Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-08-16
2001-12-04
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S286000, C060S295000, C060S285000
Reexamination Certificate
active
06324834
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the operation of an internal combustion engine in combination with an NOx-storage catalytic converter. In the area of the combustion with a lean air/fuel mixture (lambda greater than 1), the three-way catalytic converter no longer satisfies the requirements as to exhaust-gas quality. Here, NOx-storage catalytic converters are used which store emitted nitrogen oxide during lean engine operation. Stored nitrates are released and reduced to nitrogen because of the operation of the engine in the rich region (lambda less than 1). Ideally, the engine is operated lean in a first phase until the NOx-storage catalytic converter is full; that is, until the NOx-storage catalytic converter can no longer store nitrous oxides. A second phase with rich operation continues ideally from the latter for that time span which is necessary to regenerate the NOx-storage catalytic converter. The storage capability of the NOx-catalytic converter in the lean operating region is dependent upon charge and continuously reduces. If the first phase takes too long, then unwanted nitrogen oxide emissions occur. A second phase which continues too long has increased HC emissions and CO emissions as a consequence. For this reason, the problem is present to undertake the change between the two phases so that neither increased NOx emissions nor HC emissions occur.
BACKGROUND OF THE INVENTION
In this connection, it is known from U.S. Pat. No. 5973887 to estimate the NOx quantity, which is stored in a first phase, by a summed engine rpm and then to change into a second phase when the summed engine rpm exceeds a predetermined threshold value. The stored quantity is thereby modeled. The actual value of the stored quantity is not detected. The modeling can only incompletely simulate the actual stored quantity. For this reason, the first phase is either too long or too short with the above-mentioned disadvantageous consequences for the quality of the exhaust gas.
The U.S. Patent application Ser. No. 09/150,600 describes a possibility to fix the end of the second phase with rich engine operation, that is, oxygen deficiency in the exhaust gas. An oxygen-measuring probe in the exhaust gas rearward of the storage catalytic converter serves this purpose. As soon as the probe detects a crossover from a lean mixture to a rich mixture, this means that the storage catalytic converter no longer outputs sufficient oxygen for the oxidation of the hydrocarbons and the carbon monoxide and is empty of NOx containing oxygen (oxygen store and NOx store emptied). Thereupon, the second phase can be ended with oxygen deficiency and a reversal to the first phase with a lean mixture (oxygen excess) can be made. Thereby a breakthrough of CO and HC to end the regeneration phase is deliberately accepted after each storage interval. With each phase change, unwanted CO and HC emissions occur which can present problems for the maintenance of the toxic substance limit values in the sum over many phase changes. In addition, for each phase change, the oxygen store of the system is emptied and therefore fuel consumption is unnecessarily increased.
SUMMARY OF THE INVENTION
With this background, it is the object of the invention to provide a control of the regeneration of a storage catalytic converter which comes closer to the ideal of an optimal usage of the NOx storage capability by respective complete fillings and discharges of the storage catalytic converter while simultaneously reducing the unwanted HC emissions and CO emissions.
A further object is to control the regeneration of the storage catalytic converter via a control of the mixture composition of the engine in such a manner that, overall, an exhaust gas improvement results compared to known methods.
In detail, in one embodiment of the invention, a control of the air/fuel ratio during operation of the internal combustion engine having a catalytic converter and an exhaust-gas sensor mounted rearward of the catalytic converter in flow direction takes place so that, alternately, a lean operation of the engine and a rich operation of the engine is controlled with the degree of enrichment and/or the duration of the rich phases being changed in dependence upon the course of the signal of the above-mentioned exhaust-gas sensor in a previous rich phase.
Here, the engine is operated with a lean mixture in average over time.
According to the invention, the supply of reducing agent is not alone pregiven in a controlled manner with the aid of a model based on operating parameters of the engine but is adapted with the aid of an exhaust-gas probe mounted rearward of the catalytic converter.
If the above-mentioned exhaust-gas probe indicates an excess of a reducing agent in a rich phase, then the quantity of the reducing agent to be supplied for a next rich phase is reduced. This can, for example, take place via a shortening of the rich phase or via a reduction of the degree of enrichment.
For an adequate reduction, the above-mentioned exhaust-gas probe will no longer indicate too much of a reducing agent at the end of the next rich phase. Then, the quantity of the reducing agent, which is to be supplied in the next rich phases, is successively increased until a reaction of the exhaust-gas sensor, which is mounted rearward of the catalytic converter, occurs anew. The unwanted breakthrough of the reducing agent therefore takes place rarely in the method according to the invention. In this way, the quality of the exhaust gas is advantageously improved. The invention adapts the quantity of the reducing agent to be supplied in a closed working chain.
A conventional oxygen-sensitive lambda probe or, for example, an HC sensor can be used as the sensor mounted rearward of the catalytic converter.
The invention is not limited to a richness control of the engine for making HC and CO available in the exhaust gas as a reducing agent. The reducing agent can, for example, be metered in a controlled manner from other sources such as urea from a supply tank.
REFERENCES:
patent: 5325664 (1994-07-01), Seki et al.
patent: 5713199 (1998-02-01), Takeshima et al.
patent: 5771686 (1998-06-01), Pischinger et al.
patent: 5778663 (1998-07-01), Kostka
patent: 5927068 (1999-07-01), Schenk
patent: 6026640 (2000-02-01), Kato et al.
patent: 0560991 (1993-09-01), None
patent: 0690213 (1996-01-01), None
patent: 0733787 (1996-09-01), None
patent: WO 98 55742 A (1998-12-01), None
Blumenstock Andreas
Schnaibel Eberhard
Winkler Klaus
Denion Thomas
Ottesen Walter
Robert & Bosch GmbH
Trieu Thai-Ba
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