Method and device for determining a pressure in a high-pressure accumulator

1. A method for determining a pressure in a high-pressure accumulator which is hydraulically coupled to an injection valve in order to supply fluid, wherein the injection valve has a longitudinal axis, an injection needle and an actuator designed as a solid body actuator, wherein the actuator is designed to act on the injection needle, and the injection needle is designed to prevent a fluid flow through at least one injection opening in a closed position and otherwise to open up the fluid flow, the method comprising:

supplying a predefined amount of electrical energy to the actuator in order to modify an axial length of the actuator, specifically in such a manner that the injection needle is moved out of the closed position,

after the predefined amount of electrical energy has been supplied, determining a first and a second voltage value by means of the actuator at respectively different predefined moments,

determining a differential voltage value on the basis of the first and second voltage values, and

determining a first pressure which is representative of a pressure in the high-pressure accumulator on the basis of the differential voltage value.

2. The method according to claim 1 , in which the high-pressure accumulator comprises at least one pressure sensor for detecting a second pressure which is representative of the pressure in the high-pressure accumulator.

3. The method according to claim 1 , wherein the first pressure is determined when the at least one pressure sensor is defective.

4. The method according to claim 1 , wherein the first or second pressure is checked for plausibility with reference to the second or first pressure.

5. The method according to claim 1 , further comprising:

determining the first pressure on the basis of the differential voltage value with reference to a predefined characteristic diagram,

when the pressure sensor is error-free, detecting the second pressure is,

determining the differential voltage value substantially isochronously, and

adapting the characteristic diagram on the basis of the detected second pressure and the associated differential voltage value.

6. The method according to claim 1 , wherein the first voltage value is detected at a moment at which the voltage across the actuator is at maximum.

7. The method according to claim 1 , wherein the second voltage value is determined at a moment at which the voltage across the actuator is virtually stationary.

8. The method according to claim 1 , wherein after the predefined amount of electrical energy has been supplied, a plurality of voltage values is detected, and at least one of the first and second voltage value is in each case determined with reference to the formation of a mean of a respective predefined selection of the voltage values detected.

9. A device for determining a pressure in a high-pressure accumulator which is hydraulically coupled to an injection valve in order to supply fluid, wherein the injection valve comprises a longitudinal axis, an injection needle and an actuator designed as a solid body actuator, wherein the actuator is designed to act on the injection needle, and the injection needle is designed to prevent a fluid flow through at least one injection opening in a closed position and otherwise to open up the fluid flow, wherein the device is designed

to supply a predefined amount of electrical energy to the actuator in order to modify an axial length of the actuator, specifically in such a manner that the injection needle is moved out of the closed position,

after the predefined amount of electrical energy has been supplied, to detect and/or to determine a first and a second voltage value by means of the actuator at respectively different predefined moments,

to determine a differential voltage value on the basis of the first and second voltage values,

to determine a first pressure which is representative of a pressure in the high-pressure accumulator on the basis of the differential voltage value.

10. The device according to claim 9 , wherein the high-pressure accumulator comprises at least one pressure sensor for detecting a second pressure which is representative of the pressure in the high-pressure accumulator.

11. The device according to claim 9 , wherein the first pressure is determined when the at least one pressure sensor is defective.

12. The device according to claim 9 , wherein the first or second pressure is checked for plausibility with reference to the second or first pressure.

13. The device according to claim 9 , wherein the device is furthermore configured:

to determine the first pressure on the basis of the differential voltage value with reference to a predefined characteristic diagram,

when the pressure sensor is error-free, to detect the second pressure,

to determine the differential voltage value substantially isochronously, and

to adapt the characteristic diagram on the basis of the detected second pressure and the associated differential voltage value.

14. The device according to claim 9 , wherein the first voltage value is detected at a moment at which the voltage across the actuator is at maximum.

15. The device according to claim 9 , wherein the second voltage value is determined at a moment at which the voltage across the actuator is virtually stationary.

16. The device according to claim 9 , wherein the device is further configured to detect, after the predefined amount of electrical energy has been supplied, a plurality of voltage values, and to determine at least one of the first and second voltage value in each case with reference to the formation of a mean of a respective predefined selection of the voltage values detected.