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Patent Searching and Data


Title:
HYDRODYNAMIC BEARING
Document Type and Number:
WIPO Patent Application WO/2010/135135
Kind Code:
A2
Abstract:
The present invention relates to a hydrodynamic bearing (1) for a rotating rotor shaft (3) of an exhaust-gas turbocharger (2) having at least one cylindrical bearing bush (4), wherein the rotor shaft (3) has, in a region (3a) which is arranged in the bearing bush (4), a cross section (5) deviating from a circular cross section, and wherein a space (6) between the inner periphery (4a) of the bearing bush (4) and the outer periphery (3b) of the rotor shaft (3) is filled with oil.

Inventors:
HETTMANN, Joachim (Stettiner Strasse 13 B, Hochheim, Hochheim, DE)
Application Number:
US2010/034672
Publication Date:
November 25, 2010
Filing Date:
May 13, 2010
Export Citation:
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Assignee:
BORGWARNER INC. (Patent Department, 3850 Hamlin RoadAuburn Hills, Michigan, 48326, US)
HETTMANN, Joachim (Stettiner Strasse 13 B, Hochheim, Hochheim, DE)
International Classes:
F16C32/06; F01D17/04; F01D25/16; F02B39/00; F16C17/02
Foreign References:
JP2003035310A2003-02-07
JPH07145812A1995-06-06
US6024493A2000-02-15
JPH1030419A1998-02-03
Attorney, Agent or Firm:
PENDORF, Stephan A. et al. (Patent Central LLC, 1401 Hollywood BoulevardHollywood, Florida, 33020-5237, US)
Download PDF:
Claims:
CLAIMS

1. A hydrodynamic bearing (1) for a rotating rotor shaft (3) of an exhaust-gas turbocharger (2), - having at least one cylindrical bearing bush (4), wherein the rotor shaft (3) has, in a region (3a) which is arranged in the at least one bearing bush (4), a cross section (5) deviating from a circular cross section, and wherein a space (6) between the inner periphery (4a) of the bearing bush (4) and the outer periphery (3b) of the rotor shaft (3) is filled with oil.

2. The hydrodynamic bearing (I) as claimed in claim 1 , wherein the cross section (5) of the rotor shaft (3) is of elliptical or polygonal design.

3. The hydrodynamic bearing (1) as claimed in claim 1, wherein the cross section (5) of the rotor shaft (3) has a circular shape having three or more peripherally truncated circle segment regions.

4. The hydrodynamic bearing (i) as claimed in claim 3, wherein the cross section (5) of the rotor shaft (3) has a circular shape having three or more circle segment regions which are cut out in the form of wedges on the periphery.

5. The hydrodynamic bearing (1) as claimed in one of claims 1 to 4, characterized in that a region of the lubricating film with maximum oil pressure in relation to the inner periphery (4a) of the bearing bush (4) rotates synchronously with a rotational speed of the rotor shaft (3).

Description:
HYDRODYNAMIC BEARING DESCRIPTION

The invention relates to a hydrodynamic bearing for a rotating rotor shaft of an exhaust-gas turbo charger.

A rotating exhaust-gas turbocharger rotor shaft which is supported by means of cylindrical plain bearings has an instability in certain operating states (oil whirl and whip effect). Here, the rotor shaft deflects in an uncontrolled fashion, and this can result in contact between said rotor shaft and the plain bearing. This is conventionally prevented by using a multiple-wedge-surface bearing. By means of the multiple- wedge-surface bearing, the rotor shaft is "braced" or supported in the rotor system, with a plurality of pressure fields building up at the periphery of said rotor shaft and stabilizing any occurring deflections of the rotor system. The use of multiple-wedge- surface bearings has the disadvantage, however, that it is very cumbersome and expensive and in part can not yet be technically realized in the case of small supercharger designs.

It is therefore an object of the present invention to create a hydrodynamic bearing which is of simple design and is cheap to produce and which improves the damping properties even in small designs of exhaust-gas turbochargers.

Said object is achieved by means of the features of claim 1. The hydrodynamic bearing according to the invention has the advantage that it provides optimized damping of the rotor shaft on account of rotating oil pressure fields, with the oil film of the lubricant between the bearing shell and the rotor shaft being built up earlier, in particular during the starting phase of the turbocharger. In this way, more stable running of the rotor shaft can be ensured in relation to the use of a multiple-wedge-surface bearing.

The sυbclaims relate to advantageous refinements of the invention. Further details, features and advantages of the invention will emerge from the following description of exemplary embodiments on the basis of the drawing, in which:

Figure 1 shows a schematically slightly simplified sectional illustration of a turbocharger,

Figure 2 shows a schematically simplified sectional illustration of a first embodiment of a hydrodynamic bearing according to the invention with an elliptical rotor shaft.

Figure 3 shows a sectional illustration, corresponding to Figure 2. of a second embodiment of the hydrodynamic bearing with a polygonal rotor shaft. Figure 4 shows an alternative cross-sectional shape of a rotor shaft for the hydrodynamic bearing, and

Figure 5 shows a further cross-sectional shape of the rotor shaft for the hydrodynamic bearing. Embodiments of the hydrodynamic bearing according to the invention will be described below with reference to Figure 1 to Figure 5.

Figure 1 shows a schematically slightly simplified sectional illustration of a turbocharger 2 in which a hydrodynamic bearing 1 according to the invention, which will be described below on the basis of Figures 2 and 3, can be used. As can be seen from Figure 1, the turbocharger 2 has a compressor housing 8, to which a bearing housing 10 is fastened, and a turbine housing 1 1. which is connected to the bearing housing 10. A rotor shaft 3 which is arranged axially centrally in the bearing housing 10, and which is supported in each case at a region 3a of the rotor shaft 3 in bearing bushes 4, has at its compressor-side end a compressor wheel 9 which is fastened to the rotor shaft 3 and at its turbine-side end a turbine wheel 12 which is fastened to the rotor shaft 3. As can also be seen from Figure 1, an oil supply 13 is formed in the bearing housing 10, which oil supply 13 supplies a lubricant to the two hydrodynamic bearings 1 illustrated in Figure 1 and also to an axial bearing (not shown in this figure) between the compressor housing 8 and the bearing housing 10, which lubricant is discharged out of the bearing housing 10 again through an oil outlet 14.

Figure 2 shows a schematic sectional illustration of a first embodiment of the hydrodynamic bearing 1 according to the invention, having a cylindrical bearing bush 4 in which the rotor shaft 3 is arranged. In said first embodiment, the region 3a of the rotor shaft 3 in the bearing bush 4 (see Figure 1) has an elliptical cross section 5. Between an outer diameter 3b of the rotor shaft 3 and an inner diameter 4a of the bearing bush 4, the cross section 5, which deviates from the cylindrical cross section of the bearing bush 4, of the rotor shaft forms a space 6 which is filled with oil. The rotation of the rotor shaft 3 causes a pressure field 7 and 7' to be built up in each case in a region B, B', in which a spacing A between the inner periphery of the bearing bush 4 and the outer periphery of the rotor shaft (3) has a minimum value, as a result of the increased pressure of the oil in the space 6 in said region. In said first embodiment of the hydrodynamic bearing 1, in which the rotor shaft 3 has the elliptical cross section 5, the two pressure fields 7, 7' which are built up in the regions B and B' in the space 6 between the rotor shaft 3 and the bearing bush 4 rotate synchronously with the rotational speed of the rotor shaft 3. Said rotating pressure fields 7, T ensure improved positive damping if the rotor 3 is deflected on account of a certain operating state of the exhaust-gas turbocharger 2, because said deflection movement is intercepted by one of the rotating pressure fields 7, T which is fully or partially still present. Figure 3 shows a sectional illustration, corresponding to Figure 2, of a second embodiment of the hydrodynamic bearing 1 according to the invention. Here, identical components are denoted by the same reference symbols as in the first embodiment illustrated in Figure 1. In said second embodiment, the region 3 a of the rotor shaft 3 in the bearing bush 4 (see Figure 1) has a polygonal cross section 5'. In contrast to the first embodiment, the rotor shaft 3 with the polygonal cross section 5' in said second embodiment causes three pressure fields 7, 7', 7" with increased oil pressure to be built up in the three regions B, B', B", which pressure fields 7, T, 7" serve to stabilize the rotor shaft 3 in the bearing bush 4. Figure 4 shows a sectional illustration of an alternative cross-sectional shape of the rotor shaft 3 for the hydrodynamic bearing 1 according to the invention. Here, the region 3a of the rotor shaft 3 has a substantially circular cross section 5" in which three peripheral regions, the central points of which have in each case an angular interval of 120°, are truncated in the form of circle segments 15. Said cross-sectional shape illustrated in Figure 4 has the advantage over the polygonal cross section 5 illustrated in Figure 3 that it is significantly simpler and cheaper to produce on account of the circular starting cross section. Furthermore, on account of the peripherally longer regions B. B'. B", correspondingly longer pressure fields 7 with constantly higher oil pressure can be formed. Figure 5 shows an illustration, corresponding to Figure 4, of a further alternative cross-sectional shape of the rotor shaft 3 for the hydrodynamic bearing 1 according to the invention. Here, the region 3a of the rotor shaft 3 has a substantially circular cross section 5'", like the rotor shaft 3 illustrated in Figure 4. In contrast to the cross- sectional shape illustrated in Figure 4, the rotor shaft 3 has three peripheral regions whose centers have in each case an angular interval of 120° and which in each case are cut out in the form of wedge-shaped indentations 16 on the periphery 3b of the rotor shaft 3. Said indentations 16 on the periphery 3b of the rotor shaft 3 have in each case one straight region 16a which slopes inward in the rotational direction and which, at the end of the indentation 16 in the rotational direction of the rotor shaft 3, projects outward again, in the form of a shoulder 16b, to the original outer periphery 3b of the rotor shaft 3.

As a result of the above-described indentations 16, the cross-sectional shape of the rotor shaft 3 illustrated here generates a pressure which initially constantly falls slightly in the peripheral direction in relation to the oil pressure prevailing in the regions B, B', B" in the space 6 between the bearing bush 4 and the rotor shaft 3, and said pressure then rises again abruptly at the end of the indentation 16 to the pressure prevailing in the region B, B' and B". In addition to the cross-sectional shapes of the rotor shaft 3 illustrated in Figure 2 to Figure 5, use may be made of any cross-sectional shape based on polygonal cross sections or modified circular cross sections not illustrated here which generate three or more rotating pressure fields 7, 7', 7". In all the illustrated and conceivable embodiments of the hydrodynamic bearing 1 according to the invention, the pressure fields 1, T, T generated as a result of the change in the spacing A between the outer periphery 3b of the rotor shaft and the inner periphery 4a of the bearing bush 4 rotate with the same frequency as the rotor shaft 3. In this way, more stable running of the rotor shaft 3 is obtained in relation to the abovementioned multi-wedge-surface bearings, in which the pressure fields rotate with a bush rotational speed which is significantly lower than the rotor rotational speed, and which cannot satisfactorily dampen a possible deflection of the rotor shaft 3, in particular in the event of a rotational speed change occurring as a result of a load shift of the exhaust-gas turbo charger.

To supplement the disclosure, reference is explicitly made to the diagrammatic illustration of the invention in Figures 1 to 5.

LIST OF REFERENCE SYMBOLS

1 Hydrocfynamic bearing

2 Exhaust-gas turbocharger

3 Rotor shaft

3a Region of the rotor shaft in the bearing bush

3b Outer periphery of the rotor shaft

4 Bearing bush

4a Inner periphery of the bearing bush

5. 5', 5". 5"' Cross sections

6 Space between bearing bush and rotor shaft

7, T, T Pressure field of the oil

8 Compressor housing

9 Compressor wheel

10 Bearing housing

11 Turbine housing

12 Turbine w r heel

13 Oil supply

14 Oil outlet

15 Circle segment

16 Wedge-shaped indentation

16a Inwardly sloping region

16b Shoulder

A Spacing between outer periphery of rotor shaft and inner periphery of bearing bush

B, B 1 , B" Regions