JPS6038661B2 - oxygen concentration detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The main object of the present invention is to make it possible to improve the performance and reliability of an oxygen concentration detector.

In conventional oxygen concentration detectors, for example, a thin platinum film is coated on the atmosphere side and exhaust gas side by chemical plating, vapor deposition, thermal decomposition, etc. as an electrode of an oxygen concentration detection element made of a tubular zirconia solid electrolyte. (Pt) electrodes are provided.

In conventional detectors, the thin film platinum electrode obtained by various methods is used as the electrode.
Thin film platinum produced by thermal decomposition methods such as tCSOb and LO) has superior durability compared to other methods.

As the thermal decomposition conditions, for example, platinum was produced in a reducing atmosphere or an oxidizing atmosphere. However, the oxygen concentration detector has a problem in that its response is particularly slow and its basic characteristics are insufficient.

In addition, in the durability test, when exposed to high-temperature exhaust gas for a long time, there was a tendency for the response to become faster, but the characteristics were not sufficient. Therefore, in order to solve this problem, we investigated the cause of the improvement in characteristics in this durability test and found that the platinum electrode on the exhaust gas side was activated by the exhaust gas atmosphere. This activation of the electrode surface can be achieved by mechanical treatment, such as roughening the surface and increasing the number of three-phase interfaces, and it is possible to obtain sufficient basic characteristics.

However, due to surface assembling, minute cracks are formed on the surface of the oxygen concentration detection element, resulting in insufficient mechanical strength, and durability such as damage to the oxygen concentration detection element when used for a long time in a place subject to vibration. It has some drawbacks.

In view of the above points, the present invention has a configuration in which a platinum electrode formed in an oxygen concentration detection element includes a platinum thin film electrode obtained by producing a platinum electrode by a pyrolysis method in an excess fuel atmosphere of a gasoline combustion flame. The purpose is to provide an oxygen concentration detector with good basic characteristics and durability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention shown in the drawings will be described.

FIG. 1 is a sectional view of the oxygen concentration detector.

The tubular zirconia solid electrolyte 1 has a thin film platinum electrode 2 on the atmosphere side.
and a thin film platinum electrode 3 on the exhaust gas side. One of the present examples is that the materials used for electrodes 2 and 3, chloroplatinic acid (PtC 6, base LO), and anhydrous ethyl alcohol are mixed with a specific gravity of 1
．． The electrodes 2 and 3 were simultaneously immersed in a dip using a liquid mixed so as to have a concentration of 0 to 1.5. After drying this oxygen concentration detection element in air for 3 minutes at 250 oo, the atmospheric conditions include a gasoline combustion flame of 550 qo to 1100°C, an excess air ratio of 0.8 to 0.9, and a CO concentration of approximately 3 to 1%. By heating in the range of 20 to 60 minutes, chloroplatinic acid is decomposed into platinum. After this decomposition, the conductivity of each electrode surface is measured and the dipping and drying process of the electrode solution is repeated until the resistance value is in the range of 0 to 200Q.The platinum electrodes 2 and 3 are thereby formed. The surface state of the thin film platinum electrode produced in this process is now active as a detector for measuring oxygen concentration in exhaust gas, and its basic characteristics and durability are superior to those obtained by conventional thermal decomposition methods. Comparing the performance of the device, it shows extremely excellent characteristics as shown in Figure 2 (A is the typical characteristic of the conventional one, B is the characteristic based on the example of the present invention), and shows extremely excellent durability characteristics. It is a great thing.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an oxygen concentration detector according to an embodiment of the present invention, and FIG. 2 is a comparison diagram of the durability characteristics of an embodiment of the present invention and a typical conventional oxygen concentration detector. 1... Zirconia solid electrolyte 2... Thin film platinum electrode on the atmosphere side, 3... Thin film platinum electrode on the exhaust gas side. Fig. 1 Fig. 2

Claims (1)

[Claims] 1 Opposed electrodes are formed at each interface between the exhaust gas of an internal combustion engine made of a zirconia solid electrolyte and the atmosphere, and a catalyst electrode made of porous platinum is provided on the exhaust gas surface to adjust the oxygen concentration in the exhaust gas to the atmospheric oxygen. In an oxygen concentration detector that detects the air-fuel ratio in exhaust gas by comparing it with the concentration, the electrodes on the inner and outer surfaces of the zirconia solid electrolyte are composed of thin film platinum electrodes produced by thermal decomposition in the fuel-excess atmosphere of a gasoline combustion flame. An oxygen concentration detector featuring: