BEARING ASSEMBLY

Abstract

A bearing assembly is for supporting a shaft in a housing, preferably a rotor shaft of a centrifugal compressor. The bearing assembly includes at least a first bearing pair including a first rolling bearing and a second rolling bearing arranged back to back, each one of the first and second rolling bearings including an inner ring attached to the shaft, an outer ring and a plurality of rolling elements disposed between the inner ring and the outer ring. A radial gap is provided between the outer ring of the first rolling bearing and the housing and the outer ring of the second rolling bearing is in contact with the housing. Preferably, a fixing element restricts axial movement of the outer ring of the first rolling bearing with respect to the housing.

Claims

1. A bearing assembly for supporting a shaft in a housing, the bearing assembly comprising: at least a first bearing pair including a first rolling bearing and a second rolling bearing arranged back to back, each one of the first and second rolling bearings including an inner ring attached to the shaft, an outer ring and a plurality of rolling elements disposed between the inner ring and the outer ring; wherein a radial gap is provided between the outer ring of the first rolling bearing and the housing and the outer ring of the second rolling bearing is in contact with the housing.

2. The bearing assembly according to claim 1, wherein each one of the first rolling bearing and the second rolling bearing has a contact angle, the contact angle of the first rolling bearing has a value different than a value of the contact angle of the second rolling bearing.

3. The bearing assembly according to claim 1, wherein each one of the first rolling bearing and the second rolling bearing has a contact angle, the contact angle of the first rolling bearing has a value equal to a value of the contact angle of the second rolling bearing.

4. The bearing assembly according to claim 1, further comprising at least one fixing element configured to restrict axial movement of the outer ring of the first rolling bearing with respect to the housing.

5. The bearing assembly according to claim 1, wherein the bearing assembly further comprises: at least a second bearing pair spaced from the first bearing pair and including a first rolling bearing and a second rolling bearing arranged back to back, each one of the first and second rolling bearings of the second bearing pair including an inner ring attached to the shaft, an outer ring and a plurality of rolling elements disposed between the inner ring and the outer ring; and a fixing element configured to restrict axial movement of the outer ring of the first rolling bearing of the second bearing pair, the outer ring of the second rolling bearing of the second bearing pair being in contact with the housing.

6. The bearing assembly according to claim 5, wherein the first rolling bearing of the first bearing pair and the first rolling bearing of the second bearing pair are arranged facing each other.

7. The bearing assembly according to claim 5, wherein the second rolling bearing of the first bearing pair and the second rolling bearing of the second bearing pair are arranged facing each other.

8. The bearing assembly according to claim 5, wherein the first rolling bearing or the second rolling bearing of the first bearing pair is configured to abut against a first axial abutment arranged at an axial outer end of the bearing assembly and a clearance is provided between the axial abutment and the first rolling bearing or the second rolling bearing of the first bearing pair.

9. The bearing assembly according to claim 5, wherein the first rolling bearing or the second rolling bearing of the second bearing pair is configured to abut against a second axial abutment arranged at an axial outer end of the bearing assembly and a clearance is provided between the second axial abutment and the first rolling bearing or the second rolling bearing of the second bearing pair.

10. The bearing assembly according to claim 5, wherein the first bearing pair is axially fixed and the second bearing pair is axially floating.

11. A centrifugal compressor including a bearing assembly according to claim 1.

12. A centrifugal compressor comprising: a housing; a shaft disposed within the housing; and a bearing assembly configured to support the shaft within the housing and including at least a first bearing pair having a first rolling bearing and a second rolling bearing arranged back to back, each one of the first and second rolling bearings including an inner ring attached to the shaft, an outer ring and a plurality of rolling elements disposed between the inner ring and the outer ring; wherein a radial gap is provided between the outer ring of the first rolling bearing and the housing and the outer ring of the second rolling bearing is in contact with the housing.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0042] In the following, the invention is described in more detail using the exemplary embodiments depicted in the drawings. Here the exemplary embodiments and the combinations shown in the exemplary embodiments are purely exemplary and are not intended to define the scope of the invention. This scope is defined solely by the pending claims.

[0043] FIG. 1 shows a sectional view of a bearing assembly including a first bearing pair;

[0044] FIG. 2 shows a section view of a bearing assembly including a first and a second bearing pair in a first configuration;

[0045] FIG. 3 shows a section view of a bearing assembly including a first and a second bearing pair in a second configuration;

[0046] FIG. 4 shows a section view of a bearing assembly including a first and a second bearing pair in a third configuration; and

[0047] FIG. 5 shows a diagram illustrating the bearing assembly life ratio vs. the bearing ring misalignment.

DETAILED DESCRIPTION OF THE INVENTION

[0048] FIG. 1 shows a bearing assembly 1 which may be used for supporting a shaft 2 within a housing 4, in particular a rotor shaft within a centrifugal compressor. The bearing assembly 1 may also be used for a centrifugal pump.

[0049] In the example shown in FIG. 1, the bearing assembly 1 comprises a first bearing pair 3 which includes a first rolling bearing 6 and a second rolling bearing 8. The first and the second rolling bearings 6, 8 are depicted as angular contact ball bearings. However, the first and the second rolling bearings 6, 8 could also be tapered roller bearings. The first and the second rolling bearings 6, 8 are preferably arranged back to back.

[0050] Each rolling bearing 6, 8 comprises an inner ring 10, 16, respectively, an outer ring 12, 18, respectively, and a plurality of rolling elements 14, 20, respectively, interposed or disposed between the inner ring 10, 16 and the outer ring 12, 18. The inner rings 10, 16 are arranged on the shaft 2 and may be clamped together. The outer ring 18 of the second rolling bearing 8 is attached to the housing 4. Between the first rolling bearing 6 and the second rolling bearing 8, an optional distance element 22, for example a spacer ring, may be arranged. The distance element 22 may include passages 28 for supplying lubricant to the bearings 6, 8. The distance element 22 may be configured to restrict the axial movement of the outer ring 12 of the first rolling bearing 6 with respect to the second rolling bearing 8.

[0051] In the embodiment shown in FIG. 1, the bearing assembly 1 is a fixed bearing assembly. This means that restricting elements 24, 26 are arranged at both axial ends of the outer rings 12, 18 for restricting the axial movements of both outer rings 12, 18 and for clamping the outer rings 12, 18 together. The restricting elements 24, 26 may be an integral part of the housing 4 or may be attached, for example screwed, to the housing 4.

[0052] During operation, an axial load may act on the shaft 2 in a first axial direction or a second axial direction, wherein the second axial direction is opposite to the first axial direction. This axial load leads to both an axial load and a radial load acting on the bearing pair 3. The axial load acting on the shaft 2 may arise, for example, from gas forces acting on the impeller(s).

[0053] As a misalignment of the shaft 2 may induce additional radial loads to the bearings 6, 8, the bearing assembly 1 should be insensitive to such a misalignment. Therefore, a radial 30 gap is provided between the outer ring 12 of the first rolling bearing 6 and the housing 4. In contrast to that, the outer ring 18 of the second rolling bearing 8 is in contact with the housing 4.

[0054] The radial gap 30 provides a clearance between the outer ring 12 of the first rolling bearing 6 and the housing 4. Therefore, the outer ring 12 can move in the radial direction with respect to the housing 4 and will not induce any radial load on the housing 4. As no radial load will be induced, the whole bearing assembly 1 is insensitive to misalignment of the shaft 2.

[0055] In a further embodiment as illustrated in FIG. 2, the bearing assembly 1 may comprise the first bearing pair 3 and an additional second bearing pair 3. Between the first and the second bearing pairs 3, 3, the motor rotor 32 of a centrifugal compressor may be arranged.

[0056] It should be noted that the elements of the second bearing pair 3 are referenced by the same reference elements as the elements of the first bearing pair 3, wherein the elements of the second bearing pair 3 have an additional apostrophe for indicating that the elements belong to the second bearing pair 3.

[0057] The second bearing pair 3 is spaced from the first bearing pair 3 and includes a first rolling bearing 6 and a second rolling bearing 8 arranged back to back. As with the rolling bearings 6, 8 of the first bearing pair 3, the rolling bearings 6, 8 comprises an inner ring 10, 16, respectively, an outer ring 12, 18, respectively, and a plurality of rolling elements 14, 20, respectively, interposed/disposed between the inner ring 10, 16 and the outer ring 12, 18. The inner rings 10, 16 are arranged on the shaft 2 and may be clamped together. The outer ring 18 of the second rolling bearing 8 is attached to the housing 4. It should be noted that, although the housing 4, 4 is shown as separate elements, the housing 4, 4 may also be the same element and may be for example the housing of the compressor.

[0058] Between the first and the second rolling bearing 6, 8, a distance element 22 is arranged which may include passages 28 for supplying lubricant to the bearings 6, 8. The distance element 22 may restrict the axial movement of the outer ring 12 with respect to the second rolling bearing 8.

[0059] In the embodiment shown in FIG. 2, the bearing assembly 1 is a fixed/floating bearing assembly 1. This means that the axial movement of the bearing pair 3 is restricted by the restricting elements 24, 26, which are arranged at both axial ends of the inner rings 10, 16. In contrast to that, the bearing pair 3 is free in its axial movement, i.e., is floating and does not comprise any restricting elements.

[0060] In the embodiment of FIG. 2, the first rolling bearings 6, 6 are the inner rolling bearings. Thus, the bearings 6, 6 having a radial gap 30, 30 between the outer ring 12, 12 and the housing 4, 4 are the inner bearings.

[0061] In an alternative embodiment as shown in FIG. 3, the first rolling bearings 6, 6 are the outer rolling bearings. Thus, the bearings 6, 6 having a radial gap 30, 30 between the outer ring 12, 12 and the housing 4, 4 are the outer bearings.

[0062] In a further embodiment as shown in FIG. 4, in addition to having the radial gap 30, 30, the bearing pairs 3, 3 may be arranged in cross location. Thus, the bearings 6, 8 and 6, 8 are arranged in a cross arrangement so that both bearing pairs 3, 3 have the ability to support radial loads as well as axial loads, as will be described in the following.

[0063] The axial load acting on the shaft 2 leads to an axial load and a radial load acting on the bearing pairs 3, 3. In order to allow a uniform distribution of the load as well as the support of the axial load also when the axial load direction reverses, the first bearing pair 3 is configured to support both an axial load and a radial load and the second bearing pair 3 is configured to support a radial load when the axial load acts in a first axial direction. Conversely, when the axial load acts in the opposite, second axial direction, the first bearing pair 3 is configured to support a radial load and the second bearing pair 3 is configured to support both an axial load and a radial load.

[0064] For this purpose, the first rolling bearing 6 of the first bearing pair 3 being the axially outer bearing is configured as a backup bearing and abuts against an axial abutment 24 which may be the restricting element as described above. Similarly, the first rolling bearing 6 of the second bearing pair 3 being the axially outer bearing is configured as a backup bearing and abuts against an axial abutment 24 which may also be the restricting element as described above. In addition, the first rolling bearings 6, 6 each have the radial gap 30, 30, respectively, with respect to the housing 4, 4, whereas the second rolling bearings 8, 8 contact the housing 4, 4.

[0065] The abutments 24, 24 may be, for example, a respective shoulder formed on the housing 4, 4. The abutments 24, 24 may prevent a displacement of the bearing pairs 3, 3 in one axial direction. A clearance 34, 34 is provided between the first rolling bearing 6 of the first bearing pair 3 and the axial abutment 24 and between the first rolling bearing 6 of the second bearing pair 3 and the axial abutment 24. Such a clearance or gap 34, 34 allows that the first bearing pair 3 and the second bearing pair 3 can slightly move in the axial direction with respect to the axial abutment 24, 24. The clearance or gap 34, 34 may have the effect, or minimize the risk, that the pairs are not preloaded against each other. Due to the clearance 34, 34, the first rolling bearing 6 of the first bearing pair 3 and the first rolling bearing 6 of the second bearing pair 3 may move slightly towards the respective abutment 24, 24 and may also move slightly away from the respective abutment 24, 24.

[0066] When an axial load is applied in the first axial direction, the first rolling bearing 6 of the first bearing pair 3 serves as backup bearing and supports radial load, whereas the second rolling bearing 8 of the first bearing pair 3 serves as thrust bearing and supports axial as well as radial load. Conversely, when an axial load is applied in the opposite axial direction, the first rolling bearing 6 of the second bearing pair 3 serves as backup bearing and supports radial load, whereas the second rolling bearing 8 of the second bearing pair 3 serves as thrust bearing and supports axial as well as radial load.

[0067] Due to this cross arrangement of thrust and backup bearings, the direction of the axial load applied to the shaft 2 may change without any negative impact to the bearing pairs 3, 3 as each bearing pair 3, 3 may support axial as well as radial loads by having one bearing 6, 6 specialized for supporting both axial loads and radial loads and one bearing 8, 8 specialized for supporting radial loads only.

[0068] In the arrangements described with a radial gap 30, 30 at one bearing location, depending on the axial load direction, either the loads are separated such that one bearing takes axial load only and the other radial load only, or one bearing takes both axial and radial load and the other only controls clearance. This may seem disadvantageous compared to an arrangement without radial gaps, where both bearing share axial and radial load, which is the case, but only if there is no misalignment. With misalignment and increasing misalignment, the induced radial load caused by misalignment quickly shortens the life of the bearings in the arrangement without radial gaps while the bearings in the arrangements with radial gaps 30, 30 are relatively insensitive with only slight reduction in life. This can be seen in FIG. 5, which illustrates the bearing assembly life ratio on the y-axis vs. the bearing ring misalignment on the x-axis. The line with square points illustrates the bearing assembly life ratio having bearings without radial gap. In contrast to that, the line with circular points illustrates the bearing assembly life ratio of a bearing assembly having a thrust bearing with a radial gap 30, 30 and the line with triangular points illustrates the bearing assembly life ratio of a bearing assembly having a backup bearing with a radial gap 30, 30. As can be seen, both arrangements show a better bearing assembly life ratio when misalignment occurs than the bearing assembly without any radial gap.

[0069] In real applications, there is always misalignment so bearings in arrangements with radial gaps have longer lives compared to bearings in the arrangements without gaps. The arrangement where one bearing takes axial load only and the other radial load only, is slightly advantageous (line with triangular points) over an arrangement where one bearing takes both axial and radial load and the other only controls clearance (line with circular points). As can be seen in the diagram of FIG. 5, both alternatives have longer system life, at even slightly misaligned conditions, compared to having no bearing with a radial gap.

[0070] The above-described bearing assembly provides a reduced sensitivity to misalignment of a shaft with bearing pairs taking axial load in both directions while also maximizing the system life of the pairs by providing a radial gap between one outer ring of the bearing pair and the housing, while providing an easy and cost efficient arrangement.

[0071] Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention.

[0072] Moreover, combinations of features and steps disclosed in the above detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.

[0073] All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter. The invention is not restricted to the above-described embodiments, and may be varied within the scope of the following claims.

REFERENCE NUMBER LIST

[0074] 1 bearing assembly [0075] 2 shaft [0076] 3 first bearing pair [0077] 3 second bearing pair [0078] 4, 4 housing [0079] 6, 6 first rolling bearing [0080] 8, 8 second rolling bearing [0081] 10, 10 inner ring [0082] 12, 12 outer ring [0083] 14, 14 rolling elements [0084] 16, 16 inner ring [0085] 18, 18 outer ring [0086] 20, 20 rolling elements [0087] 22, 22 distance element [0088] 24, 24 restricting element [0089] 26, 26 restricting element [0090] 28, 28 lubricant passage [0091] 30, 30 radial gap [0092] 32 motor [0093] 34, 34 axial clearance