BEARING DEVICE, IN PARTICULAR FOR A SHAFT OF A TURBOCHARGER, AND TURBOCHARGER HAVING SUCH A BEARING DEVICE

Abstract

A bearing device (1), in particular for a shaft (2) of a turbocharger (3), including two journal bearings (5) and a bush-like separating element (9) for spatially separating the two bearings (5). The separating element (9) includes a separating bush which is formed in the manner of a cage having a multiplicity of apertures (16) arranged circumferentially and separated from one another by struts (17).

Description

The present invention relates to a bearing device, in particular for a shaft of a turbocharger, including two journal bearings and a bush-like separating element for spatially separating the two bearings. The present invention also relates to turbocharger having such a bearing device.

Such an assembly is used, inter alia, in the manufacture of engines. Here, for example, the turbine shaft of an exhaust-gas turbocharger rests in such a bearing device.

BACKGROUND

A bearing device of this type is disclosed in European Patent Document EP 03 95 825 B1. There, a separating element referred to as spacer is described, which has a hollow cylindrical main body whose the outer circumferential surface is provided with guide devices which project therefrom for guiding the spacer within a bearing bore. In a preferred embodiment, there is further provided a central outlet opening which permits oil within the spacer to pass radially outward therethrough. Here, however, the oil-holding capacity is quite low, and the manufacture of such a spacer is relatively expensive because it is typically made by lathing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved bearing device that is less expensive to manufacture.

The present invention provides a bearing device that is composed of at least two journal bearings and a bush-like separating element which spatially separates the two bearings. Such a bearing device is intended, in particular, for a shaft of a turbocharger, where the bearings used are typically plain journal bearings. The separating element of this assembly includes a separating bush which is formed in the manner of a cage having a multiplicity of apertures arranged circumferentially and separated from one another by struts. The cage-like structure of the separating bush allows a significant reduction in material use, and thus also a reduction in weight of the separating element. While the reduction in material use is associated with a reduction in manufacturing cost, the weight reduction also makes it possible, for example, to reduce fuel consumption when the bearing device is used in a vehicle. In addition, if oil lubrication and, in particular, floating support are provided for the device, then the corresponding apertures provide improved lubrication efficiency since, depending on the operating state, the apertures act either as pockets for intermediate storage of oil, or as enlarged openings in a flow path of the lubrication oil.

Preferably, the separating element has a larger inner diameter than the two bearings. Since the separating element is not intended to perform a supporting function for the shaft, a further reduction of both weight and material use is achieved in this manner. In addition, the space so created between the separating element and the shaft is used, for example, as an additional intermediate storage for lubrication oil.

It is also advantageous to adapt the shape of the apertures to the intended use of the bearing device. Therefore, it is preferred for the apertures to be, for example, bar-shaped to match the typically elongated shape of the separating element. More specifically, here the apertures are configured such that their dimension in the direction of the longitudinal center axis of the shaft is at least a factor of 2, preferably a factor of 5, larger than their dimension perpendicular thereto.

Further, in an advantageous embodiment, the elongated apertures, and thus also the struts, are oriented substantially parallel to the longitudinal center axis of the shaft. This achieves, for example, increased resistance to axial loads.

In addition, the number of formed apertures exceeds, for example, a value of 3, and preferably a value of 5. In this connection, the aim is always to achieve the best possible compromise between weight reduction and resistance to stresses in order to ensure a long life for the bearing device.

In accordance with another preferred embodiment, a roller bearing cage, in particular, a needle roller bearing cage, is used the separating bush. Such bearing cages are mass-produced in very large quantities and commercially available also in suitable dimensions. Such designs are well-known to those skilled in the relevant art and described in detail, for example, in German Patent Documents DE 00 00 01 009 445 A, DE 00 00 01 022 431 A and DE 00 00 01 079 901 A. In a variant, the separating element has a multi-part design, and a suitable bearing cage is used as the separating bush. The separating bush may then be completed, for example, by simple annular members to forma separating element, if it is only the axial dimension of the separating bush that is not suited for the intended application. However, it is preferred for the separating element to be made as a single part, where the separating bush alone, in particular a bearing cage, functions as the separating element. Overall, this provides the advantages of a low manufacturing cost, easy assembly, and favorable performance characteristics. The low cost is achieved, in particular, using the principle of shared identical parts; i.e, by using the bearing cage, which is already available for other purposes and whose manufacture is cost-optimized by producing it in large quantities, for example, as a stamping.

In a preferred embodiment, the two bearings and the separating element are fixed in position by an axial press-fit. This makes it possible, for example, to provide a circumferential clearance around these components, which is filled with a lubrication oil. Due to the apertures in the separating element, this oil is then able to wet, as leakage flow, the mating contact surfaces between the shaft and the bearings. In this way, a so-called “floating support” is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is described below with reference to several drawings, in which:

FIG. 1 is a cross-sectional view of a turbocharger having a bearing device according to the prior art;

FIG. 2 is a side view showing a roller bearing cage according to the prior art;

FIG. 3 is a cross section along line III-III of FIG. 2 showing the roller bearing cage according to the prior art;

FIG. 4 is a cross-sectional view showing a bearing device according to the present invention along with a turbocharger shaft supported therein; and

FIG. 5 is a cross-sectional view showing the bearing device according to the present invention without the turbocharger shaft.

Like parts are identified by the same reference numerals in all figures.

DETAILED DESCRIPTION

In the exemplary embodiment described hereinbelow, a bearing device 1 serves by way of example to support a shaft 2 (see FIG. 4) of an exhaust-gas turbocharger 3. Such an exhaust-gas turbocharger 3 is shown in FIG. 1 along with a bearing device 1 according to the prior art. Shaft 2 (not shown in this figure) has a turbine wheel 4 attached to each of its ends.

Two plain journal bearings 5 are positioned within a receiving space 6 in housing 7 of turbocharger 3 to support shaft 2. The two plain bearings 5 are fixed in position by means of an axially acting press-fit, which is provided by an abutment 8 disposed at each of the ends on the one hand and by a hollow cylindrical separating element 9 on the other hand. Separating element 9 is typically made by lathing and is therefore relatively expensive to manufacture. Radially extending and centrally positioned openings are provided to function as part of a lubrication oil flow path for both the plain bearings 5 and the separating element 9. The corresponding lubrication oil is introduced at operating pressure into a pre-chamber 11 via a hydraulic network by means of a feed pump in a manner not specifically shown. From there, the lubrication oil flows through feed channels 12 to openings 10. The lubrication oil supplied in this way forms a leakage flow which provides a lubricating film between the mating contact surfaces of the two plain bearings 5 and shaft 2. This lubricating film spreads out toward separating element 9 and is finally discharged through openings 10 therein into a discharge chamber 13, from where it is returned to the hydraulic network.

In order to improve the known bearing device, the component used as separating element 9 is substituted. In the exemplary embodiment, this component is replaced by a needle roller bearing cage 14 which, contrary to its intended use as a rolling-element carrier, is used in the bearing device as a separating element 9 to spatially separate two plain bearings 5. Due to the cage-like structure, needle roller bearing cage 14 both has a low weight and is resistant to mechanical stresses which may occur. In addition, the apertures, which form part of the lubrication oil flow path, provide improved lubrication oil flow.

In FIG. 2 and FIG. 3, such a needle roller bearing cage 14 is illustrated by way of example. This bush-like needle roller bearing cage 14 has six apertures 16, which are oriented parallel to its longitudinal center axis 15 and separated from one another by approximately bar-shaped struts 17. Since needle roller bearing cage 14 has suitable dimensions, it replaces separating element 9 completely, so that in this exemplary embodiment, the separating element 9 of the present invention does not include any additional components.

The so-implemented bearing device 1 and its immediate surroundings are shown in FIG. 4 along with shaft 2 and in FIG. 5 without shaft 2. As in the prior art embodiment shown in FIG. 1, the bearing device of the present invention is provided with oil lubrication. In this connection, both plain bearings 5 and needle roller bearing cage 14 are supported centrically and with radial clearance in receiving space 6, which is completely flooded with lubrication oil when in an operating state. Here, too, feed channels 12 serve for the supply of lubrication oil. However, in needle roller bearing cage 14, apertures 16 assume the function of openings 10 in separating element 9. The lubrication oil that is forced between the mating contact surfaces of shaft 2 and plain bearings 5 and reaches needle roller bearing cage 14 exits through these apertures.

LIST OF REFERENCE NUMERALS

1 bearing device

2 shaft

3 exhaust-gas turbocharger

4 turbine wheel

5 plain bearing

6 receiving space

7 housing

8 abutment

9 separating element

10 opening

11 pre-chamber

12 feed channel

13 discharge chamber

14 needle roller bearing cage

15 longitudinal center axis

16 aperture

17 strut

Claims

1-10. (canceled)

11. A bearing device comprising:

two journal bearings; and

a separating bush for spatially separating the two bearings, the separating bush formed as a cage having a plurality of apertures arranged circumferentially and separated from one another by struts.

12. The bearing device as recited in claim 11 wherein the separating bush has a larger inner diameter than the two bearings.

13. The bearing device as recited in claim 11 wherein the apertures are bar-shaped.

14. The bearing device as recited in claim 11 wherein the apertures are configured such that their dimension in the direction of the longitudinal center axis of the shaft is at least a factor of 2 larger than their dimension perpendicular thereto.

15. The bearing device as recited in claim 14 wherein the factor is at least a factor of 5.

16. The bearing device as recited in claim 14 wherein the apertures are oriented parallel to a longitudinal center axis.

17. The bearing device as recited in claim 11 wherein at least 3 apertures are provided.

18. The bearing device as recited in claim 11 wherein the separating bush is a roller bearing cage.

19. The bearing device as recited in claim 18 wherein the roller bearing cage is a needle roller bearing cage.

20. The bearing device as recited in claim 11 wherein the separating bush is made as a single part.

21. The bearing device as recited in claim 11 wherein the two bearings and the separating element are fixed in position by an axial press-fit.

22. A turbocharger comprising the bearing device as recited in claim 11.

23. The turbocharger as recited in claim 22 further comprising a shaft, the bearing device being for the shaft.