Method and device for determining a reference current progression for a fuel injector, for determining the instant of a predetermined opening state of the fuel injector

1. A method for determining a reference current progression for a fuel injector for an internal-combustion engine of a motor vehicle, which fuel injector has a solenoid drive, the method comprising:

applying a first voltage pulse to the solenoid drive of the fuel injector to open the fuel injector,

applying a holding voltage to the solenoid drive of the fuel injector to maintain the fuel injector open,

switching off the holding voltage,

keeping the holding voltage switched off to affect a currentless period having a predetermined duration during which substantially no current flows through the solenoid drive, wherein the predetermined duration is sufficiently short such that the fuel injector remains open during the currentless period,

ending the currentless period by applying a second voltage pulse to the solenoid drive of the fuel injector,

determining a temporal progression of a current intensity of a current that flows through the solenoid drive during the application of the second voltage pulse, the determined temporal progression constituting the reference current progression,

determining an instant of a predetermined opening state of the fuel injector based on the determined reference current progression,

determining a second temporal progression of a current intensity of a current flowing through the solenoid drive,

determining a differential progression based on the determined second temporal progression of the current intensity and the determined reference current progression, and

determining an instant at which the differential progression exhibits a predefined extreme value, wherein the determined instant corresponds to the instant of the predetermined opening state.

2. The method of claim 1 , further including storing the determined reference current progression.

3. A method for determining and instant of a predetermined opening state of a fuel injector having a solenoid drive, in an internal-combustion engine of a motor vehicle, the method comprising:

determining a reference current progression by:

applying a first voltage pulse to the solenoid drive of the fuel injector to open the fuel injector,

applying a holding voltage to the solenoid drive of the fuel injector to maintain the fuel injector open,

switching off the holding voltage,

keeping the holding voltage switched off to effect a currentless period having a predetermined duration during which substantially no current flows through the solenoid drive, wherein the predetermined duration is sufficiently short such that the fuel injector remains open during the currentless period,

ending the currentless period by applying a second voltage pulse to the solenoid drive of the fuel injector, and

determining a first temporal progression of a current intensity of a current that flows through the solenoid drive during the application of the second voltage pulse, the determined first temporal progression constituting the reference current progression,

determining a second temporal progression of a current intensity of a current flowing through the solenoid drive,

determining a differential progression based on the determined second temporal progression of the current intensity and the determined reference current progression, and

determining an instant at which the differential progression exhibits a predefined extreme value, wherein the determined instant corresponds to the instant of the predetermined opening state.

4. The method of claim 3 , further comprising:

determining a further differential progression based on the determined temporal progression of the current intensity and a further reference current progression, the further reference current progression corresponding to a temporal progression of the current intensity of the current flowing through the solenoid drive in a closed state of the fuel injector, and

determining a further instant at which the further differential progression exhibits a predefined extreme value or at which a predetermined correlation exists between the differential progression and the further differential progression.

5. The method of claim 4 , wherein the determined instant of the predetermined opening state of the fuel injector is a start-instant or end-instant of a process for opening or closing the fuel injector.

6. A method for driving a fuel injector having a solenoid drive, in an internal-combustion engine of a motor vehicle, the method comprising:

determining an instant of a predetermined opening state of the fuel injector by:

determining a reference current progression by:

applying a first voltage pulse to the solenoid drive of the fuel injector to open the fuel injector,

applying a holding voltage to the solenoid drive of the fuel injector to maintain the fuel injector open,

switching off the holding voltage,

keeping the holding voltage switched off to effect a currentless period having a predetermined duration during which substantially no current flows through the solenoid drive, wherein the predetermined duration is sufficiently short such that the fuel injector remains open during the currentless period,

ending the currentless period by applying a second voltage pulse to the solenoid drive of the fuel injector, and

determining a first temporal progression of a current intensity of a current that flows through the solenoid drive during the application of the second voltage pulse, the determined first temporal progression constituting the reference current progression,

determining a second temporal progression of a current intensity of a current flowing through the solenoid drive,

determining a differential progression based on the determined second temporal progression of the current intensity and the determined reference current progression, and

determining an instant at which the differential progression exhibits a predefined extreme value, wherein the determined instant corresponds to the instant of the predetermined opening state,

determining a difference between the determined instant and a reference instant, and

driving the fuel injector based on the determined difference by controlling a timing of a voltage pulse applied to the solenoid drive based on the determined difference.

7. A device for determining a reference current progression for a fuel injector for an internal-combustion engine of a motor vehicle, which fuel injector has a solenoid drive, the device comprising:

an application unit programmed to:

apply a first voltage pulse to the solenoid drive of the fuel injector to open the fuel injector,

apply a holding voltage to the solenoid drive of the fuel injector to maintain the fuel injector open,

switch off the holding voltage,

keep the holding voltage switched off to effect a currentless period having a predetermined duration during which substantially no current flows through the solenoid drive, wherein the predetermined duration is sufficiently short such that the fuel injector remains open during the currentless period, and

end the currentless period by applying a second voltage pulse to the solenoid drive of the fuel injector; and

a current evaluation unit programmed to:

determine a temporal progression of the current intensity of a current that flows through the solenoid drive during the application of the second voltage pulse, the determined temporal progression constituting the reference current progression,

determine an instant of a predetermined opening state of the fuel injector based on the determined reference current progression,

determining a second temporal progression of a current intensity of a current flowing through the solenoid drive,

determining a differential progression based on the determined second temporal progression of the current intensity and the determined reference current progression, and

determining an instant at which the differential progression exhibits a predefined extreme value, wherein the determined instant corresponds to the instant of the predetermined opening state.

8. The device of claim 7 , further including a storage device that stores the determined reference current progression.

9. The device of claim 7 , wherein the current evaluation unit is further configured to:

determine a second temporal progression of a current intensity of a current flowing through the solenoid drive,

determine a differential progression based on the determined second temporal progression of the current intensity and the determined reference current progression, and

determine an instant at which the differential progression exhibits a predefined extreme value, wherein the determined instant corresponds to the instant of the predetermined opening state.

10. The device of claim 9 , wherein the current evaluation unit is further configured to:

determine a further differential progression based on the determined temporal progression of the current intensity and a further reference current progression, the further reference current progression corresponding to a temporal progression of the current intensity of the current flowing through the solenoid drive in a closed state of the fuel injector, and

determine a further instant at which the further differential progression exhibits a predefined extreme value or at which a predetermined correlation exists between the differential progression and the further differential progression.

11. The device of claim 10 , wherein the determined instant of the predetermined opening state of the fuel injector is a start-instant or end-instant of a process for opening or closing the fuel injector.

12. The device of claim 10 , wherein:

the current evaluation unit is further configured to determine a difference between the determined instant and a reference instant, and

the device comprises a fuel injector controller configured to drive the fuel injector based on the determined difference by controlling a timing of a voltage pulse applied to the solenoid drive based on the determined difference.