JPH0617071Y2 - Oxygen sensor for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an oxygen sensor for an internal combustion engine, and more particularly, to a close relationship with an air-fuel ratio of an air-fuel mixture supplied to the exhaust pipe of the internal combustion engine. The present invention relates to an oxygen sensor used for measuring the oxygen concentration in a certain exhaust gas and providing a feedback signal in air-fuel ratio feedback control.

<Prior Art> Conventionally, this type of oxygen sensor has been manufactured using zirconium oxide (ZrO 2).
_The atmosphere is introduced as a reference gas inside the zirconia tube containing ₂ ) as the main component, while the outside is exposed to the engine exhaust passage and is in contact with the exhaust gas that is the gas to be measured, and is formed on the inner and outer surfaces of the zirconia tube. The oxygen concentration in the exhaust gas is measured by generating an electromotive force according to the ratio between the oxygen concentration in the atmosphere and the oxygen concentration in the exhaust gas between the electrodes. For example, the one shown in FIG. Yes (Actual Kaisho 5
9-17854, etc.).

Explaining this, the base end of the zirconia tube 2 is locked to the tip of the holder 1 attached to the exhaust pipe wall E of the engine, and the closed tip of the zirconia tube 2 is protected by the protector 3 with the slit 3a. It is covered. An inner electrode is formed on a part of the inner surface of the zirconia tube 2 by a platinum paste or the like so as to extend over the base end surface, and an outer electrode is formed on the outer surface by a platinum paste or the like. A contact plate 4 is in contact with the base end surface of the tube 2. The contact plate 4 is pressed by the tip end surface of a cylindrical isolation bush 5, and the isolation bush 5 is held by the holder 1.
The cover 6 is fixed by caulking via the disc spring 7. Then, a lead wire 9 is caulked and fixed to a terminal 8 that extends into the isolation bush 5 in a continuous manner with the contact plate 4, and the lead wire 9 is mounted in a hole at the base end portion of the isolation bush 5 and is covered by the cover 6. The rubber tube 10 is fixed by caulking and led out to the outside.

<Problems to be Solved by the Invention> By the way, in such a conventional oxygen sensor, since the engine exhaust gas flows in and out through the slit 3a formed in the protector 3, a gap space between the protector 3 and the zirconia tube 2 is formed. In some cases, the exhaust gas stagnates in the outer peripheral space of the zirconia tube 2 closer to the base end than the portion where the slit 3a cannot be exposed, particularly the portion where the slit 3a is provided, without being properly exchanged.

When the exhaust gas stagnates in a specific space in this manner, the hydrocarbon HC or the like contained in the exhaust gas fills the space, and the hydrocarbon HC and the catalyst layer (platinum deposition layer of platinum) covering the outer surface of the zirconia tube 2 are formed. Since carbon is deposited by the reaction, the protective layer covering the catalyst layer (formed by spraying a metal oxide such as magnesium spinel) is pushed up by the carbon, and peeling of the protective layer may occur. .

The present invention has been made in view of the above problems, and an object of the present invention is to prevent exhaust from stagnating in a specific space in a protector and prevent peeling of a protective layer.

<Means for Solving Problems> Therefore, in the present invention, an exhaust shielding member is provided to prevent exhaust gas from entering the zirconia tube outer peripheral space on the base end side of the protector opening further than the vicinity of the base end side edge of the zirconia tube. I did it.

<Operation> As a result, the invasion of the exhaust gas to the base end side of the zirconia tube, which has not been conventionally performed favorably, is prevented,
The engine exhaust does not stagnate in the specific space, and peeling of the protective layer due to carbon deposition can be avoided.

<Embodiment> An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The same elements as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

Along with the protector 3 caulked and fixed to the holder 1, a sub protector 12 as an exhaust shielding member is caulked and fixed to the holder 1. The sub protector 12 is made of a heat-resistant metal material such as stainless steel, and has a flange portion 12a that is caulked and fixed to the holder 1, and has the flange portion 12a at one end and is larger than the outer diameter of the zirconia tube 2. It is composed of a tubular portion 12b formed to have an inner diameter, and a fitting portion 12c that is squeezed inward at the other end of the tubular portion 12b to fit the zirconia tube 2 and the outer peripheral surface. Here, the fitting portion 12c
Is a slit 3a (opening) formed in the protector 3.
The zirconia tube 2 is fitted to the zirconia tube 2 on a plane substantially the same as the plane connecting the edges on the base end side of the zirconia tube 2.

By providing such a sub protector 12, the exhaust gas introduced into the protector 3 through the slit 3a does not enter the outer peripheral space of the zirconia tube 2 on the base end side of the fitting portion 12c. That is, the sub protector 12
Without the provision of exhaust gas, the exhaust gas sometimes stagnates in the outer peripheral space of the zirconia tube 2 which is closer to the base end side than the end edge of the slit 3a without being properly exchanged. This is to prevent the exhaust and eliminate the space where exhaust stagnates. Therefore, according to the present embodiment, the hydrocarbon HC and the like do not fill the base end side of the zirconia tube 2, carbon deposition is prevented in advance, and peeling of the protective layer can be avoided.

It is obvious that the shape of the sub protector 12 for preventing the invasion of exhaust gas is not limited to this embodiment.

<Effects of the Invention> As described above, according to the present invention, it is possible to prevent the exhaust from stagnating at the base end side of the zirconia tube, and thus prevent the deposition of carbon due to the hydrocarbon HC in the exhaust being filled. Then, there is an effect that peeling of the protective layer can be avoided.

[Brief description of drawings]

FIG. 1 is a sectional view showing an essential part of an embodiment of the present invention, FIG. 2 is a perspective view showing a sub protector as an exhaust shielding member in the same embodiment, and FIG. 3 is an overall sectional view of a conventional oxygen sensor. is there. 2 ... Zirconia tube, 3 ... Protector 3a ... Slit, 12 ... Sub protector

Claims (1)

[Scope of utility model registration request] 1. An electromotive force generated between an electrode on the outer surface brought into contact with engine exhaust and an electrode on the inner surface brought into contact with the atmosphere by coating an electrode on the inner and outer surfaces of a zirconia tube whose tip is closed. By the oxygen sensor for an internal combustion engine for detecting the oxygen concentration in the engine exhaust by, the oxygen sensor for an internal combustion engine, wherein the zirconia tube is covered with a protector having a plurality of openings, the zirconia tube base end of the protector opening An oxygen sensor for an internal combustion engine, comprising an exhaust shielding member for preventing exhaust gas from entering an outer peripheral space of the zirconia tube further on the base end side than near the side edge.