Control apparatus for engine

A control apparatus for an engine, the control apparatus comprising:

• the engine having a combustion chamber;
• a state quantity setting device mounted to the engine, the state quantity setting device configured to adjust introduction of fresh air and burned gas into the combustion chamber;
• an injector mounted to the engine, the injector configured to inject fuel;
• a spark plug disposed so as to face an inside of the combustion chamber;
• a mechanical supercharger disposed in an intake passage;
• and
• a controller connected to the state quantity setting device, the injector, and the spark plug, the controller configured to output control signals to the state quantity setting device, the injector, and the spark plug, and control the spark plug to ignite air-fuel mixture to start combustion, wherein
• after the spark plug ignites air-fuel mixture to start combustion, combustion of unburned air-fuel mixture is caused by autoignition,
• the controller is configured to output a control signal to the state quantity setting device such that, when a number of revolutions of the engine is high, a temperature in the combustion chamber before start of compression, during SPCCI (Spark Controlled Compression Ignition) combustion in which spark ignition (SI) combustion and compression ignition combustion are combined, is higher than that when the number of revolutions of the engine is low,
• the state quantity setting device has a variable valve mechanism provided to the engine and configured to receive the control signal from the controller and change an opening time of at least one of an intake valve and an exhaust valve, and
• the controller is configured to output the control signal to the state quantity setting device to continuously shorten a positive overlap period in which both the intake valve and the exhaust valve are opened as the number of revolutions of the engine increases at a given load during the SPCCI combustion in which gas to be introduced into the combustion chamber is supercharged and the spark ignition combustion and the compression ignition combustion are combined, such that the temperature in the combustion chamber before the start of compression is higher when the number of revolutions is high than when the number of revolutions is low.