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

Abstract

In a fuel injection system of an internal combustion engine that includes, but is not limited to injectors (I-I), each of which is adapted to deliver a predetermined amount of pressurized fuel to a combustion chamber of a respective cylinder (C-C) of the engine, a high-pressure accumulator volume common to the injectors (I-I) and arranged to maintain the fuel at high-pressure, a pressure sensor for measuring fuel pressure in the accumulator volume, a metering unit for adjusting the fuel pressure in the accumulator volume as a function of the measured pressure, so as to maintain a predetermined target injection pressure set-point dependent on the engine operating point by returning excess fuel to a fuel tank; and an electronic control unit arranged for controlling fuel injection timing and quantity by operating injectors control valves, the operating pressure is controlled by triggering retarded injections (INJpost) of a predetermined quantity of fuel to the combustion chamber of the cylinders (C-C) of the 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 the combustion process, thereby reducing pressure in the accumulator volume.