JPH0675056B2 - Oxygen sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for measuring an oxygen concentration in an atmospheric gas, and more particularly to a limiting current type oxygen sensor using an oxygen ion conductive solid electrolyte. .

2. Description of the Related Art Conventionally, as shown in FIG. 2, in the conventional oxygen sensor of this type, an electrode film 2 (anode 2a, anode 2a, Cathode 2b) and further said cathode 2b
For forming a closed space on the solid electrolyte plate 1 on the side
The character-shaped lid body 3 is arranged, and further, the lid body 3 is provided with an oxygen diffusion hole 4 for communicating an external space and a closed space. The diffusion hole 4 is sized to diffuse a smaller amount of oxygen than the oxygen delivery capacity of the cathode 2b.

In this configuration, when the direct current voltage is applied between the electrodes 2 after heating the oxygen sensor to an operable temperature, an ionization reaction of oxygen molecules occurs at the cathode 2b, and the ionized oxygen ions pass through the solid electrolyte plate 1 into the anode 2a. Move towards the anode
At 2a, a molecular reaction of oxygen ions occurs and the oxygen ions are discharged to the outside space. On the other hand, the inflow of oxygen into the closed space is restricted by the diffusion hole 4 provided in the lid 3, and the inflow of oxygen into the cathode 2b is diffusion-controlled. As a result, the current generated by the movement of oxygen ions in the solid electrolyte plate 1 shows a constant value after a certain voltage as the applied voltage increases. This constant current is the limiting current. Since this is almost proportional to the oxygen concentration in the atmosphere gas, the oxygen concentration can be measured by detecting the limiting current.

(For example, JP-A-59-192953 and JP-A-60-252254) Problems to be Solved by the Invention The material of the lid body 3 in which the diffusion holes 4 are formed is ceramic from the viewpoint of heat resistance and corrosion resistance. Materials are often applied. The size of the diffusion hole 4 is arbitrarily set depending on the operating temperature of the oxygen sensor and the size of the limiting current. However, it is desirable to keep the operating temperature as low as possible in order to ensure long-term reliability of the oxygen sensor. In the solid electrolyte of zirconia-based ceramic, the minimum operating temperature is about 400 from the viewpoint of oxygen ion transport capacity.
℃ or above. In order to obtain a practical limit current value at this operating temperature, the diffusion hole 4 has an extremely small diameter of several tens of μm and a length of several mm. Therefore, it is practically difficult to accurately perform the drilling process on the diffusion hole 4 in the ceramic material.
There is a problem that the characteristics are increased and the fine processing is performed, so that the productivity is poor and the cost is high.

Further, in the configuration in which the diffusion hole 4 is formed in the upper portion of the lid body 3, dust, foreign matter, etc. enter the diffusion hole 4 to change or close the diameter thereof during the manufacturing process or actual use of the oxygen sensor. I have a concern. As a result, there is a problem that the oxygen sensor characteristics change over time, which causes malfunction.

Furthermore, in order to operate the oxygen sensor, it is necessary to heat it to the operating temperature, but in the conventional heating element wound around the oxygen sensor in the form of a coil, the heating speed is slow and the heat is effective for the oxygen sensor. However, there is a problem that the power consumption becomes large and the temperature control of the oxygen sensor cannot be performed accurately because the heating element and the oxygen sensor are not in close contact with each other, and the limiting current value varies. .

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an oxygen sensor which is excellent in workability and productivity, has less variation in characteristics, and can realize stable characteristics over a long period of time. .

Means for Solving the Problems In order to solve the above problems, the oxygen sensor of the present invention has a solid electrolyte plate, electrode films formed on both surfaces of the solid electrolyte plate, and a starting end surrounding one of the electrode films. And a spiral spacer arranged so that the end and the spacer are spaced from each other on the solid electrolyte plate, partition walls facing each other of the spiral spacer, the spiral diffusion hole surrounded by the solid electrolyte plate and the seal plate, A heating element is formed on one surface of the seal plate.

Function In the above-mentioned configuration of the present invention, since the spiral diffusion hole is simultaneously formed at the time of adhering the spiral spacer, the solid electrolyte plate and the seal plate, it is not necessary to perform a difficult drilling process as in the conventional oxygen sensor. At the same time, since the spiral diffusion hole is formed in parallel with the solid electrolyte plate, invasion of dust or foreign matter into the spiral diffusion hole is prevented. In addition, since the heating element is formed in close contact with the seal plate, heat can be effectively transferred to the oxygen sensor, and the temperature of the oxygen sensor can be controlled with high accuracy.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. FIG. 1A is an exploded perspective view of an oxygen sensor, and FIG. 1B is a partially cutaway perspective view of the oxygen sensor.

In FIGS. 1 (a) and 1 (b), 1 is a solid electrolyte plate having oxygen ion conductivity, and electrode films 2 are formed on both surfaces thereof. On one surface of the solid electrolyte plate 1, a spiral spacer 5 that surrounds the electrode film 2 and has a start end and an end that are spaced from each other is arranged, and further, a seal plate 6 having a heating element 8 is arranged. The diffusion hole 7 is formed in a spiral space surrounded by the partition walls of the spiral spacer 5 facing each other, the solid electrolyte plate 1 and the seal plate 6, and oxygen diffuses into the electrode film 2 through the space.

Examples of the material of the solid electrolyte plate 1 include zirconia-based ceramics, which is the most practical in terms of long-term reliability, stability of characteristics, and the like. Among them, zirconia to which yttria is added is preferable.

Examples of the material of the electrode film 2 include platinum, gold, palladium and silver, but are not particularly limited.

The spiral spacer 5 is required to have heat resistance sufficient to withstand the operating temperature of the oxygen sensor and adhesiveness that realizes airtightness between the solid electrolyte plate 1 and the seal plate 6, and the material thereof is glass,
Examples include metals.

When the glass material to which the zirconia-based ceramic as a solid electrolyte plate 1, it is desirable thermal expansion is _{comparable, P b O-Z n O} -B 2 O 3 -S i O 2 system, K ₂ O- P _b O‐S _i O ₂ system, N
_a2 O‐K ₂ O‐P _b O‐S _i O ₂ system, N _a2 O‐C _a O‐S _i O ₂ system, K ₂ O‐C _a O
-S _i O ₂ based glass can be mentioned. By the way, in the case where the spiral spacer 5 is made of only glass, when the seal plate 6 is placed on the upper part and then heated and fired, the seal plate 6 is settled by softening of the glass and the gap of the spiral spacer 5, that is, the diffusion hole 4 is formed. Large dimensional variation. In the present invention, in order to prevent this, heat resistant particles having a melting point higher than that of the glass component are dispersed in the glass component. The heat-resistant particles prevent the seal plate 6 from settling, and a stable gap can be formed. By adjusting the sizes of the heat resistant particles, the dimensional accuracy of the gap is improved.

The screen printing method is most suitable as the means for forming the spiral spacer 5. In this case, the paste containing the glass component is added with an appropriate amount of the heat-resistant particles, mixed and dispersed, and the solid electrolyte plate 1 is formed using the pattern of the spiral spacer 5.
Is printed so as to surround the electrode film 2.

On the other hand, when the spiral spacer 5 is made of metal, a titanium foil sandwiched between silver brazing foils is most suitable. The reason is that titanium has a coefficient of thermal expansion close to that of zirconia-based ceramic applied as the solid electrolyte plate 1, heat resistance,
It has excellent adhesiveness. The silver brazing foil and the titanium foil are formed into the spiral spacer 5 by laser processing or the like.
The one processed into the pattern is used. The gap of the spiral spacer 5 is determined by the thicknesses of the silver brazing foil and the titanium foil, so that a stable gap size can always be obtained.

Examples of the material of the seal plate 6 include zirconia-based ceramics, forsterite, and the glass described in the spiral spacer 5 in terms of thermal expansion coefficient and heat resistance. The glass used as the seal plate 6 is selected to have a higher melting point than the glass used for the spiral spacer 5.

As described above, the spiral diffusion hole 7 of the present invention is composed of the partition walls facing each other of the spiral spacer 5, the spiral space surrounded by the solid electrolyte plate 1 and the seal plate 6, and the seal plate 6 is formed by the spiral spacer. After being placed on top of No. 5, it is formed by the following method.

When the spacer 5 is (1) glass printing, bonding by heating and baking.

(2) Brazing by heating and melting in a vacuum or an inert gas in the case of silver brazing foil and titanium foil.

The heating element 8 may be a printed film made of a paste of platinum, tungsten, molybdenum, a metal wire such as stainless steel, iron chromium, nichrome, or a metal foil.

The heating element made of a printed film is obtained by printing on the seal plate 6 by a screen printing method and heating and firing. However, those having poor oxidation resistance such as tungsten and molybdenum are coated with a dense protective film after printing and heated and baked in a vacuum or a non-oxidizing atmosphere.

On the other hand, the heating element made of a metal wire or a metal foil is arranged on the seal plate 6 and then applied with an electrically insulating adhesive such as glass and heat-bonded or after applying the adhesive to the seal plate 6,
It is obtained by arranging the metal wire and the metal foil and heating and bonding them.

The resistance value of the heating element 8 is appropriately set so as to obtain a temperature at which the oxygen sensor can operate, and the size of the spiral diffusion hole 7 is appropriately set according to the operating temperature of the oxygen sensor and the required limiting current value. .

Next, the operation and effect will be described based on a specific embodiment.

The constituent materials and manufacturing method of the oxygen sensor in one embodiment of the present invention shown in FIG. 1 are as follows. A glass printed film is used as the spiral spacer 5, a metal foil is applied as the heating element 8 to the oxygen sensor A, a titanium foil sandwiched with silver brazing foil is used as the spiral spacer 5, and a metal printed film is applied as the heating element 8. This was used as oxygen sensor B.

Solid electrolyte plate 1 _{ZrO 2} · Y ₂ O ₃ ceramic (Y ₂ O ₃ 8 mol%), dimensions 12 × 12 × 0.
4 ^t mm electrode film 2 Pt paste, electrode diameter 6 mm, film thickness about 5 μm Apply on both sides of the solid electrolyte plate 1 by screen printing method and calcination at 850 ° C. for 10 minutes. A printed film made of Pt paste for connecting lead wires was formed on the cathode side only as shown in FIG.

Helical spacer 5 A: Glass printing film glass _{...... P b O-Z n O} -B 2 O 3 -S i O 2 glass paste refractory particles _{...... B a O-T i O} 2 -S i O 2 system Glass powder, average particle size 50 μm Using 10 g of the glass powder mixed with 1 g of the glass paste, a spiral spacer 5 was formed by screen printing around the electrode film 2 on one surface of the solid electrolyte plate 1.
The spiral spacer 5 has the shape shown in FIG. 1, and the size of the spiral diffusion hole 7 is set to be the size shown in the above example.

Width of spiral spacer 5 0.5mm B: Titanium foil sandwiched with silver brazing foil The titanium spacer held by the silver brazing foil is laser processed to form the spiral spacer 5 shown in FIG. 1 so that the size of the spiral diffusion hole 7 becomes the size shown in the above-mentioned example, and the solid electrolyte plate is formed. The electrode film 2 is arranged on the first electrode 1.

Width of spiral spacer 5 0.5mm Seal plate 6 _{ZrO 2} · Y ₂ O ₃ ceramic (Y ₂ O ₃ 8mol%) Dimensions 11 × 12 × 0.5 ^t mm Heating element 8 B: Metal print film Pt paste is used. The heating element pattern shown in FIG. 1 is screen-printed on the seal plate 6. Formed by heating and baking at 850 ° C for 30 minutes. Resistance value 50Ω (400 ° C) A: Metal foil Stainless steel SUS-430 was used to chemically etch the heating element shown in Fig. 1. This was placed on the seal plate 6, the glass paste used in A was applied on the seal plate 6 and the heating element, and heated and baked at 450 ° C. for 30 minutes to form. Resistance value 50Ω (400 ° C) Diffusion hole 7 The seal plate 6 with the heating element 8 is placed on the spiral spacer 5 and the following bonding process is performed.

A: Heated and baked at 450 ° C for 30 minutes.

B: Brazing at 800 ° C for 5 minutes under a vacuum of 10 ^-4 torr or less.

With respect to the oxygen sensors A and B manufactured in this way, lead wires (Pt) were attached to the electrode film 2 and the heating element 8, and the characteristics were evaluated. As a result, the produced oxygen sensors A and B both showed a constant current in the applied voltage range of 1V to 2.2V. It was confirmed that the current showing this constant value is the limiting current and functions as an oxygen sensor. Further, both of the limiting current values showed about 100 μA, and it was confirmed that the above-mentioned spiral diffusion hole was formed as designed.

When the limiting current value in air is set to 100 μA, the size of the conventional diffusion hole 4 shown in FIG. 2 is 30 μm in diameter and 1 m in length.
It becomes m. On the other hand, the spiral diffusion hole 7 of the present invention shown in FIG.
The size of the is 400 μm in width, 50 μm in height, and 25 mm in length. (The sizes of the diffusion holes of the related art and the present invention shown here are representative examples with high practicability.) Here, if the opening size of both diffusion holes varies by 10%, the limiting current value is about 20%.
It will vary. It is difficult to accurately process a minute hole such as the conventional diffusion hole 4, and the area of the opening is 10
It is unavoidable that there is a variation of more than%. On the other hand, since the spiral diffusion hole 7 of the present invention is formed around the electrode film 2, both the opening area and the length can be made 20 times or more. The fact that the opening area can be designed to be large has an effect that the variation in the limiting current value can be reduced because the variation can be reduced as compared with the conventional case. The variation of the opening area of the spiral diffusion hole 7 according to the present invention is within 10%, and the limiting current value is within ± 20%.

Further, in the present invention, since the spiral diffusion hole 7 is constituted by the combination of the solid electrolyte 1, the spiral spacer 5 and the seal plate 6 which are adhered to each other, it is not necessary to perform the drilling of the ceramic unlike the conventional case. Therefore, since it is formed by an extremely simple method, it is possible to realize excellent productivity and low cost.

Further, according to the present invention, since the spiral diffusion hole 7 is formed in parallel with the solid electrolyte plate 1, it is possible to prevent dust and foreign matters from entering the diffusion hole during the manufacturing process of the oxygen sensor and in actual use, and to stabilize the characteristics. And long-term reliability can be improved.

On the other hand, the resistance value of the heating element 8 during operation of the oxygen sensors A and B is both about 50Ω, and the temperature of the oxygen sensor is 400
It was confirmed that the temperature was ℃. In addition, the power consumption required to heat the oxygen sensor is about 3 W, which is lower than the conventional heating method.

When the voltage applied to the heating element 8 is constant, the temperature of the oxygen sensor changes due to changes in wind speed and room temperature. Since the oxygen sensor of the present invention has a positive temperature characteristic, the limiting current value changes due to a temperature change, and the oxygen concentration detection accuracy deteriorates.
Therefore, in order to keep the temperature of the oxygen sensor constant, it is necessary to control the input power of the heating element 8. Since the heating element 8 according to the present invention is formed in close contact with the sealing plate 6, the heat transfer from the heating element 8 to the solid electrolyte plate 1 is performed efficiently and smoothly, so that the thermal response is fast and the set temperature is accurate. It becomes possible to maintain the oxygen concentration, and as a result, the accuracy of detecting the oxygen concentration is improved. Further, since the heat transfer from the heating element 8 to the solid electrolyte plate 1 is good, the time to reach the operating temperature is shortened, and the oxygen sensor can operate in a short time.

Effects of the Invention As described above, the oxygen sensor of the present invention has the following effects.

(1) Since the size of the oxygen diffusion hole can be made larger than in the conventional case, the relative variation of the diffusion hole can be reduced and the variation of the limiting current value can be reduced.

(2) The diffusion holes are formed by bonding a spiral spacer made of a glass printed film or a metal foil, a solid electrolyte plate and a seal plate. Therefore, unlike the conventional case, it is not necessary to make a hole, and since it can be formed by an extremely simple method, it is possible to realize excellent productivity and low cost.

(3) Since the diffusion holes are formed in parallel with the solid electrolyte plate, invasion of dust and foreign matter into the diffusion holes is suppressed, and the characteristics can be stabilized and the reliability can be improved for a long time.

(4) Since the heating element is formed on the seal plate, the heat transfer to the solid electrolyte plate is fast and efficient, so that the warm-up time of the oxygen sensor can be shortened and the power consumption can be reduced.

(5) Further, since the input power for keeping the oxygen sensor at a constant temperature is smoothly controlled, the set temperature can be kept accurately and the oxygen concentration detection precision is improved.

[Brief description of drawings]

FIG. 1 (a) is an exploded perspective view of an oxygen sensor showing an embodiment of the present invention, and FIG. 1 (b) is a partially cutaway perspective view of the oxygen sensor.
FIG. 2 is a sectional view of a conventional oxygen sensor. 1 ... Solid electrolyte plate, 5 ... Helical spacer, 6 ... Seal plate, 7 ... Helical diffusion hole, 8 ... Heating element.

Claims (3)

[Claims] 1. A solid electrolyte plate having oxygen ion conductivity, electrode films formed on both surfaces of the solid electrolyte plate, and one end of the electrode film surrounding a starting end and a terminating end spaced from each other on the solid electrolyte plate. A spiral spacer arranged so as to have, a seal plate arranged on the spiral spacer so as to face the solid electrolyte plate, partition walls facing each other of the spiral spacer, and the solid electrolyte plate. An oxygen sensor comprising a spiral diffusion hole surrounded by the seal plate and a heating element formed on one surface of the seal plate. 2. A heating element comprising a printed film of at least one of platinum, tungsten and molybdenum.
The oxygen sensor according to the item. 3. The oxygen sensor according to claim 1, wherein the heating element is made of metal adhered with an electric insulator.