Spark-ignited internal combustion engine and method of controlling the same

A method of controlling a spark-ignited internal combustion engine, which includes

• a variable compression ratio mechanism that changes a mechanical compression ratio, which is obtained by dividing a sum of the volume of a combustion chamber and a piston displacement by the volume of the combustion chamber, and
• a variable valve timing mechanism that controls a valve closing timing at which an intake valve is closed, characterized by comprising:
• controlling an amount of intake air that is supplied into the combustion chamber by changing the valve closing timing of the intake valve;
• and
• when an air-fuel ratio is increased from a first desired air-fuel ratio to a second desired air-fuel ratio, bringing the valve closing timing of the intake valve close to an intake bottom dead center until the air-fuel ratio becomes equal to the second desired air-fuel ratio, without changing a fuel injection amount.