Exhaust-gas turbocharger

Abstract

An exhaust-gas turbocharger (1) with a bearing housing (2), a shaft (5) mounted in the bearing housing (2), a turbine wheel (6) which is arranged on the shaft (5), a compressor wheel (7) which is arranged on the shaft (5), and a wheel side space (10) between a rear wall (8) of the turbine wheel (6) or compressor wheel (7) and an outer surface (11), which faces toward the rear wall (8) of the bearing housing (2). In the outer surface (11) of the bearing housing (5), there is formed at least one groove (13, 18) for disrupting the flow generated by the rotating rear wall (8).

Claims

1. An exhaust-gas turbocharger (1) comprising: a bearing housing (2), a shaft (5) mounted in the bearing housing (2) for rotating in a shaft direction of rotation, a turbine wheel (6) which is arranged on the shaft (5), said turbine wheel having a rear wall facing the bearing housing (2), and a compressor wheel (7) which is arranged on the shaft (5), said compressor wheel having a rear wall facing the bearing housing (2), wherein an air space (10) is formed between the rear wall (8) of the turbine wheel (6) or compressor wheel (7) and a bearing housing outer surface (11), which bearing housing outer surface (11) faces toward the rear wall (8) of the turbine wheel (6) or compressor wheel (7), wherein rotation of the rear wall (8) in the shaft direction of rotation generates a rotating flow of air in the air space (10) in the direction of rotation and also radially outwards producing a negative static pressure in the radially inner region of the air space (10), wherein in the bearing housing outer surface (11), there is formed at least one groove (13, 18), wherein said at least one groove (13, 18) is spiral-shaped opening radially outwardly counter to the shaft direction of rotation, or is a plurality of circular-segment-shaped grooves (18) opening radially outwardly counter to the shaft direction of rotation, wherein said at least one groove (13, 18) is dimensioned in cooperation with said rear wall (8) that upon rotation of said shaft (5) in the shaft direction of rotation said at least one groove (13, 18) decelerates the flow of air in the direction of rotation and also radially outwards and thus increases the static pressure in the radially inner region of the wheel space (10) from a more negative to a less negative static pressure.

2. The exhaust-gas turbocharger as claimed in claim 1, wherein the at least one groove (13, 18) is in the form of a pocket.

3. The exhaust-gas turbocharger as claimed in claim 1, wherein the at least one groove (13) is formed around the full circumference of the shaft.

4. The exhaust-gas turbocharger as claimed in claim 1, wherein said at least one groove (13, 18) is a plurality of radially outwardly extending grooves (13).

5. The exhaust-gas turbocharger as claimed in claim 4, wherein the radially outwardly extending grooves (13) run in a curved manner.

6. The exhaust-gas turbocharger as claimed in claim 1, wherein the shaft (5) extends through the outer surface (11) of the bearing housing (2), and wherein a seal is arranged between the shaft (5) and the outer surface (11).

7. A method for preventing oil leakage from the bearing housing of an exhaust gas turbocharger, wherein the exhaust-gas turbocharger (1) comprises: a bearing housing (2), a shaft (5) mounted in the bearing housing (2) for rotating in a shaft direction of rotation, a turbine wheel (6) which is arranged on the shaft (5), said turbine wheel having a rear wall facing the bearing housing (2), and a compressor wheel (7) which is arranged on the shaft (5), said compressor wheel having a rear wall facing the bearing housing (2), wherein an air space (10) is formed between the rear wall (8) of the turbine wheel (6) or compressor wheel (7) and a bearing housing outer surface (11), which bearing housing outer surface (11) faces toward the rear wall (8) of the turbine wheel (6) or compressor wheel (7), and the method comprising: forming in the bearing housing outer surface (11) at least one groove (13, 18), wherein said at least one groove (13, 18) is spiral-shaped opening radially outwardly counter to the shaft direction of rotation, or is a plurality of circular-segment-shaped grooves (18) opening radially outwardly counter to the shaft direction of rotation, rotating the rear wall (8) in the shaft direction of rotation to generate a rotating flow of air in the air space (10) in the direction of rotation and also radially outwards, producing a negative static pressure in the radially inner region of the air space (10), wherein said at least one groove (13, 18) is dimensioned in cooperation with said rear wall (8) that upon rotation of said shaft (5) in the shaft direction of rotation said at least one groove (13, 18) decelerates the flow of air in the direction of rotation and also radially outwards and thus increases the static pressure in the radially inner region of the wheel space (10) to a less negative static pressure.

Description

(1) FURTHER DETAILS, ADVANTAGES AND FEATURES OF THE PRESENT INVENTION BECOME APPARENT FROM THE FOLLOWING DESCRIPTION OF EXEMPLARY EMBODIMENTS WITH REFERENCE TO THE DRAWING, IN WHICH:

(2) FIG. 1 shows a schematically simplified view of an exhaust-gas turbocharger according to the invention for all exemplary embodiments,

(3) FIG. 2 shows a detail of the exhaust-gas turbocharger according to the invention as per a first exemplary embodiment,

(4) FIG. 3 shows a detail of the exhaust-gas turbocharger according to the invention as per a second exemplary embodiment,

(5) FIG. 4 shows a detail of the exhaust-gas turbocharger according to the invention as per a third exemplary embodiment, and

(6) FIG. 5 shows a detail of the exhaust-gas turbocharger according to the invention as per a fourth exemplary embodiment.

(7) FIG. 1 shows, in a schematically simplified view, the general construction of the exhaust-gas turbocharger 1 for all exemplary embodiments. The exhaust-gas turbocharger 1 comprises a bearing housing 2 in which a shaft 5 is rotatably mounted. A turbine wheel 6 is seated on one end of the shaft 5. A compressor wheel 7 is seated on the other end of the shaft 5. The compressor wheel 7 and the turbine wheel 6 have in each case a rear wall 8 and blades 9. The turbine wheel 6 is impinged on by a flow of exhaust gas. In this way, the turbine wheel 6, the shaft 5 and the compressor wheel 7 are set in rotation. The compressor wheel 7 compresses charge air for an internal combustion engine.

(8) The interior of the bearing housing 2 is filled with oil or an oil/air mixture and is sealed off with respect to the space accommodating the turbine wheel 6 and the compressor wheel 7.

(9) The rear wall 8 of the turbine wheel 6 and of the compressor wheel 7 is in each case situated opposite an outer surface 11 of the bearing housing 2. Between the outer surface 11 and the rear wall 8 there is defined, at both sides, in each case one wheel side space 10.

(10) Furthermore, FIG. 1 shows an axial direction 14 along the shaft 5. A radial direction 15 extends perpendicular to the axial direction 14. A circumferential direction 16 extends around the axial direction 14.

(11) During operation of the exhaust-gas turbocharger 1, the rear walls 8 rotate relative to the outer surfaces 11 in the wheel side space 10. In this way, a rotating flow field is generated in the wheel side space, and a radially outwardly directed gas flow is generated along the wheel rear side. This leads to a decrease in pressure in the wheel side space 10. As a result of the negative pressure gradients, which arise at some operating points of the turbocharger, with respect to the interior of the bearing housing 2, the seal of the shaft 5 with respect to the bearing housing 2 develops leaks, and oil leakage occurs. According to the invention, said oil leakage is prevented to the greatest possible extent.

(12) FIGS. 2 to 5 show four different exemplary embodiments of the design of the outer surface 11, which is situated opposite the rear wall 8, on the side of the turbine wheel 6 and/or of the compressor wheel 7. Identical or functionally identical components are denoted by the same reference numerals in all of the exemplary embodiments.

(13) According to FIG. 2, there is arranged in the outer surface 11 a circular groove 13 which is formed around the full circumference. The turbine wheel 6 or the compressor wheel 7 moves within the edge 17 provided on the outer surface 11.

(14) Furthermore, the outer surface 11 has a shaft recess 12. The shaft 5 extends through said shaft recess 12. In the assembled state, there is situated in said shaft recess 12 a seal for sealing off the interior of the bearing housing 2 with respect to the wheel side space 10.

(15) FIG. 3 shows the outer surface 11 with a groove 13 of spiral-shaped form. In this case, the groove 13 follows a logarithmic spiral. The spiral opens from the inside toward the outside counter to the direction of rotation of the shaft 5. In the example shown, the shaft 5 would thus rotate clockwise. Accordingly, the spiral-shaped groove 13 opens counterclockwise.

(16) FIG. 3 shows three further grooves 18. Said further grooves 18 are in each case of circular-segment-shaped form. The three circular-segment-shaped grooves 18 are arranged in series in the circumferential direction 16. The inner end of the groove 13 leads via a mouth 19 into one of the further grooves 18. It is the object of the inner grooves to decelerate the flow and thus increase the static pressure without disrupting the flow field.

(17) FIG. 4 shows the outer surface 11 with a plurality of (twelve in the example) radially outwardly extending grooves 13. The grooves 13 extend in the radial direction 15. This means that said grooves extend further in the radial direction 15 than in the circumferential direction 16. The circular-segment-shaped further grooves 18 already shown in FIG. 3 are additionally provided in FIG. 4.

(18) The grooves 13 in FIG. 4 are of curved form. This means that each individual groove is curved in the circumferential direction 16.

(19) FIG. 5 likewise shows an outer surface 11 having 12 radially outwardly extending grooves 13 and three circular-segment-shaped further grooves 18. By contrast to FIG. 4, the grooves 13 in FIG. 5 are both curved in the radial direction and also inclined in the circumferential direction 16. Said inclination means that a first point 20 and a second point 21 on an outer edge of the groove 13 do not lie on a straight line through the central point of the shaft 5.

(20) The embodiments of the groove 13 and further grooves 18 shown in FIGS. 2, 4 and 5 serve primarily for disrupting the radially outwardly directed flow in the wheel side space 10. By means of the spiral-shaped groove 13 in FIG. 3, the flow is diverted such that a mass flow leads via the spiral-shaped groove 13 to the radially inner region of the wheel side space 10. The number, position, depth and shape of the grooves can preferably be optimized by means of CFD calculation and test procedures for the respective application.

(21) In addition to the above written description of the invention, reference is hereby explicitly made to the diagrammatic illustration of the invention in FIGS. 1 to 5 for additional disclosure thereof.

LIST OF REFERENCE SIGNS

(22) 1 Exhaust-gas turbocharger 2 Bearing housing 3 Turbine housing 4 Compressor housing 5 Shaft 6 Turbine wheel 7 Compressor wheel 7 Rear wall 9 Blades 10 Wheel side space 11 Outer surface 12 Shaft recess 13 Groove 14 Axial direction 15 Radial direction 16 Circumferential direction 17 Edge 18 Further grooves (circular-segment-shaped) 19 Mouth 20 First point 21 Second point