Control system of compression-ignition engine

A control system of 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 performs 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:

• a variable intake mechanism configured to 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 variable intake mechanism and the spark plug,
• wherein when the engine is operated at least in a given first operating range, the controller controls the variable intake mechanism so that an air-fuel ratio (A/F) lean environment where an air-fuel ratio that is a ratio of air to fuel in the cylinder becomes higher than a stoichiometric air-fuel ratio is formed, while causing the spark plug to perform spark ignition at a given timing so that the mixture gas combusts by the partial compression-ignition combustion, and the controller controls the variable intake mechanism so that, under the same engine load condition, the close timing of the intake valve is more retarded as the engine speed decreases, within a range where an amount of air inside the cylinder decreases by retarding the valve close timing.