Patent ID: 7779819

Claim:
Control method for an overpressure valve in a common-rail fuel supply system, the method including: delivering fuel under pressure, via a high-pressure pump, to a common rail equipped with the overpressure valve that is set to discharge the fuel present in the common rail into a discharge line when the fuel pressure inside the common rail exceeds a safety value (p safety ) which guarantees the tightness and safety of the injection system; determining, during a normal use, the fuel pressure inside the common rail; feedback-piloting, during the normal use, the high-pressure pump in function of the fuel pressure inside the common rail to keep the fuel pressure inside the common rail to a desired level which is always lower than the safety value (p safety ); piloting, during a diagnostic test performed with the internal combustion engine in cut-off condition, the high-pressure pump to increase the fuel pressure inside the common rail beyond the safety value (p safety ) to reach a target pressure (p target ) having a higher value that the safety value (p safety ) in order to trigger operation of the overpressure valve; determining, during the diagnostic test, the flow (m HP ) of the high-pressure pump and/or the fuel pressure inside the common rail; comparing the flow (m HP ) of the high-pressure pump and/or the fuel pressure inside the common rail during the diagnostic test with respective threshold values (m test and p test ); and diagnosing malfunctioning of the overpressure valve if the flow (m HP ) of the high-pressure pump is less than a respective flow threshold value (m test ) and/or the fuel pressure inside the common rail is greater than a respective pressure threshold (p test ).