Electric motor with permanent magnets and submerged fuel pump with such motor

Abstract

The present disclosure relates to an electric motor for a submerged fuel pump for pumping a liquefied fluid, particularly a submerged fuel pump for pumping a liquefied fluid such as liquefied natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or a liquefied cryogenic dielectric fluid, the electric motor comprising: a rotor body attached to a motor shaft, the rotor body having a plurality of permanent magnets disposed along a periphery thereof, the rotor further comprising a mechanical magnet retention system for retaining the magnets in position within the rotor body; and a stator having coils arranged concentrically around the rotor body, the mechanical magnet retention system comprising a plurality of axially oriented slots around the periphery of the rotor body in which the permanent magnets are retained, the axially oriented slots being formed in tangent extensions laterally around the periphery of the rotor body, the slots being formed between two radially oriented side webs and a circumferential outer web, and a radially inner slot side being formed in the rotor body.

Description

[Technical Field]

[0001] The present invention relates to an electric motor for a submerged fuel pump for pumping a liquefied fluid, in particular a cryogenic submerged fuel pump for pumping a liquefied fuel such as liquefied natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or a liquefied cryogenic dielectric fluid. [Background technology]

[0002] Submerged fuel pumps for liquefied fuels such as LNG, driven by permanent magnet electric motors, are well known in the art.

[0003] WO 2015 / 081314 discloses a submerged multi-stage pump assembly including a vertically oriented pump shaft. A permanent magnet electric motor includes a rotor attached to the pump shaft and a stator disposed around the rotor. A first-stage impeller assembly includes a first impeller attached to the pump shaft. The first impeller is configured to move cryogenic fluid from a first impeller inlet to a first impeller outlet when the pump shaft is rotated by the electric motor. The disclosed pump also includes a hollow permanent magnet rotor to which the pump shaft is attached. The pump shaft is attached to the upper hollow rotor with a nut, and multiple impellers are attached to the pump shaft below the motor.

[0004] WO 2015 / 065699 discloses a rotor assembly for a permanent magnet motor for a pump assembly, including an electric submersible pump. In this rotor assembly, multiple permanent magnets are held in place by retaining clips within a rotor core. The magnets can be positioned in cavities or recesses in the surface of the rotor. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide an improved permanent magnet electric motor for a submerged fuel pump for pumping a liquefied cryogenic dielectric fluid, with the magnets located as close as possible to the annular surface of the rotor for improved efficiency. [Means for solving the problem]

[0006] The present disclosure discloses several embodiments of an electric motor for a submerged fuel pump for pumping a liquefied fluid, particularly a submerged fuel pump for pumping a liquefied fluid, such as liquefied natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or a cryogenic submerged fuel pump for pumping a liquefied cryogenic dielectric fluid, the electric motor comprising: a rotor body attached to a motor shaft, the rotor body having a plurality of permanent magnets disposed along a periphery thereof, the rotor body further comprising a mechanical magnet retention system for retaining the magnets in position within the rotor body; and a stator having coils arranged concentrically around the rotor body, the mechanical magnet retention system comprising a plurality of axially oriented slots around the periphery of the rotor body in which the permanent magnets are retained, the axially oriented slots extending tangentially laterally around the periphery of the rotor body, the slots being formed between two radially oriented side webs and a circumferential outer web, and a radially inner slot side formed in the rotor body.

[0007] The use of an internal permanent magnet synchronous motor in a submerged cryogenic fuel pump offers the advantages of high efficiency and a compact design. By placing the magnets in slots and mechanically retaining them therein, the magnets are held close to the rotor surface, ensuring the magnetic field is as strong as possible, ensuring the efficiency of the permanent magnet electric motor. Furthermore, when operating in cryogenic conditions, it is preferable to mechanically retain the magnets rather than glue them, as low temperatures can compromise the structural integrity of adhesives. Preferably, each slot may be provided with a system of leaf spring members to retain the magnets inserted in each slot.

[0008] For the permanent magnets to be most effective, it is important to position them as close as possible to the outer surface of the rotor body. It has therefore been found advantageous to form an axially oriented slot extending laterally and tangentially around the rotor body, such that the slot is formed between two radially oriented side webs and a peripheral outer web, with a radially inner slot edge formed in the rotor body. Preferably, the leaf spring members are provided within shallow recesses in the slot, such as those formed in the radially inner slot edge of the rotor body.

[0009] According to an advantageous embodiment, the leaf spring member is disposed within a shallow recess within the slot. Furthermore, the leaf spring member is preferably configured to exert a radially outward force on the magnet when the magnet is inserted into the slot, thereby holding the magnet in an outward position with minimal clearance / play. In a preferred embodiment, the magnet has a cross-sectional shape that fits snugly within the leaf spring slot.

[0010] According to an advantageous embodiment, the leaf spring member is disposed within a shallow recess within the slot. Furthermore, the leaf spring member is preferably configured to exert a radially outward force on the magnet when the magnet is inserted into the slot, thereby holding the magnet in an outward position with minimal clearance / play. In a preferred embodiment, the magnet has a cross-sectional shape that fits snugly within the leaf spring slot.

[0011] In some embodiments of the invention, the coaxial slots in the rotor are open at both ends for the insertion of magnets. Depending on the rotor design and dimensions, this may be advantageous and facilitate easy and accurate assembly of the rotor.

[0012] In some embodiments, a total of six slots are provided, evenly distributed along the cylindrical surface of the rotor, to alter the polarity of adjacent magnets on the rotor surface.

[0013] In some embodiments, a total of 12 slots are provided, distributed substantially evenly along the cylindrical surface of the rotor. The engine topology can be optimized and selected according to actual requirements. In some selected embodiments of the electric motor for a cryogenic pump of the present invention, the permanent magnets are provided in pairs with the same magnetic polarity direction, and the magnets on the surface are provided in a NNSSNNSSNNSS configuration.

[0014] In some preferred embodiments, the rotor body is made from a stack of magnetic steel, particularly electromagnetic steel, sheets that are less than 1 mm thick, preferably between 0.35 mm and 0.5 mm thick, and are glued together. In some embodiments, the leaf springs are laser cut into the stacks and are therefore made from the same material.

[0015] In accordance with the present invention, the electric motor is preferably adapted for use in a cryogenic pump for pumping liquefied fluids at high capacity and is adapted to operate at speeds up to 6,000 rpm.

[0016] In a preferred embodiment of the electric motor according to the present disclosure, the stator is provided with cooling channels arranged coaxially on its cylindrical outer surface. Furthermore, the stator is mounted within a cylindrical electric motor housing, thereby forming channels between the stator and the motor housing. This results in a compact electric motor with excellent cooling characteristics, making the electric motor suitable for driving a cryogenic pump.

[0017] In another aspect of the present invention, there is provided a submerged fuel pump for pumping a liquefied fluid, particularly a submerged cryogenic fuel pump for pumping a liquefied fuel such as liquefied natural gas (LNG), hydrogen, methanol, ethane, or liquefied petroleum gas (LPG), comprising: a housing containing a vertically oriented pump shaft having a lower fluid inlet and an upper fluid outlet; a permanent magnet electric motor as described above; and at least one impeller attached to the pump shaft for moving the cryogenic fluid from the inlet to the outlet, the pump shaft being concentrically attached to an upper end of the hollow motor drive shaft.

[0018] The invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional side view of a cryogenic submerged fuel pump according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional side view of the permanent magnet synchronous motor of the pump of FIG. [Figure 3] FIG. 3 is a cross-sectional view of the permanent magnet synchronous motor perpendicular to the view of FIG. [Figure 4] FIG. 4 is a cross-sectional view of a rotor of a permanent magnet synchronous motor without magnets attached. [Figure 5] FIG. 5 is a detailed view of section B of FIG. [Figure 6] FIG. 6 is a detailed view of section C of FIG. [Figure 7] 7 is a side view of a clamp collet that connects the motor shaft and the pump shaft shown in FIG. 2. FIG. [Figure 8] FIG. 8 is an end view of the clamp collet. DETAILED DESCRIPTION OF THE INVENTION

[0020] FIG. 1 shows a cross-sectional view of a cryogenic submerged fuel pump for pumping liquefied fuels such as liquefied natural gas (LNG), hydrogen, methanol, ethane, and liquefied petroleum gas (LPG). The pump comprises a housing 1 having a lower fluid inlet 3' and an upper fluid outlet 3''. The pump further comprises a vertically oriented pump shaft 4 and a permanent magnet electric motor 2.

[0021] The pump shaft 4 passes through the electric motor 2. A plurality of impellers 5 attached to the pump shaft 4 are mounted below the electric motor 2, and as the impellers 5 attached to the pump shaft 4 are rotated by the pump shaft 4, the impellers or vanes 5 move the cryogenic fluid from the pump inlet 3' to the pump outlet 3'' by centrifugal force, thereby forming a multi-stage centrifugal pump.

[0022] This main flow of liquefied fluid constitutes the main liquid flow from the pump inlet 3' to the pump outlet 3'', and in Figure 1 this main liquid flow is designated by the reference numeral 6. As shown in Figure 1, the main flow 6 is arranged coaxially around the electric motor 2.

[0023] As shown in Figure 1, the components of the pump are housed in a housing 1. The housing includes a number of intermediate chambers 1A, each housing an impeller 5, a lower flow branch 1B, a central motor housing section 1C, an upper flow branch 1D, and an upper outlet housing section 1E, stacked one on top of the other, with a main flow path 6 running through these housing sections 1A-1E.

[0024] The housing sections 1A to 1E are provided with external assembly flanges, and are assembled together by stay bolts 1F provided around the periphery.

[0025] The lower flow branch 1B is provided with a flow path for bypassing the main flow 6 around the electric motor 2. The lower flow branch 1B thus has a central inlet position in fluid communication with the top of the intermediate chamber 1A, and radial flow discharge positions.

[0026] The central housing section 1C is provided with radially coaxial flow channels 61 (see FIG. 3) that are in fluid communication with corresponding flow channels in the lower flow branch 1B. The upper flow branch 1D is provided with flow paths from radially outer receiving locations to central outlet flow outlets that are in fluid communication with the coaxial flow channels 61 in the central housing section 1C.

[0027] The pump's electric motor 2 is shown in more detail in Figures 2 and 3, and in greater detail in Figures 4 to 6. The electric motor 2 is contained within a motor housing 21 and includes a rotor assembly including a rotor body 23 attached to a motor shaft 22, with a plurality of permanent magnets 231 disposed along the periphery 234 of the rotor body 23. The electric motor also includes a stator 24 with coils arranged concentrically around the rotor assembly. The rotor assembly further includes a mechanical magnet retention system for holding the magnets 231 in place within the rotor body 23. The mechanical magnet retention system includes a plurality of axially oriented slots 232 around the periphery of the rotor body 234 in which the permanent magnets 231 are retained.

[0028] The rotor body 23 is securely attached to the motor shaft by any suitable means.

[0029] The motor shaft 22 is hollow and the pump shaft 4 is concentrically mounted within the hollow motor drive shaft 22 as shown in Figure 1. Assembly of the pump shaft 4 and motor shaft 22 is accomplished by a collet clamp connection at the upper ends of the shafts 4, 22 to join the motor shaft 22 and pump shaft 4. The pump shaft 4 is a smooth shaft, preferably a cylindrical elongated shaft with a uniform diameter.

[0030] The collet clamp connection that attaches the pump shaft 4 to the motor shaft 22 is a collet clamp 41, which is made from an alloy suitable as a cryogenic material, for example a metal alloy such as bronze or stainless steel.

[0031] 1, 2, and 7-8, the collet clamp connection includes a clamping collet 41 having a conical outer clamping surface 41A that engages a corresponding conical inner surface of the end section of the hollow motor shaft 22 and a cylindrical inner clamping surface 41B that clamps the collet 41 around the pump shaft 4. The clamping collet 41 is attached to the motor shaft 22 by a clamping nut 29 (see FIG. 2), which has a conical inner surface that engages a conical collar surface 41C of the collet clamp 41. The clamping nut threads onto the end of the motor shaft 22, and tightening the clamping nut 29 onto the end of the motor shaft 22 forces the clamping collet 41 into the receiving surface of the motor shaft 22.

[0032] The motor shaft 22 is supported within the motor housing 21, and consequently within the pump housing 1, by a main bearing 27 located at the upper end of the motor shaft 22, which absorbs axial forces that may occur within the pump. In some currently preferred embodiments, the main bearing 27 is a hybrid bearing, particularly a hybrid ball bearing such as a deep groove ball bearing. The lower end of the motor shaft 22 of the motor 2 is provided with a lower bearing 28 to absorb radial forces that may occur. The lower bearing 28 is a carbon guide bearing. The motor shaft 22 may be coated to increase its hardness, such as by spray coating to form a crack-free coating, thereby ensuring the performance of the motor shaft 22 under cryogenic conditions.

[0033] As shown in Figure 1, a secondary liquid flow 7 is provided for cooling the electric motor 2 and for lubricating the bearings 27, 28 therein. The secondary liquid flow 7 is a partial flow of the main flow 6. This secondary liquid flow 7 is a counter-flow liquid flow that flows from the region of the pump outlet 3'' through the electric motor 2 to a radially central space 7A above the uppermost impeller 5 above the region of the pump inlet 3'.

[0034] The upper outlet housing section 1E of the housing 1 is provided with a filter 71 at the inlet of the secondary flow path 7. This filter 71 is provided at the inlet of the secondary liquid flow path 7 and prevents contaminants in the main flow 6 from entering the motor 2 and bearings 27, 28, protecting them and extending their lifespan. The filter 71 is preferably a cryogenic filter, and more preferably, the filter 71 may be a self-cleaning filter such as a side flow filter.

[0035] The first liquid flow 6 is the main flow which increases in pressure from the inlet 3' to the outlet 3'' of the pump. The pressure difference within the pump provides a reverse secondary flow 7, with a small portion of the main flow 6 flowing back through the electric motor 2 to cool the motor and lubricate the bearings 27, 28. In this way the bearings are lubricated by the main fluid flowing through the pump.

[0036] The pressure difference is achieved by providing an outlet for the secondary flow in the radially central space 7A above the top impeller 5 (or, in one embodiment of the present invention, the single impeller, if the pump is designed with only one impeller 5).

[0037] The secondary liquid flow 7 is a partial flow of the main liquid flow 6. Due to the narrow passage through the motor 2 and the bearings 27, 28, the flow resistance in the secondary flow path 7 is very high. This means that the secondary liquid flow 7 is only a small fraction of the main liquid flow 6, for example 15-35 times less.

[0038] The cylindrical outer periphery of the stator 24 is provided with a plurality of axially oriented flow passages 25 for cooling the electric motor 2, and these flow passages 25 constitute the majority of the secondary flow passages 7 which cool the motor.

[0039] As mentioned above, the electric motor is a permanent magnet synchronous motor in which magnets are mounted in slots in the rotor. Referring to Figures 4 to 6, in the mechanical magnet retention system, each slot 232 is provided with a leaf spring member 233 for retaining the magnet 231 inserted into the slot 232. The leaf spring member 233 is mounted in a shallow recess within the slot 232 and is configured to apply a radially outward force to the magnet 231 when the magnet 231 is inserted into the slot 232 (see Figure 3). The magnet 231 has a cross-sectional shape that fits snugly into the slot 232 above the leaf spring 233.

[0040] An axially oriented slot 232 is formed extending laterally and tangentially around the rotor body such that the slot is formed between two radially oriented side webs 232 a, 232 b and a peripheral outer web 232 c, with a radially inner slot side 232 d formed in the rotor body. Additionally, the leaf spring member 233 may be provided within a shallow recess 233 a in the slot 232 formed in the radially inner slot side 232 d of the rotor body 23.

[0041] The slots 232 are coaxially disposed in the rotor 23 and may be open at both ends for insertion of the magnets 231. In the embodiment shown in Figure 3, a total of twelve slots 232 are disposed and evenly distributed along the cylindrical surface 234 of the rotor body 23. The magnetic polarity of adjacent magnets on the rotor surface is alternated for each magnet 231, and the magnets 231 on the surface 234 are disposed in the following configuration: NNSSNNSSNNSS.

[0042] In one embodiment, the rotor body 23 is made from a stack of multiple sheets made of magnetic steel, in particular electromagnetic steel. The stack of sheets may be thin, such as less than 1 mm thick, preferably between 0.35 mm and 0.5 mm. In a further embodiment, the leaf springs 233 are laser cut into the stack and made from the same material.

[0043] In this disclosure, terms such as "vertical", "horizontal", etc. are used and should be understood as terms that indicate relative orientation between associated elements, flanges, etc.

[0044] While the present invention has been described with reference to specific embodiments, it is not intended to be limited to the examples set forth. The scope of the invention is defined by the appended claims. In the context of the claims, the term "comprising" or "comprises" does not exclude other possible elements or steps. Moreover, references such as "a" or "an" should not be construed as excluding a plurality. The use of reference signs in the claims for elements shown in the figures should also not be construed as limiting the scope of the invention. Furthermore, individual features recited in different claims may be advantageously combined, and the fact that these features are recited in different claims does not exclude that combinations of features are not possible and advantageous.

[0045] The present invention has been described above with reference to certain presently preferred embodiments of a submerged fuel pump. However, it will be appreciated that the present invention allows other embodiments and modifications to be provided without departing from the scope of the present invention as defined in the appended claims.

Claims

1. 1. An electric motor for a submerged fuel pump for pumping a liquefied fluid, in particular a cryogenic submerged fuel pump for pumping a liquefied fuel such as liquefied natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or a liquefied cryogenic dielectric fluid, a rotor having a rotor body attached to a motor shaft, the rotor body having a plurality of permanent magnets disposed along a periphery thereof, the rotor further comprising a mechanical magnet retention system for retaining the magnets in position within the rotor body; a stator having coils concentrically arranged around the rotor; Equipped with the mechanical magnet retention system comprises a plurality of slots axially oriented around the periphery of the rotor body in which the permanent magnets are retained; the plurality of axially oriented slots are formed in a lateral tangential extension around the periphery of the rotor body, the slots being formed between two radially oriented side webs and a circumferential outer web, a radially inner slot side being formed in the rotor body.

2. 10. The electric motor of claim 1, wherein each slot is provided with a system of leaf spring members for retaining the magnet inserted within the slot.

3. 3. The electric motor according to claim 1, wherein the leaf spring member is provided in a shallow recess in the slot, such as formed on the radially inner side of the slot of the rotor body.

4. 4. The electric motor of claim 1, wherein the leaf spring member is configured to apply a radially outward force to the magnet when the magnet is inserted into the slot, and the leaf spring applies a radially outward holding force to the permanent magnet to hold the magnet in the slot.

5. 5. The electric motor of claim 1, wherein the magnet has a cross-sectional shape that fits snugly into the slot above the leaf spring.

6. An electric motor as claimed in any one of claims 1 to 5, wherein the coaxial slots in the rotor are open at both ends for insertion of the magnets.

7. 7. An electric motor according to claim 1, wherein a total of six slots are provided evenly distributed along the cylindrical surface of the rotor, and the magnetic polarity of adjacent magnets on the rotor surface is changed.

8. An electric motor as claimed in any one of claims 1 to 6, wherein a total of twelve slots are provided, distributed substantially evenly along the cylindrical surface of the rotor.

9. 9. The electric motor of claim 8, wherein the permanent magnets are arranged in pairs with the same magnetic polarity direction, and the magnets on the surface are arranged in an N-N-S-S-N-N-S-S-N-N-S-S configuration.

10. 10. Electric motor according to any one of the preceding claims, wherein the rotor body is made by stacking a plurality of sheets made of magnetic steel, in particular electromagnetic steel.

11. 11. An electric motor according to claim 10, wherein the sheet stack has a thickness of less than 1 mm, preferably between 0.35 mm and 0.5 mm.

12. An electric motor according to any one of claims 2 to 5, wherein the leaf springs are laser cut into the laminate and are therefore made of the same material.

13. An electric motor according to any one of the preceding claims, wherein the electric motor is adapted for use in a cryogenic pump for pumping liquefied fluids and is adapted to operate at speeds up to 6,000 rpm.

14. An electric motor according to any one of the preceding claims, wherein the stator is provided with cooling channels arranged coaxially on its cylindrical outer surface.

15. A submerged fuel pump for pumping liquefied fluids, in particular a cryogenic submerged fuel pump for pumping liquefied fuels such as liquefied natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), etc., comprising: a housing having a lower fluid inlet and an upper fluid outlet and containing a vertically oriented pump shaft; A permanent magnet electric motor according to any one of claims 1 to 14; at least one impeller attached to the pump shaft for moving the cryogenic fluid from an inlet to an outlet; Equipped with The submerged fuel pump, wherein the pump shaft is concentrically mounted on an upper end of the hollow motor drive shaft.

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