Method to determine an opening time of an electromagnetic fuel injector

1. A method to determine an opening time (T O ) of an electromagnetic fuel injector ( 4 ), which comprises a movable plunger ( 23 ) moving between a closing position and an opening position to close and open an injection valve ( 15 ), and an electromagnetic actuator ( 14 ), which is provided with a coil ( 16 ) and is designed to move the plunger ( 23 ) between the closing position and the opening position; the method comprises the steps of:

controlling the electromagnetic fuel injector ( 4 ) using a series of progressively increasing energization times (T INJ ) of the electromagnetic actuator ( 14 );

determining, for each control of the electromagnetic injector ( 4 ), the presence or the absence of a closing of the injection valve ( 15 ); and

identifying the opening time (T O ) equal to an intermediate value between the last energization time (T INJ ) of the electromagnetic actuator ( 14 ) for which the absence of a closing of the injection valve ( 15 ) was determined and the first energization time (T INJ ) of the electromagnetic actuator ( 14 ) for which the presence of a closing of the injection valve ( 15 ) was determined;

wherein the step of determining, for each control of the electromagnetic injector ( 4 ), the presence or the absence of a closing of the injection valve ( 15 ) comprises the further steps of:

applying, in a beginning instant (t 1 ) of a test, a positive voltage (v) to the coil ( 16 ) of the electromagnetic actuator ( 14 ) so as to cause a test electric current (i) to circulate through the coil ( 16 ), said test electric current (i) certainly not determining the opening of the injection valve ( 15 );

applying, in an end instant (t 3 ) of the test, a negative voltage (v) to the coil ( 16 ) of the electromagnetic actuator ( 14 ) so as to cancel the test electric current (i);

detecting a voltage comparison time development (v 2 ) at at least one end of the coil ( 16 ) of the electromagnetic actuator ( 14 ) after the cancellation of the test electric current (i);

applying, in a beginning instant (t 1 ) of an energization of the electromagnetic actuator ( 14 ), a positive voltage (v) to the coil ( 16 ) of the electromagnetic actuator ( 14 ) so as to cause an actuation electric current (i) to circulate through the coil ( 16 ), said actuation electric current (i) could maybe determine the opening of the injection valve ( 15 );

applying, in an end instant (t 2 ) of the energization of the electromagnetic actuator ( 14 ), a negative voltage (v) to the coil ( 16 ) of the electromagnetic actuator ( 14 ) so as to cancel the actuation electric current (i);

detecting a voltage actuation time development (v 1 ) at at least one end of the coil ( 16 ) of the electromagnetic actuator ( 14 ) after the cancellation of the actuation electric current (i);

calculating a voltage difference (Δv) between the voltage actuation time development (v 1 ) and the voltage comparison time development (v 2 );

calculating a first time derivative (dΔv/dt) of the voltage difference (Δv);

calculating a maximum value of the first time derivative (dΔv/dt) of the voltage difference (Δv);

identifying the presence of a closing of the electromagnetic injector ( 4 ) only if the maximum value of the first time derivative (dΔv/dt) of the voltage difference (Δv) exceeds, in absolute value, a first threshold; and

identifying the absence of a closing of the electromagnetic injector ( 4 ) only if the maximum value of the first time derivative (dΔv/dt) of the voltage difference (Δv) is, in absolute value, below the first threshold.

2. The method according to claim 1 and comprising the further steps of:

establishing an expected value of the opening time (T O ); and

centering the series of progressively increasing energization times (T INJ ) of the electromagnetic actuator ( 14 ) on the expected value of the opening time (T O ).

3. The method according to claim 1 and comprising the further steps of

establishing a time resolution in determining the presence or the absence of a closing of the injection valve ( 15 ); and

increasing the energization times (T INJ ) of the electromagnetic actuator ( 14 ) of the series of progressively increasing energization times (T INJ ) of the electromagnetic actuator ( 14 ) with an increase equal to the time resolution in determining the presence or the absence of a closing of the injection valve ( 15 ).

4. The method according to claim 1 and comprising the further step of synchronizing the voltage actuation time development (v 1 ) with the voltage comparison time development (v 2 ) by aligning, in a time-wise manner, a first instant (t 4 ) in which the actuation electric current (i) is cancelled with a second instant (t 4 ) in which the test electric current (i) is cancelled.

5. The method according to claim 1 and comprising the further steps of:

calculating a maximum value of the voltage difference (Δv);

identifying the presence of a closing of the electromagnetic injector ( 4 ) only if the maximum value of the voltage difference (Δv) exceeds, in absolute value, a second threshold; and

identifying the absence of a closing of the electromagnetic injector ( 4 ) if the maximum value of the voltage difference (Δv) is, in absolute value, below the second threshold.

6. The method according to claim 1 and comprising the further step of applying a low-pass filter, in particular a sliding-window filter, to the voltage difference (Δv).

7. The method according to claim 1 and comprising the further step of applying an anti-aliasing filter to the voltage (v) when the voltage time developments (v 1 , v 2 ) are detected.

8. The method according to claim 1 , wherein:

the coil ( 16 ) of the electromagnetic actuator ( 14 ) has a high-voltage terminal ( 100 ) and a low-voltage terminal ( 101 ); and

the voltage (v) is measured between the two terminals ( 100 , 101 ) of the coil ( 16 ) when the first and the second voltage time developments (v 2 ) are detected.

9. The method according to claim 1 , wherein:

the coil ( 16 ) of the electromagnetic actuator ( 14 ) has a high-voltage terminal ( 100 ) and a low-voltage terminal ( 101 ); and

the voltage (v) is measured between the two low-voltage terminal ( 101 ) of the coil ( 16 ) and an electric ground when the first and the second voltage time developments (v 1 , v 2 ) are detected.