Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Reexamination Certificate
1997-12-08
2001-04-10
Tung, T. (Department: 1743)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
C204S425000, C204S426000
Reexamination Certificate
active
06214209
ABSTRACT:
The invention relates to an oxygen measuring sensor in accordance with the species of the main claim. The oxygen measuring sensors of the species operate in accordance with the diffusion limiting current principle, wherein the limiting current is measured at a constant voltage applied to both electrodes of the sensor element. In an exhaust gas generated in internal combustion engines this current is a function of the oxygen concentration, as long as the diffusion of the gas to the pump electrode determines the speed of the occurring reaction. It is known, for example from DE-PS 37 28 618, to design such sensors operating in accordance with the polarographic measuring principle in such a way, that the anode as well as the cathode are exposed to the gas mixture to be measured, wherein the cathode has a diffusion barrier in order to make operating within the diffusion limiting current range possible. Such limiting current sensors are suitable for determining the lambda values in gas mixtures with excess oxygen, i.e. in lean gas mixtures.
An electrical potential of sufficient strength is applied to the electrodes of the pump cell for handing off the oxygen present between the pump electrode and the solid electrolyte in such a way, that the measured current is a function of the oxygen being diffused through the pores of the pump electrode. In accordance with the current/voltage characteristic curves of limiting current sensors, the current is independent of the applied voltage and is only determined by the concentration gradients upstream of the pump electrode, i.e. by the oxygen concentration in the gas mixture. The current/voltage characteristic curves first start with a relatively steep slope which is primarily determined by the ohmic resistance of the probe. The adjoining horizontal portion of the curve is the limiting current range, which in good probes must extend as parallel as possible in respect to the abscissa. Deviations from the parallel course of the curve are generated with higher oxygen concentrations in particular, wherein there is no longer a strict linearity between current and concentration. It depends on the strength of the diffusion resistance and the current-carrying capacity of the pump electrodes, up to which concentrations there is sufficient linearity.
ADVANTAGES OF THE INVENTION
In contrast thereto, the oxygen measuring sensor of the invention with the characterizing features of the main claim has the advantage that a linear course of the probe signal over the oxygen concentration in the gas mixture is present even at high oxygen concentrations. This results in an improved operational accuracy of the oxygen measuring sensor over the entire range of the concentrations to be measured in a lean exhaust gas. Furthermore, the response sensitivity in the course of dynamic pressure change behavior is clearly improved, which will be addressed at a later time.
Advantageous further developments of the oxygen measuring sensor of the invention are possible by means of the steps recited in the dependent claims. Pick-up of the measuring signal of the portion of the current/voltage characteristic curve which follows Ohm's law can be achieved even at high oxygen concentrations by means of the interior pump electrode extending along the diffusion direction in the diffusion conduit. The number of electrode connections can be reduced by combining the anodes of the pump cell and the measuring cell. Operation of the oxygen measuring sensor within the ohmic range of the current/voltage characteristic curve also makes it possible that merely a trimming potentiometer is sufficient for calibrating the oxygen measuring sensor.
REFERENCES:
patent: 4769124 (1988-09-01), Okada et al.
patent: 5397442 (1995-03-01), Wachsman
patent: 5494557 (1996-02-01), Hotzel et al.
patent: 3908393 (1991-01-01), None
patent: 95/30146 (1995-11-01), None
Bosch GmbH Robert
Striker Michael J.
Tung T.
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