Control device for internal combustion engine

A control device for an internal combustion engine for controlling an internal combustion engine provided with:

• an engine body;
• and
• a variable compression ratio mechanism configured to drive a motor to thereby enable change of a mechanical compression ratio of the engine body,
• which control device comprises a compression ratio control part configured to control the mechanical compression ratio to a target compression ratio,
• the compression ratio control part comprising:
• an optimum compression ratio calculating part configured to calculate an optimum compression ratio in the engine operating state based on the engine operating state;
• a permittable changed compression ratio calculating part configured to calculate a permittable changed compression ratio higher than the target compression ratio giving the effect of improvement of the fuel efficiency even if considering the amount of fuel consumed by driving the motor when the optimum compression ratio is higher than the target compression ratio;
• and
• a target compression ratio changing part configured to change the target compression ratio to the permittable changed compression ratio when the optimum compression ratio is higher than the target compression ratio and the optimum compression ratio becomes the permittable changed compression ratio or more.