Electro-chemical measuring sensor with a potential-free sensor e

Details Electro-chemical measuring sensor with a potential-free sensor e Electro-chemical measuring sensor with a potential-free sensor e

1996-01-25

1997-09-23

Bell, Bruce F.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

G01N 2726

Patent

active

056700326

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This application is a 371 of PCT/DE94/00791 filed Jul. 9, 1994.
The invention is based on an electro-chemical measuring sensor for determining the oxygen content of gases, in particular for determining the oxygen content of exhaust gases of internal combustion engines, including a potential-free arranged sensor element having an oxygen-ions-conducting solid electrolyte body, preferably in the form of a pipe closed at one end, and electrodes with electrically conducting connectors, with the sensor element being inserted with a sealing ring into a metal housing and with at least one electrically conducting connector facing the housing being electrically insulated with respect to the housing by an electrically insulating layer in the area of the sealing ring. Electro-chemical measuring sensors are embodied, for example, in the so-called finger construction, wherein a solid electrolyte body is sealingly fixed as a closed pipe in a metal housing. Among the finger sensors, a differentiation is made between potential-free and potential-bound measuring sensors. With potential-bound measuring sensors, the trace of the exterior electrode is brought into contact with the housing by means of an electrically conducting sealing ring. With potential-free measuring sensors, each electrode connection is directly supplied to a control device, so that no electric contact with the housing is permitted. In both cases a seal between the solid electrolyte body and the housing must be realized.
A potential-free measuring sensor is known from DE-OS 25 04 206, wherein a plurality of electrically insulating, ceramic seal rings made of sintered corundum with >90% Al.sub.2 O.sub.3 are employed, and which provide a hermetically sealed, electrically insulating connection between the solid electrolyte body and the metal housing. Such a seal is structurally very elaborate and also relatively prone to risks because of the multiple parallel seal with three sealing rings.
It is furthermore already known from DE-OS 26 19 746 to cover the trace on the solid electrolyte body with glazing, in particular in the areas of lower temperature.


SUMMARY AND ADVANTAGES OF THE INVENTION

In contrast to the known electro-chemical measuring sensors for determining the oxygen content of gases, the measuring sensor in accordance with the invention includes a potential-free arranged sensor element having an oxygen-ions-conducting solid electrolyte body, preferably in the form of a pipe closed at one end, and electrodes with electrically conducting connectors, with the sensor element being inserted with a sealing ring into a metal housing, with at least one electrically conducting connector facing the housing being electrically insulated with respect to the housing by an electrically insulating layer in the area of the sealing ring, and with the insulating layer being formed of a mixture of a crystalline, non-metallic material and a glass-forming material such that a glaze filled with the crystalline, non-metallic material is formed by heating. This sensor according to the invention has the advantage that sealing elements which are electrically conducting can be used for sealing the sensor element in the housing, for example a metal sealing ring or a graphite sealing ring or graphite package. By employing these compact seals, exhaust gas, water and/or fuel are prevented from reaching the interior of the sensor element. The insulating layer has a great mechanical sturdiness in respect to pressure peaks which are created by the sealing ring in the course of the joining process. The method of the invention has the advantage that it can be integrated into the manufacturing process of sensor elements. The application processes of the insulating layer are possible by means of proven technology, for example, rolling on, spraying a suspension, flame spraying, plasma spraying, printing or the like.
Advantageous further developments and improvements of the measuring sensor in accordance with the invention, and of the method of the invent

REFERENCES:
patent: 4383906 (1983-05-01), Sano et al.
patent: 4569748 (1986-02-01), Yamekawa et al.

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