JP2003227810A - Oxygen sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact oxygen sensor element that has improved gas responsiveness and can rapidly be raised in temperature. <P>SOLUTION: The oxygen sensor element provided with a sensor section 1 where a measurement a measurement electrode 5 made of platinum and a reference electrode 4 are provided on at least both mutually opposed surfaces of a long ceramic solid electrolyte substrate 3, and a heater section 2 where a platinum heater 8 is buried into a ceramic insulating layer 7, is characterized in that the electrode area of a measurement electrode 5 is 8-18 mm<SP>2</SP>, and width in a direction for orthogonally crossing the longitudinal direction of an element is 2.0-3.5 mm, and further, in a heater section 2, a pair of platinum heaters 8 is formed up and down via a ceramic insulating layer 7a, the lower end section of a platinum particle for composing at least the measurement electrode 5 is buried into the surface of the ceramic solid electrolyte substrate 3, and a zirconia film is formed at one portion of an exposure surface where no platinum particles are buried. <P>COPYRIGHT: (C)2003,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. 7, 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. A reference electrode 32 that is in contact with a reference gas such as the above, and a measurement electrode 33 that is in contact with a measured gas such as exhaust gas is formed on the outer surface of the cylindrical tube 31.

In such an oxygen sensor, generally,
A so-called theoretical air-fuel ratio sensor (λ sensor) used for controlling the ratio of air to fuel near 1 is a ceramic porous layer 34 as a protective layer on the surface of the measuring electrode 33.
Is provided, the oxygen concentration difference generated on both sides of the cylindrical pipe 31 at a predetermined temperature is detected, and the air-fuel ratio of the engine intake system is controlled. At this time, the theoretical air-fuel ratio sensor is about 700
It is necessary to heat up to an operating temperature near 0 ° C. Therefore, a rod-shaped heater 35 is inserted inside the cylindrical tube 31 in order to heat the sensor unit up to the operating temperature.

[0005]

However, in recent years, the tendency to tighten exhaust gas regulations has become stronger, 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 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, There is a problem that exhaust gas regulations cannot be fully met because the activation time) is slow.

In recent years, as a method for avoiding this problem, as shown in the schematic sectional view of FIG.
There is proposed a heater-integrated oxygen sensor element in which a reference electrode 38 and a measurement electrode 37 are provided on the outer surface and the inner surface of 6 respectively, and a platinum heater 40 is embedded inside a ceramic insulating layer 39.

However, unlike the above-mentioned conventional indirect heating method, this heater-integrated oxygen sensor is capable of rapid heating because it is a direct heating method, but the element is still large and has a sufficient rapid temperature rising property. There was a problem that it could not be secured.

It is an object of the present invention to provide a small oxygen sensor element having excellent gas responsiveness and capable of rapid temperature rise.

[0009]

As a result of studying the above problems, the present inventor has found that the gas responsiveness is very closely related to the area of the measuring electrode and the width of the oxygen sensor element. The inventors have found that by controlling these to have a predetermined size, the gas responsiveness can be enhanced and the size can be reduced, and the present invention has been completed.

That is, the oxygen sensor element of the present invention comprises a long zirconia solid electrolyte substrate flat plate on which at least two opposing surfaces are provided with a measuring portion and a reference electrode made of platinum, respectively. In the above, it was found that the above object can be achieved by setting the electrode area of the measurement electrode to 8 to 18 mm ² and the width in the direction orthogonal to the longitudinal direction of the element to 2.0 to 3.5 mm.

In such an oxygen sensor element, at least the lower end portion of the platinum particles constituting the measurement electrode is embedded in the surface of the zirconia solid electrolyte substrate, and at a part of the exposed surface where the platinum particles are not embedded, Since the zirconia film is formed, and further, the zirconia phase is present in the platinum particles forming the measurement electrode, the gas responsiveness can be enhanced, and high sensitivity can be obtained even with a small electrode area. .

Further, the oxygen sensor element of the present invention preferably comprises a heater part in which a platinum heater is embedded in a ceramic insulating layer, and the heater part is formed by co-firing with the sensor part. Alternatively, they may be formed separately and then joined and integrated by a joining material.

Further, in this heater portion, since the pair of platinum heaters are vertically formed with the ceramic insulating layer interposed therebetween, the heat generation amount can be increased even when the width of the element is reduced, and the element can be heated. The rapid temperature rise can be easily performed.

[0014]

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,
It is a schematic sectional drawing for demonstrating another example in FIG. These are generally called theoretical air-twisting ratio sensor elements, and each of them includes the sensor unit 1 and the heater unit 2 in the examples of FIGS.

In the oxygen sensor element of FIG. 1, a solid electrolyte substrate 3 made of zirconia and having oxygen ion conductivity, and a reference electrode 4 in contact with air and exhaust gas on both surfaces of the solid electrolyte substrate 3 facing each other. The measurement electrode 5 in contact therewith is formed to form 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 its tip sealed, and this hollow portion forms the air introduction hole 3a. Then, a reference electrode 4 that contacts a reference gas such as air is adhered to the inner wall of the hollow, and the outer surface of the solid electrolyte substrate 3 that faces the reference electrode 4 is in contact with a measured gas such as exhaust gas. The electrode 5 is formed.

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.

According to the present invention, in such an oxygen sensor element, the electrode area S of the measuring electrode 5 is 8 to 18 mm ² ,
And the width w in the direction orthogonal to the longitudinal direction of the element is 2.
It is important that it is between 0 and 3.5 mm. According to the present invention, when the area of the measuring electrode 5 is smaller than 8 mm ² or the width of the element is smaller than 2 mm, the element itself becomes small and the temperature of the element does not rise in the engine, resulting in poor gas response. . 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. The area of the measuring electrode is 10 to 15 mm ² , and the width of the element is 2.
The range of 8 to 3.2 mm is particularly excellent.

In the present invention, both the reference electrode 4 and the measuring electrode 5 are made of porous platinum, but as shown in FIG. 3, at least the platinum particles 21 constituting the measuring electrode 5 are formed.
It is desirable that the lower end portion of the is embedded in the zirconia solid electrolyte substrate 3, and that the zirconia film 22 is formed on a part of the exposed surface of the platinum particles 21 that is not embedded in the zirconia solid electrolyte substrate 3. Further, the zirconia phase 26 exists in the platinum particles 21 and the platinum particles 2
It is desirable that the zirconia phase 26 is contained in the No. 1 in an amount of 0.1 to 10% by volume. As described above, since the platinum particles 21 in the measurement electrode 5 have the above structure, the particle growth of the electrode particles can be suppressed. As a result, the measurement electrode 5 having a small area and good performance can be formed. .

On the other hand, the heater portion 2 has a structure in which a platinum heater 8 is embedded in a ceramic insulating layer 7 having an electric insulation property. In the oxygen sensor element of FIG.
2 has a structure 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 separately formed and bonded by the bonding material 10. Consists of.

In particular, when the difference in thermal expansion coefficient between the solid electrolyte of the sensor part 1 and the ceramic insulating layer 7 of the heater part 2 is large, it is desirable that the structure of FIG.
It is desirable that the joining portion is joined at a portion having a low temperature when the platinum heater 8 and the electrodes 4 and 5 are not formed and used. In the case where the entire surface is joined, the zirconia solid electrolyte substrate 3 of the sensor unit 1 is used in order to relieve the stress due to the difference in thermal expansion coefficient between the sensor unit 1 and the heater unit 2.
It is also possible to interpose a composite material of alumina and the alumina ceramic insulating layer 7 of the heater portion 2, or a composite compound layer of alumina and zirconia.

Incidentally, the pattern of the platinum heater 8 in the heater portion 2 has a structure that extends in the longitudinal direction of the element and is folded at the end portion in the longitudinal direction, or a waveform (meaner that is folded at the end portion in the direction orthogonal to the longitudinal direction). ) The structure may be used.

In addition, in FIG. 1, the heater section 2 enhances the heat retaining property to improve the heating efficiency of the heater section 2, and the heater section 2 reduces the stress due to the heat retaining 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.

The structure of the heater portion 2 is not particularly limited as long as it satisfies the area of the measuring electrode 5 and the width of the element according to the present invention.
As shown in, the platinum heater 8 may be formed in the same plane, but in the case of the same plane, the shape of the heater pattern is extremely restricted due to miniaturization. Therefore, as shown in FIG. 1, it is desirable to form a pair of platinum heaters 8 embedded in the ceramic insulating layer 7 above and below, in other words, between different layers via the ceramic insulating layer 7a.

More specifically, as shown in the schematic view of the platinum heater 8 pattern in FIG. 4, the pattern of the platinum heater 8 has leads formed on one end side in the elongated ceramic insulating layer 7. 8a1 extends in the longitudinal direction, a heat generating portion 8b1 is formed near the other end of the ceramic insulating layer 7, is folded back at the other end, and is then connected to the lead 8a2 via the heat generating portion 8b2. 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 at the other end of the ceramic insulating layer 7a.
It is electrically connected by a connecting body such as a via 8c relating to a.

According to this structure, in order to improve the heating efficiency, it is desirable that the heat generating portions 8b1 and 8b2 have a meander structure (waveform) pattern as shown in FIG. The portions 8b1 and 8b2 each require a predetermined width x, but when formed in the same plane, the width w of the entire element must necessarily be w> 2x, but as shown in FIG. In addition, by forming the heat generating portions 8b1 and 8b2 between different layers, the width w of the entire element is relaxed by the restriction that w> x. Therefore, the width of the entire element can be reduced and at the same time the amount of heat generation can be increased. be able to. In particular, it is desirable that w ≦ 2.5x, and further, w ≦ 2x. The thickness of the ceramic insulating layer 7a between the upper and lower platinum heaters 8 is preferably 1 to 300 μm or more, particularly 5 to 100 μm, and further preferably 5 to 50 μm from the viewpoint of electrical insulation. (Solid Electrolyte) The solid electrolyte used in the oxygen sensor element of the present invention is made of a ceramic containing ZrO _2, and contains Y ₂ O ₃ and Yb ₂ O ₃ , Sc as a stabilizer.
Partially stabilized ZrO ₂ containing 1 to 30 mol%, preferably 3 to 15 mol% of a rare earth oxide such as ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , and Dy ₂ O _{3 in} terms of oxide, or stable. ZrO ₂
Is used. In addition, Zr in ZrO ₂ is 1 to 20
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. (Electrode) 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 alloy selected from the group of rhodium, palladium, ruthenium and gold. Used. In addition, for the purpose of preventing grain growth of metal in the electrode during sensor operation, there is a so-called 3
The above-mentioned ceramic solid electrolyte component may be mixed in the electrode in an amount of 1 to 50% by volume, particularly 10 to 30% by volume for the purpose of increasing the contact points at the phase interface. Further, the electrode shape may be square or elliptical. Further, the thickness of the electrode is preferably 3 to 20 μm, and particularly preferably 5 to 10 μm. (Ceramic Insulator) On the other hand, the ceramic insulating layer 7 in which the platinum heater 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. desirable. At this time, Mg, Ca, Si for the purpose of improving the sinterability.
May be contained in a total amount of 1 to 10% by mass, but Na,
The content of the alkali metal such as K is preferably controlled to 50 ppm or less in terms of oxide in order to migrate and deteriorate the electric insulation of the heater section 2. Also,
This is because 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. (Ceramic porous layer) The ceramic porous layer 6 formed on the surface of the measuring electrode 5 has a thickness of 10 to 800 μm.
And zirconia, alumina, γ with a porosity of 10 to 50%
-It is desirable to be formed of at least one selected from the group of alumina and spinel. If the thickness of the porous layer 6 is less than 10 μm or the porosity exceeds 50%, the electrode poisoning substances P, Si, etc. easily reach the electrode and the electrode performance deteriorates. On the other hand, when the thickness of the porous layer 6 exceeds 800 μm or the porosity becomes smaller than 10%, the gas diffusion rate in the porous layer 6 becomes slow, and the gas responsiveness of the electrode deteriorates. In particular, the thickness of the porous layer 6 is 100 to 500 depending on the porosity.
μm is suitable. (Heating element) Platinum heater 8 and leads 8a1 and 8a2 embedded in ceramic insulating layer 7 of heater portion 2
As the metal, platinum alone or a metal alloy of platinum and one kind selected from the group of rhodium, palladium and ruthenium can be used. In this case, the resistance ratio between the platinum heater 8 and the leads 8a1 and 8a2 is 9: 1 to 1 at room temperature.
It is preferable to control in the range of 7: 3.

The heating pattern of the heating element 8 in the heater portion 2 is shown in FIG. 4 as well as the structure extending in the longitudinal direction and being folded back at the end portion in the longitudinal direction, as shown in FIG. 3 described later. Such a meander structure may be used.

The oxygen sensor element of the present invention has a total element thickness of 0.8 to 1.5 mm, particularly 1.0 to
1.2 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.

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. 5 by taking the method of manufacturing the oxygen sensor element of FIG. 1 as an example.

First, the solid electrolyte green sheet 11 is prepared. The green sheet 11 is obtained, for example, by adding a molding organic binder to a ceramic solid electrolyte powder having zirconia oxygen ion conductivity, a doctor blade method, an extrusion molding, or a hydrostatic molding (rubber press). Alternatively, it is produced by a known method such as press forming.

Next, on both surfaces of the green sheet 11, the pattern 12, the lead pattern 13, and the through hole (not shown) that will be the measurement electrode 5 and the reference electrode 4, respectively.
For example, the green sheet 15 and the green sheet 16 in which the air introduction holes 14 are formed after the conductive paste containing platinum is formed by a slurry dip method, screen printing, pad printing, or roll transfer.
A laminate A for the sensor unit is manufactured by interposing an adhesive such as an acrylic resin or an organic solvent, or by mechanically adhering while applying pressure with a roller or the like. At this time, the measurement electrode pattern 12 controls the printing area such that the electrode area after firing is 8 to 18 mm ² .

Further, as the platinum-containing conductive paste used at this time, in order to form an electrode having a special structure as shown in FIG. 3, 1 to 1 of zirconia composed of the above-mentioned ceramic solid electrolyte component is used. 50% by volume, especially 1
It is preferable to use platinum particles included in a proportion of 0 to 30% by volume and additionally contain an organic resin component such as ethyl cellulose.

In order to prepare such platinum particles containing a zirconia phase inside, for example, platinum powder, zirconia fine powder having a specific surface area of 30 m ² / g or more as a BET value, and a binder are added and three particles are added. 2 using rolls
By mixing for 4 hours or more, zirconia can be contained in the platinum powder.

When such a platinum particle 21 is used and fired together with a zirconia solid electrolyte compact, the platinum particle 2
Part of the zirconia phase 26 in 1 diffuses to the surface of the platinum particle 21 and covers the surface of the platinum particle 21. The zirconia on the surface of the platinum particle 21 is solid at the portion close to the zirconia solid electrolyte substrate 3. It adheres to the electrolyte substrate 3 and constitutes a part thereof. That is, a porous composite layer 24 of platinum particles 21 and precipitated zirconia particles 23 is formed on the zirconia solid electrolyte substrate 3, and the zirconia particles 23 are integrated with the zirconia solid electrolyte substrate 3. As a result, the lower part of the platinum particle 21 is embedded in the zirconia solid electrolyte substrate 3. The average particle size of the zirconia particles 23 of the composite layer 24 is smaller than that of the zirconia particles 25 of the dense zirconia solid electrolyte substrate 3. Furthermore, the zirconia on the surface of the platinum particles 21 existing in the part far from the zirconia solid electrolyte substrate 3 exists as it is, and the zirconia film 2 is formed on the top of the exposed surface of the platinum particles 21.
2 will be formed.

A zirconia phase 26 exists in the platinum particles 21, and the zirconia phase is the platinum particles 2
0.1 to 10% by volume. In the present invention, since the platinum particles 21 include the zirconia phase 26,
When the sensor is used at a high temperature, it is possible to suppress the sintering of the platinum particles 21, so that it is possible to maintain a stable sensing function. As described above, the zirconia phase 26 in the platinum particles 21 cannot be diffused to the surface of the platinum particles 21 because the zirconia phase 26 in the platinum particles 21 is insufficient in temperature and time, and remains in the platinum particles 21. Is.

Zirconia phase 26 in platinum particles 21
The content of 0.1 to 10% by volume, and particularly 3 to 7% by volume, means that in this range, the platinum particles 2
This is because when 1 is embedded in the solid electrolyte substrate 3 and at the same time the zirconia film 22 is formed on the top of the surface and the sensor is used at high temperature, the sintering of the platinum particles 21 can be sufficiently suppressed.

At this time, a porous slurry for forming the ceramic porous layer 6 may be applied by printing on the surface of the pattern to be the measurement electrode 5. (Heater part) Next, as shown in FIG. 5, a paste made of alumina powder is printed on the surface of the zirconia green sheet 17 by a slurry dip method, screen printing, pad printing, or roll transfer to form a ceramic insulating layer 18a.

Next, when forming a platinum heater on the same plane as in the oxygen sensor element of FIG. 2, a conductive paste containing platinum is formed by a slurry dip method, screen printing, pad printing, or roll transfer. After the printing is formed on the entire surface, the ceramic insulating layer may be coated.

On the other hand, as shown in FIG. 1, when the platinum heater is formed vertically with the ceramic insulating layer interposed therebetween, first, the lower heater pattern 19a and the lead pattern 20a are printed on the surface of the ceramic insulating layer 18a. Apply. Then, an insulating paste such as alumina is applied to form a ceramic insulating layer 18b, and the upper heater pattern 19b and the lead pattern 20 are formed on the surface of the insulating layer 18b.
Print coating b. Then, by again forming the ceramic insulating layer 18c by printing using the insulating paste,
A laminated body B of the heater unit 2 is produced.

At this time, in order to connect the lower heater pattern 19a and the upper heater pattern 20b, the lower heater pattern 19 from the surface is formed on the ceramic insulating layer 18b.
a through hole 21 up to a is formed, and the upper heater pattern 19 is formed.
When forming b, the through hole 21 is filled with a conductive paste. Alternatively, the tip end of the ceramic insulating layer 18b may be cut out, and a conductive paste may be applied to and connected to the cutout to form a continuous platinum heater.

When manufacturing the above-mentioned laminated body of the heater part 2, the ceramic insulating layers 18a, 18b, 18c are formed.
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. (Integration and firing) After that, the laminated body A of the sensor unit 1 and the laminated body B of the heater unit 2 are machined by interposing an adhesive such as an acrylic resin or an organic solvent, or by applying pressure with a roller or the like. These are fired after they are integrally bonded by physically adhering. The firing is performed in the temperature range of 1300 ° C. to 1700 ° C.
Bake for 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 generation of stress due to the difference in thermal expansion coefficient between them, 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 after firing by a plasma spraying method or the like to integrate the heater portion. Oxygen sensor elements can be formed.

In the above method, the case where the heater part 1 and the sensor part 2 are simultaneously fired has been described. However, after the sensor part 1 and the heater part 2 are fired separately, they are made of glass or the like. It is also possible to integrate them by joining with a suitable inorganic joining material.

[0045]

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 composed of yttria 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 green sheet of zirconia having a thickness after sintering of 0.4 mm was obtained by extrusion molding. 11 was produced.

After that, a conductive paste containing platinum powder is screen-printed on both surfaces of the green sheet 11 to form the measurement electrode and reference electrode patterns 12 and the lead pattern 13, and then the air introduction hole 14 is formed. The green sheet 15 and the green sheet 16 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 5 to 30 mm ² after firing.

Next, the surface of the zirconia green sheet 17 is screen-printed with the paste made of the above-mentioned alumina powder to burn the ceramic insulating layer 18a, and then the ceramic insulating layer 18a is baked to about 10 μm.
m of the heater pattern 19
a and the lead portion 20a 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 form the ceramic insulating layer 18
b was formed. After this, the other heater pattern 1
9b and the lead portion 20b are formed by a slurry dip method using a conductive paste containing platinum, or by screen printing, pad printing, or roll transfer, and the ceramic insulating layer 18c is formed again to form a laminate for the heater portion. Body B was produced. The heater patterns 19a and 19b were connected by via conductors formed in the ceramic insulating layer 18b.

Thereafter, the laminated body A for the sensor portion and the laminated body B for the heater portion are joined according to the manufacturing method 1 described above, and the laminated body of the heater integrated sensor element is fired at 1500 ° C. for 1 hour to form the heater integrated sensor. A device 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 becomes 1.
An oxygen sensor element integrated with a heater having a theoretical air-fuel ratio type (λ type) of 8 to 4.5 mm was produced.

As a result of investigating the fine structure of the measuring electrode 5 in the produced oxygen sensor element, it was found to have a structure as shown in FIG.

Thereafter, a mixed gas of hydrogen, methane, nitrogen, and oxygen is used to generate a mixed gas having an air-fuel ratio of 12 and 23 of 0.5.
The sensor element was alternately sprayed at an interval of 2 seconds, and 12 V was applied to the heater of the element to measure the activation time of the element. At this time, as shown in FIG. 6, the time when the voltage is applied to the heater is set to zero, and the time t until the element first shows 0.6 V at the air-fuel ratio 12 and then 0.3 V at the air-fuel ratio 12 Activation time. For comparison, a commercially available flat-plate heater integrated sensor element having a width of 4.5 mm was used for comparison. The results are shown in Table 1.

[0053]

[Table 1]

From the results shown in Table 1, the sample No. in which the area of the measuring electrode of the element is 8 to ²⁰ mm ² or the width of the element is out of the range of 2 to 3.5 mm. 1 to 4, 10, 11, and 18 all had a long activation time, whereas all of the products of the present invention had a small activation time of 10 seconds or less and had excellent characteristics. Met.

[0055]

As described in detail above, according to the present invention,
By controlling the area of the measurement electrode and the width of the element within a specific range, it is possible to provide a small oxygen sensor element having excellent gas responsiveness and capable of rapid temperature rise.

[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 diagram for explaining a fine structure of a measurement electrode in the present invention.

FIG. 4 is a schematic transparent view for explaining the structure of a heater section in the oxygen sensor element of FIG.

5 is an exploded perspective view for explaining a method of manufacturing the oxygen sensor element of FIG.

FIG. 6 is a graph for explaining a method for measuring activation time.

FIG. 7 is a schematic cross-sectional view for explaining the structure of a conventional heater-integrated oxygen sensor element.

FIG. 8 is a schematic cross-sectional view for explaining the structure of another conventional heater-integrated oxygen sensor element.

[Explanation of symbols]

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

Claims (7)

[Claims] 1. An oxygen sensor element comprising a long zirconia solid electrolyte substrate flat plate, and a sensor section provided with a measurement electrode and a reference electrode made of platinum, respectively, on at least opposite surfaces of the flat plate, the electrode area of the measurement electrode. Is 8-18m
oxygen sensor element, wherein m ^2, and and the width perpendicular to the longitudinal direction of the element is 2.0～3.5Mm. 2. The oxygen sensor element according to claim 1, further comprising a heater portion in which a platinum heater is embedded in a ceramic insulating layer. 3. The oxygen sensor element according to claim 2, wherein in the heater portion, a pair of platinum heaters are vertically formed with a ceramic insulating layer interposed therebetween. 4. A zirconia film is formed on a part of an exposed surface where at least the lower end of platinum particles constituting a measurement electrode is embedded in the surface of the zirconia solid electrolyte substrate and the platinum particles are not embedded. The oxygen sensor element according to any one of claims 1 to 3, wherein: 5. The oxygen sensor element according to claim 4, wherein a zirconia phase is present in the platinum particles forming the measuring electrode. 6. The oxygen sensor element according to claim 2, wherein the sensor portion and the heater portion are formed by simultaneous firing. 7. The sensor part and the heater part are formed separately from each other, and then bonded and integrated by a bonding material. Oxygen sensor element.