JP2003279527A - Oxygen sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact oxygen sensor element superior in gas responsivity and capable of raising temperature at a high speed. <P>SOLUTION: The oxygen sensor element is provided with a sensor, and the sensor is provided with a measuring electrode and a reference electrode made of platinum each on both opposite surfaces of a long solid electrolyte substrate in the vicinity of its tip. The oxygen sensor element is provided with a pair of electrode pads on the surfaces of the substrate in the vicinity of its rear end. The electrode area of the measuring electrode is between 8-18 mm<SP>2</SP>, and its width in the direction which intersects, at right angles, the longitudinal direction of the measuring electrode is between 2.0-3.5 mm. The calorific values of heating elements are lower at the center than at both ends in a unit length in the longitudinal direction of the heating elements, and calorific distribution of the heating elements in the longitudinal direction is made uniform to heighten the gas responsivity. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor element, and more particularly to an oxygen sensor element for controlling the ratio of air to fuel in an internal combustion engine such as an automobile.

[0002]

2. Description of the Related Art Currently, in an internal combustion engine of an automobile or the like, the oxygen concentration in the exhaust gas is detected, and the amount of air and fuel supplied to the internal combustion engine is controlled based on the detected value so that Harmful substances such as CO, H
A method of reducing C and NOx is adopted.

As the detecting element, a solid electrolyte mainly composed of zirconia having oxygen ion conductivity is formed, and a pair of electrode layers are formed on the outer and inner surfaces of a cylindrical tube having one end sealed. Type oxygen sensor is used. As a typical example of this oxygen sensor, as shown in the schematic cross-sectional view of FIG. 11, an inner surface of the cylindrical tube 31 made of ZrO ₂ solid electrolyte and having a sealed tip is made of platinum as a sensor portion and air. Is formed on the outer surface of the cylindrical tube 31, and a measurement electrode 5 is formed on the outer surface of the cylindrical tube 31 to be in contact with a measured gas such as exhaust gas.

In such an oxygen sensor, generally,
As a so-called theoretical air-fuel ratio sensor (λ sensor) used for controlling the ratio of air to fuel near 1, a ceramic porous layer 6 is provided as a protective layer on the surface of the measuring electrode 4, and a predetermined amount is provided. The oxygen concentration difference generated on both sides of the cylindrical pipe 31 is detected by the temperature, and the air-fuel ratio of the engine intake system is controlled. At this time, the stoichiometric air-fuel ratio sensor needs to be heated up to an operating temperature of about 700 ° C. Therefore,
A rod-shaped heater 35 is inserted inside the cylindrical tube 31 in order to heat the sensor unit to an operating temperature.

In recent years, the tendency to tighten exhaust gas regulations has become stronger,
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 in which the heater 35 is inserted into the cylindrical tube 31, the time required for the sensor unit to reach the activation temperature (hereinafter, It is called activation time.)
However, there was a problem that the exhaust gas regulations could not be fully met due to the slow speed.

In recent years, as a method for avoiding this problem, as shown in a schematic sectional view of FIG. 12A and a schematic plan view of FIG. 12B, a measuring electrode 37 and a reference electrode are formed on the outer and inner surfaces of a flat solid electrolyte substrate 36. There has been proposed an oxygen sensor element integrated with a heater in which a heating element 40 is embedded inside a ceramic insulating layer 39 at the same time when each of the oxygen sensor elements 38 is provided. Further, in such an oxygen sensor element, at the other end of the sensor element,
An electrode pad 42 connected via the lead 41 is formed, and a connector, a metal pin, or the like is brazed to the electrode pad 42.

[0007]

However, unlike the above-mentioned conventional indirect heating method, the conventional heater-integrated oxygen sensor is a direct heating method, so that the temperature can be rapidly raised. However, since the device itself is large, there is a limit to rapid temperature rise, and as a result, there is a problem that the activation time cannot be shortened.

An object of the present invention is to provide an oxygen sensor element which is small in size, has excellent gas responsiveness, and can rapidly raise temperature.

[0009]

The oxygen sensor element of the present invention comprises a sensor portion in which a measurement electrode made of platinum and a reference electrode are provided on opposite surfaces in the vicinity of the tip of a long solid electrolyte substrate. A ceramic insulating layer having a heater portion arranged along a longitudinal direction inside the ceramic insulating layer, wherein an electrode pad is formed on a surface near a rear end portion of the substrate, The electrode area of the measurement electrode is 8 to 1
8 mm ² , the width in the direction orthogonal to the longitudinal direction of the measurement electrode forming portion is 2.0 to 3.5 mm, and the heat generation amount per unit length in the longitudinal direction of the heating element is higher than that at both ends. By lowering the central portion, it is possible to reduce the size of the sensor element and to equalize the temperature of the measurement electrode, and thus it is possible to shorten the activation time.

Further, in the present invention, the heating element is composed of a meander pattern which advances in the longitudinal direction, and when the pattern is equally divided into three parts in the longitudinal direction, the inner area of one mountain in the central portion is determined. a, it is desirable that a> b, where b is the inner area of one mountain located at both ends, and in this case, the inner area of one mountain in the central portion of the heating element pattern is It is appropriate that a / b according to the area b of one mountain in is 1.1 to 1.5.

Further, when the heating element is formed of a meander pattern which advances in the longitudinal direction, and when the pattern is equally divided into three in the longitudinal direction, the amplitude of the portion located at the central portion is larger than the amplitude of the portions located at both end portions. By also increasing the value, the amount of heat generated in the central portion can be reduced more than at both ends.

Further, with the miniaturization, the pair of heating elements are formed in the upper and lower portions in the heater portion with the ceramic insulating layer interposed therebetween, whereby the miniaturization can be further achieved.

Further, according to the present invention, as the size is reduced,
The width in the direction orthogonal to the longitudinal direction of the element is continuously or stepwise reduced from the rear end portion to the front end portion, and the formation width of the pair of electrode pads is set to the measurement electrode formation portion. By making the width larger than the width, it is possible to secure the attachment of the connector or the metal pin to the electrode pad.

Further, in the oxygen sensor element of the present invention, the heater portion is formed by co-firing with the sensor portion, or is formed separately from each other and then joined and joined by a joining material. It may be a thing.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the basic structure of the oxygen sensor element of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view for explaining an example of the oxygen sensor element of the present invention, and FIG. 2 is a schematic sectional view for explaining another example. These are generally called theoretical air-twisting ratio sensor elements, and in the examples of FIGS.
And a heater unit 2.

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 in contact with air, and an exhaust gas on both surfaces of the solid electrolyte substrate 3 facing each other. A measurement electrode 5 that is in contact with is formed, forming the sensor unit 1 having a function of detecting the oxygen concentration.

That is, the solid electrolyte substrate 3 has a flat plate-like hollow shape with a sealed tip, and this hollow portion forms an air introduction hole 3a. Then, a reference electrode 4 that comes into contact with a reference gas such as air is adhered and formed on the hollow inner wall,
On the outer surface of the solid electrolyte substrate 3 facing the reference electrode 4,
A measuring electrode 5 is formed which is in contact with a gas to be measured such as exhaust gas.

From the viewpoint of preventing poisoning of the electrode by exhaust gas, a ceramic porous layer 6 is formed on the surface of the measuring electrode 5 as an electrode protective layer.

On the other hand, the heater portion 2 has a structure in which a heating element 8 is embedded in a ceramic insulating layer 7 having electrical insulation properties. In the oxygen sensor element of FIG.
In the oxygen sensor element of FIG. 2, the sensor part 1 and the heater part 2 are formed separately from each other, and have a bonding material 10.
It consists of the structure joined by.

Particularly, when the difference in thermal expansion coefficient between the solid electrolyte substrate 3 of the sensor portion 1 and the ceramic insulating layer 7 of the heater portion 2 is large, the structure shown in FIG.
In particular, it is desirable that the joining portion is joined at a low temperature portion when the heating element 8 and the electrodes 4 and 5 are not formed during use. In the case where the entire surface is bonded, stress due to a difference in thermal expansion coefficient between the sensor unit 1 and the heater unit 2 is relaxed, so that, for example, the zirconia solid electrolyte substrate 3 of the sensor unit 1 and the alumina ceramic insulation of the heater unit 2 are insulated. It is also possible to interpose a composite compound layer of a composite material with the layer 7 and alumina and zirconia.

In addition, in FIG. 1, the heater portion 2 has a heat insulating property so that the heating efficiency of the heater portion 2 is improved and the heater portion 2 reduces the stress due to the heat insulating material and the difference in the coefficient of thermal expansion between the materials. It is desirable to form the ceramic layer 9 having the same or similar coefficient of thermal expansion as the solid electrolyte substrate 3 on the side opposite to the side in contact with the sensor unit 1.

Further, in the oxygen sensor element of the present invention, as shown in the schematic plan view of FIG. 1, the sensor portion 1 and the heater portion 2 are formed near the tip portion of the solid electrolyte substrate 3, and 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 near the rear end portion. Then, the electrode pad 11 is appropriately applied with electric power to the platinum heater 8 and the electrodes 4, 5 of the sensor section 1 are appropriately applied.
A metal connector is used to take out a signal from the outside to the outside, but in some cases, a voltage is applied or a signal is taken out by brazing a metal pin such as Ni to a pad portion. is there.

According to the present invention, the device is miniaturized and excellent
The electrode area of the measuring electrode 5 is 8
~ 18 mm²And the width of the portion where the measurement electrode 5 is formed
However, it is important that it is 2.0 to 3.5 mm. this
Has an area of the measuring electrode 5 of 8 mm ²Less than or
If the element width is smaller than 2 mm, the element itself becomes smaller
Since the temperature of the element does not rise in the engine,
The answer is poor. On the contrary, the area of the measuring electrode 5 is 18 mm.²
Or the width of the element exceeds 3.5 mm,
Since the device is large, the rapid temperature rise property deteriorates. Measurement electrode surface
The product is 10 to 15 mm², The width of the element is 2.
The range of 8 to 3.2 mm is particularly excellent.

In the oxygen sensor element of the present invention, it is desirable that the width in the direction orthogonal to the longitudinal direction of the element be reduced continuously or stepwise from the rear end portion to the front end portion. Specifically, as shown in FIG. 3A, the width of the element is continuously increased from the front end portion to the rear end portion, in other words, the width is widened.
As shown in (b), a stepped portion v is formed between the front end portion and the rear end portion.
The width of the element becomes wider at the boundary, as shown in FIG. 3C, a tapered portion p is provided between the front end portion and the rear end portion,
Examples thereof include those that are partially continuously widened.

As described above, the width of the portion where the electrode pad 11 is provided is widened, and the width L of the portion where the electrode pad 11 is formed is made larger than the width w of the tip of the element. With this, the connector and the metal pin can be easily and firmly attached to the electrode pad 11.

According to the present invention, by controlling the area of the measuring electrode 5 and the width of the element within the above range, it is possible to enhance the rapid temperature rise property by the heater and improve the gas responsiveness by the sensor.

On the other hand, the maximum width at the rear end where the electrode pad 11 is formed is 3.7 to 6 mm, especially 4.0 to 5 m.
Suitably m.

Further, as the structure of the heater portion 2, as shown in FIG. 2, the heating elements 8 may be usually formed in the same plane. The shape of the pattern is very constrained.

Therefore, as shown in FIG. 1, by forming a pair of heating elements 8 in a cross section in a direction orthogonal to the longitudinal direction of the heater section 2 via the ceramic insulating layer 7a, the size of the heater section can be reduced. You can

More specifically, as shown in the schematic transmission diagram for explaining the structure of the heating element pattern of FIG. 4, the lead 8a1 extends in the longitudinal direction from one end side in the elongated ceramic insulating layer 7. A heat generating portion 8b1 is formed near the other end of the ceramic insulating layer 7 in a portion facing the electrode forming portion of the sensor portion 1, and after being folded back at the other end of the element, the heat generating portion 8b is formed.
2 to the lead 8a2. 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 have the other end such as the via 8c penetrating the ceramic insulating layer 7a. It is electrically connected by the connecting body.

The heating element pattern of FIG. 4 is composed of a meander structure (waveform) pattern. When the width of the heating element is x, the width x of the heating element 8 in the meander structure of FIG.
It corresponds to the maximum amplitude of the waveform. The heat generating parts 8b1 and 8
In the case where each of b2 has a predetermined width x, generally, when they are formed in the same plane, the width w of the entire element is such that a margin for embedding the heat generating portions 8b1 and 8b2 in the insulating layer 7 and the heat generating element 8b1. , 8b2 to prevent a short circuit between them, the width w of the entire element needs to be w ≧ 3x.

On the other hand, when the heat generating portions 8b1 and 8b2 are formed between different layers, the ceramic insulating layer 7a is formed even if the heat generating portions 8b1 and 8b2 are overlapped in plan view.
1 and 2 because the insulation is maintained by
As shown in, the width w of the entire device can be smaller than 3x. In particular, in order to reduce the size, it is preferable that w ≦ 2.5x, and further, w ≦ 2.3x be satisfied.

The thickness of the ceramic insulating layer 7a between the upper and lower heat generating portions 8a1 and 8b2 is 1 to 300 μm, particularly 5 to 100 μm, from the viewpoint of electrical insulation.
It is preferably 5 to 50 μm.

In the example shown in FIG. 4, the heating element 8 has a meander (corrugated) shape pattern having folds in a direction orthogonal to the longitudinal direction of the element. For example, as shown in the pattern diagram of the heating element in FIG. 5, the meandering pattern may be folded in the longitudinal direction of the element.

Further, according to the present invention, the structure shown in FIG.
Using the oxygen sensor element of No. 2, for example, as shown in FIG. 6, the mounting jig 12 for mounting the oxygen sensor element on the holder can be mounted on the tapered portion p.

Further, in the present invention, it is important that the amount of heat generated per unit length in the longitudinal direction of the heating element 8 is lower in the central portion than in both end portions. This is because when the area of the measurement electrode becomes smaller due to the miniaturization of the element as described above,
Due to the heating by the heating element 8, variations in the temperature distribution on the surface of the measuring electrode 5 are likely to occur. Even if heat shrinkage occurs due to the heating element, the soaking area is large when the area of the measuring electrode is large, but when the area of the measuring electrode is small, the temperature of the central portion of the measuring electrode is lower than that of both ends. It tends to be high, and at both ends it is easy to lower the temperature by heat sink,
Variations in temperature distribution are likely to occur in the measuring electrode 5.

According to the present invention, in order to solve the above problem, the heat generation amount in the central portion of the heat generation pattern is made lower than that in both end portions, in other words, the heat generation amount in both end portions is made higher than that in the central portion. As a result, the temperature of the surface of the measurement electrode 5 can be soaked, so that the activation time can be shortened.

In order to lower the amount of heat generated per unit length in the longitudinal direction of the heating element 8 in the central portion from both ends, as shown in FIG. 7, specifically, the heating element 8 is advanced in the longitudinal direction. When the pattern is formed by a meander-shaped pattern, and the pattern is equally divided into three in the longitudinal direction, the inner area of one mountain located in the central portion (hatched portion in FIG. 7C) is Y1, and both ends are Inner surface area of the mountain where it is located (shaded area in Figure 7 (a))
Is defined as Y2, the pattern is formed so that Y1> Y2. In particular, Y1 / Y2 means that Y1 / Y2 is 1.
A value of 1 to 1.5 is suitable. That is, it means that the larger the inner area of one mountain, the smaller the amount of heat generation.

In other words, the amplitude v2 of the central portion is larger than the amplitudes v1 and v3 of the central portions.

As another structure, as shown in the pattern diagram of the heating element of FIG. 5, in the case of a meander type pattern having a turn back in the longitudinal direction of the element, as shown in FIG. By making the line width thicker than both ends, it is possible to reduce the heat generation amount in the central portion.

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 are used as stabilizers.
Partially stabilized ZrO ₂ or stabilized containing 1 to 30 mol%, preferably 3 to 15 mol% of rare earth oxide such as O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , and Dy ₂ O _{3 in} terms of oxide. ZrO ₂
Is used. Further, 1 to 20 of Zr in ZrO ₂
By using ZrO ₂ with atomic% substituted by Ce,
The ionic conductivity is increased, and the response is further improved. Further, for the purpose of improving the sinterability, Al ₂ O ₃ or SiO ₂ can be added to the ZrO ₂ as described above, but if a large amount is contained, the creep characteristics at high temperatures deteriorate. The total amount of Al ₂ O ₃ and SiO ₂ added is preferably 5% by weight or less, more preferably 2% by weight or less.

The reference electrode 4 and the measuring electrode 5 deposited on the surface of the solid electrolyte substrate 3 are both platinum, or an alloy of platinum and one alloy selected from the group of rhodium, palladium, ruthenium and gold. Used. In addition, the purpose of preventing the particle growth of the metal in the electrode during sensor operation, the platinum particles, the solid electrolyte and the gas related to the response,
For the purpose of increasing the number of contacts at the so-called three-phase interface, the above-mentioned ceramic solid electrolyte component is contained in an amount of 1 to 50% by volume, particularly 10 to 3%.
You may mix in the said electrodes 4 and 5 in the ratio of 0 volume%.
Further, the electrode shape may be square or elliptical.
The thickness of the electrodes 4 and 5 is 3 to 20 μm, and particularly 5 to 1
0 μm is preferable.

On the other hand, it is desirable that the ceramic insulating layer 7 in which the heating element 8 is embedded is made of a dense ceramic made of alumina ceramics having a relative density of 80% or more and an open porosity of 5% or less. On this occasion,
In order to improve the sinterability, the total of Mg, Ca and Si is 1 to
The content of alkali metals such as Na and K may be 10% by mass, but the content of alkali metals such as Na and K is 50 ppm or less in terms of oxide weight in order to migrate and deteriorate the electrical insulation between the pair of heaters in the heater part 2. It is desirable to control to. Further, by setting the relative density within the above range, the strength of the substrate increases, and as a result, the mechanical strength of the oxygen sensor itself can be increased.

The ceramic porous layer 6 formed on the surface of the measuring electrode 5 is 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 of at least one kind. In particular, the thickness of the porous layer 6 is preferably 100 to 500 μm, though it depends on the porosity.

The heating element 8 and the leads 8a1 and 8a2 embedded in the ceramic insulating layer 7 of the heater portion 2 are
As the metal, platinum alone or an alloy of platinum and one kind selected from the group of rhodium, palladium and ruthenium can be used. In this case, the heating element 8 and the lead 8a1,
The resistance ratio of 8a2 is preferably controlled in the range of 9: 1 to 7: 3 at room temperature.

The oxygen sensor element of the present invention has a total element thickness of 0.8 to 1.5 mm, particularly 1.0 to 1.5 mm.
1.2 mm and the length of the element is preferably 45 to 55 mm, and particularly preferably 45 to 50 mm in view of the relationship between the rapid temperature rising property and the mounting condition of the element in the engine.

Further, according to the present invention, the tip of the element is formed by a curved surface having a radius of 100 mm or less, or the corner is C-face processed by 0.1 mm or more.
The thermal shock resistance can be improved.

Next, a method of manufacturing the oxygen sensor element of the present invention will be described with reference to the exploded perspective view of FIG. 9 by taking the method of manufacturing the oxygen sensor element of FIG. 3 (b) as an example.

First, the solid electrolyte green sheet 13 is prepared. This green sheet 13 is obtained by, for example, appropriately adding a molding organic binder to a ceramic solid electrolyte powder having oxygen ion conductivity of zirconia, a doctor blade method, an extrusion molding, or a hydrostatic molding (rubber press). Alternatively, a green sheet is manufactured by a known method such as press forming, and further, by punching or the like, a green sheet in which the width of the front end is gradually reduced from the rear end toward the front end as shown in FIG.

Next, on both surfaces of the green sheet 13, the pattern 14, the lead pattern 15 and the electrode pad pattern 16 which will be the measurement electrode 5 and the reference electrode 4, respectively.
Or a through hole (not shown) is formed by, for example, using a conductive paste containing platinum by a slurry dip method, screen printing, pad printing, or roll transfer, and then an air introduction hole 17 is formed in the green sheet 1
8 and the green sheet 19 are made to interpose an adhesive such as an acrylic resin or an organic solvent, or are mechanically adhered while applying pressure with a roller or the like to produce the laminated body A of the sensor unit 1.

At this time, a porous slurry for forming the ceramic porous layer 6 shown in FIG. 1 may be applied by printing on the surface of the pattern 14 to be the measuring electrode 5.

Next, as shown in FIG. 9, a paste made of alumina powder is printed on the surface of the zirconia green sheet 20 by a slurry dip method, screen printing, pad printing or roll transfer to form a ceramic insulating layer 21a.

Next, as shown in FIG. 1, when the platinum heaters are vertically formed with the ceramic insulating layer interposed therebetween, first, the lower surface as shown in FIGS. 7 and 8 is formed on the surface of the ceramic insulating layer 21a. Heater pattern 22a and lead pattern 2
3a is applied by printing. 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 and applied on the surface of the ceramic insulating layer 21b.
Then, the ceramic insulating layer 21c is printed again using the insulating paste to produce the laminated body B of the heater unit 2.

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, the ceramic insulating layer 2 is formed.
A through hole extending from the surface to the lower heater pattern is formed in 1b, and when forming the upper heater pattern, a conductive paste is filled in the through hole to form the via conductor 24. Alternatively, the front end 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 to connect the upper and lower heater patterns to each other. A connected heating element can be formed.

On the lower surface of the zirconia sheet 20,
The heater electrode pad pattern 25 is applied by printing using the conductive paste, and the heater lead pattern 23a,
23b is electrically connected by a via conductor 26 formed in the same manner as the via conductor 24.

In producing the laminated body B of the heater portion, the ceramic insulating layers 18a, 18b, 18c are used.
In addition to forming the insulating paste by printing as described above, an insulating sheet may be formed and laminated by a sheet forming method such as a doctor blade method using a ceramic slurry such as alumina.

Thereafter, the laminated body A of the sensor portion and the laminated body B of the heater portion are made to interpose an adhesive such as an acrylic resin or an organic solvent, or they are mechanically adhered while applying pressure with a roller or the like. After they are bonded and integrated with each other, they are fired. The firing is performed in the air or an inert gas atmosphere at a temperature range of 1300 ° C to 1700 ° C for 1 to 10 hours. In addition, in order to suppress the warpage of the sensor unit A during firing, the amount of warpage can be reduced by placing a smooth substrate such as alumina as a weight on the laminate.

When the laminated body A of the sensor portion and the laminated body B of the heater portion are simultaneously fired and integrated, in order to reduce the stress due to the difference in thermal expansion coefficient between the two, for example, a sensor is used. It is desirable to interpose a composite material of a solid electrolyte component forming the part and an insulating component forming the ceramic insulating layer of the heater part.

Thereafter, if necessary, at least one ceramic selected from the group consisting of alumina, zirconia, and spinel is formed on the surface of the measurement electrode 14 after firing by a plasma spraying method or the like, whereby the heater portion is integrated. An oxygen sensor element can be formed.

In the above method, the case where the heater portion and the sensor portion are simultaneously fired has been described. However, after the sensor portion and the heater portion are fired separately, a suitable inorganic adhesive such as glass is used. It is also possible to integrate them by joining them with a material.

[0061]

EXAMPLE A λ sensor shown in FIG. 1 was manufactured as follows according to FIG.

First, commercially available alumina powder having a purity of 99.9%, zirconia powder containing 5% by weight of Y ₂ O ₃ containing 0.1% by weight of Si, and 8% by mole of an average particle diameter of 0.1 μm. A platinum powder containing 30% by volume of zirconia containing yttria in a crystal and a platinum powder containing 20% by volume of alumina powder were prepared.

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 having a thickness after sintering of 0.4 mm was obtained by extrusion molding. 13 was produced.

Then, a conductive paste containing platinum powder is screen-printed on both surfaces of the green sheet 13 to form the measurement electrode and reference electrode patterns 14, the lead patterns 15 and the electrode pad patterns 16, and then the atmosphere. A green sheet 18 having the introduction hole 17 formed therein and a green sheet 19 were laminated with an acrylic resin adhesive to obtain a sensor unit laminate A. At this time, the area of the measurement electrode was changed so as to be 6 to 30 mm ² after firing.

Next, the surface of the zirconia green sheet 20 is screen-printed with the above-mentioned paste made of alumina powder to burn the ceramic insulating layer 21a, and then the ceramic insulating layer 21a is burned to about 10 μm.
m, and then one heater pattern 22
a and the lead pattern 23a are formed by screen-printing using a conductive paste containing platinum containing alumina, and a paste made of alumina powder is screen-printed again on this surface to have a thickness of 25 μm after firing. The ceramic insulating layer 21b was formed so that. Thereafter, the heater electrode pad 25 is printed on the lower surface of the other heater pattern 22b, the heater lead 23b, and the green sheet 20 by screen printing using a conductive paste containing platinum, and the ceramic insulating layer 21c is formed again. By forming, the laminated body B for heater parts was produced. The heater pattern 2
The space between 2a and 22b is formed by the via conductor 24 formed in the ceramic insulating layer 21b, and the heater leads 23a and 23b.
And heater electrode pad 25 are ceramic insulating layers 20, 2
Connection was made by via conductors 26 formed in 1a and 21b.

Thereafter, the laminated body A for the sensor portion and the laminated body B for the heater portion are joined according to the above-described manufacturing method, and the laminated body of the heater integrated sensor element is fired at 1500 ° C. for 1 hour to form the heater integrated sensor element. Was produced. At this time, the widths of the sensor unit laminated body and the heater unit laminated body are changed so that the width w is 1.
A theoretical air-fuel ratio type (λ type) heater integrated oxygen sensor element of 8 to 3.8 mm was produced. The width of each element of the oxygen sensor element where the sensor electrode pad and the heater electrode pad are formed was 5 mm, and the pad formation width L was 4.5 mm.

Further, a metal pin made of Ni was brazed to the electrode pad for each sensor and the electrode pad for the heater to manufacture an oxygen sensor element.

Thereafter, a voltage of 12 V was applied to the heating element with respect to the produced oxygen sensor element, and when the temperature of the surface of the measuring electrode became constant, the center of the measuring electrode and the center of both ends were measured. The temperature was measured using a thermocouple on the part. Table 1 shows the maximum difference T1- (T2 or T3) between the temperature T1 at the center and the temperatures T2 and T3 at both ends.

Further, for the oxygen sensor element, a mixed gas of hydrogen, methane, nitrogen and oxygen was used, and the air-fuel ratio was set to 11 and 2.
12 V was applied to the heater of the element while alternately spraying the mixed gas of 3 onto the sensor element at intervals of 0.5 seconds, and the activation time of the element was measured. At this time, as shown in FIG. 10, the time when the voltage was applied to the heater was set to zero, and the element first showed 0.6 V at an air-fuel ratio of 11, and then 0.3 V at an air-fuel ratio of 23.
The time t required to show is defined as the activation time of the device.

[0070]

[Table 1]

From the results shown in Table 1, the size of the element is such that the area of the measuring electrode of the element is 8 to 20 mm ² and the width of the element is ² to 3.5 mm. Is smaller than both ends, the temperature difference between the central part and both ends of the measuring electrode can be kept within ± 3 ° C., and as a result, the activation time is 10 seconds or less, which is a small element and excellent. It was possible to obtain a sensor element having excellent characteristics.

Further, in any of the oxygen sensor elements of the present invention, metal pins could be attached to the electrode pads without any trouble.

[0073]

As described in detail above, according to the present invention,
Miniaturization of the element by controlling the electrode area of the measurement electrode and the width of the measurement electrode formation part to a specific range and lowering the heat generation amount per unit length in the longitudinal direction of the heating element from the center part rather than at both ends. At the same time, the temperature of the measuring electrode surface can be equalized, and as a result, the activation time of the element can be shortened,
It is possible to provide an oxygen sensor element having excellent gas responsiveness.

[Brief description of drawings]

FIG. 1 is a schematic sectional view for explaining an example of an oxygen sensor element of the present invention.

FIG. 2 is a schematic cross-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 perspective view for explaining the structure of a heating element pattern in the present invention.

FIG. 5 is a schematic perspective view for explaining another structure of the heating element pattern according to the present invention.

FIG. 6 is a schematic perspective view for explaining an application example of the oxygen sensor element of the present invention.

FIG. 7 shows an example of a heating element pattern in the oxygen sensor element of the present invention, where (a) is the overall pattern and (b) is a pattern.
Is an enlarged view of both end portions and (c) is a central portion.

FIG. 8 shows another example of a heating element pattern in the oxygen sensor element of the present invention.

FIG. 9 is an exploded perspective view for explaining the method for manufacturing the oxygen sensor element of FIG. 3 (b).

FIG. 10 is a graph for explaining a method for measuring activation time.

FIG. 11 is a schematic cross-sectional view for explaining the structure of a conventional heater-integrated oxygen sensor element.

FIG. 12 is (a) a schematic cross-sectional view and (b) a schematic plan view for explaining another structure of a conventional heater-integrated oxygen sensor element.

[Explanation of symbols]

1 sensor 2 heater part 3 Solid electrolyte 4 Reference electrode 5 measuring electrodes 6 Ceramic porous layer 7 Ceramic insulation layer 8 heating element 9 Ceramic insulation layer

Claims (8)

[Claims] 1. A sensor portion having a measuring electrode and a reference electrode made of platinum respectively provided on opposite surfaces of a long solid electrolyte substrate in the vicinity of a front end portion thereof, and heat generation along a longitudinal direction inside a ceramic insulating layer. In an oxygen sensor element comprising a heater part having a body and a pair of electrode pads formed on the surface near the rear end of the substrate, the electrode area of the measurement electrode is 8 to 18 mm ^2. , The width in the direction orthogonal to the longitudinal direction of the measurement electrode forming portion is 2.0 to 3.
An oxygen sensor element having a length of 5 mm and a heat generation amount per unit length in the longitudinal direction of the heating element is lower in the central portion than in both end portions. 2. The heating element is composed of a meandering pattern that advances in the longitudinal direction, and when the pattern is divided into three even parts in the longitudinal direction, the inner area of one mountain located in the central portion is Y1, and both ends are Y2 for the inner area of one mountain
When it is set, it is Y1> Y2, It is characterized by the above-mentioned.
The oxygen sensor element described. 3. The area Y1 of one mountain in the central portion of the heating element pattern, and the area Y2 of one mountain in both ends Y1 / Y2 is 1.1 to 1.5. 2. The oxygen sensor element according to 2. 4. The heating element is composed of a meander pattern that advances in the longitudinal direction, and when the pattern is equally divided into three parts in the longitudinal direction, the amplitude of the portion located at the central portion is greater than the amplitude of the portions located at both end portions. Claim 1 is also large.
The oxygen sensor element described. 5. The oxygen sensor element according to claim 1, wherein in the heater portion, a pair of heating elements are vertically formed with a ceramic insulating layer interposed therebetween. 6. The width of the element in a direction perpendicular to the longitudinal direction is reduced continuously or stepwise from the rear end portion to the front end portion, and the formation width of the pair of electrode pads is The oxygen sensor element according to any one of claims 1 to 5, wherein the oxygen sensor element has a width larger than a width of the measurement electrode forming portion. 7. The oxygen sensor element according to claim 1, wherein the sensor portion and the front heater portion are formed by simultaneous firing. 8. The sensor part and the heater part are formed separately from each other, and are then bonded and integrated by a bonding material. Oxygen sensor element.