Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Patent
1997-03-24
1998-12-15
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
204425, 204426, 205784, G01N 2741
Patent
active
058491759
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
Measuring sensors for determining an oxygen concentration in gas mixtures, particularly in exhaust gases of internal combustion engines, are known. Such measuring sensors serve to adjust the setting of a fuel-air mixture for operating the internal combustion engine via the determination of the oxygen concentration in the exhaust gas. The fuel-air mixture may be in the so-called rich range, that is, the fuel is available in the stoichiometric surplus, which means that the exhaust gas only contains a small amount of oxygen compared to other partially unburnt constituents. In the so-called lean range, in which the oxygen of the air is predominant in the fuel-air mixture, the exhaust gas has a correspondingly high oxygen concentration. In a stoichiometric composition of the fuel-air mixture, both the fuel and the oxygen in the exhaust gas are reduced.
For determining the oxygen concentration in the exhaust gas, so-called .lambda. probes are known which detect a .lambda. value greater than 1 in the lean range, a .lambda. value smaller than 1 in the rich range and a .lambda. value equal to 1 in the stoichiometric range. In this process, the .lambda. probe supplies a detector voltage in a known manner, which voltage is fed to a circuit arrangement. With the assistance of the circuit arrangement, the detector voltage in known measuring sensors is transferred into a pump voltage for a measuring probe, which measuring probe is also a component of the measuring sensor and is exposed to the exhaust gas. Here, the measuring probe operates as a pump cell for which oxygen ions are pumped from a first to a second electrode of the measuring probe or vice versa, depending on the prevailing oxygen concentration in the gas mixture to be measured. Depending on whether the .lambda. probe detects a rich range, i. e., a .lambda. value smaller than 1, or a lean range, i. e., a .lambda. value greater than 1, it is determined via the circuit arrangement whether an electrode of the measuring probe connected to an active input of the circuit arrangement is connected as a cathode or an anode. The second electrode of the measuring probe is applied to ground so that either an anodic limiting current, in case of a rich measuring gas, or a cathodic limiting current, in case of a lean measuring gas, appears at the measuring probe. In case of stoichiometric operation, i. e., when the .lambda. value is equal to 1, the pump voltage is close to 0 so that there is no flow of limiting current.
The drawback of the known circuit arrangements is that, for generating the positive or negative pump voltage, a current reversing circuit must be provided which can be actuated via the detector voltage supplied by the reference probe. A measuring sensor of this type is known, for example, from German Patent 35 15 588.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method for actuating a measuring sensor for determining an oxygen concentration in a gas mixture, particularly in exhaust gases of internal combustion engines, wherein a detector voltage corresponding to the oxygen concentration and supplied by a reference probe is transferred into a pump voltage for a measuring probe by a circuit arrangement, wherein the curve of the detector voltage is used directly for determining the curve of the pump voltage, wherein a fixed voltage is added to the detector voltage to form a voltage value which effects a shift of the detector voltage such that a stepping or transition point of the detector voltage is close to the zero point, and wherein the voltage value is amplified, and is used as the pump voltage.
According to a further aspect of the invention, there is provided a circuit arrangement for actuating a measuring sensor for determining an oxygen concentration in a gas mixture, particularly in the exhaust gas of internal combustion engines, with the circuit arrangement having a first input connected to a first electrode of a reference probe, a second input connected to a first electrode of a measu
REFERENCES:
patent: 4601793 (1986-07-01), Asayama et al.
patent: 4891122 (1990-01-01), Danno et al.
Dietz Hermann
Gruenwald Werner
Robert & Bosch GmbH
Tung T.
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