Marine Propulsor

This invention relates generally to propulsion systems and more particularly to propulsors for submersible or semisubmersible vessels or surface ships.

Various systems have been proposed for water-going vessels in which one or more rotating propellers are disposed beneath the water line of the vessel for semi-submersible vessels or disposed within a portion of the hull of submersible vessels.

Typically, the propellers in submersible systems have been driven by diesel power, steam turbines or electric motors mounted within the hull of a vessel. A propeller shaft extends through the hull to the propeller mounted on the shaft outside the hull. Such systems have the disadvantages of shaft vibration and noise radiating from the shaft. Further, leaking around the shaft occurs when the seal becomes loose or worn. Alternative systems have been suggested using shaftless electric motors mounted outside of the hull with only electric power cables passing through the hull. U.S. Pat. No. 3,182,623 provides one such example of shaftless motors used to drive impellers mounted within the tail section of a submarine. A disadvantage of such system is that propulsors (electric motors and impellers) occupy almost the entire interior of the tail section. Further, traditional shaftless electric motors are either too small to effectively move a vessel or, if large enough, add significant weight to the vessel. U.S. Pat. No. 3,101,066 suggests another shaftless electric motor for propelling a submersible vessel. Again, however, the traditional motor disclosed in the U.S. Pat. No. 3,101,066 has insufficient power to drive the vessel in which it is mounted and, if the size of the conventional motor with cylindrical iron rotor and stator is increased, the size and weight of the motor become a major disadvantage.

These prior systems have failed to address the additional problems of handling the thrust imparted by the propellers in large vessels, or the problem of handling cooling and lubrication of bearings associated with a shaftless motor mounted in a submersible vessel. Further, prior systems have failed to adequately address the problems of cooling/lubricating bearings in contaminated or muddy waters. In addition, prior systems have not solved the problem of electrical noise imparted to the vessel hull by the stator of an electric motor mounted to the hull or mechanical vibration imparted by the rotor. These and other disadvantages of the prior art systems are overcome by the unique features of the propulsion system of the present invention.

It is an object of the present invention to provide an improved propulsor for submersible vessels, or surface vessels or semi-submersible vessels with underwater propulsion arrangements.

It is another object of the invention to provide a propulsor with a shaft-free motor of sufficient power to drive a marine vessel but with a motor of minimum weight and size.

A further object of the invention is to provide an improved mounting arrangement for the motor rotor including a journal bearing and a fluid supply for cooling/lubricating the journal bearing.

Another object of the invention is to provide an arrangement for handling and distributing thrust imparted by the propulsor including circumferential thrust bearings, and a fluid supply for cooling/lubricating the thrust bearing(s).

It is another object of the invention to control power to the propulsor so that a certain amount of propulsor thrust can be countered with electromagnetic forces and the position of the rotor can also be controlled by varying electromagnetic forces to dampen propulsor induced structural vibrations.

It is yet a further object of the invention to provide a shaft-free submersible motor in which rotor excitation current is inductively supplied.

It is another object of the invention to provide a marine propulsor with sound insulation between the vessel hull and the propulsor.

A further object of the invention is to provide a thrust transmitting arrangement in a dual rotor, counter-rotating marine propulsor.

Another object of the invention is to provide an improved marine propulsor with a shroud extending around the propulsor blades.

Yet a further object of the invention is to provide a marine propulsor that is modular to facilitate assembly and removal.

The marine propulsor of the present invention includes one motor in a first embodiment or two motors with counter-rotating propellers in a second embodiment. The motors include a disk-shaped rotor and two disk-shaped stators mounted in the body of vessel and being axially aligned with a longitudinal axis of the vessel. If the vessel is not itself completely submersible, the motors can be mounted in pods or cylindrically shaped casings attached below the bottom surface of the vessel. Unlike many conventional marine motors, the motor of the present invention is shaft-free. The stators are mounted in fixed positions to the vessel or propulsion pod housing and the rotor is journal mounted to the vessel or pod housing. Hereinafter, although reference may be made only to a vessel, it is to be understood that the invention is equally applicable to submersible vessels and to pods or propulsor housings mounted below a surface vessel. Electrical power is supplied to the stator windings through waterproof cables and connectors.

The propulsor blades are mounted on a hub assembly that is removably attached to the rotor. A shroud, which can be mounted to the hub assembly or the vessel housing covers the propulsor blades. In the dual counter-rotating embodiment, a single shroud can cover both blade assemblies or individual shrouds can be provided for each.

In contrast to the traditional heavy, bulky electric motors used in marine propulsors, the rotor and stators utilized in the present invention are substantially iron free. Much of the volume of the motor is occupied by electrical conductors. As a result, the disk-shaped motor is more compact and lighter than traditional motors and yet power is not sacrificed because the space utilized for conductors is greatly increased.

The thrust created by the propeller blades, attached to the rotor by the blade hub assembly, is transferred to the vessel through a circumferential thrust bearing. The thrust bearing can be a single annular bearing or a plurality of spaced bearing assemblies mounted to the vessel structure around the circumference of the vessel and positioned to cooperate with a bearing surface on the rotor or propeller hub. The rotor is journal mounted on a vessel inner housing. A journal bearing mounted on a circumferential surface of the inner housing cooperates with a circumferential bearing surface of the rotor.

The propulsor assembly with rotor, stators, thrust and journal bearings are outside the vessel housing (which may be a pressure hull in a submergent vessel) and are exposed to water. The rotor, stator and bearings are water cooled and water lubricated. To ensure a supply of clean water to these elements when operating in contaminated waters, a forced seawater supply is provided. This water supply may be either filtered water or clean water from an internal tank. This forced clean water is pumped to the journal bearings and then drawn by centrifugal force up through fluid channels in the rotor toward the thrust bearings located near the periphery of the rotor. Additionally, water can be pumped through channels in the stator for cooling.

Electrical power is generated by traditional means, including fossil fuel systems or nuclear generators. The electrical power is delivered to the two stators through a variable frequency converter or controller, for example a cycloconverter. Thus, the speed of the motor can be controlled by varying the frequency of input power. The magnitude of propulsive thrust produced by the rotating propeller blades through the water will be proportional to magnitude of power delivered to the motor. The motor speed can be brought up slowly from zero cycles/second to synchronize the speed of the rotor with the speed of the rotating magnetic field of the stator, thus preventing any slip and producing maximum propulsive thrust from the input power.

The two stators are mounted on opposite sides of the rotor. Each stator may be provided with an excitation winding (primary) and the rotor may be provided with a secondary excitation winding and rectifiers to provide the rotor excitation current. Alternately, a rotor magnetic field may be provided by permanent magnets mounted in the rotor. The rotor magnetic field reacts with a rotating magnetic field of the stator to produce rotational torque upon the rotor. Power is supplied separately to each stator from the variable frequency controller so that the magnitude of power supplied to one stator can be different than the magnitude of power supplied to the other stator. In addition to the rotational force applied to the rotor caused by the rotating magnetic field in the stators, the stators, placed on opposite sides of the rotor, will exert lateral force on the rotor due to the stator's magnetic field. If equal power is supplied to both stators, the attractive force on the rotor will be balanced between the two. However, if one stator is overenergized and the other stator is underenergized, the balance of attractive force can be shifted to the overenergized stator. This capability can be used to absorb some of the thrust forces applied against the thrust bearings. By shifting the balance of attractive magnetic forces on the rotor, its position while rotating between stators can be controlled to a certain degree to reduce the magnitude of rotor vibration that would normally be transmitted to the neighboring vessel structure.

The major components of the propulsion assembly including rotor, stators, propeller blade hub, and shroud can be individually installed or removed from the vessel. Further, each of these components may be of split construction.

This modular assembly greatly facilitates initial construction and later maintenance. The stators can be bolted to an aft member of a vessel hull section and the rotor journal mounted on an inner hull section. The propeller blade hub assembly is removably attached to the rotor and the propeller shroud can be removably attached to the blade hub or to the vessel hull. The second stator can then be mounted to a forward member of the vessel hull to complete the modular assembly of the major propulsor components. Interposed between the stators and the vessel hull sections to which they are attached will be a sound insulation layer, e.g. rubber, to absorb or reflect alternating current vibrations produced by the stator windings.

In one embodiment of the present invention, dual, counter-rotating propulsors are used with a thrust transference member interposed between the two propulsors. In this arrangement, two rotors (one with reverse blades) are journal mounted in the vessel structure on either side of the thrust transference member. Stators (four total) are mounted on either side of each rotor and are powered such that the rotors rotate in opposite directions. Thrust bearing assemblies are mounted on either side of the transference member and on the fore and aft sections of the vessel hull. In this arrangement, during forward movement, propulsion force of the forward rotor/blade assembly is transferred directly to the vessel structure through the forward thrust bearings and propulsion force of the rearward rotor/blade assembly is transferred through the thrust transference member, its thrust bearings and the forward thrust bearings to the vessel structure. During rearward movement, the opposite sequence of propulsion force transference occurs.

These and other features, objects and advantages of the present invention will be apparent from the foregoing drawings and detailed description.

FIG. 1 is a fragmentary side elevational view of the aft section of a submersible vehicle or pod or submersible propulsor housing.

FIG. 2 is an exploded perspective view of the major components (details omitted) of the propulsor assembly.

FIG. 3 is a side cross-sectional view along the line 3--3 of FIG. 1.

FIG. 4 is a diagrammatic view showing the general relationship of rotor fluid passages and the journal bearing on which the rotor is carried.

FIG. 5 is a general block diagram of the electrical supply system.

FIG. 5A shows an alternate embodiment of the electrical supply system shown in FIG. 5.

FIG. 6 is a diagrammatic view of the rotor assembly.

FIG. 7 is a diagrammatic view of the rotor frame showing the winding mounting slots.

FIG. 8 is a side view along the line 8--8 of FIG. 7.

FIG. 9 is a diagram of a typical rotor winding mounted in a slot.

FIG. 10 is a partial diagrammatic view of a stator showing the position of salient pole windings.

FIG. 11 is a diagrammatic view of a stator with the windings in a lap wound configuration.

FIG. 12 is a block diagram representation of the apparatus for providing rotor excitation current.

FIG. 13 is a representation illustrating the dual, counter-rotating propulsor embodiment.

FIG. 1 illustrates a fragmentary view of the marine vehicle in which the present invention would be incorporated. This vehicle could be a submersible vessel, as shown for example in U.S. Pat. No. 3,101,066, in which instance body 10 may be a pressure hull. Alternately, the vehicle could be a surface vessel, in which instance the propulsor of the present invention may be mounted in a pod or cylindrical or cigar-shaped propulsor housing attached below the bottom surface of the vessel and below water, as shown for example in U.S. Pat. No. 4,389,197. In either situation, the marine propulsor of the present invention will be installed in a section 12 of body 10, having generally a cylinder or frustum shape or configuration. Also shown in FIG. 1 is a shroud 14 covering the blades of the propulsor assembly. Fins 16 may be mounted at the end of a submersible vessel or on an attached pod or propulsor housing.

As best shown in FIG. 2, the propulsor assembly is of modular construction, facilitating installation and removal. FIG. 2 illustrates the general relationship of the major components of the assembly, with details omitted. Shroud 14 is shown with four rib supports 18 that include openings 20 to accommodate rotating blades 22. Openings 20 divide each rib support 18 into preswirl struts 18a and postswirl struts 18b (FIGS. 2 and 3.). Shroud 14 may of course be much larger than shown in relation to the blades 22 and blade hub 24. In installing the propulsor assembly, forward stator 26 may be mounted to a forward section of vessel housing 10 and rearward stator 28 may be mounted to a rearward section of vessel housing 10. Rotor 30 is journal mounted to an inner housing section. Blade hub 24 is fit over rotor 30 with rotor keys 32 being received within hub key slots 34 thus fixing hub 24 relative to rotor 30. As rotor 30 rotates, hub 24 and blades 22 are rotated through the water causing a propulsion force that is transmitted to the vessel through thrust bearings in contact with thrust bearing surface 36. Bearing surface 36 may be on rotor 30 rather than hub 24 as shown. Each of the stators 26 and 28, rotor 30, blade hub 24, and shroud 14 may be of split construction to further ease installation and removal.

FIG. 3 is a cross sectional view of the vessel body section 12 with propulsor assembly installed. The forward stator 26 and rearward stator 28 are mounted to front body portion 38 and rear body portion 40 of the vessel. Interposed between stators 26,28 and body sections 38 and 40 is sound attenuating material shown generally as 42. This material 42 may be any suitable acoustic insulation, e.g. rubber, wood, or fiberglass. This material will absorb or deflect alternating current (ac) waves generated by the stator windings and will dampen ac vibrations of the vessel body. This insulation prevents the body of the vessel from amplifying and transferring noise from the motor to the water surrounding the vessel.

The stators 26 and 28 and rotor 30 are disk shaped, as best shown in FIG. 2, without a drive shaft or other mechanism occupying their center. As a result, the central section 44 of the vessel body 10, which is a substantially cylindrical housing, can be open as shown generally at 120 in FIG. 3. Central housing 44 can provide space for assemblies connecting the fore and aft of the vessel, thus permitting the aft of the vessel to be used, for example, for launching smaller vehicles or torpedoes (e.g. where the vessel is a submarine). The rear body section 40 of the vessel can be detachably connected to front section 38 by a bolting flange 46 extending from central housing 44. Rear section 40 can be connected to flange 46 by bolts 48, or other suitable means.

The rotor 30 is journal mounted on central housing 44. A journal bearing, shown generally at 48, carries the rotor 30. The journal bearing 48, described in greater detail in connection with FIG. 4, is water cooled and lubricated. Forced seawater is supplied from either a clean water tank (not shown) or through a filtered seawater inlet (not shown) through main fluid conduits 50 and secondary fluid conduits 52 which lead to journal bearing 48 and also to thrust bearing assemblies 54. The thrust bearing assemblies 54 are mounted on a peripheral area of the front and rear body sections 38 and 40 around their circumference to transfer (through bearing surface 36 of blade hub 24) the propulsive force created by the rotating blades 22 of the assembly to the vessel body 10. Bearing surface 36 may also be on rotor 30. The thrust bearing assemblies may comprise solid annular bearings or a plurality of spaced thrust bearing assemblies (e.g. conventional tilting pad type) mounted on the circumference of each of the front and rear body sections. The water forced through conduits 52 cools and lubricates thrust bearing assemblies 54.

The rotor 30 and stators 26 and 28 are located outside of body 10 and are cooled by the surrounding water. They operate in water and at submergent water pressure, thus requiring no complex seals between the motor and the body of the vessel. In muddy or contaminated waters, clean or filtered water can be passed through the rotor and stators through tertiary passages 56. For the sake of simplicity, tertiary passages 56 are shown passing through rotor 30 only in the upper half of FIG. 3 while passages 56 are shown passing through stators 26 and 28 only in the lower half of FIG. 3. Cooling water can be pumped through the rotor and/or stators through fluid conduits 52. Alternatively, cooling water can be brought in through a filtered inlet 58 in shroud 14. Again, for simplicity in the drawing, this alternative is shown only in the upper half of FIG. 3. Inlet 58 feeds a cooling water passage 60 that extends through shroud 14, pre-swirl strut 18a and post swirl strut 18b. Struts 18a and 18b can be movably mounted to shroud 14 and/or body 10 to improve backing capabilities and maneuverability. Cooling passage 60 extends through limbers or passages 66 that supply water to tertiary passages 56.

FIG. 4 illustrates the relationship of tertiary passages 56 in the rotor 30 to the journal bearing. Filtered seawater or a fluid is pumped (by a conventional pump, not shown) through main fluid conduit 50 and secondary conduit 52 until it reaches the journal bearing 48. Alternatively, seawater may be directed through shroud 14 and limbers or passages 66 to journal bearing 48, as best shown in FIG. 3. Journal bearing 48 may take many forms, such as a plain cylindrical bearing, or as shown in FIG. 4 may include a plurality of spaced rubber staves or plates 68 mounted on an outer circumferential surface of vessel central housing 44. Water passes out of conduit 52 into the interstices 70 between staves 68. As rotor 30 turns, water is drawn between staves 68 and rotor bearing surface 72 to lubricate and cool journal bearing 48. Also, due to centrifugal force, water is drawn up through passages 56 in rotor 30 to cool the rotor and also to supply a cooling and lubricating fluid to thrust bearing assemblies 54. As best seen in FIG. 3, the outlets of passages 56 are in the vicinity of thrust bearing assemblies 54 and bearing surface 5 of blade hub 24.

FIG. 5 illustrates in general block form the electrical power system. The vessel propulsion power 74 may be any conventional power generator, e.g. fossil fuel, nuclear, etc. Optionally, the system may include an ac-to-dc converter system 76 to provide dc power on dc bus 78 to variable frequency (v.f.) inverter controllers 80 and 82. The v.f. inverter controllers invert power supplied on the dc bus 78 to ac power at a desired frequency. Two v.f. inverter controllers are provided to individually supply power to stators 26 and 28. Alternatively, as shown in FIG. 5A, ac-to-dc converter system 76 may be eliminated by utilizing v.f. cycloconverters 80A and 82A that directly convert the vessel propulsion ac power to the desired frequency. Power is supplied to the stator windings through waterproof cables and connectors, shown generally as 106 and 108. A conventional controller 88 (e.g. programmable computer) is utilized to operate v.f. controllers 80 and 82 to vary allocation of power between stators 26 and 28. The speed of rotor 30 will be proportional to the frequency of power supplied to stators 26 and 28. An advantage of the v.f. controller is that the motor speed can be increased slowly from zero cycles/second to a desired operating speed while maintaining synchronization between the rotor speed and the speed of the rotating magnetic field of the stator, thus preventing slip and maximizing torque.

Utilization of separate power inputs for the two stators 26 and 28 provides a unique advantage in controlling the electromagnetic forces on the rotor 30. Stators 26 and 28 are mounted on opposite sides of the rotor as illustrated in FIGS. 2 and 3. Alternating current in the stator windings will set up a rotating magnetic field that will react with a rotor magnetic field to produce torque and a resultant propulsive force via blades 22. In addition, the stator magnetic fields will exert lateral force on the rotor. If controller 88 is operated to cause v.f. controllers 80 and 82 to supply equal magnitudes of power to stators 26 and 28, the attractive forces on the rotor will be balanced between the two stators. However, controller 88 can be operated to cause v.f. controllers 80 and 82 to overenergize one stator and underenergize the other, thereby shifting the balance of attractive forces to the overenergized stator. This capability can be used to electromagnetically counter the thrust forces by increasing the balance of attractive magnetic forces in a lateral direction opposite to the direction of thrust. This can relieve the forces applied against thrust bearings 54 and eliminate contact of the bearing surfaces. As a result, transmission of vibration forces of the rotor assembly to the supporting structure is minimized. The electromagnetic imbalance effectively absorbs propulsive thrust forces on the rotor assembly and reduces propulsor induced structural vibration.

As mentioned previously, the motor of the present invention is shaftless, has a disk-shaped rotor and stators, and is substantially iron-free. Iron-free, disk-shaped machines are disclosed generally in U.S. Pat. No. 4,691,133. In contrast to conventional iron motors generally used in marine vessels, the rotor/stator windings of the motor of the present invention contribute a larger proportion of the weight of the rotor and stators. Utilizing the space of the rotor/stator for windings provides sufficient power to drive the vessel without increasing the size or weight of the motor as would be required in a conventional iron motor. Referring to FIG. 3, the radial dimension D of the rotor 30 and stators 26 and 28 is at least 10% of the nominal diameter ND of the vessel body section 12 at the point where the propulsor assembly is mounted. This radial dimension provides sufficient space for a large number of windings to be mounted in the rotor and stators, yet leaves the inner portion of the vessel open for utilization of the aft section.

FIG. 6 shows an example of the rotor assembly including a salient pole construction of the rotor, the blade hub, and blades. A large number of salient pole windings 84 is mounted in the disk-shaped rotor with frame 122. Rotor excitation windings (secondary), shown generally at 86, are mounted in a slot in the interior circumference of rotor 30, and the journal bearing surface is shown at 72. Blade hub 24 is mounted on rotor 30 as previously discussed. Thrust bearing surface 36 may either be a surface on hub 24 or rotor 30. Blades 22 (individual blades not shown) are fixed on the outer circumference of blade hub 24, as best shown in FIG. 2.

FIG. 7 is an illustration of rotor frame 122 showing a plurality of mounting slots 88 for the rotor salient pole windings. Rotor excitation winding (secondary) slots are shown at 90. As shown in FIG. 8, first slots 92 and second slots 94 are provided for dual salient pole rotor windings where the motor would be mounted in a vessel with backup, redundant systems. FIG. 8 further illustrates the rotor excitation winding slots 90 and a wiring channel 96. Rectifiers may also be mounted in wiring channel 96. FIG. 9 is an illustration of a typical salient pole winding 84 mounted via mounting bolts 98 in slots 88. FIG. 10 is a partial view of the stator 26 or 28 with a plurality of salient pole stator windings 100 mounted inside, and primary excitation windings shown generally at 102. FIG. 11 is an alternate embodiment of stators 26 or 28 with the stator windings 104 in a lap wound configuration.

FIG. 12 is a representative view of the apparatus for providing rotor excitation current. A rotor excitation controller 114 supplies an alternating current source to primary excitation windings 102 through cables 116 and 118 respectively. Controller 114 permits the rotor excitation to be variable. Secondary excitation windings 86 in rotor 30 are inductively coupled to primary windings 102 to provide rotor excitation current. This ac current is rectified by dc rectifier circuits 110 to provide a dc current to rotor windings 84, thus creating magnetic poles as shown. Rectifier circuits 110 are connected to provide, with duplicate rotor windings 84, a redundant circuit. As an alternative to the induction circuit shown in FIG. 12, permanent magnets (111) may be installed in rotor 30. As a further alternative, low reluctance magnetic material may be mounted in the rotor, or the induction circuit shown in FIG. 12, permanent magnets, and low reluctance magnetic material may be combined in the rotor/stator assembly to provide the rotor magnetic field.

FIG. 13 is a representation illustrating the dual, counter-rotating propulsor embodiment of the present invention. In this embodiment, two rotors 30 (one with reverse blades 22 mounted on hub 24) are journalled in the vessel body 10 on either side of a thrust transference member 112. Stators 26,28 (four total) are mounted in section 12 of vessel body 10 on either side of each rotor 30, and are powered in a conventional manner such that rotors 30 rotate in opposite directions. Thrust bearing assemblies 54 are mounted on either side of thrust transference member 112 and on fore and aft sections of the vessel body 10. In the embodiment illustrated in FIG. 13, during forward movement, propulsive forces produced by the forward rotor assembly (rotor 30, hub 24, and blades 22) are transferred directly to the vessel structure through forward thrust bearing assemblies 54. Propulsive forces of the rearward rotor assembly are transferred through the thrust transference member 112, to the thrust bearing assemblies 54 mounted on the thrust transference member 112, to the forward thrust bearing assemblies 54, and finally to the vessel structure. Similarly during rearward movement, the propulsive forces produced by the rearward rotor assembly are transferred directly to the vessel structure while propulsive forces produced by the forward rotor assembly are transferred through thrust transference member 112 and the intermediate thrust bearing assemblies. As an alternative, and shown only in the lower half of FIG. 13, the thrust transference member may be secured to the vessel structure as shown generally at 122 or be a portion of the vessel structure. In this alternative embodiment, propulsive forces of both rotor assemblies are transferred directly to the vessel structure through the thrust bearing assemblies.

The present invention has been described and shown in relation to various preferred embodiments. Detailed descriptions and illustrations of certain known components and operations have been omitted for the sake of clarity and understanding of the present invention. Conventional components and principles will be readily appreciated by those having ordinary skill in the art as will various modifications and changes that can be made to the embodiments disclosed, such embodiments, modifications, and changes being intended to fall within the scope of the invention a defined by the following claims.