Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-08-23
2001-06-12
Warden, Sr., Robert J. (Department: 1744)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S406000, C204S408000, C204S424000, C123S688000
Reexamination Certificate
active
06245205
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a diagnosis of a potentiometric electrically heated exhaust-gas probe for controlling combustion processes with a periodic exchange between combustions with oxygen deficiency and oxygen excess.
BACKGROUND OF THE INVENTION
A potentiometric electrically heated exhaust-gas probe is disclosed, for example, in U.S. Pat. No. 4,310,401. This probe is used to control combustion processes such as in heater equipment or in internal combustion engines for motor vehicles. For motor vehicles, various countries have statutory requirements as to on-board monitoring of all exhaust-gas relevant components. A fault which can lead to a deterioration of the exhaust gas must be detected and displayed via a fault lamp. In this context, the invention relates especially to the diagnosis of all electrical faults of the exhaust-gas probe during its operation. As electrical fault, especially short circuits of the connecting leads of the probe are noted, such as a short circuit to the battery voltage, a short circuit to ground, a break in the cable, et cetera.
The control of combustion processes takes place often with a so-called two-point control strategy. Here, the probe is subjected to the exhaust gas of the combustion process and distinguishes between oxygen rich and oxygen deficient exhaust gas. For oxygen-rich exhaust gas, the air/fuel mixture, which is supplied to the combustion process, is enriched with fuel until the resulting exhaust gas is oxygen deficient. Thereafter, a leaning of the mixture takes place by reducing the metering of fuel until the occurrence of an oxygen excess in the exhaust gas. In this way, the composition of the combusting air/fuel mixture varies periodically between oxygen deficiency and oxygen excess. The probe signal changes in fault-free probe operation back and forth between a first region of high signal values (oxygen deficiency) and a second region of low signal values (oxygen excess). These two regions are separated by a third region which is run through very rapidly for each change between the first and second regions when the probe operation is free of faults.
A known probe diagnosis evaluates a longer dwell time of the probe signal in the above-mentioned third region as a fault because this performance is typical for an electrical fault such as a break in the signal and ground leads between the probe and the control apparatus. This diagnosis has been shown to be especially reliable for specific types of probes but has shown deficiencies with respect to other types of probes. Especially in the case of planar lambda=1 probes such as disclosed in U.S. Pat. No. 4,310,401, cable breaks in experimental operation have not been detected with sufficient reliability.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a reliable diagnosis of electrical faults in probes of the type disclosed in U.S. Pat. No. 4,310,401.
The diagnostic arrangement of the invention is for a potentiometric, electrical exhaust-gas probe for the control of combustion processes with a periodic change of the composition of the combusting air/fuel mixture between oxygen deficiency and oxygen excess. The exhaust-gas probe is heated by an electric heater and outputs a probe signal when the exhaust-gas probe operates without fault which changes between a first region of high signal values (oxygen deficiency) and a second region of low signal values (oxygen excess) with the first region of high signal values and the second region of low signal values being separated by a third region of values. The diagnostic arrangement includes: means for outputting a fault announcement when the probe signal lies within the third region longer than a pregiven longest duration; and, means for also outputting a fault announcement when changes of the current supplied to the electric heater occur within the pregiven longest duration and when the probe signal has temporarily left the third region of values after the change of the heater current.
The invention is based on the recognition that the problems observed for the planar lambda=1 probe are related to the arrangement of the probe heater and the measurement electrodes on a planar chip. In specific operating states, it can happen that unwanted in-coupling resistances and in-coupling capacitances occur between the probe heater and the Nernst cell of the probe.
The Nernst cell comprises a solid electrolyte and electrodes which, on the one hand, are subjected to the exhaust gas and, on the other hand, are subjected to a reference gas such as air. The probe voltage lies within a plausible voltage region, that is, outside of the above-mentioned third region and can therefore not be detected as a fault by the known probe diagnosis. As a secondary fault, the problem is present that the above-described control of the air/fuel mixture causes the air/fuel mixture to become lean to such an extent that ignition misfires occur. In the extreme case, a catalytic converter, which is used in motor vehicles, can disintegrate and the vehicle itself can be consumed in flames. Before the extreme case occurs, such a leaning of the mixture already causes a significant and detectable deterioration in driving performance.
The advantage of the invention is that all faults, which occur in planar probes, can be reliably detected with an additional expansion of function in the electric probe diagnosis so that the above-mentioned faults and deteriorations cannot occur.
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patent: 2937048 (1981-04-01), None
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Raff Lothar
Schnaibel Eberhard
Olsen Kaj K.
Ottesen Walter
Robert & Bosch GmbH
Warden, Sr. Robert J.
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