DE102021108884A1 - Radial foil bearing with wedge gap geometry integrated into the outer ring - Google Patents

Abstract

According to the invention, a radial foil bearing (1) with an outer ring-integrated wedge gap geometry is proposed, which has a plurality of offset contour segments (5) which are provided to form the pressure-building wedge gap (11) between the shaft (6) to be supported and the cover foil (4).

Description

Radial foil bearings are provided for the aerodynamic mounting of shafts, with a supporting gas/air cushion being formed between the shaft and the radial foil bearing. The functionality is similar to that of a hydrodynamic plain bearing, with the difference that the shaft is supported by the radial foil bearing via an air cushion and not by a liquid cushion of a hydrodynamic plain bearing. What both functional forms have in common is that only the rotary movement of the shaft leads to the formation of the supporting cushion.

Foil bearings differ from conventional aerodynamic bearings by having a compliant, resilient structure between the rotating shaft and the stationary housing member. Due to this feature, they are less rigid than conventional air bearings, but they can be adapted to geometric changes in the air gap, e.g.

To form the supporting air cushion, the radial foil bearing usually has a cover foil that is in contact with the stationary shaft and a corrugated foil that is arranged radially between the cover foil and the outer ring of the bearing and can deflect elastically in the radial direction. Thus, basically, the radial foil bearing has two foils in contact with each other and an outer ring supporting the foils so that the radial foil bearing can be accommodated in a housing. The outer ring can also be formed in one piece from the housing into which the foils of the radial foil bearing are inserted.

If the shaft is rotated relative to the radial foil bearing, the air present in the air gap defined by standstill is displaced. Above a certain shaft speed, an air cushion forms between the cover film and the shaft, on which the shaft can slide. The foil package with its corrugated foil and its radial spring effect ensures that fluctuations in air pressure or vibrations of the shaft in the radial direction do not affect the bearing and thus keep the air cushion stable.

Various designs of film bearings are known in the prior art. In addition to the radial foil bearings, there are also axial foil bearings that can develop an axial load capacity. The arrangement of the foils of the bearing and their geometric design are varied and adapted to each application.

Functionally, radial foil bearings require an air gap designed as a wedge gap to form a supporting gas/air cushion between the shaft and the cover foil, in which pressure is built up during operation due to the shaft rotation and the resulting dynamic gas/air flow, so that the shaft can rotate at a sufficiently high pressure Speed differs from the radial foil bearing and is supported without contact by the gas/air cushion or a gas/air film.

According to the prior art, this wedge gap geometry is produced in various ways. For example, the required wedge gap between the cover film and the rotating shaft to be supported can be formed by the formation of the wave shape of the corrugated foil with increasing/decreasing foil wave height from one wave to the following wave.

the EP 3 409 960 A1 shows a radial foil bearing, whereby a ramp-shaped contour of the cover foil is produced by placing a further foil underneath or in between at least one point on the circumference (see Fig 2 ). The gap between the cover foil and the corrugation narrows in the area of the additionally enclosed foil.

The object of the invention is to provide an alternative design of the wedge gap for generating the supporting gas/air cushion.

A radial foil bearing with an outer ring, at least one corrugated foil and at least one cover foil, with the at least one corrugated foil being arranged radially between the outer ring and the at least one cover foil, solves the problem in that a supporting gas/air cushion is formed between the cover foil and of a shaft to be carried by the radial foil bearing, the inner circumferential surface of the outer ring has a geometry of at least two contour segments, each in the shape of a circular arc, the centers of which do not lie one above the other.

For this purpose, the corrugations of the corrugated foil advantageously always have the same height from one corrugation to the next corrugation. This is preferable for the economical production of the corrugated foil or corrugated foils.

In other words, the invention provides for the contour segments to be arranged eccentrically with respect to the outer lateral surface of the outer ring if an outer ring is present with a circular outer lateral surface that can define a center point. The center of the contour segment is thus offset to the center of the outside outer surface. A shaft arranged concentrically to the center of the outer lateral surface (during operation) then forms with its shaft peripheral surface and the contour segment a radial distance that varies along a progressive angle between the cover film of the contour segment and the shaft peripheral surface.

According to the invention, it is therefore advantageously proposed to design all corrugations of the corrugated spring foils with the same height and instead to generate the wedge gap geometry between the cover foil and the corrugation by the outer ring inner lateral surface geometry.

Compared to the prior art, smaller and therefore more optimal wedge gap openings can thus be realized in that all spring shafts can be manufactured with the same height and therefore more precisely and easily. Thus, the invention also avoids having to design the individual wave heights with an even smaller manufacturing tolerance; for example, with a wave height tolerance smaller than the wave height difference of the wedge gap. Such narrow wave height tolerances cannot be achieved with the known manufacturing processes, such as bending, rolling, embossing in connection with the unfavorable forming behavior of the stainless steel used. For this reason, in practice, the wedge gap opening is correspondingly enlarged at the expense of the optimal pressure build-up, which leads to a reduction in the bearing load capacity.

An embodiment of the invention provides that the arcuate geometry of a contour segment is an arcuate shape with a constant curvature in the circumferential direction or an arcuate shape with a curvature that changes in the circumferential direction, for example as part of a logarithmic spiral. Thus, the geometry of a contour segment does not have to be circular in the sense of an arc of a circle, but can assume a course in the circumferential direction, with each curved section of the contour forming a center point that coincides with the center points of the other curved sections of the same contour.

In an advantageous embodiment of the invention, the number of contour segments is equal to the number of cover films and/or the number of contour segments is equal to the number of corrugated films. Ideally, three contour segments, each with a corrugated foil and a cover foil, are provided as a foil package, which are arranged offset by 120° in the circumferential direction in order to achieve stable centering and support of the shaft during operation within the radial foil bearing. This means that each of the three wedge gap geometries is largely identical to one another.

The inner lateral surface of the outer ring is preferably composed of several contour segments with the same geometry.

A radial foil bearing arrangement according to the invention with a radial foil bearing solves the problem by forming a supporting gas/air cushion between the cover foil and the shaft carried by the radial foil bearing, with the inner lateral surface of the outer ring having the geometry of at least two contour segments in the shape of a circular arc, the centers of which are not on the axis of rotation the shaft is in operation.

In an alternative according to the invention, the outer ring is designed as a housing opening and is therefore an integral part of a housing, after which the contour segments are designed directly from the housing opening. This eliminates the need for an extra outer ring of the radial foil bearing and arranges the corrugated and cover foils directly in the housing opening.

The geometry of the contour segment is preferably produced by sintering, broaching or extrusion, which represent economical production processes for forming the geometry of the contour segments.

The contour segments, advantageously designed as a circular arc, are designed in such a way that in the static state there is an osculation ratio between 100.5% and 105% between the shaft radius of the shaft to be supported and the supporting area of the cover film. The osculation ratio is calculated from (bearing radius / shaft radius) x 100. “Bearing radius” means the radius of the cover foil.

• 1 einen Außenring des erfindungsgemäßen Radialfolienlagers,
• 2 eine Detailansicht eines Kontursegmentes des Außenringes nach 1,
• 3 eine erfindungsgemäße Radialfolienlageranordnung und
• 4 eine Detailansicht eines Kontursegmentes der Radialfolienlageranordnung nach 3.

Advantageous embodiments of the invention are shown in the figures. Show it:

• 1 an outer ring of the radial foil bearing according to the invention,
• 2 a detailed view of a contour segment of the outer ring 1 ,
• 3 a radial foil bearing arrangement according to the invention and
• 4 a detailed view of a contour segment of the radial foil bearing arrangement 3 .

1 shows an outer ring 2 of the radial foil bearing 1 according to the invention. The outer ring 2 of the radial foil bearing 1 has on its inner peripheral surface 7 three contour segments 5 which follow one another in the peripheral direction. Viewed in the circumferential direction, each contour segment 5 has a course as a continuous change in the radial distance from the axis of rotation 10. In other words, the Outer ring 2 in the circumferential direction does not have the same radial thickness. Its radial thickness increases or decreases steadily in the circumferential direction. Each contour segment 5 is delimited in the circumferential direction by a step 15 which extends in the axial direction and which serves as a stop edge for the foils and can optionally have an opening in the inner corner. The radial offset of two successive contour segments 5 creates a stop edge 16 on this groove 15, on which the cover and/or the corrugated foil 4, 3 of a foil pack can come into contact with the end face of at least one of the foils 3, 4.

2 shows a detailed view of a contour segment 5 of the outer ring 1 . This contour segment 5 is designed as a circular arc and has an offset 12 of its center 8 to the axis of rotation 10 of the shaft 6 to be supported.

3 shows a radial foil bearing arrangement 9 according to the invention. This radial foil bearing arrangement 9 has the radial foil bearing 1 according to the invention with a shaft 6 rotating in the direction of rotation 14 within the radial foil bearing 1 . The wedge gap 11 formed between the cover film 4 and the outer peripheral surface of the shaft 6 is located in the area of the 12 o'clock, 4 o'clock and 8 o'clock positions in this illustration. Following the direction of rotation 14 of the shaft 6, the wedge gap 11 tapers along the contour segment 5. This narrowing of the wedge gap 11 is caused by the in 2 described offset 12 achieved.

4 shows a detailed view of a contour segment 5 of the radial foil bearing arrangement 9 3 . The corrugated foil 3 has an almost constant corrugation height from corrugation to corrugation along the circumferential direction. The wedge gap 11 between the shaft 6 and the cover film 4 is formed solely by the offset 12 of the contour segment 5 .

Reference List

1

radial foil bearing

2

outer ring

3

corrugated foil

4

cover sheet

5

contour segment

6

Wave

7

inner lateral surface

8th

midpoint (contour segment)

9

Radial foil bearing arrangement

10

axis of rotation

11

wedge gap

12

offset

13

radius of curvature

14

Direction of rotation (shaft)

15

groove

16

stop edge

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 3409960 A1 [0008]

Claims (7)

Radial foil bearing (1) with - an outer ring (2), at least one corrugated foil (3) and at least one cover foil (4), wherein - the at least one corrugated foil (3) radially between the outer ring (2) and the at least one cover foil (4) is arranged, characterized in that in order to form a supporting gas/air cushion between the cover film (4) and a shaft (6) to be supported by the radial film bearing (1), the inner lateral surface (7) of the outer ring (2) has a geometry of at least two has arcuate contour segments (5) whose centers (8) are not superimposed. Radial foil bearing (1) after claim 1 , characterized in that the arcuate geometry of a contour segment (5) is - an arcuate shape with a constant curvature in the circumferential direction or - an arcuate shape with a curvature that varies in the circumferential direction, for example as part of a logarithmic spiral. Radial foil bearing (1) according to one of the preceding claims, characterized in that the number of contour segments (5) is equal to the number of cover foils (4) and/or the number of contour segments (5) is equal to the number of corrugated foils (3). Radial foil bearing (1) according to one of the preceding claims, characterized in that the inner lateral surface (7) of the outer ring (2) is composed of several contour segments (5) with the same geometry. Radial foil bearing arrangement (9) with a radial foil bearing (1) according to one of the preceding claims with - the outer ring (2), at least one corrugated foil (3) and at least one cover foil (4), wherein - the at least one corrugated foil (3) radially between the outer ring (2) and the at least one cover foil (4), - and a shaft (6) arranged in the radial foil bearing (1), characterized in that in order to form a supporting gas/air cushion between the cover foil (4) and of the shaft (6) carried by the radial foil bearing (1), the inner lateral surface (7) of the outer ring (2) has the geometry of at least two contour segments (5) each in the shape of a circular arc, the centers (8) of which are not on the axis of rotation (10) of the shaft ( 6) are in operation. Radial foil bearing arrangement (9) or radial foil bearing (1) according to one of the preceding claims, characterized in that the outer ring (2) as a housing opening is an integral part of a housing, after which the contour segments (5) are formed directly from the housing opening. Radial foil bearing arrangement (9) or radial foil bearing (1) according to one of the preceding claims, characterized in that the geometry of the contour segment (5) is produced by sintering, broaching or extrusion.

Images