Patent ID: 7383680

Claim:
A process for controlling the lean operation of an internal combustion engine, provided with a nitrogen oxide storage catalyst, the process comprising: performing a first operating phase (lean operation), comprising storing, as a storage phase, nitrogen oxides produced by the internal combustion engine for a specific storage time in the nitrogen oxide storage catalyst, switching to a second operating phase (rich operation) after the storage time expires, by a control device as the engine control at a specific switching instant for a specific discharge time as the discharge phase in which the nitrogen oxides which have been stored during the storage time are discharged from the nitrogen oxide storage catalyst, flowing the nitrogen oxide mass upstream of the nitrogen oxide storage catalyst and/or downstream of the nitrogen oxide storage catalyst each being integrated over the same time interval, determining a switching operating point in a first process step, to establish the instant of switching from the storage phase to the discharge phase, at least from the integral value of the nitrogen oxide mass flow upstream and/or downstream of the storage catalyst, and comparing the respective switching operating point in a second process step to a definable operating field which is optimized-with respect to a fuel savings potential as a function of a load acceptance of the internal combustion engine, which is formed by a plurality of individual operating points for one new and one aged storage catalyst; determining a relative nitrogen oxide slip as the difference between the nitrogen oxide mass flow which has flowed into the nitrogen oxide storage catalyst and the nitrogen oxide mass flow which has flowed out of the nitrogen oxide storage catalyst to establish the switching instant from the storage phase to the discharge phase relative to the storage time, and bringing the quotient of the integral values of the nitrogen oxide mass flow upstream and downstream of the nitrogen oxide storage catalyst into a relative relationship with a definable degree of nitrogen oxide conversion which has been derived from the exhaust boundary value, so that when these given switching conditions are present in the case of a switching operating point which is within the operating field, switching from the storage phase (lean operation) to the discharge phase (rich operation) is carried out at the switching instant which has been optimized with respect to fuel consumption and the storage potential, whereby when a switching operating point is located within an operating field, the engine control enables lean operation and thus switching between the storage phase and the discharge phase of the nitrogen oxide storage catalyst, while the engine control conversely dictates lambda operation of the internal combustion engine at which lambda is equal to 1 for a switching operating point which departs from a definable operating field.