Propulsion unit and propulsion system for a ship

Abstract

The invention relates to a propulsion unit for a propulsion system of a ship. The propulsion unit comprises a rotatable lower housing, a steering section arranged on top of the lower housing, a propeller shaft, torque transmission means coupled to the propeller shaft, and a coupling assembly comprising a flexible coupling and an intermediate coupling. The intermediate coupling is fixedly attached to the flexible coupling, one of the flexible coupling or the intermediate coupling directly connected and rotationally fixed to the torque transmission means and the other one configured to be rotationally fixed to a shaft of a motor of the propulsion system. The torque transmission means, the flexible coupling and the intermediate coupling are configured to be substantially aligned along a common vertical axis when in use. The flexible coupling is configured to compensate for misalignment between the motor shaft and the torque transmission means. The invention further relates to a propulsion system comprising such propulsion unit.

Description

[0001] Propulsion unit and propulsion system for a ship

[0002] Technical field of the invention

[0003] The present invention concerns a propulsion unit for a propulsion system of a ship. More specifically, the invention concerns a propulsion unit comprising a specific arrangement of torque transmission means and a coupling assembly. The invention further concerns a propulsion system.

[0004] Background of the invention

[0005] Propulsion systems are an essential part of a ship and comprise at least an engine or a motor connected to a propeller shaft. In pod-type propulsion systems, the propeller shaft may be located partially within a lower housing attached to below the hull of the ship. The lower housing may be rotatable around a vertical axis to allow steering of the ship.

[0006] A critical aspect of the functionality and reliability of propulsion systems is the lubrication and protection of internal moving parts. The components, such as bearings, gears, pinions, and the propeller shaft, are subject to significant mechanical stresses and require continuous lubrication to minimize friction and wear. In some solutions, the lower housing is filled with oil, which serves as a lubricant and a coolant. The oil ensures smooth operation, reduces the risk of overheating, and provides a protective barrier against corrosion by seawater.

[0007] Some components, however, cannot be placed in oil and thus in some known propulsion units, an oil-free compartment between a steering section and the motor may be provided to house various bearings and couplings. Such compartment is typically kept free of oil, while the lower housing may be filled with oil. A problem with known propulsion units is the large total height of the propulsion unit, especially inside the hull of the ship. A further problem is the large total height of the machine room in which a portion of the propulsion unit is located. The machine room height may be further limited by the lifting height needed to lift a portion of the propulsion unit to access other parts during maintenance. Some ship types, such as tugs and cargo vessels, especially benefit from reduction in machine-room height. Another problem of the known propulsion units is the recurring need for maintenance of the bearings and couplings located in the compartment between the steering section and the motor. As the lower housing is intended to operate in seawater environment, the integrity of the oil-filled environment within the lower housing is paramount. Any breach or failure in the sealing system can lead to oil leakage and / or seawater entering the propulsion system, which not only compromises the lubrication of critical components but also poses environmental hazards and affects the overall performance of the propulsion system. Consequently, effective monitoring and maintenance strategies are needed to detect and address leaks promptly. Monitoring of leaks in the lower housing is especially important in rotatable lower housing propulsion systems as moving parts may lead to more wear and require more seals. The access for maintenance, however, is challenging and often requires significant amount of costs and time due to many heavy and fixed parts.

[0008] Summary of the invention

[0009] An object of the invention is to provide for a propulsion system of a ship a propulsion unit that solves at least some of the problems of prior art propulsion systems. Another object of the invention is to provide a propulsion system comprising such propulsion unit. An aim of this invention is to reduce the height of the propulsion unit and especially the height of the propulsion unit inside the hull of the ship. A further aim may be to enable reduction of the required height of the machine room in which a portion of the propulsion unit is located. The invention is defined in the independent claims.

[0010] The propulsion unit according to the invention comprises a rotatable lower housing, a steering section arranged on top of the lower housing, a propeller shaft arranged at least partially inside the lower housing, torque transmission means arranged at least substantially inside the lower housing and coupled to the propeller shaft so as to transfer rotational motion to the propeller shaft, and a coupling assembly comprising a flexible coupling and an intermediate coupling, the intermediate coupling being fixedly attached to the flexible coupling, one of the flexible coupling or the intermediate coupling being directly connected and rotationally fixed to the torque transmission means and the other one being configured to be rotationally fixed to a shaft of a motor of the propulsion system. The torque transmission means, the flexible coupling and the intermediate coupling are configured to be substantially aligned along a common vertical axis when in use. The flexible coupling is configured to compensate for misalignment between the motor shaft and the torque transmission means. The flexible coupling and / or the intermediate coupling may be arranged fully or partially, such as substantially, within the steering section, which may reduce the height of the propulsion unit or system inside the hull of the ship, which may thus allow to reduce the height of the machine room in which part of the propulsion unit or system is located. Immersing the flexible coupling in oil may reduce the maintenance needs. Providing the propulsion unit with both the flexible coupling and the intermediate coupling enables an improved construction of the powertrain that is robust, has an improved misalignment compensation, and may simplify maintenance tasks.

[0011] Preferably, the flexible coupling is directly connected and rotationally fixed to the torque transmission means, while the intermediate coupling is configured to be rotationally fixed to the motor shaft to further simplify maintenance tasks and allow reduction to the machine room height. In this configuration only the motor shaft and a portion of the intermediate coupling needs to be lifted in order to move motor away from the propulsion unit, hence reducing the total height and weight of the liftable portion compared to if the intermediate coupling and the flexible coupling were connected the other way around, as then the whole flexible coupling as well as a portion of the intermediate coupling would have to be lifted. Moreover, such configuration with intermediate coupling connected to the motor shaft allows to split the motor from the flexible coupling unit, making assembly and disassembly easier as it can be done in smaller parts.

[0012] Functionally, the steering section may be defined as a link between the moving parts, such as the rotatable lower housing, and the stationary parts of the propulsion system.

[0013] The steering section may comprise a rotatable steering pipe configured to be fixedly attached to a rotatable lower housing of the propulsion system and rotationally mounted to a stationary portion of the propulsion system, and a seal housing configured to be fixedly mounted to a stationary portion of the propulsion system and arranged to surround and be in contact with the rotatable steering pipe. The steering pipe may thus be rotatable relative to the seal housing. The steering section may be configured to allow efficient oil supply into and leak monitoring for the rotatable lower housing through the same side of a steering section via the fixed seal housing and the rotatable steering pipe. This may contribute to a more compact construction and may provide easier assembly, access, and / or maintenance. Moreover, such construction allows to locate any monitoring and / or oil supply and / or return pump-sets nearby each other, on the same side of the propulsion system, thus enabling shorter routing of pipes and thus reducing loss of flows.

[0014] One way to configure the steering section for oil supply and leak monitoring is by providing the seal housing with a plurality of grooves perpendicular to the rotation axis of the steering pipe. In such configuration, the grooves are provided into the inner surface of the seal housing facing the outer surface of the steering pipe. At least one of the grooves is configured to form a portion of an oil supply channel for guiding oil at least between the outer surface of the seal housing and the inner surface of the steering pipe and at least one of the other grooves is configured to form a portion of a monitoring channel configured to guide fluids, such as sea water, oil and / or flush fluid, in case of a leak. In such configuration, the seal housing may further be provided with a plurality of connection ports, each connection port connecting the outer surface of the seal housing to one of the plurality of grooves. Additionally, the seal housing may be further provided with a plurality of bores extending from the outer surface of the steering pipe facing the seal housing to the opposite inner surface of the steering pipe with each bore being aligned with any one groove of the plurality of grooves.

[0015] Function of the flexible coupling may be defined as coupling a propeller shaft of the propulsion system with a motor of the propulsion system.

[0016] The lower housing may comprise a pod for housing a propeller shaft, and a strut connecting the pod to the steering section.

[0017] The flexible coupling may be an oil-resistant, such as a full-steel, coupling.

[0018] The flexible coupling may comprise through holes for allowing oil flow. Such through holes may allow oil flow into the inside of the flexible coupling, thus lubricating inner parts of the flexible coupling and of the intermediate coupling.

[0019] The coupling assembly and the torque transmission means may be configured to be immersed in oil. The coupling assembly, or at least the flexible coupling may alternatively be lubricated by feeding oil through a lubrication channel, such as passing through the motor shaft. The steering section may be configured to be filled with oil. Filling with oil may provide lubrication and cooling for moving parts such as bearings and couplings.

[0020] The torque transmission means may be a pinion shaft comprising a shaft and a pinion gear manufactured as a single, monolithic piece of material. Using a monolithic pinion shaft simplifies construction, reduces the number of moving parts and thus the need for maintenance and may also reduce the total height of the torque transmission means.

[0021] The torque transmission means may be directly coupled to a gear-unit of the propeller shaft. This further contributes to the simplicity of the construction, reduced maintenance and / or possibly reduced total height between the flexible coupling and the propeller shaft.

[0022] The torque transmission means may be connected to the flexible coupling or the intermediate coupling by a spline connection, keyway connection, shrink fitting, or conical fitting.

[0023] The intermediate coupling may comprise a curved toothed coupling and a curved toothed casing, wherein the curved toothed coupling is configured to be directly and fixedly connected to the shaft of the motor or to the torque transmission means and comprises teeth on the outer surface that are rotationally fixed to teeth on the inner surface of the curved toothed casing, said curved toothed casing fixedly attached to the flexible coupling. Providing the intermediate coupling in an arrangement of the curved toothed casing and a curved toothed coupling enables easy maintenance, e.g., of the steering section and the flexible coupling as the motor shaft with the curved toothed coupling may be simply lifted as the curved toothed coupling can move axially with respect to the curved toothed casing. Such arrangement may reduce the number, length and / or weight of parts that must be lifted or disassembled to access the steering section and / or the lower housing.

[0024] The curved toothed coupling may be tiltable relative to the vertical axis to compensate for misalignment between the motor shaft and the torque transmission means and / or to dampen vibrations.

[0025] The flexible coupling may comprise a housing and a hub flexibly coupled to the housing of the flexible coupling. Flexibly coupled means that some relative motion between the housing and the hub is permitted to reduce vibrations and accommodate misalignments, while allowing torque transmission through the flexible coupling. Such arrangement of the flexible coupling into a housing and a hub may contribute to improved vibration dampening and misalignment compensation. The hub may be a grooved hub configured to receive spring plates into the grooves, such hub may also be referred to as an innerstar.

[0026] In current application, fixedly attached and rotationally fixed are intended to mean fixedly attached or rotationally fixed to at least a part of an object, if not necessarily the whole object. Hence, although the housing is flexibly coupled to the hub, the flexible coupling may be considered rotationally fixed to another part, such as the motor shaft or the torque transmission means, if said part is rotationally fixed to the housing or the hub.

[0027] The hub of the flexible coupling may be tiltable relative to the vertical axis to compensate for misalignment between the motor shaft and the torque transmission means and / or to dampen vibrations.

[0028] The housing of the flexible coupling may comprise a spherical stud on which the hub rests for adjusting angular misalignment.

[0029] The propulsion unit may further comprise an isolation flange to electrically isolate flexible coupling from the intermediate coupling and the motor shaft.

[0030] The propulsion unit and / or system may further comprise a braking device for slowing down, stopping, and / or preventing the rotation of the propeller shaft. Preferably, the braking device is a holding brake for preventing or blocking rotation of the propeller, which may, e.g., be forced to rotate by hydrostatic forces, the effect referred to as windmilling. The braking device may be automatically engageable when the propulsion unit is not in operation to prevent propeller windmilling. The braking device may be a disc brake. The braking device is preferably located at the non-driving end of the motor shaft. Alternatively, the braking device may be located inside the lower housing or the steering section by creating a dry space around the braking device or utilizing an enclosed braking device.

[0031] The propulsion unit may comprise at least one bearing arranged around the torque transmission means at least half-way or closer to the coupling assembly from the propeller shaft. The propulsion unit may comprise at least two bearings arranged around the torque transmission means. The one or more bearings may support the weight of the torque transmission means and / or flexible coupling thus improving robustness and stability.

[0032] The propulsion system according to the invention comprises the propulsion unit as described above and a motor with a shaft. The motor is arranged directly on top of the steering section and the shaft of the motor is rotationally fixed to the intermediate coupling or the flexible coupling. The motor may be an electric motor. The motor shaft may be partially received into the steering section.

[0033] The propulsion system may further comprise a propeller fixedly mounted to the propeller shaft outside the lower housing.

[0034] Brief description of the drawings

[0035] Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

[0036] Fig. 1 shows a three-dimensional sectional view as well as front and side two- dimensional cross-section views of a propulsion system of a ship according to an embodiment of the invention,

[0037] Fig. 2 shows two-dimensional side and perpendicular cross-sectional views of a portion of a steering section for a propulsion system of a ship,

[0038] Fig. 3 shows a three-dimensional sectional view and a two-dimensional crosssection of a steering section according to an embodiment of the invention,

[0039] Fig. 4 shows a sectional view of a portion of a steering section,

[0040] Fig. 5 shows a sectional view of a portion of a steering section,

[0041] Fig. 6 shows a top view of a portion of a steering section,

[0042] Fig. 7 shows a three-dimensional view, a sectional view and an insert of a steering pipe of a steering section, and

[0043] Fig. 8 shows a flowchart of the method according to the invention. Detailed of embodiments of the invention

[0044] Fig. 1 shows a propulsion system 300 of a ship according to an embodiment of the invention. The propulsion system produces thrust force for a ship. The ship can be any kind of a ship, such as a ferry, tug or anchor handler, trawler, dredger, general cargo vessel, or frigate or other naval vessel. For clarity, a three-dimensional view, a front cross-section, and a side cross-section are show in Figs. 1A, 1 B, and 1 C respectively as well as an enlarged view of the propulsion system around the flexible coupling 160 in Fig. 1 D.

[0045] The propulsion system 300 comprises a propulsion unit 200 and a motor 301 located above, preferably directly above, the propulsion unit. Preferably, the motor 301 is an electric motor, which may be beneficial for environment and provide a reduced carbon footprint. The propulsion unit comprises a rotatable lower housing 201 , a propeller shaft 202 arranged at least partially inside the lower housing 201 , optionally a propeller 203 fixedly mounted to the propeller shaft outside the lower housing and thus rotating together with the propeller shaft, and torque transmission means 204, such as a pinion shaft or an intermediate shaft integrated with a pinion wheel, arranged at least partially, such as substantially, inside the lower housing and arranged to be at a perpendicular angle, as shown in Fig. 1 , or tilted away from perpendicular, such as making an angle below or above 90 degrees to the propeller shaft. The propulsion unit, shown in the figures, further comprises a steering section 100 comprising at least a steering pipe 101 and a seal housing 102. The motor 301 is shown arranged directly on top of the steering section 100, e.g. on a top plate 170 of the steering section.

[0046] The rotating motion of the motor 301 in Fig. 1 is configured to be transmitted to the propeller 203 by means of at least a propeller shaft 202, torque transmission means 204 and a flexible coupling 160. The propeller shaft may comprise a gear-unit 204a for coupling propeller shaft to the torque transmission means 204. Fig. 1 D illustrates that the flexible coupling may comprise a housing 160a and a hub 160b and the flexible coupling may be fixedly connected to the torque transmission means 204 by a spline connection 204b. Other connection types such as keyway connection, shrink fitting, conical fitting, or others may also be used. The propulsion system of Fig. 1 D further comprises an intermediate coupling 161a, 161 b fixedly attached to the flexible coupling. Together, the flexible coupling and the intermediate coupling may be said to make a coupling assembly, i.e. , the coupling assembly comprises the flexible coupling and the intermediate coupling. The intermediate coupling in Fig. 1 D is rotationally fixed to a shaft 301 a of the motor 301 of the propulsion system 300. The torque transmission means, the flexible coupling and the intermediate coupling are configured to be substantially aligned along a common vertical axis when in use, and the flexible coupling is configured to compensate for misalignment between the motor shaft and the torque transmission means. While not shown in the figures, the coupling assembly can be installed in the system in a configuration rotated by 180 degrees. In such case, the flexible coupling 160 would be rotationally fixed to the motor shaft 301a, while the intermediate coupling 161 would be directly connected and rotationally fixed to the torque transmission means 204. The fixing of the flexible coupling and / or the intermediate coupling to the motor shaft and / or the torque transmission means may be achieved, for example by a spline connection 204b, keyway connection, shrink fitting, conical fitting, or other known means.

[0047] The flexible coupling may thus couple torque transmission means to the motor via the intermediate coupling placed on top of (as shown in Fig. 1 ) or below the flexible coupling for correcting any misalignments. The flexible coupling may reduce or eliminate any unwanted torque-difference between the motor and the propeller. The torque transmission means may comprise additional intermediate shafts. The flexible coupling 160 may be coupled to the motors’ shaft 301a directly via the intermediate coupling, or via additional shafts. Transmission of rotational motion from the motor to the propeller shaft and thus propeller may comprise a different arrangement of shafts and gearboxes as would be known by a skilled person.

[0048] The flexible coupling 160 may be a torsional vibration damper or a coupling comprising springs or rubber coupling parts. As shown in Fig. 1 D, the flexible coupling comprises a housing 160a and a hub 160b flexibly coupled to the housing of the flexible coupling. Flexible coupling 160 is preferably an oil-resistant coupling, such as a full steel coupling, configured to be immersed in oil thus providing lubrication, cooling and reducing the need for recurring maintenance. As the lower housing 201 is configured to be filled with oil in order to lubricate and cool the propeller shaft 202 and any other moving parts within the lower housing, the steering section 100 may also be filled with oil via an oil supply channel. Preferably, the whole steering section is filled with oil, both inside of the steering pipe as well as the space surrounding the seal housing, thus providing lubrication to all the moving parts, such as, e.g., slewing bearing and any gears located on the outside of the slewing bearing. The flexible coupling 160 may thus be arranged inside the steering section 100 to be surrounded by the steering pipe 101 and immersed in oil. The flexible coupling may, however, extend into the lower housing. The flexible coupling may comprise through holes for allowing oil flow (not shown) through the flexible coupling, thus also inner parts of the flexible coupling hub as well as curved toothed coupling and casing may all be immersed in and lubricated by the oil. Such arrangement enables reduction of the total height of the propulsion system 300. As the steering section 100 and the motor 301 are arranged inside the hull of the ship, such arrangement of the flexible coupling within the steering section may further save space inside the hull.

[0049] The intermediate coupling 161 is shown in Fig. 1 D to comprise a curved toothed coupling 161 a and a curved toothed casing 161 b. The curved toothed coupling is directly and fixedly connected to the shaft of the motor, such as by shrink fitting, although in the inverted configuration as mentioned before, the curved toothed coupling may be fixedly connected to the torque transmission means. The curved toothed coupling comprises teeth on the outer surface that are rotationally fixed to the teeth on the inner surface of the curved toothed casing. Curved toothed casing is fixedly attached to the flexible coupling, such as by bolts, as seen in Fig. 1 D. Similar to the flexible coupling, the intermediate coupling may be configured to be immersed in oil. Also, the intermediate coupling may be arranged fully inside the steering section or extend at least partially into the lower housing.

[0050] To compensate for misalignment between the motor shaft and the torque transmission means and / or to dampen vibrations, the curved toothed coupling and / or the hub of the flexible coupling may be tiltable relative to the vertical axis. Moreover, the housing of the flexible coupling may comprise (not shown) a spherical stud on which the hub may rest for adjusting angular misalignment. Fig. 1 D further shows an isolation flange 162 between the intermediate coupling and the flexible coupling to electrically isolate the flexible coupling from the intermediate coupling and the motor shaft.

[0051] The torque transmission means 204 is shown in Fig. 1 as a pinion shaft comprising a shaft and a pinion gear manufactured as a single, monolithic piece of material and directly coupled to the gear-unit 204a of the propeller shaft.

[0052] Figs.1 A-D further illustrate that the propulsion unit may comprise two bearings 205, 206. Preferably, at least one, a first, bearing is present, such as the bearing 205 arranged around the torque transmission means 204 at least half-way or closer to the coupling assembly from the propeller shaft. The first bearing may be axial support bearing. Preferably, there is a second bearing 206 arranged around the torque transmission means, the second bearing being closer to the propeller shaft than the first bearing. The second bearing may be a radial bearing of the torque transmission means. Additional bearings may be provided to support the propeller shaft.

[0053] Although not shown in the figures, the propulsion unit may comprise a braking device for slowing down, stopping, and / or preventing the rotation of the propeller shaft. The braking device may be arranged anywhere along the powertrain, i.e., inside the lower housing, inside the steering section or inside the motor 301 , but preferably on the non-driving end of the motor shaft 301a to avoid customization for the braking device inside the oil filled spaces.

[0054] According to the invention, both oil supply to the lower housing and leak monitoring may be achieved through the steering section 100. More specifically, oil supply and monitoring may be carried out through the seal housing 102 and the steering pipe 101 of the steering section 100 as will be described below in connection to different views of a steering section and its parts in Figs. 2-7.

[0055] Oil supply and / or monitoring channels from the seal housing 102 to outside of the steering section 100 may be further provided by a plurality of conduits 130 as shown in Fig. 1 A as well as Figs. 4 and 6. In the embodiment of Fig. 1 , the steering section 100 further comprises a connection hub 131 integrated into or onto the stationary portion of the steering section 100, such as the top plate 170. The plurality of conduits 130 connect the connection hub and the seal housing, whereas the connection hub may be configured to be further connected to external lines, such as oil supply or monitoring lines. Connection hub, however, is not necessary, and the conduits may connect the seal housing to a different part of the propulsion system or an external component.

[0056] Oil supply and / or monitoring channels from the steering pipe 101 towards the lower housing 201 may be further provided by a plurality of pipes 110a, 110b, 210, as illustrated in Figs. 1 , 3, 5, and 6. As shown in Fig. 1 , the lower housing 201 may comprise a plurality of pipes 210 for guiding fluid flow for oil supply and / or leak monitoring. The pipes 210 are fixedly attached to the lower housing and extend to the lower part of the lower housing 201. The pipes 210 may extend from the steering section 101 . However, as shown in Fig. 3, the steering section may further comprise another set of pipes 110a, 110b extending from the steering pipe 101 towards the pipes 210 and / or towards a connection block 120 if present. A pipe for oil supply may extend to the bottom portion of the lower housing, such as below the propeller shaft. Such oil pipe may be beneficial for homogenous filling of the lower housing as well as easier drainage when needed. However, such oil pipe may also be omitted, in which case oil may be supplied directly from the steering pipe 101 into the steering section and the lower housing. The propeller shaft 202 may comprise a propeller shaft seal 202a configured to isolate the lower housing internal space from the seawater surrounding the lower housing. A number of monitoring pipes may extend to a monitoring void arranged in proximity of a propeller shaft 202 for monitoring propeller shaft seal 202a leakage.

[0057] The steering pipe 101 of Fig. 1 is fixedly attached to and thus rotatable with the rotatable lower housing 201 while being rotationally mounted, such as via a slewing bearing 173 and optionally further parts (see Fig. 3 for more details), to a stationary portion of the propulsion system, such as a top plate 170 of the steering section 100. The seal housing 102 is fixedly mounted to a stationary portion of the propulsion system, such as a flange 174. Figures 2-7 show different views and parts of the steering section 100 as discussed below.

[0058] A two-dimensional cross-section of the steering section 100 according to an embodiment of the invention is shown in Fig. 2A. The steering section 100 comprises a rotatable steering pipe 101 surrounded by and in contact with a seal housing 102. The steering pipe is configured to be fixedly attached to a rotatable lower housing 201 of the propulsion system 300 and to be rotationally mounted to a stationary portion of the propulsion system as illustrated in Fig. 1 . The steering pipe is thus configured to be rotatable together with the lower housing. The seal housing is configured to be fixedly mounted to a stationary portion of the propulsion system and thus configured to be stationary relative to the hull of the ship. The steering pipe is thus configured to be rotatable relative to the seal housing, which makes transfer of fluids, such as oil or sea water, through the seal housing and the steering pipe difficult.

[0059] The difficulty is overcome by providing the seal housing 102 with a plurality of grooves 103 perpendicular to the rotation axis 101 c of the steering pipe, providing the seal housing 102 with a plurality of connection ports 104, providing the steering pipe with a plurality of bores 105 and configuring said grooves, connection ports and bores to form at least one oil supply channel and at least one leak monitoring channel, said channels configured to guide fluids, such as oil, seawater and / or flushing fluids, through the steering pipe and seal housing.

[0060] The grooves are provided into the inner surface 102b of the seal housing, the inner surface 102b facing the outer surface 101 a of the steering pipe. Preferably, the grooves are continuous around the inner perimeter of the seal housing, preferably running continuously around the entire perimeter of the inner surface 102b. The grooves are preferably circular. The grooves do not extend all the way to the outer surface 102a of the seal housing, instead each of the plurality of connection ports 104 connect the outer surface of the seal housing to one of the plurality of grooves 103. The path through the seal housing and the steering pipe is completed by the plurality of bores 105 extending through the steering pipe, i.e. from the outer surface 101 a of the steering pipe facing the seal housing 102 to the opposite inner surface 101 b of the steering pipe. Each bore is aligned with any one groove, preferably a different one, of the plurality of grooves so as to form a channel enabling flow of fluids through the steering pipe and the seal housing. The seal housing may be made of bronze.

[0061] At least one of the grooves, such as the top larger groove in Fig. 2A, is configured to form a portion of an oil supply channel for guiding oil at least between the outer surface of the seal housing and the inner surface of the steering pipe. The oil supply channel is formed by an aligned set of a connection port, a groove and a bore referred to in short as an oil connection port, oil groove and oil bore. There may be more than one, such as two or more, oil supply channels and thus also a corresponding number, such as two or more, of each of connection ports, grooves and bores forming such oil supply channels. Fig. 2A illustrates four monitoring channels configured to guide fluids, such as sea water, oil and / or flush fluid, in case of a leak. Monitoring may be performed by a sensor detecting presence of seawater and / or oil. A monitoring unit for processing of the monitoring data may be located above the steering section and may comprise a sensor. Three of the shown monitoring channels are formed by an aligned set of a connection port, a groove and a bore, in short referred to as a monitoring connection port, groove and bore respectively, whereas one monitoring channel is formed by an aligned set of a connection port and a groove but without a bore. A monitoring channel thus may or may not comprise a bore and thus may connect the outer surface of the seal housing to the groove for monitoring, e.g., of seal housing seals 140 and optionally further to the inner surface of the steering pipe for monitoring of, e.g., propeller shaft seals 202a. The steering section comprises at least one, but may comprise any number, such as 2-10, preferably 2-5, monitoring channels. Preferably, the steering section 100 comprises at least one monitoring channel for monitoring leaks at the seal housing seals 140 and at least one monitoring channel for monitoring leaks at a propeller shaft seal 202a of the propulsion system. The number of connection ports 104 may be the same as or, as illustrated in Fig. 2A, higher than the number of the grooves. The number of bores 105, may be the same or less or higher than the number of the grooves 103.

[0062] It should be noted that while Fig. 2A illustrates all the bores and connection ports visible at a single cross section, this choice was made for simplicity and the arrangement of the bores and connection ports does not have to be such. Preferably the bores and / or the connection ports are radially offset for space optimisation and access convenience as seen in Figs. 3-7.

[0063] It should further be noted that Fig. 2A illustrates the moment when the bores are aligned with the connection ports within the plane of the cross-section. A bore and a connection port, however, are essentially through-holes, preferably cylindrical as seen in Figs. 2-7, although other shapes are possible. Fig. 2B illustrates a perpendicular cross-section along the plane marked by l-l lines in Fig. 2A along one of the monitoring channels. Fig. 2A itself is a cross section along the ll-ll line of Fig. 2B. Fig. 2B shows the monitoring channel forming a path for fluid flow through the steering pipe and the seal housing. From Fig. 2B one can understand that once the steering pipe 101 rotates, the bore 105 and the connection port 104 will not anymore be aligned, however, the monitoring channel will still allow the flow of fluids as the groove 103 always connects the respective connection port and bore.

[0064] Steering section of Figs. 2-6 further comprises a plurality of seals 140 on the inner surface 102b of the seal housing 102 configured to prevent flow of fluids from and / or into the grooves 103 in a direction along the rotation axis of the steering pipe 101 . Each seal may comprise a face seal arranged into a recess on the inner surface of the seal housing. At least a portion of the seals of the seal package are in contact with the steering pipe. There is at least one seal 140 above and at least one seal 140 below each groove 103. Figs. 2-6 illustrate nine seals with two seals located below the lowest located groove 103, three seals located above the top groove 103, and the remaining seals being arranged each between any two adjacent grooves. The number of seals below and / or above any groove may be different. A benefit of having at least two seals below the lowest groove is to provide backup in case the lowest located seal wears out as the lowest seal is configured to be exposed to seawater, which deteriorates the seal. A benefit of having at least three seals above the top groove is to provide spare seals for easier and quicker maintenance. The second and all higher seals above the topmost groove may thus be referred to as spare seals. Figs. 2-6 thus illustrate two spare seals, but a different number, such as one, three or more may be provided.

[0065] The seal housing 102 may be configured to be movable along a vertical direction, i.e. along the rotational ais 101 c of the steering pipe, for seal inspection and / or replacement. Procedure for seal replacement may comprise raising at least a part of the lower housing 201 above water, draining the steering section 100 from oil, detaching the seal housing 102 or a flange 174 to which the seal housing may be attached, from the steering section and lowering the seal housing 102 and optionally the flange 174 until the conduits 130 on the outside of the seal housing can be accessed. The conduits are then disconnected, and the seal housing lowered further until the seals 140 become accessible for exchanging. During seal exchange, an old seal may be cut and one of the spare seals may be relocated from its current location to the location of the removed old seal. The presence of prepared spare seals allows for a quicker and easier as well as cheaper seal replacement without needing to fully empty oil from the lower housing and without disassembling the steering section from the lower housing. Without the prepositioned spare seals, the propulsion system would need to be opened for introducing a continuous seal in the inner perimeter of the seal housing.

[0066] Fig. 3A illustrates a three-dimensional cross section of the steering section 100 showing the seal housing 102 comprising a plurality of grooves 102 and a plurality of seals 140 and the steering pipe 101 as described earlier. In addition, Fig. 3 illustrates that the steering section 100 may comprise a top plate 170 that is stationary with respect to the hull of the ship. The steering pipe 101 may be rotationally mounted to the top plate 170 via a slewing bearing 173, attachment plate 171 , and attachment means 172. Other rotational mounting arrangements are possible as would be understood by a person skilled in the art. For clarity, Fig. 3B shows a two-dimensional cross section view of a steering section 100 according to an embodiment of the invention.

[0067] Figs. 3, 5, and 6 illustrate that the steering section may comprise a plurality of pipes 110a, 110b connected to the plurality of bores 100 and extending toward or into the lower housing 201 of the propulsion system 300. At least part of the pipes 110a, 110b, such as the pipe for suppling oil 110a, may extend substantially to the bottom of the lower housing, such as below the propeller shaft 202. Each pipe 101 is connected to a different bore 105. Not all bores need to be connected to a pipe, e.g., the bore for oil supply may be left open into the inner part of the steering pipe. Instead of the steering section 100 comprising the pipes 110a, 110b, the bores 105 may be configured to be connected to such plurality of pipes. The pipes 110a, 110b may be provided separately, such as provided later, or provided as part of the lower housing 201 . Fig. 5 illustrates how a monitoring pipe 110b is connected to a groove 103 via a bore 105.

[0068] Figs. 3 and 6 further show that a steering section 100 may comprise a connection block or junction block 120 attached to the inner surface 102b of the steering pipe. The steering section or the lower housing may comprise a first plurality of pipes 110a, 110b connected between the plurality of bores 105 and the connection block 120. The connection block 120 may be configured to be connected to a second plurality of pipes 210 (see Fig. 1 ) extending into the lower housing of the propulsion system. The second plurality of pipes 210 may be part of the lower housing 201 . The lower housing 201 may further comprise a second connection block attached to the lower housing and configured to be connected to the connection block 120 of the steering section and / or to the first 110a, 110b and / or second 210 plurality of pipes. Fig. 4 illustrates how a conduit 130 connects to a groove 103 via a connection port 104. Each conduit 130 of the steering section 100 should connect to one of the connection ports 104 of the seal housing 102. Multiple conduits 130 and thus multiple corresponding connection ports 104 can, however, connect to one groove 103. This may be beneficial, for example, for providing a circular path for flushing at least the respective conduits, connection ports and groove. As mentioned earlier, the other end of each conduit may then be connected to external lines directly or via a connection hub 131 (see Fig. 1 ).

[0069] Fig. 6 provides a more detailed view of the conduits 130 labelled as 130a, 130b, and 130c, showing a top view of the steering section 100 comprising the seal housing 102 and the steering pipe 101 , with the conduits 130 connected to the seal housing 102 and the pipes 110a, 110b connected between the steering pipe 101 and the connection block 120. Steering section 100 of Fig. 6 may be the same as illustrated in Fig. 2. Steering section of Fig. 6 comprises one oil supply conduit 130a and five monitoring conduits 130b, 130c. The number of conduits 130 may be different, but preferably the same or more than the number of grooves 103. The group of three conduits 130b shown on the left is configured to monitor leaks at the propeller shaft seals 202a, one conduit being used for monitoring of leaking seawater and / or oil, while the other two conduits being used for flush and drain respectively, such as for cleaning the monitoring channels after a leak or for maintenance purposes. The group of three conduits 103b may be connected to the three connection ports 104 and the three grooves 103 shown in the middle of the seal housing 102 of Fig. 2A. The group of two conduits 130c shown at the bottom are configured to form part of the monitoring channels for monitoring leaks at the seal housing 102 seals 140 where during monitoring one of the conduits is used, whereas during flushing both conduits may be used to create a circular path for flushing and / or draining. The group of two conduits 130c may be connected to the two connection ports 104 aligned with the lowest groove 103 of the seal housing 102 as shown in Fig. 2A. The pipes 1 10a, 110b can be respectively also labelled as an oil supply pipe 110a and three monitoring pipes 110b.

[0070] The monitoring channels may be configured to be free of fluids, unless there is a leak or if a flush or drain of monitoring channel is being performed.

[0071] Fig. 7A shows an embodiment of the steering pipe 101 of the steering section 100 comprising bores 105. Fig. 7B shows a sectional view of the same steering pipe 101. Steering pipe 101 of Figs. 7A, B further comprises a plurality of inserts 150 arranged inside the bores 105. An enlarged view of such an insert is shown in Fig. 7C. The inserts 150 are preferably made of substantially low corrosion materials, such as Inconel. As can be seen in Fig. 7C, the insert may comprise a different, preferably larger, diameter towards the inner surface 101 b of the steering pipe for secure coupling of a pipe 110a, 110b inside the insert 150. Such inserts are especially needed if the steering pipe is made of a welding and / or cladding friendly and in-expensive material that may be not resistance to corrosion. The inserts may be pressed and / or welded inside the bores that are drilled in the steering pipe. Once the inserts are positioned, the outer surface 101a of the steering pipe may be machined or polished.

[0072] Steering pipe 101 may further comprise a cladding or any other layer 101 d on the outer surface 101a of the steering pipe 101 as shown in Fig. 7A. The cladding may be a laser cladding. The cladding layer may improve the longevity of the steering pipe and provide a wear-free and corrosion-free surface for the seals 140 to run on.

[0073] Figs. 7A and B further shows attachment holes 172a into which attachment means 172 shown in Fig. 5 may be inserted for fastening the steering pipe 101 to the attachment plate 171 . Other attachment means, however, are possible.

[0074] Fig. 8 illustrates the method 400 according to the invention for supplying 401 oil and monitoring 402 for leaks for a propulsion system 300 of a ship comprising a steering section 100 according to the invention. The method comprises supplying 410 oil through the steering pipe 101 and the seal housing 102 of the steering section 100 and monitoring 402 for leaks through at least the seal housing 102 and optionally also through the steering pipe 101 of the steering section 100 as described earlier in connection to steering section 100, propulsion unit 200 and propulsion system 300 description.

[0075] It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above but may vary within the scope of the appended claims. Considerations concerning the various embodiments of the propulsion unit may be flexibly applied to the embodiments of the propulsion system mutatis mutandis and vice versa as would be appreciated by a skilled person.

Claims

Claims:1 . A propulsion unit (200) for a propulsion system (300) of a ship, the propulsion unit comprising:- a rotatable lower housing (201 ),- a steering section (100) arranged on top of the lower housing,- a propeller shaft (202) arranged at least partially inside the lower housing,- torque transmission means (204) arranged at least substantially inside the lower housing and coupled to the propeller shaft so as to transfer rotational motion to the propeller shaft, and- a coupling assembly comprising a flexible coupling (160) and an intermediate coupling (161 a, 161 b), the intermediate coupling being fixedly attached to the flexible coupling, one of the flexible coupling (160) or the intermediate coupling (161 a, 161 b) being directly connected and rotationally fixed to the torque transmission means (204) and the other one being configured to be rotationally fixed to a shaft (301 a) of a motor (301 ) of the propulsion system (300), wherein the torque transmission means, the flexible coupling and the intermediate coupling are configured to be substantially aligned along a common vertical axis when in use, and wherein the flexible coupling is configured to compensate for misalignment between the motor shaft and the torque transmission means.

2. The propulsion unit according to claim 1 , wherein the flexible coupling is an oil resistant, such as a full-steel, coupling.

3. The propulsion unit according to any of the preceding claims, wherein the flexible coupling comprises through holes for allowing oil flow.

4. The propulsion unit according to any of the preceding claims, wherein the coupling assembly and the torque transmission means are configured to be immersed in oil.

5. The propulsion unit according to any of the preceding claims, wherein the steering section is configured to be filled with oil.

6. The propulsion unit according to any of the preceding claims, wherein the torque transmission means is a pinion shaft comprising a shaft and a pinion gear manufactured as a single, monolithic piece of material.

7. The propulsion unit according to any of the preceding claims, wherein the torque transmission means is directly coupled to a gear-unit (204a) of the propeller shaft (202).

8. The propulsion unit according to any of the preceding claims, wherein the torque transmission means is connected to the flexible coupling or the intermediate coupling by a spline connection (204b), keyway connection, conical fitting, or shrink fitting.

9. The propulsion unit according to any of the preceding claims, wherein the intermediate coupling comprises a curved toothed coupling (161 a) and a curved toothed casing (161 b), wherein the curved toothed coupling is configured to be directly and fixedly connected to the shaft of the motor or to the torque transmission means and comprises teeth on the outer surface that are rotationally fixed to teeth on the inner surface of the curved toothed casing, said curved toothed casing fixedly attached to the flexible coupling.

10. The propulsion unit according to claim 9, wherein the curved toothed coupling is tiltable relative to the vertical axis to compensate for misalignment between the motor shaft and the torque transmission means and / or to dampen vibrations.11 . The propulsion unit according to any of the preceding claims, wherein the flexible coupling comprises a housing (160a) and a hub (160b) flexibly coupled to the housing of the flexible coupling.

12. The propulsion unit according to claim 11 , wherein the hub of the flexible coupling is tiltable relative to the vertical axis to compensate for misalignment between the motor shaft and the torque transmission means and / or to dampen vibrations.

13. The propulsion unit according to claim 11 or 12, wherein the housing of the flexible coupling comprises a spherical stud on which the hub rests for adjusting angular misalignment.

14. The propulsion unit according to any of the preceding claims, further comprising an isolation flange (162) to electrically isolate flexible coupling from the intermediate coupling and the motor shaft.

15. The propulsion unit according to any of the preceding claims, further comprising a braking device for slowing down, stopping, and / or preventing the rotation of the propeller shaft.

16. The propulsion unit according to any of the preceding claims, wherein the propulsion unit comprises at least one bearing (205) arranged around the torque transmission means at least half-way or closer to the coupling assembly from the propeller shaft.

17. The propulsion unit according to any of the preceding claims, wherein the propulsion unit comprises at least two bearings (205, 206) arranged around the torque transmission means.

18. A propulsion system (300) for a ship, the propulsion system comprising the propulsion unit (200) according to any of the preceding claims and a motor (301 ) with a shaft (301 a), the motor arranged directly on top of the steering section (100) and the shaft of the motor rotationally fixed to the intermediate coupling (161 ) or the flexible coupling (161 ).

19. The propulsion system of claim 18, wherein the motor is an electric motor.

20. The propulsion system of claim 18 or 19, wherein the motor shaft is partially received into the steering section.21 . The propulsion system of any of the claims 18-20, further comprising a propeller (203) fixedly mounted to the propeller shaft outside the lower housing.

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