JPH02222832A - Oxygen concentration sensor - Google Patents

Abstract

PURPOSE:To enable the formation of the same electrode layer with a uniform thickness and width by forming a reference gas side electrode layer within a long groove arranged from an internal tip of a ceramic tube to an internal rear end by a drip coating. CONSTITUTION:A ceramic tube has a cavity 1a formed inside. An electrode 2 on the side of a gas to be measured is attached with a fixed width on an external surface of the ceramic tube 1 and furthermore, a coating of a substance having a catalytic nature such as platinum and porous ceramic is applied on the surfaces of the electrode 2 on the side of the gas to be measured and the ceramic tube 1. A groove 15 is provided from the internal tip to internal rear end of the ceramic tube 1. Then, a specified electrode material is guided to the groove 15 with a drip coating to form a reference gas side electrode layer 3 with a uniform width and thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to oxygen concentration sensors, and more particularly to sensors of the type installed in motor vehicles and used to measure oxygen concentration in exhaust gas.

BACKGROUND OF THE INVENTION Oxygen concentration sensors of this type generally have a test tube-like ceramic tube with one end closed and electrode layers provided on the inner and outer surfaces. Typically, the outer surface of the ceramic tube is placed in the exhaust pipe so that it is exposed to exhaust gas, and a voltage is generated between the outer surface and inner electrodes depending on the difference in oxygen partial pressure between the exhaust gas and the outside air. This voltage is detected by appropriate means and processed as a parameter for feedback control of the air-fuel ratio.

Conventional examples of such oxygen concentration sensors and ceramic tubes will be explained in detail with reference to FIGS. 1 to 3.

In Figures 1 and 2 (a) and (b), the shape of the ceramic tube 1 used in the oxygen concentration sensor is approximately 250 mm.
It has a test tube shape with one end closed and made of zirconium oxide which exhibits electrolytic properties at temperatures above ℃. The ceramic tube 1 has a cavity 1a formed inside.

A gas-to-be-measured electrode 2 of a certain width is attached to the outer surface of the ceramic tube 1, and a material exhibiting catalytic properties such as platinum and a porous material are attached to the surfaces of the gas-to-be-measured electrode 2 and the ceramic tube 1. Coated with ceramic. On the other hand, on the inner surface of the ceramic tube 1 there is a constant gas side electrode 2
A reference gas side electrode 3 made of the same kind of material is attached. The rear end of the ceramic tube 1 is fitted into a holder 4, and the holder 4 is fixed to the side surface of the exhaust pipe 5.

Further, as shown in FIG. 3, the holder 4 is attached to one end of a coaxially extending cylindrical metal tube 6.
A substantially cylindrical insulating insulator 7 is arranged inside.

The rear end opening of the ceramic tube 1 fitted inside the holder 4 is pressed against the ceramic tube 1 by one end of an insulating insulator 7 via a plate 8. A louver 1 having a hole 9 is provided at the tip of the ceramic tube 1 located inside the exhaust pipe 5.
0 is engaged, and the exhaust gas comes into contact with the outer surface of the ceramic tube 1 through the hole 9 of the louver 10.

On the other hand, the other end of the insulating insulator 7 is urged toward the ceramic tube 1 by an airtight rubber 11 and a disc spring 12 provided at the other end of the metal cylinder 6.

Further, a through hole 7a is formed inside the insulating insulator 7, and a lead wire 14 is connected to a terminal 13 made of soft metal such as stainless steel.
is connected.

In the oxygen concentration sensor having the above configuration, the ceramic tube 1
Due to the existence of a cavity (not shown) provided between the airtight rubber 11 and the lead wire 14, the air inside is communicated with the outside air via the through hole 7a inside the insulating insulator 7 and the plate 8. The oxygen partial pressure of the air inside the ceramic tube 1 is always kept equal to the outside air.

On the other hand, a potential difference is generated between the outer surface of the ceramic tube 1 that is in contact with the exhaust gas and the inner surface that is in contact with the outside air, depending on the difference in the partial pressure of oxygen in the exhaust gas and the outside air, between the inner surface and the outer surface electrode.

In the manufacturing process of the oxygen concentration sensor with such a configuration,
Although the base gas side electrode layer is provided by drop coating from the tip of the inner surface to the rear end of the inner surface, there is a problem in that it is actually quite difficult to apply the drop coat uniformly.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an oxygen concentration sensor in which the width and thickness of a reference gas side electrode layer provided on the inner surface of a ceramic tube can be easily provided by drop coating.

In the oxygen concentration sensor according to the present invention, a longitudinal groove is provided from the tip of the inner surface to the rear end of the inner surface of the ceramic tube, and the reference gas side electrode layer is provided within the longitudinal groove by drop coating.

EXAMPLE Hereinafter, an example of the oxygen concentration sensor according to the present invention will be described in detail with reference to FIG. 4 and FIGS. 5(a) and 5(b).

As shown in FIG. 4, in the ceramic tube 1 of the oxygen concentration sensor according to the present invention, a longitudinal groove 15 is provided from the tip of the inner surface of the ceramic tube 1 to the rear end of the inner surface.
A reference gas side electrode layer is provided within 5 by drop coating,
Other than this point, the configuration is completely the same as the conventional example.

In manufacturing the oxygen concentration sensor having the above configuration, a groove 1 is formed from the tip of the inner surface of the ceramic tube 1 to the rear end of the inner surface.
5 is provided, and a predetermined electrode material is applied dropwise to the groove 15 to guide the reference gas side electrode layer 3 having a uniform width and thickness. The operation of the oxygen concentration sensor of the present invention is completely the same as that of the conventional example.

Effects of the Invention From the above, it is clear that in the manufacturing process of the oxygen concentration sensor according to the present invention, the reference gas side electrode layer is formed by applying molten metal dropwise into a groove previously provided on the inner surface of the ceramic tube. As a result, a uniform thickness and width can be formed, so there is no wastage of material and workability can be facilitated.

[Brief explanation of the drawings] Figure 1 is an axial cross-sectional view of a conventional ceramic tube, Figure 2 (a)
2(b) is a sectional view perpendicular to the axial direction of the ceramic tube, FIG. 3 is an axial sectional view of the oxygen concentration sensor, and FIG. 4 is an axial sectional view of the ceramic tube according to the present invention. Figure 5(a) is a front view of the same ceramic tube, Figure 5(a) is a front view of the same ceramic tube.
Figure (b) is a sectional view perpendicular to the axial direction of the ceramic tube. Explanation of symbols of main parts 1... Ceramic tube 2... Measured gas side electrode 3... Reference gas side electrode 4... Holder 7... ... Insulating insulator 6 ... Metal tube 15 ... Longitudinal groove Applicant: Japan Electronics Co., Ltd.

Claims (1)

[Claims] A ceramic tube formed in the shape of a test tube and fixed to be exposed in an exhaust passage of an internal combustion engine; a gas-side electrode layer provided from an outer end of the ceramic tube to a rear end of the outer surface; and a reference gas side electrode layer provided from an inner surface tip to an inner surface rear end, a groove is provided on the inner surface of the ceramic tube, and the reference gas side electrode layer is provided in the groove by drop coating. An oxygen concentration sensor featuring: