Control device and control method for internal combustion engine

A control method for an internal combustion engine,

• the internal combustion engine comprising:
• a variable compression ratio mechanism that varies an actual compression ratio of the internal combustion engine by changing a top dead center position of a piston reciprocating in a cylinder;
• a variable valve mechanism that varies a valve overlap period of intake and exhaust valves by changing an actual valve timing of at least one of the intake and exhaust valves;
• and a variable valve control portion that controls the variable valve mechanism within a range that avoids interference between the piston and the intake and exhaust valves,
• the control method comprising:
• setting a steady-state target compression ratio as a target value of the actual compression ratio during a steady state such that the target compression ratio becomes lower with increase in actual intake air amount;
• determining a scavenging demand value indicating a degree of demand for increasing the actual intake air amount by increase of the valve overlap period;
• setting a corrected target compression ratio by correcting the steady-state target compression ratio by the scavenging demand value;
• and
• at the time when the actual intake air amount should be increased by increasing the valve overlap period, correcting the steady-state target compression ratio by the scavenging demand value to set a corrected target compression ratio, and then, controlling the variable compression ratio mechanism to lower the top dead center position of the piston and thereby vary the actual compression ratio according to the corrected target compression ratio so that the actual compression ratio varied by the variable compression ratio mechanism becomes lower than the steady-state target compression ratio.