Fuel injection system

Fuel injection system according to one of the foregoing claims, wherein the piezoelectric element (10, 20, 30, 40, 50 or 60) is discharged from a second voltage to a third voltage, characterized in that the control unit determines the value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60) based upon the second voltage and the third voltage.

Fuel injection system according to one of the foregoing claims, wherein the piezoelectric element (10, 20, 30, 40, 50 or 60) is discharged from a second voltage to a third voltage within a discharging time, characterized in that the control unit determines the value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60) based upon the discharging time, and, in particular an estimated value of, a current discharging the piezoelectric element (10, 20, 30, 40, 50 or 60).

Fuel injection system according to one of the foregoing claims, characterized in that the control unit determines the value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60) based upon the quotient of the third voltage and the charge the piezoelectric element (10, 20, 30, 40, 50 or 60) is carrying, based upon the quotient of the charge the piezoelectric element (10, 20, 30, 40, 50 or 60) is carrying and the third voltage, based upon the quotient of the difference between the second voltage and the third voltage and the product of the discharging time and the current discharging the piezoelectric element (10, 20, 30, 40, 50 or 60), or based upon the quotient of the product of the discharging time and the current discharging the piezoelectric element (10, 20, 30, 40, 50 or 60) and the difference between the second voltage and the third voltage.

Fuel injection system according to one of the foregoing claims, characterized in that the control unit is able to determine a possible fault of the piezoelectric element (10, 20, 30, 40, 50 or 60) or electric circuitry driving the piezoelectric element (10, 20, 30, 40, 50 or 60) based upon a calculated value of the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60) and a value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60) at a former stage, in particular based upon a comparison of the value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60) and a former value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60).

Fuel injection system according to one of the foregoing claims wherein the fuel injection system comprises a switch (11, 21,31, 41, 51 or 61) for discharging the piezoelectric element (10, 20, 30, 40, 50 or 60), characterized in that the control unit is able to determine a possible short cut of the switch (11, 21,31, 41, 51 or 61) based upon the value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60).

Method for operating a fuel injection system comprising a piezoelectric element (10, 20, 30, 40, 50 or 60) for controlling the amount of injected fuel, in particular for operating a fuel injection system according to one of the foregoing claims, characterized in that a possible fault of the piezoelectric element (10, 20, 30, 40, 50 or 60) or an electric circuitry driving the piezoelectric element (10, 20, 30, 40, 50 or 60) is determined based upon a value related to the capacitance of the piezoelectric element (10, 20, 30, 40, 50 or 60).