Method and device for operating a pneumatic system with a compressed air supply unit and an air spring unit, pneumatic system comprising a compressed air supply unit and an air spring unit, and vehicle

1. A method for operating a pneumatic system having a compressed air supply system and an air spring system, the method comprising:

determining at least one deflection of at least one air spring of the pneumatic system, wherein the air spring is configured to be connected to a gallery of the pneumatic system in a selectively gas-conveying manner via a valve in a valve block;

determining at least one bellows volume of a spring bellows of the at least one air spring based on the at least one determined deflection;

indicating a pneumatic surrogate model for the at least one bellows volume and/or for a pressure accumulator volume of a pressure accumulator of the pneumatic system based on a mass flow balance for a balance volume; and

calculating, based on the pneumatic surrogate model, at least one pressure value of the at least one bellows volume, the pressure accumulator volume, and/or the balance volume.

2. The method as claimed in claim 1 , wherein the at least one pressure value is calculated during a change in state of the pneumatic system,

wherein the change in state is a change in the at least one deflection or one control operation of the air spring supply or a switching operation of at least one valve.

3. The method as claimed in claim 1 , wherein the at least one pressure value is corrected by a pressure value measured by a pressure sensor.

4. The method as claimed in claim 3 , wherein the measured pressure value is measured by the pressure sensor in a period of time in which no control operation of the air spring system takes place.

5. The method as claimed in claim 3 , wherein the measured pressure value is measured by the pressure sensor during a control operation.

6. The method as claimed in claim 1 , wherein the at least one deflection is measured by means of a level sensor.

7. The method as claimed in claim 1 , wherein the pneumatic surrogate model is created by:

determining an initial pressure prevailing in the balance volume,

determining at least one individual initial pressure in at least one individual volume which is not part of the balance volume,

determining all air mass flows flowing into the balance volume or flowing out of the balance volume,

determining a total air mass located in the balance volume and/or determining at least one individual air mass located in a volume,

calculating the pressure with an air mass, a volume and a measured temperature based on a gas equation.

8. The method as claimed in claim 7 , wherein the determination of all mass air flows flowing into the balance volume or out of the balance volume involves:

determining, through calculation, at least one bellows air mass flow by a diaphragm equation, taking account of at least one spring bellows pressure and at least one actual spring bellows flow cross section, and/or

determining, through calculation, at least one accumulator air mass flow by a diaphragm equation, taking account of at least one accumulator pressure and at least one actual accumulator flow cross section, and/or

determining through calculation a supply air mass flow by a diaphragm equation, taking account of at least one air drier pressure and at least one actual supply flow cross section,

balancing a total air mass, taking account of all air mass flows.

9. The method as claimed in claim 7 , wherein determining the air drier pressure further comprises:

determining, through calculation, a compressor air mass flow by a diaphragm equation, taking account of at least one compressor pressure and at least one actual compressor flow cross section, and/or

determining, through calculation, a vent air mass flow by a diaphragm equation, taking account of at least one vent pressure and at least one actual vent flow cross section.

10. The method as claimed in claim 7 , wherein the initial pressure prevailing in the balance volume is determined based on the measured pressure determining.

11. The method as claimed in claim 7 , wherein the initial pressure prevailing in the balance volume is determined based on the calculated pressure of a preceding application cycle of the pneumatic surrogate model.

12. The method as claimed in claim 7 , wherein the compressor pressure and/or the compressor air mass flow is determined by a delivery flow characteristic curve.

13. The method as claimed in claim 12 , wherein the delivery flow characteristic curve is adapted depending on environmental parameters and/or a compressor supply voltage.

14. The method as claimed in claim 9 , wherein the vent pressure is provided by atmospheric ambient pressure.

15. The method as claimed in claim 1 , wherein the compressed air is generated by a compressor if the determined pressure or the measured pressure lies below a minimum pressure value.

16. The method as claimed in claim 1 , wherein compressed air is released via a vent connection if the determined pressure or the measured pressure lies above a maximum pressure value.

17. A device for the control and regulation of a pneumatic system, wherein the device is configured to implement the method as claimed in claim 1 and has a pressure determination unit and a pressure regulator.

18. A pneumatic system comprising:

a compressed air supply system;

an air spring system;

a pressure accumulator;

a gallery and at least one air spring configured to be connected to the gallery via a valve of a valve block in a selectively gas-conveying manner; and

a device configured to perform the method as claimed in claim 1 for operating the pneumatic system, the device including a pressure determination unit and a pressure regulator.

19. A vehicle, having the pneumatic system as claimed in claim 18 .

20. The method according to claim 1 , wherein the pressure accumulator volume of the pressure accumulator of the pneumatic system is an air drier volume of an air drier of the pneumatic system.