Method and apparatus for controlling an internal combustion engine coupled to a passive selective catalytic reduction aftertreatment system

Method for operating a direct-injection internal combustion engine fluidly coupled to a passive SCR system including a three-way catalytic converter upstream to an ammonia-selective catalytic reduction catalyst, the method comprising:

• determining an engine torque command;
• selecting a preferred engine control scheme comprising
• a SI combustion mode, and
• a preferred air/fuel ratio to achieve a minimum fuel consumption and maintain combustion stability at an acceptable level for an engine operating point corresponding to the engine torque command;
• determining a preferred engine fueling rate comprising a minimum engine fueling rate to achieve the engine operating point corresponding to the engine torque command at the preferred air/fuel ratio when employing the preferred engine control scheme;
• and
• employing a transition from a HCCI combustion mode to the preferred engine control scheme comprising the SI combustion mode to control the engine at the preferred engine fueling rate, comprising
• substantially immediately controlling a fuel injection timing, an engine spark timing and an engine valve lift from respective HCCI combustion mode settings to respective SI combustion mode settings,
• only after the fuel injection timing, the engine spark timing, and the engine valve lift settings are operative at the respective SI combustion mode settings, coordinating a transition to the preferred air fuel ratio coincident with a transition from a HCCI combustion mode engine valve phase setting to a SI combustion mode engine valve phase setting, and
• once the transition to the SI combustion mode engine valve phase setting is complete, operating the engine at the preferred air/fuel ratio.

A direct-injection internal combustion engine system, comprising:

• a direct-injection internal combustion engine including a fuel injection system, a spark ignition system, a valve lift control system and a valve phase control system;
• a three-way catalytic converter coupled to an exhaust gas stream from internal combustion engine upstream to an ammonia-selective catalytic reduction catalyst;
• and
• a controller configured to transition the internal combustion engine from an HCCI combustion mode to a SI combustion mode, comprising
• determining a preferred air/fuel ratio to achieve a minimum fuel consumption and maintain combustion stability at an acceptable level for a predetermined engine operating point during the SI combustion mode;
• substantially immediately controlling a fuel injection timing, an engine spark timing and an engine valve lift from respective HCCI combustion mode settings to respective SI combustion mode settings;
• only after the fuel injection timing, the engine spark timing, and the engine valve lift settings are operative at the respective SI combustion mode settings, coordinating a transition to the preferred air/fuel ratio coincident with a transition from a HCCI combustion mode engine valve phase setting to a SI combustion mode engine valve phase setting;
• and
• once the transition to the SI combustion mode engine valve phase setting is complete, operating the engine at the preferred air/fuel ratio.