Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1997-04-29
1998-12-08
Tung, T.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204426, 204428, 277192, 277193, 277227, G01N 27407
Patent
active
058463917
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention starts with a seal for a sensor element of a gas sensor according to the generic type in the Main claim. Such a seal is known from the DE-OS 43 18 789 where the sensor element is arranged in a longitudinal bore of a housing by means of two seal elements and an additional, deformable seal that is arranged between the seal elements. The two seal elements consist of magnesium-aluminum silicate (steatite). Rough-pressed metal powder or graphite is listed as material for the additional seal.
SUMMARY OF THE INVENTION
The inventive seal The present invention is a seal for a sensor element for a gas sensor, in particular for determining the oxygen content in exhaust gases of internal combustion engines, which seals the sensor element in a longitudinal bore of a metallic housing, characterized in that a sealing arrangement is provided, which comprises at least two seal elements, arranged one above the other, and that the one seal element is composed of boron nitride and the other seal element of steatite has the advantage that it is gas-tight as well as impermeable for liquids, in particular fuel, and additionally has a high temperature resistance.
Through the measures listed in the dependent claims, advantageous modifications of the seal described in the Main claim are possible. An easy handling of the seal during assembly is achieved if as sealing rings the steatite seal elements are inserted in the presintered condition and the boron nitride seal element is inserted in the hot-pressed condition and if these are deformed during the assembly through the effects of a force in such a way that the seal element material conforms to the sensor element, and the housing and the sensor element is thus kept gas-tight inside the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
Three embodiments of the invention are shown in the drawing and are explained in more detail in the following description.
FIG. 1 shows a cross section through a gas sensor with a sealing arrangement according to a first exemplary embodiment,
FIG. 2 the gas sensor with a sealing arrangement according to a second exemplary embodiment, and
FIG. 3 the gas sensor with a sealing arrangement according to a third exemplary embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The FIGS. 1, 2 and 3 show a gas sensor 10, for example an electrochemical oxygen sensor with a metallic housing 12, which has a thread 13 as fastening means for installation in a measuring gas tube that is not shown. The housing 12 has a longitudinal bore 15 with a shoulder-type ring surface 16. The shoulder-type ring surface holds, for example, a metallic seal ring 18, on which a molded ceramic part 21 rests on the measuring gas side. The molded ceramic part 21 on the measuring gas side has a continuous opening 22 on the measuring gas side that extends in the direction of the longitudinal bore 15.
Furthermore, a molded ceramic part 23 is also arranged on the connection side in the longitudinal bore 15, at a distance to the molded ceramic part 21 on the measuring gas side. The molded ceramic part 23 on the connection side has a centrally located, continuous opening 24 on the connection side that also extends in the direction of the longitudinal bore 15. The opening 22 on the measuring gas side of the molded ceramic part 21 on the measuring gas side and the connection-side opening 24 of the connection-side molded ceramic part 23 are aligned with each other. A platelike sensor element 27 with an end segment 28 on the measuring gas side and an end segment 29 on the connection side is located in the openings 22, 24.
The measuring gas side end segment 28 of the sensor element 27 projects from the housing 12 and is surrounded by a protective tube 31, which is attached to the housing 12. The protective tube 31 has intake and discharge openings 32 for the gas to be measured. The connection side end segment 29 has connection contacts 34 that also project from the housing 12. The connection contacts 34 are contacted with a contact plug with connecting
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Friese Karl-Hermann
Hans Anton
Weyl Helmut
Wiedenmann Hans-Martin
Robert & Bosch GmbH
Tung T.
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