Method for monitoring nitrogen oxide storage catalyst of internal combustion engine, involves determining operability of storage catalyst, when differential value of actual air ratio over time is smaller than predetermined value

摘要

The operation of storage catalyst (6) in internal combustion engine (1) is checked with respect to stoichiometric operation. The actual air ratio in exhaust gas is determined with respect to integral of actually supplied air mass flow and stoichiometric air requirement based on determined air ratios. The inoperability of storage catalyst is determined, when differential value of actual air ratio over time exceeds predetermined value. The operability of storage catalyst is determined, when differential value of actual air ratio over time is smaller than predetermined value.