Control system for an internal combustion engine

A method for controlling a direct-injection four-stroke internal combustion engine having at least one cylinder, an intake passage supplying air to the cylinder, and an exhaust passage removing exhaust gas from the cylinder, the method comprising:

• detecting a mass air flow upstream of the cylinder;
• detecting an intake air density in the cylinder;
• calculating an in-cylinder trapped intake air amount based on a cylinder volume and the detected intake air density;
• and
• estimating a difference between the intake air amount detected by the mass air flow meter and the in-cylinder trapped intake air amount, the estimated difference being an estimated scavenging amount representing a fresh air blowby amount passing from the intake passage into the exhaust passage.

A control system for an internal combustion engine, comprising:

• an in-cylinder intake air density detecting means configured to detect an intake air density in a cylinder;
• an in-cylinder intake air trapped amount calculating means configured to calculate an in-cylinder trapped intake air amount based on a cylinder volume and the intake air density;
• a mass air flow meter configured to detect a mass air flow upstream of the cylinder;
• and
• an estimated scavenging amount calculating means configured to estimate a difference between the intake air amount detected by the mass air flow sensor and the in-cylinder trapped intake air amount as an estimated scavenging amount representing a fresh air blowby amount passing from an intake passage into an exhaust passage.