Internal combustion engine driven with change-over of compression ratio, air-fuel ratio, and boost status

摘要

With an increase in torque demand, the internal combustion engine of the invention successively changes over a combination of a compression ratio, an air-fuel ratio, and a boost status of an air-fuel mixture from (1) settings of a high compression ratio, a lean air-fuel ratio, and a non-boosting state, (2) settings of the high compression ratio, the lean air-fuel ratio, and a boosting state, (3) settings of a low compression ratio, the lean air-fuel ratio, and the boosting state, to (4) settings of the low compression ratio, a stoichiometric air-fuel ratio, and the boosting state. The changeover strategy desirably widens a driving area of the internal combustion engine at the high compression ratio of a high thermal efficiency or at the lean air-fuel ratio. Under the condition of a large torque demand, the internal combustion engine is driven with boosting the stoichiometric air-fuel mixture at the low compression ratio to output a sufficiently large torque. The arrangement of the invention adequately changes over the compression ratio, the air-fuel ratio, and the boost status of the internal combustion engine, thus simultaneously enhancing the thermal efficiency and the maximum output of the internal combustion engine.