Exhaust gas turbocharger for an internal combustion engine and method of operating an exhaust gas turbocharger

1 . An exhaust gas turbocharger for an internal combustion engine including a compressor ( 2 ) and a turbine ( 3 ), a shaft ( 4 ) interconnecting the compressor ( 2 ) and the turbine ( 3 ) in a rotationally fixed manner, and an electric machine ( 20 ) with a clutch ( 5 ) for connection of the electric machine ( 20 ) to the exhaust gas turbocharger, a disk-shaped flywheel ( 10 ) rotatably supported on the shaft ( 4 ) and being connectable to the exhaust gas turbocharger via the clutch ( 5 ) for driving the exhaust gas turbocharger at least temporarily, the disk-shaped flywheel ( 10 ) being drivable by the electric machine ( 20 ) for maintaining a certain minimum speed of the flywheel ( 10 ), said clutch ( 5 ) comprising a first disk ( 11 ), which is connected in a rotationally fixed manner to the shaft ( 4 ) of the exhaust gas turbocharger ( 1 ), a pole structure ( 31 ) disposed adjacent the first disk ( 11 ) and extending around the flywheel ( 10 ) and a yoke ( 15 ) including a coil ( 30 ), with an air gap ( 51 ) preventing friction between the first disk ( 11 ) and the pole structure ( 31 ).

2 . The exhaust gas turbocharger as claimed in claim 1 , wherein the disk-shaped flywheel ( 10 ) is provided with the pole structure ( 31 ).

3 . The exhaust gas turbocharger as claimed in claim 1 , wherein the pole structure ( 31 ) comprises at least two spaced disks ( 32 , 36 ).

4 . The exhaust gas turbocharger as claimed in claim 3 , wherein the spaced disks ( 32 , 36 ) are annular disks.

5 . The exhaust gas turbocharger as claimed in claim 3 wherein the first disk ( 11 ) is arranged between the spaced disks ( 32 , 36 ) of the pole structure ( 31 ).

6 . The exhaust gas turbocharger as claimed in claim 3 , wherein the spaced disks ( 32 , 36 ) of the pole structure ( 31 ) have a toothed structure ( 44 ) with teeth ( 45 ) and tooth gaps ( 46 ), the teeth ( 45 ) on one of the spaced disks ( 32 ; 36 ) being arranged opposite the tooth gaps ( 46 ) on the other of the spaced disks ( 36 ; 32 ).

7 . The exhaust gas turbocharger as claimed in claim 3 , wherein the spaced disks ( 32 , 36 ) of the pole structure ( 31 ) are held together by means of a strap ( 38 ) of a non-magnetic material.

8 . The exhaust gas turbocharger as claimed in claim 1 , wherein the flywheel ( 10 ) comprises a rotor ( 21 ) of the electric machine ( 20 ), a disk ( 35 ) which is held in the pole structure ( 31 ), a tubular element ( 34 ) and the pole structure ( 31 ).

9 . The exhaust gas turbocharger as claimed in claim 1 , wherein the pole structure ( 31 ) is connected in a rotationally fixed manner to a rotor ( 21 ) of the electric machine ( 20 ) via a support disk ( 35 ) and a tubular element ( 34 ).

10 . The exhaust gas turbocharger as claimed in claim 1 , wherein the clutch ( 5 ) is arranged between the compressor ( 2 ) and turbine ( 3 ) of the exhaust gas turbocharger ( 1 ).

11 . The exhaust gas turbocharger as claimed in claim 1 , wherein the clutch ( 5 ) is one of an eddy current clutch and a hysteresis clutch.

12 . The exhaust gas turbocharger as claimed in claim 1 , wherein the flywheel ( 10 ) is maintained at a minimum rotational speed, corresponding to a rated rotational speed (n kontS ) selectively by means of the exhaust gas turbocharger ( 1 ) or by means of the electric machine ( 20 ).

13 . A method for operating an exhaust gas turbocharger for an internal combustion engine, including An exhaust gas turbocharger for an internal combustion engine including a compressor ( 2 ) and a turbine ( 3 ), a shaft ( 4 ) interconnecting the compressor ( 2 ) and the turbine ( 3 ) in a rotationally fixed manner, and an electric machine ( 20 ) with a clutch ( 5 ) for connection of the electric machine ( 20 ) to the exhaust gas turbocharger, a disk-shaped flywheel ( 10 ) rotatably supported on the shaft ( 4 ) and being connectable to the exhaust gas turbocharger via the clutch ( 5 ) for driving the exhaust gas turbocharger at least temporarily, the disk-shaped flywheel ( 10 ) being drivable by the electric machine ( 20 ) for maintaining a certain minimum speed of the flywheel ( 10 ), said clutch ( 5 ) comprising a first disk ( 11 ), which is connected in a rotationally fixed manner to the shaft ( 4 ) of the exhaust gas turbocharger ( 1 ), a pole structure ( 31 ) disposed adjacent the first disk ( 11 ) disposed around the flywheel ( 10 ) and a yoke ( 15 ) including a coil ( 30 ), with an air gap ( 51 ) preventing friction between the first disk ( 11 ) and the pole structure ( 31 ), said method comprising the steps of connecting the electric machine to the exhaust gas turbocharger via the clutch ( 5 ), and, at a rotational speed n ATL of the exhaust gas turbocharger which is higher than a rated rotational speed n kontS of the flywheel ( 10 ), inactivating the electric machine for driving the flywheel ( 10 ) but causing said electric machine ( 20 ) to absorb excess energy which is available from the exhaust gas turbocharger in a generator mode of operation of the electric machine ( 20 ), and feeding said energy, into a motor vehicle onboard power system, while driving the flywheel by the exhaust gas turbocharger, and, at a rotational speed n ATL of the exhaust gas turbocharger which is lower than the rated rotational speed n kontS , using the electric machine ( 20 ) to drive the flywheel ( 10 ) when a rotational speed n S of the flywheel ( 10 ) drops below the rated rotational speed n kontS .

14 . The method as claimed in claim 13 , wherein at rotational speeds n ATL of the exhaust gas turbocharger which correspond at least approximately to the rated rotational speed n kontS , the flywheel ( 10 ) is accelerated by the exhaust gas turbocharger ( 1 ) with the clutch ( 5 ) closed.

15 . The method as claimed in claim 13 , wherein at rotational speeds n ATL of the exhaust gas turbocharger which are lower than the rotational speed ns of the flywheel ( 10 ) the exhaust gas turbocharger ( 1 ) is driven by the flywheel ( 10 ) for the acceleration of the turbocharger.