Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1996-03-21
1997-12-30
Tung, T.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204425, 204429, G01N 27407
Patent
active
057025800
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a measuring sensor for determining the oxygen content in gas mixtures, in particular in exhaust gasses of internal combustion engines.
2. Background of the Related Art
Measuring sensors of this generic type are known. For example, DE-A1-36 32 456 discloses a probe for regulating the fuel-air mixture for internal combustion engines. This has a first pump cell with two porous electrodes, which are disposed on opposite sides of a first plate made of an oxygen ion conducting solid electrolyte, as well as a second pump cell which likewise has two porous electrodes, which in turn are disposed on opposite sides of a second plate made of an oxygen ion conducting solid electrolyte. Each porous electrode of the two pump cells contacts a gas chamber which is disposed between the pump cells and for its part communicates with the internal combustion engine exhaust gas to be measured via a conduit which functions as a diffusion limiting element. One of the porous electrodes of the first pump cell, namely the electrode which is not connected with the gas chamber, is simultaneously used as an internal standard oxygen reference. This electrode is connected via a leakage throttle element to the other electrode of the first pump cell, which communicates with the gas chamber. This disposition produces a measuring probe and reference probe which are each embodied as a pump cell.
By means of a measuring sensor of this kind, the composition of the exhaust gas of the internal combustion engine can be evaluated as to whether, in the fuel-air mixture with which the internal combustion engine is operated, fuel or oxygen are present in a stoichiometric surplus or whether the fuel and the air correspond to the stoichiometry. This is possible since the composition of the fuel-air mixture determines the composition of the exhaust gas in a known manner. In the so-called rich range--when there is a stoichiometric surplus of fuel--considerable quantities of unspent or partially burned fuel are found in the exhaust gas, while the oxygen component is relatively low. In the so-called lean range--when there is a stoichiometric preponderance of oxygen--the oxygen content in the exhaust gas is correspondingly high. In a stoichiometric composition of the fuel-air mixture, both fuel and oxygen are minimized in the exhaust gas. A common measure for the fuel-air ratio is the so-called lambda value measured in the exhaust gas, which is >1 in the lean range, <1 in the rich range and =1 in the exactly stoichiometric range. The lambda value can be determined by means of the measuring sensor mentioned at the beginning so that it is possible to control the fuel-air mixture for the internal combustion engine via an evaluation circuit connected to the measuring sensor.
The previous patent application DE 43 32 487 discloses a measuring sensor for determining the oxygen content of gas mixtures, in which a measuring probe and a reference probe are each embodied as a pump cell with a common electrode and are disposed in layers on a common substrate. The electrodes of the two pump cells are mutually enclosed by a solid electrolyte.
The known measuring sensors have in common that on the one hand, they are exposed to a high temperature exhaust gas of internal combustion engines, and on the other hand, require a minimum operating temperature for their use so that they often have an additional heat source. In this case, it is disadvantageous that, because of different heat expansion coefficients of the materials used, thermal stress occurs in the measuring sensors, which can lead to damage or destruction of the measuring sensor.
SUMMARY OF THE INVENTION
In contrast thereto, the measuring sensor according to the invention with the features mentioned in claim 1, has the advantage of having an improved thermal stress capability. Since the measuring probe and the reference probe are embedded separately in a common base substrate and the solid electrolytes are embodied by solid elect
REFERENCES:
patent: 4250010 (1981-02-01), Kondo et al.
patent: 4724061 (1988-02-01), Nyberg
patent: 4765880 (1988-08-01), Hayakawa et al.
patent: 4810350 (1989-03-01), Mantese et al.
De La Prieta Claudio
Dietz Hermann
Eisele Ulrich
Gruenwald Werner
Lindemann Gert
Robert & Bosch GmbH
Tung T.
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