An exhaust-gas turbocharger of said type is known from DE 10 2012 202 341

Al .

Tests carried out in the context of the invention have shown that the bearing arrangement of the exhaust-gas turbocharger known from said document exhibits a tendency for destabilization of a wave profile of a rotor and for noise generation. The expression "wave profile" is to be understood to mean the rotational movement behavior of the rotor (assembly composed of charger shaft, turbine wheel and compressor wheel), which is influenced by pulsating load on the turbine, by the inherent residual imbalance of the rotor, and by mechanical vibrations of the engine and which is itself excited to perform vibrations.

It is therefore an object of the present invention to provide an exhaust-gas turbocharger of the type specified in the preamble of claim 1 , with which it is possible to stabilize the wave profile and positively influence acoustic frequency bands emitted by the bearing arrangement.

This object is achieved by the features of claim 1.

By means of bearing play at a bearing bushing, it is possible for the rotational speed of the bearing bushing to be varied by way of the shear forces in the oil of the radical bearing arrangement. The minimum oil gap provided between bearing bushing and charger shaft can be kept the same as before.

The dependent claims contain advantageous developments of the invention.

Claims 8 and 9 define a radial bearing arrangement according to the invention as an independently marketable object of the exhaust-gas turbocharger according to the invention.

Further details, features and advantages of the invention become apparent from the following description of exemplary embodiments with reference to the drawing, in which:

Figure 1 is a sectional illustration of an exhaust-gas turbocharger according to the invention, which is illustrated by way of its core assembly, with only the compressor housing and the turbine housing not being illustrated, these however being provided in the case of the exhaust-gas turbocharger according to the invention;

Figure 2 shows an enlarged detail sectional illustration of the bearing arrangement according to the invention;

Figure 3 shows an illustration, corresponding to Figure 2, of one of the bearing bushings of the bearing arrangement as per Figure 2; and

Figures 4-6 are illustrations corresponding to Figure 3 for the purpose of illustrating different groove configurations of the charger shaft.

In Figure 1, an exhaust-gas turbocharger 1 according to the invention is illustrated by way of its core assembly, with only a compressor housing and a turbine housing not being illustrated.

Accordingly, Figure 1 shows a charger shaft 2 which is mounted on a bearing housing 3 by way of a bearing arrangement 4. The bearing arrangement 4 has a first bearing bushing 5 and, spaced apart therefrom, a second bearing bushing 6, said bearing bushings being separated from one another by a spacer sleeve 7.

The illustration also shows a compressor wheel 18 and a turbine wheel 17 which are fixed to the two ends of the charger shaft 2.

Figure 2 shows the construction of the bearing arrangement 4 according to the invention in detail. As already discussed above on the basis of Figure 1, said bearing arrangement 4 has two bearing bushings in the form of the bearing bushings 5 and 6.

Figure 2 also illustrates that the first bearing bushing 5 has a bore 13 and the second bearing bushing 6 has a bore 8, which are each oriented at least approximately at right angles with respect to the longitudinal axis L of the bearing arrangement 4.

Here, figure 3 shows that, in the embodiment illustrated, the bore 8 is fluidically connected to, or issues into, a groove 10 of the charger shaft 2. An oil volume situated in the groove 10 is larger than that in a radial gap 15 formed on the first bearing bushing 5. The oil gap which is enlarged in said region thus gives rise to lower shear forces at said location, and thus to a reduction in rotational speed of the bushing.

As is clear from the illustrations of Figures 4 to 6, the grooves may be of symmetrical or asymmetrical form. The groove 10 and the groove 11 illustrated in Figure 5 are in this case of symmetrical configuration. Here, the groove 10 has an approximately rectangular cross section, whereas the groove 11 has a triangular cross section, as can be seen from Figures 4 and 5. The groove 12 of a symmetrical form has the cross section of a right-angled or isosceles triangle, the acute angle of which is arranged adjacent to the transverse bore 8.

In summary, it can thus be stated that, owing to the embodiment of the bearing arrangement 4 according to the invention as discussed above, rotational speed regulation is possible by way of non-constant shear forces. This is achieved according to the invention in that, without the minimum oil gap being increased, a greater oil volume is provided radially between the charger shaft 2 and at least one of the bearing bushings 5, 6. In said revolving oil volume, shear forces in the oil inevitably lead to a different frictional torque between the respective bearing bushing 5 or 6 and the charger shaft 2. As a result, the bushings 5, 6 rotate asynchronously, such that the excitation of and generation of body-borne noise in the two bearing bushings 5, 6 is also asynchronous. Accordingly, the excitations take place at different frequencies, at which, in turn, the amplitudes are smaller.

In addition to the above written disclosure of the invention, reference is explicitly made to the illustrative presentation of the invention in Figures 1 to 6.

LIST OF REFERENCE SIGNS

Exhaust-gas turbocharger

2 Charger shaft

3 Bearing housing

4 Bearing arrangement

5 First bearing bushing

6 Second bearing bushing

7 Spacer sleeve / spacer

8 Transverse bore

9 Oil gap

10-12 Grooves

13 Transverse bore

14, 16 Outer edges

15 Radial gap

17 Turbine wheel

18 Compressor wheel

S 1 , S2 Bearing plays

L Longitudinal axis

A Spacing of the bearing bushings 5 and 6 between their axial outer edges 14 and 16 lying against the charger shaft 2