such as the above, and a measurement electrode 33 that comes into contact with a measured gas such as exhaust gas are formed on the outer surface of the cylindrical tube 31.
[0004]
In such an oxygen sensor, a so-called theoretical air-fuel ratio sensor (λ sensor) that is generally used for controlling the ratio of air to fuel near 1 is a ceramic porous as a protective layer on the surface of the measurement electrode 33. A layer 34 is provided, and an oxygen concentration difference generated on both sides of the cylindrical tube 31 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 up to an operating temperature of about 700 ° C. For this reason, a rod heater 35 is inserted inside the cylindrical tube 31 to heat the sensor unit to the operating temperature. Yes.
[0005]
[Problems to be solved by the invention]
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 formed by inserting the heater 35 into the cylindrical tube 31 as described above, the time required for the sensor unit to reach the activation temperature (hereinafter, There is a problem that exhaust gas regulations cannot be fully met because the activation time is slow.
[0006]
In recent years, as a method for avoiding this problem, a measurement electrode 37 and a reference electrode 38 are provided on the outer surface and the inner surface of a flat solid electrolyte substrate 36 as shown in the schematic cross-sectional view of FIG. A heater-integrated oxygen sensor element in which a heating element 40 is embedded is proposed. In such an oxygen sensor element, an electrode pad 42 connected via a lead 41 is formed at the other end of the sensor element, and a connector, a metal pin, or the like is brazed to the electrode pad 42.
[0007]
However, unlike the conventional indirect heating method described above, the conventional heater-integrated oxygen sensor is a direct heating method, so that rapid temperature increase is possible. However, it is desired to further increase the rate of temperature increase. However, since the element itself is large, there is a limit to rapid temperature increase, and as a result, there is a problem that the activation time cannot be shortened.
[0008]
An object of the present invention is to provide an oxygen sensor element that is small in size and excellent in gas responsiveness and capable of rapid temperature increase.
[0009]
[Means for Solving the Problems]
The oxygen sensor element of the present invention includes a sensor unit provided with a measurement electrode and a reference electrode made of platinum on opposite sides in the vicinity of one end of a long zirconia solid electrolyte substrate flat plate, respectively, In the oxygen sensor element comprising a terminal electrode in the vicinity of the end, the width in the direction perpendicular to the longitudinal direction of the element is continuously or gradually smaller from the rear end toward the front end, and The formation width of the pair of electrode pads is larger than the width of the tip portion, so that the sensor portion and the heater portion can be downsized while ensuring the attachment of the connector and the metal pin to the electrode pad, and the gas in the sensor portion Responsiveness and rapid temperature rise can be improved.
[0010]
Further, when the size of the sensor unit, that the electrode area of the measuring electrode is 8～18Mm ^2, also, the width direction of the element perpendicular to the longitudinal direction of the tip 5mm or more parts from the device, 2 It is important that the thickness is 0.0 to 3.5 mm.
[0011]
Further, in the oxygen sensor element of the present invention, it is desirable to include a heater part in which a heating element is embedded in a ceramic insulating layer, and this heater part is formed by simultaneous firing with the sensor part, or They may be formed separately from each other, and then joined and integrated with a joining material.
[0012]
Further, in this heater portion, a pair of heating elements are formed vertically with a ceramic insulating layer interposed therebetween, more preferably a maximum width x in a direction perpendicular to the longitudinal direction of one heating element, and an oxygen sensor element The maximum width w in the direction perpendicular to the longitudinal direction of the element has a relationship of w ≦ 2.5x, so that even when the element width is reduced, the amount of heat generation can be increased, and the element can be rapidly increased. Temperature can be easily performed.
[0013]
The sensor unit and the heater unit may be formed by simultaneous firing, or may be formed separately from the sensor unit and the heater unit, and then bonded and integrated with a bonding material. Good.
[0014]
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. FIG. 1 is a schematic cross-sectional view for explaining an example of the oxygen sensor element of the present invention, and FIG. 2 is a schematic cross-sectional view for explaining another example. These are generally referred to as theoretical air-twist ratio sensor elements, and both include the sensor unit 1 and the heater unit 2 in the examples of FIGS.
[0015]
In the oxygen sensor element of FIG. 1, a ceramic solid electrolyte substrate 3 made of zirconia and having oxygen ion conductivity, a reference electrode 4 that is in contact with air, and a measurement that is in contact with exhaust gas are provided on both opposing surfaces of the solid electrolyte substrate 3. The electrode 5 is formed, and the sensor unit 1 having a function of detecting the oxygen concentration is formed.
[0016]
That is, the solid electrolyte substrate 3 has a flat plate-like hollow shape with the tip sealed, and the hollow portion forms the air introduction hole 3a. A reference electrode 4 in contact with a reference gas such as air is deposited on the hollow inner wall, and measurement is performed on the outer surface of the solid electrolyte substrate 3 facing the reference electrode 4 with a measured gas such as exhaust gas. An electrode 5 is formed.
[0017]
Further, from the viewpoint of preventing electrode poisoning by exhaust gas, a ceramic porous layer 6 is formed on the surface of the measurement electrode 5 as an electrode protective layer.
[0018]
On the other hand, the heater unit 2 has a structure in which a heating element 8 is embedded in a ceramic insulating layer 7 having electrical insulation. In the oxygen sensor element of FIG. 1, the heater unit 2 is integrated with the sensor unit 1 by firing. In the oxygen sensor element of FIG. 2, the sensor unit 1 and the heater unit 2 are formed separately from each other and joined by a joining material 10.
[0019]
In particular, when the difference in thermal expansion coefficient between the solid electrolyte substrate 3 of the sensor unit 1 and the ceramic insulating layer 7 of the heater unit 2 is large, the structure shown in FIG. 2 is desirable. In addition, it is desirable to join at a low temperature part in use where the electrodes 4 and 5 are not formed. Further, in the case of bonding over the entire surface, for example, the zirconia solid electrolyte substrate 3 of the sensor unit 1 and the alumina ceramic insulation of the heater unit 2 are alleviated in order to relieve stress due to the difference in thermal expansion coefficient between the sensor unit 1 and the heater unit 2. A composite material with the layer 7, alumina and zirconia may be interposed between the composite compound layers.
[0020]
In FIG. 1, the heater unit 2 is a sensor unit in order to increase the heating efficiency of the heater unit 2 and to increase the heating efficiency of the heater unit 2. It is desirable to form a ceramic layer 9 having the same or similar thermal expansion coefficient as that of the solid electrolyte substrate 3 on the side opposite to the side in contact with 1.
[0021]
Further, as shown in the schematic plan view of FIG. 3, the oxygen sensor element of the present invention has a sensor portion 1 and a heater portion 2 formed near the front end portion of the solid electrolyte substrate 3, and the vicinity of the rear end portion of the substrate 3. A pair of electrode pads 11 connected to the measurement electrode 5 and the reference electrode 4 via leads 10 are formed on the surface of the electrode. A metal connector is used for the electrode pad 11 to appropriately apply power to the platinum heater 8 and to extract signals from the electrodes 4 and 5 of the sensor unit 1 to the outside. In some cases, voltage application and signal extraction may be used by brazing a metal pin such as Ni to the pad portion.
[0022]
The oxygen sensor element of the present invention is characterized in that the width in the direction perpendicular to the longitudinal direction of the element is small continuously or stepwise from the rear end portion toward the front end portion. Specifically, as shown in FIG. 3A, the width continuously increases from the front end portion to the rear end portion of the element, in other words, the width becomes wider, as shown in FIG. As shown in FIG. 3 (c), the taper portion between the front end portion and the rear end portion is widened from the front end portion to the rear end portion. For example, p may be provided so that the width is partially continuously increased.
[0023]
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.
[0024]
In addition, according to the present invention, the electrode area of the measurement electrode 5 is 8 to 18 mm ² in order to achieve excellent gas responsiveness as well as downsizing of the element, and in a portion of 5 mm or more, particularly 10 mm or more from the tip of the element. The width in the direction orthogonal to the longitudinal direction is desirably 2.0 to 3.5 mm. On the other hand, the maximum width at the rear end portion where the electrode pad 11 is formed is suitably 3.7 to 5 mm, particularly 4.0 to 4.5 mm.
[0025]
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 by the heater and improve the gas responsiveness by the sensor.
[0026]
Further, the structure of the heater portion 2 is not particularly limited as long as the area of the measurement electrode 5 and the width of the element are satisfied based on the present invention. Normally, as shown in FIG. Although they may be formed in the same plane, in the case of the same plane, the shape of the heater pattern is very restricted as the size is reduced.
[0027]
Therefore, 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 size of the heater portion can be reduced.
[0028]
More specifically, as shown in the schematic transmission diagram for explaining the structure of the heating element pattern in FIG. 4, 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.
[0029]
The heating element pattern of FIG. 4 is composed of a meander structure (waveform) pattern. When the width of the heating element is x, in the meander structure of FIG. 4 , 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.
[0030]
On the other hand, when the heat generating portions 8b1 and 8b2 are formed between different layers, the insulating properties are maintained by the ceramic insulating layer 7a even when the heat generating portions 8b1 and 8b2 overlap each other in plan view. And as shown in FIG. 2, the width w of the entire device 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.
[0031]
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.
[0032]
In the example of FIG. 4, 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. 5, it may be a meander pattern having a folding in the longitudinal direction of the element.
[0033]
Furthermore, according to the present invention, using the oxygen sensor element shown in FIG. 3 (c), for example, as shown in FIG. Can be attached to.
[0034]
The solid electrolyte used in the oxygen sensor element of 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 are used as stabilizers. _3, Dy ₂ O ₃ or the like 1 to 30 mol% of rare earth oxide in terms of oxide, preferably the partially stabilized ZrO ₂ or stabilized ZrO ₂ containing 3 to 15 mol% are used. 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 the ionic conductivity is increased and the responsiveness is further improved. 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.
[0035]
The reference electrode 4 and the measurement electrode 5 deposited on the surface of the solid electrolyte 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 for the purpose of increasing the contact at the so-called three-phase interface between the platinum particles, the solid electrolyte and the gas related to the responsiveness, The components may be mixed in the electrodes 4 and 5 at a ratio 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 electrodes 4 and 5 is preferably 3 to 20 μm, particularly preferably 5 to 10 μm.
[0036]
On the other hand, the ceramic insulating layer 7 in which the heating element 8 is embedded is preferably composed of a dense ceramic made of alumina ceramics having a relative density of 80% or more and an open porosity of 5% or less. At this time, Mg, Ca and Si may be contained in total in an amount of 1 to 10% by mass for the purpose of improving sinterability. However, the content of alkali metals such as Na and K is migrated to the heater part. In order to deteriorate the electrical insulation between the pair of heaters in No. 2, it is desirable to control to 50 ppm or less in terms of oxide weight. In addition, by setting the relative density within the above range, the substrate strength increases, and as a result, the mechanical strength of the oxygen sensor itself can be increased.
[0037]
The ceramic porous layer 6 formed on the surface of the measuring electrode 5 is at least one selected from the group consisting of zirconia, alumina, γ-alumina and spinel having a thickness of 10 to 800 μm and a porosity of 10 to 50%. It is desirable to be formed by. When the thickness of the porous layer 6 is less than 10 μm or the porosity exceeds 50%, the electrode poisoning substance P, Si, etc. easily reach the electrode and the electrode performance is deteriorated. On the other hand, when the thickness of the porous layer 6 exceeds 800 μm or the porosity is less than 10%, the diffusion rate of the gas in the porous layer 6 becomes slow, and the gas responsiveness of the electrode is deteriorated. In particular, the thickness of the porous layer 6 is suitably 100 to 500 μm, although it depends on the porosity.
[0038]
The heating element 8 and the leads 8a1 and 8a2 embedded in the ceramic insulating layer 7 in the heater section 2 use platinum as a metal or an alloy of platinum and one selected from the group of rhodium, palladium, and ruthenium. Can do. In this case, the resistance ratio between the heating element 8 and the leads 8a1 and 8a2 is preferably controlled in the range of 9: 1 to 7: 3 at room temperature.
[0039]
The oxygen sensor element of the present invention has a total thickness of 0.8 to 1.5 mm, particularly 1.0 to 1.2 mm, and an element length of 45 to 55 mm, particularly 45 to 50 mm. It is preferable from the relationship between the rapid temperature rise property and how the element is mounted in the engine.
[0040]
Furthermore, according to the present invention, the thermal shock resistance can be improved by forming the tip of the element with a curved surface having a radius of 100 mm or less, or by processing the C-surface with a corner of 0.1 mm or more.
[0041]
Next, a method for manufacturing the oxygen sensor element of the present invention will be described with reference to the exploded perspective view of FIG. 7, taking the method of manufacturing the oxygen sensor element of FIG. 3B as an example.
[0042]
First, a solid electrolyte green sheet 13 is prepared. For example, the green sheet 13 may be formed by appropriately adding an organic binder for molding to a ceramic solid electrolyte powder having oxygen ion conductivity of zirconia, by a doctor blade method, extrusion molding, or isostatic pressing (rubber press). Alternatively, the green sheet is manufactured by a known method such as press forming, and further, a green sheet having a small width in the front end portion from the rear end portion toward the front end portion as shown in FIG. 7 is manufactured by punching or the like.
[0043]
Next, a pattern 14, a lead pattern 15, an electrode pad pattern 16, a through hole (not shown) or the like that becomes the measurement electrode 5 and the reference electrode 4, respectively, are formed on both surfaces of the green sheet 13. The green sheet 18 and the green sheet 19 in which the air introduction hole 17 is formed are interposed with an adhesive such as an acrylic resin or an organic solvent after the conductive paste is used for the slurry dipping method, screen printing, pad printing, or roll transfer. Alternatively, the laminated body A of the sensor unit 1 is manufactured by mechanically adhering while applying pressure with a roller or the like.
[0044]
At this time, a porous slurry for forming the ceramic porous layer 6 of FIG. 1 may be formed by printing on the surface of the pattern 14 to be the measurement electrode 5.
[0045]
Next, as shown in FIG. 7, a paste made of alumina powder is printed on the surface of the zirconia green sheet 20 by a slurry dip method, or screen printing, pad printing, or roll transfer to form the ceramic insulating layer 21a.
[0046]
Next, as shown in FIG. 1, when the platinum heater is formed up and down with the ceramic insulating layer interposed therebetween, first, the lower heater pattern 22a and the lead pattern 23a are printed on the surface of the ceramic insulating layer 21a. . Then, an insulating paste such as alumina is applied to form the ceramic insulating layer 21b, and the upper heater pattern 22b and the lead pattern 23b are printed on the surface of the ceramic insulating layer 21b. And the laminated body B of the heater part 2 is produced by printing again the ceramic insulating layer 21c using an insulating paste.
[0047]
At this time, in order to connect the lower heater pattern 22a and the upper heater pattern 22b, after forming the ceramic insulating layer 21b, a through hole extending from the surface to the lower heater pattern is formed in the ceramic insulating layer 21b. When the upper heater pattern is formed, the via conductor 24 is formed by filling the through hole with a conductive paste. Alternatively, the front end portion of the ceramic insulating layer 21b is cut out so that a part of the lower heater pattern 22a is exposed, and a conductive paste is applied to the cutout portion to connect the upper and lower heater patterns. A connected heating element can be formed.
[0048]
Further, a heater electrode pad pattern 25 is printed and applied to the lower surface of the zirconia sheet 20 using the conductive paste, and the heater lead patterns 23a and 23b are via conductors formed in the same manner as the via conductors 24. The electrical connection is made by 26.
[0049]
In preparing the laminate B of the heater section, the ceramic insulating layers 18a, 18b, and 18c are formed by printing and applying an insulating paste as described above, and using a ceramic slurry such as alumina. An insulating sheet can be formed and laminated by a sheet forming method such as a blade method.
[0050]
Thereafter, the laminated body A of the sensor part and the laminated body B of the heater part are bonded together by interposing an adhesive such as an acrylic resin or an organic solvent, or by mechanically bonding the two while applying pressure with a roller or the like. 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.
[0051]
Further, when the laminated body A of the sensor part and the laminated body B of the heater part are simultaneously fired and integrated, for example, a sensor part is formed in order to reduce the generation of stress due to the difference in thermal expansion coefficient between them. It is desirable to interpose a composite material of the solid electrolyte component to be formed and the insulating component forming the ceramic insulating layer of the heater portion.
[0052]
Thereafter, if necessary, the heater portion was integrated by forming at least one ceramic selected from the group of alumina, zirconia, and spinel on the surface of the measurement electrode 14 after firing by plasma spraying or the like. An oxygen sensor element can be formed.
[0053]
In the above method, the heater part is described as being formed by simultaneous firing with the sensor part. However, after the sensor part and the heater part are separately fired, they are joined with a suitable inorganic adhesive such as glass. It is also possible to integrate them.
[0054]
【Example】
The λ sensor shown in FIG. 1 was produced as follows according to FIG.
[0055]
First, a commercially available purity of 99.9% alumina powder, 5 mol% Y ₂ O ₃ containing zirconia powder containing 0.1 wt% Si, and 8 mol% yttria with an average particle diameter of 0.1 μm are included. A platinum powder (1) containing 30% by volume of zirconia in the crystal and a platinum powder (2) containing 20% by volume of alumina powder were prepared.
[0056]
First, a polyvinyl alcohol solution was added to zirconia powder containing 5 mol% Y ₂ O ₃ to prepare a slurry, and a zirconia green sheet 13 having a thickness after sintering of 0.4 mm was prepared by extrusion molding. did.
[0057]
Thereafter, a conductive paste containing platinum powder (1) is screen-printed on both sides of the green sheet 13 to print and form the measurement electrode and reference electrode pattern 14, the lead pattern 15 and the electrode pad pattern 16. The green sheet 18 having the introduction hole 17 and the green sheet 19 were laminated with an acrylic resin adhesive to obtain a laminate A for sensor section. At this time, the area of the measurement electrode was changed so as to be 5 to 30 mm ² after firing.
[0058]
Next, the surface of the zirconia green sheet 20 is screen-printed using the paste made of the above-mentioned alumina powder to form the ceramic insulating layer 21a so as to be about 10 μm after firing, and then one heater pattern 22a and lead pattern 23a are formed. Then, a conductive paste (2) containing platinum containing alumina was printed by screen printing, and a paste made of alumina powder was screen printed again on this surface to form a ceramic insulating layer 21b. Thereafter, a heater electrode pad 25 is formed on the lower surface of the other heater pattern 22b, heater lead 23b, and green sheet 20 by screen printing using a conductive paste containing platinum, and a ceramic insulating layer 21c is formed again. By forming, the laminated body B for heater parts was produced. The heater patterns 22a and 22b are connected by via conductors 24 formed in the ceramic insulating layer 21b, and the heater leads 23a and 23b and the heater electrode pads 25 are connected by via conductors 26 formed in the ceramic insulating layers 20, 21a and 21b. did.
[0059]
Thereafter, the sensor unit laminate A and the heater unit laminate B were joined in accordance with the manufacturing method described above, and the heater integrated sensor element laminate was baked at 1500 ° C. for 1 hour to produce a heater integrated sensor element. . At this time, by changing the widths of the sensor unit laminate and the heater unit laminate, the theoretical air-fuel ratio type (λ type) heater integrated oxygen having a width L2 (= w) of 1.8 to 3.8 mm. A sensor element was produced. Note that the widths of the elements in the portions where the sensor electrode pads and heater electrode pads of each oxygen sensor element are formed were all 5 mm, and the electrode pad formation width L1 was 4.5 mm.
[0060]
Further, metal pins made of Ni were brazed to each sensor electrode pad and heater electrode pad.
[0061]
Thereafter, a mixed gas of hydrogen, methane, nitrogen, and oxygen is used to spray a mixed gas having an air-fuel ratio of 11 and 23 alternately on the sensor element at intervals of 0.5 seconds, and 12 V is applied to the heater of the element to apply the element. The activation time was measured. At this time, as shown in FIG. 8, the time during which the voltage is applied to the heater is set to zero. First, the element shows 0.6 V at the air-fuel ratio 11 and then the time t until it shows 0.3 V at the air-fuel ratio 23 Activation time.
[0062]
[Table 1]

[0063]
In any of the oxygen sensor elements of the present invention, it was possible to attach a metal pin to an electrode pad without any trouble. In addition, regarding the size of the element, from the result of Table 1, the activation time was set to 10 by setting the area of the measurement electrode of the element to 8 to 18 mm ² and the width of the element to 2 to 3.5 mm. It was possible to obtain a sensor element having an excellent characteristic with a small element of less than a second.
[0064]
【The invention's effect】
As described above in detail, according to the present invention, the width in the direction perpendicular to the longitudinal direction of the element is continuously or gradually reduced from the rear end portion toward the front end portion, and the pair of electrode pads By making the formation width larger than the width of the tip portion, it is possible to reduce the size of the sensor portion and the heater portion in the oxygen sensor element, and it is possible to improve gas responsiveness.
[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 sectional view for explaining another example of the oxygen sensor element of the present invention.
FIG. 3 is a schematic plan view of an oxygen sensor element according to the present invention.
FIG. 4 is a schematic transmission diagram for explaining the structure of a heating element pattern in the present invention.
FIG. 5 is a transparent view for explaining another structure of the heating element pattern in the present invention.
FIG. 6 is a schematic perspective view for explaining an application 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. 3 (b). FIG.
FIG. 8 is a graph for explaining a method for measuring activation time.
FIG. 9 is a schematic cross-sectional view for explaining the structure of a conventional heater-integrated oxygen sensor element.
10A is a schematic cross-sectional view and FIG. 10B is a schematic plan view for explaining the structure of another conventional oxygen sensor element integrated with a heater.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sensor part 2 Heater part 3 Solid electrolyte 4 Reference electrode 5 Measuring electrode 6 Ceramic porous layer 7 Ceramic insulating layer 8 Platinum heater

Claims (6)

A sensor unit provided with a measurement electrode and a reference electrode each made of platinum is provided on both opposing surfaces in the vicinity of the front end of the long solid electrolyte substrate . In the oxygen sensor element including the electrode pad, the electrode area of the measurement electrode is 8 to 18 mm ² , and the width of the element in the direction orthogonal to the longitudinal direction in the portion of 5 mm or more from the tip of the element is 2.0. with a ～3.5Mm, the width direction of the element perpendicular to the longitudinal direction of the device is continuously toward the distal end from the rear end, or stepwise reduced, and the pair of electrode pads An oxygen sensor element characterized in that a formation width is larger than a width of a tip portion. Oxygen sensor element according to claim 1, characterized by comprising a heater unit obtained by embedding a heating element in the ceramic insulating layer. 3. The oxygen sensor element according to claim 2 , wherein in the heater portion, the pair of heating elements are formed vertically with a ceramic insulating layer interposed therebetween. The maximum width x in the direction orthogonal to the longitudinal direction of the heating element and the maximum width w in the direction orthogonal to the longitudinal direction of the oxygen sensor element have a relationship of w ≦ 2.5x. The oxygen sensor element according to claim 2 or 3. The oxygen sensor element according to any one of claims 2 to 4, wherein the sensor part and the front heater part are formed by simultaneous firing. And the sensor portion, said after forming a heater unit and each separately, the oxygen sensor element according to any one of claims 2 to 4, characterized in that formed by integrally bonding a bonding material.

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