Measuring and testing – Gas analysis – Gas of combustion
Patent
1996-08-08
1997-11-11
Dombroske, George M.
Measuring and testing
Gas analysis
Gas of combustion
73 2331, 73 3105, 73116, 60276, G01N 27416, G01N 27419
Patent
active
056866542
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, particularly in exhaust gases of internal combustion engines, of the generic type of the main claim. namely, one having a first electrochemical pump cell and a second electrochemical pump cell, having an internal reference gas source and a measuring gas chamber which is connected to the gas mixture, having electrodes for the first and the second pump cell, and having a first pumping voltage for the first pump cell and a second pumping voltage for the second pump cell, with oxygen being pumped into the reference gas source by means of the first pumping voltage and the second pumping voltage driving a pumping current, which is measured as a measure for the partial oxygen pressure. A measuring sensor of the generic type is known from DE 36 32 456 C2, wherein, instead of atmospheric air as comparison gas or reference gas, oxygen is pumped from the gas mixture to be measured into an internal reference gas source. For this purpose, a first pump cell and a second pump cell, each having two electrodes, and a gas chamber are provided, with respectively one electrode of the first and second pump cell being arranged in the gas chamber and the gas chamber being connected with the gas mixture via a diffusion barrier. The second electrode of the first pump cell is connected with the internal reference gas source. The second electrode of the second pump cell is exposed to the gas mixture. With the first pump cell, oxygen is constantly pumped under the action of a pumping current from the measuring gas chamber into the internal reference gas source. The second pump cell is operated by means of a bidirectional control such that an approximately constant partial oxygen pressure is generated in the measuring gas chamber by pumping oxygen in or out. The pumping voltage of the second pump cell is compared to a constant reference voltage. The pumping current is controlled bidirectionally by way of the voltage difference. The pumping current itself serves as measure for the oxygen content in the gas mixture.
SUMMARY OF THE INVENTION
The measuring sensor having the characterizing features of the main claim, namely, characterized in that the first pumping voltage (U.sub.P1) and the second pumping voltage (U.sub.P2) are set such that by way of the first pumping voltage (U.sub.P1) more oxygen is pumped into the reference gas source than is pumped out of the reference gas source by second pumping voltage (U.sub.P2), which has the advantage that it can operate without a bidirectional control of the pumping current, which means that the evaluation electronics can be simplified.
Advantageous modifications of the sensor according to the invention are possible by means of the measures listed in the dependent claims. The first pump cell may be acted upon by a first operating voltage (U.sub.B1) and the second pump cell may be acted upon by a second operating voltage (U.sub.B2) so that, under the action of the corresponding Nernst voltages, the first pumping voltage (U.sub.P1) is always larger than the second pumping voltage (U.sub.P2) at a polarity which is reversed compared to the first pumping voltage (U.sub.P1).
The operating voltage (U.sub.B1) of the first pump cell (10) may be dimensioned according to the condition U.sub.B1 >2U.sub.Nf -U.sub.B2, with U.sub.Nf =Nernst voltage is the rich gas mixture. The second operating voltage (U.sub.B2) advantageously has the value of the Nernst voltage at .lambda.=1, preferably 450 mV.
An electrode of the first pump cell and an electrode of the second pump cell may be arranged in the reference gas source. The electrode of the first pump cell and of the second pump cell may be arranged in the reference gas source and may be joined to form one electrode. The one electrode of the second pump cell may be arranged in the measuring gas chamber and the measuring gas chamber may be connected to the gas mixture via a diffusion barrier. The reference gas
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Friese Karl-Hermann
Gruenwald Werner
Dombroske George M.
Robert & Bosch GmbH
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