Bearing sleeve, bearing cap, method for manufacturing a vibration-damping element for a rotating shaft, electric motor

Abstract

The invention relates to a bearing shell for a rotating shaft (4), wherein the wall (6) of the bearing shell (2) has a wall thickness (8) which is less than 10% of the diameter of the bearing shell (2). The invention is characterized in that the bearing shell (2) is composed of a plurality of layers (12) which are joined to one another in material terms in the axial direction (20), the layers each having a layer thickness (14) of 10 μm to 200 μm, and the wall (6) has a closed cavity (16) which is filled with a powder (18).

Description

TECHNICAL FIELD

[0001] The invention relates to a bearing sleeve, to a bearing cover, to an electric motor and to a method for producing a damping element. BACKGROUND

[0002] In rotating machines, the rotor has a dynamically changing relative movement in the radial direction and also in the axial direction with respect to the almost stationary stator or housing. This problem in principle not only concerns electric motors but also internal combustion engines. In electric motors, this concerns in particular bearing covers with bearing sleeves which serve as damping elements. In internal combustion engines, this concerns the bearings of camshafts and of crankshafts. The problem is described below here exemplarily for electric motors.

[0003] The relative movement with respect to the movement can be formed differently and dynamically both along the rotor axis and also in the axial direction of the rotor. This in fact dynamically changes the respective local gap size of the rotor and the stator at each point of location on the rotor surface.

[0004] The rotor itself is here dynamically moved in different resonance modes which are essentially caused and influenced by the generated electromagnetic forces, the mechanical centrifugal forces (for example unbalance), and the dynamic stiffness of the rotor, the rotor bearing in the housing, the housing itself and the bearings of the housing. In electric motors, the medium in the rotor gap can also play a role, especially if the medium is not a gas but a fluid, for example water or silicone oil, which generates damping. The mechanical action chain can here be described as a series of the following elements:

[0005] - on the one hand the geometric tolerances of the rotor, the bearings and the structure of the rotor or housing. For example unbalance, bearing gap or different thermal expansion coefficients or eccentricities in the radial direction and / or stiffness differences also play a role. In addition, different magnetic fields and inductivities occur along the radial direction. This is caused by material differences, fluctuations in the electrical excitation current and induced eddy currents. In addition, the overall structure plays a role in the different local temperature rises in operation which produce a dynamic self-oscillation of the resonance of the rotor shaft for each specific control and load situation.

[0006] The resulting dynamic relative movement of the rotor axis acts both directly and indirectly on the so-called outer bearing ring.

[0007] Due to the so-called mechanical action chain, highly dynamic excitation and transmission of mechanical collision events of the bearing and the bearing sleeve with a relative movement in the range of a few μm in the self-oscillation of the excited resonance of the rotor axis, up to the transmission into the bearing cover, are produced. This is generally referred to as dynamic bearing gap. Through this collision event, mechanical vibrations are also produced in the housing and the housing bearings which in turn produce vibrations which produce structure-borne sound which also manifests itself as an acoustic phenomenon.

[0008] In order to reduce engine noise and vibrations, the following measures are taken according to the prior art, however these measures usually significantly reduce the bearing stiffness and can thereby cause greater gap sizes:

[0009] On the one hand, inertial masses are installed and the dimensions of the mechanical components are designed redundantly if necessary in order to move the resonance frequencies into a non-critical range, in particular away from the range of the application rotational speed. Furthermore, the installation of O-rings of rubber on the bearing seats of the rotor is a well-proven method. Furthermore, magnetic bearings are also sometimes used for the rotor. However, as has been set out, these measures all lead to greater gap sizes in the engine. SUMMARY

[0010] The technical problem addressed by the present application is to improve the damping of the rotor vibrations generated in the bearing and / or in the bearing sleeve and bearing cover and at the same time to ensure that the bearing stiffness in the radial and axial direction is maintained or even increased. Furthermore, it is also important to reduce the generation of mechanical vibrations and noise of the engine.

[0011] The technical problem is solved according to the application by a bearing sleeve for a rotating shaft, wherein the wall of the bearing sleeve has a wall thickness which is less than 10% of the diameter of the bearing sleeve, it being provided that the bearing sleeve consists of a plurality of materially bonded layers in the axial direction, which layers each have a layer thickness of 10 μιη to 200 μιη, and the wall has a closed cavity which is filled with a powder. The technical problem is also solved according to the application by a bearing cover comprising a bearing sleeve of the aforementioned type. The technical problem is also solved according to the application by an electric motor having a bearing cover of the aforementioned type.

[0012] The technical problem is also solved according to the application by a method for manufacturing a damping element by means of a screen printing process, the method comprising the following steps:

[0013] - printing a first sub-area of a first layer with a first screen printing paste,

[0014] - printing a second sub-area of the first layer with a second screen printing paste,

[0015] - wherein the second sub-area is surrounded by the first sub-area in the layer plane,

[0016] - drying the first layer,

[0017] - continuing to print further layers until a three-dimensional green body is formed, in which the second sub-areas of the layers form a volume which is surrounded by the first sub-area,

[0018] - the heat treatment process is carried out at a treatment temperature at which the material of the first screen-printed paste is subjected to a sintering process and at which the material of the second screen-printed paste is essentially not subjected to a sintering process.

[0019] The bearing sleeve for a rotating shaft according to the invention has a wall, which has a wall thickness which is less than 10% of the diameter of the bearing sleeve. The bearing sleeve is characterized in that it consists of a plurality of layers which are joined to one another by material bonding. These layers each have a layer thickness of 80 to 300 μm. Furthermore, the wall has a closed cavity which is filled with a powder.

[0020] The bearing sleeve thus has a very thin wall relative to the overall diameter of the bearing sleeve, which wall consists of layers which are joined to one another by material. These layers which are joined to one another by material can be produced in the layer thickness by means of an additive manufacturing process, in particular by means of a screen printing process. Screen printing is suitable for realizing a cavity having a very thin wall with a powder filling as an additive manufacturing process. This powder filling in the closed cavity here produces particularly strong damping properties, which in turn serve to reduce the vibrations and the acoustic phenomena and the structure-borne sound which arise here. The reduction is not achieved here by means of measures which result in a higher gap size, such as O-ring seals as described in the prior art. The bearing sleeve described here is generally a damping element which can in principle also be used in other vibration-loaded locations in devices which act mechanically. It is particularly expedient to arrange the bearing sleeve in a bearing cap which serves as a cover for a housing of an electric motor. The shaft of a rotor is thus guided into the motor housing by means of the bearing cap and by means of the bearing sleeve. In this regard, an electric motor comprising a bearing cap having the bearing sleeve is also part of the invention.

[0021] In another design form of the invention, the bearing sleeve has a cavity, the largest cross-sectional area of which is less than 5 mm 2 , in particular less than 3 mm 2 . The term "largest cross-sectional area" is understood here as the cross section which results from the cut cavity in a sectional view, which has the largest possible dimensions. It is generally sought to design the largest cross-sectional area to be less than 3 mm 2 , wherein the defined cross section is more complex in terms of manufacture due to the cavity having a smaller cross section.

[0022] The geometrically measured degree of filling of the cavity is at least 60%, preferably at least 80%, particularly preferably 90% in this case. It is endeavored to design the degree of filling as high as possible, which respectively means a technical challenge for manufacturing reasons. The degree of filling of the cavity or the technical implementation of filling the cavity with powder will be explained in detail in the description of the method. The geometrically measured degree of filling is understood here as the degree of filling of the cavity by pouring in the powder. The individual particles of the powder filling are not taken into account in the given degree of filling, respectively the spaces between them in the order of magnitude of the size of the particles.

[0023] Metal alloys, in particular iron-based metal alloys, or alloys comprising iron are preferred materials for the bearing bush or the bearing bush wall. Such alloys can be produced in a practical manner by the advantageous screen printing process described or by other additive manufacturing processes and can be consolidated into the desired shape by a heat treatment process in the form of a sintering process.

[0024] The powder arranged in the cavity comprises here again a material which has a higher melting point than the wall structure. If the wall structure is composed of iron-based metal as described, it is suitable for example to design the powder as tungsten-based. This has the advantage in production that the wall structure of the bearing bush can be formed by a sintering process or other corresponding heat treatment process, while in the interior of the cavity, the material placed there does not melt and is not sintered. The example of tungsten also shows that in another advantageous embodiment, the powder in the cavity also has a higher density than the material of the wall structure. This results in a higher damping behavior than with materials having a lower density.

[0025] A further part of the invention is a method for producing a damping element, for example the bearing bush. The following steps are carried out here preferably by means of a screen printing process: First, a first sub-area of a first layer is printed with a first screen printing paste. Subsequently, a second sub-area of the first layer is printed with a second screen printing paste. The second sub-area is designed here such that it is surrounded by the first sub-area in the respective layer plane. This results in the formation of a volume area (volume) filled with the second screen printing paste when a plurality of layers is constructed on top of one another. A drying step of the first layer follows, which can also be divided into two sub-steps, wherein the drying step is carried out first after printing the first sub-area and a further drying step is carried out after printing the second sub-area.

[0026] The printing process on the first and second sub-areas is carried out successively and produces further layers therefrom until a three-dimensional green body is formed. In the green body, the second sub-area of each layer forms a volume which is surrounded by the first sub-area as mentioned. A heat treatment process is then carried out with a process temperature at which the material of the first screen printing paste carries out a sintering process and at which the material of the second screen printing paste does not essentially carry out a sintering process.

[0027] As mentioned before, a plurality of volumes is produced by the method which are surrounded by the material of the first area in the green body. Due to the presence of the material of the second area, for example tungsten alloy, the material of the first area, for example iron-based construction, surrounds the volumes. The material of the first area, for example iron alloy, is sintered to a self-supporting structure, a wall structure of the damping element, for example a bearing sleeve, by the heat treatment process or sintering process. The material of the second area which forms the volumes is not sintered or only sintered to a lower extent in the process temperature. The material of the second area dissociates to a powder when the damping element moves to a greater extent. After the heat treatment process, the volumes of the green body form a powder-filled cavity of the damping element, in particular a bearing sleeve. The powder in the cavity produces a clear damping effect for the strongly vibration-loaded component.

[0028] In principle, a debinding process can be added after the manufacture of the green body by means of the screen printing process and before the heat treatment process (sintering process), which is also preferably a thermal process in this case. The binder of the screen printing paste is burnt off here, for example by thermal decomposition. The temperature in the heat treatment process for debinding is generally below the temperature of the heat treatment for the sintering process. The debinding process or the sintering process is carried out here such that until the maximum sintering temperature is reached, all volatile components of the second screen printing paste are completely removed in the process until the point in time at which the first material forms a wall region through which no gas can pass. BRIEF DESCRIPTION OF DRAWINGS

[0029] Further features and other components of the application are explained in detail on the basis of the following drawings. Reference is made here to purely schematic design forms of the application which do not constitute a restriction on the scope of protection.

[0030] In the drawings:

[0031] Figure 1 a three-dimensional exploded view of an electric motor with a bearing cover,

[0032] Figure 2 a three-dimensional view of a bearing cover with a bearing sleeve,

[0033] Figure 3 a three-dimensional view of a damping element in the form of a bearing sleeve with a layered construction,

[0034] Figure 4 Showing according to Figure 3 The cross-sectional view obtained by cutting through the bearing sleeve wall using section IV.

[0035] Figure 5 Showing the cross section Figure 3 According to Figure 3 A cross-sectional view of a local region V on the outer surface of the bearing sleeve.

[0036] Figure 6 Show along Figure 3 A cross-sectional view of the interior of section VI in the diagram.

[0037] Figure 7 A schematic diagram of the screen printing process is shown.

[0038] Figure 8 Showing according to Figure 3 The layered structure of the blank during the preparation stage of the vibration damping element.

[0039] Figure 9 The debonding process of the blank is shown.

[0040] Figure 10 The heat treatment process, in the form of a green body, is shown as a sintering process.

[0041] Figure 11 Show Figure 8 The cut Figure X A cross-sectional view of I, and

[0042] Figure 12 Show Figure 8 The cut Figure X Cross-sectional view of II. Detailed Implementation

[0043] Figure 1 An overview view of an electric motor 30 is shown. The electric motor 30 is shown in a three-dimensional exploded view. The motor includes a bearing cover 28, a rotating shaft 4, a stator 60, and a rotor 58 arranged on the rotating shaft 4. The stator 58, rotor 60, and shaft 4 are supported in a housing 62, wherein the bearing cover 28 covers the housing 62 and the shaft 4 is guided outward through the bearing cover 28. For this purpose, a bearing sleeve 2 is installed in the bearing cover 28, in which a bearing (not shown), such as a ball bearing, is also installed. Figure 2 A more detailed view of the bearing cap 28 is given in the figure. The bearing sleeve 2 can also be commonly referred to as the damping element 32.

[0044] As described, in motors, for example Figure 1In the illustrated electric motor 30, a dynamic relative motion, either radially or axially, is typically generated in the rotor 58 relative to the nearly stationary stator and housing 62, which is shown here as stator 60. The resulting resonance then acts via shaft 4 onto the bearing sleeve 2 of a bearing (not shown here). The bearing sleeve 2 is typically cast into a bearing cover 28. The bearing cover 28 is, in many cases, designed as an aluminum casting, which results in low vibration damping and relatively low rigidity, despite its low density. This typically generates a self-resonant vibration between shaft 4 and rotor 58, and here, highly dynamic excitation and transmission of collision events with relative motion in the range of several μm within the bearing and the bearing sleeve 2 surrounding the bearing. These relative movements are then transmitted to the housing 62 in the form of mechanical vibrations, which may produce vibrational and acoustic phenomena, i.e., significant noise. Against this backdrop, the following describes how the bearing sleeve 2, in the form of a vibrating element 32, can be designed so that the vibrations are not transmitted to the bearing cover 28 and also to the housing 62 to the aforementioned extent. This allows vibrations and undesirable acoustic phenomena at the motor to be reduced or suppressed.

[0045] Therefore, bearing sleeve 2, as Figure 3 The layered design shown comprises multiple layers 12, ranging from 10 μm to 200 μm, stacked to form a sleeve 2. The sleeve 2 has a wall thickness less than 10% of the diameter 10 of the bearing sleeve 2. That is, the wall thickness 8 is relatively narrower than the diameter 10. When the diameter of the bearing sleeve 2 is typically 40-70 mm, the wall thickness is usually between 4 mm and 7 mm and can be even lower. A wall thickness of 2 mm is also common. The wall structure 26 of the bearing sleeve 2 has a cavity 16 filled with powder 18.

[0046] exist Figure 4 The text shows the path along the... Figure 3 The cross-sectional view is shown by line IV. Cavity 16 is designed in a rhomboid shape here purely by example. Cavity 1 can also be honeycomb-shaped, i.e., hexagonal, circular, or irregular. Powder 18 located in the cavity serves as a vibration damping device, which absorbs vibrations transmitted to the bearing sleeve 2 within the wall structure 26 through cavity 16.

[0047] exist Figure 5 and Figure 6 The following are shown respectively Figure 3 Screenshots V and VI are shown. The layered structure of bearing sleeve 2 is shown enlarged here. Figure 5 A view of the bearing sleeve 2 as seen from the outside is shown by indicating the cavity 16 only with dashed lines. Figure 6 It shows Figure 3 Screenshot VI shown is obtained by cutting through the interior of the wall structure 26 of the bearing sleeve 2, thereby revealing...Figure 6 A cross-sectional view of the cavity 16 is directly shown. Advantageously, the cavity 16 is filled with powder 18 to the greatest extent possible. This results in... Figure 6 The powder filling degree shown is 24. Figure 6 Line 24 shows the height of the powder 18 filling the cavity 16. The aim is to design the filling degree 24 to be as high as possible. The powder filling degree 24 should preferably be greater than 60%. Figure 6 The diagram shows a very advantageous design, in which the powder filling degree 24 is approximately 95%.

[0048] The bearing sleeve 2 or damping element 32 is advantageously used to reduce vibrations applied to the bearing cap 28 or housing 62 via the rotating shaft 4. However, the layered structure and the powder-filled cavity with very low wall thickness place high demands on the manufacturing technology of the bearing sleeve 2. A suitable manufacturing method to meet the high requirements of the bearing sleeve 2 is described below.

[0049] Figure 7 This schematically illustrates screen printing process 34, in which a squeegee 66 moves on a screen 64. Screen printing pastes 40, 44 (e.g.) Figure 11 and Figure 12 (As shown) Here, it is screen-printed onto the substrate 68 or an existing layer via screen printing 64.

[0050] Therefore, firstly as Figure 8 The first layer 38 is produced as shown, and another layer 46 is printed on the first layer until a three-dimensional blank 48 is produced. The blank 48 here includes a closed volume 50, which corresponds to the cavity 16 of the bearing sleeve 2 after the manufacturing process is completed. The production of this volume 50 can be referred to... Figure 11 and Figure 12 ,in, Figure 11 It shows along Figure 8 The radial section of line XI in the middle and Figure 12 Similarly, it shows along Figure 8 The axial section of the dashed box XII in the figure.

[0051] Figure 11 This illustrates an exemplary (in principle, not different from the other layer 46) first layer 38, which has a first sub-region 36, produced by a first screen printing paste 40 in a first screen printing step. A second region 42 is left blank in this first screen printing step. This region 42 is produced by a second screen printing paste 44 in a second screen printing step. For this purpose, two different templates are typically placed on the screen, so that the second screen printing paste is printed directly into the blank area left blank in the first step in the second step.

[0052] Furthermore, Figure 12 A layered construction is shown and thereby the sequence of the plurality of layers is shown, in which further layers 46 are printed onto the first layer 38 with the method. It is suitable here that after each printing process a short drying process takes place, for example by means of an ultraviolet lamp.

[0053] This drying process can last for 5 seconds, for example. If further drying processes are carried out after drying the first sub-area 36 and after printing the second sub-area 42, then one layer can be printed within 15-20 seconds. For a common layer thickness of 100 μιη, a height of 1 mm can be constructed in the blank 48 within about 200 seconds. This refers here to the layer thickness applied at the time of printing. This layer thickness is different from the layer thickness 14 defined with respect to the bearing shell, in which a shrinkage of 20% by volume is generally taken into account in the sintering process. The manufacturing times described represent above-average manufacturing speeds for additive manufacturing processes.

[0054] The materials used for manufacturing the blank 48 or the bearing shell 2 are also set forth below. It is suitable to use a material based on an iron base for the first screen printing paste. Here, a suitable organic or inorganic binder is provided for the respective powder of the material to be manufactured, i.e. a powder of an iron alloy, for example, in order to produce a screen printing paste that is suitable rheologically. The first screen printing paste is thereby advantageously provided with particles composed of iron powder, typically an iron alloy, in order to form the wall structure 26 of the bearing shell 2 substantially also on the basis of an iron base. The second screen printing paste 44 printed into the second sub-area 42 here comprises a functional proportion of a material that has a high damping action on one side, i.e. possibly also a high density, and here has a higher sintering temperature or melting temperature than the iron alloy used. The necessity for this will be set forth below with reference to the explanations of Figure 9 and Figure 10 The sintering temperature of a material is lower than the melting temperature, since a complete melting of the material or of the particles does not take place at the time of sintering. Rather, a diffusion process takes place between the individual particles in the boundary region during the sintering process, sometimes also with local melting. The melting temperature is therefore higher than the sintering temperature, however the sintering temperature is generally associated with the melting temperature, so that a material that has a higher sintering temperature than other materials also has a higher melting temperature. A ceramic material with a high density and a high sintering temperature is therefore suitable as a material for the second screen printing paste 44, however a material with a high melting temperature and a high density, such as tungsten, is also suitable.

[0055] Now to Figure 8The billet 48 shown undergoes a debinding process 54, in which the organic binder is preferably reduced in the absence of oxygen, and the decomposition of the binder is continuously removed from the environment, for example, through gas exchange. Common debinding is carried out at temperatures, for example, between 200°C and 400°C. A heat treatment process 52 is also performed, in which the billet 48 is sintered. As already described, the sintering temperature of the material to be sintered is below its melting temperature; suitable sintering temperatures for ferrous alloys are between 900°C and 1400°C. The sintering process here follows a prescribed temperature profile that precisely matches the corresponding metal alloy. The heat treatment process 52 is preferably carried out in an inert gas environment.

[0056] exist Figure 10 After the heat treatment process 52 shown, the previous blank 48 is no longer referred to as a blank, but now refers to the bearing sleeve 2 or the preform of the bearing sleeve 2 that is still to be processed. This bearing sleeve 2 shown is now, for example, placed in a die-casting mold and recast with aluminum during the die-casting process, so that the material of the bearing cap 28 mentioned above fits tightly around the bearing sleeve.

[0057] List of reference numerals

[0058] 2 bearing sleeves

[0059] 4. Rotating axis

[0060] 6. Bearing sleeve wall

[0061] 8 Wall thickness

[0062] 10. Diameter of the bearing sleeve

[0063] 12 floors

[0064] 14 layers thick

[0065] 16. Cavity

[0066] 18 Powder

[0067] 20 Axial

[0068] 21 Radial

[0069] 22. Cross-section of the cavity

[0070] 24 Powder Filling Degree

[0071] 26-wall structure

[0072] 28 Bearing cap

[0073] 30 Electric Motors

[0074] 32 Vibration damping elements

[0075] 34. Screen Printing Process

[0076] 36 first sub-region

[0077] 38 first layer

[0078] 40 first screen printed paste

[0079] 42 second sub-region

[0080] 44 second screen printed paste

[0081] 46 further layer

[0082] 48 green body

[0083] 50 volume

[0084] 52 heat treatment process

[0085] 54 debinding process

[0086] 58 rotor

[0087] 60 stator

[0088] 62 housing

[0089] 64 screen

[0090] 66 squeegee

[0091] 68 green body

Claims

1. A bearing sleeve for a rotating shaft (4), wherein The wall (6) of the bearing bushing (2) has a wall thickness (8) which is less than 10% of the diameter of the bearing bushing (2), characterized in that the bearing bushing (2) is composed of a plurality of layers (12) which are joined to one another in material terms in the axial direction (20), the layers each having a layer thickness (14) of 10 μm to 200 μm, and the wall (6) has a closed cavity (16) which is filled with a powder (18).

2. The bearing sleeve of claim 1, wherein, The bearing sleeve (2) has a cavity (16) with a maximum cross-sectional area (22) of less than 5 mm 2 .

3. The bearing sleeve of claim 2, wherein, The bearing sleeve (2) has a cavity (16) with a maximum cross-sectional area (22) of less than 3 mm 2 .

4. Bearing bush according to one of claims 1 to 3, characterized in that The powder filling (24) of the cavity (16) is at least 60%.

5. The bearing sleeve of claim 4, wherein, The powder filling (24) of the cavity (16) is at least 80%.

6. Bearing bush according to one of claims 1 to 3, characterized in that The wall structure (26) of the bearing bushing (2) is composed of a metal alloy.

7. The bearing sleeve of claim 6, wherein, The metal alloy is an iron alloy.

8. The bearing sleeve according to one of claims 1 to 3, characterized in that The powder (18) in the cavity (16) comprises a material which has a higher melting temperature than the material of the wall structure (26) of the bearing bushing (2).

9. The bearing sleeve of claim 8, wherein, The powder (18) in the cavity (16) comprises a material which has a higher density than the material of the wall structure (26).

10. A bearing cover comprising a bearing bushing (2) according to one of claims 1 to 9.

11. An electric motor (1) having a bearing cover (28) according to claim 10.

12. A method for producing a bearing bushing according to one of claims 1 to 9 by means of a screen printing process (34), the method comprising the following steps: - printing a first subregion (36) of a first layer (38) with a first screen printing paste (40), - printing a second subregion (42) of the first layer (38) with a second screen printing paste (44), - wherein the second subregion (42) is surrounded by the first subregion (36) in the layer plane, - drying the first layer (38), - continuing to print further layers (46) until a three-dimensional green body (48) is produced, in which the first layer (38) and the second subregions (42) of the further layers (46) form a volume (50) which is surrounded by the first subregion (36), - carrying out a heat treatment process (52) at a treatment temperature at which the material of the first screen printing paste (40) carries out a sintering process and at which the material of the second screen printing paste (44) essentially does not carry out a sintering process.

13. The method of claim 12, wherein, The first screen printing paste (40) comprises an iron-based material.

14. The method according to claim 12 or 13, characterized in that, A debinding process (54) is carried out before the heat treatment process (52).

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