Measuring sensor for determining the oxygen content of gas mixtures

#The present application claims the right of foreign priority with respect to Application No. P 43 33 232.3 filed in Germany on Sep. 30, 1993, the subject matter of which is incorporated herein by reference.

#1. Field of the Invention

#The invention relates to a measuring sensor having a pump cell reference for determining the oxygen content of gas mixtures, particularly the oxygen content of exhaust gases of internal combustion engines, in the lean, neutral and rich ranges. The invention further relates to use of the novel measuring sensor to control the oxygen content of the composition of the fuel-air mixture being supplied to an internal combustion engine.

#The invention is further described by the accompanying Figures in which:

#FIG. 1 shows a longitudinal section of an embodiment of a measuring sensor according to the invention, including a schematic representation of a control circuit;

#FIG. 2 shows a characteristic curve of such a measuring sensor, namely, the dependency of the lambda value on the pump flow I.sub.M in the measuring cell;

#The measuring sensors having pump cell reference according to the present invention are favorable with respect to production technology, display the desired high sensitivity when used for controlling the composition of the fuel-air mixture supplied to an internal combustion engine, and operate reliably over long periods of time. The pressure-equalization connection from the oxygen reference zone to the atmosphere contributes to this. It prevents reducing components from diffusing out of the gas mixture, such as exhaust gases of an internal combustion engine, into the oxygen reference zone. The danger of such diffusion is present because the oxygen partial pressure at the oxygen reference electrode cannot lead to a convection current in the pressure-equalization connection due to the low pump flow. The circuit arrangement is clearly simpler compared to the one disclosed in Federal Republic of Germany Published Application No. 3,632,456. In terms of production technology, the embodiment of measuring sensor according to the present invention, in which the heating means and oxygen reference cell are spatially and functionally combined, is particularly elegant.

#With the measuring sensors according to the invention, the oxygen content of exhaust gases from internal combustion engines can be determined in the rich, neutral and lean ranges, and the composition of the fuel-air mixture supplied to the engines can be controlled. As can be seen in FIGS. 1, 4 and 5, the measuring sensors include a measuring cell A and a reference cell B having porous electrodes 1 through 3, with electrode 2 being common to both cells. Electrodes 1 through 3 are connected to a fixed electrolyte 4. Exhaust gas is supplied to electrode 2 by way of a diffusion hole 20 and a diffusion barrier 5.

#Electrodes 1 and 2, which are generally composed of platinum, are part of the measuring cell. They are advisably 0.5 to 2 .mu.m thick and porous. Thicker electrodes impede the passage of the gases, and thus increase the time required by the sensors with respect to changes in the oxygen content of the exhaust gas.