Radial foil bearing and method for producing a radial foil bearing

Abstract

The invention relates to a radial foil bearing with at least one bearing foil which is arranged and designed in the radial direction between an inner contour of a bearing cartridge and an outer contour of a rotor in such a way that the rotor is rotatably mounted about a rotational axis by the radial foil bearing after reaching a lift-off speed with the formation of a gas film within the bearing foil. In order to improve the radial foil bearing with regard to its manufacturability and / or its function during operation in a gas conveying device, the bearing foil in the radial foil bearing comprises a sleeve-like base body with a helical slot.

Description

The invention relates to a radial foil bearing having at least one bearing foil which is arranged and designed in the radial direction between an inner contour of a bearing cartridge and an outer contour of a rotor in such a way that the rotor is mounted rotatably about an axis of rotation after a lifting speed has been reached, forming a gas film within the bearing foil by the radial foil bearing. The invention further relates to a method for producing such a radial foil bearing.Prior ArtFoil bearings, in particular radial foil bearings, are known, for example, from German laid-open specifications DE 10 2018 222 572 A1 and DE 10 2018 222 603 A1. Foil bearings of this type are used, for example, in an air compressor of a fuel cell system for the radial bearing of a rotor shaft of an electromotive drive of the air compressor. Spring foils of such radial foil bearings are disclosed for example in the United States patent US 5,427,455, wherein a spring foil is provided for example with a plurality of spring elements representing a cantilever beam spring pattern in the radial foil bearing.Disclosure of the InventionThe object of the invention is to improve a radial foil bearing according to the preamble of claim 1 with regard to its m producible 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.The object is achieved in a radial foil bearing having at least one bearing foil which is arranged and designed in the radial direction between an inner contour of a bearing cartridge and an outer contour of a rotor in such a way that the rotor is mounted rotatably about an axis of rotation by the radial foil bearing after a lifting speed has been reached, forming a gas film within the bearing foil, by the radial foil bearing, in that the bearing foil comprises a sleeve-like base body having a helical slot in the radial foil bearing. The sleeve-like base body preferably has substantially the shape of a straight circular cylinder jacket. The bearing foil is, for example, a cover foil or a spring foil of the radial foil bearing. Depending on the embodiment of the radial foil bearing, only one of a plurality of bearing foils can comprise the sleeve-like base body with the helical slot. Depending on the design of the radial foil bearing, however, two or more foils can also comprise the sleeve-like base body with the helical slot. Depending on the embodiment of the radial foil bearing, it is also possible for at least one bearing foil to comprise a sleeve-like base body having more than one helical slot. However, the exemplary embodiment is particularly preferred in which the sleeve-like base body comprises only exactly one helical slot. The embodiment of the bearing foil with the helical slot has proven to be advantageous both with regard to the function and to the production of the claimed radial foil bearing. The claimed radial foil bearing is advantageously used in an air compressor, in particular in a fuel cell system. Of course, the claimed radial foil bearing can also be used in another way, for example in a turbine, in a fan or in a dental application, for example in a dental drill.A preferred exemplary embodiment of the radial foil bearing is characterized in that the bearing foil with the helical slot is positioned and held in the radial foil bearing only by its shape, its arrangement and, if appropriate, its prestress, that is to say without any fastening means. A further advantage of the special bearing foil with the helical slot is that the bearing foil can be fastened within the radial foil bearing without additional fastening means, i.e. solely by the bearing foil itself. Furthermore, special recesses within the bearing cartridge for fastening the bearing foil can advantageously also be dispensed with. Thus, the load on the bearing foil in the region of the helical slot can be advantageously kept low. The helical slot in the bearing foil allows the load-bearing capacity to be maintained over the entire circumference of the bearing foil in the radial foil bearing. This is particularly advantageous compared to conventional radial foil bearings which have foils with slots running in the axial direction.A further preferred exemplary embodiment of the radial foil bearing is characterized in that the bearing foil with the helical slot is designed as a spring foil. The spring foil embodied in this way is arranged in the radial direction between a cover foil and the bearing cartridge. The spring foil advantageously serves to prestress the cover foil in the direction of the rotor. Conventional spring foils are equipped for this purpose with protruding spring tabs, for example. The embodiment of the bearing foil with the helical slot simplifies the production of the spring foil considerably. The spring foil is also referred to in English as a spring foil or beam foil.A further preferred exemplary embodiment of the radial foil bearing is characterized in that the bearing foil with the helical slot is designed as a cover foil. Here, a presumed disadvantage which relates to the permeability of the bearing foil in the region of the helical slot for gas, in particular for air, is deliberately accepted. If the slit is made sufficiently small, the desired function of the cover sheet can be maintained sufficiently stably with respect to the formation of the gas film within the bearing cartridge. The cover film is also referred to in English as a bump foil.A further preferred exemplary embodiment of the radial foil bearing is characterized in that the spring foil and the cover foil are positioned and held in the radial foil bearing by frictional forces, wherein the spring foil, the cover foil and the bearing cartridge are configured in terms of friction such that a coefficient of friction between the bearing cartridge and the spring foil and / or between the spring foil and the cover foil is always greater than a coefficient of friction between the cover foil and the rotor. This can be achieved, for example, by a special coating of the cover film on its inner surface facing the rotor. It can thus be realized in a simple manner that the friction between the rotor and the cover foil always remains less than the friction between the other friction partners.A further preferred exemplary embodiment of the radial foil bearing is characterized in that the helical slot runs continuously between two opposite ends of the sleeve-like base body. This simplifies the production of the bearing foil considerably.A further preferred exemplary embodiment of the radial foil bearing is characterized in that the helical slot is configured so as to start with only one complete helix. The sleeve-like base body is advantageously equipped with the helical slot in such a way that the helical slot is only cut once in each cross section through the sleeve-like base body. In this way, in particular the desired function of the cover film with the helical slot can be realized.A further preferred exemplary embodiment of the radial foil bearing is characterized in that the radial foil bearing comprises a spring foil having a helical slot and a cover foil having a helical slot. This simplifies the production of the radial foil bearing considerably. The two bearing foils with the helical slot can be arranged with their helices in the same direction or in opposite directions in the radial foil bearing. Both embodiments may be advantageous. Particularly advantageously, the bearing foils do not have to be fixed in the circumferential direction in the bearing cartridge. For axial securing of the bearing foils, conventional axial securing rings can be used, for example.In a method for producing a radial foil bearing described above, the object indicated above is alternatively or additionally achieved in that at least one of the bearing foils is formed from a flat foil body which has the shape of a parallelogram. One side of the parallelogram is referred to as the film length. A side of the parallelogram arranged at an angle thereto is also referred to as a ramp. Therefore, the extension of the ramp in the direction of the film length can also be referred to as ramp length. In a particularly preferred embodiment, the sheet-like film body has the shape of a parallelogram in which the film length is equal to the ramp length. The sheet body may be formed of the same or similar sheet material as conventional bearing sheets.A preferred exemplary embodiment of the method is characterized in that a plurality of foil bodies is cut out from a strip of sheet metal material. The strip of sheet material is, for example, unwound from a corresponding coil. The film bodies can then be cut off easily. Particularly advantageously, the sheet-like film bodies remain connected to one another, for example, at two points, in a similar manner to a leadframe. Thus, the production of the bearing foils in large numbers can be further simplified.A further preferred exemplary embodiment of the method is characterized in that the sheet-like film body / bodies is / are treated with heat and / or prebent. These processes can also be carried out in a largely automated manner.The invention further relates to a bearing foil, in particular a cover foil and / or spring foil, and / or a foil body for a radial foil bearing described above. The parts mentioned can be purchased separately.The radial foil bearing serves particularly advantageously in an air compressor, which is also referred to as a turbomachine, for supporting a shaft, at the ends of which at least one impeller, for example a compressor impeller, is fastened. The shaft with the impeller is also referred to as a rotor.The invention optionally also relates to an air compressor, which is preferably driven by electric motor and has a rotor described above, which is mounted by at least one radial foil bearing described above.Further advantages, features and details of the invention will become apparent from the following description, in which various exemplary embodiments are described in detail with reference to the drawing.BRIEF DESCRIPTION OF THE DRAWINGThe following are shown: FIG. 1 shows an electric machine with a three-part rotor shaft in longitudinal section; FIG. 2 shows a radial foil bearing with two bearing foils in cross section; FIG. 3 shows a greatly exaggerated non-round, i.e. non-circular, inner contour of the radial foil bearing from FIG. 2 ; FIGS. 4 and 5 show two perspective representations of a bearing foil with a sleeve-like base body which has a helical slot; FIG. 6 shows a sheet metal material strip from which sheet-like film bodies are cut out, in a plan view; and FIG. 7 shows a sheet-like film body which is suitable for illustrating a storage film as is illustrated in FIGS. 4 and 5.DESCRIPTION OF THE EMBODIMENTSFIG. 1 shows an electrically driven turbomachine 1 having a compressor wheel 2 and a turbine wheel 4 in longitudinal section. 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.The turbine wheel 4 is connected in terms of drive to the compressor wheel 2. The two wheels 2 and 4 belong to a rotor 6, For the rotationally fixed connection between the compressor wheel 2 and the turbine wheel 4, the rotor 6 comprises a motor shaft 7.For the electric drive, the turbomachine 1 comprises an electric machine 9. the electric machine 9 is designed as an electric motor having a motor housing 10 and a motor winding 11. A magnet 12 designed as a permanent magnet is arranged in the motor shaft 7 designed as a hollow shaft.During operation in a fuel cell system, compressor wheel 2 of turbomachine 1 is driven via turbine wheel 4. In addition, the compressor wheel 2 is driven via the electric motor 9.The rotor 6 with the motor shaft 7 is rotatably mounted in the motor housing 10 of the electric machine 9 with the aid of two radial bearings 13, 14. The radial bearings 13, 14 are advantageously designed as foil air bearings.On the compressor side 3, a compressor scroll casing 15 is mounted on the motor casing 10. The compressor scroll casing 15 comprises a compressor inlet 16, via which air to be compressed is supplied to the turbomachine 1.On the turbine side 5, a turbine scroll casing 17 is mounted on the engine casing 10. The turbine scroll casing 17 includes a turbine outlet 18 through which expanded air exits. The energy generated when the air is expanded is used to drive the compressor wheel 2.The motor shaft 7 can also be referred to as a rotor shaft because it serves to represent a rotor 19 in the electric machine 9. The rotor 19 comprises a magnet section 20 in which the magnet 12 is arranged. Two shaft sections 21, 22 are fastened to the mutually remote ends of the magnet section 20. The magnet 12 is surrounded in the magnet section 20 by a bandage 23.FIG. 2 shows a radial foil bearing 30 with a bearing cartridge 33. The radial foil bearing 30 serves for the radial mounting of a rotor 31; the rotor 31 is, for example, a rotor 19 as is shown in FIG. 1 in the turbomachine 1. The radial foil bearing 30 is, for example, the radial bearing 13 or the radial bearing 14 in FIG. 1.The rotor 31 is radially mounted about an axis of rotation 32 within the bearing cartridge 33 with the aid of the radial foil bearing 30. The radial foil bearing 30 comprises two bearing foils 34, 35. The bearing foil 35 is a cover foil.The cover foil 35 and the spring foil 34 serve for the dynamic representation of a fluid film between the rotor 31 and the radial foil bearing 30, wherein the cover foil 35 and / or the spring foil 34 deform. From this deformation or from these deformations there results a non-round inner contour 86 for the rotor 31. Non-round inner contour 86 means in particular that the inner contour represented with the aid of the cover foil 35 is not ideally circular.The non-round inner contour 86 can be realized in different ways in the radial foil bearing 30. Particularly advantageously, the non-round inner contour 86 with the slotted spring foil 34 is realized in combination with the slotted cover foil 35 in the radial foil bearing 30 shown in FIG. 2.In FIG. 3, the non-round inner contour 86 of the cover foil 35 or of the bearing cartridge 33 is shown greatly exaggerated for illustrating the non-roundness. Arrows indicate a maximum radius 88 and a minimum radius 89. The radii of different sizes serve to represent non-circular shapes 91, 92, 93 on the non-circular inner contour 86. the non-circular inner contour 86 substantially has the shape of a triangle with rounded corners 81 to 83.Air is advantageously used in the radial foil bearing 30 for mounting the rotor 31. Therefore, the radial foil bearing 30 is also referred to as an air bearing. An occurring bearing gap or lubrication gap, or a plurality of, for example three, occurring bearing gaps or lubrication gaps, between the rotor 31 and the non-round inner contour 86 is or are decisive both for a rotor dynamic behavior of the turbomachine 1 illustrated in FIG. 1, which is also referred to as a turbomachine, and for its service life, in particular for the number of realizable start-stop processes with the turbomachine 1.FIGS. 4 and 5 show a storage film 40 in various perspectives. The bearing foil 40 is, for example, a cover foil 35 or a spring foil 34 of the radial foil bearing 30 in FIG. 2 The bearing foil 40 comprises a sleeve-like base body 41 with a helical slot 42.The helical slot 42 extends continuously from one end 43 to an opposite end 44 of the sleeve-like base body 41; the helical slot 42 is embodied and arranged in the sleeve-like base body 41 in such a way that the helical slot 42 is only cut once in any desired cross section 45 through the sleeve-like base body 41.FIG. 6 shows how the bearing foil 40 can be produced cost-effectively from a strip of sheet material 55. The strip of sheet material 55 is, for example, unwound from a roll, also referred to as a coil. By means of a suitable cutting tool, for example with a laser cutting device, foil bodies 51 to 53 are cut out of the strip of sheet material 55. The film bodies 51 to 53 each have the shape of a parallelogram. Corners of the film bodies 51 to 53 can be rounded during the cutting process.Dimension lines are used to reference a film length 61, a film width 62 and a ramp length 64 of a ramp 63. The film length 61 denotes the extent of the film body 51 in the longitudinal direction of the sheet material strip 55. the film width 62 corresponds to the width of the sheet material web 55. the ramp 63 is defined by a ramp angle 60.In FIG. 6, the ramp length 64 is smaller than the film length 61, but in a particularly preferred embodiment, the ramp length, unlike that shown in FIG. 6, is equal to the film length 61.In FIG. 7, a film body 50 is shown, which also has the shape of a parallelogram. A ramp length 70 is equal to the film length.The production of a plurality of storage films 40, as shown in perspective in FIGS. 4 and 5, can be automated to the greatest possible extent. The unwinding and cutting of the sheet material, which serves as the starting material for producing the bearing foils 40, is preferably carried out continuously.Bulges and / or spring tabs can advantageously be produced in the same process in the bearing foil 40. The method may include cutting operations, punching operations, embossing operations, and / or ECM operations, where the capital letters ECM are the terms Electro Chemical Machining. Depending on the desired shape and production volume, laser cutting can also be used.In FIG. 6, small connecting sections 65, 66, 67, 68 between the film bodies 51 to 53 are indicated by rectangles. This illustrates that the bearing foils 51 to 53 are not initially completely separated from one another during the cutting, but instead remain connected to one another in one piece, similarly to leadframes, which are also referred to as leadframe, before the foil bodies 51 to 53 are later separated from one another. This cutting process can be carried out mechanically using a conventional cutting tool or else by laser cutting.Conventional heat treatment methods provide the film bodies 51 to 53 with their material properties desired as required in each case in a further method step, in particular with regard to their stability, rigidity, friction properties and / or wear resistance.In a further method step, the film bodies 51 to 53 or 50 are bent in order to impart the desired circular cylindrical shell-shaped shape to them. The bending is effected, for example, with the aid of rollers and / or rollers. The connecting sections 65 to 68 are advantageously only completely severed at the end.It can be seen in FIG. 2 that a helical slot 74 formed in the spring foil 34 is arranged in the storage cartridge 33 at the very top in FIG. 2, i.e. at twelve o'clock middays. In contrast, a helical slot 75 in the cover film 35 is arranged offset in the clockwise direction in the circumferential direction. The helical slot 75 in the cover sheet 35 is arranged at approximately fourteen o'clock.The positions of the slots 74, 75 shown in FIG. 2 are preferably for illustration purposes. The positions of the slots 74, 75 can vary not only along the axial extension of the bearing cartridge 33, as is caused by their helical shape, but also relative to one another. The helical slots 74, 75 can also be formed in mutually opposite helical directions in a particularly advantageous manner. That is, for example, one slot is directed clockwise and the other slot is directed counter-clockwise. Thus, for example, it is ensured in a simple manner that the slots 74, 75 can intersect but advantageously do not overlap, at least do not completely overlap.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2018 222 572 A1

[0002] DE 10 2018 222 603 A1

[0002] U.S. Pat. No. 5,427,455

[0002]

Claims

Radial foil bearing (30) having at least one bearing foil (40) which is arranged and designed in the radial direction between an inner contour of a bearing cartridge (33) and an outer contour of a rotor (31) in such a way that the rotor (31), after a lifting rotational speed has been reached, is mounted rotatably about an axis of rotation (32) by the radial foil bearing (30), forming a gas film within the bearing foil (40), characterized in that the bearing foil (40) comprises a sleeve-like base body (41) having a helical slot (42) in the radial foil bearing (30).Radial foil bearing according to claim 1, characterised in that the bearing foil (40) with the helical slot (42) is positioned and held in the radial foil bearing (30) only by its shape, its arrangement and optionally its prestress, that is to say without any fastening means.Radial foil bearing according to one of the preceding claims, characterized in that the bearing foil (40) with the helical slot (42) is designed as a spring foil (34).Radial foil bearing according to one of the preceding claims, characterized in that the bearing foil (40) with the helical slot (42) is designed as a cover foil (35).Radial foil bearing according to Claims 3 and 4, characterized in that the spring foil (34) and the cover foil (35) are positioned and held in the radial foil bearing (30) by frictional forces, wherein the spring foil (34), the cover foil (35) and the bearing cartridge (33) are configured in terms of friction such that a coefficient of friction between the bearing cartridge (33) and the spring foil (34) and / or between the spring foil (34) and the cover foil (35) is always greater than a coefficient of friction between the cover foil (35) and the rotor (31).Radial foil bearing according to one of the preceding claims, characterized in that the helical slot (42) runs continuously between two opposite ends (43, 44) of the sleeve-like base body (41).Radial film bearing according to one of the preceding claims, characterized in that the helical slot (42) is formed so as to start with only one complete helix.Radial film bearing according to one of the preceding claims, characterized in that the radial film bearing (30) comprises a spring film (34) with a helical slot (42) and a cover film (35) with a helical slot (42).Method for producing a radial foil bearing (30) according to one of the preceding claims, characterized in that at least one of the bearing foils (40) is formed from a flat foil body (50) which has the shape of a parallelogram.Method according to claim 9, characterised in that a plurality of flat foil bodies (51, 52, 53) is cut out from a strip of sheet material (55).Method according to claim 9 or 10, characterised in that the sheet-like film body / bodies (50; 51-53) is / are treated with heat and / or pre-bent.Bearing foil (40), in particular cover foil (35) and / or spring foil (34), and / or foil body (50; 51-53) according to one of Claims 1 to 8.

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