Method for correcting a modeled ammonia mass flow and a modeled nitrogen oxide mass flow and for controlling an SCR catalyst system

摘要

The invention relates to a method for correcting (78, 79) a modeled ammonia mass flow (qmod) and a modeled nitrogen oxide mass flow (qmod) between two SCR catalysts arranged one behind the other in an exhaust gas line in an SCR catalyst system which has only one reductant dosing unit upstream of the two SCR catalysts. Catalysts. A first sum value is formed (S) by adding (74) the modeled ammonia mass flow (qmod) and the modeled nitrogen oxide mass flow (qmod). A second sum value (S) is determined from the signal (qmess) of a sensor arranged between the two SCR catalysts with a sensitivity to ammonia and nitrogen oxides. For the correction (78, 79) a ratio (V) of the two sum values (S, S2) is formed. In a method for controlling (80) the SCR catalyst system (20), the modeled ammonia mass flow (qmod) and the modeled nitrogen oxide mass flow (qmod) between the two SCR catalysts are corrected by means of the correction method.