JPH03138559A - Oxygen sensor and production thereof - Google Patents

Abstract

PURPOSE:To obtain the sensor which is small in the thickness of a solid electrolyte layer and is small in heat capacity by providing a groove communicating with the hollow part of a heater body via a through-hole on the outer peripheral surface corresponding to the exothermic part of a heater body. CONSTITUTION:The sensor is constituted of the hollow heater body 1 which contains the exothermic part 11 near the inside surface at the front end and is sealed at the front end, the groove 2 which is formed on the outer peripheral surface corresponding to the exothermic part 11 of the body 1 and communicates via the through-hole 21 with the hollow part 10 of the body 1 and the solid electrolyte layer 5 which is provided with a pair of porous cell electrodes 3, 4 to face each other on both surfaces, is so formed as to cross the aperture 20 of the groove 2 and has 20 to 200mum thickness. Since a protective layer 7 is formed on the surface of the electrode 4, the electrode comes into contact with an exhaust gas via this protective layer. Since the electrode 3 has a supporting layer 6, the electrode comes into contact with the outdoor air infiltering the inside of the groove 2 via this supporting layer 6. The depression of the solid electrolyte layer 5 into the groove 2 is prevented by such supporting layer 6 and protective layer 7. The deterioration of the solid electrolyte layer 5 and the cell electrode 4 formed on the surface thereof by the sticking of the mists in the exhaust gas thereto is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an oxygen sensor for detecting the oxygen concentration in exhaust gas by installing it in the exhaust gas pipe of an automobile, for example, and an effective manufacturing method thereof. .

(Prior Art) Measuring the oxygen concentration in automobile exhaust gas is extremely important in adjusting the air-fuel ratio of the engine. As a means for detecting such oxygen concentration, two cell electrodes are placed oppositely on both sides of a solid electrolyte base material such as zirconia, and one cell electrode is placed in contact with the exhaust gas, and the other cell electrode is placed in contact with the outside air. Oxygen sensors that detect the oxygen concentration in exhaust gas by measuring the electromotive force (proportional to the oxygen concentration ratio between exhaust gas and outside air) between both cell electrodes are mainly used. There is. The electromotive force mentioned above is also affected by temperature, and since the exhaust gas side is exposed to high temperatures,
In order to accurately detect oxygen concentration, it is necessary to keep the temperature of the measurement site as constant as possible so that it is not affected by the exhaust gas temperature, and for this reason, a heater is also installed in parallel.

(Problems to be Solved by the Invention) The above oxygen sensor generally includes a heater base material, a heater electrode,
It is manufactured by a method in which a solid electrolyte, cell electrodes, etc. are laminated and fired all at once.

However, in the case of the above method, the solid electrolyte layer has at least two
It requires a thickness of 00 μm or more.

In addition, platinum is mainly used for cell electrodes, and zirconia is mainly used for solid electrolyte layers, but when firing these, it is necessary to do so in an oxygen atmosphere, so base metals such as tungsten are used as heater electrodes. cannot be used,
Since precious metals such as platinum have to be used, the cost increases accordingly. Therefore, it is possible to fire the sensor part and the heater part separately and then integrate them, but since each part must have strength, it is necessary to increase the thickness, which increases the heat capacity. This increases the power consumption.

(Purpose of the Invention) The present invention was made in view of the above, and provides a novel oxygen sensor that has a thin solid electrolyte layer, allows the use of base metals as a heater electrode, and has a small heat capacity, and an effective manufacturing method thereof. We aim to provide the following.

(Means for Solving the Problems) 3-4- The oxygen sensor of the present invention that achieves the above object and its manufacturing method will be explained based on the accompanying drawings. Fig. 1 is a perspective view showing an example of the oxygen sensor of the present invention, Fig. 2 is a longitudinal cross-sectional view taken along the line nn in Fig. 1, Fig. 3 is an enlarged view of the section marked with ■ in Fig. 2, and Fig. 4 is a main It is a process diagram of the invention method.

That is, the oxygen sensor of the present invention includes a hollow heater body 1 which has a built-in heat generating part 11 near the inner surface on the tip side and whose tip is sealed, and a hollow heater body 1 formed on the outer circumferential surface of the heater body 1 corresponding to the heat generating part 11. A groove 2 communicating with the hollow part 10 of the heater main body 1 through a through hole 21, and a pair of porous cell electrodes 3.4 attached on both sides so as to straddle the opening 20 of the groove 2. It is characterized by comprising a solid electrolyte layer 5 with a thickness of 20 to 200 μm formed by a thin film method.

In the above, it is desirable to interpose a porous support layer 6 between the solid electrolyte layer 5 and the groove opening 2°, and to cover the surface of the solid electrolyte layer 5 with a porous protective layer 7.

In addition, the method for manufacturing the oxygen sensor described above includes a hollow heater body 1 which has a built-in heat generating part 11 near the inner surface on the tip side and whose tip is sealed.
Step (1) of forming a groove 2 communicating with the hollow part 10 of the heater main body 1 through the through hole 21 on the outer circumferential surface corresponding to the heat generating part 11.
), a step (II) of filling the groove 2 with resin r, and a step (II) of forming a porous support layer 6 on the surface of the filled resin r so as to straddle the opening 20 of the groove 2 ) and the step of forming one porous cell electrode 3 on the support layer 6 (I
V), a step (V) of burning off and removing the resin r, a step (VI) of forming a solid electrolyte layer 5 on the cell electrode 3 by a thin film method, and a step (VI) of forming the solid electrolyte layer 5 on the surface of the solid electrolyte layer 5. The gist is that it consists of a step (■) of forming a porous cell electrode 4 and a step (■) of covering the solid electrolyte layer 5 including the cell electrode 4 on the front side with a protective layer 7.

Although it is of course possible to form the heat generating part 11 built into the heater body 1 with an electrode of a noble metal such as platinum, it is preferable to form it with an electrode of a base metal such as tungsten in terms of cost and the like.

The heater body 1 is molded from a heat-resistant and insulating material such as alumina ceramic, and has a heating wire 1.1a, which serves as the heat generating portion 11-, buried near the inner surface on the front side thereof, and the heating wire 11a. The electrode wires 1] b, i l b are led out through the thickness of the main body 1 to the base end,
The base ends of the electrode wires 11b and llb are connected to an external power source (not shown). Further, a pair of cell electrode wires 31 and 41 are formed on the outer peripheral surface of the heater body and extend to the base end thereof. The cell electrode wires 31.41 are electrically connected to the cell electrodes 3.4 at their tips, and their base ends are connected to an electromotive force measuring device (not shown).

The solid electrolyte layer 5 is made of zirconia or the like by vapor deposition or CV
It is formed using a thin film method such as the D method. The reason for setting the thickness to 20 to 200 μm is that if it is less than 20 μm, the cell electrode 3.4 will not be able to withstand the thermal stress applied during use, and will be destroyed, whereas if it exceeds 200 μm, its function will not change. This is because the processing cost 1~ only increases.

The cell electrode 3.4 is a porous electrode containing platinum as a main component, and is formed by other thin film techniques such as transfer, printing, or vapor deposition. At the time of this formation, the cell electrode wires 31 and 41 previously formed on the outer peripheral surface of the heater main body 1
The cell electrode wires 3 and 41 are electrically coupled to each other, and the cell electrode wires 3 and 41 are not limited to platinum, but base metals such as tungsten can also be used. Among these cell electrodes 3.4, the cell electrode 4 on the outer surface side is in contact with the exhaust gas directly or through the protective layer 7 when measuring the oxygen concentration in the exhaust gas,
The cell electrode 3 on one side is connected to the hollow part 10 of the heater main body 1
and comes into contact with the outside air that has entered the groove 2 through the through hole 21 either directly or via the support layer 6.

Both the support layer 6 and the protective layer 7 need to be porous to allow the permeation of oxygen (ions), and are preferably formed by spraying a spinel structure material. The support layer 6 supports the solid electrolyte layer 5 including the cell electrodes 3.4 formed thereon to prevent it from sinking into the groove 2.

On the other hand, the protective layer 7 protects the cell electrodes 4 and the solid electrolyte layer 5 to prevent them from being damaged, but when sprayed with a spinel structure material, it also functions as a diffusion rate controlling layer, This makes it possible to apply the oxygen sensor as a limiting current type sensor.

(Function) The oxygen sensor configured as described above is disposed, for example, in the exhaust gas pipe of an automobile so as to be perpendicular to the gas flow.

In this state, the cell electrode 4 is in contact with the exhaust gas through the protective layer 7 if it is formed, and the cell electrode 3 is in contact with the exhaust gas through the support layer 6 if it is formed. It comes into contact with the outside air that has entered the groove 2 through the groove. Then, the heating wire 11 of the heater main body 1. When conductive to the cell electrode 3.a, the heat generating portion 11 generates heat, and the vicinity thereof is heated to a constant temperature, and both cell electrodes 3.
4 will be maintained at approximately the same temperature. Both cell electrodes3.
When the electrode wires 31.41 of 4 are connected to an electromotive force measuring device, an electromotive force is generated between both cell electrodes 3.4 according to the difference in chemical potential between the two electrodes based on the difference in oxygen concentration at the surface measurement site. This is detected. ” When the support layer 6 and the protective layer 7 are formed, the solid electrolyte layer 5 is prevented from sinking into the groove 2, and the exhaust gas from the solid electrolyte layer 5 and the cell electrode 4 formed on its surface is prevented. Deterioration due to adhesion of mist inside is prevented.

In addition, in the manufacturing method shown in FIG. 4, in step (1), grooves 2 and through holes 21 are formed in the heater body 1, which is formed by embedding the heating wire 11a and its electrode wires 11b and llb in predetermined locations.
is formed by cutting or by winding a sheet with grooves and holes formed therein. In step (II), the groove 2
was filled with resin r, and a support layer 6 and a cell electrode 3 were formed on this filled resin r [Step (III) and Step (■)
] After that, when the resin r is burnt out and removed [step (■)], the groove 2 becomes a space that communicates with the hollow part 10 of the heater main body 1 through the through hole 21, and the support layer 6 is inserted into the opening 20. and the cell electrode 3 remains so as to straddle it. Therefore, when the solid electrolyte layer 5 and the cell electrode 4 are formed on this [step (VI) and step (■)], the support layer 6, the cell electrode 3, the solid electrolyte layer 5, and the cell electrode 4 cover the groove 2. It is formed into a single layered structure. Since the solid electrolyte layer 5 is formed by the thin film method as described above and is supported by the support layer 6,
There is no need to increase the thickness more than necessary, and the overall heat capacity is reduced. Further, since the heater body 1 is not subjected to firing treatment in an oxygen atmosphere, an inexpensive base metal electrode such as tungsten can be used as the heat generating portion 11 built into the heater body 1. Furthermore, forming the protective layer 7 in step (■) prevents the cell electrode 4 formed on the solid electrolyte layer 5 from deteriorating due to adhesion of mist such as p, s, and pb contained in the exhaust gas. When this protective layer 7 is formed by thermal spraying of a spinel structure material, it also functions as a diffusion control layer and can be applied as a limiting current type sensor.

(Example) Next, examples will be described.

In FIGS. 1 to 3, the heater body 1 has a cylindrical shape with a sealed distal end and an open proximal end, and a heat generating section 11 is formed along the circumferential direction near the inner circumferential surface of the distal end. heating wire 11
a is buried, and its electrode wires 11b and llb are buried in the main body 1.
It is integrally enclosed within its thickness along its longitudinal direction and is led out to the proximal end. This lead-out end has a power supply (not shown)
are concatenated.

A groove 2 along the circumferential direction is dug in the outer circumferential surface of the heater body 1 corresponding to the heat generating part 11, and a branch groove 2' orthogonal to the groove 2 is further formed along the longitudinal direction of the main body 1, The branch groove 2
A through hole 21 communicating with the hollow part of the main body 1 is bored at the bottom of the main body 1. The reason for forming the branch grooves 2' in this way is that the through holes 2'
This is to remove the drilling position No. 1 from the heat generating part 11.

As described above, the support layer 6, the cell electrode 3, the solid electrolyte layer 6, and the cell electrode 4 are integrally stacked and formed in the openings 20 and 20' of the groove 2 and the branch groove 2', and further protect them. Covered by layer 7. In this laminated structure, it goes without saying that each cell electrode 3.4 is electrically coupled to an electrode wire 31.41 formed on the outer peripheral surface of the heater main body 1.

A boss portion 12 is formed in the middle of the heater body 1, and in actual use, this boss portion 1 is attached to the measurement port of the exhaust gas pipe.
2 are inserted so that they are in contact with each other. Since the procedure for measuring oxygen concentration is as described above, its explanation will be omitted here in 1-2-.

Incidentally, in the case of rotation, a cylindrical heater body 1 is illustrated as an example, but the heater body 1 is not limited to this, and a laminated type can also be adopted as long as it is a hollow body. Also, the electrode wire 31. of the cell electrode 3.4.
41 is formed in an exposed manner on the outer peripheral surface of the heater main body 1, but it goes without saying that it is desirable to cover this with an insulating material.

(Effect of the invention) As described above, the oxygen sensor of the present invention has two solid electrolyte layers.
Since it is extremely thin at 0 to 200 μm, the overall heat capacity is small and power consumption is reduced. Furthermore, since the solid electrolyte layer and cell electrodes are formed by a thin film method, the heater body is not subjected to firing in an oxygen atmosphere, and therefore an inexpensive base metal electrode is used as the heat generating part built into the body. It can be used. Furthermore, when a support layer is provided, the solid electrolyte layer, which is the main body of the sensor, and the cell electrodes attached to both sides of the solid electrolyte layer are supported by the support layer. There is no fear of falling inside. Furthermore, when the main body of these sensors is covered with a protective layer, deterioration due to mist of P;S, PB, etc. in the exhaust gas is also prevented.

In addition, in the manufacturing method of the present invention, the grooves are filled with resin that is later burnt out and removed, and a solid electrolyte layer is formed on top of the resin, so each layer can be formed by a thin film method or the like. As a result, the overall heat capacity can be reduced, and an inexpensive base metal electrode can be used as the heat generating portion, contributing to reductions in manufacturing costs and the like.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of the oxygen sensor of the present invention, Fig. 2 is a longitudinal cross-sectional view taken along the line nn in Fig. 1, Fig. 3 is an enlarged view of the section marked with ■ in Fig. 2, and Fig. 4 is a main It is a process diagram of the invention method. (Explanation of symbols) 1... Heater body. Hot part, 2... Groove, 3.4... Cell electrode, holding layer, 7... Protective layer. DESCRIPTION OF SYMBOLS 10...Hollow part, 11...Opening part, 21...Through hole, 5...Solid electrolyte layer, 6...Japanese Patent Application Laid-Open No. 3-138559 (6)

Claims (1)

[Scope of Claims] 1. A hollow heater body with a built-in heat generating part near the inner surface on the tip side and a sealed tip, and a hollow heater body formed on the outer circumferential surface of the heater body corresponding to the heat generating part and formed through a through hole. A solid electrolyte layer with a thickness of 20 to 200 μm formed by a thin film method to span the opening of the groove, which has a groove communicating with the hollow part of the heater body and a pair of porous cell electrodes attached to both sides. An oxygen sensor consisting of 2. The oxygen sensor according to claim 1, wherein a porous support layer is interposed between the solid electrolyte layer and the groove opening, and the surface of the solid electrolyte layer is covered with a porous protective layer. 3. The oxygen sensor according to claim 1 or 2, wherein the heat generating portion is made of a base metal electrode. 4. Forming a groove that communicates with the hollow part of the heater body through a through hole on the outer circumferential surface of the hollow heater body, which has a heat generating part built-in near the inner surface on the tip side and whose tip is sealed, corresponding to the heat generating part. a step of filling the groove with resin; a step of forming a porous support layer on the surface of the filled resin so as to span the opening of the groove; and a step of forming one porous cell electrode on the support layer. a step of burning and removing the resin, a step of forming a solid electrolyte layer on the cell electrode by a thin film method, and a step of forming the other porous cell electrode on the surface of the solid electrolyte layer. A method for manufacturing an oxygen sensor comprising the steps of: and covering the solid electrolyte layer including the cell electrode on the surface side with a protective layer. 5. The manufacturing method according to claim 4, wherein the heat generating portion is made of a base metal electrode.