Control system for compression-ignition engine

A control system for a compression-ignition engine including a cylinder, an intake passage, an exhaust passage, an intake port communicating the intake passage to the cylinder, an intake valve configured to open and close the intake port, an exhaust port communicating the exhaust passage to the cylinder, an exhaust valve configured to open and close the exhaust port, an injector configured to inject fuel into the cylinder, and a spark plug configured to ignite a mixture gas containing the fuel injected by the injector and air, the engine executing partial compression-ignition combustion in which the mixture gas is spark-ignited with the spark plug to be partially combusted by spark ignition (SI) combustion and the remaining mixture gas self-ignites to be combusted by compression ignition (CI) combustion, comprising:

• an intake variable mechanism configured to change an open timing of the intake valve;
• and
• a controller including a processor configured to control parts of the engine, including the intake variable mechanism and the spark plug, wherein
• while the engine is operating within a given first operating range and a second operating range that is on a higher engine load side of the first operating range, the controller controls the intake variable mechanism to form a gas-fuel ratio (G/F) lean environment in which an air-fuel ratio that is a ratio of air to fuel inside the cylinder is near a stoichiometric air-fuel ratio and burnt gas remains inside the cylinder, and controls the spark plug to spark-ignite the mixture gas so as to combust by the partial compression-ignition combustion at a given timing,
• while the engine is operating within the first operating range, the controller controls the intake variable mechanism to advance, as the engine load increases at a constant engine speed, the open timing of the intake valve on an advancing side of a top dead center of exhaust stroke, and
• while the engine is operating within the second operating range, the controller controls the intake variable mechanism to retard, as the engine load increases at a constant engine speed, the open timing of the intake valve on the advancing side of the top dead center of the exhaust stroke.