Method and device for determining a fuel pressure present at a direct injection valve

1. A method for determining a fuel pressure present at a direct injection valve comprising a solenoid drive having a coil and an armature, the method comprising:

switching off a current flow through the coil of the solenoid drive, thereby de-energizing the coil, leading to a closing of the direct injection valve,

during a time period which includes a closing time of the direct injection valve, detecting a voltage induced in the de-energized solenoid drive by decaying eddy currents resulting from the de-energizing of the coil and by a movement of the armature, and

determining the fuel pressure based on the detected induced voltage.

2. The method of claim 1 , comprising determining the fuel pressure based on a maximum value of the induced voltage detected in the solenoid drive.

3. The method of claim 1 , wherein a value for the determined fuel pressure present at the direct injection valve is used as a virtual value for a further fuel pressure present at least one further direct injection valve.

4. The method of claim 1 , further comprising:

detecting a further induced voltage which is induced in a further solenoid drive of a further direct injection valve, within a time period that includes a closing time of the further direct injection valve, and

determining a further fuel pressure based on the detected further induced voltage.

5. The method of claim 1 , further comprising:

detecting the fuel pressure with a pressure sensor,

comparing the fuel pressure determined based on the detected induced voltage with the fuel pressure detected by the pressure sensor, and

outputting a fault message if the determined fuel pressure deviates from the measured fuel pressure by more than a predefined threshold value.

6. The method of claim 1 , wherein the fuel pressure is determined from a previously known characteristic diagram of maximum values of induced voltages and associated fuel pressures.

7. The method of claim 6 , wherein the characteristic diagram is determined by a calibration method that includes:

operation of the direct injection valve for various fuel pressures, wherein an induced voltage is measured for each fuel pressure, and

storage of a plurality of value pairs that each comprise a pressure value and an associated voltage value.

8. The method of claim 7 , wherein the direct injection valve is operated for various fuel pressures under predefined constant operating conditions.

9. The method of claim 8 , wherein the constant operating conditions are defined by maintaining at least one of:

a stoichiometric air ratio,

a predefined cooling water temperature,

a predefined oil temperature, and

a predefined temperature for a control unit of an internal combustion engine comprising the direct injection valve.

10. The method of claim 7 , further comprising adaptation of the value pairs stored in the characteristic diagram using a regression curve.

11. A device for determining a fuel pressure present at a direct injection valve comprising a solenoid drive having a coil and an armature, the device comprising:

a switch configured to switch off a current flow through the coil of the solenoid drive, thereby de-energizing the coil, leading to a closing of the direct injection valve,

a detection unit configured to detect a voltage induced in the de-energized solenoid drive within a time period that includes a closing time of the direct injection valve, the voltage being induced in the de-energized solenoid drive by decaying eddy currents resulting from the de-energizing of the coil and by a movement of the armature, and

an evaluation unit programmed to determine the fuel pressure on the basis of the detected voltage.

12. The device of claim 11 , wherein the evaluation unit is programmed to determine the fuel pressure based on a maximum value of the induced voltage detected in the solenoid drive.

13. The device of claim 11 , wherein:

the detection unit is configured to detect a further induced voltage which is induced in a further solenoid drive of a further direct injection valve, within a time period that includes a closing time of the further direct injection valve, and

the evaluation unit is programmed to determine a further fuel pressure based on the detected further induced voltage.

14. The device of claim 11 , wherein:

the detection unit comprises a pressure sensor configured to detect the fuel pressure, and

the evaluation unit is programmed to compare the fuel pressure determined based on the detected induced voltage with the fuel pressure detected by the pressure sensor, and output a fault message if the determined fuel pressure deviates from the measured fuel pressure by more than a predefined threshold value.

15. A computer program for determining a fuel pressure present at a direct injection valve comprising a solenoid drive having a coil and an armature, wherein the computer program is stored in computer-readable media and executable to:

switch off a current flow through the coil of the solenoid drive, thereby de-energizing the coil, leading to a closing of the direct injection valve,

during a time period which includes a closing time of the direct injection valve, detect a voltage induced in the de-energized solenoid drive by decaying eddy currents resulting from the de-energizing of the coil and by a movement of the armature, and

determine the fuel pressure based on the detected induced voltage.