Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2001-11-28
2003-10-28
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S285000
Reexamination Certificate
active
06637190
ABSTRACT:
The invention relates to a process for the desulfurization of at least one NO
x
storage catalytic converter which is arranged in an exhaust pipe of an internal-combustion engine, having the features listed in the preamble of claim 1.
Processes for the desulfurization of NO
x
storage catalytic converters are known. In these processes, during the desulfurization what are known as regeneration parameters, such as a minimum temperature at the NO
x
storage catalytic converter and an operating mode of the internal-combustion engine with &lgr;≦1, have to be set.
When the operating mode of the internal-combustion engine involves &lgr;<1, a concentration of reducing gas components, such as CO, HC or H
2
, predominates in the exhaust gas over a concentration of oxygen (rich atmosphere). At &lgr;>1, the oxygen concentration is dominant (lean-burn atmosphere). While the internal-combustion engine is operating in a lean-burn atmosphere, SO
2
is formed as well as NO
x
, on account of fluctuating levels of sulfur in the fuel mix being burned. Like the NO
x
, this SO
2
, in a lean-burn atmosphere, is absorbed by the NO
x
storage catalytic converter; the absorption of SO
2
may lead to the formation of local inhomogeneities as a result of the formation of sulfate grains. This process leads to a reduction in a catalytically active surface region and in a capacity of the NO
x
storage catalytic converter and offers a point of attack for corrosive processes which cause permanent damage to the NO
x
storage catalytic converter.
It is known to measure a degree of sulfurization of the NO
x
storage catalytic converter on the basis of recording an efficiency with regard to a reduction of NO
x
(conversion reaction). For example, DE 197 47 222 C1 describes establishing an NO
x
storage capacity which has been reduced by sulfur poisoning by recording the NO
x
concentration, which rises relatively rapidly downstream of the NO
x
storage catalytic converter, in lean-burn phases.
If the degree of sulfurization reaches a threshold value, it is also known to initiate the desulfurization by at least temporarily influencing an operating parameter of the internal-combustion engine (measure). These measures comprise, for example, late ignition, reinjection before or during a combustion operation or a cylinder-selective trimming of the internal-combustion engine, and therefore lead to an increased fuel consumption. These measures are often taken in order to increase an exhaust-gas temperature upstream of the NO
x
storage catalytic converter and then to reach the minimum temperature at the NO
x
storage catalytic converter. A drawback of the known processes is that the desulfurization is initiated only on the basis of the efficiency of the conversion reaction, i.e. after the threshold value has been reached, and therefore relatively favorable operating states of the internal-combustion engine which occur in practice and in which the threshold value has not been reached, yet the temperature of the NO
x
storage catalytic converter is close to the minimum temperature, remain unused. This leads to an increased fuel consumption.
The invention is based on the object of making the desulfurization of the NO
x
storage catalytic converter significantly more dynamic, i.e. of including not just the degree of sulfurization of the catalytic converter but also the regeneration parameters in order to assess the need for desulfurization.
This object is achieved by the process for the desulfurization of at least one NO
x
storage catalytic converter arranged in the exhaust pipe of an internal-combustion engine by the features given in claim 1. The fact that the desulfurization is initiated, not only by the degree of sulfurization, but also as a function of a current lambda value and/or a current temperature of the NO
x
storage catalytic converter means that the desulfurization can be carried out significantly more efficiently, i.e. so that more fuel is saved. Furthermore, it is advantageous that it is possible to maintain a smaller size of the sulfate grains formed by the desulfurization, since overall the desulfurization takes place more frequently.
In a preferred configuration of the process, a characteristic variable which is formed from the degree of sulfurization, the lambda value and the NO
x
storage catalytic converter temperature is determined in order to assess the need for desulfurization. The characteristic variable lies within a characteristic diagram which can be characterized by means of a ratio of a load to a rotational speed of the internal-combustion engine. This characteristic diagram can be divided into any desired number of regions in which, for example, the threshold value for the desulfurization is reduced as the temperature rises. In this way, it is possible to react very dynamically to given operating states with regard to initiating the desulfurization.
Further preferred configurations of the invention will emerge from the remaining features listed in the subclaims.
REFERENCES:
patent: 5402641 (1995-04-01), Katoh et al.
patent: 5437153 (1995-08-01), Takeshima et al.
patent: 5771685 (1998-06-01), Hepburn
patent: 5983627 (1999-11-01), Asik
patent: 6134883 (2000-10-01), Kato et al.
patent: 6161377 (2000-12-01), Boegner et al.
patent: 6167695 (2001-01-01), Itou et al.
patent: 6263666 (2001-07-01), Kubo et al.
patent: 6305160 (2001-10-01), Hammerle et al.
patent: 6308515 (2001-10-01), Bidner et al.
Denion Thomas
Nguyen Tu M.
Norris & McLaughlin & Marcus
Volkswagen Aktiengesellschaft
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