Daimler Ag

Uwe Hofmann

Bernd Christner

Markus Paule

Michael-Rainer Busch

Alexander Kaiser

Dirk Herbstritt

Tobias Peters

Jens Franz

A determination of a quality of a reducing agent solution containing ammonia used to reduce nitrogen oxides involves actuating a metering unit that delivers metered quantities of reducing agent solution into an engine's discharged exhaust gas and determining an efficiency value that is at least correlated with the efficiency of the SCR catalytic converter and comparing the efficiency value to a predefinable limit value. If an efficiency value not corresponding to proper functioning of the SCR exhaust emission control system is identified by the comparison, a switch is made to a diagnostic mode in a second method step. If a predefinable deviation of the efficiency value from a limit value is identified after expiration of the second method step time period, a third method step is performed for conditioning the SCR catalytic converter. A fourth step involves an adaptation mode in which a deviation from the efficiency value is determined.

Method for determining a quality of a reducing agent solution containing ammonia used to reduce nitrite oxide

In a system with an SCR catalytic converter, a correction by a changeable long term adaption factor to a target dosing rate is provided for the model dosing rate and a correction by a changeable short term adaption factor to an assumed actual filling state for the ammonia filling level value. A dosing unit controllable by a control unit adds an ammonia-containing reducing agent to the exhaust gas and an exhaust gas enriched with ammonia according to the dosing is fed to the SCR catalytic converter. An ammonia filling level value for a filling level of ammonia stored in the SCR catalytic converter and a model dosing rate for dosing the reducing agent into the exhaust gas are calculated by a computer model.

Method for operating an exhaust gas treatment system having an SCR catalytic converter

In an operating and diagnostic method for an SCR exhaust gas aftertreatment system which has an SCR catalytic converter with ammonia storage capacity, a signal of an exhaust gas sensor that is sensitive to nitrogen oxide and ammonia and is arranged downstream of the SCR catalytic converter, is measured. In a normal operating mode, ammonia is supplied to the SCR catalytic converter corresponding to a filling level model for ammonia stored in the SCR catalytic converter, in such a way that the ammonia filling level of the SCR catalytic converter is held at least approximately at a predefinable nominal value (or value range). The normal operating mode is interrupted if an exhaust gas sensor signal that exceeds a predefinable first limit value, is registered, and the set urea dosing rate is increased by a predefinable degree in relation to the value provided in the normal operating mode. Thereafter, a return is made to the normal operating mode, or a switch is made to a diagnostic operating mode, as a function of the profile of the signal of the exhaust gas sensor.

Operating and diagnostic method for an SCR exhaust-gas aftertreatment system

In a method for regenerating a nitrogen oxide storage catalytic converter arranged in an exhaust pipe of an internal combustion engine, a constant value is set in a first regeneration phase for the air/fuel ratio &#x3bb;of the air/fuel mixture fed to the internal combustion engine when a predeterminable triggering threshold value for the nitrogen oxide concentration in the exhaust gas on the output side of the nitrogen oxide storage catalytic converter is exceeded. The first regeneration phase is followed by a second regeneration phase, in which the time rate of change d &#x3bb;/dt of the air/fuel ratio &#x3bb;is set as a function of the mass flow of the exhaust gas flowing through the nitrogen oxide storage catalytic converter or as a function of an internal combustion engine operating variable linked with the mass flow of exhaust gas.

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Reichelsheim, Germany

Uwe Hofmann