Fluid injector and method for operating a fluid injector

1. A method for operating a fluid injector having a longitudinal axis and a valve body, a valve needle received in the valve body and axially moveable between a closing position that prevents a fluid injection and further positions that permit the fluid injection, an armature mechanically coupled to the valve needle for displacing the valve needle away from the closing position, and a solenoid assembly having at least a first and second coil and being operable to magnetically actuate the armature via an electrical signal, the method comprising:

applying the electrical signal to the first coil to generate a primary magnetic field to move the armature to thereby displace the valve needle away from the closing position,

evaluating a voltage across terminals of the first coil, and

controlling the second coil with a further electrical signal to saturate a magnetic field in a portion of the valve body located between the armature and the solenoid assembly during evaluating the voltage.

2. The method of claim 1 , comprising measuring the voltage between a point in time when the electrical signal is terminated and a point in time when the valve needle reaches the closing position.

3. The method of claim 1 , further comprising:

evaluating the voltage during one injection event of the fluid injector, and

using the evaluation result as a feedback signal for controlling the electrical signal in a subsequent injection event.

4. The method of claim 1 , wherein the further electrical signal through the second coil is phased with the electrical signal through the first coil to optimize global power consumption.

5. A fluid injector having a longitudinal axis, the fluid injector comprising:

a valve body,

a valve needle received in the valve body and axially moveable between a closing position that prevents a fluid injection and further positions that permit the fluid injection,

an armature mechanically coupled to the valve needle for displacing the valve needle away from the closing position, and

a solenoid assembly comprising at least a first and second coil and operable to magnetically actuate the armature via an electrical signal,

wherein the fluid injector is configured to:

feed the electrical signal to the first coil to generate a primary magnetic field to move the armature to thereby displace the valve needle away from the closing position, and

control the second coil to saturate a magnetic field in a portion of the valve body located between the armature and the solenoid assembly to provide a constant magnetic flux in the valve body during evaluating a voltage across terminals of the first coil.

6. The fluid injector of claim 5 , further comprising a calibration spring that biases the valve needle towards the closing position,

wherein the fluid injector is configured to feed a further electrical signal to the second coil while the first coil is de-energized and the valve needle is moved towards the closing position by a spring force generated by the calibration spring.

7. The fluid injector of claim 5 , wherein the second coil is electrically separated from the first coil.

8. The fluid injector of claim 5 , wherein the first coil and the second coil are controllable separately from each other.

9. The fluid injector of claim 5 , wherein the second coil overlaps axially with a portion of the valve body which has a reduced thickness.

10. The fluid injector of claim 5 , wherein the second coil overlaps axially with the first coil.

11. The fluid injector of claim 10 , wherein the second coil is located between a portion of the first coil and the valve body.

12. The fluid injector of claim 5 , wherein the second coil is located within a U-shaped profile, the open end of which is directed toward the valve body.

13. The fluid injector of claim 12 , wherein the profile is made from a ferromagnetic material.

14. An internal combustion engine, comprising:

a fluid injector comprising:

a valve body,

a valve needle received in the valve body and axially moveable between a closing position that prevents a fluid injection and further positions that permit the fluid injection,

an armature mechanically coupled to the valve needle for displacing the valve needle away from the closing position, and

a solenoid assembly comprising at least a first and second coil and operable to magnetically actuate the armature via an electrical signal,

wherein the fluid injector is configured to:

feed the electrical signal to the first coil to generate a primary magnetic field to move the armature to thereby displace the valve needle away from the closing position, and

control the second coil to saturate a magnetic field in a portion of the valve body located between the armature and the solenoid assembly to provide a constant magnetic flux in the valve body during evaluating a voltage across terminals of the first coil.

15. The internal combustion engine of claim 14 , the fluid injector further comprising a calibration spring that biases the valve needle towards the closing position,

wherein the fluid injector is configured to feed a further electrical signal to the second coil while the first coil is de-energized and the valve needle is moved towards the closing position by a spring force generated by the calibration spring.

16. The internal combustion engine of claim 14 , wherein the second coil is electrically separated from the first coil.

17. The internal combustion engine of claim 14 , wherein the first coil and the second coil are controllable separately from each other.

18. The internal combustion engine of claim 14 , wherein the second coil overlaps axially with a portion of the valve body which has a reduced thickness.

19. The internal combustion engine of claim 14 , wherein the second coil overlaps axially with the first coil.

20. The internal combustion engine of claim 19 , wherein the second coil is located between a portion of the first coil and the valve body.