Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-11-05
2001-04-03
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S285000, C060S286000, C060S295000, C060S301000
Reexamination Certificate
active
06209316
ABSTRACT:
The invention relates to a method of operating a diesel engine having an engine controller which controls the operation of the diesel engine as a function of characteristic maps and permits rich/lean control of the diesel engine.
In order to reduce the pollutant emission of a diesel engine, the latter are operated, for example, with an exhaust-gas cleaning system through which the exhaust gases from the diesel engine flow. For the purpose of cleaning, NO
x
adsorber systems can be used, which are distinguished by a high potential NO
x
storage capacity. Such exhaust-gas cleaning systems, also referred to as NO
x
adsorber catalytic converters, store the nitrogen oxides (NO
x
) of internal combustion engines under specific preconditions, providing said engines are operated “lean”. Lean operation is present if the combustion air ratio lambda (&lgr;) is greater than 1, that is to say if there is hyperstoichiometric combustion, in which there is residual oxygen in the exhaust gas. In order to regenerate such NO
x
adsorber systems, which are referred to as storage catalytic converters because of their storage capacity, a reducing exhaust gas with the highest possible reducing-agent content is needed in order that the NO
x
stored in the NO
x
adsorber catalytic converter can be released and converted to nitrogen oxide NO
2
. An internal combustion engine produces reducing exhaust gas when there is “rich” combustion, that is to say hypostoichiometric combustion with &lgr;<1, in which there is no or only a little residual oxygen in the exhaust gas.
As a result of the heterogeneous mixture formation method, diesel engines operate with excess oxygen (&lgr;>1) over the entire characteristic map area. In order to be able to use an NO
x
adsorber system for cleaning the diesel engine exhaust gases in diesel engines, it must also be possible for the diesel engine to be changed over from time to time to rich operation, that is to say the diesel engine must have operating phases in which there is hypostoichiometric combustion with &lgr;<1.
DE 43 34 763 A1 discloses a method of operating an internal combustion engine, an adsorption device for nitrogen oxides (NO
x
) being arranged in an exhaust-gas cleaning system and adsorbing NO
x
when the combustion air ratio lambda is lean (&lgr;>1) and releasing adsorbed NO
x
when the combustion air ratio becomes rich (&lgr;<1). In this known method, the temperature of the NO
x
adsorption device is increased by injecting fuel into the exhaust gas and reduced by blowing air into the exhaust gas, in order to keep the operating temperature of the NO
x
storage device within a fixed range.
DE 195 43 219 C1 discloses a method of the type cited at the beginning in which a sensor for registering the NO
x
concentration in the exhaust-gas stream is arranged downstream of the storage catalytic converter and, when an NO
x
storage threshold value is reached, this value varying in accordance with a characteristic map as a function of speed and engine load, said sensor triggers a changeover from operating the diesel engine with &lgr;>1 to operating with &lgr;<1, in order to regenerate the storage catalytic converter in the rich operation of the diesel engine (&lgr;<1). For this purpose, in the known method, an engine controller comprises a computer which effects a changeover to rich or lean operation of the diesel engine as a function of predetermined changeover criteria, and a sensor system which communicates with the computer and monitors parameters which are needed for changeover criteria, as well as a memory which communicates with the computer and in which the characteristic maps for the operation of the diesel engine are stored.
A diesel engine is normally operated in such a way that the maximum output is developed with the minimum fuel consumption. In addition, further boundary conditions, such as exhaust-gas emission values, the development of smoke and quietness of running, are taken into account when tuning the engine operation. The consequence of the abovementioned requirements is that a diesel engine is usually optimized for lean operation. In the case of an exhaust-gas cleaning system with a storage catalytic converter, this optimal operation of the diesel engine must be interrupted from time to time for rich operation, during which the adsorber catalytic converter is regenerated.
The present invention is concerned with the problem of configuring a method of the type cited at the beginning in such a way that the overall operating behaviour of the diesel engine is improved, taking into account the alternating phases of lean operation and rich operation.
The invention is based on the general idea of providing specific changeover criteria for a changeover from lean operation to rich operation of the diesel engine, and specific changeover criteria for changing back from rich operation to lean operation, a changeover to rich operation, which is less beneficial in terms of engine operation, being carried out only when all the changeover criteria provided in this respect have been satisfied, and a change back to lean operation, which is more beneficial with regard to the engine operating behaviour, or termination of the rich operation being carried out if one of the changeover criteria provided in this respect has already been satisfied. With the aid of these measures, it is possible to select the changeover criteria in such a way that, on the one hand, rich operation of the diesel engine is carried out only when this is necessary for the regeneration of the adsorber system and that, on the other hand, rich operation is carried out for only as long as is required for the regeneration of the adsorber system, and/or rich operation is terminated or interrupted when this is required in order to maintain a specific engine operating behaviour.
In the method according to the invention, a specific changeover criterion for changing over from lean to rich operation of the diesel engine is the maintenance of a regeneration temperature of a storage catalytic converter element through which the exhaust gases from the diesel engine flow. Maintaining the regeneration temperature of the storage or adsorber catalytic converter means that the regeneration time and thus the duration of the rich operating phase can be shortened, since the storage catalytic converter has the capability of releasing adsorbed NO
x
and simultaneously converting this into molecular nitrogen N
2
only above a specific temperature.
According to a development of the method according to the invention, in order to monitor the regeneration temperature, a temperature sensor can be used which is arranged in the exhaust-gas train upstream of the inlet to the storage catalytic converter element and communicates with the sensor system, the regeneration temperature, at which a changeover to rich operation can be carried out, preferably lying in a predetermined temperature range.
In a particular embodiment of the exhaust-gas cleaning device of the diesel engine, an oxygen-consuming catalytic converter element, in particular an oxidation catalytic converter, can be connected upstream of the storage catalytic converter element. In an expedient refinement of the method according to the invention, in a converter system constructed in this way, the temperature sensor can be arranged between the storage catalytic converter element and the oxygen-consuming catalytic converter element, by which means, in addition to the monitoring of the regeneration temperature, monitoring of the release of energy as a consequence of the exothermic reactions in the oxygen-consuming catalytic converter element can also be carried out.
In the method according to the invention, a further changeover criterion which must be satisfied for a changeover from lean to rich operation of the diesel engine, is the presence of a specific level of adsorption of a storage catalytic converter element through which the exhaust gases from the diesel engine flow. This measure prevents changing over too frequently to rich operat
Duvinage Frank
Fausten Hans
Fekete Nicholas
Kerckhoff Anton
Krutzsch Bernd
Daimler-Chrysler AG
Denion Thomas
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Trieu Thai-Ba
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