Internal combustion engine system and control method for internal combustion engine

A control method for an internal combustion engine,

• the internal combustion engine including a turbocharged engine and an electronic control unit,
• the turbocharged engine including a plurality of intake cams different in cam profile, an EGR system, and an ignition device, the intake cams being configured to drive an intake valve, the EGR system being configured to introduce exhaust gas flowing through an exhaust system, as an external EGR gas, in to an intake system, the ignition device being configured to ignite an air-fuel mixture in a cylinder,
• the electronic control unit being configured to set a target value of an EGR rate in accordance with an operating state identified with engine torque and engine speed, the EGR rate being expressed as a ratio of the external EGR gas to intake air, the control method comprising:
• in a first operation region where the target value of the EGR rate is set to a specified EGR rate, selecting, via the electronic control unit, a first cam as a driving cam of the intake valve, and setting, via the electronic control unit, closing timing of the intake valve to a first crank angle section including a crank angle that offers a highest suction efficiency under a condition where the engine speed and turbocharging pressure are fixed;
• and
• in a second operation region, selecting, via the electronic control unit, a second cam as the driving cam, setting, via the electronic control unit, the closing timing to a second crank angle section positioned at a more advanced side than the first crank angle section, and changing, via the electronic control unit, ignition timing of the ignition device to a more advanced side than the ignition timing of the ignition device in the first operation region,
• the second operation region positioned closer to a high-speed side than the first operation region, the second operation region having the target value of the EGR rate set to a value lower than the specified EGR rate, the second cam being smaller in valve duration and lift amount than the first cam, the second crank angle section being lower in suction efficiency than the first crank angle section.