Method and system for controlling operating pressure in a common-rail fuel injection system, particularly for a diesel engine

A system for controlling operating pressure in a fuel injection system of an internal combustion engine, including:

• a plurality of injectors (I1-I4), each of which is adapted to deliver a predetermined amount of pressurized fuel to a combustion chamber of a respective one of a plurality of cylinders (C1-C4) of the internal combustion engine;
• a high-pressure accumulator volume common to said plurality of injectors (I1-I4) and arranged to maintain the fuel at high-pressure;
• a sensor for measuring fuel pressure in an accumulator volume;
• an adjustor for adjusting the fuel pressure in the accumulator volume as a function of the fuel pressure, so as to maintain a predetermined target injection pressure set-point dependent on an engine operating point by returning excess fuel to a fuel tank;
• and
• an electronic controller arranged for controlling a fuel injection timing and quantity by operating injectors control valves, the electronic controller is arranged to control an injection timing by triggering retarded injections (INJpost) of a predetermined quantity of fuel to the combustion chamber of the plurality of cylinders (C1-C4) of the internal combustion engine during a respective exhaust stroke, when pressure above a predetermined threshold (THover) is detected in the accumulator volume, so as to discharge fuel from the accumulator volume without it taking part to a combustion process, thereby reducing pressure in the accumulator volume,
• said electronic controller being further arranged to:
• supply fuel under a predetermined target high pressure to an accumulator volume common to a plurality of electrically controlled fuel injectors (I1-I4), each of which is adapted to deliver the predetermined amount of pressurized fuel to the combustion chamber of a respective cylinder (C1-C4) of the internal combustion engine;
• measure fuel pressure in the accumulator volume;
• and
• adjust the fuel pressure in the accumulator volume as a function of the fuel pressure, so as to maintain the predetermined target injection pressure set-point dependent on the engine operating point by returning excess fuel to the fuel tank;
• control injection timing by triggering retarded injections (INJpost) of the predetermined quantity of fuel to the combustion chamber of the plurality of cylinders (C1-C4) of the internal combustion engine during the respective exhaust stroke, when pressure above the predetermined threshold (THover) is detected in the accumulator volume, so as to discharge fuel from the accumulator volume without it taking part to the combustion process, thereby reducing pressure in the accumulator volume.