EP2995550A1

EP2995550A1 - A propulsion unit

Info

Publication number: EP2995550A1
Application number: EP14184386.2A
Authority: EP
Inventors: Jukka Varis
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2014-09-11
Filing date: 2014-09-11
Publication date: 2016-03-16

Abstract

The propulsion unit comprises a first housing (21) extending downwards from a hull (10) of a vessel and a second housing (22) attached to a lower end (21A) of the first housing (21). A first shaft (31) extends in a first direction within the first housing (21) and a second shaft (41) extends in a second direction within the second housing (22). The second shaft (41) protrudes from the second housing (22). A transmission (34, 44) connects the first shaft (31) to the second shaft (41). A propeller (50, 51) is attached to the second shaft (41) outside the second housing (21). A first electric motor (60) is positioned within the first housing (21). The first electric motor (60) comprises a rotor (61) and a stator (62) surrounding the rotor (61). The rotor (61) extends along an axial direction of the first shaft (31) and is attached to the first shaft (31). The first electric motor (60) drives the propeller (50, 51) via the first shaft (31), the transmission (34, 44) and the second shaft (41). The first electric motor (60) is directly cooled to sea water surrounding the first housing (21).

Description

FIELD OF THE INVENTION

The present invention relates to a propulsion unit according to the preamble of claim 1.

BACKGROUND ART

Prior art propulsion units normally comprise a first housing, a second housing, an electric motor, a shaft, and a propeller. The first housing is a longitudinal housing extending in a first direction downwards from a hull of a vessel and the second housing is a longitudinal housing extending in a second direction perpendicular to the first direction. The first housing is rotatably attached to the hull of the vessel. The electric motor is positioned within the second housing. The shaft passes in the second direction through the electric motor and is rotatable supported with bearings within the second housing. The propeller is attached to an outer end of the shaft protruding from one end of the second housing.
In propulsion units where a high thrust at low speed is needed, there is further a nozzle surrounding the perimeter of the propeller. The nozzle is supported at the second and/or the first housing. The nozzle forms a central duct with an axial flow path for water from a first end to a second end of the nozzle. The thrust produced by the propeller is amplified by the nozzle at low speeds. The nozzle may produce up to 40% of the total thrust at low speeds, whereby the propeller produces 60% of the total thrust. Nozzles are used in so called Dynamic Positioning (DP) vessels used in oil drilling. There may be several struts in such vessels and the vessel is kept steady in position by the struts. A big thrust is thus needed at low speed in order to keep the vessel continuously in position in rough seas.
JP patent publication 2000142576 discloses a watercraft propulsion apparatus for luxurious passenger boats. The apparatus has a casing arranged in a hollow portion of the hull. The casing comprises a vertically positioned electric motor and a vertical shaft passing through the electric motor. The lower end of the vertical shaft extends from the bottom of the casing into a strut and is connected with a transmission to a horizontal shaft. A propeller is connected to the outer end of the horizontal shaft protruding from one end of the strut. The electric motor is completely within the casing and the casing is completely within the hull of the vessel.
WO patent publication 2009/141254 discloses an azimuth propeller device for a vessel. The device has a longitudinal housing placed in water below a hull of the vessel. The housing comprises a first shaft having an outer end protruding from an end of the housing. A propeller is attached to the outer end of the first shaft. The housing is supported with a hollow arm at the hull of the vessel. The hollow arm is rotatable supported with bearings at a support structure surrounding the hollow arm. A second shaft extends in the hollow arm from the housing to the interior of the hull of the vessel. The lower end of the second shaft is connected via a transmission to the first shaft. A first electric motor is positioned within the hull of the vessel around the second shaft so that the rotor of the first electric motor is connected to the second shaft. In order to keep the mounting height of the azimuth propeller device low, the first electric motor is designed as a ring motor which is annularly arranged around the second shaft. A second electric motor is positioned within the hull of the vessel at the upper end of the hollow arm so that the rotor of the second electric motor is connected to the hollow arm. The second electric motor is also designed as a ring motor annularly arranged around the hollow arm. The first electric motor drives the propeller and the second electric motor turns the hollow arm and thereby also the housing in relation to the hull of the vessel.
US patent 7,641,526 discloses a marine vessel and an azimuthing thruster assembly. The vessel has a hull and a hull bottom, with a first well and a second well formed in the hull. The wells extend in the vertical direction within the hull of the vessel and face downwards toward a sea floor. The wells comprise a movable canister, which is integrally connected to an azimuthing thruster. The canisters and thereby also the thrusters can be lowered to a deployed position from a retracted position. The propeller in the azimuting thruster is driven by a vertically in the canister positioned first electric motor. The first electric motor is connected with a vertical shaft and a transmission to the propeller shaft extending in the strut. The azimuting thruster has a propeller connected to the propeller shaft and a nozzle surrounding the propeller. The thruster is positioned completely within the canister within the hull of the ship in the retracted position and in the water below the bottom of the hull in the deployed position. The first electric motor will in all situations be positioned within the canister within the hull of the vessel. The azimuting thruster is connected to a turning wheel within the hull of the vessel. The turning wheel and thus also the azimuting thruster is rotated with a second electric motor connected to the turning wheel.
The problem in prior art propulsion units comprising a first housing, a second housing and an electric motor within the second housing and a propeller outside the second housing driven by the electric motor is lack of torque at low speed. The nozzle surrounding the outer perimeter of the propeller will increase the thrust of the arrangement at low speed. There is however a need for more torque at low speed and thus more thrust at low speed in the previously mentioned DP vessels.
The problem in prior art propulsion units where the electric motor is positioned within the hull of the vessel and the propeller is driven by two shafts connected with an angle transmission is related to the service of the electric motor. The service of the electric motor has to be done from inside of the vessel i.e. it is not possible to change the whole strut with electric motor from the outside of the hull of the vessel.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to achieve an improved propulsion unit.
The propulsion unit according to the invention is characterized by what is stated in the characterizing portion of claim 1.
The propulsion unit comprises:

a cylindrical first housing extending in a first direction downwards from a bottom of the hull of the vessel, an upper end of said first housing extending through an opening in the bottom of the hull into the interior of the hull, said first housing being rotatable attached within the hull by means of a slewing bearing,
a second housing being attached to a lower end of the first housing,
a first shaft having a first end and a second opposite end, an axial centre line of the first shaft extending in a first direction within the first housing, said first shaft being rotatably supported with first radial and axial bearings,
a second shaft having a first end and a second opposite end, an axial centre line of the second shaft extending in a second direction within the second housing, said second shaft being rotatably supported with second radial and axial bearings, said second end of the second shaft protruding from the second end of the second housing,
a transmission connecting the first end of the first shaft to the second shaft,
a propeller being attached to the second end of the second shaft outside the second end of the second housing, said propeller rotating with the second shaft,

The propulsion unit comprises further:

a first electric motor being positioned within the first housing, said first electric motor comprising a rotor and a stator surrounding the rotor, said first electric motor being directly cooled to sea water surrounding the first housing through a shell of the first housing, said rotor extending along the axial centre line of the first shaft and being attached to the first shaft, whereby the first electric motor drives the propeller via the first shaft, the transmission and the second shaft.

The position of the first electric motor within the upper portion of the strut makes it possible to use a smaller and cheaper first electric motor compared to an electric motor positioned within the lower portion of the strut.
The first electric motor can be of any technology that is available today. The rotation speed of the first electric motor could be higher compared to the rotation speed of an electric motor that drives the propeller directly. This is due to the transmission, which makes it possible to lower the rotation speed of the first electric motor to a rotation speed suitable for the propeller. The torque that can be produced by an electric machine is proportional to the volume of the active parts in the electric machine. By using e.g. a gear ratio of 4 in the transmission, one could reduce the volume of the first electric motor by one fourth. The outer diameter of the first electric motor could thus be halved compared to a first electric motor driving the propeller directly if the length of the electric motors would be kept the same. The power P of an electric machine is P=M*ω. The power of the electric machine will thus increase when the rotation speed ω of the electric machine is increased in a situation where the torque M of the electric machine is kept the same.
The first electric motor positioned in the first housing can be cooled directly to the sea water surrounding the first housing. The stator of the first electric motor can be arranged so that heat produced in the stator is transferred directly to the shell of the first housing and further from the shell to the sea water surrounding the first housing. This means that a separate cooling system, which is needed in case the first electric motor is situated within the vessel or within a movable canister can be eliminated in the invention.
The removal of the electric motor from the second housing makes it possible to optimize the second housing. The second housing can be shortened and the form of the second housing can be improved in view of hydrodynamic properties. The axial length of the second housing can be made much smaller e.g. 60% smaller compared to a situation where the electric motor is situated within the second housing. This means that the propulsion unit can be installed in a narrower vessel. A shorter second housing means a smaller diameter rotating around the vertical shaft of the propulsion unit. The dimensions of a possible service opening in the bottom of the vessel through which the strut can be lifted into the vessel can also be made smaller in a corresponding way.
The production of heat in the second housing will decrease dramatically as only the bearings and the transmission produce heat in the second housing. The cooling of the second housing directly to the surrounding sea water will thus be sufficient.
The lower temperature in the second housing will also have a beneficial impact on the life time of the sealing between the second shaft and the second housing. Said sealing will only be subjected to the heat produced by the radial bearing near the sealing. The operation temperature of the sealing will thus be lower, which will prolong the life time of the sealing.
This arrangement is especially suitable to be used in the previously mentioned DP vessels. The thrust needed in the DP vessels where the invention is especially suitable is in the range of 50 to 150 tons. The power of the electric motor in these applications is in the order of megawatts. The diameter of the outer periphery of the propeller is in the order of several meters.
In order to exemplify the dimensions one could refer to a prior art Azipod® arrangement for a DP vessel delivered by the applicant. The power of the electric motor within the prior art propulsion unit is 20 MW, the torque of the electric motor is 1340 kNm, the diameter of the outer periphery of the propeller is 5.5 m and the axial length of the total entity is 11.4 m. A propulsion unit according to the invention having a similar output would result in a reduction of the length of the total entity to 4 to 5 m. The propulsion unit according to the invention forms a compact integrated package.
The position of the first electric motor within the first housing means that the torque of the first electric motor does not affect the steering torque of the propulsion unit. The stator of the first electric motor is within the first housing and the first housing is rigidly connected to the second housing where the transmission between the first shaft and the second shaft is positioned. The torque of the stator and the torque of the first pinion are acting in the opposite direction within the housing arrangement. The load acting on the steering arrangement including the slewing gear ring, the pinion, the gear box and the second electric motor is lower compared to a solution with a separate first electric motor. This leads to a lower weight and lower costs for these components.
The propulsion unit can further in one advantageous embodiment comprise an annular nozzle being fixedly supported on the first and/or on the second housing. The axial centre line of the second shaft forms also an axial centre line of the annular nozzle. The annular nozzle surrounds an outer perimeter of the propeller and forms a duct for water flowing through the interior of the annular nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which:

Figure 1 shows a propulsion unit according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a propulsion unit according to the invention. The propeller is pushing the vessel forwards in a first direction S1. The propulsion unit 20 comprises a first housing 21, a second housing 22, a first shaft 31, a second shaft 41, a transmission 34, 44, a propeller 51, an annular nozzle 70 and a first electric motor 60.
The first housing 21 extends downwards from a hull 10 of a vessel. An upper end 21 B of the first housing 21 extends through an opening 11 in the bottom of the hull 10 of the vessel into the interior of the hull 10 of the vessel. The opening 11 in the bottom of the vessel is sealed against sea water with a slewing seal 27. A second housing 22 is rigidly attached to a lower end 21A of the first housing 21. The first housing 21 forms a support member for the second housing 22. A part of the upper portion 21 of the strut 20 extends through the hull 10 of the vessel into the vessel into an enclosed compartment 80 within the hull 10 of the vessel. The second housing 22 has the form of a torpedo and comprises a first end 22A and a second end 22B. The first housing 21 and the second housing 22 could be formed as two separate entities or as a single entity.
The first shaft 31 has a first end 31A and a second opposite end 31 B. An axial centre line Y of the first shaft 31 extends in a first direction within the first housing 21. The first shaft 31 is rotatably supported with first radial and axial bearings 32, 33 within the first housing 21. One of the radial bearings 32, 33 of the first shaft 31 is advantageously a combined radial and axial bearing. A combined radial axial bearing is needed in order to carry the load caused by the first shaft 31 and the gear.
The second shaft 41 has a first end 41 A and a second opposite end 41 B. An axial centre line X of the second shaft 41 extends in a second direction within the second housing 22. The second shaft 41 is rotatably supported with second radial bearings 42, 43 within the second housing 22. The second end 41 B of the second shaft 41 protrudes from the second end 22B of the second housing 22. The second direction X is essentially perpendicular to the first direction Y. One of the radial bearings 42, 43 of the second shaft 41 is advantageously a combined radial and axial bearing. A combined radial axial bearing is needed in order to transfer the axial thrust produced by the propeller 51 from the second shaft 41 to the second housing 22 and the first housing 21 and further to the hull 10 of the vessel.
The transmission 34, 44 connects the first end 31A of the first shaft 31 to the second shaft 41. The transmission 34, 44 is formed of a first pinion 34 attached to the first shaft 31 and a second pinion 44 attached to the second shaft 41. The cogs on the periphery of the pinions 34, 44 are in contact with each other so that the rotation of the first shaft 31 also rotates the second shaft 41. The first shaft 31 will rotate at a first rotation speed determined by the first electric motor 60. The second shaft 41 will on the other hand rotate with a second different rotation speed determined by the transmission 34, 44 i.e. the pitch diameters of the pinions 34, 44. The second rotation speed will be lower than the first rotation speed. The propeller 50, 51 is thus driven by the first electric motor 60 at a speed which is lower than the rotation speed of the first electric motor 60.
A propeller 50 comprising a hub 50 provided with propeller blades 51 is attached to the second end 41 B of the second shaft 41. The propeller may also be a monoblock type propeller in which the propeller hub 50 and the propeller blades 51 are integrated into a monoblock construction. The propeller hub 50 is attached to the second end 41 B of the second shaft 41 outside the second end 22B of the lower portion 22 of the strut 20. The propeller 50, 51 rotates with the second shaft 41.
The annular nozzle 70 is fixedly supported at the first housing 21 and/or at the second housing 22. The axial centre line X of the second shaft 41 forms also an axial centre line of the annular nozzle 70. The annular nozzle 70 surrounds an outer perimeter of the propeller 50, 51 and forms a duct 75 with an axial flow path for water flowing through the interior of the annular nozzle 70. The annular nozzle 70 is attached to the first housing 21 with a first support part 73 and to the second housing 22 with a second support part 74. The second support part 74 extends downwards from the second housing 22. The rotating propeller 50, 51 causes water to flow through the central duct 75 from the first end 71 of the central duct 75 to the second end 72 of the central duct 75 in a second direction S2, which is opposed to the first direction S1. The thrust produced by the propeller 50, 51 is amplified by the annular nozzle 70 at low speeds. The situation can be such that the propeller 50, 51 produces 60% of the total thrust and the annular nozzle 70 produces 40% of the total thrust at low speeds. A nozzle 70 around the propeller 50, 51 is advantageously used in propulsion units in so called Dynamic Positioning (DP) vessels used in oil drilling. There can be several propulsion units in such vessels and the vessel is kept steady in position by the propulsion units. A big thrust is thus needed at low speed in order to keep the vessel continuously in position especially in rough seas.
The first electric motor 60 is positioned within the first housing 21. The first electric motor 60 comprises a rotor 61 and a stator 62 surrounding the rotor 61. The rotor 61 of the first electric motor 60 extends along the axial centre line Y of the first shaft 31. The rotor 61 of the first electric motor 60 is attached to the first shaft 31 so that the first shaft 31 rotates with the rotor 61 of the first electric motor 60. The rotation of the rotor 61 of the first electric motor 60 is thus transferred to rotation of the first shaft 31. The rotation of the rotor 61 of the first electric motor 60 is thus transferred via the first shaft 31, the transmission 34, 44 and the second shaft 41 to the propeller 51. The first electric motor 60 drives the propeller 51.
The first housing 21 is attached via a cylindrical part 27 to a slewing gear ring 24 within the hull 10 of the vessel. A second electric motor 65 is connected via a gear box 66 and a third shaft 67 to a third pinion 68 being in contact with the slewing gear ring 24. The cogs on the periphery of the third pinion 68 are in contact with the cogs on the periphery of the slewing gear ring 24. The second electric motor 65 will thus turn the slewing gear ring 24 and thereby also the first housing 21 as well as the second housing 22 fixedly attached to the first housing 21. The first housing 21 is thus rotatable supported on the hull 10 of the vessel by the slewing bearing 26 and can be rotated 360 degrees around a vertical centre axis Y in relation to the hull 10 of the vessel. The figure shows only one second electric motor 65 connected to the slewing gear ring 26, but there could naturally be two or more second electric motors 65 driving the slewing gear ring 26.
The electric power needed in the first electric motor 60 is produced within the hull 10 of the ship. The electric power can be produced by a generator connected to a combustion engine. The electric power to the stator 62 of the first electric motor 60 is supplied by cables and/or bus bars running from the generator within the interior of the hull 10 of the vessel to the strut 20. A slip ring arrangement 90 is needed in connection with the compartment 80 within the hull 10 in order to transfer electric power from the stationary hull 10 to the rotatable strut 20.
The first electric motor 60 can be made rather long, which means that the torque produced by the first electric motor 60 can be increased. The torque of an electric motor is proportional to the volume of the electric motor. The volume of the first electric motor 60 is increased by the length of the rotor 61 and the stator 62 of the first electric motor 60. The first electric motor 60 can be designed so that sufficient cooling of the stator 62 directly to the surrounding sea water through the shell of the first housing 21 can be achieved. The sea water flowing on the outer surface of the first housing 21 will cool the shell of the first housing 21. The stator 62 of the first electric motor 60 can be arranged in contact with the shell of the first housing 21. The cooling of the stator 62 can thus be arranged as a passive cooling directly to the sea water.
The axial length X1 of the second housing 21 and the annular nozzle 70 is much smaller than the corresponding length of a propulsion arrangement where the first electric motor 60 is within the second housing 22. The axial length Y1 + Y2 of the first electric motor 60 can be adapted according to the axial length of the first housing 21. At least 90% of the axial length of the first electric motor 60 is outside the hull 10 of the vessel i.e. surrounded by water. The situation where at least 90% of the axial length of the first electric motor 60 is outside the hull 10 of the vessel leads to a situation where an efficient cooling of the first electric motor 60 directly to the sea water surrounding the first electric motor 60 is possible. It would naturally be more advantageous to have 100% of the axial length of the first electric motor 60 outside the hull 10 of the vessel, but the arrangement is often such that the first housing 21 extends a little bit into the hull 10 of the vessel.
The swivel axis of the propulsion unit 20 coincides with the swivel axis Y of the first shaft 31 in the embodiment shown in the figures. The first housing 21 could, however, extend in an inclined direction downwards from the hull 10. The propulsion unit 20 would thus be tilted in relation to the hull 10. This might in some circumstances result in hydrodynamic advantages. The swivel axis of the propulsion unit 20 could still be vertical, but the centre axis Y of the first shaft 31 would be inclined in relation to the vertical direction in the same way as the first housing 21.
The centre axis X of the second shaft 41 is directed in the horizontal direction in the embodiment shown in the figures. The centre axis X of the second shaft 41 could, however, be inclined in relation to the horizontal direction. The second housing 22 would thus be inclined in relation to the horizontal direction. This might in some circumstances result in hydrodynamic advantages.
The angle α between the swivel axis of the first shaft 31 i.e. the first axial centre line Y and the swivel axis of the second shaft 41 i.e. the second axial centre line X is advantageously 90 degrees. The angle α between the first swivel axis and the second swivel axis could on the other hand be less than 90 degrees or more than 90 degrees. The transmission 34, 44 has to be adapted to the angle α between the first and the second axial centre lines Y, X.
The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

A propulsion unit comprising:
a cylindrical first housing (21) extending in a first direction downwards from a bottom of the hull (10) of the vessel, an upper end (21 B) of said first housing (21) extending through an opening (11) in the bottom of the hull (10) into the interior of the hull (10), said first housing (21) being rotatable attached within the hull (10) by means of a slewing bearing (26),

a second housing (22) being attached to a lower end (21 A) of the first housing (21),

a first shaft (31) having a first end (31A) and a second opposite end (31 B), an axial centre line (Y) of the first shaft (31) extending in a first direction within the first housing (21), said first shaft (31) being rotatably supported with first radial and axial bearings (32, 33),

a second shaft (41) having a first end (41 A) and a second opposite end (41 B), an axial centre line (X) of the second shaft (41) extending in a second direction within the second housing (22), said second shaft (41) being rotatably supported with second radial and axial bearings (42, 43), said second end (41 B) of the second shaft (41) protruding from the second end (22B) of the second housing (22),

a transmission (34, 44) connecting the first end (31 A) of the first shaft (31) to the second shaft (41),

a propeller (50, 51) being attached to the second end (41 B) of the second shaft (41) outside the second end (22B) of the second housing (22), said propeller (50, 51) rotating with the second shaft (41),

characterized in that the propulsion unit further comprises:
a first electric motor (60) being positioned within the upper portion (21) of the strut (20), said first electric motor (60) comprising a rotor (61) and a stator (62) surrounding the rotor (61), said first electric motor (60) being directly cooled to sea water surrounding the first housing (21) through a shell of the first housing (21), said rotor (61) extending along the axial centre line (Y) of the first shaft (31) and being attached to the first shaft (31), whereby the first electric motor (60) drives the propeller (50, 51) via the first shaft (31), the transmission (34, 44) and the second shaft (41).
A propulsion unit according to claim 1, characterized in that more than 90% of an axial length (Y1) of the first electric motor (60) is situated within the first housing (21) below the bottom of the hull (10) of the vessel.
A propulsion unit according to claim 1 or 2, characterized in that the second direction (X) is essentially perpendicular in relation to the first direction (Y).
A propulsion unit according to any one of claims 1 to 3, characterized in that there is an annular nozzle (70) fixedly supported at the propulsion unit, said axial centre line (X) of the second shaft (41) also forming an axial centre line of the annular nozzle (70), said annular nozzle (70) surrounding an outer perimeter of the propeller (50, 51) and forming a duct (75) for water flowing through the interior of the annular nozzle (70).