JPS63290952A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To eliminate the need for a correction operation to match the shrinkage rate on calcination of a frame body and detecting element and a heater element by calcining said frame body and element and the heater element as separate bodies. CONSTITUTION:A heater insertion recess 7 is formed to the frame body 3 constituted by laminating and integrating sheets formed of yttria-stabilized zirconia and the heater element 8 formed as the separate body is inserted and fixed into this recess 7. The heater element 8 is, therefore, housed into the recess 7 in the state of having no press welded parts joined to the yttria-stabilized zirconia material. Generation of crack and exfoliation by a difference in the coefft. of expansion between the yttria-stabilized zirconia material and the heater element 8 is thereby obviated and the need for the correction operation to match the shrinkage rate of calcination of the yttria-stabilized zirconia material and the heater element is eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an oxygen concentration detector, and particularly to an oxygen concentration detector that is optimal for detecting the oxygen concentration in combustion gas and controlling the air-fuel ratio of a vehicle. be.

[Conventional technology]

Using a solid electrolyte such as stabilized zirconia, a standard electrode and a detection electrode are formed on both sides of the solid electrolyte sheet, and oxygen ions are transferred by bringing these electrodes into contact with oxygen at different pressures. An oxygen concentration detector is used to detect oxygen concentration.

For example, “Nis Ni E J (SAE), N085
0378 (1985) pages 53 to 59, there is a description regarding this type of stacked oxygen concentration detector.

The stacked oxygen concentration detector described here uses Y2O
A detection element is provided in which a platinum standard electrode and a detection electrode are respectively formed on both sides of a stabilized zirconia sheet doped with C.3 to maintain a tetragonal system stably up to a low temperature range. Further, a heating element and a lead-out electrode part are formed of platinum on an alumina sheet, and a heater element is provided in which the alumina sheet is laminated on the heat-generating element and lead-out electrode part.

In the laminated oxygen concentration detector described in the above-mentioned document, the frame is formed by laminating yttria-stabilized zirconia sheets, and the above-mentioned detection element and heater element are directly joined at the air inlet. It has a laminated and fired structure.

In an oxygen concentration detector having such a structure, the electric resistivity of the ittria-stabilized zirconia material of the detection element changes depending on the amount of Y2O3 added, so the amount of Y2O3 added is adjusted to obtain a predetermined detection output current value. Selected.

On the other hand, the expansion coefficient of the Ittria stabilized zirconia material is
It is known that it changes depending on the amount of Y2O added.
For example, if the addition amount is 5 mol % and 6 mol %, 10
A difference in expansion coefficient of XIO-7/'C may occur. In addition, Y,! 400°C to soo'c in the low addition amount range of 03
Phase dislocations exist in a distributed manner within the range of , and there is a region where the expansion coefficient becomes abnormally large at a specific temperature.

On the other hand, since the alumina material of the heater element is widely used for semiconductor integrated circuits, a material with an expansion coefficient of 80.times.10@-7/'C is generally used due to the limitations of the characteristics of the standard. Further, the alumina material does not have a phase transition unlike the yttria-stabilized zirconia material, and the expansion coefficient exhibits a substantially monotonically increasing characteristic from room temperature to 1000°C.

Furthermore, when creating the stabilized zirconia green sheet for forming the frame and the detection element, and the alumina green sheet for forming the heater element, different solvents, binders, plasticizers and dispersions are used to improve castability. The agents are mixed in their respective proportions.

For this purpose, stabilized zirconia green sheets and alumina green sheets are prepared by using the types and ratios of solvents mentioned above.
Its shrinkage rate is changing.

In the oxygen concentration detector described in the above-mentioned literature, the Y2 of the zirconia material is
After setting the amount of O3 added, and considering the types and ratios of solvents, binders, plasticizers, and dispersants mixed in the alumina and zirconia materials, and performing correction operations in a constant temperature bath, the alumina and zirconia materials were prepared. It is necessary to prevent cracking or peeling between the sensing element and the heater element during pressure bonding and firing due to the difference in expansion coefficient and contraction rate.

[Problem that the invention seeks to solve]

As mentioned above, ittria-stabilized zirconia material has
400 °C to 800 °C in the low addition amount range of Y2O3.

Since a phase transition exists in the temperature range of C and the expansion coefficient increases, it is extremely difficult to match the difference in expansion coefficient with alumina material whose expansion coefficient increases monotonically from room temperature to 1000'C.

Furthermore, it is not easy to perform a correction operation in a thermostatic chamber to match the shrinkage rates of the yttria-stabilized zirconia material and the alumina material immediately before they are bonded and crimped.

In this case, for example, if you are trying to obtain a set shrinkage rate of 15%, and the shrinkage rate of the alumina material is 15% and the shrinkage rate of the ittria-stabilized zirconia material is 18%, then the zirconia material is preset in a constant temperature bath. It is necessary to set the temperature and time to achieve a final shrinkage rate of 15%.

However, since this correction operation is affected by the temperature distribution in the thermostatic oven and the indoor environmental conditions up to the time of lamination, variations are likely to occur, and these variations may cause cracking or peeling during firing.

In addition, in the oxygen concentration detector described in the above-mentioned document, the ittria-stabilized zirconia sheet forming the frame, the detection element, and the heater element are not symmetrical in the stacking direction, resulting in thermal deformation distortion and warpage. This can lead to cracking and peeling.

Furthermore, a platinum electrode is used in the detection element to take advantage of the catalytic action, and the platinum electrode, which is formed as a film with a thickness of 1 to 3 μm on the yttria-stabilized zirconia sheet, can be used in an inert gas or oxidizing atmosphere. Can be fired at 1500°C. However, even if the heating element and lead-out electrode part are printed with tungsten on alumina for the heater element, the firing must be carried out at 1600° C. in a reducing gas atmosphere. Because of such a difference in firing temperature and firing atmosphere, the heating element and the lead-out electrode portion of the heater element must also be formed of platinum.

In this case, the lead-out electrode portion must be formed wide in order to lower the resistance value, and there is also the drawback that the manufacturing cost of the heater element portion accounts for as much as 60% of the total manufacturing cost.

The present invention was made in view of the current state of this type of oxygen concentration detector as described above, and its purpose is to eliminate the bonding point between the ittria-stabilized zirconia material part and the heater element part, thereby preventing the expansion of the art material. By preventing the occurrence of cracks and peeling due to differences in coefficients, and by firing and forming the detection element and heater element separately, it is possible to eliminate the need for correction operations to match the firing shrinkage rates of both, and to prevent the heating element and lead-out electrode part of the heater element from forming. It is an object of the present invention to provide an oxygen concentration sensor that can be manufactured using tungsten, for example, to reduce manufacturing costs.

[Means for solving problems]

In order to achieve the above-mentioned object, in the present invention, a detection element and a heater element, each having a standard electrode and a detection electrode formed on both sides of a solid electrolyte sheet, are incorporated into a frame, and the oxygen concentration in the gas to be detected is determined as described above. In an oxygen concentration detector that detects by the movement of ions within a solid electrolyte sheet, the frame body is formed by laminating and integrating a plurality of sheets, the sheet and the solid electrolyte sheet are formed of ittria-stabilized zirconia, and the frame body is formed by laminating and integrating a plurality of sheets; A heater insertion recess is formed in the body, and a separately formed heater element is inserted and fixed into the heater insertion recess.

[Effect]

In the present invention, a heater insertion recess is formed in a frame formed by laminating and integrating sheets made of ittria-stabilized zirconia, and a separately formed heater element is inserted and fixed into this heater insertion recess. . For this reason, the heater element is accommodated in the heater insertion recess without the bonding and crimping portion with the ittria-stabilized zirconia material.

Therefore, there is no occurrence of cracking or peeling due to the difference in expansion coefficient between the ittria-stabilized zirconia material and the heater element material, and there is no need for a correction operation to match the firing shrinkage rates of the ittria-stabilized zirconia material and the heater element material.

Furthermore, the heating element and the lead-out electrode portion of the heater element can be made of, for example, tungsten.

〔Example〕

Embodiments of the present invention will be described in detail below based on the manufacturing method thereof with reference to FIGS. 1 to 5.

Here, FIG. 1 is a cross-sectional view showing the configuration of the main part of the embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line of FIG. 1, and FIG. 3 is a frame body and detection FIG. 4 is an exploded perspective view showing the structure of the heater element portion in an embodiment of the present invention, and FIG. 5 is a sectional view showing the structure of the embodiment of the present invention.

In the embodiment of the present invention, in order to obtain a green sheet having a shape as shown in FIGS. 3A to 3G, which forms a frame or a detection element, a green sheet original plate having a thickness of 0.25 mm and a width of 511 is used. is formed as follows.

For this purpose, a solvent, a binder,
A plasticizer and a dispersant are mixed to create a slurry using a kneading machine, and this slurry is passed through a casting device to a thickness of 0.
A green sheet original plate having a width of 25w and a length of 5fl and a length of approximately 50mm is prepared.

Green sheets A, E, and G shown in FIG. 3 are green sheet original plates obtained as described above and used in their original shapes. In addition, a rectangular atmosphere inlet 4 is formed from one end of the green sheet B, and a slit-shaped gas inlet 5 to be detected is formed in the green sheet D continuously from the one end. , a rectangular sensing hole 6 is formed.

Furthermore, a rectangular heater insertion recess 7 is formed in the green sheet F from one end side.

A platinum standard electrode 2a having a predetermined shape is formed on the surface of the Grinshi+-C to a thickness of, for example, 3 μm by printing,
On the back surface, a platinum detection electrode 2b having the same thickness and a predetermined shape is formed by printing, and is dried at room temperature for 2 hours to obtain the detection element 1.

Next, as shown in FIG. 3, each green sheet and the detection element 1 are
are laminated in multiple layers and integrated under pressure.

In this case, the lamination between mutually adjacent layers is carried out under a pressure of 2 kg/cffl for 5 minutes at 70 °C. Furthermore, when all the layers are laminated, the weight is 10 kg/at 80°C.
Apply pressure cA for 15 minutes and press to shape the external shape.

In this state, for degreasing treatment, the temperature was raised at a rate of 16C/min, maintained at 140°C for 30 minutes, and further heated at 1°C.
The temperature was raised at a heating rate of 300°C/min.

When it reaches C, let it cool naturally.

After degreasing in this way, 15
The temperature is increased to 1500°C at a temperature increase rate of 0°C/hour, and the temperature is maintained at 1.500'C for 1 hour, followed by natural cooling to perform a sintering treatment.

By performing the above-mentioned sintering process, ittria-doped zirconia becomes tetragonal stabilized zirconia that is stable down to low temperatures, and oxygen vacancies are created, allowing the movement of oxygen ions. state.

Next, at a temperature of 900°C in an inert gas atmosphere, the Ni lead wires 13 and 14 are fixed to the standard electrode 2a and the detection electrode 2b through silver solders as shown in FIG. It is embedded in glass 15 and fixed to the frame 3.

In addition, in the manufacturing process mentioned above, Green Sea) A, B
, E, F, and G are processed to be shorter than the lengths of green sheets C and D, and when assembled to the frame 3, the end of the detection element 1 is connected to the atmosphere inlet. It is arranged so as to protrude slightly from 4.

The heater element inserted and fixed into the heater insertion recess 7 described above is manufactured as follows.

99% alumina (A/2203) powder is mixed with a solvent, a binder, a plasticizer, and a dispersant to create a slurry using a kneader, and this slurry is applied to a casting machine.
A green sheet original plate having a thickness of 0.125 and a dragon width of 31 is prepared.

From this green sheet original plate, a green sheet 20 having a length of approximately 4711 mm and a green sheet 21 slightly shorter than this green sheet 20 are formed.

The heating element 9 and the lead-out electrode portion 9a are formed on the green sheet 20 described above by printing a tungsten base, and then dried at room temperature for 10 hours. After this drying process, Grin Sheet 21 was laminated and 2 kg was layered at a temperature of 80°C.
Crimp for 10 minutes at a pressure of /ca.

After that, the external shape is pressed, and for degreasing treatment, the temperature is raised at a rate of 1°C/min, and the temperature is raised to 140°C for 3
The temperature was held for 0 minutes, and the temperature was further increased at a temperature increase rate of 1°C/minute, and when the temperature reached 300°C, it was allowed to cool naturally.

After performing the degreasing treatment in this way, the
The temperature was raised to 1600°C at a heating rate of 160°C.
After being held at 0'C for 1 hour, it is naturally cooled and sintered.

Next, in an inert gas or reducing gas, the Ni lead wire 1
1.12 is fixed to the electrode lead-out portion 9b via silver solder as shown in FIG. 4, and the bonded portion is overcoated with glass.

In this way, as shown in FIG.
and 21 are integrally laminated to form a heater element 8. This heater element 8 is inserted and fixed into the heater insertion recess 7 formed in the frame 3 described above.

In the embodiment, as shown in FIGS. 1 and 2, alumina insulating powder 10 is arranged on the circumferential surface of the heater element 8, and the heater element 8 is inserted into the heater insertion recess 7, so that the heater element 8 and the insertion recess are Alumina insulating powder 10 is filled between the spaces 7. Do not compact this alumina insulating powder 10,
The space between the heater element 8 and the heater insertion recess 7 is filled uniformly,
The opening of the heater insertion section 7 has an expansion coefficient of 80X10-
7/0C borosilicate glass filled, 1.1 in air
The melt sealing process is carried out at a temperature of 00'C for 1 hour.

In the embodiment of the present invention, the whole is fixed to a metal tube 17 via a powder 18 and a glass 19, as shown in FIG.
Furthermore, it is fixed to a plug body 22 having a protective tube, a packing 23 is covered at the relay part of the lead wire, and it is used while being fixed to the plug body 22 by an outer tube 24.

The operation of the embodiment of the present invention having the above configuration will be described next.

When the heater element 8 accommodated in the heater insertion recess 7 of the frame body 3 is energized, the heating element 9 generates heat, the temperature of the frame body 3 rises, and the temperature of the detection element 1 also rises.

In this detection element 1, when the temperature of the solid electrolyte sheet of yttria-stabilized zirconia exceeds approximately 600°C, the solid electrolyte sheet operates as an oxygen ion conductor.

Therefore, from the opening 25 formed in the outer cylinder 24 in FIG.
Atmospheric air passes through a conduit 25a embedded in the glass 19 and comes into contact with the standard electrode 2a from the air inlet 4. On the other hand, a gas to be detected, such as exhaust gas, introduced into the sensing hole 6 from the gas inlet 5 to be detected comes into contact with the detection electrode 2b.

For this reason, oxygen ions move to the solid electrolyte sheet of the detection element 1 based on the oxygen pressure difference between the standard electrode 2a and the detection electrode 2b, making it possible to measure the oxygen concentration in the gas to be detected.

b The alumina insulating powder 10 filled between the heater element 8 and the insertion recess 7 acts as a thermal conductor that quickly transfers the heat of the heater element 8 to the frame 3, and also prevents leakage caused by energization of the heater element 8. It also functions as an insulator to prevent electric current.

That is, as the temperature rises, the electrical resistance of the ittria-stabilized zirconia decreases, so the alumina insulating powder 10 prevents leakage current from the heater element 8 from flowing into the detection element 1.

Therefore, the presence of the alumina insulating powder 10 prevents leakage current from the heater element 8 from flowing into the detection element 1 and reducing the accuracy of the detection output.

Furthermore, even if the heater element 8 is displaced due to heating, the displacement of the heater element 8 is absorbed by the movement of the alumina insulating powder 10 filled on its peripheral surface, so the alumina insulating powder 10 acts as a buffer material. As a result, cracking of the heater element 8 is prevented.

As mentioned above, the frame body 3 and detection element 1 made of ittria-stabilized zirconia and the heater element 8 made of alumina are fired separately, so a correction operation is required to match the firing shrinkage rates of both. is not necessary, and the problem of reduced product yield is solved. Furthermore, since there is no direct bonding and pressure-bonding part between the yttoria-stabilized zirconia material and the alumina material due to the structure, cracking or peeling due to the difference in expansion coefficients between the two is prevented.

Furthermore, since the frame body 3, the detection element 1, and the heater element 8 are formed by firing separately, platinum is not used for the heating element 9 of the heater element 8 and the lead-out electrode part 9a, and instead, a cheap metal such as tungsten can be used. can be used, reducing the overall manufacturing cost to approximately 6.
It is possible to reduce it by 0%.

Further, in the example, since the overall shape is symmetrical in the stacking direction of the sheets, there is almost no warpage due to thermal stress during heating, and durability against thermal shock is improved.

In the example, a heater element is explained in which an alumina sheet is laminated on an alumina substrate on which a heating element is formed, but the heater element is not limited to that in the example. It is possible to have a structure in which the organic film is sandwiched between organic films and inserted into the heater insertion recess together with the alumina insulating powder, and then the organic film is incinerated. Alternatively, a heating element coated with an organic or inorganic substance may be inserted and housed in the heater insertion recess together with alumina insulating powder.

〔Effect of the invention〕

According to the present invention, since the frame, the detection element, and the heater element are fired separately, there is no need for a correction operation to match the firing shrinkage rates of both, which reduces the number of man-hours and prevents the production of products due to variations in shrinkage rates. It is possible to eliminate the decrease in yield. Furthermore, since the detection element and the heater element are fired separately, there is no need to use platinum for the heating element of the heater element, and manufacturing costs are significantly reduced.

Furthermore, according to the present invention, since there is no direct bonding part between the yttria-stabilized zirconia material and the heater element due to the structure, the generation of defective products due to cracking or peeling due to the difference in expansion coefficient between the two is prevented, and the stacking direction of the sheets is By making it a symmetrical shape,
Warpage due to heating is reduced and durability against thermal shock is also increased.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the configuration of the main parts of an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line shown in FIG. 1, and FIG. An exploded perspective view showing the configuration;
FIG. 4 is an exploded perspective view showing the structure of a heater element portion in an embodiment of the invention, and FIG. 5 is a sectional view showing the structure of the embodiment of the invention. 1--------1 detection element, 2a------1 standard electrode, 2b-111111 detection electrode, 3-111--frame body, 4-=----- Atmospheric inlet, 5--detected gas inlet, 6--sensing hole, 7--
Heater insertion recess, 8--Heater element, 9--Heating element, 9 a--1 lead-out electrode section, 9 b--1 electrode lead-out section, 10-----Alumina insulating powder ,11,
12------Ni lead wire, 13, 14---
-----Ni lead wire, 15-11-11-glass, 17-----metal tube, 18-----1 powder, 1
9-------1-Glass, 20-------Grin sheet, 21-------G Figure 3 Figure 4

Claims (1)

[Claims] 1. A detection element and a heater element each having a standard electrode and a detection electrode formed on both sides of a solid electrolyte sheet are incorporated into a frame, and the oxygen concentration in the gas to be detected is determined within the solid electrolyte sheet. In the oxygen concentration detector that detects by the movement of ions, the frame body is formed by laminating a plurality of sheets into one, the sheet and the solid electrolyte sheet are made of ittria-stabilized zirconia, and a heater is inserted into the frame body. An oxygen concentration detector characterized in that a recess is formed, and a separately formed heater element is inserted and fixed into the heater insertion recess. 2. The oxygen concentration detector according to claim 1, wherein the frame is symmetrical in the stacking direction of the plurality of sheets. 3. The oxygen concentration detector according to claim 1, wherein the heater element has a structure in which an alumina sheet is laminated on an alumina substrate on which a heating element is formed. 4. The heater element consists of an organic film sandwiching a heating element.
The oxygen concentration detector according to claim 1, wherein the oxygen concentration detector is incinerated in the heater insertion recess. 5. The heater element is inserted and fixed by filling inorganic powder between the heater element and the heater insertion recess, as claimed in any one of claims 1 to 4. Oxygen concentration detector. 6. The oxygen concentration detector according to any one of claims 1 to 5, wherein the heater insertion recess into which the heater element is inserted is melt-sealed with glass.