Bearing assembly for an electrically driven compressor

Abstract

The present invention relates to a bearing assembly for an electrically driven compressor (10) having a housing (12) in which a shaft (14) is rotatably received at a first bearing portion (16) and a second bearing portion (18), and at least one compressor impeller (20) is received on the shaft (14), wherein a shaft disc (60) is provided in the region of the first bearing portion (16). The first bearing portion (16) is configured as an axial bearing and includes a first foil assembly (34) comprising at least one first foil strip (66) of higher stiffness extending in the circumferential direction and at least one second foil strip (72) of lower stiffness extending in the circumferential direction. Furthermore, the present invention relates to the use of the bearing assembly as an axial bearing for axially fixing a shaft (14) with a compressor impeller (20) in an electric compressor (10) supplying air to a fuel cell system or high-speed fluid machinery.

Description

Technical Field

[0001] This invention relates to a bearing assembly for an electrically driven compressor having a housing in which a shaft is rotatably received at a first bearing portion and a second bearing portion, and at least one compressor impeller is received on the shaft, with a shaft disc disposed in the region of the first bearing portion. Furthermore, this invention relates to the use of this bearing assembly as an axial bearing for axially fixing a shaft with a compressor impeller in an electric compressor or high-speed fluid machinery used for supplying air to a fuel cell system. Background Technology

[0002] DE 10 2018 213 697 A1 relates to an air bearing, a bearing unit, and a compressor. The air bearing, particularly a bearing unit for a compressor, includes an outer ring (enclosing a central opening for reception in a shaft), a resiliently deformable spring foil disposed in the opening, and a top foil disposed in the opening. The spring foil is arranged between the outer ring and the top foil. The spring foil has an integrally constructed base, a first material region having a first spring stiffness, and a second material region having a second spring stiffness, wherein each first material region is staggered relative to each second material region in the circumferential direction of the opening, and wherein the first spring stiffness is higher than the second spring stiffness. Furthermore, a bearing unit comprising an air bearing and a shaft rotatably supported in the opening of the air bearing, and a compressor, particularly for a fuel cell system, are disclosed.

[0003] DE 10 2021 209 720 A1 relates to an axial bearing assembly and a compressor having the axial bearing assembly. The axial bearing assembly includes a rotatable shaft within a housing, having a bearing disc disposed on the shaft, with a bearing plate on each side of the bearing disc. The bearing plates are at least indirectly connected to the housing. Bearing elements are supported on the bearing plates, and the bearing disc is capable of being at least indirectly abutted against the bearing elements. An annular intermediate element is disposed between the two bearing plates in the direction of the shaft's axis of rotation. At least one of the bearing elements is integrally constructed with the intermediate element, and the intermediate element is configured to be elastically deformable in the direction of the shaft's axis of rotation. Summary of the Invention

[0004] According to the present invention, a bearing assembly is arranged in an electrically driven compressor having a housing in which a shaft is rotatably received at a first bearing portion and a second bearing portion, and at least one compressor impeller is received on the shaft, and a shaft disc is disposed in the region of the first bearing portion. The first bearing portion is configured as an axial bearing and has a first foil assembly comprising at least one first foil strip with higher stiffness extending in the circumferential direction and at least one second foil strip with lower stiffness extending in the circumferential direction.

[0005] The bearing assembly proposed according to the invention advantageously enables: adjustable axial clearance with a defined preload and compensation for tilting at high load points of the compressor.

[0006] In an advantageous extension of the bearing assembly proposed according to the invention, the at least one first foil strip with higher stiffness and the at least one second foil strip with lower stiffness are arranged spaced apart from each other in the radial direction.

[0007] In an advantageous extension of the bearing assembly proposed according to the invention, the at least one first foil strip with high stiffness preferably has a stiffness in the range of 1 N / µm to 5 N / µm.

[0008] The bearing assembly proposed according to the present invention also has the following feature: the at least one second foil strip with low stiffness has a stiffness in the range of 0.1 N / µm to 0.5 N / µm.

[0009] The above design provides a bearing assembly that, on the one hand, enables adjustable axial clearance with a defined preload due to the low-stiffness spring element, and on the other hand, compensates for tilting at high load points in an electrically driven compressor through at least one high-stiffness element. The bearing assembly according to the invention advantageously features that the at least one first foil strip and the at least one second foil strip each have a wave structure, which extends in the circumferential direction and is spaced apart from each other by troughs.

[0010] In the bearing assembly proposed according to the present invention, the corrugated structure in the at least one first foil strip and the at least one second foil strip is formed by at least two sections or two longitudinal sections.

[0011] In the bearing assembly proposed according to the invention, the wave structures in the at least one first foil strip and the at least one second foil strip are preferably constructed in an alternating sequence when viewed circumferentially. The bearing assembly proposed according to the invention is further characterized in that the wave structure in the at least one first foil strip is implemented with a first arc length, and the wave structure in the at least one second foil strip is implemented with the same second arc length, wherein the first arc length is smaller than the second arc length. Due to the design of the first and second arc lengths in the at least one first foil strip or the at least one second foil strip, the aforementioned defined stiffness range can be substantially predetermined.

[0012] In the bearing assembly proposed according to the present invention, the wave structure in the at least one second foil strip and the at least one first foil strip is characterized in that the wave structure in the at least one second foil strip exceeds the wave structure in the at least one first foil strip by a height difference.

[0013] Furthermore, in the bearing assembly proposed according to the invention, a wave structure formed with a first arc length in the at least one first foil strip imparts high stiffness to the at least one first foil strip. In this context, in the bearing assembly proposed according to the invention, the wave structure formed with a second arc length in the at least one second foil strip is constructed such that it imparts lower stiffness to the at least one second foil strip.

[0014] Furthermore, the present invention relates to the use of the bearing assembly as an axial bearing for fixing a shaft with a compressor impeller in the axial direction at a bearing location, whether in an electric compressor for supplying air to a fuel cell system, or in high-speed fluid machinery, particularly in booster devices, exhaust gas turbochargers, or gas turbines.

[0015] Advantages of this invention: Two independently designed spring characteristics are provided at the axial bearing location (by at least one foil assembly with higher stiffness and at least one second foil assembly with lower stiffness, also extending in the circumferential direction). These characteristics enable, on the one hand, adjustment of the axial clearance with a defined preload force through the action of the lower stiffness, and on the other hand, compensation for tilting at high load points of the compressor through the at least one spring element with higher stiffness.

[0016] The bearing assembly proposed according to the invention can be designed in such a way that the requirements defined above can be met when using foil bearings. The bearing assembly proposed according to the invention ensures that: firstly, at least one first foil strip with lower stiffness extending in the circumferential direction (e.g., having a longitudinal section) engages with the top foil, and as the rotational speed further increases and under higher predefined loads, foil strips with higher stiffness spring elements engage. The bump foil is always supported on the substrate.

[0017] In a foil bearing, the top foil, together with the rotor, surrounds an air film and, through a corresponding structure, possesses properties conducive to pressure build-up. Below the top foil are one or more bottom foils, namely foil strips with lower or higher spring stiffness. These foil strips are achieved through an arch (wave foil). The top foil and the one or more bottom foils are divided into multiple segments. The various segments constitute a parallel connection of spring elements, in this context, a first foil strip with lower stiffness and a second foil strip with higher stiffness.

[0018] The present invention provides a bearing assembly with optimized mounting and tilting characteristics, wherein, regarding mechanical advantages, it should be noted that a better defined spring characteristic facilitates the selection of a suitable clearance, allowing consideration of the profile clearance between the impellers and thus its impact on the overall machine efficiency. In this region, a spring characteristic curve that is as soft as possible is helpful, as this allows for the generation of similar preload within the manufacturing tolerances of all involved components. The stiffer of the two spring assemblies (in the form of at least one foil strip) can be optimized for the expected tilting of the compressor rotor relative to the bearing at high load points.

[0019] Furthermore, the solution proposed according to the invention provides thermal advantages, enabling continuous contact between the corrugated foil and the substrate, thereby achieving improved heat transfer from the bearing clearance to the cooled substrate through improved thermal conductivity. Unlike current designs (where the unloaded side has a larger flow cross-section), cooling flow experiences similar conditions on both axial bearing sides. In this case, there is more cooling flow on that side, but this is more necessary on the loaded side. By using the bearing assembly proposed according to the invention, the condition of a larger flow cross-section can be significantly improved by applying a preload at at least one axial bearing location.

[0020] The solution proposed according to the invention allows for very simple manufacturing, for example, by stamping with a subsequent embossing step, requiring only two processing steps. Furthermore, it should be emphasized that the foil strip with two independent spring stiffnesses proposed according to the invention provides a bearing implementation suitable for mass production, because tolerance variations can be better incorporated into the design. Attached Figure Description

[0021] Embodiments of the invention are described in more detail with reference to the accompanying drawings and the following description. The drawings show: Figure 1 The longitudinal section of an electrically driven compressor having an axial bearing assembly according to the present invention. Figure 2 Detailed view of the foil strip. Figure 3 Top view of the foil strip. Figure 4 The basis for the unfolded foil strip Figure 3 A three-dimensional view of the arrangement, and Figure 5 The bearing assembly proposed according to the present invention has a set of characteristic curves for first and second load regions.

[0022] In the following description of embodiments of the invention, the same or similar elements are designated by the same reference numerals, and in some cases, repeated descriptions of these elements are omitted. The accompanying drawings are for illustrative purposes only. Detailed Implementation

[0023] Figure 1 A longitudinal section of an electrically driven compressor 10 having at least one bearing assembly according to the invention is shown. The electric compressor 10 is shown housed in a housing 12. The electrically driven compressor 10 includes a shaft 14, which may be integrally or in multiple parts and supported on a first bearing portion 16 and a second bearing portion 18. A compressor impeller 20 is located at the end of the shaft 14 located on one side of the first bearing portion 16. The shaft 14 of the electrically driven compressor 10 is driven by a rotor 24, which is surrounded by a stator 22 with minimal clearance between components. The intake side of the electric compressor 10 is indicated by reference numeral 26, while the pressure side of the electric compressor is indicated by reference numeral 28.

[0024] A first foil bearing 30 is located in the region of the first bearing portion 16, and a second foil bearing 32 is located in the region of the second bearing portion 18. The first foil bearing 30 or the second foil bearing 32 serves as an axial bearing for the shaft 14. A shaft disc 60 is located in the region of the first bearing portion 16 to provide axial support. The shaft disc 60 may be part of the shaft 14. Furthermore, it is possible for the shaft disc 60 to be used as a separate component, for example, by heat-shrink mounting to the periphery of the shaft 14 in the region of the first bearing portion 16, or by torsionally connecting it to the shaft 14 via a sliding key or the like.

[0025] From the basis Figure 2 The diagram shows a detailed view of the foil strip 62 of the first foil assembly 34. This foil strip may, for example, be part of a first foil bearing 30, which is received at the first bearing portion 16 of the shaft 14 in the housing 12 of the electric compressor 10.

[0026] From the basis Figure 3 and Figure 4 The diagrams show foil strips 66 and 72 in their unfolded form, for example, according to... Figure 1 The first foil bearing 30 shown is received together at the first bearing portion 16, which serves as an axial bearing.

[0027] Figure 3 The arrangement (shown as unfolded form 64) illustrates a first foil strip 66 with high stiffness. The first foil strip 66 comprises a series of square segments 68 formed with a first width 70. A trough 80 is located between each pair of square segments 68. Each pair of square segments 68 forms an arch. Each arch, comprising two square segments 68, is separated by a trough 80 located between two adjacent arches. Figure 3 Two first foil strips 66 with higher stiffness, shown as an unfolded form 64, are formed with a first width 70. Between the two first foil strips 66 with higher stiffness is a second foil strip 72 with lower stiffness. This second foil strip is formed with a second width 75, which is chosen to be smaller than the first width 70 of the first foil strips 66 with higher stiffness. In the second foil strip 72 with lower stiffness, each pair of longitudinal segments 74 forms an arch, which, similar to the first foil strips 66 with higher stiffness, are separated by troughs 80. The troughs in the first foil strips 66 with higher stiffness are indicated by reference numeral 80, and the crests are indicated by reference numeral 82 at the junctions of the square segments 68 of the first foil strips 66 with higher stiffness.

[0028] according to Figure 4 The stereoscopic view shows the perspective from the side. Figure 3 The arrangement. From Figure 4As can be seen in the illustration, the square segments 68 of the first foil strip 66, which has high stiffness, each form an arch with a first arc length 88. This similarly applies to two segments with a width of 70... Figure 4 The first foil strip 66, which has high rigidity and is arranged in parallel to each other, is shown in three dimensions.

[0029] The second foil strip 72, with lower stiffness, arranged between the two first foil strips, each has an arch formed by two longitudinal segments 74, each arch having a second arc length 90. Due to the different arc lengths 88 and 90 of the first foil strip 66 with higher stiffness and the second foil strip 72 with lower stiffness, this arrangement of the foil strips 62 can form a bearing assembly that, on the one hand, allows for adjustable axial clearance with a defined preload through the second foil strip 72 with lower stiffness, and on the other hand, allows for adjustment according to… Figure 3 and Figure 4 The diagram shows that the first foil strip 66, which has higher stiffness and is arranged as a pair next to the second foil strip 72 with lower stiffness, compensates for the tilt at the high load point of the electric compressor 10. This is according to the invention... Figure 3 and Figure 4 The bearing assembly shown in the unfolded form 64 allows for the design of the bearing assembly according to the invention with respect to the two aforementioned criteria. At least one second foil strip 72 with lower stiffness engages first with the top foil and only engages with the first foil strip 66 with higher stiffness at higher, predefined loads. The bearing assembly proposed according to the invention ensures that: firstly, at least one second foil strip 72 with lower stiffness extending in the circumferential direction engages with the top foil, and only at higher, predefined loads, i.e., with increasing rotational speed, does the second foil strip 66 with higher stiffness engage. The first foil strip 66 with higher stiffness and the second foil strip 72 with lower stiffness are divided into various, for example, square segments 68 and longitudinal segments 74, which form arched segments. The various segments constitute a parallel connection of spring elements.

[0030] From the basis Figure 3 and Figure 4 The diagram also shows that the two first foil strips 66 with higher stiffness, shown here in unfolded form 64, and the second foil strip 72 with lower stiffness received between the two first foil strips, are arranged in an alternating order 76. This means that, as in Figure 4 As shown, at least one peak 82 in a second foil strip 72 with lower stiffness is located in the troughs 80 of two first foil strips 66 with higher stiffness arranged on both sides of the second foil strip. Here, the peak 82 formed by the longitudinal segment 74 in the second foil strip 72 with lower stiffness extends beyond the peaks 82 in the two adjacent extended first foil strips 66 with higher stiffness.

[0031] This means that the arch formed in the second foil strip 72 with a larger second arc length 90 is higher than a height difference 94, that is, the bearing assembly proposed according to the invention first forms a soft spring wave line, and thus enables the adjustability of the axial clearance with a defined preload.

[0032] According to Figure 1 At higher speeds, the shaft 14 shown is compensated for by two first foil strips 66 with higher stiffness arranged adjacent to the second foil strip 72 with lower stiffness, which compensate for any tilting that may occur in the electric compressor 10 or its shaft 14 at high load points. These first foil strips have significantly stiffer spring characteristics and are able to compensate for tilting at high load points of the electrically driven compressor 10, i.e., at high speeds.

[0033] according to Figure 5 The example characteristic curves shown illustrate the first load region 100 and the second load region 102. According to... Figure 5 The characteristic curve is extended as follows: regarding the maximum increase of 86 (in 10... -4 Draw the bearing load 96 (in meters). Figure 5 As can be seen in the diagram, in the first load region 100, at least one second foil strip 72 with lower stiffness of the bearing assembly proposed according to the invention is used. Therefore, in the first load region 100, due to the action of the at least one second foil strip 72 with lower stiffness, the shaft 14 or rotor 24 is oriented relative to the two bearing portions, i.e., relative to the first bearing portion 16 and the second bearing portion 18, which, for example, initially rests against the shaft disc 60. If, for example, the axial clearance is set to 480µm, the two bearing portions 16, 18 have a preload of approximately 10N in the basic state. With a clearance of 480µm, in the basic state, a clearance of 240µm is obtained at one bearing portion. With a load of 70N (200µm) on one side, the other side will still have a preload of 480-200=280µm, i.e., approximately 5N. Assuming a clearance due to manufacturing is + / -20µm, the resulting preload is between approximately 3N and 7N. Therefore, by means of the gradual trend of spring stiffness, i.e. by means of the at least one second foil strip 72 with lower stiffness, preload is always present in the unloaded state of the first bearing portion 16 and the second bearing portion 18 within the tolerance range.

[0034] In contrast, tilt compensation can be achieved in the second load region 102. Here, the most linear characteristics possible of the at least one foil strip 66 with high stiffness are advantageous.

[0035] Therefore, in the bearing assembly proposed according to the invention, two first foil strips 66 with higher stiffness and a second foil strip 72 with lower stiffness, extending in the circumferential direction, are successively engaged with each other. Firstly, axial clearance is compensated by the action of the at least one second foil strip 72 with lower stiffness, while at higher load points of the electrically driven compressor 10, compensation for tilt is achieved by the action of the at least one first foil strip 66 with higher stiffness or by the contact of the first foil strip with the shaft disc 60 of the shaft 14.

[0036] The corresponding foil strips 66 and 72 can be implemented on the bearing assembly proposed according to the present invention (whether used at the first bearing portion 16 or the second bearing portion 18) using different bump foils with different heights and radii. Furthermore, the stiffness requirements for the first load region 100 and the second load region 102 (such as...) Figure 5 As shown, this can be achieved through other structural measures. Therefore, for example, a bending beam can be arranged by stacking multiple foils on top of each other; spring foils with different heights can be used, as in radial bearings. In principle, the stiffness can also be divided into two regions for radially acting foil bearings (i.e., using at least one first foil strip 66 with higher stiffness and at least one additional second foil strip 72 with lower stiffness), as described above.

[0037] The present invention provides a bearing assembly that forms two well-defined, independent spring characteristics, which can be designed separately for the two task areas described above. Mechanically, the better-defined spring characteristics facilitate the selection of appropriate clearances and thus influence the impeller profile clearance and, consequently, the overall efficiency of the machine. To adjust the axial clearance in this region, a spring characteristic curve that is as soft as possible is required, capable of achieving similar preload within the manufacturing tolerances of all participating components. The stiffer of the two springs can be optimally designed for the desired tilt of the rotor 24 relative to the bearing portion, i.e., the desired tilt relative to the first bearing portion 16 or the second bearing portion 18, which in the present case, in the assembly proposed according to the invention, is at least one first foil strip 66 with higher stiffness.

[0038] Regarding the thermal advantages achievable with the bearing assembly proposed according to the invention, it should be mentioned that the continuous contact between the corrugated foil and the substrate, i.e., the bearing disk 60, results in improved heat transfer from the bearing clearance to the cooled substrate due to improved thermal conductivity. Cooling flow experiences similar conditions on both axial bearing sides, i.e., the first bearing portion 16 or the second bearing portion 18. Normally, the unloaded side has a larger flow cross-section, resulting in more cooling flow on that unloaded side due to the larger flow cross-section. However, a more intense cooling of the loaded side is required, which can be improved by the solution proposed according to the invention.

[0039] The bearing assembly proposed according to the invention is advantageously used as an axial bearing for axially fixing a shaft 14 with a compressor impeller 20 in an electric compressor 10 for, for example, supplying air to a fuel cell system. Furthermore, the bearing assembly proposed according to the invention can be used in high-speed fluid machinery, particularly turbochargers, or in internal combustion engines or gas turbines. Additionally, turbo compressors can also be equipped with foil bearings according to the bearing assembly proposed according to the invention.

[0040] The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, various modifications are possible within the scope given by the claims, and these modifications are within the capabilities of those skilled in the art.

Claims

1. A bearing assembly for an electrically driven compressor (10), the compressor having a housing (12) in which a shaft (14) is rotatably received at a first bearing portion (16) and a second bearing portion (18), and at least one compressor impeller (20) is received on the shaft (14), and a shaft disc (60) is disposed in the region of the first bearing portion (16), characterized in that, The first bearing portion (16) is configured as an axial bearing and has a first foil assembly (34), the first foil assembly including at least one first foil strip (66) with higher stiffness extending in the circumferential direction and at least one second foil strip (72) with lower stiffness extending in the circumferential direction.

2. The bearing assembly according to claim 1, characterized in that, The at least one first foil strip (66) having higher stiffness and the at least one second foil strip (72) having lower stiffness are spaced apart from each other in the radial direction by a spacing (92).

3. The bearing assembly according to claims 1 and 2, characterized in that, The at least one first foil strip (66) having high stiffness has a stiffness in the range of 1 N / µm to 5 N / µm.

4. The bearing assembly according to claims 1 and 2, characterized in that, The at least one second foil strip (72) having lower stiffness has a stiffness in the range of 0.1 N / µm to 0.5 N / µm.

5. The bearing assembly according to any one of claims 1 to 4, characterized in that, The at least one first foil strip (66) and the at least one second foil strip (72) each have a crest (82), which are separated by a trough (80) when viewed in the circumferential direction.

6. The bearing assembly according to any one of claims 1 to 5, characterized in that, The crests (82) in the at least one first foil strip (66) and the at least one second foil strip (72) are formed by at least two square segments (68) or two longitudinal segments (74).

7. The bearing assembly according to any one of claims 1 to 6, characterized in that, The peaks (82) in the at least one first foil strip (66) and the at least one second foil strip (72) are formed in a sequence (76) that alternates with each other when viewed in the circumferential direction.

8. The bearing assembly according to any one of claims 1 to 7, characterized in that, The peaks (82) in the at least one first foil strip (66) are implemented with a first arc length (88), which is smaller than a second arc length (90), and the peaks (82) in the at least one second foil strip (72) are formed with the second arc length.

9. The bearing assembly according to any one of claims 1 to 8, characterized in that, The peak (82) in the at least one second foil strip (72) exceeds the peak (82) in the at least one first foil strip (66) by a height difference (94), the height difference being between 30µm and 150µm.

10. The bearing assembly according to any one of claims 1 to 9, characterized in that, The wave crest (82) formed with a first arc length (88) in the at least one first foil strip (66) imparts high stiffness to the at least one first foil strip (66).

11. The bearing assembly according to any one of claims 1 to 10, characterized in that, The wave crest (82) formed with a second arc length (90) in the at least one second foil strip (72) imparts a lower stiffness to the at least one second foil strip (72).

12. Use of the bearing assembly according to any one of claims 1 to 11 as an axial bearing, the bearing assembly being used to fix a shaft (14) with a compressor impeller (20) in the axial direction in an electric compressor (10) or high-speed fluid machinery, especially a booster, exhaust gas turbocharger or gas turbine, that supplies air to a fuel cell system.

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