Method and device for controlling spark-ignition direct injection engine

A control device of a spark-ignition direct injection engine, comprising:

• an engine body having a cylinder in which a geometric compression ratio is set to 12:1 or above;
• a fuel injection valve for directly injecting fuel into the cylinder at a predetermined injection timing;
• an ignition plug for spark-igniting a gas mixture inside the cylinder at a predetermined ignition timing;
• a compression ratio adjusting mechanism for adjusting an effective compression ratio of the engine body by changing activation modes of intake and exhaust valves for performing intake and exhaust for the cylinder, the activation modes including at least opening and closing timings of the intake and exhaust valves;
• and
• a controller for controlling an operation of the engine body through controlling the fuel injection valve, the ignition plug, and the compression ratio adjusting mechanism;
• wherein, when an operating state of the engine body is within a particular operating range where an engine speed is comparatively low and a load is high, the control by the controller includes:
• setting the effective compression ratio to be 10:1 or above;
• retarding a spark ignition timing with respect to an MBT, and setting a retarding amount of the spark ignition timing within a first engine speed range of the particular operating range, where the engine speed is relatively low, to be larger than a retarding amount of the spark ignition timing within a second engine speed range, where the engine speed is higher than the first engine speed range;
• setting an injection mode of the fuel to divided injections in which the injection is performed at least twice in a period from an intake stroke to an earlier-half stage of a compression stroke;
• performing, within the first engine speed range, a final injection of the divided injections in the earlier-half stage of the compression stroke;
• and
• performing, within the second engine speed range, the final injection of the divided injections in a late stage of the intake stroke and the at least one injection other than the final injection in a middle stage of the intake stroke.