Marine propulsion unit

Abstract

A marine propulsion unit is provided. The marine propulsion unit comprises a dual rotor electric motor having an inner rotor and an outer rotor; a contra rotating propeller having an inner shaft propeller and an outer shaft propeller; a drive shaft having an inner shaft connecting the inner rotor to the inner shaft propeller and an outer shaft connecting the outer rotor to the outer shaft propeller; and a slip ring unit for transmitting an electric current to the dual rotor electric motor.

Description

MARINE PROPULSION UNITTECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to a marine propulsion unit. Further embodiments relate to a marine vessel.BACKGROUND

[0002] To propel marine vessels, marine propulsion units with a high efficiency and good maintainability are desired. Particularly, for marine propulsion units, an adaptability to different marine vessels is desirable.DISCLOSURE OF THE INVENTION

[0003] In view of the foregoing, the present disclosure is directed to a marine propulsion unit and a marine vessel.

[0004] According to an aspect of the present disclosure, a marine propulsion unit is provided. The marine propulsion unit comprises a dual rotor electric motor having an inner rotor and an outer rotor; a contra rotating propeller having an inner shaft propeller and an outer shaft propeller; a drive shaft having an inner shaft connecting the inner rotor to the inner shaft propeller and an outer shaft connecting the outer rotor to the outer shaft propeller; and a slip ring unit for transmitting an electric current to the dual rotor electric motor.

[0005] According to another aspect of the present disclosure, a marine vessel comprising a marine propulsion unit according to any of the embodiments described herein is provided.

[0006] According to some embodiments, the marine propulsion unit is configured to propel a marine vessel. In some embodiments, the marine propulsion unit comprises a shaftline marine propulsion unit. In particular, the marine vessel may comprise at least one marine propulsion unit according to embodiments described herein. The marine vessel as described herein comprises seagoing or inland marine vessels. In particular, the marine vessel comprises ships and boats. In some embodiments, the marine vessel comprises merchant ships, in particular for transporting goods. In particular, the marine vessel may comprise acontainer vessel, a Ro-Ro or car carrier, a tanker or shuttle tanker, a liquid natural gas (LNG) carrier or a floating storage and regasification unit. In some embodiments, the marine vessel comprises ferries, in particular single and double-ended ferries, cruise ships, water buses, yachts. In some embodiments, the marine vessel comprises offshore energy vessels, in particular service operation vessels (SOVs), cable laying vessels (CLVs), foundation installation vessels (FIVs), offshore construction (OCVs) and support vessels (OSVs), platform supply vessels (PSVs), and anchor-handling tug supply vessels (AHTS). In some embodiments, the marine vessel comprises research and survey vessels or other special purpose vessels, such as dredgers, heavy lift vessels or towboats. In some embodiments, the marine vessel comprises ice-going marine vessels, in particular icebreakers or marine vessels having an ice-class assigned by a classification society. In some embodiments, the marine vessel may comprise navy or coast guard vessels. In some embodiments, the marine vessel may comprise submarine vessels or unmanned remotely operated underwater vehicles (ROVs).

[0007] The marine vessel typically comprises a hull. Typically, the hull defines a vessel interior and a vessel exterior. Space confined by the hull and configured to be isolated from sea water may be defined as the vessel interior. Space outside the hull, and in particular the sea, may be defined as the vessel exterior. Typically, the vessel interior is substantially free of sea water and substantially dry. In some embodiments, the vessel interior is configured to transport cargo and / or persons.

[0008] In some embodiments, the marine vessel may comprise a plurality of marine propulsion units. In particular, the marine vessel may comprise 2, 3, 4, or more marine propulsion units. Typically, each of the plurality of marine propulsion units may be controlled separately.

[0009] The marine propulsion unit typically comprises at least one shaft-line marine propulsion unit. Typically, in the shaft-line marine propulsion unit, the electric motor, particularly a dual rotor electric motor, which may also be described as contra-rotating electric motor, is arranged within the hull of the marine vessel. The electric motor is connected to a propeller unit via a shaft-line or drive shaft. The propeller unit is typically arranged at a stem of the marine vessel. Particularly, the propeller unit is typically arrangedat a skeg of the marine vessel. Typically, for a shaft-line marine propulsion unit, a stemfacing side of the marine propulsion unit may be described as the driving end (DE) side of the marine propulsion unit. Typically, for a shaft-line marine propulsion unit, a vessel-center facing side of the marine propulsion unit may be described as the non-driving end (NDE) side of the marine propulsion unit.

[0010] In typical embodiments, the propeller unit comprises an outer shaft propeller and an inner shaft propeller. In other words, the propeller unit may be named a contra rotating propeller. Typically, the outer shaft propeller is arranged closer to the hull than the inner shaft propeller. In a pushing propeller unit, the outer shaft propeller may also be described as the front propeller and the inner shaft propeller may be described as the rear propeller; and vice versa for a pulling propeller unit. Typically, the outer shaft propeller and the inner shaft propeller are arranged adjacent to each other. The contra rotating propeller has a motorfacing end, particularly a motor-facing axial end, facing the motor. The outer shaft propeller and the inner shaft propeller rotate about the rotation axis of the propeller unit. In other words, the outer shaft propeller and the inner shaft propeller rotate about the same rotation axis.

[0011] Typically, the propeller unit comprises a contra rotating propeller unit. In particular, the outer shaft propeller may be configured to rotate in a first direction, particularly about the rotation axis of the propeller unit, and the inner shaft propeller may be configured to rotate in a second direction opposite to the first direction, particularly about the rotation axis of the propeller unit. In other words, the outer shaft propeller may rotate clockwise and the inner shaft propeller may rotate counterclockwise, or vice versa, about the same rotation axis. A contra rotating propeller unit may advantageously allow for a higher hydrodynamic efficiency than other propeller concepts, in particular with respect to single propellers.

[0012] In some embodiments, the outer shaft propeller has a first diameter and the inner shaft propeller has a second diameter, with the second diameter being different from the first diameter, particularly the first diameter being larger than the second diameter. Typically, the outer shaft propeller comprises a first number of first blades and the inner shaft propeller comprises a second number of second blades. Typically, the second number may be differentfrom the first number. The outer shaft propeller may comprise 3, 4, 5, 6 or 8 first blades. The inner shaft propeller may comprise 3, 4, 5, 6 or 8 second blades. In some embodiments, the outer shaft propeller comprises one first blade more than the inner shaft propeller comprises second blades. Exemplarily, the outer shaft propeller comprises 6 first blades and the inner shaft propeller comprises 5 second blades. In some embodiments, the outer shaft propeller and the inner shaft propeller may comprise the same number of blades, in particular 3, 4, 5, 6 or 8 first and second blades, respectively. The outer shaft propeller and / or the inner shaft propeller may each be manufactured as a monoblock or in components, as a built-up propeller.

[0013] The propeller unit is driven by an electric motor. The electric motor is typically a dual rotor electric motor. The dual rotor electric motor may also be described as a contrarotating motor. Typically, the electric motor has a power, particularly a rated electric power, of at least 100 kW, at least 200 kW, at least 1 MW, at least 2 MW, at least 5 MW, at least 10 MW or at least 15 MW. The electric motor is typically arranged within the hull of the marine vessel. Typically, a rotation axis of the electric motor is identical to a rotation axis of the propeller unit. The output shaft of the electric motor is typically coaxial to the drive shaft of the propeller unit. In typical embodiments, for a propeller unit comprising an outer shaft propeller and an inner shaft propeller, in particular for the contra rotating propeller unit, the outer shaft propeller and the inner shaft propeller may be driven by the same electric motor.

[0014] The electric motor comprises a dual rotor electric motor with an outer rotor and an inner rotor configured to rotate in opposite directions about a rotation axis of the electric motor. Typically, the rotation axis of the electric motor may be coaxially with the rotation axis of the propeller unit. Typically, the electric motor is a synchronous electric motor. Typically, the outer rotor comprises windings to be supplied with an electric current for the operation of the electric motor. The inner rotor may be a permanent magnet rotor or an externally excited synchronous rotor.

[0015] Typically, the dual rotor electric motor comprises a perforated tube. The perforated tube may substantially have a cylinder shape, particularly with a cage-like structure. In some embodiments, the perforated tube may, at least in part, form an outer contour of the dual rotor electric motor. The perforated tube is configured to transmit a torque of the outer rotorto the propeller unit. The perforated tube supports an outer rotor winding of the outer rotor. Particularly, the outer rotor winding is connected to the perforated tube. In some embodiments, the outer rotor comprises a plurality of axial beams between a core of the outer rotor winding and the perforated tube. In particular, the outer rotor may comprise at least 3, at least 6, at least 12, or at least 24 axial beams. Typically, the axial beams are arranged parallel to an axis, particularly the rotating axis, of the perforated tube. Typically, the plurality of axial beams is arranged substantially parallel with respect to each other. The plurality of axial beams is typically configured to transmit a torque from the outer rotor core, which particularly accommodates the windings, to the perforated tube. The plurality of axial beams are configured to allow air to flow from an interior of the motor, particularly via radial slots in a core of the outer rotor winding of the outer rotor, towards the perforated tube, and particularly towards the radial openings in the perforated tube. The core of the outer rotor winding is typically a steel core.

[0016] In some embodiments, the drive shaft of the propeller comprises an outer shaft and an inner shaft. The outer shaft and inner shaft are typically coaxially arranged. Typically, the outer rotor drives the outer shaft. In some embodiments, the outer shaft, in particular a drive end outer shaft, comprises at least one hatch. Typically, the at least one hatch can be configured to provide access to a bearing supporting the inner shaft in the outer shaft. The at least one hatch may permit maintenance to be done on the inner shaft and / or on the outer shaft from within the marine propulsion unit. Particularly, disassembling of the marine propulsion unit may advantageously be avoided.

[0017] In some embodiments, the outer shaft and / or the inner shaft may comprise at least one shaft coupling. In particular, the outer shaft and / or the inner shaft comprising at least one shaft coupling advantageously allows to modularly adapt the marine propulsion unit to the marine vessel. Exemplarily a length of the shaft may be adapted dependent on a size of the marine vessel. Typically, the inner rotor drives the inner shaft. Typically, the inner shaft is arranged inside the outer shaft; in other words, an inside radius of the outer shaft exceeds an outside radius of the inner shaft. The inner shaft and the outer shaft rotate about the same rotation axis, and in particular about the rotation axis of the electric motor.

[0018] Typically, the at least one shaft coupling is arranged for removably separating the drive shaft between the rotating propeller and the dual rotor electric motor. The at least one shaft coupling typically allows for separating the inner shaft and the outer shaft. In typical embodiments, the marine propulsion unit comprises exactly one shaft coupling, exactly two shaft couplings or exactly three shaft couplings. A shaft coupling, particularly a first shaft coupling, may typically be arranged in the proximity of the rotating propeller or the dual rotor electric motor. A shaft coupling, particularly a second shaft coupling, may typically be arranged in the proximity of the rotating propeller or the dual rotor electric motor, particularly for the first shaft coupling being arranged at the respective opposite end of the drive shaft. In other words, with the first shaft coupling being arranged at the proximity of the rotating propeller, the second shaft coupling would be arranged at the proximity of the dual rotor electric motor, and vice versa. A shaft coupling being arranged in the proximity of the rotating propeller or of the dual rotor electric motor may be described as being arranged at a distance not exceeding 10% of a total length of the drive shaft. A shaft coupling, particularly a third shaft coupling, may typically be arranged in an intermediate position along the drive shaft. Particularly, the shaft coupling may be arranged between 20% and 80% of an overall length of the drive shaft or between 30% and 70% of an overall length of the drive shaft.

[0019] The at least one shaft coupling can advantageously allow to adapt a length of the drive shaft variably based upon modular components of the marine propulsion unit. Similarly, a maintenance of the marine propulsion unit may be facilitated. Exemplarily, the same dual rotor electric motor and / or the same contra rotating motor may be used for drive shafts with different lengths, particularly for marine vessels with different preferred arrangements of the marine propulsion unit.

[0020] Typically, the inner shaft is supported by at least one drive end (DE) inner bearing and a non-drive end (NDE) inner bearing. Typically, the outer shaft is supported by at least one DE outer bearing and an NDE outer bearing. The NDE inner bearing and / or the NDE outer bearing may each comprise an axial bearing and a radial bearing, particularly within the same bearing housing. The NDE inner bearing and the NDE outer bearing may form an NDE bearing unit.

[0021] With the NDE bearing unit, the shafts of the marine propulsion unit can be supported in a space-efficient arrangement and, at the same time, the maintenance, repair and replacement of parts of the bearing arrangement, or parts of / at a bearing housing is facilitated.

[0022] Typically, the bearing arrangement includes a first axial bearing between the inner shaft and the outer shaft for allowing the transfer of axial forces between the inner shaft and the outer shaft. In some embodiments, the bearing arrangement includes the first axial bearing between the inner shaft and the outer shaft, a second axial bearing arranged between a bearing housing wall and the inner shaft, and a third axial bearing arranged between a bearing housing wall and the outer shaft. The arrangement of the axial bearings between the shafts as well as a common placement of the axial bearing(s) for both shafts allows for an efficient, space-saving, and compact arrangement of the bearings used for the drive shaft of the marine propulsion unit.

[0023] According to some embodiments, the bearing unit may include an oil seal. In particular, the oil seal may be located between the inner shaft and the outer shaft, especially between a flange of the inner shaft and a flange of the outer shaft. In some embodiments, the oil seal may be located under (inside) the first bearing. Especially, the oil seal may be removable through the at least one hatch. More specifically, the first bearing may be removed at least partly to open up a maintenance route / space for maintenance, repair or exchange of the oil seal, especially via the hatch. In some embodiments, the oil seal may include an oil seal housing. According to some embodiments, the oil seal housing part can be fastened to one of the inner shaft and the outer shaft, or both (or the respective flanges of the shafts). Typically, the oil seal may contain elastic lip seals against a liner.

[0024] According to some embodiments described herein, at least one of the axial bearings (and / or, optionally, at least one of the radial bearings) of the bearing arrangement is a pad bearing. A pad bearing provides a reliable function with a simple design. In some embodiments, the pad bearing can easily be removed from the bearing housing due to its simple design and uncomplicated mounting possibilities.

[0025] Employing a contra rotating electric motor may advantageously allow to drive the contra rotating propeller with a single electric motor gearlessly. In other words, a torque ofthe dual rotor electric motor is transmitted to the contra rotating propeller without a gearbox. Thereby, a more compact and efficient drive train may be provided.

[0026] Typically, the drive shaft is supported by a non-drive end (NDE) thrust bearing. The NDE thrust bearing is typically arranged separately from the dual rotor electric motor and / or from the slip-ring unit. Typically, the NDE thrust bearing comprises a slide bearing, particularly a hydrodynamic bearing. In some embodiments, the NDE thrust bearing comprises a roller bearing. Typically, employing a slide bearing as the NDE thrust bearing may be preferred. Particularly, additional pumps may be avoided for a hydrodynamic bearing. Having a slide bearing as NDE thrust bearing may advantageously reduce a maintenance effort.

[0027] In some embodiments, the marine propulsion unit comprises at least one support bearing. The at least one support bearing is typically configured to support the drive shaft between a propeller bearing and a drive end bearing. Typically, the at least one support bearing is arranged between 20% and 80%, particularly between 30% and 70%, of an overall between a propeller bearing and a drive end bearing. Particularly for a long drive shaft, exemplarily in twin screw marine vessels, the at least one support bearing may advantageously provide an additional mechanical support and may be associated with an improved performance and reduced wear-and-tear. In some embodiments, particularly for an exposed shaft, at least one of the at least one support bearing may be arranged outside the ship hull.

[0028] In some embodiments, the marine propulsion unit comprises a slip-ring unit. The slip-ring unit is configured to transmit an electric current to the dual rotor electric motor, particularly to the outer rotor of the dual rotor electric motor. The slip-ring unit is typically arranged on a vessel center facing side of the dual rotor electric motor. The slip-ring unit typically comprises a slip-ring housing and a slip-ring assembly arranged within the housing. Typically, the slip-ring assembly comprises at least one slip-ring element which is in contact with the outer rotor.

[0029] Typically, the slip-ring housing can be understood as a casing which is configured to accommodate the slip-ring assembly separately in the marine vessel. The slip-ring housing is configured to prevent dust, in particular carbon dust, from entering the interior of thevessel, which advantageously allows for avoiding contamination. Typically, the slip-ring housing is arranged separately from the dual rotor electric motor. In some embodiments, the slip-ring unit includes a set of seals at both ends of the slip-ring assembly, at the slip-ring housing and the outer rotor to seal the slip-ring housing against the outside. In particular, the set of seals are configured to seal the slip-ring housing in an area between the slip-ring housing and an outer surface of the outer rotor.

[0030] The slip-ring unit is typically cooled by a slip-ring unit cooling system. Typically, the slip-ring unit cooling system is based on cooling air being circulated and / or is cooling liquid based. Typically, the slip-ring cooling system is connectable to a low temperature liquid cooling medium vessel cooling system. Typically, the low temperature liquid cooling medium vessel cooling system is a low temperature water vessel cooling system. The low temperature water of the low temperature water vessel cooling system may particularly be cooled by sea water. In some embodiments, the slip-ring unit may be cooled using an oil, exemplarily a transformer oil.

[0031] In some embodiments, the marine propulsion unit further includes an inflow filter unit at the slip-ring housing for the slip-ring assembly. The inflow filter unit is configured to filter air entering the slip-ring housing. The inflow filter unit may be integrated in the slipring housing. The inflow filter unit may also be arranged at an opening in the slip-ring housing. According to embodiments, more than one inflow filter units can be provided. Typically, the inflow filter unit is an air filter configured to filter out dirt particles from a motor cooling airflow entering the slip-ring housing. Thereby, a contamination of the slipring unit can be adventurously avoided or reduced.

[0032] Typically, the slip-ring element includes a sliding contact, in particular brushing means fixed in the slip-ring housing which are configured to transfer electrical power, signal or data to a corresponding slip-ring arranged on the outer surface of the outer rotor by contacting the corresponding slip-ring element. In some embodiments, the slip-ring unit comprises an excitation slip-ring for providing an electric current to the inner rotor of the dual rotor electric motor. Typically, a rotating part of the slip-ring unit is connected to the outer rotor of dual rotor electric motor with a dismountable connection. The dismountable connection may exemplarily comprise a flanged joint, a keyed joint, a tapered joint or ashrink fitted joint. Particularly, the rotating part of the slip-ring unit may be replaced and / or mounted without dismounting the outer rotor. Having the rotating part of the slip-ring unit connected to the outer rotor of the dual rotor electric motor with a dismountable connection may advantageously allow for a more modular and scalable marine propulsion unit, and may improve the maintainability and / or the assemblage of the marine propulsion unit.

[0033] In some embodiments, the marine propulsion unit comprises an excitation slip-ring unit, particularly for providing an electric current to the inner rotor. The excitation slip-ring unit may be distinct and / or separated from the motor slip-ring unit or may be integrated into the motor slip-ring unit.

[0034] In some embodiments, the marine propulsion unit comprises a cooling air system for providing cooling air to the dual rotor electric motor. In some embodiments, the cooling air system comprises a cooling air unit which integrates at least some parts of the cooling air system in a single unit. In some embodiments, the cooling air system is formed by a plurality of distinct sub-systems. The cooling air system typically comprises an air fan and a heat exchanger. The air fan is typically configured to propel air through the cooling air system. Particularly, the air fan may provide cooling air to the dual rotor electric motor and may draw the cooling air from the dual rotor electric motor, particularly after cooling the contra rotating motor. Typically, the air fan is configured to generate an overpressure in an ingoing air channel and a negative pressure in an outgoing air channel. In some embodiments, the cooling air system is an annular cooling air system with at least a part, and particularly all of the cooling air entering and / or exiting the dual rotor electric motor annularly. An annular cooling air system may be particularly favorable for compact marine propulsion units with a compact dual rotor electric motor. In some embodiments, the cooling air system is an annular cooling air system with at least a part of the cooling air entering and / or exiting the dual rotor electric motor axially. An axial cooling air system may be particularly favorable for an electric motor with a larger diameter.

[0035] In some embodiments, the slip-ring unit cooling system is distinct from the cooling air system. In particular, the slip-ring unit cooling system may have a distinct cooling air circuit separated from an air circuit of the cooling air system of the dual rotor electric motor.In other words, the slip ring unit is cooled using a slip ring cooling system independent of the cooling air system for cooling the dual rotor electric motor.

[0036] An axial distance of the motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at least two times, at least three times, at least four times, preferably at least two times, an axial length of the dual rotor electric motor. In some embodiments, the drive shaft of the marine propulsion unit has a length of at least 10 meters, at least 20 meters or at least 30 meters. Having an extensive drive shaft may advantageously allow to position the dual rotor electric motor and the contra rotating propeller at positions in the vessel most suitable for each of the components of the marine propulsion unit. Exemplarily, the dual rotor may be arranged at a particularly accessible position. In some embodiments, earthing of the drive shaft and / or of bearings is facilitated, particularly by an improved accessibility.

[0037] Typically, the motor-facing end of the contra-rotating propeller is a motor-facing end of the outer shaft propeller. Particularly, the motor-facing end of the contra-rotating propeller may be a most motor-facing edge of a propeller blade of the contra rotating propeller. In some embodiments, the motor-facing end of the contra-rotating propeller may be a most motor-facing connection of a propeller blade of the contra rotating propeller with the drive shaft, and particularly with the outer shaft. Typically, the propeller-facing end of the dual rotor electric motor is a propeller-facing end of the inner rotor and / or of the outer rotor. In some embodiments, the propeller-facing end of the dual rotor electric motor is a propeller-facing end of an electric motor housing or a propeller-facing end of windings of the dual rotor electric motor. The axial distance of the motor-facing end of the contra rotating propeller to the propeller-facing end of the dual rotor electric motor is typically defined along the rotation axis of the drive shaft or along the rotation axis of the dual rotor electric motor or along the rotation axis of the contra rotating propeller. Typically, the rotation axis of the drive shaft, the rotation axis of the dual rotor electric motor and the rotation axis of the contra rotating propeller are at least parallel and typically identical.

[0038] Typically, the marine propulsion unit according to embodiments described herein is part of a marine vessel. Particularly, the marine propulsion unit propels the marine vessel. The marine propulsion unit is typically installed in a ship yard. Maintaining the marinepropulsion unit may comprise disassembling at least part of the marine propulsion unit. Particularly, maintaining the marine propulsion unit may comprise disassembling the at least one shaft coupling, maintaining or replacing a part of the marine propulsion unit, and reassembling the drive shaft at the at least one shaft coupling.

[0039] Embodiments of the present disclosure provide marine propulsion units with an improved performance and a good maintainability. The marine propulsion units described herein allow for modular marine propulsion units well adaptable to marine vessel requirements. Particularly, having a long drive shaft may advantageously allow to increase a dimension of the dual rotor electric motor, particularly a diameter of the dual rotor electric motor to increase a torque of the electric motor. A larger distance between the propeller and the electric motor typically improves the accessibility and maintainability of the marine propulsion unit advantageously.BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings relate to embodiments of the disclosure and are described in the following:FIG 1 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG 2 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG 3 schematically illustrates a dual rotor electric motor according to embodiments described herein;FIG 4 schematically illustrates a slip-ring unit according to embodiments described herein; andFIG 5 schematically illustrates an NDE bearing according to embodiments described herein.DETAILED DESCRIPTION OF EMBODIMENTS

[0041] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield a further embodiment. It is intended that the description includes such modifications and variations. In the figures, elements may be depicted with exaggerated dimensions to improve the comprehensibility of the detailed description of embodiments. In particular, relations of lengths and widths of components shown may be distorted. Further, some elements may be depicted with enlarged dimensions while other elements in the same figure are depicted, relatively, with reduced dimensions.

[0042] Fig. 1 schematically illustrates a marine propulsion unit 2000. The marine propulsion unit 2000 is arranged within the hull 2100 of the marine vessel. Particularly, the marine propulsion unit 2000 is arranged in a shaft-line configuration with a dual rotor electric motor 1 being arranged within the hull 2100 of the marine vessel. The marine propulsion unit 2000 comprises the dual rotor electric motor 1, a drive shaft 2500 connecting the dual rotor electric motor 1 to the propeller unit with the outer shaft propeller 9 and the inner shaft propeller 10. The outer shaft propeller 9 and the inner shaft propeller 10 are arranged at a skeg of the hull 2100 of the marine vessel. The marine propulsion unit 2000 comprises a plurality of shaft bearings 41, 42. Particularly, the marine propulsion unit 2000 comprises drive end, DE, bearings (not shown in the figures) and non-drive end bearings 41, 42, specifically an NDE outer bearing 41 and an NDE inner bearing 42. The marine propulsion unit comprises a propeller end shaft bearing 2530 and an adjacent shaft seal (not explicitly shown). A cooling air system 16 is arranged within the hull 2100 to provide cooling air to the dual rotor electric motor 1. A slip-ring unit 19 is arranged between the dual rotor electric motor 1 and the non-drive end bearings 41, 42. The slip-ring unit 19 is arranged separately from the dual rotor electric motor 1. Particularly, the slip-ring unit 19 is arranged within a slip-ring unit housing separate from the dual rotor electric motor 1.

[0043] The drive shaft 2500 has a length exceeding twice a length of the dual rotor electric motor 1. The drive shaft 2500 comprises a first shaft coupling 2510 and a second shaft coupling 2520. The first shaft coupling 2510 is arranged proximate to the dual rotor electric motor 1. The second shaft coupling 2520 is arranged proximate to the contra rotating propeller 9, 10.

[0044] Fig. 2 schematically illustrates a marine propulsion unit 2000. The drive shaft 2500 of the marine propulsion unit 2000 has a length exceeding a fourth of a length of the dual rotor electric motor 1. The drive shaft 2500 is supported by a first support bearing 45 and a second support bearing 46. Part of the drive shaft 2500 is arranged outside a hull of the marine vessel. Particularly, the first support bearing 45 and the second support bearing 46 support the drive shaft 2500 at a section of the drive shaft 2500 outside the hull of the marine vessel.

[0045] Fig. 3 schematically illustrates a dual rotor electric motor 1 in a side view as used in embodiments described herein. The inner rotor of the dual rotor electric motor 1 is connected to a DE inner shaft 8 and an NDE inner shaft 48 of the drive shaft 2500. The outer rotor is connected to a perforated tube 4. The perforated tube 4 transmits the torque of the outer rotor to an DE outer shaft 7 of the drive shaft 2500 via a DE outer rotor end flange 6. The perforated tube 4 transmits the torque of the outer rotor to the NDE outer shaft 47 via a DE outer rotor end flange 5. The DE outer rotor end flange 5 comprises a plurality of flange openings 106. The plurality of flange openings 106 are arranged substantially symmetrical around a rotation axis of the perforated tube 4 and / or the dual rotor electric motor 1. The perforated tube 4 comprises a plurality of radial openings. The plurality of radial openings comprises a plurality of first openings 104 and a plurality of second openings 105. In the embodiments of Fig. 3, the plurality of radial openings are substantially quadratical with rounded corners. In the embodiments of Fig. 4, the plurality of radial openings are arranged in a substantially rectangular, and particularly quadratical, pattern.

[0046] Fig. 4 schematically illustrates a slip-ring unit 19, as used in embodiments described herein, in more detail. The slip-ring unit comprises a slip-ring assembly 240. The slip-ring assembly 240 includes three slip-ring elements 240a, 240b, 240c. Each slip-ring element 240a, 240b, 240c includes brushing means 242 which are in contact with acorresponding slip-ring 243 arranged on the outer surface of the outer shaft 47 of the outer rotor 3 for transmitting power to the outer rotor 3. The slip-ring assembly 240 is arranged in a top part 221 of a slip-ring housing of the slip-ring unit 9. Due to abrasion of the brushing means 242 sliding at the slip-rings 243, carbon dust is generated inside the slip ring housing. To prevent the carbon dust from escaping the slip-ring housing, seals 245 at both end of the slip-ring assembly 240 are provided which seal the air inside the slip-ring unit 19 from the air outside of the slip-ring unit 19. The seals 245 are arranged at the slip-ring housing and are pressed against the outer surface of outer rotor 3 to seal the area between the outer rotor 3 and the slip-ring housing. In particular, the seals 245 are pressed against the NDE outer shaft 47 of the outer rotor 3. According to embodiments, the slip-rings 243 can be mounted on a sleeve layer included at the outer surface of the outer shaft 47, wherein the seals 245 are pressed against the sleeve layer of the outer shaft 47 to seal the air within the slip-ring unit 19 from the air outside the slip-ring unit 19. Cooling air enters the slip-ring unit 19 via an inflow filter unit 235. The inflowfilter unit 235 is configured to filter the air of the cooling air to prevent dirt, or dust, like oil particle, entering the slip-ring unit 19.

[0047] In Fig. 5, a part of a marine propulsion unit as described herein, is schematically shown. Particularly, a bearing unit 40 is shown including a bearing arrangement 401 and a bearing housing 407. Typically, the bearing housing may at least partly be filled with a lubricant, such as oil. In some embodiments, the bearing(s) of the bearing arrangement 401 are lubricated, such as oil lubricated. The bearing arrangement 401 includes bearings 402 -406 for supporting both the inner shaft 48 and the outer shaft 47 of the drive shaft. Typically, the outer shaft 47 may include a flange 471, especially at the end of the outer shaft 47. In some embodiments, the NDE side of the outer shaft may be the part of the outer shaft to be supported by the bearing arrangement. In some embodiments, the outer shaft 47 may have a substantially L-like shape for providing the flange 471 at the end of the outer shaft 47. According to some embodiments, the inner shaft 48 may include a flange 481 extending from the inner shaft 48. In some embodiments, the NDE side of the inner shaft may be the part of the inner shaft to be supported by the bearing arrangement. In some embodiments, the flange 471 of the outer shaft 47 and / or the flange 481 of the inner shaft 48 may be integrally formed with the rest of the respective shaft. Alternatively, or additionally, the flange 471 and / or the flange 481 may be connected to the rest of the respective outer shaft,e.g. by screws, bolts, mortise joints, some kind of tongue and groove arrangement, or the like.

[0048] According to some embodiments, the flange 471 of the outer shaft 47 and / or the flange 481 of the inner shaft 48 may extend from the surface of the part of the respective shaft, which runs substantially parallel to the rotation axis, from about 100 mm to about 400 mm, more typically from about 150 mm to about 350 mm, and even more typically from about 200 mm to about 300mm in radial direction. Typically, the extension of the flange 471 of the outer shaft 47 and / or the flange 481 of the inner shaft 48 in axial direction may be between about 50 mm to about 400 mm, more typically between about 100 mm and about 350 mm, and even more typically between about 150 mm and about 300 mm. According to some embodiments, the flanges 471 and 481 may be arranged and configured with respect to each other for enabling the montage of two shafts and / or for enabling the montage of the common axial bearing at one of the flanges, e.g. by one flange extending the other flange slightly in radial direction.

[0049] Typically, the bearing unit 40 is adapted and configured for supporting the flange 471 of the outer shaft 47 and the flange 481 of the inner shaft 48.

[0050] The bearing unit 40 includes a bearing arrangement 401 including bearings for supporting the inner shaft 48 and the outer shaft 47. In some embodiments, the bearings of the bearing arrangement 401 are configured and placed for supporting the inner shaft 48 and the outer shaft 47 by supporting the flange 481 of the inner shaft 48 and the flange 471 of the outer flange 47. An oil seal 430 may be located between shaft flanges 481 and 471. According to embodiments described herein, the bearing arrangement 401 may include one or more axial bearings 402, 403, 404 for the inner shaft 48 and the outer shaft 47. According to some embodiments, which may be combined with other embodiments described herein, the bearing arrangement 401 may include radial bearings 405, 406 for the inner shaft 48 and the outer shaft 47 of the marine propulsion unit.

Claims

CLAIMS1. A marine propulsion unit (2000) comprising:a dual rotor electric motor (1) having an inner rotor and an outer rotor;a contra rotating propeller having an inner shaft propeller (10) and an outer shaft propeller (9);a drive shaft (2500) having an inner shaft connecting the inner rotor to the inner shaft propeller and an outer shaft connecting the outer rotor to the outer shaft propeller; anda slip-ring unit (19) for transmitting an electric current to the dual rotor electric motor.

2. The marine propulsion unit of claim 1, wherein a non-drive end, NDE, thrust bearing (41, 42) supporting the drive shaft comprises a slide bearing.

3. The marine propulsion unit of claim 2, wherein the NDE thrust bearing is arranged separately from the dual rotor electric motor.

4. The marine propulsion unit of any of the preceding claims, wherein the dual rotor electric motor has a rated electric power of at least 200 kW.

5. The marine propulsion unit of any of the preceding claims, wherein a torque of the dual rotor electric motor is transmitted to the contra rotating propeller without a gearbox.

6. The marine propulsion unit of any of the preceding claims, wherein the slip-ring unit is arranged within a slip-ring unit housing separate from the dual rotor electric motor.

7. The marine propulsion unit of any of the preceding claims, wherein the slip-ring unit is cooled using a slip-ring cooling system independent of a cooling air system (16) for cooling the dual rotor electric motor.

8. The marine propulsion unit of claim 7, wherein the slip-ring cooling system is connectable to a low temperature liquid cooling medium vessel cooling system.

9. The marine propulsion unit of claim 8, wherein the low temperature liquid cooling medium vessel cooling system is a low temperature water vessel cooling system.

10. The marine propulsion unit of any of the preceding claims, wherein the marine propulsion unit comprises at least one shaft coupling (2510, 2520).

11. The marine propulsion unit of claim 10, wherein the at least one shaft coupling is arranged for removably separating the drive shaft between the contra rotating propeller and the dual rotor electric motor.

12. The marine propulsion unit of any of the preceding claims, wherein a rotating part of the slip-ring unit is connected to the outer rotor of dual rotor electric motor with a dismountable connection.

13. The marine propulsion unit of any of the preceding claims, wherein an axial distance of a motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at least two times an axial length of the dual rotor electric motor.

14. The marine propulsion unit of any of the preceding claims, further comprising at least one support bearing (45, 46) for supporting the drive shaft between a propeller bearing (2530) and a drive end, DE, bearing.

15. A marine vessel comprising a marine propulsion unit according to any of the preceding claims.

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