Patent ID: 7856960

Claim:
A control method of a direct injection system of the common-rail type provided with: a high-pressure fuel pump which comprises at least one pumping element formed by a cylinder having a pumping chamber in which a movable piston slides in reciprocal motion, an intake valve of the pumping chamber in communication with an intake pipe, and a delivery valve of the pumping chamber in communication with a delivery pipe feeding fuel to a common rail supplying injectors; and a shut-off valve, which controls the flow rate of the high-pressure fuel pump, is arranged along the intake pipe and upstream from the intake valve, is separated and independent from the intake valve, and is of the open/closed type so that during an opening time of the shut-off valve the high-pressure pump takes in a maximum flow rate which may cross the shut-off valve while during a closing time of the shut-off valve the high-pressure pump does not take in anything; and the control method comprising: feeding the pressurized fuel to the common rail by means of the high-pressure pump which receives the fuel through the shut-off valve; cyclically controlling the opening and closing of the shut-off valve to choke the flow rate of fuel taken in by the high-pressure pump; adjusting the flow rate of fuel taken in by the high-pressure pump by varying a ratio between a duration of the opening time and a duration of the closing time of the shut-off valve; determining a lower limit value of the opening time of the shut-off valve; and reducing a driving frequency of the shut-off valve so that a real opening time of the shut-off valve is always over a lower limit value.