Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-01-19
2001-04-17
Walberg, Teresa (Department: 3742)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S277000, C060S285000
Reexamination Certificate
active
06216448
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the diagnosis of catalytic converters which are used to convert toxic substances in the exhaust gas of internal combustion engines. The invention especially relates to the diagnosis of an NOx storage catalytic converter during the operation of an internal combustion engine.
BACKGROUND OF THE INVENTION
The three-way catalytic converter no longer satisfies the requirements as to the conversion of nitrogen oxide in the operating region of the combustion of lean air/fuel mixtures (&lgr;>1). Here, NOx storage catalytic converters are used which store the nitrogen oxides emitted in lean engine operation. Stored nitrates are released and converted to nitrogen by the operation of the engine in the rich region (&lgr;<1).
The use of NOx storage catalytic converters in this connection is disclosed, for example, in U.S. Pat. No. 5,473,887.
Statutory requirements provide for an on-board diagnosis of the vehicle components, which are relevant to toxic emissions, such as catalytic converters. In this connection, it is known, for example, from U.S. Pat. No. 3,969,932, to apply the signals of oxygen-sensitive exhaust gas probes, which are mounted forward and rearward of the catalytic converter, for evaluating a three-way catalytic converter. The known method is based upon the oxygen storage capability of an operational three-way catalytic converter. In this connection, U.S. Pat. No. 3,969,932 discloses a change of the air/fuel mixture composition from &lgr;=0.95 (rich, fuel-rich mixture, oxygen deficiency) to &lgr;=1.05 (lean, fuel-poor mixture, oxygen excess). The exhaust-gas sensor mounted forward of the catalytic converter reacts thereto virtually without delay. The oxygen storage locations of the catalytic converter are at first not occupied because of the oxygen deficiency in the exhaust gas, which is present for &lgr;=0.95. The oxygen storage locations are successively occupied after the switchover to oxygen excess forward of the catalytic converter. Accordingly, at first there continues to be an oxygen deficiency rearward of the catalytic converter. After a time span, which is dependent upon the oxygen storage capability of the catalytic converter, an oxygen excess also occurs rearward of the catalytic converter which triggers a change of the signal of the rearward exhaust-gas sensor. The time delay, that is, the phase shift between the reactions of both exhaust-gas sensors, is less with decreasing capability of oxygen storage of the catalytic converter and can therefore be used for evaluating the oxygen storage capability for diagnosing the catalytic converter.
This known method is not easily transferrable to a catalytic converter, which in addition to a storage capability for oxygen also has a storage capability for nitrous oxides. Catalytic converters of this kind can usually still store nitrogen oxides when their oxygen storage capability is already exhausted and an exhaust-gas sensor, which is mounted rearward of the catalytic converter, indicates an oxygen excess. The time delay between the reactions of both exhaust-gas sensors after a changeover from rich to lean mixture therefore supplies no statement for NOx storage catalytic converters as to their NOx storage capability.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and an arrangement for evaluating the NOx storage capability of an NOx storage catalytic converter, which can be realized with components, which are already available in modern motor vehicles such as oxygen-sensitive exhaust-gas sensors forward and rearward of the catalytic converter.
An embodiment of the invention is for a method of diagnosing a catalytic converter arranged in the exhaust-gas system of an internal combustion engine. The catalytic converter is configured to have an oxygen storage capability and a nitrogen oxide storage capability. The method includes the steps of: providing and mounting a signal-emitting exhaust-gas probe rearward of the catalytic converter; repeatedly increasing and decreasing the oxygen concentration of the exhaust gas forward of the catalytic converter in such a manner that the signal of the exhaust-gas probe changes to reflect the increase and decrease of the oxygen concentration; detecting a first phase shift between a decrease of the oxygen concentration and a subsequent reaction of the exhaust-gas probe and detecting a second phase shift between a subsequent increase in said oxygen concentration and a subsequent reaction of the exhaust-gas probe; determining the difference between the first and second phase shifts; and, outputting and/or storing a fault signal when this difference does not reach a pregiven threshold.
The invention is based on the situation that an oxygen deficiency in the exhaust gas rearward in the catalytic converter only occurs when the oxygen-storage locations as well as the nitrous oxide storage locations in the NOx storage catalytic converter are empty. If the catalytic converter is first filled with oxygen and nitrogen oxides, for example, because of an operation of the engine with a lean mixture, and if hydrocarbons (HC) and carbon monoxide (CO) are generated in the exhaust gas for the regeneration of the catalytic converter because of a rich mixture adjustment, then the following processes take place: the hydrocarbons and the carbon monoxide reduce the stored nitrogen oxides. The oxygen stored and bonded in the form of nitrous oxides is released with the remaining oxygen stored in the catalytic converter so that the oxygen excess is at first maintained rearward of the catalytic converter.
The exhaust-gas sensor, which is arranged rearward of the catalytic converter, reacts only to the oxygen deficiency forward of the catalytic converter when the oxygen storage locations as well as the nitrous oxide storage locations of the catalytic converter are empty. The time delay between influencing the exhaust gas forward of the catalytic converter by introducing reduction agents and the reaction of the rearward exhaust-gas probe is therefore dependent upon the sum of the oxygen storage capability and the NOx storage capability and can therefore be principally used for evaluating the NOx storage capability as a diagnostic criterion. However, a portion of the above-mentioned time delay is caused by the oxygen storage capability. A further object of the invention is to quantitatively detect this portion and to consider the same in the determination of the NOx storage capability.
A conventional oxygen-sensitive lambda probe or, for example, an HC sensor can be utilized as a sensor which is mounted rearward of the catalytic converter. The invention is not limited to a rich control of the engine for making HC and CO available in the exhaust gas as reducing agents. The reducing agent can also be metered in a controlled manner from other sources such as urea from a supply tank.
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Schnaibel Eberhard
Schumann Bernd
Winkler Klaus
Dahbour Fadi H.
Ottesen Walter
Robert & Bosch GmbH
Walberg Teresa
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