Method for regenerating a catalytic converter

Details Method for regenerating a catalytic converter Method for regenerating a catalytic converter

1999-09-24

2001-05-15

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S277000, C060S301000

Reexamination Certificate

active

06230487

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the regeneration of a three-way storage catalytic converter or a NOx-storage catalytic converter. The exhaust-gas quality of present day spark-ignition engines is determined by the converting power of the exhaust-gas catalytic converter. This is so in lambda=1 operation as well as in lean operation as is typical for gasoline direct injected engines.
BACKGROUND OF THE INVENTION
The conversion capacity can drop reversibly as well as irreversibly. It has been observed that sulfur intakes into the catalytic converter reduce the conversion capacity thereof. These sulfur intakes are caused by the sulfur components of the fuel. The intakes are dependent upon temperature and can be again released during operation of the engine. In this connection, reference can be made to SAE Paper 750697. The sulfur content in the fuel can fluctuate in dependence upon a fuel oil company (and/or the particular state in the United States of America). The fluctuation can be between 15 ppm and 1,000 ppm. It is therefore of interest not to deteriorate the exhaust gas notwithstanding an operation with fuel having a large sulfur content.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method which permits a regeneration of catalytic converters in the operation of internal combustion engines with the least possible disturbing side effects such as the formation of odors, the increase in fuel consumption or a deterioration in the driving comfort.
The method of the invention is for improving the quality of exhaust gas, which is reduced by the action of sulfur, in a combustion process with an exhaust-gas catalytic converter. The method includes the steps of: determining the oxygen storage capability of the catalytic converter; comparing the oxygen storage capability to a threshold value; and, if there is a drop below the threshold value, performing at least one of the following additional steps: increasing the temperature of the exhaust gas; and, generating an exhaust-gas composition forward of the catalytic converter which operates in a reducing manner.
According to a feature of the invention, a sulfur regeneration is carried out during operation with sulfur-containing fuel in order to free the catalytic converter of sulfur and to improve the quality of the exhaust gas.
The operation with sulfur-containing fuel can be determined via a reduction of the oxygen storage capability because the sulfur occupies the storage places in the catalytic converter which would otherwise be assumed by O
2
molecules. The oxygen storage capability can be determined by a conventional method for determining the oxygen storage capability of catalytic converters (catalytic converter diagnosis).
In the event that a first detection of the oxygen storage capability results in a reduced conversion or oxygen storage capability, a method for regenerating the catalytic converter is carried out. A regeneration of the catalytic converter of sulfur takes place at high temperatures and with a slightly rich mixture (&lgr;<1). There are various possibilities to carry out the sulfur regeneration and three such possibilities are presented below:
(a) artificially reducing the efficiency of the engine, for example, by retarded ignition angles. This leads to a high exhaust-gas temperature. The sulfur can be regenerated with a simultaneously rich mixture. Advantageously, the enrichment is so matched to the ignition angle shift that the mutually opposed influences on the engine torque of the two measures compensate. An advantage of this possibility lies in the fact that it can be executed at any time.
(b) another possibility involves waiting for an operating point having a high air mass throughput of the engine (for example, full load). In this way, high catalytic converter temperatures are obtained. An enrichment of the mixture takes place in many engines at high load in order to protect components. In this way, an automatic sulfur regeneration results.
(c) Another possibility provides for charging the catalytic converter to a maximum with oxygen during overrun operation with the fuel metering switched off. When fuel metering is resumed, a slight mixture enrichment takes place in order to remove excess oxygen from the catalytic converter. If the ignition angle is now made to be retarded, the sulfur can here also be regenerated. The regeneration strategy in accordance with the invention can, for example, at the start of a trip, provide a catalytic converter diagnosis to determine the oxygen storage capability of the catalytic converter. If the oxygen storage capability lies above a predetermined threshold, then no further measures are taken. If the oxygen storage capability lies below a threshold, then a sulfur regeneration takes place with a subsequent renewed catalytic converter diagnosis.
If the oxygen storage capability then still lies below a threshold value, then an irreversible damage to the catalytic converter by deterioration has to be assumed. No further measures then take place with respect to the regeneration strategy. If the oxygen storage capability improves by the regeneration, then a reversible sulfur poisoning is present. In this case, a counter is started which defines a measure for the sulfur introduced. As a measure, the quotient of the consumed fuel and the engine efficiency is considered. The engine efficiency results from the operating parameters which are present in the control apparatus and is therefore known in principle. A higher efficiency reduces the quotient. This considers the situation that a certain regeneration is associated with high load conditions. A renewed diagnosis is undertaken when the counter has reached a predetermined value Z1. In the case that the oxygen storage capability has again dropped, a renewed sulfur regeneration is carried out. The counter z(S) is reset and the next diagnosis with sulfur regeneration is carried out before the value Z1 is reached. In the event that the oxygen storage capability has not dropped when reaching the value Z1, the next diagnosis with sulfur regeneration is carried out only after a longer time span (for example, after Z1+offset). In this way, an automatic adaptation of the distances between the regeneration phases takes place to the actual requirement determined by the characteristics of the catalytic converter and the sulfur content of the fuel.


REFERENCES:
patent: 5402641 (1995-04-01), Katoh et al.
patent: 5655363 (1997-08-01), Ito et al.
patent: 5724808 (1998-03-01), Ito et al.
patent: 5743084 (1998-04-01), Hepburn
patent: 5850735 (1998-12-01), Araki et al.
patent: 5974790 (1999-11-01), Adamczyk et al.
patent: 5974791 (1999-11-01), Hirota et al.
“Exhaust Sulfur Oxide Measurement Using Air Dilution” by M. E. Griffing et al, SAE Paper 750697, Fuels and Lubricants Meeting, Houston, Texas, Jun. 1975.

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