Method to determine a closing instant of an electromagnetic fuel injector

1. A method to determine a closing instant (t 5 ) 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:

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) 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 injection, 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) determining the opening of the injection valve ( 15 );

applying, in an end instant (t 3 ) of the injection, 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 an absolute minimum of the first time derivative (dΔv/dt) of the voltage difference (Δv);

identifying the closing instant (t 5 ) of the electromagnetic fuel injector ( 4 ) based on the 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 , wherein the test to detect the voltage comparison time development (v 2 ) is carried out immediately before each fuel injection, so that a voltage comparison time development (v 2 ) is used to determine the closing instant (t 5 ) of the electromagnetic fuel injector ( 4 ) of one single corresponding injection.

3. The method according to claim 1 , wherein the test to detect the voltage comparison time development (v 2 ) is carried out every now and then, so that a voltage comparison time development (v 2 ) is used to determine the closing instant (t 5 ) of the electromagnetic fuel injector ( 4 ) of different injections.

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 to the instant (t 5 ) of the absolute minimum of the first time derivative (dΔv/dt) of the voltage difference (Δv) a predetermined time advance, which makes up for the phase delays introduced by all the filters applied.

8. 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.

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 terminals ( 100 , 101 ) of the coil ( 16 ) when the first and the second voltage time developments (v 1 , v 2 ) are detected.

10. 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 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.

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

establishing a rotation speed objective and a torque objective to be generated for an internal combustion engine ( 2 ) where the electromagnetic fuel injector ( 4 ) is installed;

determining a total fuel quantity (Q) to be injected based on the rotation speed objective and on the torque objective to be generated;

controlling the electromagnetic fuel injector ( 4 ) using a first injection time (T INJ1 ) for which a corresponding closing time (T C ) is to be determined;

determining a first partial fuel quantity (Q 1 ) which is actually injected using the first injection time (T INJ1 );

determining a second partial fuel quantity (Q 2 ) which is equal to the difference between the total fuel quantity (Q) and the first partial fuel quantity (Q 1 );

determining a second injection time (T INJ2 ) based on the second partial fuel quantity (Q 2 ) and to exactly inject the second partial fuel quantity (Q 2 ); and

controlling the electromagnetic fuel injector ( 4 ) using the second injection time (T INJ2 ).

12. The method according to claim 11 and comprising the further step of choosing the first injection time (T INJ1 ) so that the difference between the total fuel quantity (Q) to be injected and the first partial fuel quantity (Q 1 ) exceeds a predetermined threshold value.