Method and system for engine control

A method for an engine coupled with a continuously variable transmission (CVT), comprising:

• for a driver demand,
• estimating a first fuel economy associated with maintaining a first compression ratio to a second fuel economy associated with transitioning to a second compression ratio while operating with a knock-adjusted and friction-adjusted engine speed-load profile;
• and
• in response to the second fuel economy being higher than the first fuel economy, transitioning to the second compression ratio via mechanical adjustments to a piston position and transitioning to the knock-adjusted and friction-adjusted engine speed-load profile via adjustments to a speed ratio of the CVT.

A vehicle system, comprising:

• an engine with a cylinder;
• a VCR mechanism coupled to a piston of the cylinder for varying a compression ratio of the engine via mechanical alteration of a piston position within the cylinder;
• a continuously variable transmission (CVT) coupling the engine to vehicle wheels, the CVT having a plurality of speed ratios;
• and
• a controller with computer readable instructions stored on non-transitory memory for:
• estimating a first fuel economy associated with maintaining a first compression ratio to a second fuel economy associated with transitioning to a second compression ratio;
• if the second fuel economy is higher, predicting a fuel penalty associated with operating with a modified engine speed-load profile at the second compression ratio;
• and
• if the fuel penalty adjusted second fuel economy is higher than the first fuel economy, actuating the VCR mechanism to transition to the second compression ratio while selecting one of the plurality of speed ratios to provide the modified engine speed-load profile.