Turbo compressor, in particular for a fuel cell system

1. A turbo compressor ( 10 ) having a first compressor unit ( 101 ) and a second compressor unit ( 102 ), wherein the first compressor unit ( 101 ) comprises a first compressor ( 11 ) arranged on a first shaft ( 14 ) driven by a drive unit ( 20 ), wherein the second compressor unit ( 102 ) comprises a second compressor ( 12 ) and an exhaust gas turbine ( 13 ), and wherein the second compressor ( 12 ) and the exhaust gas turbine ( 13 ) are arranged on a second shaft ( 24 ),

wherein the first compressor ( 11 ) and the second compressor ( 12 ) are connected in series,

wherein the second shaft ( 24 ) is supported by at least one shaft bearing ( 241 , 242 ),

wherein the first compressor ( 11 ) and the second compressor ( 12 ) are arranged in an air feed line ( 3 ),

wherein, between the first compressor ( 11 ) and the second compressor ( 12 ), a bearing line ( 243 ) branches off from the air feed line ( 3 ) to supply the shaft bearing ( 241 , 242 ) with fluid pressure, and

wherein a bearing line valve ( 244 ) is arranged in the air feed line ( 3 ) between the second compressor ( 12 ) and a point where the bearing line ( 243 ) branches off.

2. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that the second shaft ( 24 ) is configured to be driven by a second drive unit ( 25 ).

3. The turbo compressor ( 10 ) as claimed in claim 2 , characterized in that the first drive unit ( 20 ) is embodied as a high-voltage electric motor and the second drive unit ( 25 ) as a low-voltage electric motor.

4. The turbo compressor ( 10 ) as claimed in claim 2 , characterized in that the first drive unit ( 20 ) is embodied as a low-voltage electric motor and the second drive unit ( 25 ) as a high-voltage electric motor.

5. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that a heat exchanger ( 19 ) is arranged between the first compressor ( 11 ) and the second compressor ( 12 ).

6. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that a compressed-air brake is arranged on the second shaft ( 24 ), wherein the compressed-air brake is connected to the bearing line ( 243 ).

7. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that the air feed line ( 3 ) is an air feed line ( 3 ) of a fuel cell system ( 1 ), and that the exhaust gas turbine ( 13 ) is arranged in an exhaust line ( 4 ) of the fuel cell system ( 1 ).

8. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that a third compressor ( 15 ) is arranged on the first shaft ( 14 ).

9. The turbo compressor ( 10 ) as claimed in claim 8 , characterized in that the first compressor ( 11 ) and the third compressor ( 15 ) are connected in parallel.

10. The turbo compressor ( 10 ) as claimed in claim 8 , characterized in that the first compressor ( 11 ) and the third compressor ( 15 ) are connected in series.

11. The turbo compressor ( 10 ) as claimed in claim 8 , wherein the air feed line ( 3 ) is an air feed line ( 3 ) of a fuel cell system ( 1 ), characterized in that the first compressor ( 11 ), the second compressor ( 12 ), and the third compressor ( 15 ) are arranged in the air feedline ( 3 ) of the fuel cell system ( 1 ) and that the exhaust gas turbine ( 13 ) is arranged in an exhaust line ( 4 ) of the fuel cell system ( 1 ).

12. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that a compressor bypass valve ( 16 ) is arranged in parallel with the second compressor ( 12 ).

13. The turbo compressor ( 10 ) as claimed in claim 1 , characterized in that an exhaust bypass valve ( 16 ) is arranged in parallel with the exhaust gas turbine ( 13 ).

14. A fuel cell system ( 1 ) comprising a turbo compressor ( 10 ) as claimed in claim 1 , a fuel cell ( 2 ), an air feed line ( 3 ) for feeding an oxidizing agent into the fuel cell ( 2 ), and an exhaust line ( 4 ) for discharging the oxidizing agent from the fuel cell ( 2 ), wherein the compressor ( 11 ) and the second compressor ( 12 ) are arranged in the air feed line ( 3 ) and wherein the exhaust gas turbine ( 13 ) is arranged in the exhaust line ( 4 ).

15. A method for starting a fuel cell system ( 1 ) comprising a turbo compressor ( 10 ) as claimed in claim 1 , a fuel cell ( 2 ), and an exhaust line ( 4 ) for discharging the oxidizing agent from the fuel cell ( 2 ), wherein the method comprises the following steps:

closing the bearing line valve ( 244 ) or keeping the bearing line valve ( 244 ) closed,

starting delivery of the oxidizing agent in the air feed line ( 3 ) due to starting of the drive unit ( 20 ), and

opening bearing line valve ( 244 ) when a minimum pressure in the shaft bearing ( 241 , 242 ) is reached.

16. A method for stopping a fuel cell system ( 1 ), wherein the fuel cell system ( 1 ) comprises a turbo compressor ( 10 ) as claimed in claim 1 , a fuel cell ( 2 ), and an exhaust line ( 4 ) for discharging the oxidizing agent from the fuel cell ( 2 ), wherein the method comprises the following steps:

closing the bearing line valve ( 244 ), and

stopping the drive unit ( 20 ) when the speed of the second shaft ( 24 ) falls below a speed limit.

17. A method for starting a fuel cell system ( 1 ),wherein the fuel cell system ( 1 ) comprises a turbo compressor ( 10 ) as claimed in claim 1 , a fuel cell ( 2 ), and an exhaust line ( 4 ) for discharging the oxidizing agent from the fuel cell ( 2 ), wherein a compressor bypass valve ( 16 ) is arranged in parallel with the second compressor ( 12 ), wherein an exhaust bypass valve ( 17 ) is arranged in parallel with the exhaust gas turbine ( 13 ), and wherein the method comprises the following steps:

opening the compressor bypass valve ( 16 ) and the exhaust bypass valve ( 17 ) or keeping the compressor bypass valve ( 16 ) and the exhaust bypass valve ( 17 ) opened,

starting delivery of the oxidizing agent in the air feed line ( 3 ) due to starting of the drive unit ( 20 ), and

closing the compressor bypass valve ( 16 ) and the exhaust bypass valve ( 17 ) when a minimum pressure in the shaft bearing ( 241 , 242 ) is reached.

18. A method for stopping a fuel cell system ( 1 ),wherein the fuel cell system ( 1 ) comprises a turbo compressor ( 10 ) as claimed in claim 1 , a fuel cell ( 2 ), and an exhaust line ( 4 ) for discharging the oxidizing agent from the fuel cell ( 2 ), wherein a compressor bypass valve ( 16 ) is arranged in parallel with the second compressor ( 12 ), wherein an exhaust bypass valve ( 17 ) is arranged in parallel with the exhaust gas turbine ( 13 ), and wherein the method comprises the following steps:

opening the compressor bypass valve ( 16 ) and the exhaust bypass valve ( 17 ), and

stopping the drive unit ( 20 ) when the speed of the second shaft ( 24 ) falls below a speed limit.