JPH0247546A - Oxygen sensor of internal combustion engine - Google Patents

Abstract

PURPOSE:To avoid the damage of an electrode by a construction wherein a protective layer formed of porous gamma-alumina is provided on the exhaust side and a decomposing-absorbing layer formed of silicon dioxide containing a catalyst for decomposing a silicon compound is provided under said layer. CONSTITUTION:Platinum electrodes 2 and 3 are formed on the inner and outer surfaces of a solid electrolyte 1 for a concentration cell whose fore end part is blocked and which is cylindrical and oxygen-ion-conductive, and platinum is evaporated on the outside to form an oxidation catalyst layer 4. Moreover, a decomposing-adsorbing layer 6 formed of silicon dioxide containing platinum, rhodium or palladium of 0.3 to 5% as a catalyst for decomposing a silicon compound is formed on the layer 4, and the outside of the layer 6 is covered with a protective layer 7 formed of porous gamma-alumina. The protective layer 7 has high porosity and therefore clogging due to the silicon compound in an exhaust hardly occurs. The decomposing-adsorbing layer 6 decomposes the silicon compound into silicon and absorbs it, and therefore the damage of the platinum electrode 3 can be avoided.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is installed in the exhaust system of an internal combustion engine, and measures the air-fuel ratio of the engine intake air-fuel mixture, which is closely related to the exhaust gas via the oxygen concentration in the exhaust. This invention relates to an oxygen sensor for detecting oxygen.

<Prior art> Conventionally, as this type of oxygen sensor, there is one having a sensor part structure as shown in FIG.
(Refer to Publication No.-89160, etc.).

To explain what is shown in FIG. 2, platinum electrodes 2.3 are formed on each part of the inner and outer surfaces of an oxygen ion conductive solid electrolyte 1 for concentration batteries, which is represented by cylindrical zirconium oxide with a closed tip. Then, platinum is deposited on the outside to form an oxidation catalyst layer 4, and magnesium spinel is further thermally sprayed on top of the oxidation catalyst layer 4 to form a protective layer 5.

Here, while the atmosphere is guided inside the solid electrolyte 1 as reference air, the outside of the solid electrolyte 1 is brought into contact with the exhaust gas by facing the engine exhaust passage, and the oxygen concentration in the atmosphere that comes into contact with the inner surface is adjusted. The oxygen concentration in the exhaust gas is detected by generating a voltage between the platinum electrodes 2 and 3 that corresponds to the ratio of the oxygen concentration in the exhaust gas that contacts the outer surface.

<Problems to be Solved by the Invention> However, in such conventional oxygen sensors, silicon compounds (e.g. dimethyl silicon) contained in the exhaust gas adhere to the protective layer of magnesium spinel and cause clogging. There are problems in that the response is deteriorated, the platinum electrode is poisoned, and as shown in FIG. 3, the electromotive force increases as indicated by the broken line on the lean side, resulting in a deterioration in detection accuracy.

In addition, this phenomenon often occurs when gasoline mixed with alcohol (mainly methanol) is used as fuel. This is because the methanol in the fuel dissolves the silicon contained in the piping coating and packing. it is conceivable that.

SUMMARY OF THE INVENTION In view of these conventional problems, an object of the present invention is to provide an oxygen sensor in which the protective layer is not clogged and the electrodes are not poisoned.

Means for Solving the Problems> In order to achieve the above object, the present invention provides an oxygen sensor in which electrodes are formed on both sides of a solid electrolyte for a concentration battery having oxygen ion conductivity, in which the exhaust gas of the solid electrolyte is An oxidation catalyst layer made of platinum is formed on the side surface, a decomposition adsorption layer made of silicon dioxide containing a catalyst for decomposing silicon compounds is formed on the outside thereof, and a protective layer made of porous γ-alumina is further formed on the outside thereof. The configuration includes the following.

<Function> In the above structure, the protective layer is formed of porous T-alumina to prevent clogging even if silicon compounds adhere to it, while the inside thereof contains a catalyst for decomposing silicon compounds. By providing a decomposition/adsorption layer made of silicon dioxide, the silicon decomposed by the silicon compound decomposition catalyst can be selectively adsorbed by the silicon dioxide, thereby making it possible to avoid poisoning of the electrode.

<Example> An embodiment of the present invention will be described below with reference to FIG.

Incidentally, the same parts as in the prior art are given the same reference numerals.

Platinum electrodes 2.3 are formed on each part of the inner and outer surfaces of an oxygen ion conductive solid electrolyte 1 for a concentration battery, typically made of cylindrical zirconium oxide with its tip closed, and platinum is deposited on the outside. An oxidation catalyst layer 4 is formed, and a decomposition adsorption layer 6 made of silicon dioxide containing 0.3 to 5% of platinum, rhodium or palladium as a catalyst for decomposing a silicon compound is further formed as a structure according to the present invention on top of the oxidation catalyst layer 4. The outside thereof is covered with a protective layer 7 made of porous T-alumina.

Here, the protective layer 7 made of porous γ-alumina has a porosity of porous T-alumina of 0.5 cc/g or more and a specific surface area of 100 m"7g or more, and is different from the conventional protective layer of magbusium. Since the porosity is much higher than that of spinel, which is 0.03 cc/g, clogging is unlikely to occur even if silicon compounds in the exhaust gas adhere to it.In addition, the decomposition and adsorption layer 6 below it is made of platinum, rhodium or Silicon compounds are decomposed into silicon by a palladium catalyst for decomposing silicon compounds, and silicon dioxide, which selectively adsorbs silicon, can adsorb silicon. Also, the silicon compound does not enter, and the platinum electrode 3 can be prevented from being poisoned.

This makes it possible to prevent deterioration of the oxygen sensor.

<Effects of the Invention> As explained above, according to the present invention, a protective layer made of porous T-alumina having a much higher porosity than conventional protective layers is formed on the exhaust side, thereby preventing clogging. A decomposition adsorption layer made of silicon dioxide containing a catalyst for decomposing silicon compounds is provided below the decomposition adsorption layer to cover the electrode, and the silicon compounds are decomposed.
It is possible to avoid poisoning of the electrode by adsorption.

Thereby, deterioration of the oxygen sensor can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional example, and FIG. 3 is a diagram showing electromotive force characteristics.

Claims (1)

[Claims] Electrodes are formed on both sides of a solid electrolyte for concentration batteries that has oxygen ion conductivity, and one side is placed on the reference air side, and the other side is placed in the engine exhaust gas to control the oxygen concentration in the exhaust gas. In an oxygen sensor for an internal combustion engine that detects the air-fuel ratio of an air-fuel mixture taken into the engine through An oxygen sensor for an internal combustion engine, characterized in that it has a decomposition and adsorption layer made of silicon dioxide contained therein, and further provided with a protective layer made of porous γ-alumina on the outside thereof.