HK1142941B - Hydrodynamic axial bearing - Google Patents

Description

Hydrodynamic axial bearing

Technical Field

The present invention relates to the field of hydrodynamic (hydrodynamics) axial bearings (axialerwung) for rotating shafts, such as are used, for example, in exhaust gas turbochargers.

The invention relates to a hydrodynamic axial bearing with a floating disk (Schwimmscheibe) and to such a floating disk.

Background

When the fast-rotating rotor is loaded with axial thrust, a loadable axial bearing is used. Hydrodynamic axial bearings are used, for example, in exhaust gas turbochargers for taking up high axial forces caused by the fluid and for guiding the turbine shaft in the axial direction. In order to improve the tilt position compensation capability and the wear behavior in such applications, free-floating disks (so-called floating disks) can be used in hydrodynamic axial bearings between the bearing comb (Lagerkamm) rotating at the shaft rotational speed and the non-rotating bearing housing.

Further examples relating to this can be found in documents GB1095999, EP0840027, EP1199486 and EP 1644647. The radial guidance of the floating disk is effected on the rotary body, i.e. on the shaft or on the bearing combs, by means of radial bearings integrated into the floating disk (as disclosed, for example, in EP 0840027) or on a stationary bearing ring (Lagerbund) which concentrically surrounds the rotary body (as disclosed, for example, in EP 1199486). The lubrication of such hydrodynamic axial bearings is usually effected by means of lubricating oil from the lubricating oil system itself or, in the case of an exhaust-gas turbocharger, by the lubricating oil system of the internal combustion engine connected to the exhaust-gas turbocharger.

During operation, a loadable lubricating film is established between the floating disk, which rotates at only approximately half the shaft speed, and the shaft or the bearing combs arranged on the shaft. For this purpose, profiled annular surfaces are usually provided on both sides of the floating disk, which annular surfaces each form a lubrication gap together with a flat (eben) sliding surface. The profiled annular surface comprises wedge surfaces oriented at least in the circumferential direction, which together with the flat sliding surface form a convergent gap. If sufficient lubricant is sucked in (hineinziehen) in the converging gap, a loadable lubricating film is formed. The lubricant is spread in the radial direction (verbreiten) due to the centrifugal force of the rapidly rotating floating disc.

The frictional torque at the axial and radial sliding surfaces of the floating disk influences the rotational speed of the floating disk. At high shaft speeds the floating disc rotational speed is typically below 50% of the shaft rotational speed, i.e. the floating disc rotates at less than half the shaft rotational speed. Thereby, different relative speeds are obtained in the two axial lubrication gaps. The relative speed of the shaft relative to the floating disk is greater than the relative speed of the floating disk relative to the bearing housing.

The gap heights occurring in the two axial lubrication gaps are different due to different relative speeds and different centrifugal forces. Since the bearing is dimensioned for the smallest lubrication gap that occurs each time, the bearing gap is overdimensioned, which can lead to unnecessarily large power losses and to unnecessarily large oil penetration

Disclosure of Invention

The object of the invention is therefore to optimize a hydrodynamic axial bearing with floating disks with respect to power loss and oil penetration.

This object is achieved according to the invention by the load-bearing capacity of the two bearing gaps on both sides of the floating disc being different in size, so that the minimum lubrication gap is the same at the design point. The bearing capacity in relation to the rotational speed, minimum lubrication clearance and oil properties is referred to as the load capacity of the bearing.

According to the invention, different load-carrying capacities are achieved by the geometrically formed different lubricating gaps. The space between the parts forming the axial bearing (i.e. between the bearing housing and the floating disk on the one hand and between the floating disk and the bearing comb rotating with the shaft on the other hand), which is bounded by the profiled annular surface and the flat sliding surface, is referred to herein as a lubrication gap.

The surface dimensions of the two axial lubrication gaps can be individually determined by the radial step of the floating disk, so that the minimum gap height in the two lubrication gaps is the same size at the design point. In this case, the side of the floating disk facing the bearing shell is advantageously equipped with a larger bearing surface than the side facing the bearing comb.

The size of the circular surface formed by radial reduction can also be reduced. The reduction can be effected here radially inwardly, radially outwardly or both radially inwardly and outwardly.

The profiled annular surface and the flat sliding surface which together form the lubrication gap are referred to as the bearing surface of the axial bearing. The reduction in size of the bearing surface is likewise achieved if, for example, only one of the two profiled annular surfaces has the same size, which is reduced in the radial direction and flat. The same effect is achieved if two identically dimensioned annular surfaces interact with such a flat sliding surface (i.e. for example one of the sliding surfaces does not extend radially over the entire annular surface).

Variations in load bearing may also be achieved by geometric variations in the shaping in the circumferential direction. The number of segments can thus be reduced from six to five, for example. Or the oil groove extension in the axial direction may be enlarged.

With the embodiment mentioned, the minimum lubrication gap heights on both sides of the floating disk can be balanced (angleichen) despite the fact that the relative speed between the floating disk and the bearing housing on the one hand and the relative speed between the floating disk and the bearing comb on the other hand differ.

Alternatively, one or both sides of the floating disk can be designed as flat sliding surfaces and the profiled annular surface can be arranged on the shaft or on the bearing comb. For example, if the side of the floating disk facing the shaft is designed as a flat sliding surface and the annular surface is shaped corresponding to the shaft, then rapidly rotating annular surfaces are each shaped in the two bearing parts.

Drawings

Embodiments of the invention are explained in detail below with the aid of the drawings. Wherein:

figure 1 shows a first embodiment of an axial bearing with a stepped floating disk according to the invention,

figure 2 shows a second embodiment of an axial bearing with floating discs (with differently shaped annular faces) designed according to the invention,

fig. 3 shows a sectional view through a third embodiment of an axial bearing with a stepped floating disk according to the invention.

Detailed Description

Fig. 1 and 2 show two embodiments of a hydrodynamic axial bearing according to the invention, wherein in each case in the middle of the figures a section is shown which is guided through the axial bearing along an axis. The axial bearing comprises a floating disk 30, which floating disk 30 is arranged axially between the bearing housing 20 and the bearing comb 11 arranged on the shaft 10 and rotating with the shaft. Alternatively, the bearing comb can be integrated into the shaft as a radially projecting projection, so that the floating disk is arranged axially between the bearing housing and the shaft projection. Views of the floating disk from the corresponding side are shown in the left and right regions of the figure, respectively. On the left side, the floating disk 30A is shown as viewed in direction A, and on the right side, the floating disk 30B is shown as viewed in direction B.

The profiled annular surface of the floating disk 30A facing the bearing shell has an absolute speed v_S(i.e. counterclockwise as viewed in direction a in the illustrated embodiment). Here, the lubricating oil (as indicated by the broad arrow) introduced radially into the annular surface region of the floating disk between the floating disk 30 and the bearing housing 20 via the lubricating grooves 31 is sucked into the wedge surfaces 32 counter to the direction of rotation of the floating disk. The pressure necessary for the load-bearing capacity of the axial bearing is established by the narrowing of the lubrication gap between the wedge surface 32 and the flat sliding surface on the opposite bearing housing. The maximum pressure is obtained in the transition region from the wedge surface 32 to the stop surface 33.

The shaped annular surface of the floating disk 30B facing the bearing comb is at an absolute speed v_S(i.e. clockwise as viewed in direction B in the embodiment shown). However, because the bearing combs 11 are more than twice as fast v in the same direction_WRotating, thereby producing a relative speed v of the profiled annular surface_RThe relative velocity v_RCounterclockwise travel is viewed in direction B. Here, the relative velocity v_RGreater than absolute velocity v_S. Again, the wide arrow indicates how the lubricating oil is guided radially outward through the lubricating grooves and is sucked into the wedge surfaces in the circumferential direction.

In the embodiment according to fig. 1, the floating disk 30 has a radial step such that the side facing the bearing shell 20 extends radially beyond the side facing the bearing comb 11. Thus, the radial elongation of the two sides of the floating disc is different. The annular surface formed on the side facing the bearing housing has a ring width r_GThe ring width r_GGreater than the annular width r of the annular surface on the side of the floating disk facing the bearing comb_W。

Due to the high relative speed at which the wedge surface of the profiled annular surface on the side of the floating disk facing the bearing comb rotates along the flat sliding surface on the bearing comb, a lubrication gap (despite a small bearing surface) is formed, which corresponds to the lubrication gap between the bearing housing and the side of the floating disk facing the bearing housing.

In the embodiment according to fig. 2, the floating disk 30 has two sides of the same size, but the shaped annular surfaces thereof are of different design. The profiled annular surface is divided into a plurality of segments 34, wherein the segments comprise a lubrication groove 31, a wedge surface 32 and an adjacent stop surface 33. The annular surface on the left side, which rotates more slowly relative to the stationary bearing housing, has more sections 34 than the annular surface on the side facing the bearing comb sides, which rotates at a higher relative speed.

Alternatively, the load-bearing capacity can be changed, for example, when the angle of inclination (steigingswinkel) of the wedge surface is changed and thus the range with the maximum load-bearing capacity is narrowed or expanded. The transition between the wedge surface 32 and the stop surface 33 can be realized by means of an edge or as a continuously extending, edge-free surface. In the latter case, it is not necessary to distinguish between wedge surface and stop surface, so that the wedge surface can also be raised continuously to the next lubrication groove, for example, at a continuously decreasing angle.

In the embodiment according to fig. 3, the floating disk 30 again has a radial step, so that the side facing the bearing shell 20 extends radially beyond the side facing the bearing comb 11. Furthermore, a chamfer is applied on the radial inner side of the side facing the bearing comb and the inner radius of the shaped annular surface is slightly increased outward. The inner edge of the flat sliding surface at the bearing comb is offset radially outward, as a result of which the bearing surface of the lubrication gap between the floating disk 30 and the bearing comb 11 is additionally reduced compared to the first embodiment.

In the floating disc of a hydrodynamic axial bearing, it is necessary to supply both sides with lubricating oil. For this purpose, according to the invention, at least one supply opening 35 is integrated (einlassen) into the floating disk. The supply hole 35 connects both sides of the floating disc and allows lubricating oil to be supplied from one side to the other. Optionally, the floating disk has a supply hole for each lubrication groove on the side facing the bearing comb.

In the embodiment shown, the lubricating oil is conducted via a lubricating oil feed line 22 in the bearing housing into the region of the lubricating gap between the floating disk 30 and the bearing housing 20. By rotating the profiled annular surface, the lubricating oil is conveyed radially outward along the lubricating groove 31 and is sucked into the wedge surface in the circumferential direction. The lubricating oil is likewise supplied to the region of the lubricating gap between the floating disk 30 and the bearing comb 11 via the supply opening 35 arranged in the region of the lubricating groove 31. Here, if the supply hole self-lubricating clearance is directed away from the axial direction with a lubricating oil supply at an angle towards the outer edge, the lubricating oil flow is assisted by the rotation of the floating disc.

The supply groove in the region of the radial bearing of the floating disk can be dispensed with to a large extent due to the supply opening. This reduces the penetration of lubricating oil through the decoupling gap (endkopplungsspall) between the bearing comb 11 and the bearing ring 21 (bearing ring 21 is present when the floating disk 30 is mounted on the stationary bearing housing). It is particularly advantageous if the decoupling gap opens into the injection space of, for example, an exhaust gas turbocharger in the region of the radial bearing of the floating disk without additional sealing elements.

List of reference numerals

10 shaft

11 bearing comb-shaped part

20 bearing housing

21 bearing ring

22 lubricating oil input pipeline

30 floating disc

30A Floating disc, bearing cage side (viewed in direction A)

30B Floating disc, bearing comb side (viewed in direction B)

31 lubrication groove

32 wedge surface

33 stop surface

34 shaped annular surface section

35 supply hole

r_GBearing cage side ring width

r_WBearing comb side ring width

v_RRelative speed of floating disk with respect to bearing comb

v_SSpeed of floating disc

v_WSpeed of bearing comb

Claims (12)

1. Hydrodynamic axial bearing of a shaft (10) which is rotatably mounted in a bearing housing (20), the axial bearing comprising a floating disk which is arranged axially between the bearing housing and a bearing comb (11) arranged on the shaft, wherein the bearing housing (20) and the floating disk (30) and the bearing comb (11) are each formed with a lubrication gap which is limited by a profiled annular surface and a flat sliding surface, wherein the profiled annular surface comprises a plurality of wedge surfaces (32) which each narrow the lubrication gap in the circumferential direction, characterized in that the lubrication gaps formed on both sides of the floating disk by the profiled annular surface and the flat sliding surface have different geometric dimensions from one another.

2. Hydrodynamic axial bearing in accordance with claim 1 characterized in that the lubrication gaps on both sides of the floating disc have different radial dimensions.

3. Hydrodynamic axial bearing according to claim 1 or 2, characterized in that the two annular surfaces forming the lubrication gap on both sides of the floating disc (30) are each divided into a different number of segments (34), wherein in each case one segment (34) comprises one wedge surface (32).

4. Hydrodynamic axial bearing according to claim 1 or 2, characterized in that the two profiled annular surfaces forming the lubrication gap on both sides of the floating disc have differently configured wedge surfaces (32).

5. Hydrodynamic axial bearing according to claim 1 or 2, characterized in that the profiled annular surfaces comprise a wedge surface (32) and a flat stop surface (33), and that the two profiled annular surfaces forming the lubrication gap on both sides of the floating disc have different area ratios of the stop surface (33) to the wedge surface (32).

6. Hydrodynamic axial bearing according to claim 1 or 2, characterized in that the floating disc (30) is radially stepped on one side relative to the other.

7. Hydrodynamic axial bearing according to claim 1 or 2, characterized in that at least one supply hole (35) is incorporated into the floating disc (30), wherein the at least one supply hole (35) connects two sides of the floating disc to each other.

8. Hydrodynamic axial bearing according to claim 7, characterized in that the floating disc has a radial lubrication groove (31) and the at least one supply hole (35) opens into the lubrication groove (31) at least on one side of the floating disc.

9. Hydrodynamic axial bearing, in accordance with claim 7 or 8, characterized in that the at least one supply hole (35) is directed radially outwards at an angle.

10. An exhaust-gas turbocharger comprising a shaft as claimed in claim 1 with a hydrodynamic axial bearing as claimed in any of the foregoing claims.

11. A floating disk for use in a hydrodynamic axial bearing between a bearing housing and a shaft which is rotatably mounted in the bearing housing, the floating disk having a profiled annular surface with a plurality of wedge surfaces (32) on both sides, wherein the wedge surfaces are designed in such a way that they each narrow a lubrication gap between the floating disk and a flat sliding surface in the circumferential direction, characterized in that the lubrication gaps formed by the profiled annular surface and the flat sliding surface on both sides of the floating disk have different geometric dimensions from one another.

12. Floating disc according to claim 11, characterized in that the two profiled annular surfaces are divided into a different number of segments (34) respectively, wherein correspondingly one segment (34) comprises one wedge surface (32).