Gyro Stabilizer Assembly

Abstract

The present disclosure includes a housing (13) defining a chamber (12) for holding an operating pressure, a flywheel (33) mounted within the chamber (12) for enabling rotation about a spin axis (Z) under the operating pressure, a flywheel shaft (34) on which the flywheel (33) is mounted within the housing (12), and a bearing lubrication system (10). The flywheel shaft (34) is supported by a first spin bearing (21) and a second spin bearing (31) disposed at opposite end regions of the flywheel shaft (34) for rotating the flywheel (33) about the spin axis (Z), the first spin bearing (21) and the second spin bearing (31) are disposed within the housing (12) for use under operating pressure or under differential pressure, and the bearing lubrication system (10) includes an oil sump or reservoir (70) disposed or configured to collect liquid lubricant (O) under gravity from the first spin bearing (21) and the second spin bearing (31). The gyro stabilizer assembly (1) includes an oil circuit (71, 79, 50, 561) for circulating the liquid lubricant (O) from the first spin bearing (21) to the second spin bearing (31), the bearing lubrication system (10) including a rotary disc pump (60) for circulating the liquid lubricant (O) to the first spin bearing (21) and the second spin bearing (31) via the oil circuit (71, 79, 50, 561, the rotary disc pump (60) being coupled to the flywheel shaft (34) or being driven by the flywheel shaft (34). The present disclosure also relates to a vehicle, particularly a watercraft, that includes the gyro stabilizer assembly (1).

Description

[Technical Field]

[0001] The present disclosure relates to a gyro stabilizer assembly, and more particularly to a gyro stabilizer assembly having an improved bearing lubrication system.

[0002] The gyro stabilizer assemblies of the present disclosure are typically designed for use on marine vessels and are best understood in the context of such an example. However, it will be understood that the gyro stabilizer assemblies of the present disclosure are not limited to that particular application and may be designed for many other applications, such as for use on other fixed and floating structures, other vehicles, hoist systems, and / or camera mounts. [Background technology]

[0003] The discussion of background art in this specification, including any document references, should not be taken in any way as an acknowledgement that such background art is well known art or forms part of the general general knowledge in the art in Australia or any other country.

[0004] The structure and operation of marine gyro stabilizer assemblies are generally very well understood. These devices are increasingly being adopted on commercial and recreational vessels. A gyro stabilizer assembly typically consists of a rotating flywheel mounted on a gimbal frame that allows a rotational degree of freedom. The gimbal frame is rigidly mounted within the vessel. Due to the specific manner in which the flywheel is constrained in its rotational motion, the angular momentum of the rotating flywheel combines with the precession of the flywheel to generate a large, time-varying torque to directly counteract the dynamic rolling motion of the vessel caused by wind and / or waves. Without any intervention, the vessel's rolling motion combines with the angular momentum of the flywheel to cause precession. This combines with the angular momentum to produce a stabilizing torque that directly counteracts undesirable rotational motion of the vessel (e.g., wave-induced rolling). By arranging the gimbal in a specific manner, a roll stabilizing device is created that utilizes naturally occurring gyrodynamic physics and requires no further intervention to function. An example of a gyro stabilizer assembly for a marine vessel is described in the applicant's Australian patent application AU2017216483A1, the contents of which are incorporated herein in their entirety by direct reference.

[0005] Because the outer rim of a gyroscopic stabilizer flywheel rotates at high speeds, gimbal frames often consist of a chamber surrounding the flywheel that is evacuated to allow the flywheel to rotate in a vacuum. This reduces air resistance on the flywheel, reducing the power required to maintain the flywheel's rotational speed (rpm). It also reduces heat generated by air resistance on the rotating flywheel rim, improving efficiency. The rotational bearings used to position and support the flywheel around its spin axis are subjected to both high loads and high rotational speeds, which also generate heat and noise. Spin bearings and spin motors are typically placed in a vacuum chamber, avoiding the problems associated with sealing the vacuum chamber where the spin axis exits. However, having the rotational bearings in a vacuum chamber makes lubrication and cooling of the bearings difficult. In particular, the rotational bearings and flywheel shaft are difficult to cool by contacting a coolant jacket because they are rotating.

[0006] Pending Australian patent application AU2017216483A1 describes an arrangement with an oil lubrication system for lubricating and cooling bearings, in which the oil flow rate to the bearings can be selected to provide both lubrication and heat exchange with the oil. An oil lubrication system is desirable for noise reduction, bearing life extension, and heat removal within the bearings. In this system, oil is drawn from a sump by one or more scavenge pumps. To operate the scavenge pumps, rotary shaft seals on the flywheel shaft separate the upper and lower bearing chambers from a vacuum chamber surrounding the flywheel. One seal is located below the upper bearing chamber, and the other seal is located above the lower bearing chamber. The upper and lower bearing chambers are connected by a drain line between them. This arrangement allows the flywheel to rotate under partial or near-vacuum conditions, at pressures low enough that air resistance is substantially reduced or eliminated. Meanwhile, the bearing chamber (which is manifolded to operate at the same pressure) can operate at a pressure high enough for the scavenge pump to effectively pump oil to the spin bearings.

[0007] However, the arrangement described in AU2017216483A1 has the disadvantages of requiring a dual vacuum pressure management system for the vacuum chamber and the bearing chamber, and of the rotating shaft seal components being subject to rotational resistance from high contact surface speeds, resulting in wear, associated costs for maintenance and / or subsequent replacement, and higher power requirements to maintain the desired flywheel speed (rpm).

[0008] To address these shortcomings, the present applicant has developed a new gyrostabilizer arrangement that does not require a rotary shaft seal to separate or isolate the rotary bearing from the operating pressure of the flywheel chamber. An example of such a gyrostabilizer assembly is described in the present applicant's International Patent Application PCT / AU2021 / 050197, published as WO2021 / 174315A1, the contents of which are incorporated herein by direct reference in their entirety. This new arrangement has the advantage of simplifying the arrangement by eliminating the need for a dual vacuum pressure management system and reducing the number of parts and potential points of failure, thereby making the gyrostabilizer assembly more reliable and robust. However, it has been found that operating pressures in the flywheel chamber that are roughly vacuum (absolute pressure) below approximately 0.1 bar can cause problems with bearing lubrication in general, and with the circulation of lubricating oil in particular. Pressure values ​​shown herein are absolute pressure values ​​unless otherwise noted. Summary of the Invention [Problem to be solved by the invention]

[0009] It would therefore be desirable to provide a new gyro stabilizer arrangement that substantially overcomes or ameliorates one or more of the above-mentioned disadvantages. In this regard, it would be desirable to provide a new gyro stabilizer assembly with a lubrication system that can reliably lubricate and cool the bearings when operating in a rough or partial vacuum. [Means for solving the problem]

[0010] According to one broad aspect, the present disclosure provides a gyroscopic stabilizer assembly including: a housing defining a chamber for holding an operating pressure; a flywheel mounted in the chamber to enable rotation about a spin axis under the operating pressure; a flywheel shaft on which the flywheel is mounted within the housing; and a bearing lubrication system. The flywheel shaft is supported by first and second spin bearings disposed at opposite end regions of the flywheel shaft to rotate the flywheel about the spin axis. The first and second spin bearings are disposed within the housing for use under operating pressure or differential pressure. The bearing lubrication system includes an oil circuit for circulating lubricant to the first and second spin bearings from an oil sump or reservoir positioned or configured to collect lubricant from the first and second spin bearings under gravity. The bearing lubrication system includes a rotary disc pump for circulating lubricant to the first and second spin bearings via the oil circuit. The rotary disc pump is coupled to or driven by the flywheel shaft.

[0011] In one embodiment, the pump comprises a rotary disc pump, a type of centrifugal pump, having an impeller with at least one substantially flat disc, preferably two (or more) substantially flat discs, mounted generally parallel and spaced apart. The impeller is typically vaneless and, as it rotates, uses the principles of boundary layers and viscous drag to propel lubricant (e.g., oil) from an oil sump or reservoir along a lubricant circuit. The impeller of a rotary disc pump is preferably vaneless, allowing it to rotate at very high speeds with substantially laminar lubricant flow and without significant vibration or cavitation. The rotary disc pump is preferably a hermetic rotary disc pump. It preferably includes a first solid (e.g., flat or smooth) disc mounted at a uniform distance from at least a second axially aligned (e.g., flat or smooth) annular disc, preferably of substantially the same outer diameter as the first disc. A central opening in the annular disc allows for central flow or passage of oil through the impeller and into the space between the discs. This pump or "pump means" in the oil sump or reservoir can be thought of as a "return pump" for returning lubricating oil from the reservoir to the lubricating oil circuit.

[0012] In one embodiment of the present disclosure, a rotary disc pump includes a plurality of axially aligned annular discs, preferably having substantially the same outer diameter as the first disc. The plurality of annular discs may be mounted in a stacked array above the first disc, preferably spaced substantially uniformly from one another and / or from the first disc. The central opening of each annular disc is also desirably substantially uniform, again allowing for central flow or passage of oil into the impeller and into the spaces between each disc. For example, an impeller may be mounted in a stacked array with two, three, four, or five annular discs in combination with solid discs. By combining multiple annular discs with (at least) one solid disc, the pressure head generated by the pump and the efficiency of the pump are substantially improved compared to a single annular disc. However, the improvement in pressure head and efficiency tends to decrease when the number of discs exceeds five. Desirably, the number of discs provided in the impeller ranges from two to eight, preferably five. Each flat annular disc preferably has a radial width in the range of about 20% to about 40% of the outer diameter of the disc. Thus, the central opening of the annular disc preferably has a diameter in the range of about 20% to about 60% of the outer diameter of the disc. More preferably, the radial width of each annular disc is in the range of about 25% to about 30% of the outer diameter of the disc. Thus, the central opening of the annular disc more preferably has a diameter in the range of about 40% to about 50% of the outer diameter of the disc. Each disc preferably has a thickness in the range of about 0.5% to about 2% of the outer diameter of the disc.

[0013] In an embodiment of the present disclosure, the spacing between each disk of the impeller is preferably in the range of 0.2 mm to 5.0 mm, more preferably in the range of 0.2 mm to 2.0 mm, even more preferably in the range of 0.2 mm to 1.5 mm, and particularly preferably 0.5 mm. The thickness of each disk is preferably in the range of 0.5 mm to 2.0 mm. The outer diameter of the disk is preferably in the range of about 100 mm to about 200 mm, more preferably in the range of about 100 mm to about 150 mm, for example, a diameter of about 120 mm. The distance between the top disk of the impeller and the upper casing plate of the housing is in the range of 0.05 mm to 0.2 mm. The pins or bolts interconnecting the disks of the impeller preferably have an elliptical cross-sectional shape (e.g., a 1:2 ratio) so as to present a low profile in the direction of rotation of the impeller (i.e., with the short elliptical dimension parallel to the radius of the disk).

[0014] In one embodiment, the rotary disc pump's impeller is directly coupled to the flywheel shaft for rotation (i.e., there are no gears). In this manner, the pump's impeller can rotate with the gyroscopic flywheel shaft at speeds ranging from about 3,000 rpm to about 10,000 rpm. Because the impeller's hydrodynamic resistance is low, the pump does not require gears, and high rotational speeds do not lead to excessive wear or significant cavitation effects in the lubricating oil.

[0015] In this way, the gyrostabilizer assembly of the present disclosure can utilize a simpler structural arrangement without a rotating shaft seal that separates or isolates the spin bearing from the operating pressure of the flywheel chamber, as described in WO 2021 / 174315 A1, while still providing effective lubrication and cooling of the gyrostabilizer spin bearing via lubricant swept and pumped at rough vacuum operating pressures of less than 0.5 bar, preferably less than 0.5 bar, preferably less than 0.2 bar, and more preferably in the range of about 1 mbar to 100 mbar (absolute). Rotary disk pumps can largely avoid cavitation problems at the rough vacuum pressures present in vacuum chambers and are also effective against "splash" inlet conditions at the pump that can occur in heavily "dry-run" vacuum chambers.

[0016] In one embodiment, one or both of the first and second spin bearings may include, for example, a lubricant labyrinth disposed around the bearing. In this regard, the labyrinth of the first (upper) spin bearing is preferably applied to the first bearing and operates to prevent lubricant (oil) flowing through the first bearing from flowing onto the flywheel. If oil were to be dragged along the chamber wall by the rotating flywheel, this would waste power. The labyrinth of the second (lower) spin bearing is preferably applied to the second bearing and prevents lubricant (oil) flowing through the second bearing from reaching the thrust bearing. The lubricant labyrinth directs cooling lubricant to an oil sump or reservoir via a passage designed for this purpose. The oil sump or reservoir is configured and arranged within or on the housing so that lubricant supplied, circulated, and / or dispensed to the first and second spin bearings is drained from the respective bearings to return to the reservoir under gravity. In this regard, it is understood that the lubricant is typically an oil, such as a synthetic oil, which preferably has a vapor pressure of less than 40 mbar at 80°C.

[0017] The term "spin bearing" as used throughout this document should be understood as a reference to a bearing designed to mount or support a flywheel shaft for rotation, preferably free rotation, about a spin axis. As such, the term "spin bearing" should be understood as a rotation bearing and includes a range of rotation bearing designs such as hydrodynamic bearings and rolling bearings.

[0018] For example, an inner race for the rolling elements is rigidly attached to the flywheel shaft to rotate with the shaft, and an outer race is rigidly fixed to the housing. For example, an inner race for the rolling elements is rigidly attached to the flywheel shaft to rotate with the shaft, and an outer race is rigidly fixed to the housing. In an alternative embodiment, the first and second spin bearings can be configured as plain bearings, for example, plain hydrodynamic bearings.

[0019] In one embodiment, the operating pressure is at least a partial vacuum, such that the chamber in which the flywheel is mounted forms a vacuum chamber. This reduces air resistance against the flywheel, reducing the power required to maintain the flywheel's rotational speed (rpm) and reducing the heat generated by air resistance against the rotating flywheel. In this way, the entire vacuum chamber of the gyrostabilizer assembly forms a single chamber operating at one vacuum pressure. As mentioned above, the operating pressure is preferably about 0.2 bar or less, preferably in the range of 1 to 100 mbar.

[0020] In one embodiment, the lubrication oil circuit, in which lubrication oil is circulated from an oil sump or reservoir to the bearings and then back to the oil sump or reservoir, preferably includes an additional pump external to the housing and vacuum chamber as a start-up, stop-down, and / or "pressure boost" pump. This external pump may be referred to as a "feed pump," and is preferably a vaned or positive displacement pump, preferably magnetically coupled to a brushless electric motor.

[0021] In one embodiment, the bearing lubrication system includes at least one lubricant outlet, particularly a lubricant injection port, for targeted delivery or injection of oil lubricant at each of the first and second bearings. Thus, the bearing lubrication system can have an "oil jet" system. The oil flow rate is preferably selected to exchange heat generated in the bearings with the oil. Injection of oil through the lubricant injection port allows the oil to be targeted toward the inner race of each bearing and / or the rolling or sliding elements therein, providing effective cooling for these components. Therefore, a pump or "pumping means" provided within the reservoir for supplying lubricant (i.e., oil) from the reservoir to the first and second spin bearings is preferably designed to prime and provide the pressure required to drive the oil through the lubricant outlet port at the required speed. In this regard, the pump or "pumping means" can consist of a single pump stage or multiple pump stages. By carefully selecting or designing the pumping means to provide the required pressure and flow rate, the pumping means can be arranged and sized to meet the requirements for circulating oil through one or more filters and / or one or more heat exchangers in the oil circuit and then through the oil delivery outlet.

[0022] As mentioned above, the lubrication system can also form a cooling system for the spin bearings. In this way, the lubricant (i.e., oil) typically acts as a coolant, carrying heat away from the first and second spin bearings. To this end, the lubrication oil circuit of the bearing lubrication system can include one or more heat exchangers to remove heat from the oil before it is supplied to the first and second spin bearings. In this regard, the walls of the oil labyrinth can form a heat sink or heat exchanger for the oil. Alternatively, or in addition, the walls of the flywheel housing and / or the oil sump or reservoir can form a heat sink or heat exchanger for the oil when it returns to the reservoir under gravity and / or when it is circulated from the reservoir to the spin bearings, optionally via a cooling medium provided in the housing or oil sump walls (e.g., a water jacket) and / or optionally via fin elements formed in the walls. This heat is then rejected (e.g., overboard) as heated cooling water. It should be noted that in the gyrostabilizer assemblies of the present disclosure, degassing of the oil is not required due to the extremely low air concentration in the oil at pressures of 1 to 30 mbar absolute. This is beneficial because it simplifies oil handling in the lubrication circuit and helps ensure that the delivery port functions to provide a directed jet with sufficient flow velocity to penetrate the boundary layer to provide the necessary mixing and heat transfer. However, the oil is typically filtered before refilling.

[0023] In one embodiment, the lubrication oil circuit includes an oil accumulator for storing oil and maintaining oil pressure to mitigate fluctuations in oil pressure from the pump. The oil accumulator can therefore support injection pressure during periods of oil splash conditions at the pump and / or periods when there may be no oil supply at the pump inlet to the sump pump, such as when the gyrostabilizer may be stuck at a high precession angle (e.g., 70°) for an extended period (e.g., 2 minutes) during a vessel U-turn. The oil accumulator is preferably a bladder-type or piston-type oil accumulator. The oil pressure maintained by the oil accumulator in the lubrication oil circuit is preferably in the range of approximately 1.2 bar to approximately 3.2 bar. A non-return valve (check valve) is preferably located upstream of the oil accumulator to prevent backpressure from the oil accumulator back into the oil sump or reservoir.

[0024] Both horizontal and vertical orientations of the flywheel shaft are contemplated for the gyroscope assemblies of the present disclosure, each presenting challenges for lubrication in terms of getting lubricant (e.g., oil) to the respective spin bearings and then recovering the lubricant for reapplication.

[0025] In a preferred embodiment, the flywheel shaft is mounted in a generally vertical orientation within the housing so as to rotate about a generally vertical spin axis. The first and second bearings thus form upper and lower spin bearings, respectively. In such a configuration, the gyroscope assembly of the present disclosure typically includes an additional lower spin bearing (i.e., a third spin bearing) as a thrust bearing to axially support the flywheel and flywheel shaft. A vertical flywheel shaft orientation is preferred because it allows the housing to be configured as a pendulum with a natural stable point near the vertical. This means that no extra mechanism is required to ensure that the precession angle of the gyroscope assembly remains "centered" around the mid-stroke. Oil returning from the upper and lower bearings is directed to a common reservoir or oil sump located in the lower region or bottom of the housing and vacuum chamber. The oil in the reservoir / oil sump is scavenged and (re)circulated by a rotary disc pump located within the reservoir / oil sump.

[0026] In one embodiment, the pump or "pump means" in the bearing lubrication system's oil sump or reservoir includes a two-stage pump arrangement for increasing the pump outlet pressure, with a rotary disc pump preferably forming the first stage and a vaned centrifugal pump forming the second stage.

[0027] In one embodiment, the gyroscopic stabilizer assembly includes an electric motor for driving the rotation of the flywheel about the spin axis. In one embodiment, the spin motor is mounted within the chamber. In an alternative embodiment, the spin motor is mounted outside the chamber and coupled to the flywheel shaft via either an insulated magnetic coupling or a sealed shaft connection. A magnetic coupling is preferred to avoid the need for a rotary shaft seal. If a shaft connection to the spin motor mounted outside the chamber is required, a rotary shaft seal would still be required. However, the advantage here is that this arrangement isolates the flywheel shaft from the large radial motion (runout). Furthermore, the shaft connecting the spin motor to the flywheel shaft can be relatively small in diameter because it only needs to transmit a relatively small spin torque. This limits the speed of the seal interface (speed decreases as the circumference decreases at a given rotational speed), significantly extending the possible rotational speed before the seal capacity is reached and reducing the rotational resistance of the seal. In contrast, in current arrangements, the rotary shaft seal is located on the flywheel shaft, which must withstand the full gyroscopic torque, which fully reverses with each rotational speed cycle. Therefore, shaft diameters and circumferences are much larger, leading to higher contact surface speeds, higher wear, and technical challenges regarding extended seal life.

[0028] According to another aspect, the present disclosure provides a gyroscopic stabilizer assembly for a marine vessel. The gyroscopic stabilizer assembly includes a housing defining a chamber for maintaining a partial vacuum, a flywheel mounted in the chamber for enabling rotation about a spin axis under the partial vacuum, a flywheel shaft mounted in the housing for rotating the flywheel about the spin axis, and a bearing lubrication system. The flywheel shaft is rotatably supported by a first bearing at one end region of the flywheel shaft and by a second bearing at the other end region of the flywheel shaft. The first bearing and the second bearing are disposed within the housing for operation under partial vacuum. An oil sump or reservoir is disposed within or on the housing for collecting oil from the first bearing and the second bearing under gravity. The bearing lubrication system is configured to supply oil from the oil sump or reservoir to the first bearing and the second bearing via an oil circuit. The bearing lubrication system includes a rotary disc pump for pumping or circulating oil through the oil circuit.

[0029] In an embodiment of the gyrostabilizer assembly of the present disclosure, the rotary disc pump in the reservoir is coupled to and driven by the flywheel shaft. However, alternatively, the rotary disc pump may be separate from (i.e., not coupled to) the flywheel shaft and driven by a separate electric motor. As explained above, a rotary disc pump is a type of centrifugal pump having an impeller with at least one substantially flat disc, preferably two (or more) substantially flat discs, mounted generally parallel and spaced apart from one another. The impeller is typically vaneless and can rotate at high speeds with substantially laminar flow of lubricating oil without generating significant vibration or cavitation. The rotary disc pump is preferably a sealed rotary disc pump. It preferably includes a first solid flat disc mounted in a uniformly spaced relationship to a second axially aligned annular flat disc having substantially the same outer diameter as the first disc.

[0030] As noted above, because the structure and operation of marine gyro stabilizers are generally very well understood, this specification does not aim to provide a detailed description of all of the components of a gyro stabilizer assembly, such as the flywheel, flywheel shaft, gimbal bearing, etc. Rather, this specification directs those skilled in the art to other publications for descriptions or explanations of those components.

[0031] According to another aspect, the present disclosure provides a watercraft, such as a boat, including or incorporating a gyrostabilizer assembly of the present disclosure according to any one of the above-described embodiments. The gyrostabilizer assembly is typically rigidly secured to the hull of the watercraft, for example adjacent the keel.

[0032] According to a further aspect, the present disclosure provides a hoisting system, e.g., for use with a crane, including a gyroscopic stabilizer assembly of the present disclosure according to any of the above-described embodiments. In this context, the gyroscopic stabilizer assembly is designed or adapted to be suspended from the lifting system together with a load to damp or suppress undesirable oscillatory rotation of the suspended load during a lifting operation, e.g., oscillatory rotation caused by wind gusts. Preferably, at least one gyroscopic stabilizer assembly is provided for and / or mounted along each axis of stabilization required.

[0033] The term "gyrostabilizer assembly" as used throughout the document will be understood to refer to a gyrostabilizer device or gyrostabilizer unit that may be incorporated into or installed on a vehicle, such as a watercraft, or other device that is subject to undesirable rotational motion (such as rolling motion due to waves) to counteract and / or reduce such undesirable motion. [Brief explanation of the drawings]

[0034] For a more complete understanding of the present invention and its advantages, exemplary embodiments thereof will be described in more detail in the following description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of a gyro stabilizer assembly according to a preferred embodiment. [Figure 2] FIG. 1 is a schematic perspective view of an impeller of a rotary disc pump for an oil sump or reservoir of a gyrostabilizer assembly according to an embodiment. [Figure 3] FIG. 1 is a schematic cross-sectional side view of an impeller of a rotary disc pump provided in an oil sump or reservoir of a gyrostabilizer assembly. [Figure 4] 1 is a chart showing the change in pump efficiency and outlet head or pressure of a rotary disc pump with the change in the number of discs in the impeller. [Figure 5] 1 is a schematic cross-sectional view of a hull of a watercraft including a gyro stabilizer assembly according to an embodiment of the present disclosure. [Figure 6] FIG. 1 is a schematic perspective view of a hoisting system including a gyro stabilizer assembly according to an embodiment of the present disclosure.

[0035] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate certain embodiments of the invention and, together with the description, serve to explain the principles of the invention. Other embodiments and many of the attendant advantages of the invention will be readily appreciated as the same become better understood by reference to the following detailed description.

[0036] It will be understood that common and / or well-understood elements that may be useful or necessary in commercially feasible embodiments have not necessarily been depicted in order to facilitate a more abstract view of the embodiments. Additionally, it should be noted that elements in the figures are not necessarily drawn to scale relative to each other. Also, while certain acts or steps in method embodiments may be described or depicted in a particular order of occurrence, those skilled in the art will understand that such specificity with respect to order is not actually required. DETAILED DESCRIPTION OF THE INVENTION

[0037] Referring to FIG. 1, a gyrostabilizer assembly 1 according to a preferred embodiment is illustrated schematically. The gyrostabilizer assembly 1 includes a housing 13 enclosing a chamber 12 for supporting a partial vacuum V (e.g., an operating pressure in the range of approximately 1 to 100 mbar) and a flywheel 33 integral with or fixed to a generally vertically oriented flywheel shaft 34 that is mounted within the vacuum chamber 12 for rotation about a generally vertical spin or rotation axis Z at the operating pressure. The flywheel shaft 34 to which the flywheel 33 is fixed and supported is mounted within the housing 13 via upper and lower rotation bearings 21, 31 (also referred to as "spin bearings") located at opposite end regions of the shaft 34 and via a lower thrust bearing 32 for rotation of the flywheel 33 about the spin axis Z. The flywheel 33 may be integral with or attached to the shaft 34. In this embodiment, the upper and lower bearings 21, 31 take the form of movable rolling element bearings, with rolling elements (e.g., steel balls or rollers) held between an inner race rigidly fixed to the shaft 34 and an outer race rigidly fixed to the housing 13. The generally vertical orientation of the flywheel shaft 34 and spin axis Z allows the housing 13 to be installed or mounted as a pendulum about a generally horizontal axis with a natural stability point near vertical. As a result, no mechanism is required to ensure that the precession angle of the gyroscope assembly 1 remains centered around the mid-stroke. The gyroscope assembly 1 includes an electric drive motor or spin motor 52 for driving rotation of the flywheel 33 about the spin axis Z, the electric motor 52 being mounted to the housing 13 and operably coupled to the flywheel shaft 34 via a magnetic coupling 53.

[0038] The gyrostabilizer assembly 1 further includes a lubrication system 8 (oil-based) for the upper and lower spin bearings 21, 31 configured to circulate oil O from an oil sump or reservoir 70 to each bearing 21, 31. The lubrication system 8 thus includes an oil circuit 9 with a series of interconnected lines or conduits 71, 79, 50, 51, 58, 59, 65 through which the oil O is circulated from the oil sump or reservoir 70 to each spin / thrust bearing 21, 31, 32 and then back to the reservoir 70. Thus, the lines or conduits 71, 79, 50, 51, 65 of the oil circuit 9 may be both (partially) external and (partially) internal to the housing 13 through which the oil O is supplied from the oil sump or reservoir 70 to each spin / thrust bearing 21, 31, 32. The upper and lower rotary bearings 21, 31 are configured and arranged within the housing 13 such that oil O circulated or supplied to the rotary bearings 21, 31 is discharged from the respective bearings 21, 31 under gravity and returned to the oil sump or reservoir 70. In this regard, the lubrication system 8 includes at least one pump 60 coupled to and driven by the flywheel shaft 34 within the oil sump or reservoir 70 to circulate the oil O to the first and second rotary bearings 21, 31 via the oil circuit 9. The pump 60 is configured as a rotary disc pump, a type of centrifugal pump, equipped with an impeller 6, as shown in FIGS. 2 and 3 . The impeller 6 comprises two substantially flat discs 6a, 6b, one disc 6a being generally solid and circular, and the other disc 6b being generally annular or ring-shaped, mounted coaxially in a generally parallel manner at a distance from one another by threaded stems, bolts, or other fasteners 7, with the discs being spaced apart by approximately 0. These stems or bolts 7 interconnecting the discs 6a, 6b of the impeller 6 have an elliptical cross-sectional shape (e.g., a 1:2 ratio) for a low profile in the direction of rotation of the impeller 6 (i.e., with the short elliptical dimension parallel to the disc radius). The flat annular disc 6b has a central opening 5 for allowing oil to pass into the space between the discs.The space between the disks 6a and 6b has a central opening 5 for oil passage, and its outer diameter is substantially the same as that of the flat solid disk 6a. The radial width w of the annular disk 6b is approximately 25% of the disk's outer diameter (120 mm). Therefore, the central opening 5 of the annular disk has a diameter approximately 50% of the disk's outer diameter. The thickness t of each disk 6a and 6b is preferably in the range of approximately 0.5 mm to 2.0 mm. The impeller 6 is vaneless and, as it rotates, uses the principles of boundary layer and viscous drag to push oil O from the oil sump or reservoir 70 along the lubricating oil circuit 9. Because the impeller 6 of the rotary disk pump 60 is vaneless, the lubricating oil flows substantially laminarly, allowing it to rotate at high speeds without generating significant vibration or cavitation. In this way, the impeller 6 of the rotary disk pump 60, together with the gyroscopic flywheel shaft 34, can rotate at speeds ranging from approximately 3,000 rpm to approximately 10,000 rpm. Due to the low hydrodynamic resistance of the impeller 6, the pump 60 does not require gears and the high rotational speeds do not cause significant cavitation effects in the oil.

[0039] Referring to FIG. 4, it should be noted that the pump 60 may include an impeller 6 having a plurality of axially aligned annular disks 6b stacked above a solid disk 6a and uniformly spaced relative to each other and the solid disks 6a. The central opening 5 of each annular disk 6b is also substantially uniform, again allowing for central passage of oil O into the impeller 6 and into the spaces between each disk 6a, 6b. For example, the impeller may include two, three, four, or five annular disks 6b mounted in a stacked arrangement in combination with a solid disk 6a. As can be seen in FIG. 4, increasing the number of rotary disks 6a, 6b can significantly improve the pressure head generated by the pump 60 as well as its efficiency, although improvements tend to diminish when the number of disks exceeds five. Figure 4 shows the disc pump efficiency and pressure head for synthetic (polyalphaolefin) oil O at a flow rate of 7 liters / min and 80 °C. The computational fluid dynamics (CFD) results are calculated at a pump inlet pressure of 30 mbar, a disc diameter of 120 mm, and a shaft speed of 4800 rpm.

[0040] The rotary disc pump 60 operates to circulate or supply oil from a reservoir 70 to the upper and lower bearings 21, 31. Because the spin axis Z is vertical, the oil O supplied to the upper and lower bearings 21, 31 is naturally guided by gravity to the oil sump or reservoir 70. That is, the oil sump or reservoir 70 is located at the bottom of the housing 13 below the vacuum chamber 12 and collects the oil. In this way, the vacuum chamber 12 becomes a single chamber operating at a single pressure V. This not only reduces the air resistance of the flywheel 33, thereby reducing both the power required to maintain the flywheel speed (rpm) and the heat generated by air resistance against the rotating flywheel 33, but also enables a simpler design of the gyrostabilizer assembly 1, since no rotary shaft seals are required to isolate the upper and lower rotary bearings 21, 31 from the operating pressure V of the flywheel chamber 12. This simple configuration of the gyrostabilizer assembly 1 results in easier small-scale manufacture of the gyrostabilizer assembly 1.

[0041] Referring to FIG. 1 , the lubrication oil circuit 9 includes an additional positive displacement pump 75 external to the housing 13 and vacuum chamber 12, which functions as a start-up, stop-down, and boost pump. This additional positive displacement pump 75 can thus be employed to generate oil pressure in the lubrication oil circuit 9 before the flywheel 33 and flywheel shaft 34 begin operating (i.e., before the rotary disc pump 60 is activated). This positive displacement pump 75 can also operate to boost oil pressure in the lines or conduits 71, 79, 50, and 51 when the rotary disc pump 60 is operating, to improve oil supply to the bearings 21 and 31. This external positive displacement pump 75 may be, for example, a vaned centrifugal pump magnetically coupled to a brushless electric motor. From the positive displacement pump 75, oil flows through a check valve 77 and a filter 38 through the oil circuit 9, and oil O flows through a conduit 79 to the oil cooler 39. The oil cooler 39 is shown as two heat exchanger units 40, 41 connected in series, with cooling water supplied or flowing in through line or conduit 42 and flowing out through line or conduit 44. Oil exits the cooler 39 and flows to the oil accumulator 36. The oil accumulator 36 stores the oil and maintains oil pressure to buffer fluctuations in oil pressure from the pumps 60, 75. The oil pressure maintained by the oil accumulator in the oil circuit 9 is preferably in the range of about 1.5 bar to about 3 bar (absolute). A check valve (i.e., check valve) 77 located upstream of the oil accumulator 36 prevents back pressure from the oil accumulator 36 from acting on the oil sump or reservoir 70. In this way, the oil accumulator 36 can support the oil spurting pressure in the bearings 21, 31, 32 due to oil splash conditions in the pump 60 and / or when the oil supply may be absent for a period of time at the inlet to the oil sump pump 60, for example, when the gyrostabilizer 1 experiences an extended period at a high precession angle (e.g., about 70°) during a U-turn of the vessel. The oil accumulator 36 is preferably a bladder-type or piston-type oil accumulator.Downstream of the oil accumulator 36, the oil flow is then split between a line 50 to the upper rotary bearing 21 and a line 51 to the lower rotary bearing 31 and thrust bearing 32. It will be appreciated that the oil accumulator 36 can be located anywhere along the oil circuit 9 between the positive displacement pump 75 and the branches to the two conduits 50, 51.

[0042] The oil lubrication system 8 includes one or more oil outlets 54, 64, 67 in each of the upper and lower rotary bearings 21, 31 and the thrust bearing 32 for targeted delivery or injection of oil O through the oil circuit 9. The oil flow rate is selected to allow a desired amount of heat generated in the bearings 21, 31, 32 to be exchanged with the oil. Thus, the oil lubrication system 8 also forms a cooling system for the bearings 21, 31, 32, with the oil acting as a coolant to remove heat from the bearings. In particular, oil injection through the oil outlets 54, 64 ensures that the oil O is injected toward the rolling elements of the rotary bearings 21, 31 with sufficient velocity and pressure to mix with the boundary layer oil for effective lubrication and cooling. To this end, the oil circuit 9 includes heat exchangers 40, 41 for removing heat from the oil before it is delivered to the upper and lower bearings 21, 31. In this regard, the walls 72 of the oil sump or reservoir 70 may form or function as a heat exchanger for the oil O as it returns under gravity to the reservoir 70, optionally via a cooling medium provided in the walls 72 (e.g., in the form of a water jacket) and / or via fin elements (not shown) formed in the walls. As mentioned above, the oil circuit 9 includes at least one filter 38 for filtering the oil O before re-injection at the oil outlets 54, 64, 67.

[0043] 1 , the upper and lower bearings 21, 31 are provided with oil labyrinths 55, 62 around them to prevent oil O applied to the bearings 21, 31 from flowing to places where it should not, such as onto the flywheel 33 or onto the thrust bearing 32, which is cooled separately via line 65 and jet nozzle 67. These oil labyrinths 55, 62 direct the flow of oil via oil return lines or passages 58, 59, 68 to an oil sump or reservoir 70. As mentioned above, the oil sump or reservoir 70 is located within or on the housing so that oil supplied, circulated, or dispensed to the first and second rotary bearings 21, 31 and the thrust bearing 32 flows out of the respective bearings 21, 31, 32 via the respective oil labyrinths 55, 62 and returns to the reservoir 70 under gravity. The oil is preferably a synthetic oil with a vapor pressure of less than 40 mbar at 80°C.

[0044] The following tests were carried out using a rotary disc pump operating at rough vacuum, either alone or in combination with a vaned boost pump. Test: Rotary disc pump 60 operated at 4800 rpm under rough vacuum. The rotary disc pump (vaneless / vaned) was tested to deliver up to 6.7 l / min of synthetic polyalphaolefin oil at an absolute suction pressure of 32 mbar and an outlet pressure of 1.3 bar at an oil temperature of 65°C. Test 2: A rotary disc pump 60 was operated at 4800 rpm in rough vacuum in combination with a vaned boost pump or a positive displacement pump 75. The closed rotary disc pump was connected in series with the vaned boost pump during the test, pumping synthetic (polyalphaolefin) oil at an absolute suction pressure of 37 mbar up to 1.8 l / min, delivering an absolute pressure of 1.1 bar at the disc pump outlet and 3.2 bar at the vaned pump outlet, with an oil temperature of 74°C. Test 3: A rotary disc pump 60 was coupled with a vaned positive displacement pump 75 and operated at 3000 rpm in rough vacuum. During the test, the closed rotary disc pump was connected in series with a vaned boost pump to pump up to 9.5 l / min of synthetic (polyalphaolefin) oil at an absolute suction pressure of 14 mbar, providing 0.6 bar absolute pressure at the disc pump outlet and 3.1 bar absolute pressure at the vane pump outlet, with an oil temperature of 69°C. Test 4: A rotary disc pump 60 was coupled with a vaned positive displacement pump 75 (air / oil mixed flow) operating at low pressure at 4800 rpm. The closed rotary disc pump was connected in series with a vaned boost pump during the test, pumping up to 11.7 liters / minute of synthetic (polyalphaolefin) oil at an absolute suction pressure of 332 mbar. At an oil temperature of 70°C, it delivered 1.0 bar absolute pressure at the disc pump outlet and 3.1 bar absolute pressure at the vaned pump outlet.

[0045] Advantages of rotary disc pumps include the ability to run dry without damage, the ability to operate at high temperatures, the benefit of high viscosity fluids, essentially no cavitation in a vacuum and virtually laminar flow, little maintenance required, low manufacturing costs, low height, no break-in period required, the ability to pump gas-liquid mixtures, suitable for operation at high RPMs, and no interference with the starter pump.

[0046] 5, there is shown a vessel S, such as a ship, yacht, or boat, including a gyrostabilizer assembly 1 according to the embodiment of the present disclosure described above. The gyrostabilizer assembly 1 is rigidly fixed to the hull H of the vessel S adjacent to the keel K.

[0047] Referring to Figure 6, there is shown a hoisting system, such as a crane C, including a gyroscopic stabilizer assembly 1 according to an embodiment of the present disclosure as described above. In this context, the gyroscopic stabilizer assembly 1 is designed to be suspended from an operating hoisting system to damp or suppress undesired oscillatory rotation of a load L during hoisting operations, such as oscillatory rotation caused by wind gusts. A gyroscopic stabilizer assembly 1 is provided for and / or mounted along each axis of stabilization required.

[0048] While specific embodiments of the present invention have been illustrated and described herein, it will be recognized by those skilled in the art that various alternative and / or equivalent embodiments exist. It should be understood that each exemplary embodiment is merely an example and is not intended to limit the scope, applicability, or configuration of the present invention in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment. It will be understood that various changes can be made in the function and arrangement of elements described in the exemplary embodiments without departing from the scope as defined by the appended claims and their legal equivalents. In general, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0049] In general, the present disclosure is intended to cover any adaptations or variations of the specific embodiments discussed herein. As an example, those skilled in the art will readily understand that the gyrostabilizer assembly 1 and systems of the present disclosure are not limited to being made from any particular material described in the specific embodiments. Rather, those skilled in the art will understand that a range of suitable materials exists, and they can readily select an appropriate material based on the known mechanical properties of that material that are suitable for use in the present disclosure. Because the present disclosure involves many fields of engineering, it is expected that the intended "person skilled in the art" will consist of a group or team of individuals with technical expertise and / or qualifications in one or more fields or disciplines, including mechanical engineering, marine engineering, and hydraulic engineering.

[0050] It is also understood that, as used herein, the terms “comprise,” “comprising,” “include,” “including,” “contain,” “containing,” “have,” “having,” and variations thereof, are intended to be understood in an inclusive (i.e., non-exclusive) sense unless the context indicates otherwise. Any process, method, device, apparatus, or system described herein is understood in a non-exclusive sense such that it is not limited to the described features, integers, portions, elements, or steps, but may include other features, integers, portions, elements, or steps not expressly described and / or inherent in such process, method, device, apparatus, or system. Furthermore, the indefinite articles “a” and “an,” as used herein, are intended to be understood to mean one or more unless expressly stated otherwise. Furthermore, the terms “first,” “second,” “third,” etc., are used merely as labels and are not intended to impose numerical requirements on the importance of their objects or to establish an order of importance. Additionally, references to positional terms such as "lower" and "upper" used in the above description should be taken in the context of the illustrated embodiments and should not be taken as limiting the invention to the literal interpretation of the terms, but rather as would be understood by one of ordinary skill in the art in the appropriate context. [Explanation of symbols]

[0051] 1 Gyro Stabilizer Assembly 5 Central opening 6 impeller 6a Flat solid disc 6b Annular or ring-shaped disc 7 Stems, bolts or fasteners 8 Oil Lubrication System 9 Oil Circuit 12 Vacuum chamber 13. Housing 21 Upper bearing 31 Lower bearing 32 Thrust bearing 33 Flywheel 34 Flywheel shaft 36 Oil accumulator 38 filters 39 Oil cooler 40 Heat exchanger 41 Heat exchanger 42 Cooling water supply line 44 Cooling water supply line 50 Oil supply line 51 Oil supply line 52 Electric Motor 53 Magnetic Coupling 54 Oil outlet 55 Oil Labyrinth 58 Oil return line 59 Oil return line 60 Pump 62 Oil Labyrinth 64 Oil outlet 65 Oil supply line 67 Oil outlet 68 Oil return line 70 Oil sump or reservoir 71 Oil supply line 72 Oil sump / reservoir wall 75 positive displacement pump 77 Check valve 79 Oil supply line Z shaft rotation or spin axis V partial vacuum O Lubricating oil / oil W is the radial width of the annular disc t is the thickness of the annular disc S ship H Hull K Keel C. Hoisting equipment or crane L cargo

Claims

1. a housing defining a chamber for holding an operating pressure; a flywheel mounted within said chamber for rotation about a spin axis under operating pressure; a flywheel shaft having a flywheel mounted within the housing; a bearing lubrication system; Equipped with the flywheel shaft is supported by first and second spin bearings located at opposite end regions of the flywheel shaft for rotating the flywheel about the spin axis; the first spin bearing and the second spin bearing are disposed within the housing for use under operating pressure or differential pressure; the bearing lubrication system includes an oil circuit for circulating the lubricant to the first spin bearing and the second spin bearing from an oil sump or reservoir positioned or configured to collect the lubricant under gravity from the first spin bearing and the second spin bearing; the bearing lubrication system includes a rotary disc pump for circulating lubricant through the oil circuit to the first spin bearing and the second spin bearing; The gyro stabilizer assembly, wherein the rotary disc pump is coupled to or driven by the flywheel shaft.

2. 2. The gyrostabilizer assembly of claim 1, wherein the impeller of the rotary disc pump is rotated by the flywheel shaft at a speed ranging from about 3,000 rpm to about 10,000 rpm, preferably from 5,000 rpm to 10,000 rpm.

3. 3. The gyro stabilizer assembly of claim 1, wherein the rotary disc pump is disposed in an oil sump or reservoir submerged in the lubricant.

4. the rotary disc pump impeller includes at least two flat discs mounted in an axially aligned and generally parallel arrangement; 4. A gyrostabilizer assembly according to claim 1, wherein the two flat discs preferably comprise a solid first disc and a second annular disc of substantially the same outer diameter as the first disc.

5. a rotary disc pump coupled to or driven by said flywheel shaft forming a first stage of a two-stage pump arrangement; 5. A gyrostabiliser assembly according to any one of claims 1 to 4, wherein a vaned centrifugal pump forms the second stage of the two-stage pump arrangement.

6. the lubricant is an oil such as a synthetic oil, 6. A gyrostabiliser assembly according to any one of claims 1 to 5, wherein the oil preferably has a vapour pressure of less than 40 mbar at 80°C.

7. 7. The gyrostabilizer assembly according to claim 1, wherein the oil circuit provided outside the housing includes an oil accumulator for storing lubricant and maintaining the pressure of the lubricant.

8. the oil circuit includes a positive displacement pump external to the housing that circulates the lubricant from the oil sump or reservoir to the bearings and back, the positive displacement pump acting as a start, stop and boost pump; 8. A gyrostabiliser assembly according to any one of claims 1 to 7, wherein the positive displacement pump is preferably a vaned pump, preferably magnetically coupled to a brushless electric motor.

9. the first spin bearing and the second spin bearing are provided with lubricant labyrinths around their peripheries to prevent lubricant supplied to the first spin bearing and the second spin bearing from flowing into the flywheel; 9. The gyrostabilizer assembly according to claim 1, wherein the lubricant labyrinth redirects the lubricant so that it flows through a passageway to the oil sump or reservoir.

10. 10. The gyrostabilizer assembly according to claim 1, wherein the bearing lubrication system includes lubricant outlets, in particular injection ports, for targeted release or injection of lubricant at each of the first spin bearing and the second spin bearing.

11. 11. The gyro stabilizer assembly of claim 1, wherein the first spin bearing and the second spin bearing are constructed and arranged within the housing such that lubricant circulated through the first spin bearing and the second spin bearing flows out of each of the first spin bearing and the second spin bearing to return to the oil sump or reservoir under gravity.

12. the flywheel shaft is vertically mounted within the housing for rotation about a vertical spin axis; 12. The gyro stabilizer assembly of claim 1, wherein the first spin bearing and the second spin bearing comprise upper and lower spin bearings, respectively.

13. an electric motor for driving rotation of the flywheel about the spin axis; 13. A gyro stabilizer assembly according to claim 1, wherein the electric motor is mounted on the outside of the housing and is coupled to the flywheel shaft via a magnetic coupling.

14. the operating pressure is such that the chamber in which the flywheel is mounted forms a vacuum chamber; A gyrostabiliser assembly according to any one of claims 1 to 13, wherein the operating pressure is preferably a partial or rough vacuum in the range of about 1 mbar to 100 mbar.

15. a housing defining a chamber for holding a partial vacuum; a flywheel mounted within the chamber to enable rotation about a spin axis under partial vacuum; a flywheel shaft mounted within the housing for rotating the flywheel about the spin axis; a bearing lubrication system; Equipped with the flywheel shaft is rotatably supported by a first bearing at one end region of the flywheel shaft and by a second bearing at the other end region of the flywheel shaft; the first bearing and the second bearing are disposed within the housing to operate under a partial vacuum; an oil sump or reservoir disposed within or on the housing to collect oil from the first bearing and the second bearing under gravity; the bearing lubrication system is configured to supply oil from the oil sump or reservoir to the first bearing and the second bearing via an oil circuit; 10. A gyro stabilizer assembly for a marine vessel, wherein the bearing lubrication system includes a rotary disc pump for pumping or circulating oil through the oil circuit.

16. 16. The marine gyro stabilizer assembly according to claim 15, wherein the rotary disc pump in the reservoir is coupled to and driven by the flywheel shaft.

17. 16. The marine gyro stabilizer assembly according to claim 15, wherein the rotary disc pump is decoupled from the flywheel shaft and driven by an electric motor.

18. 18. A marine gyrostabilizer assembly according to any one of claims 15 to 17, wherein the rotary disc pump includes at least two flat discs mounted in a generally parallel arrangement, preferably including a solid flat first disc and an annular flat second disc of the same outer diameter as the axially aligned first disc.

19. A watercraft, in particular a boat or motor yacht, comprising a gyro stabilizer assembly according to any one of claims 1 to 18, the gyro stabilizer assembly being fixed to the hull of the vessel.

20. A hoisting device comprising a gyro stabilizer assembly according to any one of claims 1 to 18, wherein the gyro stabilizer assembly is adapted to be suspended together with cargo.

21. a housing defining a chamber for holding an operating pressure; a flywheel mounted within said chamber for rotation about a spin axis under operating pressure; a flywheel shaft having a flywheel mounted within the housing; a bearing lubrication system; Equipped with the flywheel shaft is supported by first and second spin bearings located at opposite end regions of the flywheel shaft for rotating the flywheel about the spin axis; the first spin bearing and the second spin bearing are disposed within the housing for use under operating pressure or differential pressure; the bearing lubrication system includes a lubricant circuit for circulating the lubricant to the first spin bearing and the second spin bearing from an oil sump or reservoir positioned or configured to collect the lubricant under gravity from the first spin bearing and the second spin bearing; the bearing lubrication system includes pump means within the oil sump or reservoir for circulating the lubricant through the lubricant circuit to the first spin bearing and the second spin bearing; 10. A gyroscopic stabilizer assembly according to claim 9, wherein said pump means is coupled to said flywheel shaft and driven by said flywheel shaft.

22. the pump means in the oil sump or reservoir comprises a rotary disc pump; 22. The gyrostabilizer assembly of claim 21, wherein the impeller of the rotary disc pump is rotated by the flywheel shaft at a speed ranging from about 3,000 rpm to about 10,000 rpm, preferably from 5,000 rpm to 10,000 rpm.

23. 23. The gyro stabilizer assembly of claim 22, wherein the rotary disc pump is disposed in an oil sump or reservoir submerged in the lubricant.

24. the pump means provided within the oil sump or reservoir comprises a two-stage pump arrangement; a rotary disc pump coupled to and driven by the flywheel shaft forming a first stage of the two-stage pump arrangement; 24. A gyrostabiliser assembly according to any one of claims 21 to 23, wherein a vaned centrifugal pump forms the second stage of the two-stage pump arrangement.

25. the lubricant is an oil such as a synthetic oil, 25. A gyrostabiliser assembly according to any one of claims 21 to 24, wherein the oil preferably has a vapour pressure of less than 40 mbar at 80°C.

26. 26. A gyrostabilizer assembly as claimed in any one of claims 22 to 25, wherein the impeller includes a plurality of disks mounted in an axially aligned, generally parallel arrangement relative to one another.

27. 27. The gyrostabilizer assembly according to any one of claims 22 to 26, wherein the outer diameter of each disk of the impeller is in the range of about 100 mm to about 200 mm.

28. 28. A gyrostabilizer assembly according to any one of claims 22 to 27, wherein the radial width of each annular disc is in the range of about 20% to about 40% of the outer diameter of the annular disc.

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