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 phase-variable mechanism configured to simultaneously change an open timing and a close timing of the intake valve;
• and
• a controller including a processor configured to control parts of the engine, including the intake phase-variable mechanism and the spark plug, wherein
• the controller controls the intake phase-variable mechanism to form a gas-fuel ratio (G/F) lean environment in which burnt gas remains inside the cylinder and an air-fuel ratio that is a ratio of air to fuel inside the cylinder is near a stoichiometric air-fuel ratio, 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, and
• the controller controls the intake phase-variable mechanism to retard, as an engine speed increases at a constant engine load, the close timing of the intake valve on a retarding side of a bottom dead center of intake stroke and the open timing of the intake valve on an advancing side of a top dead center of exhaust stroke, so that a rate of change in the open timing of the intake valve with respect to the engine speed in a high engine speed range is greater than that in a low engine speed range.