Bearing arrangement of an electrically driven compressor

Abstract

The invention relates to a bearing arrangement of an electrically driven compressor (10) having a housing (12), in which a shaft (14) is rotatably received at a first bearing point (16) and at a second bearing point (18) and at least one compressor impeller (20) is received on the shaft (14), wherein a shaft plate (60) is provided in the region of the first bearing point (16). The first bearing point (16) is designed as an axial bearing and comprises a first foil arrangement (34) which comprises at least one first foil strip (66) extending in the circumferential direction and having a higher rigidity, and at least one second foil strip (72) extending in the circumferential direction and having a lower rigidity. The invention also relates to the use of the bearing arrangement as an axial bearing for fixing a shaft (14) together with the compressor impeller (20) in the axial direction in an electric compressor (10) for supplying air to a fuel cell system or fast-running turbo-machines.

Description

[0001] Description

[0002] title

[0003] Bearing arrangement of an electrically driven compressor

[0004] Technical area

[0005] The invention relates to a bearing assembly for an electrically driven compressor having a housing in which a shaft is rotatably mounted at a first bearing point and a second bearing point. At least one compressor impeller is mounted on the shaft, and a shaft washer is provided in the region of the first bearing point. Furthermore, the invention relates to the use of the bearing assembly as an axial bearing for axially fixing a shaft including the compressor impeller in an electric compressor for supplying air to a fuel cell system or high-speed turbomachines.

[0006] State of the art

[0007] DE 10 2018 213 697 A1 relates to an air bearing, a bearing unit, and a compressor. An air bearing, in particular for a bearing unit of a compressor, comprises an outer ring surrounding a central opening for receiving in a shaft, a spring foil arranged in the opening, which is elastically deformable, and an upper foil arranged in the opening. The spring foil is arranged between the outer ring and the upper foil. The spring foil has a one-piece base body, furthermore first material regions with a first spring stiffness and second material regions with a second spring stiffness, wherein each of the first material regions is arranged offset from each of the second material regions in the circumferential direction of the opening, and wherein the first spring stiffness is higher than the second spring stiffness.Furthermore, a bearing unit is disclosed which comprises an air bearing and a shaft rotatably mounted in the opening of the air bearing, as well as a compressor, in particular for a fuel cell system. DE 10 2021 209 720 A1 relates to an axial bearing arrangement and a compressor with an axial bearing arrangement. The axial bearing arrangement comprises a rotatable shaft in a housing, with a bearing disk arranged on the shaft and a bearing plate on each side of the bearing disk. The bearing plates are at least indirectly connected to the housing. Bearing elements are supported on the bearing plates, against which the bearing disk can be brought into contact, at least indirectly. An annular intermediate element is arranged between the two bearing plates in the direction of the axis of rotation of the shaft.At least one of the bearing elements is formed integrally with the intermediate element and the intermediate element is designed to be elastically deformable in the direction of the axis of rotation of the shaft.

[0008] Disclosure of the invention

[0009] According to the invention, a bearing arrangement is proposed which is arranged in an electrically driven compressor, comprising a housing in which a shaft is rotatably received at a first bearing point and at a second bearing point, and at least one compressor impeller is received on the shaft, and a shaft washer is provided in the region of the first bearing point. The first bearing point is designed as an axial bearing and has a first foil arrangement which comprises at least one circumferentially extending first foil strip with higher rigidity and at least one circumferentially extending second foil strip with lower rigidity.

[0010] The bearing arrangement proposed according to the invention advantageously enables the axial play to be adjusted with a defined preload and compensates for misalignment at high-load points of the compressor.

[0011] In an advantageous development of the bearing arrangement proposed according to the invention, the at least one first foil strip with higher rigidity and the at least one second foil strip with lower rigidity are separated from one another by a distance in the radial direction.

[0012] In an advantageous development of the bearing arrangement proposed according to the invention, the at least one first foil strip with higher stiffness has a stiffness that is preferably in the range between 1 N / pm and 5 N / pm. The bearing arrangement proposed according to the invention is further designed such that the at least one second foil strip with lower stiffness has a stiffness in the range between 0.1 N / pm and 0.5 N / pm.

[0013] With the design outlined above, a bearing arrangement can be provided that, thanks to a spring element with lower rigidity, enables the adjustment of the axial play with a defined preload, and, thanks to the at least one element with higher rigidity, enables the compensation of misalignments at high-load points of an electrically driven compressor. Advantageously, the bearing arrangement proposed according to the invention is designed such that the at least one first foil strip and the at least one second foil strip each have corrugations that extend in the circumferential direction and are separated from one another by corrugation troughs.

[0014] In the bearing arrangement proposed according to the invention, the corrugations in the at least one first foil strip and the at least one second foil strip are formed by at least two sections or two longitudinal sections.

[0015] In the bearing arrangement proposed according to the invention, the corrugations in the at least one first foil strip and the at least one second foil strip are preferably formed in an alternating sequence relative to one another in the circumferential direction. The bearing arrangement proposed according to the invention is further characterized in that the corrugations in the at least one first foil strip are designed with an arc width that is smaller than a second arc width in which the corrugations are designed in the at least one second foil strip. Due to the design of the first and second arc widths in the at least one first foil strip and the at least one second foil strip, respectively, the stiffness ranges defined above can be essentially predetermined.

[0016] In the bearing arrangement proposed according to the invention, the corrugations in the at least one second foil strip and in the at least one first foil strip are designed such that the corrugations in the at least one second foil strip exceed those in the at least one first foil strip by a height difference. Furthermore, in the bearing arrangement proposed according to the invention, it is provided that the corrugations in the at least one first foil strip, which are formed in the first arc width, impart greater rigidity to the at least one first foil strip. In this context, in the bearing arrangement proposed according to the invention, the corrugations in the at least one second foil strip, which are formed in the second arc width, are designed such that they impart lower rigidity to the at least one second foil strip.

[0017] Furthermore, the invention relates to the use of the bearing arrangement as an axial bearing for fixing a shaft including a compressor impeller at a bearing point in the axial direction, whether in an electric compressor for supplying air to a fuel cell system or in high-speed turbomachines, in particular charging devices, exhaust gas turbochargers or gas turbines.

[0018] Advantages of the invention

[0019] Due to the two independent spring characteristics defined at an axial bearing point, represented by the at least one foil arrangement with higher stiffness and the at least one second foil arrangement with lower stiffness, which also extends in the circumferential direction, two defined, independent spring characteristics are available, by means of which, on the one hand, an adjustment of an axial play with a defined preload can be achieved through the effectiveness of the lower stiffness and, on the other hand, a compensation of low positions at high load points of the compressor can be assumed by the at least one spring element with higher stiffness.

[0020] The solution proposed according to the invention makes it possible to design a bearing arrangement using foil bearings in such a way that the requirements defined above can be met. The bearing arrangement proposed according to the invention ensures that at least a first foil strip extending in the circumferential direction and having lower stiffness, for example having longitudinal sections, initially engages with a top foil. As the speed increases further and higher, predefined loads occur, a foil strip with spring elements having higher stiffness engages. The bump foil is constantly in contact with the base plate. In foil bearings, the top foil encloses an air film with the rotor and, thanks to its appropriate structure, has properties that promote pressure build-up.Beneath the top foil are one or more bottom foils, referred to as foil strips with lower or higher spring stiffness. These foil strips are formed by arches (bump foils). The top foil and the one or more bottom foils are divided into segments. The individual segments represent a parallel connection of spring elements, in this context, the first foil strip with lower stiffness and the second foil strip with higher stiffness.

[0021] The solution proposed according to the invention provides a bearing arrangement with optimized assembly and misalignment properties. Regarding mechanical advantages, it should be noted that better-defined spring characteristics are helpful in selecting a suitable clearance, so that effects on the contour gap between the impellers and thus on the overall efficiency of the machine can be taken into account. In this area, a spring characteristic that is as soft as possible is helpful, with which similar preloads can be generated within the manufacturing tolerances of all components involved. The stiffer of the two spring arrangements, in the form of at least one foil strip, can be optimally designed for the misalignment of the compressor rotor with respect to the bearing that is to be expected at high load points.

[0022] Furthermore, the solution proposed according to the invention can achieve thermal advantages in that constant contact between the bump foil and the base plate can be maintained, enabling improved heat transfer from the bearing gap to the cooled base plate through improved heat conduction. Cooling flow finds similar conditions on both axial bearing sides, in contrast to previous designs where the unloaded side has larger flow cross-sections. In this case, more cooling flow would flow on this side, which is, however, more necessary on the loaded side. The circumstance of larger flow cross-sections can be significantly improved by the defined preload applied to the at least one axial bearing location using the bearing arrangement proposed according to the invention.

[0023] The solution proposed by the invention allows for very simple production, for example, by punching followed by a stamping step, so that only two processing steps are required. Furthermore, it should be emphasized that the foil strips proposed by the invention with two separate spring stiffnesses provide a stock design that is suitable for series production, since tolerance variations can be better incorporated into the design.

[0024] Short description of the drawings

[0025] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0026] They show:

[0027] Figure 1 shows a longitudinal section through an electrically driven compressor with an axial bearing arrangement proposed according to the invention,

[0028] Figure 2 shows a detailed view of a foil strip,

[0029] Figure 3 a top view of foil strips,

[0030] Figure 4 is a perspective view of the arrangement according to Figure 3, also developed and

[0031] Figure 5 Characteristic curves of the bearing arrangement proposed according to the invention with first and second load ranges.

[0032] Embodiments of the invention

[0033] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only schematically illustrate the subject matter of the invention.

[0034] Figure 1 shows a longitudinal section through an electrically driven compressor 10 with at least one bearing arrangement proposed according to the invention. It depicts an electric compressor 10 housed in a housing 12. The electrically driven compressor 10 comprises a shaft 14, which may be formed in one or more parts and is supported at a first bearing point 16 and a second bearing point 18. A compressor impeller 20 is located at an end of the shaft 14 located on the side of the first bearing point 16. The shaft 14 of the electrically driven compressor 10 is driven by a rotor 24, which is enclosed by a stator 22, forming a minimal gap between the components. An intake side of the electric compressor 10 is designated by reference numeral 26, while its pressure side is designated by reference numeral 28.

[0035] In the area of ​​the first bearing point 16 there is a first foil bearing 30, while in the area of ​​the second bearing point 18 there is a second foil bearing 32. The first foil bearing 30 or the second foil bearing 32 serves as an axial bearing for the shaft 14. In the area of ​​the first bearing point 16 there is a shaft washer 60 to represent the axial bearing. The shaft washer 60 can be part of the shaft 14; it is also possible to use the shaft washer 60 as a separate component, for example by shrinking it onto the circumference of the shaft 14 in the area of ​​the first bearing point 16 or by connecting it to the shaft 14 in a rotationally fixed manner via a key or the like.

[0036] The illustration in Figure 2 shows a detailed view of a foil strip 62 of a first foil arrangement 34. This can, for example, be part of the first foil bearing 30, which is received at the first bearing point 16 of the shaft 14 in the housing 12 of the electric compressor 10.

[0037] The illustrations according to Figures 3 and 4 show foil strips 66, 72, each shown as developed views, which are received, for example, at the first bearing point 16 serving as an axial bearing with the first foil bearing 30 as shown in Figure 1.

[0038] Figure 3 shows that in this arrangement, shown as a developed view 64, a first film strip 66 with a higher stiffness is shown. The first film strip 66 consists of sequences of angular sections 68 which are formed in a first width 70. Between each two angular sections 68 there is a trough 80. Each two angular sections 68 form an arch. The individual arches, each comprising two angular sections 68, are separated by a trough 80 lying between two adjacent arches. The two first film strips 66 with higher stiffness shown in Figure 3 as a developed view 64 are formed in a first width 70. Between the two first film strips 66 with higher stiffness there is a second film strip 72 with a lower stiffness. This is formed in a second width 75 which is selected to be less than the first width 70 of the first film strip 66 with higher stiffness.In the second foil strip 72 with lower stiffness, two longitudinal sections 74 each form arches, which in the second foil strip 72 with lower stiffness are separated by wave troughs 80, analogous to the first foil strips 66 with higher stiffness. Reference numeral 80 designates a wave trough in the first foil strip 66 with higher stiffness, and position 82 designates a wave crest located at the junction of the angular sections 68 of the first foil strip 66 with higher stiffness.

[0039] The perspective view according to Figure 4 shows the arrangement according to Figure 3 from the side. From the view according to Figure 4, it can be seen that the angular sections 68 of the first film strip 66 with higher rigidity each form an arc having a first arc width 88. This applies analogously to the two first film strips 66 with higher rigidity, which are formed with a width 70 and are shown in perspective in Figure 4 and lie parallel to one another.

[0040] The second foil strip 72 with lower stiffness arranged between these has arches formed by two longitudinal sections 74, each of which has a second arch width 90. Due to the different arch widths 88, 90 of the first foil strip 66 with higher stiffness and the second foil strip 72 with lower stiffness, this arrangement of foil strips 62 can be used to form a bearing arrangement which, on the one hand, enables the adjustment of an axial play with a defined preload by the second foil strip 72 with lower stiffness and, at the same time, enables the compensation of misalignments at high-load points of the electric compressor 10 by the first foil strips 66 with higher stiffness arranged as a pair next to the second foil strip 72 with lower stiffness in the illustrations according to Figures 3 and 4.The bearing arrangement proposed according to the invention, as shown in the developed views 64 according to Figures 3 and 4, enables a design of the bearing arrangement according to the invention with regard to the two criteria mentioned above. The at least one second foil strip 72 with lower stiffness initially engages with a top foil, and only at higher, predefined loads does the first foil strip 66 with higher stiffness engage. The bearing arrangement proposed according to the invention ensures that initially at least one second foil strip 72 extending in the circumferential direction with low stiffness engages with a top foil, and only at higher, predefined loads, i.e. with increasing 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 individual, for example, angular sections 68 and longitudinal sections 74 that form arcuate sections. The individual segments represent a parallel connection of said spring elements.

[0041] From the illustration in Figures 3 and 4 it can also be seen that the two first film strips 66 with higher stiffness, shown here in the developed view 64, and the second film strip 72 with lower stiffness arranged between them are arranged in an alternating sequence 76. This means that, as shown in Figure 4, for example, a wave crest 82 in the at least one second film strip 72 with lower stiffness lies in a wave trough 80 of the two first film strips 66 with higher stiffness arranged on either side of it. The wave crest 82 formed by the longitudinal sections 74 in the second film strip 72 with lower stiffness projects beyond the wave crests 82 located in the two adjacent first film strips 66 with higher stiffness.

[0042] This means that the arches formed in the larger, second arch width 90 in the second foil strip 72 are higher by a height difference 94, ie according to the bearing arrangement proposed according to the invention they initially form a soft spring wave line and thus enable the axial play to be adjusted with a defined preload.

[0043] At higher speeds of shaft 14, as shown in Figure 1, any misalignment of the electric compressor 10 or its shaft 14 at high-load points is compensated for by the two first, higher-stiffness foil strips 66 arranged adjacent to the second, low-stiffness foil strip 72. These have a significantly stiffer spring characteristic and enable the compensation of misalignments at high-load points of the electrically driven compressor 10, i.e., at high speeds.

[0044] The example characteristic curves shown in Figure 5 show a first load range 100 and a second load range 102. The characteristic curve according to Figure 5 runs in such a way that a bearing load 96 is plotted against an increase max H 86, which is in the 10' 4m range From the illustration in Figure 5 it can be seen that in the first load range 100 the at least one second foil strip 72 with lower rigidity of the bearing arrangement proposed according to the invention is used. In the first load range 100 the shaft 14 or the rotor 24 is aligned with the two bearing points, ie with the first bearing point 16 and the second bearing point 18, due to the effectiveness of the at least one second foil strip 72 with lower rigidity, which for example first rests on the shaft washer 60. If for example an axial play is set to 480 pm, both bearing points 16, 18 have a preload of approx. 10 N in the basic state. With a play of 480 pm this would result in a play of 240 pm at one bearing point in the basic state. If one side is loaded to 70 N (200 pm), the other side would still have a preload of 480 - 200 = 280 pm, i.e. approx. 5 N.Assuming a manufacturing-related play of + / - 20 pm, this would result in a preload of between approximately 3 N and 7 N. Thus, the flat profile of the spring stiffness, i.e., the at least one second foil strip 72 with lower stiffness, ensures that, within the tolerances, a preload always exists in the unloaded state of the first bearing point 16 and the second bearing point 18.

[0045] In contrast, the second load range 102 provides the possibility of compensating for misalignment. In this case, a characteristic of the at least one foil strip 66 that is as linear as possible and has a higher stiffness is advantageous.

[0046] The two circumferentially extending first foil strips 66 with higher rigidity and the second foil strips 72 with lower rigidity used in the bearing arrangement proposed according to the invention thus engage one after the other. Initially, the axial play is compensated for by the effectiveness of the at least one second foil strip with lower rigidity 72, whereas at higher load points of the electrically driven compressor 10, the compensation of misalignments is achieved by the effectiveness of the at least one first foil strip 66 with higher rigidity or its contact with the shaft washer 60 of the shaft 14.

[0047] It is possible to implement the respective foil strips 66, 72 on the bearing arrangements proposed according to the invention, whether used at the first bearing point 16 or at the second bearing point 18, using different bump foils with different heights and radii. Furthermore, the stiffness requirements for the first load range 100 and the second load range 102, as shown in Figure 5, can be achieved by further design measures. For example, bending beams can be arranged using several foils one above the other; it is possible to use spring foils with different heights, as in the radial bearings. In principle, it is possible to implement the above-described division of stiffness, i.e.to use at least one first foil strip 66 with higher stiffness and at least one further second foil strip 72 with lower stiffness also in two areas for radially effective foil bearings.

[0048] The solution proposed according to the invention provides a bearing arrangement that forms two defined, independent spring characteristics, each of which can be individually designed for the two task areas outlined above. From a mechanical point of view, it is advantageously achieved that better defined spring characteristics are useful in selecting a suitable clearance and thus have an impact on the contour gap of impellers and thus the overall efficiency of the machine. To adjust the axial clearance in this area, a spring characteristic that is as soft as possible is required, which allows similar preloads within the framework of the manufacturing tolerances of all components involved. The stiffer of the two springs can be optimally designed for the expected misalignment of the rotor 24 towards the bearing point, ieto the first bearing point 16 or to the second bearing point 18, in the present case the at least one first foil strip 66 with higher rigidity of the arrangement proposed according to the invention.

[0049] With regard to the thermal advantages achievable by the bearing arrangement proposed according to the invention, it should be mentioned that constant contact between the bump foil and the base plate, i.e. the shaft washer 60, results in an improvement in heat transfer from the bearing gap to the cooled base plate through improved heat conduction. The cooling flow encounters similar conditions on both axial bearing sides, i.e. at the first bearing location 16 and the second bearing location 18 respectively. In the normally prevailing state, the unloaded side has much larger flow cross-sections, so that more cooling flow flows on this unloaded side due to the larger flow cross-sections. However, the loaded side requires more intensive cooling, which could be improved by the solution proposed according to the invention.

[0050] The bearing arrangement proposed according to the invention is advantageously used as an axial bearing for axially securing a shaft 14 including a compressor impeller 20 in an electric compressor 10 for supplying air, for example, a fuel cell system. Furthermore, the bearing arrangement proposed according to the invention can be used in high-speed turbomachines, in particular turbocharging devices, or for internal combustion engines or gas turbines. Furthermore, turbocompressors with foil bearings can be equipped with the bearing arrangement proposed according to the invention.

[0051] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of one skilled in the art.

Claims

Claims 1. Bearing arrangement of an electrically driven compressor (10) with a housing (12) in which a shaft (14) is rotatably received at a first bearing point (16) and at a second bearing point (18), and at least one compressor impeller (20) is received on the shaft (14) and a shaft disk (60) is provided in the region of the first bearing point (16), characterized in that the first bearing point (16) is designed as an axial bearing and has a first film arrangement (34) which comprises at least one first film strip (66) extending in the circumferential direction and having higher rigidity and at least one second film strip (72) extending in the circumferential direction and having lower rigidity.

2. Bearing arrangement according to claim 1, characterized in that the at least one first foil strip (66) with higher rigidity and the at least one second foil strip (72) with lower rigidity are separated from one another in the radial direction by a distance (92).

3. Bearing arrangement according to claims 1 and 2, characterized in that the at least one first foil strip (66) with higher stiffness has a stiffness in the range between 1 N / pm and 5 N / pm.

4. Bearing arrangement according to claims 1 and 2, characterized in that the at least one second foil strip (72) with lower stiffness has a stiffness in the range between 0.1 N / pm and 0.5 N / pm.

5. Bearing arrangement according to 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 wave crests (82) which, viewed in the circumferential direction, are separated by wave troughs (80).

6. Bearing arrangement according to claims 1 to 5, characterized in that the wave 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 angular sections (68) or two longitudinal sections (74).

7. Bearing arrangement according to claims 1 to 6, characterized in that the wave crests (82) in the at least one first foil strip (66) and the at least one second foil strip (72) are formed in an alternating sequence (76) with respect to one another in the circumferential direction.

8. Bearing arrangement according to claims 1 to 7, characterized in that the wave crests (82) in the at least one first foil strip (66) are designed in a first arc width (88) which is smaller than a second arc width (90) in which the wave crests (82) are formed in the at least one second foil strip (72).

9. Bearing arrangement according to claims 1 to 8, characterized in that the wave crests (82) in the at least one second foil strip (72) exceed the wave crests (82) in the at least one first foil strip (66) by a height difference (94) which is between 30 pm and 150 pm.

10. Bearing arrangement according to claims 1 to 9, characterized in that the wave crests (82) in the at least one first foil strip (66), which are formed in the first arc width (88), impart a higher rigidity to the at least one first foil strip (66).

11. Bearing arrangement according to claims 1 to 10, characterized in that the wave crests (82) in the at least one second foil strip (72), which are formed in the second arc width (90), impart a lower rigidity to the at least one second foil strip (72).

12. Use of the bearing arrangement according to one of claims 1 to 11 as an axial bearing for fixing a shaft (14) together with compressor impeller (20) in the axial direction in an electric compressor (10) for air supply. supply of a fuel cell system or high-speed turbomachines, in particular charging devices, exhaust gas turbochargers or gas turbines.

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