Patent ID: 7159543

Claim:
An engine comprising: a cylinder; a piston slideably received in the cylinder; a crankshaft connected to the piston; a multi-link piston crank mechanism connected to the crankshaft for controlling movement of the piston such that an acceleration of the piston at top dead center is less than an acceleration of the piston at bottom dead center; a determining device that determines an operating condition of the engine; a combustion mode control device that controls the engine to operate at an air-fuel ratio leaner than a stoichiometric air-fuel ratio when the determining device determines that the operating condition of the engine is in a predetermined first operating region; a compression ratio change device connected to the multi-link piston crank mechanism configured and arranged to change a compression ratio of the engine between a low compression mode and a high compression mode based on an engine speed and an engine load such that as the engine speed becomes lower, a lower limit of the engine load for the low compression mode is lowered.