JPS5995452A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To eliminate the variation of a standard oxygen chamber, and to obtain a laminated type lean oxygen sensor having stable pumping capability, by reinforcing a solid electrolyte against heat compression, preventing deformation and cracking, and eliminating distortion at the time of heat treatment. CONSTITUTION:The sensor consists of a solid electrolyte 5' for pump cell forming a pump cell side electrode 2', a solid electrolyte 6' for sensor cell forming a sensor side electrode 3', and a solid electrolyte 7' in which holes 8' are bored for a standard oxygen chamber. The solid electrolyte 7' for standard oxygen chamber is a plate form having small holes 8', the solid electrolyte 5 for the pump and the electrolyte 6' for the sensor are cell, sandwiching the solid electrolyte 7' for the standard oxygen chamber sandwiched at the same state as the state where a plate is inserted, and compressed into a body to be used for reinforcement at sintering. By setting the ratio of the diameter of the hole 8' to the thickness of the electrolytes 5', 6' for the pump cell and the sensor cell as <=1, it is possible to eliminate distorsion and cracking of the holes 8' and the variance in volume of the standard oxygen chamber. Thus, very high accurate control of oxygen partial pressure is made possible by controlling the electric current of the pump and the mass production of oxygen sensors is accomplished easily.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an oxygen control system used for air-fuel ratio control in automobile engines, oxygen partial pressure control in general industrial furnaces, or combustion control in home heaters, etc. The present invention relates to an improvement in an oxygen sensor using an ion-conducting solid electrolyte, and relates to an oxygen sensor that eliminates changes in the volume of a reference oxygen chamber and stabilizes the pump function.

[Prior art]

The basis of the oxygen sensor currently in practical use is to expose one electrode to the gas to be measured (oxygen partial pressure is pg) between electrodes sandwiching a solid polymer, and use the other electrode as a reference. It is exposed to gas (oxygen partial pressure is Pr)
% The difference between Pg and Pr is the signal voltage (v
8).

However, in the type of oxygen sensor that detects by exposing one electrode to the gas to be measured and the other electrode to the reference gas,
The detectable oxygen partial pressure range is becoming narrower, and it is no longer in line with the trends of the times.

For example, in the case of automobiles, in order to maintain the maximum purification efficiency of the three-way hazardous substance purification device that purifies CO, hydrocarbons, and NOx contained in automobile exhaust gas, the automobile engine has an air-fuel ratio of 14 I need to drive at .5.

For this air-fuel ratio control, the reference gas side is the atmosphere, the measured gas side is the exhaust gas, and stabilized ZrO2 is used as the solid electrolyte.
Oxygen senna using senna is widely used.

In this oxygen sensor, the output voltage VS changes stepwise with the air-fuel ratio reaching 14.5.

From this point of view, lean fuel systems have been put into practical use in automobile engines in order to achieve high output and lower fuel consumption, with air-fuel ratios ranging from 14.5 to 2.
There is a growing need for an oxygen sensor that can reliably detect and control lean mixtures such as 2.

An oxygen sensor that satisfies this need has a reference gas inside the oxygen sensor, and the oxygen sensor is used by exposing the entire oxygen sensor to the gas to be measured while arbitrarily adjusting the partial pressure Pr of this reference gas. A sensor (hereinafter referred to as Lean 02 sensor) is desirable.

This Lean 02 sensor has a first electrode 1 as shown in FIG.
A solid electrolyte 5 is sandwiched between the electrode 2 and the second electric shuttle 2 to constitute an oxygen pump cell, and a solid electrolyte 6 is sandwiched between the second electrode 2 and the third electrode 4 to constitute a sensor cell. .

In this case, the second electrode 2 is a porous film of metal such as Pt,
This hole is formed as a kind of base cell.

When the Lean 02 sensor configured in this way is exposed to a gas to be measured and a direct current Ip (hereinafter referred to as pump current) is supplied so that the first electrode 1 is negative and the second electrode 2 is positive, the gas to be measured is Oxygen therein is transported from the first electrode 1 to the second electrode 2 through the solid electrolyte M5, increasing the oxygen partial pressure Pr in the hole of the second electrode 2. Furthermore, if the direction of the pump current Ip is reversed, the oxygen partial pressure Pr in the hole of the second electrode 2 decreases, so by adjusting the pump current Ip, the oxygen partial pressure Pr can be arbitrarily set. .

On the other hand, in the sensor cell, the oxygen partial pressure Pr in the hole of the second electrode 2
A signal voltage Vs is output between the second electrode 2 and the third electrode 4 due to the difference between the oxygen partial pressure pg and the oxygen partial pressure pg of the gas to be measured.

In this way, the oxygen partial pressure Pr in the hole of the second electrode 2 can be arbitrarily set by the pump current Ip, so that the oxygen partial pressure can be set over a wider range than in the sensor having a structure in which a solid electrolyte is sandwiched between a pair of electrodes. Highly accurate oxygen concentration detection is possible in this area.

However, in this sensor (Fig. 1), since the second electrode 2 is shared between the pump cell and the sensor cell, the signal output Vs is affected by the pump current rp, which is a technical problem that makes it difficult to put it into practical use. There is a problem.

In order to solve this problem, the second electrode is separated into a pump cell power supply shaft 2 and a sensor cell power supply shaft 3, respectively, as shown in FIG. A structure in which solid electrolytes 5 and 6 were integrated was devised. This space 8 becomes a reference oxygen chamber that holds oxygen flowing in by the pump current Ip. However, this sensor (FIG. 2) has the following drawbacks in the manufacturing process.

That is, there are two methods for integrally molding the solid electrolytes 5 and 6 so as to have the space 8 via the connecting member 7.

As a first means, solid electrolytes 5 and 6 are formed by forming and sintering the pump cell side electrode 2 and the sensor cell (It!l electrode 3).
There is a method of sandwiching and adhering the connecting member 7, but with this method, it is difficult to adhere the connecting member 7 until the airtightness of the space 8 is guaranteed.
The drawback is that it is difficult and expensive to manufacture.

As a second alternative to this, there is a method of bonding the solid electrolytes 5 and 6, which are formed bodies (green sheets) of solid electrolyte ceramic powder before sintering, and the connecting member 7, and then sintering them together. Solid electrolytes 5 and 6 are in a state of being spanned by connecting member 7, and since there is no part that supports the gravity of the solid electrolyte part exposed in space 8, this solid electrolyte part is This causes deformation, which causes variations in the volume of the space 8 when mass-produced, making it difficult to obtain a sensor with a stable pumping function. [Object of the Invention] The present invention solves the above-mentioned drawbacks. The present invention aims to provide a laminated glue 702 sensor.

[Summary of the invention]

ffD The present invention prevents the deformation of the solid electrolyte during sintering and eliminates variations in the volume of the standard oxygen chamber. A solid electrolyte for a pump cell formed by forming a sheet, a solid electrolyte for a sensor cell formed by forming a sensor cell side electrode, and a solid electrolyte for a standard oxygen chamber formed by forming one or more holes in the green sheet. By sandwiching this solid electrolyte for the reference oxygen chamber between the pump cell side electrode and the sensor cell side electrode, the solid electrolyte for the pump cell? 1. The solid electrolyte for the sensor cell was reinforced by the solid electrolyte chamber for the reference oxygen chamber, and the solid electrolytes for both the pump cell and sensor cell were crimped and sintered to prevent deformation. Features.

By setting the ratio of the diameter of the hole drilled in the solid electrolytic chamber for the reference oxygen chamber and the thickness of the solid-state Wjfl for the pump cell and sensor cell to 1 or less, variations in the volume of the reference oxygen chamber can be further reduced. It is characterized by the fact that

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below.

First, for detailed explanation, an outline of the embodiment will be explained. In FIG. 3, the Lean 02 sensor includes a pump cell solid electrolyte 5' forming a pump cell side electrode 2', a sensor cell solid electrolyte 6' forming a sensor cell side electrode 3', and a hole 8'. The standard oxygen chamber solid electrolyte 7' is made of a solid electrolyte 7'.

The solid electrolyte 7' for the reference oxygen chamber is in the form of a single plate with small holes 8', so the solid electrolyte 5' for the pump cell and sensor cell sandwiching the solid electrolyte 7' for the reference oxygen chamber and 6' are just the same as the state in which the plates are sandwiched, and serve as reinforcement when crimped and integrated and sintered.

Also, if the diameter of the hole 8' is too large compared to the thickness of the solid electrolytes 5' and 6' for the pump cell and the sensor cell, the solid electrolyte 5 for the pump cell and the sensor cell will be ' and 6' are deformed at the hole 8', so by setting the ratio of the diameter of the hole 8' and the thickness of the solid electrolytes 5' and 6' for the pump cell and the sensor cell to 1 or less, There is no deformation or cracking at the hole 8' portion, and variations in the volume of the reference oxygen chamber (hole 8') can be eliminated.The details will be explained in more detail below. First, a binder such as butyral resin and an organic solvent are added to solid electrolyte powder to form a slurry, and then a sheet-like molded body (green sheet) is created by slip casting using the Doctor Plaid method. This green sheet is cut into a desired shape, and the solid electrolyte 5' for pump cell shown in FIG.
, a solid electrolyte 6' for the sensor cell and a solid electrolyte 7' for the reference oxygen chamber are formed. These solid electrolytes 5', 6',
7' both use ZrO2 stabilized with Y2O3.

Pump cell side electrodes 2' are attached to the thus formed solid electrolytes 5' and 6' for the pump cell and sensor cell, respectively.
and the sensor cell side electrode 3' are formed by a screen printing method using a material made of a paste of metal powder with an organic substance. Further, the reference oxygen chamber solid electrolyte 7' has a plurality of holes 8' formed therein by punching or the like.

The thus formed solid electrolytes 5' and 6' for the pump cell and the sensor cell are placed between the pump cell side electrode 2' and the sensor cell side electrode 3' in the solid electrolyte chamber 7 for the reference oxygen chamber.
' are placed on top of each other so as to sandwich the green sheets, and the temperature is higher than the glass transition point of the binder contained in the green sheets, and 5Kf/1.
A pressure of Yn2 to 30 Kg/crn2 is applied, and the pieces are bonded together by thermocompression. Thereafter, each solid electrolyte powder is heat-treated at a sintering temperature until it has sufficient airtightness. In this state, the holes 8' are connected to the electrodes 2' and 3 on the pump cell side and the sensor cell side.
' or solid electrolyte 5 for pump cells and sensor cells
', 6' are integrated with the solid electrolyte 7' for the reference oxygen chamber to form a reference oxygen chamber that is kept airtight. ◎1 and 4 are electrodes made of gold nine by sputtering. , are connected to lead wires 9a and 9d, respectively. In the figure, 9a and 9b are lead wires for supplying pump current, and 9c and 9d are lead wires for taking out signal voltage. Note that IO is a porous ceramic retention membrane.

FIG. 4 shows the relationship between the diameter of the hole 8' provided in the standard oxygen chamber solid electrolyte 7' and the thickness of the pump cell and sensor cell solid electrolytes 5' and 6' in the thermocompression bonding process and the heat treatment process. This is a diagram showing how variations in the volume of the oxygen chamber are affected. The track 1iA represents the variation in the standard oxygen chamber, and the track ll11B represents the crack failure rate of the solid electrolyte.

The operation of this embodiment configured as above will be explained. First, the manufacturing process of this embodiment will be explained using FIG.

In the figure, a stabilized zirconia green sheet 5' having a thickness of 0.3 ttan and cut into a desired shape.

6', 7' through holes 5d, 7c, φ0.3mm,
Open 7d, 6b, 6c, 6d. In addition, the green sheet 7' has a plurality of through holes 8' with a diameter of 0.2 am.
Open the day. Platinum paste is printed on the green sheet 5' to form the pump cell side electrode 2', and the hole 5d is filled with platinum base (5d'), dried at 150°C for 30 minutes, and the green sheet 7' is placed on top of this. Match. In this state, the holes 5d and 7d communicate with each other, and the hole 7C is located on the platinum paste 7c' formed on the green sheet 2'. On the other hand, platinum paste is printed on the green sheet 6' to form the sensor cell side electrode 3'. At this time, the hole 6b is filled with platinum paste. In this state, it is dried at 150° C. for 30 minutes, turned over and placed on top of sheet 7, and heated to 120° C. while applying a load of 20 KLi/Crn2 for 10 minutes to thermocompress the three layers of green sheets. In this thermocompression bonding process, the green sheets 5' and 6' may be deformed or cracks may occur due to the pressure bonding force around the plurality of holes 8' formed in the green sheet 7'.

After bonding the three layers of green sheets in this way,
Platinum paste is printed over the holes 5d and 6c, and the holes are filled with the platinum paste, and the thick film portion a is formed.

Form b, e, d. In this state, after drying at 150°C for 30 minutes, heat treatment is performed at 1500°C for 2 hours in the air and fired to integrate the three layers of green sheets to obtain non-porous ZrO2 and metallize the platinum paste. .

In this heat treatment process, the thermoplastic resin (indah) is softened, the solid electrolyte exposed in the hole 8' formed in the green sheet 7' is deformed, and the electrodes 2' and 3' on the pump cell side and the sensor cell side come into contact with each other. Alternatively, the volume of the hole 8' may be changed.Subsequently, a layer is formed on both sides of the ZrO2 layer.This electrode a1+'4 is connected to the thick parts a and d of platinum. Next, four φ0.10 platinum leads 9
a + 9b + 9c + 9d as platinum thick film part a
-d, and plasma spray spinel powder over the entire surface to form a porous preservation film, completing the Lean 02 sensor.

In the thermocompression bonding step of the manufacturing process described above, the green sheet 7' (standard r: solid electrolyte for 1 cable chamber) can be regarded as a single plate with small holes 8'. Green sheets 5' and 6' (
The solid material for the pump cell and the sensor cell is the same as when a single plate is sandwiched between them, and is eventually reinforced by the green sheet 7', so that the strength against the pressing force is maintained.

Furthermore, as shown in FIG. 4, the ratio (pore diameter/solid electrolyte thickness) between the diameter of the hole 8' provided in the green sheet 7' and the thickness of the green sheets 5' and 6' is set to 1 or less, 8′
There is no deformation or cracking of the surrounding green sheets 5' and 6' due to the pressure force, and no deformation of the surrounding green sheets occurs during the heat treatment process.

In addition, green sheets 5', 6', and 7' made by adding a binder to stabilized zirconia powder are integrated into a non-porous sintered body by firing, and the holes 8' are made airtight. It is formed as a reference oxygen chamber with.

In addition, the green sheets 5', 6', and 7' are made of materials with the same composition and particle size distribution, and the difference in thermal expansion between them during the drying and heat treatment processes during the manufacturing process is minimized to improve the adhesion between them. and maintain mechanical strength.

〔Effect of the invention〕

According to the oxygen sensor of the present invention as described in detail above, one or more holes are provided in the solid electrolyte to form a reference oxygen chamber solid electrolyte, and this reference oxygen chamber electrolyte is used for pump cells and sensor cells. Since the solid electrolytes for the pump cell and the sensor cell are sandwiched together, the result is the same as if they were sandwiching a single plate, and they are reinforced by the standard oxygen chamber electrolyte and do not deform under pressure. .

In addition, by keeping the ratio of the diameter of the hole provided in the solid electrolyte for the standard oxygen chamber to the thickness of the solid electrolyte for the pump cell and sensor cell to 1 or less, deformation and cracking of the solid electrolyte during the thermocompression bonding process can be prevented. It was also possible to prevent deformation of the solid electrolyte due to softening of the thermoplastic binder during the heat treatment process.

In this way, by reinforcing the thermocompression bonding force of the solid electrolyte, preventing deformation and zero cracking, and preventing deformation during heat treatment, changes in the volume of the standard oxygen chamber are eliminated and stable pump performance is achieved. We were able to obtain an oxygen sensor.

By being able to accurately obtain the volume of the reference oxygen chamber in this way, it is possible to precisely control the oxygen partial pressure over a wide range by adjusting the pump current. Mass production becomes easier, and the practical effects are significant.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of a conventional glue-in 02 sensor. FIG. 3 shows the lean 0 according to the embodiment of the present invention.
FIG. 2 is a cross-sectional view of two sensors. FIG. 4 is a diagram showing the influence of the pore diameter provided in the standard oxygen solid electrolyte and the solid electrolyte thickness in the thermocompression bonding process and the heat treatment process. FIG. 5 is a diagram showing the manufacturing process of an embodiment of the present invention. l...electrode, 2'...pump cell side electrode, 3'...
- Sensor cell side electrode, 4... Electrode, 5'... Solid electrolyte for pump cell, 6'... Solid electrolyte for sensor cell, 7'... Solid electrolyte for reference oxygen chamber. Agent Patent Attorney Tadashi Akimoto Figure 1 Figure 2 Cause Figure 3

Claims (1)

[Claims] 1. A solid electrolyte for a pump cell is formed by adding an organic binder to solid electrolyte powder to form a plate-shaped green sheet, and forming a pump cell side electrode on the green sheet, and forming a sensor cell side electrode. A solid electrolyte for a sensor cell is formed by forming one or more holes in the green sheet, and a solid electrolyte for a reference oxygen chamber is formed by forming one or more holes in the green sheet. 1. An oxygen sensor, which is sandwiched between electrodes on the sensor cell side, and is characterized in that solid electrolytes for a pump cell and a sensor cell, and a solid electrolyte for a reference oxygen chamber are integrated by thermocompression bonding, and then sintered. 2. A solid electrolyte for a pump, which is formed by adding an organic binder to solid electrolyte powder to form a plate-shaped green sheet, and forming a pump cell side electrode on the green sheet, and a solid electrolyte for a sensor cell, which is formed by forming a sensor cell side electrode. electrolyte and
a solid electrolyte for a reference oxygen chamber formed by drilling one or more holes in the green sheet, the diameter of the hole provided in the solid electrolyte for the reference oxygen chamber and the solid electrolyte for the pump cell and sensor cell; The ratio (hole diameter/thickness of the solid electrolyte for the pump cell and the sensor cell) is 1 or less, and the solid electrolyte for the reference oxygen chamber is sandwiched between the pump cell side electrode and the sensor cell side electrode. An oxygen sensor characterized in that a solid electrolyte for a sensor cell and an electrolyte for a base oxygen chamber are integrated by thermocompression bonding and then sintered.