Control device for internal combustion engine

A control device for an internal combustion engine which is configured to control an engine, the engine comprising:

• two types of intake cams for driving an intake valve;
• a turbocharger including an exhaust turbine and an intake compressor;
• an exhaust gas purifying catalyst which is provided on a downstream of the exhaust turbine;
• an EGR device which is configured to introduce exhaust gas on the downstream side of the exhaust gas purifying catalyst into an upstream side of the intake compressor as an external EGR gas;
• and
• an ignition device which is configured to ignite air-fuel mixture in a cylinder,
• wherein the control device is configured to, based on an operation condition of the engine which is specified by engine torque and engine speed, set a target EGR rate and a target air-fuel ratio and select from the intake cams a drive cam for the intake valve,
• wherein the control device is further configured to, when the engine is operated in a high EGR operation region where the target EGR rate is set to a predetermined high EGR rate:
• select a first cam as the drive cam;
• and
• set a closing timing of the intake valve to a first crank angle section including a crank angle at which inhalation efficiency is the highest under a condition where engine speed and supercharging pressure are fixed,
• wherein the control device is further configured to, when the engine is operated in a low EGR operation region where is located on a higher torque and higher engine speed side relative to the high EGR operation region and the target EGR rate is set to a lower rate than the predetermined high EGR rate:
• select a second cam as the drive cam which has smaller operation angle and smaller lift amount than those of the first cam;
• set the closing timing of the intake valve to a second crank angle section which is located on an advanced side relative to the first crank angle section and whose inhalation efficiency is lower than that during the first crank angle section;
• and
• change an ignition period of the ignition device to an advance period relative to the ignition period which is set when the engine is operated in the high EGR operation region,
• wherein the control device is further configured to, when the engine is operated in an operation region where the high EGR operation region is overlapped with a rich operation region where the target air-fuel is set to a rich value:
• change the target EGR rate to a lower value than the predetermined high EGR rate;
• select the second cam as the drive cam;
• set the closing timing to the second crank angle section;
• and
• change the ignition period to the advance period.