Radial foil bearing

Abstract

The invention relates to a radial foil bearing (30) comprising a rotor (31) which is rotatably mounted about an axis of rotation by means of the radial foil bearing (30) after a lift-off speed has been reached with formation of a gas film within an elastically deformable top foil. In order to improve the radial foil bearing in terms of its producibility and / or its function during operation, the top foil comprises at least three bearing support surface bodies which are spaced apart from one another in a rotor circumferential direction and integrally connected to a top foil frame, wherein the bearing support surface bodies are attached to the top foil frame so as to be movable relative to the top foil frame.

Description

[0001] R.415074

[0002] - 1 -

[0003] Description

[0004] title

[0005] radial foil bearings

[0006] The invention relates to a radial foil bearing with a rotor which, after reaching a lift-off speed, is rotatably mounted about an axis of rotation within an elastically deformable cover film by the radial foil bearing.

[0007] State of the art

[0008] Foil bearings, in particular radial foil bearings, are known, for example, from German patent applications DE 10 2018 222 572 A1 and DE 10 2018 222 603 A1. Such foil bearings are used, for example, in an air compressor of a fuel cell system for the radial support of a rotor shaft of an electric motor drive of the air compressor. Spring foils of such radial foil bearings are disclosed, for example, in American patent US 5,427,455, wherein a spring foil is equipped, for example, with a plurality of spring elements that form a cantilevered beam spring pattern in the radial foil bearing.

[0009] Disclosure of the invention

[0010] The object of the invention is to improve a radial foil bearing according to the preamble of claim 1 with regard to its manufacturability and / or its function in operation in a gas conveying device, in particular in an air compressor, where very high rotational speeds of, for example, one hundred thousand revolutions per minute can occur.

[0011] The task is, in a radial foil bearing with a rotor that, after reaching a lift-off speed, rotates around a rotational axis R.415074 through the radial foil bearing, forming a gas film within an elastically deformable cover film.

[0012] - 2 - rotatably mounted, is achieved by the cover film comprising at least three bearing support bodies spaced apart from one another in a rotor circumferential direction, which are integrally connected to a cover film frame, wherein the bearing support bodies are movably connected to the cover film frame relative to the cover film frame. The bearing support bodies can also be referred to as bearing pads and, in operation of the radial film bearing, serve to form a non-circular inner contour facing the rotor with convergent-divergent gap profiles for the formation of the gas film between the rotor and the bearing support bodies. The cover film is advantageously made of a suitable elastically deformable material. This is preferably a sheet material. The claimed radial film bearing is used, for example, for the support of a high-speed shaft in a turbomachine, which is designed, for example, as an air compressor in a fuel cell system.The radial foil bearing used enables significantly more start-stop cycles in a simple manner than comparable conventional radial foil bearings.

[0013] A preferred embodiment of the radial foil bearing is characterized in that the bearing support bodies are mechanically decoupled from the cover foil frame via at least two webs each. This ensures in a simple manner that the bearing support bodies can move independently of one another in order to build up the desired gas film for rotor support during operation of the radial foil bearing. Depending on the cover foil design, the cover foils can be pre-bent before installation in the radial foil bearing. However, it is also possible to install the cover foils without such pre-bending. Depending on the cover foil design, the bearing support bodies can also be pre-bent relative to the cover foil frame to provide a desired preload of the respective bearing support body towards the rotor.According to another preferred embodiment, an additional foil, such as a spring foil, can also be used to pre-tension the bearing support bodies towards the rotor. In the installed state, such a spring foil, also called a beam foil or spring foil, is arranged on the side of the top foil facing away from the rotor. The webs are advantageously designed to be large and arranged such that the desired load-bearing function for the gas film during operation of the radial foil bearing is achieved primarily or solely by the bearing support bodies R.415074.

[0014] - 3 - is realized. The cover foil frame advantageously serves mainly or exclusively to position the cover foil and, if necessary, to secure it against twisting.

[0015] Another preferred embodiment of the radial foil bearing is characterized in that at least one U-shaped clearance is provided between the bearing support bodies and the cover foil frame. This U-shaped clearance prevents unwanted entanglement between the bearing support bodies and the cover foil frame. Depending on the design of the cover foil, the U-shaped clearance can also advantageously serve to allow the desired passage of gas into a gas bearing gap between the respective bearing support body and the rotor.

[0016] Another preferred embodiment of the radial film bearing is characterized in that the cover film frame is positioned in a bearing receptacle to prevent rotation. This reliably prevents unwanted twisting of the cover film during operation of the radial film bearing. Depending on the design of the cover film, the cover film frame can be fixed in the bearing receptacle, for example, by a material bond. Alternatively or additionally, fastening means can be used to fix the cover film frame in the bearing receptacle.

[0017] Another preferred embodiment of the radial foil bearing is characterized in that the cover foil frame has an inlet edge and an outlet edge at opposite ends in the rotor circumferential direction, which are arranged in a recess of the bearing housing. One end of the cover foil frame advantageously serves to fix the cover foil in the recess. Depending on the design of the cover foil, it may be sufficient if the end of the cover foil, for example, the end with the outlet edge, abuts a boundary wall in the recess of the bearing housing. Alternatively or additionally, the end, for example, the end with the outlet edge, of the cover foil frame can also be fixed in the recess of the bearing housing by means of a material bond, for example, by welding, and / or with a suitable fastening device. R.415074

[0018] - 4 -

[0019] Another preferred embodiment of the radial foil bearing is characterized in that the bearing support bodies have a rectangular shape. This simplifies the production of the cover foil. Furthermore, the rectangular bearing support bodies allow for a very stable implementation of the desired function with regard to the formation of the gas film between the rotor and the cover foil.

[0020] Another preferred embodiment of the radial film bearing is characterized in that the cover film frame has a rectangular shape. This has also proven advantageous with regard to the manufacture and function of the cover film.

[0021] Another preferred embodiment of the radial foil bearing is characterized in that the bearing support surfaces constitute a total bearing area that is larger than one-third, in particular one-half, of the area of ​​a sheet metal strip from which the cover foil is formed. The cover foil is produced, for example, by stamping or etching from the sheet metal material. The claimed embodiment of the cover foil offers the particular advantage that the cover foil is only one piece. This simplifies the production and assembly of the cover foil.

[0022] Another preferred embodiment of the radial foil bearing is characterized in that the radial foil bearing has a bearing diameter of less than twenty-five millimeters, wherein the cover foil has a thickness greater than one hundred micrometers. Due to the claimed embodiment of the radial foil bearing with the mechanical decoupling of the bearing support bodies, relatively thick foils can advantageously be used for small bearing diameters. The cover foils with a thickness greater than one hundred micrometers, especially in combination with small bearing diameters of less than twenty-five millimeters, behave significantly more robustly and offer greater resilience against otherwise undesirable wear.

[0023] Another preferred embodiment of the radial foil bearing is characterized in that the bearing support surfaces are pre-tensioned towards the rotor by a spring foil. The spring foil is particularly advantageously also made in one piece. The spring foil comprises, for example, R.415074

[0024] - 5 -

[0025] Spring elements, in particular spring tabs or spring feet, serve to pre-tension the bearing support bodies of the cover film towards the rotor. The spring film can be designed in the same or a similar way to a conventional spring film.

[0026] The invention further relates to a cover film and / or a spring film for a radial film bearing as described above. The cover film and the spring film are available separately.

[0027] The invention may optionally also relate to a method for producing a cover film for a previously described radial film bearing. The invention may optionally also relate to a method for assembling a cover film into a previously described radial film bearing.

[0028] The radial foil bearing is particularly advantageous in an air compressor, also known as a turbomachine, for supporting a shaft to which at least one impeller, for example a compressor impeller, is attached at either end. The shaft with the impeller is also called the rotor.

[0029] The invention may also relate to a preferably electrically driven air compressor with a previously described rotor, which is supported by at least one previously described radial foil bearing.

[0030] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing.

[0031] Brief description of the drawing

[0032] They show:

[0033] Figure 1 shows an electric machine with a multi-part rotor shaft in longitudinal section;

[0034] Figure 2 shows an enlarged section of a radial foil bearing with a spring foil and a cover foil in the area of ​​a recess in a bearing housing in cross-section; R.415074

[0035] - 6 -

[0036] Figure 3 shows a first embodiment of the cover film from Figure 2 in a top view;

[0037] Figure 4 shows a similar representation to that in Figure 3 according to a second embodiment of the cover film; and

[0038] Figure 5 shows an embodiment of the claimed radial foil bearing in cross-section.

[0039] Description of the exemplary implementations

[0040] Figure 1 shows a longitudinal section of an electrically driven turbomachine 1 with a compressor wheel 2 and a turbine wheel 4. The compressor wheel 2 is arranged on a compressor side 3 of the turbomachine 1. The turbine wheel 4 is arranged on a turbine side 5 of the turbomachine 1.

[0041] The turbine wheel 4 is driven by the compressor wheel 2. The two wheels 2 and 4 belong to a rotating assembly 6. The rotating assembly 6 includes a motor shaft 7 to provide a rotationally fixed connection between the compressor wheel 2 and the turbine wheel 4. The motor shaft 7 is partially designed as a hollow shaft and is rotatable about a pivot axis 8.

[0042] For electric drive, the turbomachine 1 comprises an electric machine 9. The electric machine 9 is designed as an electric motor with a motor housing 10 and a motor winding 11. A magnet 12, designed as a permanent magnet, is arranged in the motor shaft 7, which is designed as a hollow shaft.

[0043] In operation within a fuel cell system, the compressor wheel 2 of the turbomachine 1 is driven firstly by the turbine wheel 4. Secondly, the compressor wheel 2 is driven by the electric motor 9.

[0044] The drive unit 6 with the motor shaft 7 is rotatably mounted in the motor housing 10 of the electric machine 9 by means of two radial bearings 13, 14. The radial bearings 13, 14 are advantageously designed as foil air bearings. R.415074

[0045] - 7 -

[0046] On compressor side 3, a compressor spiral casing 15 is attached to the motor housing 10. The compressor spiral casing 15 includes a compressor inlet 16, through which air to be compressed is supplied to the turbomachine 1.

[0047] On turbine side 5, a turbine spiral casing 17 is attached to the motor housing 10. The turbine spiral casing 17 includes a turbine outlet 18 through which expanded air exits. The energy generated during the expansion of the air is used to drive the compressor wheel 2.

[0048] The motor shaft 7 can also be called a rotor shaft because it serves to represent a rotor 19 in the electric machine 9. The rotor 19 comprises a magnetic section 20 in which the magnet 12 is arranged. Two shaft sections 21, 22 are attached to the opposite ends of the magnetic section 20. The magnet 12 is surrounded in the magnetic section 20 by a bandage 23, which can also be called a sleeve.

[0049] Figure 2 shows a section through a radial foil bearing 30 in a cross-section through a rotor 31. The rotor 31 is, for example, a shaft section of an electrically driven shaft.

[0050] Rotor 31, for example, is rotor 19 as shown in Figure 1 in the turbomachine 1. Radial foil bearing 30, for example, is radial bearing 13 or radial bearing 14 in Figure 1.

[0051] The rotor 31 is radially supported about an axis of rotation within a bearing receptacle 35 by means of the radial foil bearing 30. The bearing receptacle 35 is represented, for example, by a bearing cartridge 33. However, the bearing receptacle 35 can also be represented by a different housing body.

[0052] The radial foil bearing 30 comprises a spring foil 34, which is clamped radially between a cover foil 45 and the bearing cartridge 33. For this purpose, the spring foil 34 is equipped with spring elements 37 or is spring-embossed. R.415074

[0053] - 8 -

[0054] In Figure 2, an arrow indicates the direction of rotor rotation 38, in which the rotor 31 rotates about the axis of rotation during operation of the radial foil bearing 30. The cover foil 45 serves to form a non-circular inner contour in the bearing receptacle 35 of the bearing cartridge 33. This non-circular inner contour on the inside of the cover foil 45 essentially creates wedge-shaped gas bearing gaps during operation of the radial foil bearing 30.

[0055] In the embodiment of the radial foil bearing 30 shown in Figure 2, the recess 36 is designed as a triangular groove. In the triangular groove 36, both the spring foil 34 and the cover foil 45 are fixed at a fixing point 39.

[0056] With respect to the rotor direction 38, the triangular groove 36 has a groove start 41 and a groove end 42. The triangular groove 36 comprises a long groove flank 46 and a short groove flank 47, which is angled away from the long groove flank 46.

[0057] The spring foil 34 and the cover foil 45 lie flat against the long groove flank 46 with their first foil end sections. More precisely, the first foil end section of the spring foil 34 lies against the long groove flank 46. The first foil end section of the cover foil 45 lies flat against the first end section of the spring foil 34.

[0058] The second foil end sections of the spring foil 34 and the cover foil 45 project into the recess 36, but are spaced apart from the first foil end sections of the bearing foils 34, 45. The end of the cover foil 45 projecting into the triangular groove 36 forms an inlet edge 43. The other end of the cover foil 45 forms an outlet edge 44.

[0059] A distance between the inlet edge 43 and the foil end sections of the bearing foils 34, 45 abutting the long groove flank 46 allows for thermal expansion of the two bearing foils 34, 45 during operation without them touching each other.

[0060] Figures 3 and 4 show two embodiments of a cover film 50; 60, each in a top view. The cover films 50; 60 are manufactured, for example by stamping, from a sheet metal strip 48. The sheet metal strip 48 is made of an elastic metal. R.415074

[0061] - 9 -

[0062] The cover film 50; 60 has three bearing support bodies 51, 52, 53; 61, 62, 63 each to represent the functionally required non-circular inner contour. In combination with the spring film 34 shown in Figure 2, the bearing support bodies 51, 52, 53; 61, 62, 63 serve in the operation of the radial film bearing.

[0063] 30 to form a gas film between the cover film 50; 60 and the rotor

[0064] 31 in Figure 2.

[0065] The non-circular inner contour disclosed, among other things, in the aforementioned German patent application DE 10 2018 222 603 A1, can be represented using the bearing cartridge 33. Alternatively or additionally, the spring foil 34 can be used to represent the non-circular inner contour.

[0066] In the cover sheets 50; 60 shown in Figures 3 and 4, the bearing support bodies 51 to 53; 61 to 63 serve advantageously, preferably in combination with a spring action of spring elements of the spring sheet, to represent the non-circular inner contour.

[0067] The bearing surface bodies 51 to 53; 61 to 63 of the cover sheets 50; 60 are integrally connected to a cover sheet frame 58; 68 via two webs 55, 56; 65, 66 each. The cover sheet frames 58; 68 each have the shape of a rectangle that surrounds the bearing surface bodies 51 to 53; 61 to 63. The bearing surface bodies 51 to 53; 61 to 63 also have the shape of rectangles.

[0068] Figure 3 shows that each bearing support body 51 to 53 is surrounded by a U-shaped free space 59. The webs 55, 56 define a pivot axis which, in Figure 3, runs in a vertical direction, i.e., transversely to a longitudinal extension of the cover film 50.

[0069] In the cover sheet 60 shown in Figure 4, each bearing support body 61 to 63 is enclosed by two U-shaped recesses 67, 69. Between the U-shaped recesses 67 and 69, the webs 65, 66 are indicated, which here also define a pivot axis in a direction vertical in Figure 4, i.e., transverse to the longitudinal extent of the cover sheet 60. R.415074

[0070] - 10 -

[0071] In Figures 3 and 4, the left end of the sheet metal strip 48, from which the cover film 50; 60 is formed, defines the inlet edge 43 in the installed state of the radial film bearing. Similarly, the right end of the sheet metal strip 48 in Figures 3 and 4 represents the outlet edge 44 of the radial film bearing in the installed state.

[0072] If the recess 36, unlike the one shown in Figure 2, is designed as a rectangular groove instead of a triangular one, then the opposite ends of the cover sheets 50; 60 are interlocked, for example, in a finger-like manner. Depending on the design of the cover sheets 50; 60 in combination with the spring sheet and depending on pre-bending, an assembly aid in the form of an insertion funnel may be necessary during assembly.

[0073] Figure 5 shows a cross-section of the radial foil bearing 30 without the rotor. The rotor, not shown, rotates clockwise in the bearing receptacle 35 of the radial foil bearing 30.

[0074] The spring foil 34 is equipped with spring feet 71, 72 extending from a connection point 73. The free ends of the spring feet 71, 72 are supported in the bearing receptacle 35, which is represented by the bearing cartridge 33.

[0075] The spring feet 71, 72, supported internally on the bearing receptacle 35, advantageously serve to preload each bearing support body 51, 52, 53 radially inwards against the rotor (not shown). The bearing support bodies 52, 53 are also referred to as pads.

[0076] The webs 55, 56 shown in Figure 3 each form a pivot axis 75 for one of the bearing support bodies 51, 52, 53. The pivot axis 75 extends perpendicular to the plane of the drawing in Figure 5.

[0077] The radial foil bearing 30 has a bearing diameter 77, which is advantageously less than 25 millimeters. The two bearing foils, advantageously both the cover foil 45 and the spring foil 34, each have a thickness 78 greater than 100 micrometers. R.415074

[0078] - 11 -

[0079] In the embodiment shown in Figure 5, the two bearing foils, i.e., the spring foil 34 and the cover foil 45, are fixed at their opposite ends in a recess 36 designed as an M-slot 70. The bearing foils are arranged in the bearing receptacle 35 such that the

[0080] The bearing support bodies or pads 51 to 53 are not mounted on the pivot axes 75, but rather spaced circumferentially from the pivot axes 75 and pre-tensioned radially inwards by the spring feet 71, 72 of the spring foil 34. In the area of ​​the three pivot axes 75 of the cover foil 45, the spring foil 34 is advantageously designed to be particularly flexible. This prevents undesirable damage to the cover foil 45 in the area of ​​the webs 55, 56.

Claims

R.415074 - 12 - Claims 1. Radial foil bearing (30) with a rotor (31) which is rotatably mounted about an axis of rotation by the radial foil bearing (30) after reaching a lift-off speed and forming a gas film within an elastically deformable cover foil (45;50;60), characterized in that the cover foil (50;60) comprises at least three bearing support bodies (51, 52, 53; 61, 62, 63) spaced apart from each other in a rotor circumferential direction, which are integrally connected to a cover foil frame (58;68), wherein the bearing support bodies (51, 52, 53; 61, 62, 63) are movably connected to the cover foil frame (58;68) relative to the cover foil frame (58;68).

2. Radial foil bearing (30) according to claim 1 , characterized in that the bearing support surface bodies (51 ,52,53;61 ,62,63) are mechanically decoupled from the cover foil frame (58;68).

3. Radial foil bearing (30) according to one of the preceding claims, characterized in that at least one u-shaped free space (59;67,69) is provided between the bearing support body bodies (51 ,52,53;61 ,62,63) and the cover foil frame (58;68).

4. Radial foil bearing (30) according to one of the preceding claims, characterized in that the cover foil frame (58;68) is positioned in a bearing receptacle (35) in a rotationally fixed manner.

5. Radial foil bearing (30) according to claim 4, characterized in that the cover foil frame (58;68) has an inlet edge (43) and an outlet edge (44) at opposite ends in the direction of the rotor circumference, which is arranged in a recess (36) of the bearing receptacle (35).

6. Radial foil bearing (30) according to one of the preceding claims, characterized in that the bearing support surface bodies (51 ,52,53;61 ,62,63) have a rectangular shape. R.415074 - 13 - 7. Radial film bearing (30) according to one of the preceding claims, characterized in that the cover film frame (58; 68) has a rectangular shape.

8. Radial film bearing (30) according to one of the preceding claims, characterized in that the radial film bearing (30) has a bearing diameter (77) that is less than twenty-five millimeters, wherein the cover film (50; 60) has a thickness (78) that is greater than one hundred micrometers.

9. Radial foil bearing (30) according to one of the preceding claims, characterized in that the bearing support surfaces (51, 52, 53; 61, 62, 63) are pre-tensioned in the direction of the rotor (31) by a spring foil (34).

10. Cover foil (50; 60) and / or spring foil (34) for a radial foil bearing (30) according to one of the preceding claims.

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