Method for changing the operating mode of a direct-injection otto cycle internal-combustion engine

Abstract

A direct-injection Otto cycle internal-combustion engines can be operated in the stratified charge mode with a later fuel injection during the compression cycle and a lean mixture formation and, with an operating mode with a homogeneous mixture formation, by fuel injection during the intake cycle which is provided for higher load ranges of the internal-combustion engine. The exhaust gases of the internal-combustion engine are decontaminated by an NO,storage catalyst which must be periodically regenerated during a homogeneous mixture formation and at rich fuel/air ratios (&lgr;). To permit a fast change of the operating mode and particularly the regeneration of the storage catalyst without changing the running performance of the internal-combustion engine, the fuel quantity to be injected per power cycle, is apportioned during a homogeneous operating phase during the change of operating modes, corresponding to the actual intake air flow rate by adjusting the respective injection time. Isochronously and proportionally to the change of the injection time, the ignition point in time is adjusted in the direction of a late ignition. The homogeneous operating phase is limited by a change-over point in time at which the injection end of the fuel injection is shifted into the power cycle provided for the demanded operating mode.