Multi body rotor for a compressor.

Abstract

The invention relates to a rotor for compressors or expanders assembled from multiple parts that are coaxially joined together. The rotor comprises a core part (1) with a cylindrical sleeve (3) and end caps (5) at the ends of the sleeve, and end parts having a central coaxial passage (7). In mounted condition the rotor is configured such that: the end cap axially overlaps with the sleeve and is provided with a central coaxial protrusion (11) extending axially outwards of the sleeve fittingly in radial direction in the passage, the end part is at its side abutting the core part provided with a first annular recess (9) radially extending to the passage, and the protrusion is at its outer circumference provided with a second annular recess (10) which in axial direction partially overlaps with the end part.

Description

[0001] Multi body rotor for a compressor .

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to compressors and / or expanders . More specifically the invention is related to rotors , more particularly rotors composed of multiple bodies , that are used in high speed motors , for such compressors and / or expanders that are used in high speed generators or alternators .

[0004] BACKGROUND OF THE INVENTION

[0005] In compressors motors are used to drive an impeller in order to compress a gas . Such motors typically require to be operable at high speeds up to ranges of 35 k to 40 k rpm. At these high speeds the rotors used are preferably composed of a single piece having the advantage of providing sufficient bending stiffness .

[0006] It may however be desirable to use rotors , such as e . g . magnetic rotors , that require the use of different materials introducing the need to axially split the rotor in multiple pieces . As a consequence such a rotor is composed of multiple different bodies that need to be co-axially j oined together . Inherently, compared to a single body rotor, providing a multi body rotor with a desired bending stiffness is more difficult .

[0007] Multi body rotor designs are known . Some of them even may succeed in providing reasonable bending stiffness but suffer among others from a lack of radial alignment making them unreliable and unsuited for the envisaged use .

[0008] SUMMARY OF THE INVENTION

[0009] It is an obj ective of the present invention to provide an alternative multi body rotor capable of being operated at high speeds for a prolonged time .

[0010] Also an obj ective of the invention is to provide a multi body rotor which bodies can be j oined efficiently and reliably .

[0011] One more obj ective of the present invention is to provide a multi body rotor with sufficient bending stiffness and with sufficient mutual radial alignment of the respective rotor bodies .

[0012] To at least partially address one or more of the mentioned or other challenges and / or to at least partially meet one or more of the mentioned or other obj ectives , the present invention concerns a multi-part rotor for use in high speed motors for compressors or expanders , or for use in high speed generators or alternators .

[0013] The rotor comprises a core part and an end part that are coaxially mountable . The core part comprises a cylindrical sleeve and an end cap , which, in mounted condition of the rotor, is provided at the side of the core part abutting the end part . The end part is provided with a central coaxial passage . The core part and the end part can be made of the same materials or of different materials . In particular in case of a magnetic rotor , the cylindrical sleeve , wherein a magnet , such as for instance a permanent magnet , e . g . a neodymium or a samarium-cobalt magnet , is encapsulated, may for instance be made of titanium. The end parts are typically made of steel , although also other metals may be used . The end cap and the sleeve of the core part , although not required, are typically made of the same material . In the cylindrical sleeve also an asynchronous motor core or a solid squirl cage rotor can be incapsulated .

[0014] The rotor according to the invention, in mounted condition, is configured in a way that :

[0015] - the end cap of the core part axially overlaps with the sleeve and is provided with a central coaxial protrusion extending axially outwards of the sleeve in the passage of the end part and extending fittingly, at least partially, in radial direction in the passage ,

[0016] - the end part is at its side abutting the core part provided with a first annular recess radially extending to the passage or vice versa, meaning that the core part is provided at its side abutting the end part with a first annular recess radially extending to the passage , and

[0017] - the protrusion of the end cap is at its outer circumference provided with a second annular recess which in axial direction partially overlaps with the end part .

[0018] This configuration of the rotor ensures that there is a well- defined radial contact area between the end part and the core part primarily at their outer side edges , hence providing a sufficient bending stiffness . A further advantage thereof is that even in case the end part and / or core part have imperfections at their abutting cross sides and / or in case the surfaces of their abutting cross sides are not perfectly machined, the radial contact area will still be near their outer edges , hence ensuring sufficient bending stiffness . This configuration further provides that the core part is fittingly arranged in the end part , thus ensuring a sufficient mutual radial alignment of the end part and the core part even after extensive use . Moreover, the axial length over which the end part and the core part contact each other , or in other words the axial fit length, is kept limited by introducing the second annular groove in order to avoid a negative impact on overall bending stiffness and to minimize friction forces while ensuring proper alignment . Hence , in combination , the configuration with both the first and the second annular recess contributes to a multi-part rotor not only with sufficient bending stiffness but also with sufficient mutual radial alignment between the parts of the rotor .

[0019] In an embodiment of the invention, the end part and the core part of the rotor are configured such that in mounted condition of the rotor the second annular recess of the central protrusion of the end cap in axial direction partially overlaps with the first annular recess of the end part . This position of the second annular reces s not only ensures a desired axial fit length, but also avoids any potential friction at the inner side edge at the abutting side of the end part . The end part and the core part of the rotor according to the invention are j oined by inserting the central protrusion of the end cap of the core part in the passage of the end part until the end part and the core part abut at or near their corresponding outer side edges . Preferably, at least a part of a section of the central coaxial protrusion of the end cap of the core part which in mounted condition extends in the passage of the end part has an outer diameter which is larger than the inner diameter of the part of the passage wherein it is fitted . This allows to obtain a good axial fit between the end part and the core part by press-fitting the central protrusion of the core part in the end part and / or by heating the end part and the core part when j oining them. One may opt to bevel an outer edge of the central coaxial protrusion inward at or near its free end, which facilitates its insertion in the end part .

[0020] The passage in the end part of the rotor according to the invention may comprise a first passage section, and a second passage section wherein in mounted condition the central protrusion of the core part extends , the diameter of the second passage section being larger than the diameter of the first section . One may opt to provide a stepwise transition between the first and the second passage section such that the step defines a radially oriented bottom edge of the second passage section, and the passage is configured such that in mounted condition there is a gap between the central protrusion and the bottom edge . Hence radial contact between the central protrusion and the end part is avoided, thereby ensuring such radial contact does not affect the bending stiffness of the rotor . In one more embodiment of the invention, the end part and the core part of the rotor are configured such that the core part and the end part have the same outer diameter at their abutting sides . Preferably, the first annular recess is configured, e . g . by choosing a depth, being the dimension in the axial direction of the rotor in mounted condition, such that in mounted condition the end part at its abutting side abuts the core part only with an abutment section located between the outer perimeter of the first annular recess and the outer abutment side edge of the end part .

[0021] One may opt to configure the end cap of the core part of the rotor such that the outer diameter of the end cap is smaller than or equal to the inner diameter of the cylindrical sleeve . This allows to assemble the core part by inserting the end cap in the cylindrical sleeve and then to mutually connect them . In practice , such connection may e . g . be realized by providing a laser weld between the outer surface of the end cap and the inner surface of the cylindrical sleeve . In case of such option, the first annular recess is preferably configured such that the abutment section of the end part radially overlaps both with the sleeve and with the end cap . This allows to avoid, when operating the rotor at elevated speed, exerting too much load on the connection between the cylindrical sleeve and the end cap as this could negatively affect lifetime of the core part .

[0022] In yet one more embodiment of the invention, in mounted condition of the rotor, the end part and the core part of the rotor are connected and mutually attracted to one another by a tension fastener arranged in the passage of the end part . In practice , a threaded hole may be provided in the central protrusion of the end cap into which an end of the tension fastener may be screwed . Examples of such tension fastener comprise a tie bolt or a stretch bolt .

[0023] The invention also concerns a compressor or expander comprising a rotor according to one or more embodiments as previously described or an arbitrary combination of such embodiments .

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] With the intention of better showing the characteristics of the invention, hereafter, as an example without any limitative character, a preferred form of embodiment is described of a multi-part rotor , with reference to the accompanying drawings , wherein : figure 1 schematically depicts a multi-part rotor according to an embodiment of the invention; figure 2 schematically depicts a longitudinal section of the rotor shown in fig . l ; figure 3 schematically depicts an enlarged view of the section indicated in Fig . 2 with F3 .

[0026] DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0027] Figures 1 to 3 depict an example of a multi-part rotor for use in high speed motors for compressors or expanders . An impeller 6 is mounted coaxially with a rotor at one end of the rotor . The multi-part rotor comprises a core part 1 coaxially mounted between two end parts 2 .

[0028] The core part 1 comprises a cylindrical sleeve 3 , wherein in this example a permanent magnet 4 is encapsulated, and two end caps 5 each being provided at a corresponding end of the cylindrical sleeve . The cylindrical sleeve and the end caps may for example be made of titanium or a titanium alloy or another non-f erromagnetic metal . The permanent magnet may for example be a neodymium or a samarium-cobalt magnet .

[0029] The end caps 5 of the core part of the rotor have an outer diameter larger than or equal to the inner diameter of the cylindrical sleeve . The core part 1 is assembled by inserting the end caps in the cylindrical sleeve 3 carrying the permanent magnet at the corresponding ends till the end caps 5 at their outermost circumference axially completely overlap with the cylindrical sleeve 3 . The respective end caps are connected to the cylindrical sleeve by providing a laser weld between the outermost surface of the end cap and the inner surface of the cylindrical sleeve in the overlapping region . The invention is of course not limited to this .

[0030] The end parts 2 have at their sides , abutting with the core part 1 , the same outermost diameter as the core part . This still allows to use a same shaped core part and realize different sizes , shapes and / or forms of the rotor by mounting different end parts , being shaped such that they match the outer diameter of the core part at their abutting side , to the core part . Alternatively, the end parts 2 have at their sides abutting with the core part 1 a different outermost diameter .

[0031] The end parts 2 are each provided with an axially central passage 7 having a circular cross-section . The passage 7 comprises in the axial direction a first passage section and a second passage section, the diameter of the second passage section being larger than the diameter of the first section . A stepwise transition is provided between the first and the second passage section such that the step defines a radially oriented bottom edge of the second passage section .

[0032] Each end cap is provided with a central coaxial protrusion 11 extending axially outwards of the cylindrical sleeve 3 . The protrusion 11 has a generally cylindrical shape . In mounted condition of the rotor , the central coaxial protrusion extends in the second passage section of the corresponding end part 5 . A part of a section of the central coaxial protrusion of the end cap of the core part , which in mounted condition extends in the passage of the end part , has prior to assembling the parts of the rotor, an outermost diameter which is equal to or larger , typically up to a few percent , than the inner diameter of the second passage section wherein it extends .

[0033] When assembling the rotor, the end parts 2 and the core part are j oined by press-fitting the central protrusion 11 of the corresponding end cap 5 of the core part 1 in the second section of passage 7 of the end part and / or by fitting the end part and the core part while heating when j oining them . The end part is typically made of a metal . Preferably the end part is made of a metal , such as steel with a thermal expansion coefficient higher than the material , in this example titanium is used for fabricating the end cap . This difference in thermal expansion is mainly usefull during operation . . Moreover to facilitate the insertion in the end part 2 , the outer edge of the central coaxial protrusion 11 is beveled inward at or near its free end .

[0034] After having j oined the end parts 2 and the core part 1 , there is still a gap 12 between the central protrusion 11 and the bottom edge of the second passage section . This gap is typically a few millimeters . As a consequence there is only an axial and no radial contact between the central protrusion 11 of the core part 1 and the corresponding end part 2 .

[0035] In this example , the end parts 2 are at their sides abutting the core part 1 provided with an annular recess 9 which radially extends to the central passage 7 . When j oining the core part 1 and the end parts 2 , the core part is fitted into the respective end parts till the core part abuts the end part . The annular recess 9 in each end part is configured such that radial contact region of each end part includes at least an abutment section 13 defined as the area between the outer perimeter of the annular recess and the outer abutment side edge of the end part . Moreover , the annular recess 9 is configured such the abutment section 13 of the end part 2 radially overlaps both with the cylindrical sleeve 3 and with the end cap 5 of the core part 1 . The depth of the annular recess 9 , being the dimension in the axial direction of the rotor in mounted condition, is typically chosen such that in mounted condition the end part at its abutting side abuts the core part primarily with the abutment section 13 . However, the depth of the annular recess 9 may also be chosen such that in mounted condition the end part at its abutting side abuts the core part only with the abutment section 13 . In the latter case a cavity is formed between the end part and the core part at the level of the annular recess 9 . Anyhow, the well-defined contact area in the abutment section 13 ensures sufficient bending stiffness is obtained .

[0036] It is of course also possible that the annular recess 9 is provided in the core part instead of in the end parts .

[0037] At the outer circumference of the central coaxial protrusion 11 of each end cap 5 an annular recess 10 is formed in the protrusion . In mounted condition the annular recess 10 overlaps with the end cap 5 . The length of the axial fit between the core part 1 and the corresponding end part 2 is hence dependent on the axial length of the annular recess 10 in the protrusion 11 . The configuration is such that the axial fit is only over a short length . This not only reduces the friction force between the core part 1 and each end part 5 , but also reduces the required attractive forces to keep the core part and the end parts together . The position of the annular recess 10 in the protrusion 11 is chosen such that it overlaps in axial direction with the annular recess 9 formed in the end part . This has the advantage of avoiding any potential friction at the inner side edge at the abutting side of the end part . Each end part 2 and the core part 1 of the rotor are connected and mutually elastically attracted to one another by a tie bolt arranged in the central passage 7 of each end part . A threaded hole is provided in the central protrusion 11 of each end cap into which a threaded end of the tie bolt 14 is screwed .

[0038] Although in the description above , the invention is described in relation to use in high speed motors , the invention can also be used in high speed generators and alternators .

[0039] The present invention is in no way limited to the form of embodiment described by way of an example and represented in the figures , however, such an improved invention for determining a connectivity fault in an energy storage system can be realized in various forms without leaving the scope of the invention .

Claims

Claims .1 . A multi-part rotor for use in high speed motors for compressors or expanders, or for use in high speed generators or alternators comprising a core part (1) and an end part (2) that are coaxially mountable, the core part comprising a cylindrical sleeve (3) , wherein a permanent magnet (4) or a asynchronous motor core or a solid squirl cage rotor is encapsulated, and an end cap (5) , which, in mounted condition of the rotor, is provided at the side of the core part abutting the end part, and the end part being provided with a central coaxial passage (7) , characterized in that, in mounted condition of the rotor, the end cap axially overlaps with the sleeve and is provided with a central coaxial protrusion (11) extending axially outwards of the sleeve in the passage and extending fittingly, at least partially, in radial direction in the passage, the end part is at its side abutting the core part provided with a first annular recess (9) radially extending to the passage or vise versa, and the protrusion is at its outer circumference provided with a second annular recess (10) which in axial direction partially overlaps with the end part.

2. The rotor according to claim 1, characterized in that the second annular recess (10) in axial direction partially overlaps with the first annular recess (9) .

3. The rotor according to any of the preceding claims, characterized in that at least a part of a section of the central coaxial protrusion (11) extending in the passage (7) has an outer diameter which is larger than the inner diameter of the part of the passage wherein it is fitted.

4. The rotor according to any of the preceding claims, characterized in that an outer edge of the central coaxial protrusion (11) is beveled inward at or near its free end.

5. The rotor according to any of the preceding claims, characterized in that the core part (1) and the end part (2) have at their abutting sides the same outer diameter .

6. The rotor according to any of the preceding claims, characterized in that outer diameter of the end cap (5) is larger than or equal to the inner diameter of the sleeve ( 3 ) .

7. The rotor according to any of the preceding claims, characterized in that first annular recess (9) is configured such that the end part (2) at its abutting side abuts the core part (1) only with an abutment section (13) located between the outer perimeter of the first annular recess and the outer abutment side edge of the end part.

8. The rotor according to claim 7, characterized in thatthe abutment section (13) radially overlaps both with the sleeve (3) and with the end cap (5) .

9. The rotor according to any of the preceding claims, characterized in that the end part (2) and the core part (1) are connected and mutually attracted to one another by a tension fastener (14) arranged in the passage ( 7 ) .

10. The rotor according to claim 9, characterized in that a threaded hole is provided in the protrusion (11) of the end cap (5) into which an end of the tension fastener (14) is screwed.

11. The rotor according to claim 9 or 10, characterized in that the tension fastener (14) is a tie bolt or a stretch bolt.

12. The rotor according to any of the preceding claims, characterized in that the passage (7) in the end part (2) comprises a first passage section and a second passage section wherein the central protrusion (11) extends, the diameter of the second passage section being larger than the diameter of the first section.

13. The rotor according to claim 12, characterized in that there is a stepwise transition between the first and the second passage section such that the step defines a radially oriented bottom edge of the second passage section, and the passage (7) is configured such that there is a gap (12) between the central protrusion(11) and the bottom edge.

14. The rotor according to any of the preceding claims, characterized in that the sleeve (3) is made of titanium and the end part (2) is made of steel.

15. A compressor or expander comprising a rotor according to any of the preceding claims.

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