Combustion changeover control for engine

An engine control apparatus comprising:

• an internal combustion engine;
• a combustion system for varying an actual fuel air ratio of an air fuel mixture for the engine gradually from a first desired ratio level for a first combustion mode to a second desired ratio level for a second combustion mode in accordance with a fuel air ratio control signal, and changing over an actual combustion condition in the engine from the first combustion mode to the second combustion mode in response to a first-mode-to-second-mode combustion changeover command signal;
• an EGR system for recirculating exhaust gas from the engine to an intake air flow into the engine, and for varying an actual EGR quantity from a first desired EGR quantity for the first combustion mode to a second desired EGR quantity for the second combustion mode in accordance with an EGR control signal;
• a sensor for sensing an engine operating state of the engine;
• and
• a controller for producing a first-mode-to-second-mode combustion changeover request signal for requesting a combustion changeover from the first combustion mode to the second combustion mode in accordance with the engine operating state sensed by the sensor, for performing a fuel air ratio changeover operation to vary the actual fuel air ratio gradually from the first desired ratio level for the first combustion mode to the second desired ratio level for the second combustion mode by varying the fuel air ratio control signal in response to the changeover request signal, for performing an EGR changeover operation to vary the actual EGR quantity from the first desired EGR quantity to the second desired EGR quantity by varying the EGR control signal in response to the changeover request signal, and for producing the first-mode-to-second-mode combustion command signal to command the combustion changeover from the first combustion mode to the second combustion mode at a combustion changeover timing, the controller determining the combustion changeover timing by monitoring the EGR changeover operation as well as the fuel air ratio changeover operation.

An engine control process for an internal combustion engine equipped with a combustion system for changing over a combustion condition in the engine among a plurality of combustion modes in accordance with an engine operating condition, and an EGR system for recirculating part of exhaust gas from the engine to an intake air flow into the engine, the engine control process comprising:

• a first step for producing a first-mode-to-second-mode combustion changeover request signal for requesting a changeover from a first combustion mode to a second combustion mode;
• a second step for varying an actual equivalent ratio, in response to the changeover request signal, gradually from a first desired ratio level for the first combustion mode to a second desired ratio level for the second combustion mode;
• a third step for calculating an EGR quantity of the EGR system during a gradual variation of the actual equivalent ratio from the first ratio level to the second ratio level;
• a fourth step for calculating a modified equivalent ratio in consideration of the EGR quantity;
• and
• a fifth step for changing over the combustion condition from the first combustion mode to the second combustion mode in accordance with the modified equivalent ratio.