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 a volume of a combustion chamber and a piston displacement by the volume of the combustion chamber, wherein the volume of the combustion chamber is defined as the volume of the combustion chamber when the piston is at a compression top dead center, and
• a variable valve timing mechanism that controls a valve closing timing at which an intake valve is closed, 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, wherein
• when the air-fuel ratio is increased from the first desired air-fuel ratio to the second desired air-fuel ratio, the mechanical compression ratio is reduced, and
• wherein when the air-fuel ratio is increased from the first desired air-fuel ratio to the second desired air-fuel ratio, an actual compression ratio, which is obtained by dividing the sum of the volume of the combustion chamber and the actual piston displacement by the volume of the combustion chamber, is increased.

A spark-ignited internal combustion engine comprising:

• a variable compression ratio mechanism that changes a mechanical compression ratio, which is obtained by dividing a sum of a volume of a combustion chamber and a piston displacement by the volume of the combustion chamber, wherein the volume of the combustion chamber is defined as the volume of the combustion chamber when the piston is at a compression top dead center;
• and
• a variable valve timing mechanism that controls a valve closing timing at which an intake valve is closed, wherein
• an amount of intake air that is supplied into the combustion chamber is controlled 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, the valve closing timing of the intake valve is brought 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, wherein when the air-fuel ratio is increased from the first desired air-fuel ratio to the second desired air-fuel ratio, the mechanical compression ratio is reduced when an actual compression ratio, which is obtained by dividing a sum of the volume of the combustion chamber and an actual piston displacement by the volume of the combustion chamber, exceeds an allowable limit.

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 a volume of a combustion chamber and a piston displacement by the volume of the combustion chamber, wherein the volume of the combustion chamber is defined as the volume of the combustion chamber when the piston is at a compression top dead center, and
• a variable valve timing mechanism that controls a valve closing timing at which an intake valve is closed, the method 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, wherein when the air-fuel ratio is increased from the first desired air-fuel ratio to the second desired air-fuel ratio, the mechanical compression ratio is reduced when an actual compression ratio, which is obtained by dividing a sum of the volume of the combustion chamber and an actual piston displacement by the volume of the combustion chamber, exceeds an allowable limit.