JP3346589B2 - Underwater propulsion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an underwater propulsion device,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated motor type propulsion system for a ship, which is improved to enable high thrust, light weight, low noise, and easy maintenance.

[0002]

2. Description of the Related Art Integrated motor type propulsion systems are already known. Such a propulsion device can be generally used for ships, but its main use is as a secondary drive device for submarines where reliability, controllability, and low noise are important. Many of the known single motor propulsion systems are equipped with "canned" or wet-winding motors whose output shaft is connected to a propeller. The propeller is typically surrounded by a shroud to increase thrust, and the motor is located just in front of or behind the propeller. However, as the "canned" motor is located just in front of or behind the water flow generated by the propeller, a barrier to liquid flow is formed, which reduces the effective thrust by the propulsion device. In order to reduce the thrust loss due to such a barrier, a high-speed and small-diameter motor was used. But,
The higher the rotational speed of the shaft, the higher the cavitation of the propeller, which generates a high level of noise.

To overcome these shortcomings, the Applicant has developed an integrated motor type propulsion device as disclosed in US Pat. No. 4,831,297. This particular propulsion device is similar in structure to a jet engine, with the major components being a cylindrical shroud with inlet and outlet, a shaft mounted concentrically within the shroud by a plurality of support vanes. It comprises a propeller having a hub rotatably mounted, and an electric motor for driving a propeller including an annular rotor provided around the propeller blades and a stator integrally provided in the shroud. The novel design of this known propulsion system significantly increases the thrust output of the propulsion system at a given weight and size, while at the same time allowing the propeller to generate a very free water flow by hydrodynamically forming the shroud. Therefore, the amount of generated noise is reduced. The low noise of the propulsion device is further enhanced by the sound insulation properties of the shroud.

[0004] While the above-described integrated motor type propulsion system is a remarkable advance in technology, applicants have noticed that there is much room for improvement in the design of this system. For example, thrust and radial bearings lubricated with water need to be replaced periodically, which requires the device to be dry docked. In addition, if the bearing parts need to be inspected or replaced, the thruster must be almost completely disassembled because the location of the bearing is the location. Applicants have noticed that the support vanes located upstream of the propeller cause cavitation in the water around the propeller during operation of the propulsion device, which not only causes noise, but also reduces the efficiency of the device. . Applicant may also
In the induction motor configuration adopted in this known propulsion device, if the electromagnetic coupling between the rotor and the stator is to be effectively realized, an inevitable result is that the distance between the outer diameter of the rotor and the inner diameter of the stator is extremely large. I noticed that it was getting smaller. Such a small spacing not only creates a drag due to the thin water film interposed between the stator and the rotor, but also flows through the rotor (which is always present to some extent due to the imbalance of the magnetic field generated by the stator). Increasing the harmonic current increases noise and vibrates the rotor. If the distance between the inner diameter of the stator and the outer diameter of the rotor must be reduced, a high level of mechanical shock may be applied to the propulsion device, or foreign matter in seawater may become jammed between the stator and the rotor. In that case, important parts of the propulsion device will be damaged.

There is a need for an improved integrated motor propulsion system for submarines and the like that includes a bearing assembly that does not require dry docking and that can be relatively easily and easily serviced and maintained. It is clear. Ideally, such a propulsion device would be quieter than known devices and the rotor-to-stator spacing would be less likely to be damaged by mechanical shocks or clogged by seawater debris. Therefore, a design which does not need to be narrowed is adopted.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an integrated motor type propulsion device which overcomes or at least alleviates the above-mentioned disadvantages of the prior art devices, and the propulsion device of the present invention which achieves this object. Includes a shroud having a water inlet and a drain as main parts thereof, a propeller having a hub rotatably mounted on a shaft in the shroud, a rotor provided around the propeller, and a stator provided on the inner periphery of the shroud. A motor assembly for driving the propeller and a bearing assembly interposed between the hub and shaft of the propeller and lubricated and cooled by surrounding water surrounding the device. The bearing assembly may include a thrust mechanism for circulating the flow of lubrication / cooling water between the bearing surfaces. In addition, one or more water inlets located downstream of the propeller may be provided on the shaft to provide a constant lubrication / cooling water flow to the bearing assembly, and these water inlets may be covered by a filter. You may. By providing these water suction ports on the downstream side, it is possible to more reliably prevent foreign substances contained in surrounding water from entering the bearing assembly.

The bearing assembly reduces friction between these two device parts by including both a thrust bearing interposed between the propeller and the upstream end of the shaft and a radial bearing cartridge disposed on the inner periphery of the propeller hub. be able to. The device of the present invention can also include a cover that is removably attached to the thrust bearing to facilitate access to the thrust bearing and the radial bearing cartridge during maintenance operations. The removable cover is connected to the propeller hub and is configured to rotate integrally with the propeller as the device is operated, or is detachably fixed to the inlet end of the shaft and remains stationary with respect to the rotating propeller. As separate components. Removable covers configured to remain stationary have the advantage of reducing noise generated during operation of the propulsion device. If necessary, the impact resistance of the device can be increased by supplementing struts between the stationary removable cover and the shroud.

A plurality of blade members connect the shaft of the device to the inner surface of the shroud. To further reduce the amount of noise generated by the flow of water through the shroud, in one embodiment, all of these vanes are connected to a portion of the shaft located between the propeller hub and the shroud outlet end. The blade members not only support the shaft concentrically within the shroud, but also increase thrust by the propulsion device by cooperating with the blades of the propeller.

[0009] The rotor of the AC motor used to drive the propeller of the device generates the required magnetic field in the rotor by utilizing permanent magnets instead of induction windings. The use of permanent magnets not only increases the overall efficiency of the motor (because impedance losses due to induction windings are avoided), but also more advantageously the gap between the rotor outer diameter and the stator inner diameter Can be increased without impairing the magnetic coupling between the two. When the gap is widened, the fluid drag acting on the rotor is reduced, and the harmful harmonic current generated in the rotor is weakened due to the irregular magnetic field generated by the rotor and the stator, reducing the vibration of the rotor. Thus, a smooth and quiet operation can be obtained. The wider gap reduces the possibility of foreign matter in the seawater clogging here and damaging the device.

[0010] The rotor may also include a plurality of conductive damper bars on the perimeter of the permanent magnet, thereby forming a cage structure that facilitates synchronization of the rotor with fluctuating magnetic fields generated by the stator. These damper bars also serve to insulate the magnet from demagnetizing currents, such as the frequency currents described above, or currents caused by short circuits in the device. To accommodate the conductive damper bar and to isolate it from the magnet, the individual permanent magnets may be covered with a pole cap. To increase the current carrying capacity of the car structure, a conductive wedge may be interposed between the permanent magnets in the rotor. The stator slots are preferably oblique slots in order to further reduce noise.

With the structural components described above, a propulsion device that is lighter, has higher output, and has lower noise than known devices can be obtained.

The above and other objects and features of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As can be seen from FIGS. 1, 2, 3 and 4, in which the same components are provided with the same reference numbers, the propulsion device 1 according to the invention has an inlet 5 and an outlet 7, the interior of A shroud assembly 3 having the shape of a Kort nozzle is included as a main part. Shroud assembly 3 by a plurality of blade members 11
The fixed shaft 9 is attached along the rotation axis inside. The blade member 11 connects the shaft 9 to the shroud assembly 3.
In addition to being supported in the propeller 13, the propeller 13 is disposed in an inclined direction (as is apparent from FIG. 4).
It also has the function of increasing the thrust generated by this. The propeller 13 is arranged inside the shroud assembly 3.
The propeller 13 includes at its center a hub 15 rotatably mounted on the fixed shaft 9 by a bearing assembly 17. The propeller 13 also includes a plurality of angled vanes 19 having inner ends mounted at regular intervals around the hub 15 and having outer ends connected to a rotor 23 of an electric motor 24 integral with the center of the shroud assembly 3. . The motor 24 also includes a stator 25 that is closely spaced around the rotor 23. A stator terminal post assembly 27 is provided at the upper end of the propulsion device 1 for connecting the stator 25 of the propulsion device 1 to a power supply 28, which in the preferred embodiment comprises a variable frequency cycloconverter.

As shown in FIGS. 2 and 5, the bearing assembly 17 of the propulsion device 1 is provided with a radial bearing cartridge 30 and a thrust thrust mechanism for minimizing friction between the propeller 13 and the shaft 9 in both the circumferential direction and the axial direction. The bearing assembly 45 is included. 5, the radial bearing cartridge 30 includes a tubular bushing 32, preferably formed of Monel metal, which is preferably formed of Monel metal and includes a pair of bolt lugs 34 each including a threaded hole 35. The hub 15 is fixed around the inner diameter of the hub 15. The screw hole 35 is screwed with a bolt 37 present in the flared upstream portion 36 of the hub 15. Bolt 37
Needless to say, the tubular bushing 32 rotates together with the hub 15 with respect to the fixed shaft 9 when fixing the position shown in FIG. A pair of rubber bearing sleeves 38a, 38b are also provided around the inner diameter of the tubular bushing 32.
These sleeves are located in an annular recess 40 formed along the inner surface of the tubular bushing 32 to prevent axial movement between the bearing sleeves 38a, 38b and the tubular bushing 32. Each of the rubber bearing sleeves 38a, 38b includes a plurality of spiral grooves 42 on each of its inner diameters which allow the bearing sleeves 38a, 38b to expel foreign matter in seawater which constantly flows between the sleeves 38a, 38b and the shaft 9. help.

The thrust bearing assembly 45 includes a primary thrust bearing 47 configured to receive an axial load generated by the propeller 13 during operation of the apparatus 1 and a "windmilling" when the motor 24 is not operating. "Propeller 1
3 including a secondary thrust bearing 75 configured to receive a much smaller load.

The primary thrust bearing 47 includes an annular runner 51 formed from a slanted annular pad 51 that supports an annular rubber ring 53. The inclined annular pad 51 is preferably formed of monel metal. The inclined annular pad 51 and the rubber ring 53 are connected to the screw hole 55 of the pad 51 and the hub 15.
Of the hub 15 via bolts 57 provided on the flared upstream portion 36. The primary thrust bearing 47 is also fixed to the non-rotating shaft 9 and also includes a bearing ring 60 slidably engaging the annular rubber ring 53 of the runner 49 during operation of the device 1. A plurality of radial grooves 61 are formed around the bearing ring 60 to create a seawater lubrication film between the rubber ring 53 and the ring 60 of the runner 49.
Is provided. The groove 61 also circulates seawater between the runner 49 and the ring 60 constantly, and also serves to reduce wear by dissipating frictional heat. The bearing ring 60 includes a plurality of link pin supports 6 fixed to a support pad 64.
2a and 62b. The support pad 64 is a key 66 that prevents the pad 64 from rotating with respect to the shaft 9.
Is fixed to the non-rotating shaft 9. The holding stud 6 is provided on the side of the support pad 64 opposite to the bearing ring 60.
9 attaches the bumper plate 67. The bumper plate 67 includes the plate 67 and the support pad 64.
The pad 6 can be slightly "wobbled" relative to the pad 64 in response to a slight misalignment between
4 has a concave surface engaging with the convex surface. The bumper plate 67 is mechanically integrated with the structure of the primary thrust bearing 47, but forms part of the secondary thrust bearing 75. Lock nut 72 is lock nut washer 7
In cooperation with 4, the support pad 64 is axially fixed to the non-rotating shaft 9.

The secondary thrust bearing 75 is located upstream of the primary thrust bearing 47 and includes a runner 77 formed on an annular rubber ring 79. Like the bearing ring 60 described above, the annular rubber ring 79 also includes a groove 80 for generating a seawater film between the ring 79 and the facing annular support pad 81. Preferably annular support pad 81
Is also formed of Monel metal. The annular support pad 81 includes a plurality of radial thrust holes 83 to facilitate the circulation of seawater through the entire bearing assembly 17. The inner end of the thrust hole 83 is a pad 81
Communicates with the central opening 84 of During operation of the device 1, the pads 81 act as thrust means for forcing seawater to circulate on various bearing surfaces in the bearing assembly 17.

At the upstream end of the shaft 9, a removable round cover 85 for preventing unfiltered seawater from flowing into the bearing assembly 17 is provided. In this embodiment of the present invention, the removable cover is attached to the runner 77 of the secondary thrust bearing 75.
The cover is rotated with respect to the non-rotating shaft 9 when the electric motor 24 operates. For this reason, the cover 85 includes a plurality of recesses 87 that receive mounting bolts 89 that are screwed into screw holes provided on the upstream peripheral edge of the annular support pad 81. Detachable cover 85
A plurality of water holes 91 are provided around the front surface of the cover assembly 85 to allow sufficient seawater to flow into the cover 85 to prevent generation of a pressure difference that hinders seawater flow between bearing surfaces in the bearing assembly 17. Preferably, a filter 92 for preventing foreign substances from flowing into the cover 85 together with seawater is incorporated in each of the water holes 91.

The cover 8 in which the entire bearing assembly 17 is detachable.
5. Lock nut and lock nut washer 72,
74, the key 66, and the mounting bolts 57, 37, so that the primary and secondary thrust bearings 47,
Both the 75 and the radial bearing cartridge 30 are easily accessible from the front. In this way, since the access can be easily made from the front, maintenance work such as repair or replacement of parts can be performed without removing the entire propulsion device 1 from the mounted ship or putting the ship in the dry dock. . This is an important advantage since no matter how well designed the individual components of the bearing assembly 17 are subject to repair or replacement during the service life of the propulsion device 1.

At the downstream end of the shaft 9, the aforementioned blade 11
And a vane hub 95 connected to the respective inner ends of the blades. A mounting bolt 97 connects the blade hub 95 to the downstream end of the non-rotating shaft 9. The blade hub 95 includes a plurality of water holes 99, which are also covered with a filter material 102 to prevent foreign matter from flowing into the hollow interior 104 of the blade hub 95 together with the surrounding seawater. 2 and 5, the hollow interior 104 of the vane hub 95 communicates with the center hole 106 of the non-rotating shaft 9.

The manner in which seawater circulates through the bearing assembly 17 can best be understood with particular reference to FIG. As indicated by arrows, the surrounding seawater passes through the filter material 102 from the downstream water inlet 99 and further passes through the hollow interior 1 of the blade hub 95.
04 flows through the center hole 106 of the shaft 9.
From the center hole, the pad passes through the center opening 84 of the pad 81 and passes through a plurality of thrust holes 83. The pressurized water flow generated under the centrifugal force acting on the seawater passing through the thrust hole 83 flows backward from the outer end of the thrust hole 83 again along the outer periphery of the support pad 64 of the primary thrust bearing 47, and the bearing ring 60 And flows into the central opening of the runner 49 of the primary thrust bearing 47, and from there through the space between the rubber bearing sleeves 38a, 38b and the outer surface of the non-rotating shaft 9, the radial opening 10 extends.
Emitted from 7. Although a certain amount of seawater flows in the water holes 91 of the detachable cover 85 described above, the water holes 91 are dimensioned to have a much smaller cross-sectional area than the water holes 99 of the blade hub 95. With such dimensions, most of the seawater used to lubricate and cool the various bearing surfaces of the bearing assembly 17 is drawn into the device 1 from the downstream end, and the filter material 102 is inserted into the water holes 99. Because it exists
It is possible to prevent foreign matter from flowing into the center hole 106 of the shaft 9 together with seawater.

FIGS. 7 and 8 show details of the electric motor 24 driving the propeller 13 of the device 1. As already mentioned, the electric motor 24 is a rotor 23 provided around the blades 19 of the propeller 13 so as to be closely surrounded by a stator 25 "canned" in the shroud assembly 3 as a seed. An AC motor consisting of In a preferred embodiment, the AC motor 24 is preferably of the permanent magnet type. Although an induction type AC motor can be used, a permanent magnet type AC motor is preferred for two reasons. First, the efficiency of permanent magnet motors is about 10% higher than induction type motors. Second, this high efficiency can be achieved with a slightly wider gap between the outer peripheral edge of the rotor 23 and the inner peripheral edge of the stator 25. With the propulsion device 1 in operation, this wide gap is a standard 0.635 c
As large as 1.31 cm (0.50 inch) for gaps of 0.25 inch (m) or less. Adopting a wide gap (as opposed to a narrow gap) not only reduces the frictional losses created by the seawater turbulent film between the rotor 25 and the stator 25, but also creates a specific point in the propulsion device. The amount of noise generated can also be reduced. Another advantage is that the amount of harmonic current (caused by the undesirable asymmetry of the magnetic field emanating from the stator windings) is relatively small, and therefore the oscillations caused by interaction with the harmonic current in rotor 23 are also reduced. . Vibration due to misalignment “sway” of the rotor 23 due to rotation in the stator 25 is also reduced. Due to the wide gap made possible by using a permanent magnet for the motor 24, the rotor 23 in the stator 25 is formed by foreign matter entering this gap.
Is less likely to be hindered or stopped, and the overall resistance of the device 1 to external impacts is increased. That is, the rotor 23 is less susceptible to damage caused by the impact of misalignment with respect to the stator 25. All of these are important advantages, especially for submarine applications.

As is particularly apparent from FIG.
Includes a plurality of equally spaced stator core windings 110. Each stator core winding 110 is connected to a lead wire 111 of the terminal post assembly 27. Each stator core winding 110 is housed in a slot in a stator core 112 (not shown in FIGS. 7, 8 but shown in FIGS. 2 and 5) made of laminated magnetic steel that conducts a magnetic field generated from the winding 110. Is done.
A plurality of holding bars 114 are welded around the outer diameter of the iron core 112 to integrally hold the laminated ring forming the iron core 112. All parts of the stator 25 are the inner wall 118 and the outer wall 12.
The housing is housed in a watertight stator housing 116 defined by a zero.

The rotor 23 of the electric motor 24 is formed by a plurality of trapezoidal magnets 125 provided in a magnet housing ring 127 made of carbon steel. Each magnet 125 is preferably formed of an NbBfe alloy having excellent magnetic field capacity and BH curve characteristics. Each magnet 125 is held within magnet housing ring 127 by a zirconium-copper rotor wedge 128 secured to ring 127 via bolts 129. In the preferred embodiment, about 20 trapezoidal magnets 125 are incorporated in the rotor 23. Each magnet 12
Four dampers consisting of solid copper rods on top of five
A bar 130 is provided. The damper bar 130 is a magnetic pole cap member 13 fixed to the upper end of each magnet 125.
3 are arranged in the concave portions. The purpose of the damper bar 130 and the rotor wedge 129 is to allow the rotor 23
Is to protect the magnet 125 from harmonic currents generated on the top surface of the magnet 125. Specifically, if a harmonic current is generated, the damper bar 130 and the rotor wedge 1 having high conductivity are used.
Concentrate on 28 and dissipate safely. If the rotor 23 does not have the damper bar 130 and the rotor wedge 128, the harmonic current flows directly through the magnet 125, ultimately demagnetizing the magnet. Also, damper bar 1
The combination of the rotor 30 and the rotor wedge 128
Form a kind of cage structure that facilitates the start-up.

As is evident from FIGS. 5, 6 and 8, the rotor 23, like the stator 25, is "canned" in a watertight housing 134. The rotor housing 134 includes an inner wall 136, an outer wall 138, a front wall 140, and a rear wall 142 (all shown in FIG. 5). As is particularly apparent from FIG. 6, the rear wall 142 of the rotor housing 134
Is connected to the rotor inlet ring 144, which has a serrated rear wall 146 that is complementary to the serrated front wall 148 of the opposed stator inlet ring 150.
including. The complementary sawtooth shapes of the rear wall 146 and the front wall 148 of the rotor and stator inlet rings 144, 150, respectively, allow the surrounding seawater to be contained therein and the foreign particles contained therein to remove the outer peripheral edge of the rotor 23 and the stator 25. To define a tortuous path that is passed through while preventing it from flowing into the gap between the inner perimeters. The outer peripheral edge of the rotor 23 has a plurality of spiral grooves 151 for circulating foreign matter when it enters the gap between the rotor 23 and the stator 25 and making it easier to remove.
including. The flow path formed by the spiral groove 151 is indicated by an arrow in the upper part of FIG.

Referring to FIGS. 2 and 5, shroud assembly 3
The details will be explained. This assembly 3 has mounting bolts 15
6 includes a funnel-shaped inlet flow straightening plate 154 secured to the upstream side of the stator housing 116. Stator housing 1
At the downstream side of the blade 16, a blade mounting ring 158 is fixed via a mounting bolt 160. An outlet ring 162 is fixed to the downstream edge of the blade mounting ring 158 via a bolt 164. The inlet straightening plate 15
The funnel shape of FIG. 4 and the frusto-conical shape of the blade mounting ring 158, together with the stator housing 116, provide a Kort nozzle profile that maximizes the thrust of the propeller 13 mounted inside the shroud assembly 3. Form.

FIGS. 9 and 10 show another embodiment of the propulsion device 1 of the present invention. Unlike the previous embodiment, in this embodiment, the detachable cover 167 is attached to the hub 15 of the propeller 13.
As a result, the disturbance of the surrounding seawater which occurs not only when the cover rotates but also reduces the efficiency of the propulsion device 1 but also undesirably causes noise is minimized. The removable cover 167 of this embodiment includes a threaded recess 169 in the center of its interior,
The threaded recess can be screwed into the threaded stud 171 fixed to the upstream end of the thread. This embodiment also includes a plurality of fixed and detachable reinforcing columns 174. These reinforcing columns 173 enhance the impact resistance of the device 1, and are an important consideration when the present invention is applied to a submarine. Except for the fixed removable cover 167, the threaded stud 171 provided on the shaft 9, and the reinforcing column 173, this embodiment uses the first material described above in all materials.
This is the same as the embodiment.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a propulsion device of the present invention.

FIG. 2 is a sectional view of the propulsion device shown in FIG. 1 taken along line 2-2.

FIG. 3 is a front view of the propulsion device shown in FIG.

FIG. 4 is a rear view of the propulsion device shown in FIG.

5 is an exploded cross-sectional view of the propulsion device shown in FIG. 1, showing parts of a bearing disposed between a shaft of the propulsion device and a hub of the propeller.

FIG. 6 illustrates how the serrated surfaces of the rotor inlet ring and stator inlet ring define a tortuous flow path between the stator and the rotor that helps prevent foreign matter from flowing into this space. FIG. 5 is an enlarged view of a portion surrounded by a circle 142 in FIG.

FIG. 7 is a sectional view of the propulsion device shown in FIG. 1 taken along line 6-6.

8 is an enlarged view of a portion surrounded by a circle 7 in FIG. 7, showing details of the structure of the stator and the rotor.

FIG. 9 is a perspective view of an embodiment of the propulsion device of the present invention having a non-rotatable removable front cover, rather than a front cover that rotates with the hub of the propeller.

10 is a sectional view of the propulsion device shown in FIG. 9 taken along line 9-9.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Underwater propulsion device 5 Water suction port 7 Drain port 85 Cover 125 Permanent magnet 128 Wedge 130 Damper bar 180 Motor or motor assembly 182 Hub 184 Stator 186 Shroud 190 Rotor 192 Propeller 200 Shaft 202 Blade assembly 216 Bearing surface

────────────────────────────────────────────────── ─── Continued on the front page (72) James Albert Drake, Inventor United States Pittsburgh, PA PA 241 (72) Inventor Carl Bendell Bergmark, USA Harridge Center Street, PA, Pennsylvania 718 (56) References JP Sho 59 -166067 (JP, A) JP-A 4-29492 (JP, U) JP-A 63-90973 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B63G 8/08

Claims (9)

(57) [Claims] 1. A propeller means having a shroud having a water inlet and a water outlet, a hub rotatably mounted in the shroud on one end of the shaft facing the water inlet of the shroud, and a hub of the propeller means and an inlet of the shaft. A bearing assembly including a thrust bearing disposed between the ends, a rotor provided around the propeller means, and a stator provided in the shroud so as to be electromagnetically coupled with the rotor while maintaining a space between the propeller means; An underwater propulsion device comprising: a motor to be driven; a cover covering a thrust bearing; and water circulating means for circulating surrounding water to a bearing surface of the bearing assembly to lubricate and cool the bearing assembly. 2. The underwater propulsion device according to claim 1, wherein an access to the thrust bearing is facilitated by detachably attaching the cover to the shaft. 3. The underwater propulsion according to claim 1, wherein the cover is attached to the inlet end of the shaft via a fastener means provided at the center of the upstream end to minimize the unevenness of the outer surface of the cover. apparatus. 4. A cover is mounted by a plurality of struts between the cover and the shroud so as to cover the inlet end of the shaft in a stationary state even when the propeller means rotates, thereby reducing noise caused by rotation of the hub and of the propulsion device. The underwater propulsion device according to claim 1, wherein impact resistance is enhanced. 5. A portion comprising a plurality of blade members connected between a shroud and a shaft for supporting the shaft along a rotational axis of the shroud, the blade members being located between a hub of the shaft and a drainage port of the shroud. The underwater propulsion device according to claim 1, wherein the connection to the underwater propulsion means reduces noise generated by the propeller means and increases thrust of the device. 6. The underwater propulsion device according to claim 1, wherein the bearing assembly includes a radial bearing between the shaft and a hub of the propeller means. 7. The underwater propulsion according to claim 1, wherein the water circulation means includes a water suction port, and the water suction port is substantially aligned with a drain port of the shroud so that foreign particles in the water do not flow into the water suction port. apparatus. 8. The underwater propulsion according to claim 7, further comprising a filter means between the water inlet and the surrounding water to prevent foreign particles existing in the surrounding water from flowing into the water inlet. apparatus. 9. The at least one radial bearing for discharging foreign particles that have entered between the relative motion surfaces of the radial bearing.
The underwater propulsion device according to claim 6, comprising two spiral grooves.