Control device for direct-injection spark-ignition engine and method of setting fuel injection timing of the same

A method of setting fuel injection timing of a direct-injection spark-ignition engine having a tumble generator for creating a tumble in a combustion chamber and a fuel injector which injects fuel into the combustion chamber in a direction opposite to tumble flow such that a combustible mixture is produced around a spark plug at an ignition point in a stratified charge combustion region which is a low-speed low-load operating range of the engine, said method comprising the steps of:

• calculating target load according to the amount of depression of an accelerator pedal and engine speed;
• determining the ignition point according to the target load and the engine speed in the stratified charge combustion region;
• and
• setting as a fuel injection ending point a point generally fixed crank angle before the ignition point regardless of variations in the engine speed.

A control device for a direct-injection spark-ignition engine having an intake port formed to create a tumble in a combustion chamber, a spark plug located at an upper central part of the combustion chamber, a fuel injector which is located at a peripheral part of the combustion chamber and injects fuel into the combustion chamber in a direction opposite to tumble flow such that a combustible mixture is produced around the spark plug at an ignition point in a stratified charge combustion region which is a low-speed low-load operating range of the engine, said control device comprising:

• a high-pressure fuel pump capable of regulating fuel pressure applied to the injector;
• an engine speed sensor for detecting engine speed;
• an accelerator depression sensor for detecting the amount of depression of an accelerator pedal;
• an airflow sensor for detecting the amount of intake air;
• and
• an engine control unit which detects engine operating conditions based on outputs from the engine speed sensor and the accelerator depression sensor and, based on the detected engine operating conditions and an output from the airflow sensor, controls the fuel pressure such that a fuel spray from the injector is progressively intensified with an increase in the engine speed in the stratified charge combustion region, causes the injector to inject the fuel before the ignition point on compression stroke in the stratified charge combustion region, and controls the ignition point and fuel injection timing such that and the interval between a fuel injection ending point and the ignition point becomes shorter with an increase in the engine speed under the same engine load within the stratified charge combustion region.