DESCRIPTION The invention relates to an adjustable turbine, in particular to a turbine having a variable flow inlet cross section.

Adjustable turbines are known which have a multiplicity of guide vanes which are pivotable about their own respective axes, such that the turbine wheel can be impinged on by flow in a manner dependent on an available exhaust-gas volume flow rate. Even though very good results can be achieved by this, such turbines with adjustable guide vanes are cumbersome to produce, and accordingly expensive, owing to a high number of parts that move relative to one another. DE 25 39 711 Al has disclosed a spiral housing for a turbomachine, in particular an exhaust-gas turbocharger. The spiral housing has a cross section that is adjustable at least in regions. Furthermore, in the spiral housing, a tongue is provided which is guided in sliding fashion and which is displaceable in a circumferential direction and by means of which the spiral inlet cross section can be varied.

It is an object of the present invention to provide an adjustable turbine which is easy to control and which is realized using simple means.

This object is achieved by the features of claim 1. The dependent claims relate to preferred refinements of the invention.

Accordingly, a turbine for an exhaust-gas turbocharger is provided, the turbine having a turbine housing, a drum arranged in the turbine housing and rotatable about an axis of rotation, a turbine wheel arranged rotatably in the drum, at least one volute formed in the turbine housing, and at least one aperture, formed in the drum, for conducting a gas flow from the at least one volute to the turbine wheel. Here, an inlet cross-sectional area of the volute can be varied by changing an angle of rotation of the drum relative to the turbine housing, and the drum being mounted in the turbine housing by way of bearing elements. By virtue of the fact that the drum is mounted in the turbine housing by way of bearing elements, said drum cannot become jammed in the turbine housing during operation, even in the presence of intense temperature fluctuations. The reliability and controllability of the turbine are simplified by way of this refinement, whereby series production is made possible. As bearing elements, use may be made of plain bearing elements or of roller bearing elements.

In one embodiment, guide vanes for guiding the gas flow to the turbine wheel are arranged in the aperture. The guide vanes serve to realize a flow that is directed toward the turbine wheel, whereby a torque that is output by the turbine can be increased.

In one refinement, it may be provided that, at at least one rotational angle of the drum, a bypass duct that issues into a turbine outlet is connected in fluid-conducting fashion, by a spacing between the guide vanes, to the volute (radial wastegate functionality). Accordingly, at particular operating points, the turbine can be bypassed, whereby the output power can be manipulated. In an alternative or additional refinement, an axial wastegate bore is provided which is arranged in the drum and which, at one rotational angle of the drum, can be placed in overlap with a wastegate port (axial wastegate functionality). In this way, a bypass can be created between the turbine inlet and the turbine outlet. In one advantageous refinement, two volutes are formed in the turbine housing.

In this way, when the invention is used on an internal combustion engine, the exhaust gases from individual cylinders, or merged exhaust gases from multiple cylinders, can be conducted into one of the two volutes. It is self-evidently also possible for more than two volutes to be provided.

In one refinement, the bypasses at both volutes are opened simultaneously at the same rotational angle. In this way, exhaust gas can be partially or fully discharged when a maximum rotational speed or a maximum pressure is reached. Through the use of bores, it is possible, in a manner dependent on a degree of overlap of the wastegate port and the wastegate bore, for the discharged exhaust-gas stream to be finely adjusted by way of the rotational angle. In an alternative embodiment, the bypasses (radial or axial wastegate functionality) of both volutes are configured such that, at particular rotational angles, only one of the volutes is connected in fluid-conducting fashion to the turbine outlet and such that, at a further rotational angle, both volutes are connected in fluid- conducting fashion to the turbine outlet. By means of this refinement, an additional degree of freedom is created for the control of the turbine in that, at certain operating points, the exhaust gas is discharged from the individual volutes in selective fashion.

In one refinement, an inner contour of the drum is designed correspondingly to an outer contour of the turbine wheel. Accordingly, the leakage of exhaust gas past the turbine can be kept low.

The adjustable turbine may also be used in a multi-stage supercharging system. Here, it may be advantageous if the volute can be completely closed by means of the drum in order to deactivate the turbine.

Further details, advantages and features of the present invention can be found in the following description of exemplary embodiments with reference to the drawing, in which: Figure 1 shows a turbine according to the invention for an exhaust-gas turbocharger for all exemplary embodiments;

Figures 2 - 4 show the mode of operation of the turbine according to the invention as per a first exemplary embodiment;

Figures 5 - 7 show the mode of operation of the turbine according to the invention as per a second exemplary embodiment; Figures 8 - 10 show different positions of the drum in the turbine as per a third exemplary embodiment; and

Figures 11 - 13 show possible design embodiments of a turbine.

A number of exemplary embodiments of a turbine 28 in an exhaust-gas turbocharger 1 will be explained below on the basis of Figures 1 to 13. Here, the figures are of a schematic nature and show only those parts of the turbine 28 which are relevant to the invention. Identical or functionally identical components are denoted, in part, by the same reference numerals in the exemplary embodiments.

As per Figure 1, the exhaust-gas turbocharger 1 comprises, for all exemplary embodiments, a turbine housing 2 of the turbine 28, a bearing housing 3, and a compressor housing 4. A turbine wheel 5 of the turbine 28 is arranged in the turbine housing 2. A compressor wheel 6 is arranged in the compressor housing 4. The turbine wheel 5 is connected rotationally conjointly to the compressor wheel 6 via a shaft 7. The shaft 7 is mounted in the bearing housing 3 by means of a shaft bearing 10. The shaft 7 extends along an axis 12. A turbine inlet 8 is formed in the turbine housing 2. Said turbine inlet 8 is formed by two volutes 16, 17. Exhaust gas is conducted to the turbine wheel 6 via said two volutes 16, 17. The exhaust gas is conducted out of the turbine housing 2 via a turbine outlet 9. Owing to the two volutes 16, 17, the turbine housing 2 is in the form of a dual-flow housing.

During operation of the exhaust-gas turbocharger 1, a gas flow passes to the turbine wheel 5 via the two volutes 16, 17. In this way, the shaft 7 and the compressor wheel 6 are set in rotation. Here, the compressor wheel 6 may provide charge air for a combustion engine (not illustrated), in particular an internal combustion engine.

Figure 1 also schematically shows a by means of schematically illustrated bearing elements 19 a drum 11 in the turbine 28, which drum is situated radially outside the turbine wheel 5 in the turbine housing 2. The drum 11 is mounted by means of the bearing elements 19 so as to be rotatable about the axis 12. Here, it is for example possible for three bearing elements 19 to be arranged in uniformly distributed fashion around the circumference of the drum 11. Here, the drum 11 is referred to as a drum merely owing to its cylindrical outer contour. Shapes deviating from a substantially cylindrical shape are also possible according to the present invention.

Figures 2 to 4 show, in a schematically simplified illustration, the design and mode of operation of the drum 11 in the first exemplary embodiment. The drum 11 has a closure surface 13 on its shell surface 21. Furthermore, an aperture 14 is formed in the shell surface 21.

Figure 3 shows a section through the first volute 16 perpendicular to the axis 12. Figure 4 shows a section through the second volute 17, likewise perpendicular to the axis 12. Here, the volutes 16, 17 are almost completely closed by the closure surface 13, and the turbine 28 is thus depicted in a deactivated position.

The drum 11 can be rotated through a rotational angle v, whereby the apertures 13 open up a larger area of the volutes 16, 17. As illustrated in Figures 3 and 4, it is also possible, in at least one position, for the volutes 16, 17 to be closed off for the purpose of completely shutting off the turbine 28.

Figures 5 to 7 show, in a schematically simplified illustration, the design and mode of operation of the turbine 28 as per the second exemplary embodiment. In the second exemplary embodiment, multiple guide vanes 18 are arranged in the aperture 14. By way of said guide vanes 18, the exhaust gas is conducted to the turbine wheel 5 in optimized fashion in terms of flow.

The illustration in Figure 5 also shows bearing elements 19 for the rotatable mounting of the drum 11. A similar or identical bearing arrangement may also be used in the first exemplary embodiment. The bearing elements 19 are in the form of rolling bodies and are connected rotatably to the turbine housing 2 by way of journals 20. The bearing elements 19 roll on the shell surface of the drum 11. Other arrangements of the bearing elements 19 themselves are possible in which journals 20 are not used, for example arrangements involving pockets 36 formed in the turbine housing 2, as illustrated in Figure 11. Instead of separate pockets 36, it is also possible for one pocket 36 in the form of a groove, that is to say one pocket extending all the way around the circumference, to be provided for accommodating numerous bearing elements 19 arranged closely side-by-side.

For generating the rotational movement 15 of the drum 11, use is preferably made of an actuator 30, for example in the form of an electric motor or pneumatic control capsule, which, by way of a motion link arrangement 29, is designed to rotate the drum 11 and set particular rotational angles v.

Figures 6 and 7 show the fully open state of the two volutes 16, 17.

Figures 8 to 10 show different positions of the drum 11. Each of the figures shows the section through the first volute 16. At high rotational speeds, a greater inlet cross-sectional area A(v) can be opened up until the inlet cross-sectional area reaches a maximum value A 100 that can be set, as illustrated in Figure 8.

It can be seen that an inlet cross-sectional area A(v) varies with the rotational angle v; this also applies analogously to the other exemplary embodiments. In this way, a flow speed with which the gas flow impinges on the turbine wheel 5 changes, such that different operating points can be set in accordance with demand. In particular, in the presence of low volume flow rates, the inlet cross-sectional area A(v) can be kept small, such that the exhaust gas impinges at high speed on the turbine 5 and a high torque is generated, as illustrated in Figure 9.

The guide vanes 18 have a first spacing 24 to one another. The final guide vane 18 as viewed in the flow direction has a second spacing 25 to the adjacent closure surface 13. The second spacing 25 is greater than the first spacing 24. Accordingly, the drum 11 can, as shown in Figure 10, be positioned such that a bypass duct 23 that issues into the turbine outlet is connected in fluid-conducting fashion to the volute 16. Said bypass duct 23 constitutes a so-called "wastegate duct" which conducts the exhaust gas directly into the turbine outlet (see Figure 1 , reference sign 9), bypassing the turbine wheel 5. The positioning here is adjacent to the rotational angle (v) at which the inlet cross-sectional area A(v) is at a maximum (A 100). Accordingly, when a maximum volume flow rate is reached, part of the volume flow can be discharged. In this way, both an adjustable turbine 28 and also finely controllable radial wastegate functionality are realized by means of a single component (specifically the rotatable drum).

Figures 11 to 13 show a schematically simplified depiction of details of the turbine 28 according to the invention as per the second exemplary embodiment.

The sectional view in Figure 11 shows the arrangement of the drum 11 in the turbine housing 2. A drum length 26 and a turbine wheel length 27 are shown. Here, the two lengths are measured in the direction of the axis 12. The drum length 26 is greater than the turbine wheel length 27. In this way, the turbine wheel 5 is, at its radially outer side, completely surrounded by the drum 11. Furthermore, an inner contour 33 of the drum 11 is designed correspondingly to the outer contour 34 of the turbine wheel 5.

Figure 12 shows an isometric view of the drum 11. Figure 13 shows a section parallel to the axis 12. The ends of the aperture 14, or the transition from the aperture 14 to the closure surface 13, are/is in this case shown in schematically simplified form with sharp transitions. It is inherently also possible for smooth transitions to be provided here. In addition to the above written description of the invention, reference is hereby explicitly made, for additional disclosure thereof, to the diagrammatic illustration of the invention in Figures 1 to 13. LIST OF REFERENCE SYMBOLS

1 Exhaust-gas turbocharger

2 Turbine housing

3 Bearing housing

4 Compressor housing

5 Turbine wheel

6 Compressor wheel

7 Shaft

8 Turbine inlet

9 Turbine outlet

10 Shaft bearing

1 1 Drum

12 Axis

13 Closure surface

14 Aperture

15 Rotary movement

16 First volute

17 Second volute

18 Guide vane

19 Bearing elements

20 Journal

21 Shell surface

22 Intermediate spaces

23 Bypass (wastegate duct)

24 First spacing

25 Second spacing

26 Drum length

27 Turbine wheel length

28 Turbine

29 Motion link arrangement

30 Actuator

31 Wastegate bore 33 Outer contour

34 Inner contour

35 Wastegate port

36 Pocket

A(v) Inlet cross-sectional area as a function of v A 100 Inlet cross-sectional area at maximum opening v Rotational angle of the drum