Control system for internal combustion engine

A control system for an internal combustion engine including:

• a plurality of cylinders;
• a plurality of fuel injection valves provided in the plurality of cylinders respectively, each of the plurality of fuel injection valves being configured to directly inject a fuel into a corresponding one of the cylinders by moving a needle and opening injection holes;
• a high-pressure pump configured to increase a pressure of the fuel and feed the fuel under pressure;
• a common rail configured to store the fuel, a reference pressure of the fuel being increased by the high-pressure pump;
• a plurality of fuel passages provided independently of each other, each of the fuel passages extending from the common rail to the injection holes of a corresponding one of the plurality of fuel injection valves;
• and
• a control chamber provided in each of the plurality of fuel injection valves, the control chamber being connected to a corresponding one of the fuel passages which leads to the injection holes of the corresponding fuel injection valve,
• the control system comprising an electronic control unit configured to:
• (i) reduce a pressure of the fuel in the control chamber to be lower than a pressure of the fuel in the fuel passage connected to the control chamber, in each of the plurality of fuel injection valves,
• (ii) move the needle in a direction to open the injection holes by reducing the pressure of the fuel such that a first pressure difference as a pressure difference between the pressure of the fuel in the control chamber and the pressure of the fuel in the fuel passage connected to the control chamber is equal to or larger than a predetermined pressure difference, in each of the plurality of fuel injection valves, so as to move the needle in a direction to open the injection holes, and
• (iii) reduce the reference pressure by executing pressure reducing operation in a second injection valve, such that the first pressure difference after executing the reference pressure reducing operation is smaller than the predetermined pressure difference during fuel injection by a first injection valve, and after a lapse of a predetermined period from start of fuel injection by the first injection valve, the first injection valve being one of the plurality of the fuel injection valves which is currently injecting the fuel, the second injection valve being at least one of the plurality of fuel injection valves which is different from the first injection valve.