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A device for controlling the exhaust-gas turbocharging of an internal combustion engine having an exhaust-gas turbocharging device, has an estimated value unit for determining a mass flow through a turbine system, a regulating unit for determining a regulating exhaust-gas back pressure as a function

A device for controlling the exhaust-gas turbocharging of an internal combustion engine having an exhaust-gas turbocharging device, has an estimated value unit for determining a mass flow through a turbine system, a regulating unit for determining a regulating exhaust-gas back pressure as a function of a nominal charge pressure and an actual charge pressure, and also a unit for generating at least one actuating signal for at least one actuator of the turbine system as a function of the regulating exhaust-gas back pressure and of the mass flow through the turbine system, wherein the estimated value unit has a turbine system model for determining an estimated overall efficiency of the turbine system and a model for determining an estimated overall efficiency of a compressor system having at least two compressors, and wherein the regulating unit is set up to determine the regulating exhaust-gas back pressure using the estimated overall efficiencies

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1. A device for controlling exhaust-gas turbocharging of an internal combustion engine with an exhaust-gas turbocharging device, comprising: an estimated value unit which comprises a physical model of the internal combustion engine,a regulating unit for determining a regulating exhaust-gas back pres

1. A device for controlling exhaust-gas turbocharging of an internal combustion engine with an exhaust-gas turbocharging device, comprising: an estimated value unit which comprises a physical model of the internal combustion engine,a regulating unit for determining a regulating exhaust-gas back pressure or at least one other regulating intermediate variable in dependence upon a nominal charge pressure and an actual charge pressure, either measured as an operating parameter or derived from an operating parameter,an actuating signal generating unit for generating at least one actuating signal for at least one actuator of a turbine system of the exhaust-gas turbocharging device,wherein the estimated value unit includes a turbine system model for determining a current estimated overall efficiency of the turbine system, and a compressor system model for determining a current overall efficiency of a compressor system of the exhaust-gas turbocharging device having at least a low-pressure compressor and a high-pressure compressor and arranged in an intake system of the internal combustion engine,wherein the compressor system model is configured to determine the current overall efficiency of the compressor system based on current operating parameters of the internal combustion engine and on overall efficiencies of the low-pressure compressor and the high-pressure compressor as modeled by engine maps, andwherein the regulating unit is configured to determine the regulating exhaust-gas back pressure or the at least one other regulating intermediate variable based on the current estimated overall efficiencies of the turbine system and of the compressor system. 2. The device according to claim 1, wherein the estimated value unit is set up to determine a mass flow through a turbine system of the exhaust-gas turbocharging device set up in an intake tract of the internal combustion engine, in dependence upon operating parameters of the internal combustion engine, whereby the actuating signal generating unit is set up for generating at least one actuating signal in dependence upon the estimated miss flow through the turbine system or additionally in dependence upon an exhaust-gas pressure downstream of the turbine system, and upon an exhaust gas temperature upstream of the turbine system. 3. The device according to claim 1, wherein the compressor system model is set up for determining the overall efficiency of the compressor system as ηC=ηC,LP·ηC,HP·a/(ηC,HP·b+ηC,LP·c+b·c)or as a variable derived therefrom, whereby ηC stands for the overall efficiency of the compressor system, ηC,LP stands for the efficiency of the low-pressure compressor, and ηC,HP stands for the efficiency of the high-pressure compressor, and whereby a, b, c stand for variables which only depend on the actual charge pressure, on a suction pressure measured as an operating parameter upstream of the compressor system and on a prevailing intermediate pressure in the intake tract between the low-pressure compressor and the high-pressure compressor. 4. The device according to claim 1, wherein the regulating unit comprises a controller as well as a pilot control for determining a pilot control exhaust-gas back pressure in dependence upon operating parameters of the internal combustion engine, on the nominal charge pressure and on the estimated overall efficiencies of the turbine system and of the compressor system, with the controller being set up for determining the regulating exhaust-gas back pressure by using the pilot control exhaust-gas back pressure. 5. The device according to claim 4, wherein the operating parameters used by the pilot control for determining the pilot control exhaust-gas back pressure or variables derived therefrom comprise a suction pressure upstream of the compressor system, an exhaust-gas pressure downstream of the turbine system, an intake air temperature upstream of the compressor system, an exhaust-gas temperature upstream of the turbine system, a mass flow through the compressor system and the estimated mass flow through the turbine system, but no internal operating parameters of the compressor system or of the turbine system. 6. The device according to claim 1, further comprising, for the decoupling of a control circuit of the exhaust-gas turbocharging device from a control circuit of the exhaust-gas recirculation device of the internal combustion engine, a decoupling unit which is set up for determining a decoupling mass flow by correcting the estimated mass flow through the turbine system in dependence upon a state variable or controlled variable of the exhaust-gas recirculation control, whereby the inverse turbine system model generates the at least one actuating signal in dependence upon the decoupling mass flow. 7. The device according to claim 1, wherein the turbine system modeled by the turbine system model and by the inverse turbine system model comprises at least two turbines to power the at least two compressors. 8. The device according to claim 7, wherein among the turbines are a high-pressure turbine and a low-pressure turbine connected in series downstream of the high-pressure turbine. 9. The device according to claim 7, wherein the turbine system comprises in each case at least one actuator controlled by the actuating signal generating unit both for a first and also for a second of the said turbines. 10. The device according to claim 9, wherein the actuating signal generating unit is set up for generating at least one actuating signal for the at least one actuator of the first turbine, as well as at least one actuating signal for the at least one actuator of the second turbine such that dependent on whether a threshold value of a controlled variable is exceeded or is not reached, either only the at least one actuating signal assigned to the first turbine is varied, whereas the at least one actuator of the second turbine takes a constant external position, or only the at least one actuating signal assigned to the second turbine is varied, whereas the at least one actuator of the first turbine takes a constant external position, whereby if the threshold value is exceeded or is not reached, a switch is made between two different engine maps included in the inverse turbine system model. 11. The device according to claim 1, wherein the inverse turbine system model for generating the at least one actuating signal comprises at least one engine map in dependence upon a pressure quotient which is generated from the regulating exhaust-gas back pressure, and an exhaust-gas pressure measured or calculated as an operating parameter downstream of the turbine system, and generated by a pressure- and temperature-normalized mass flow which is generated in dependence upon the estimated mass flow through the turbine system. 12. The device according to claim 11, wherein the at least one engine map of the inverse turbine system model reads out a combined actuating signal, which can be assigned to at least a first actuator and a second actuator such that during a monotonous varying of the combined actuating signal first of all at a constant first position of the second actuator, the first actuator is monotonously varied, from a first to a second position of the first actuator, whereby on reaching the second position of the first actuator, the second actuator is monotonously varied from a first to a second position of the second actuator. 13. The device according to claim 11, wherein the actuating signal generating unit is set up for generating the pressure- and temperature-normalized mass flow in dependence upon the regulating exhaust-gas back pressure and an exhaust-gas temperature measured as an operating parameter in the exhaust tract upstream of the turbine system. 14. The device according to claim 10, wherein the at least one engine map used by the inverse turbine system model shows no dependence on the internal operating parameters of the turbine system. 15. The device according to claim 1, wherein an overall efficiency of the turbine system is determined by means of a combined actuating signal in the estimated value unit. 16. The device according to claim 1, wherein in the estimated value unit an exhaust-gas back pressure upstream of the turbine system is determined by means of a combined actuating signal. 17. The device according to claim 1, wherein, for determining the overall efficiency of the turbine system, the turbine system model comprises at least one engine map in dependence upon a pressure quotient generated from the regulating exhaust-gas back pressure, and an exhaust-gas pressure measured as an operating parameter downstream of the turbine system, and upon a current position of the at least one actuator. 18. The device according to claim 17, wherein the at least one engine map used by the turbine system model shows no dependence upon the internal operating parameters of the turbine system, at a given position of the at least one actuator of the turbine system. 19. An internal combustion engine, comprising an exhaust-gas turbocharging device with a turbine system set up in an intake tract of the internal combustion engine, and a compressor system, having at least two compressors, set up in an intake tract of the internal combustion engine, wherein the internal combustion engine comprises a device for controlling exhaust-gas turbocharging comprising: an estimated value unit which comprises a physical model of the internal combustion engine,a regulating unit for determining a regulating exhaust-gas back pressure or at least one other regulating intermediate variable in dependence upon a nominal charge pressure and an actual charge pressure, either measured as an operating parameter or derived from an operating parameter,an actuating signal generating unit for generating at least one actuating signal for at least one actuator of a turbine system of the exhaust-gas turbocharging device,wherein the estimated value unit includes a turbine system model for determining a current estimated overall efficiency of the turbine system, and a compressor system model for determining a current overall efficiency of a compressor system of the exhaust-gas turbocharging device having at least a low-pressure compressor and a high-pressure compressor and arranged in an intake system of the internal combustion engine,wherein the compressor system model is configured to determine the current overall efficiency of the compressor system based on current operating parameters of the internal combustion engine and on overall efficiencies of the low-pressure compressor and the high-pressure compressor as modeled by engine maps, andwherein the regulating unit is configured to determine the regulating exhaust-gas back pressure or the at least one other regulating intermediate variable based on the current estimated overall efficiencies of the turbine system and of the compressor system. 20. The device according to claim 1, wherein the actuating signal generating unit includes the inverse turbine system model for generating at least one actuating signal in dependence upon the regulating exhaust-gas back pressure or at least one other regulating intermediate variable, and on at least one further operating parameter or estimated value determined by the estimated value unit.