Abstract:
In one general aspect, a shaftless external propulsion system as described herein provides a sleeve configured to be externally mounted over a hull of a marine vehicle. In addition, the shaftless propulsion system provides a rotor and a first stator mounted on the sleeve. The rotor includes a rotor hub that cooperates with a rotor bearing to enable the rotor to rotate about the sleeve, the rotor further comprising rotor blades attached to the rotor hub. The rotor and the first stator are disposed between a collar located at a first end of the sleeve and a collar hub located at an opposite end of the sleeve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This applications claims the benefit of U.S. Provisional Application No. 60/774,809, filed Feb. 14, 2006, which is incorporated herein by reference. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The following description was made in the performance of official duties by employees of the Department of the Navy, and, thus the claimed invention may be manufactured, used, licensed by or for the United States Government for governmental purposes without the payment of any royalties thereon. 
    
    
     TECHNICAL FIELD 
     The following description relates generally to a marine shaftless propulsion system, and in particular to an external shaftless propulsion system for a marine vehicle. 
     BACKGROUND 
     Shaftless propulsion systems are an alternative to the traditional shafted propeller-and-seal systems used by marine vehicles, such as undersea vehicles. Disadvantages of traditional shafted propeller-and-seal systems include mechanical vibrations and noise that propagate down the shaft and become radiated noise. The shaft itself adds considerable weight to the marine vehicle, and leaks may develop due to shaft seal wear. Shafted systems also are labor and cost intensive to both install and maintain. 
     A shaftless propulsion system (SPS) typically uses an electric motor integrated within the hull of the marine vehicle. One such shaftless propulsion system is described in U.S. Pat. No. 5,078,628 to Chester A. Garis, Jr. (hereinafter referred to as the &#39;628 patent). As shown in FIGS. 1 and 3 of the &#39;628 patent, the shaftless propulsion system is installed within the body  10  of the marine vehicle. As shown in FIG. 2 of the &#39;628 patent, the shaftless propulsion system includes a rotor  30  and one or more stators  26 ,  28 . In the system of the &#39;628 patent, the two stator disks  26 ,  28  are secured to the body (hull)  10  of the marine vehicle and, in essence, become part of the body  10 . The stators  26  and  28  and rotor  30  are disk shaped, without a drive shaft or other mechanism occupying their center. A blade hub  24  with blades  22  is attached to the rotor  30 . The propeller blades  22  extend beyond the circumference of the vehicle housing. The system also includes a shroud  14  with rib supports  18  and openings  20  to accommodate rotating blades  22 . 
     In the system of the &#39;628 patent, the rotor  30  and the stators  26 ,  28  are located outside of the vessel 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  10  of the vessel. The rotor  30  is positioned between the two stators  26 ,  28  and is accompanied by a journal bearing  48  that is positioned between the rotor  30  and the body  10 . As shown in FIG. 3 of the &#39;628 patent, the shaftless propulsion system is installed between two sections  38 ,  40  of the pressure hull which, after installation, are bolted and secured together. In particular, the rotor  30  is journal mounted on a central housing  44 , and the rear body section  40  of the vessel can be detachably connected to the front section  38  of the vessel by a bolting flange  46  extending from the central housing  44 . The rear section  40  can be connected to the flange  46  by bolts  48 . 
     In addition to the positioning of the stators and rotors, the &#39;628 patent discloses a cooling system that also is installed within the hull of the marine vehicle. The journal bearing  48  is water cooled and lubricated. Cooling fluid such as filtered seawater is pumped with an onboard pump through a piping system that is sea-connected. The cooling fluid is pushed out through the main fluid conduits  50  and the secondary fluid conduits  52  which lead to the journal bearing  48  and thrust bearing assemblies  54 . 
     U.S. Pat. No. 5,509,830 to Chester A. Garis, Jr. (hereinafter referred to as the &#39;830 patent) describes an improved cooling and lubricating system for a marine propulsor such as the propulsor described in the &#39;628 patent. The blades of the propulsor are used to bring in cooling water, thereby dispensing with the need for a separate pump and piping system. Also, U.S. Pat. No. 5,286,116 to Chester A. Garis, Jr. (hereinafter referred to as the &#39;116 patent) describes an improved motor and bearing assembly for use in an axial gap electric motor of a marine propulsor such as the propulsor described in the &#39;628 patent. The bearing assembly of the &#39;116 patent is configured to permit the stator-to-rotor gap and the bearing clearance to be adjusted after final assembly. 
     One of the most significant disadvantages of the shaftless propulsion system taught by the &#39;628, &#39;830, and &#39;116 patents is that the stators are located within the body of the undersea marine vehicle and are attached to the hull. The problem with the system of the &#39;628 patent stems from the fact that undersea marine vehicles compress with increasing depth during a dive. When the undersea marine vehicle dives, the hydrostatic pressure outside the hull exceeds the atmospheric pressure inside the hull. This pressure difference compresses not only the hull, but also the rotor bearing attached to the hull and the stators attached to the hull. Typical depths can compress the hull by several inches in diameter, and the compression increases with increasing depth. Although the diameter of the stators and rotor bearings of the shaftless propulsion system are reduced due to compression during a dive, the diameter of the rotor remains unchanged because the rotor is not attached to the hull and is completely immersed in the seawater surrounding the marine vehicle. As a result, the gap between the rotor and the rotor bearing increases as the depth of the marine vehicle increases. At or near the surface of the ocean, the gap between the rotor and the rotor bearing is small. At increased depth, the hull (and rotor bearing) radius decreases due to hydrostatic pressure, enlarging the gap between the rotor and the rotor bearing. The enlarged gap leads to several adverse consequences. 
     When the gap between the rotor and the rotor bearing increases, the rotor is able move so that it is no longer concentric with the rotor bearing and the stators. This non-concentric movement can cause several problems. For example, the windings of the stator are no longer parallel with the rotor windings, which causes reduced efficiency of the motor and reduced output of the propulsor. In addition, the surface area of the rotor bearing that is in contact with the rotor is reduced, which leads to increased bearing wear. Also, the play from the enlargement of the gap between the rotor and the rotor bearing may cause the rotor to have impact collisions with the rotor bearing when the marine vehicle changes direction. The impact collisions between the rotor and rotor bearing cause further wear of the bearing surface and also act as a source of radiated noise. Furthermore, if the space between the outer circumferential edge of the rotor blades and the shroud is not sufficient, the non-concentric movement due to an enlarged gap between the rotor and the rotor bearing may lead to collisions between the rotor blades and the shroud. Such collisions could damage the rotor blades and the shroud, and also would act as a source of radiated noise. 
     In summary, the shaftless propulsion system taught by the &#39;628 patent could be rendered noisy, damaged and/or non-functional due to the dive-induced non-concentric movement of the rotor that is caused by the enlarged gap between the rotor and the rotor bearing experienced during the dive. 
     Another disadvantage of the shaftless propulsion system as taught by the &#39;628, &#39;830, and &#39;116 patents lies with the maintenance of the system and the repair/replacement of worn or damaged parts. In order to repair or replace the shaftless propulsion system of the &#39;628 patent, the marine vehicle must be placed in drydock. For example, the marine vehicle may need to be disassembled and/or the hull cut open in order to access the stators and rotor bearing. Placing a marine vehicle in drydock is expensive and time consuming. With respect to the problem of adjusting the rotor bearing without drydocking the vessel, the solution offered by the &#39;116 patent is not adequate. The &#39;116 patent attempts to address the goal of not taking the undersea vehicle apart to adjust the bearing by providing a bearing in which the gap is adjustable by manually adjusting nuts and screws, where the screws penetrate through the pressure hull. Such penetrations through the pressure hull are disadvantageous for obvious reasons. 
     SUMMARY 
     In accordance with the present invention, a marine shaftless external propulsor is disclosed herein that overcomes the disadvantages of the prior art. In particular, disclosed herein is a shaftless propulsion system that does not shrink under the compressive forces of the ocean encountered when an undersea marine vehicle dives. 
     According to the present invention, during a dive of the undersea marine vehicle the stator(s) and rotor of the shaftless propulsion system are completely immersed in water and are not connected directly to the hull of the undersea marine vehicle. In addition, the stators and rotor of the shaftless propulsion system of the present invention are attached to the outside of the hull of the undersea marine vehicle by an attachment mechanism. Because the hull compresses under the hydrostatic pressure encountered during a dive, the attachment mechanism must be sufficiently flexible, adjustable, and/or self-adjusting to keep the propulsion system attached to the undersea marine vehicle, provide for forward and reverse thrust, and do so while still permitting the relative motion of the hull compression to take place without adversely affecting vehicle propulsion. 
     In the shaftless propulsion system of the present invention, one or more stators are secured to a sleeve that is external to the hull of the undersea marine vehicle. A rotor with rotor bearing is fit over the external sleeve. A collar and collar hub attached to the sleeve secure the stator into position and prevents the rotor/stator assembly from coming apart when the rotor is rotating. The collar fits over stanchions that are connected to the hull. The stanchions are fit with springs between the collar and the edge points of the stanchion. The spring loading allows the hull of the undersea marine vehicle to compress without significant compression of the collar occurring. This arrangement enables the undersea marine vehicle to dive safely without the stator and rotor diameters shrinking as the hull of the undersea marine vehicle compresses. 
     In one general aspect, a shaftless external propulsion system includes a sleeve configured to be externally mounted over a hull of a marine vehicle and a rotor and first stator mounted on the sleeve. The rotor includes a rotor hub that cooperates with a rotor bearing to enable the rotor to rotate about the sleeve. The rotor further includes rotor blades attached to the rotor hub. The rotor and first stator are disposed between a collar located at one end of the sleeve and a collar hub located at the opposite end of the sleeve. 
     Implementations may include one or more of the following. For example, the sleeve may be removably attached to a stanchion mounted on an external surface of the hull. The stanchion may include a stanchion protrusion. The sleeve may be removably attached to the stanchion by removably attaching the collar hub to the stanchion protrusion. The collar hub may further include a collar hub bracket and the collar hub bracket may be removably attached to the stanchion protrusion. For example, the collar hub bracket may be removably attached to the stanchion protrusion by a bolt inserted through an aperture of the collar hub bracket and an aperture of the stanchion protrusion. In other implementations, the collar hub and/or the collar may be removably attached to the sleeve. Further implementations may include a fairing. 
     In another implementation, a second stator is mounted on the sleeve and the rotor is disposed between the first stator and the second stator. In addition, the rotor, the first stator, and the second stator are disposed between a collar located at one end of the sleeve and a collar hub located at the opposite end of the sleeve. 
     In yet another implementation, a first elastic member is positioned on a first surface of the stanchion protrusion between the first surface of the stanchion protrusion and a first surface of the collar hub bracket. The first elastic member may be, for example, a spring. A first damping mechanism may be positioned on the first surface of the stanchion protrusion between the first surface of the stanchion protrusion and the first surface of the collar hub bracket. 
     Furthermore, a second elastic member may be located on a second surface of the stanchion protrusion opposite from first surface of the stanchion protrusion and positioned between the second surface of the stanchion protrusion and a second surface of the collar hub bracket. The second elastic member may be, for example, a spring. A second damping mechanism may be positioned on the second surface of the stanchion protrusion between the second surface of the stanchion protrusion and the second surface of the collar hub bracket. 
     In another general aspect, a shaftless external propulsion system includes a means for supporting a propulsor, where the support means is configured to be externally mounted over a hull of a marine vehicle. The system also includes a means for mounting the support means over the hull of the marine vehicle and a propulsor. The propulsor includes a rotor and a first stator mounted on the support means. The rotor includes a rotor hub that cooperates with a rotor bearing to enable the rotor to rotate about the support means. The rotor further includes rotor blades attached to the rotor hub. The rotor and the first stator are disposed between a first means for containment of the rotor and first stator located at one end of the support means and a second means for containment of the rotor and first stator located at the opposite end of the support means. 
     Implementations may include one or more of the following. For example, the mounting means may further include a means for compensating for hull contraction during a dive of the marine vehicle. 
     In another general aspect, an attachment mechanism for attaching a shaftless external propulsion system to a hull of a marine vehicle includes an attachment surface bracket configured to be attached to an attachment surface of a shaftless external propulsion system. The shaftless external propulsion system is configured to be externally mounted over a hull of a marine vehicle. The attachment surface bracket is configured to be removably attached to a stanchion protrusion of a stanchion mounted on an external surface of the hull by a bolt inserted through an aperture of the attachment surface bracket and an aperture of the stanchion protrusion. 
     Implementations may include one or more of the following. For example, a first elastic member may be positioned on a first surface of the stanchion protrusion between the first surface of the stanchion protrusion and a first surface of the attachment surface bracket. Also, a second elastic member may be located on a second surface of the stanchion protrusion that is opposite from the first surface of the stanchion protrusion and positioned between the second surface of the stanchion protrusion and a second surface of the collar hub bracket. 
     The present invention has numerous advantages including, but not limited to, enabling the propulsor to be attached externally to the hull such that it can be removed for repairs without drydocking the undersea marine vehicle, enabling both the stator and the rotor to exist in the ocean environment such that their radii do not shrink or compress when the undersea marine vehicle dives nor do their radii expand when the undersea marine vehicle surfaces, and interfacing the collar with stanchions that are connected to the hull of the undersea marine vehicle such that the hull radius can shrink under the compression of diving conditions and expand as the undersea marine vehicle rises toward the surface, yet the external propulsor will remain attached to the undersea marine vehicle. 
     It is therefore an object of the present invention to provide a shaftless propulsion system that can operate such that the dimensions of the components of the shaftless propulsion system are independent of undersea marine vehicle depth. It is another object of the present invention to provide a shaftless propulsion system that has lower costs associated with the installation, removal, repair, and replacement of the shaftless propulsion system. It is a further object of the present invention to provide a shaftless propulsion system where the installation, removal, repair, and replacement of the shaftless propulsion system can be accomplished without drydocking the undersea marine vehicle. 
     Other objects, features, and advantages will be apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of an exemplary shaftless propulsion system. 
         FIG. 2  is a side view of the exemplary shaftless propulsion system of  FIG. 1  mounted on an exemplary marine vehicle. 
         FIG. 3  illustrates the attachment and/or removal of the exemplary shaftless propulsion system of  FIG. 2  to the exemplary marine vehicle. 
         FIG. 4  illustrates an exemplary attachment mechanism for attaching the shaftless propulsion system of  FIG. 2  to the exemplary marine vehicle. 
         FIG. 5A  is an end view of the exemplary shaftless propulsion system of  FIG. 2  when the exemplary marine vehicle is at a first depth. 
         FIG. 5B  is an end view of the exemplary shaftless propulsion system of  FIG. 2  when the exemplary marine vehicle is at a second depth. 
         FIG. 6  is a side view of the exemplary shaftless propulsion system of  FIG. 2  including an exemplary fairing. 
         FIG. 7  is an end view of the exemplary shaftless propulsion system of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 and 2 , a shaftless propulsion system  100  includes a rotor  105 , a first stator  115 , and a second stator  120  each mounted on a sleeve  125 . The rotor  105  includes a rotor hub  107  and rotor blades  110 . A rotor bearing  118  enables the rotor hub  107  to rotate about the sleeve  125 . The rotor blades  110  act to propel the shaftless propulsion system  100  as the rotor  105  rotates about the sleeve  125 . 
     The rotor  105 , first stator  115 , and second stator  120  are mounted between a collar  130  formed at one end of the sleeve  125  and a collar hub  135  attached to the opposite end of the sleeve  125 . The collar  130  and collar hub  135  assist in holding the rotor  105 , first stator  115 , and second stator  120  in place on the sleeve  125 . The collar hub  135  may be attached to the sleeve  125  using a variety of known techniques, including screws, bolts, or welding. In some implementations, the collar hub  135  may be formed as part of the sleeve  125 . In other implementations, the collar  130  is removable from the sleeve  125  and may be attached to the sleeve using known techniques. Also, in some implementations the second stator  120  may be omitted. 
     As shown in  FIG. 2 , the shaftless propulsion system  100  is externally mounted on the marine vehicle. In particular, the shaftless propulsion system  100  is mounted to stanchions  205 ,  210  fixed to the hull  215  of the marine vehicle. Although two stanchions  205 ,  210  are shown, more stanchions could be used or a single stanchion could be used to mount the shaftless propulsion system  100  to the hull  215 . The stanchions  205 ,  210  must be seaworthy. The stanchions  205 ,  210  may include a curtain or skirt designed to reduce turbulent flow noise. In other implementations, other known methods could be used to externally mount the shaftless propulsion system  100  to the hull  215 . The shaftless propulsion system  100  is not integrated with the hull  215 , but rather is designed to fit over the external surface of the hull  215 . 
     Electrical power is supplied to the shaftless propulsion system  100  by electrical cables (not shown) extending through the hull  215 . Cable openings must be properly sealed to prevent leaks from occurring. Known methods, such as compressible tubing, may be used to prevent leaks in the hull penetrations. In one implementation, electrical power is supplied by electrical cables that are run through one or more of the stanchions  205 ,  210  and connect to the shaftless propulsion system  100 . Electrical power may be supplied to the first stator  115 , the second stator  120 , or the rotor  105  of the shaftless propulsion system  100 , or to various combinations thereof. Usually, electric power will be supplied to the first stator  115  and the second stator  120 , and the rotor  105  will be powered by magnetic induction. 
     In some implementations, one or more streamlined pieces (not shown) may be added in front of (i.e., forward of) and/or to the rear of (i.e., aft of) various components of the shaftless propulsion system  100  in order to streamline the flow. For example, such streamlined pieces may be added to streamline the flow over stanchions  205 ,  210  and collar  130  in order to avoid vortices development and subsequent noise generation. In one implementation, one or more tapered pieces of, for example, a triangular or approximately triangular cross-sectional shape (also known as a fairing) can be fastened to the hull forward of stanchions  205  and  210  and aft of collar  130 . These fairings can be made in sections with a gap between the hull and the fairing to account for the hull&#39;s radial movement with changing depth and also for ease of installation. The overall shape of these fairings may be a hollowed cone through the height center axis. 
       FIG. 3  illustrates that the shaftless propulsion system  100  is removable from the hull  215 . In particular, the shaftless propulsion system  100  is removably mounted to the stanchions  205 ,  210 . As shown in  FIG. 2 , the shaftless propulsion system  100  typically is mounted forward of the control surfaces. The control surfaces include the rudder  220  and stern plane  225 . In other implementations, the shaftless propulsion system  100  may be mounted aft of the control surfaces  220 ,  225 . Depending upon the relative location of the shaftless propulsion system  100  and the control surfaces  220 ,  225 , it may be necessary to at least partially remove the control surfaces  220 ,  225  in order to remove or install the shaftless propulsion system  100 . Installation or removal of the shaftless propulsion system  100 , including possible removal and re-installation of the control surfaces  220 ,  225 , may be accomplished without placing the marine vehicle in drydock. 
       FIG. 4  illustrates one exemplary mechanism for removably attaching the shaftless propulsion system  100  to the hull  215  of the marine vehicle. In particular, the collar hub  135  is attached to a stanchion  205 . As shown, the collar hub  135  includes a collar hub bracket  403  with collar hub bracket arms  405 ,  410 . Collar hub bracket arms  405 ,  410  have apertures  407 ,  412  respectively. The stanchion  205  includes a stanchion protrusion  415  extending from stanchion base  420 . The stanchion protrusion  415  has an aperture  417 . 
     To attach the collar hub  135  to the stanchion  205 , the collar hub bracket arms  405 ,  410  of the collar hub bracket  403  are positioned over the stanchion protrusion  415  such the stanchion protrusion  415  is between bracket arms  405 ,  410 . Collar hub bracket arm  405  is positioned over one face  418  of the stanchion protrusion  415  and collar hub bracket arm  410  is positioned over another face  419  of the stanchion protrusion  415 . As shown, the face  418  is on the opposite side of the stanchion protrusion  415  from face  419 . 
     Elastic member  425  is positioned between collar hub bracket arm  405  and face  418  of the stanchion protrusion  415 . Elastic member  430  is positioned between collar hub bracket  410  and face  419  of the stanchion protrusion  415 . Elastic members  425 ,  430  may be, for example, springs such as coil springs or leaf springs. Elastic members  425 ,  430  allow the hull  215  to compress during a dive without significant compression of the collar hub  135  or other components of the shaftless propulsion system  100 . Thus, the marine vehicle may dive without shrinkage of the stator  115 ,  120  or rotor  110  diameters as the hull  215  compresses. 
     A bolt  450  is positioned through the aperture  407  of collar hub bracket arm  405 , the aperture  417  of stanchion protrusion  417 , and the aperture  412  of collar hub bracket arm  410 . The bolt  450  also may be positioned through elastic members  425 ,  430 . The bolt  450  is secured by a washer  435  and nut  440 . 
     Some implementations may eliminate collar hub bracket arm  410  and elastic member  430 . The collar hub bracket arms  405 ,  410  may be attached to the stanchion protrusion  415  using other known methods. At least one damping mechanism, such as damping mechanisms  460  and  461 , may be used in conjunction with or in place of elastic members  425 ,  430 . 
     Referring to  FIG. 5A , when the marine vehicle is at a first depth there is a first gap G 1  between the hull  215  of the marine vehicle and the rotor  105  of the externally mounted shaftless propulsion system  100  that is due at least in part to compression of the hull  215  at the first depth. The rotor blades  110  and control surfaces  220 ,  225  also are shown. Referring to  FIG. 5B , when the marine vehicle is at a second depth there is a second gap G 2  between the hull  215  of the marine vehicle and the rotor  105  of the externally mounted shaftless propulsion system  100  that is due at least in part to compression of the hull  215  at the second depth. In this example the second depth is greater than the first depth, and the second gap G 2  is larger than the first gap G 1  because the hull  215  is compressed to a greater degree at the second depth than at the first depth. However, the diameter of the rotor  105  is not changed because the shaftless propulsion system  100  is completely surrounded by seawater external to the hull  215  of the marine vehicle due to the external mounting of the shaftless propulsion system  100 . The attachment mechanism attaching the shaftless propulsion system  100  to the hull  215  compensates for the shrinkage of the hull diameter as the depth increases. 
       FIGS. 6 and 7  illustrate an exemplary implementation of a fairing  610  for the shaftless propulsion system  100  of  FIG. 2 . The fairing  610  surrounds the shaftless propulsion system  100  and has sufficient clearance between the fairing  610  and the rotor blades  110  to avoid impact collisions. Fairing supports  605 ,  607  are used to support the fairing  610 . As shown, fairing support  605  is attached to stanchion  205  and fairing support  607  is attached to stanchion  210 . In some implementations, the fairing support may be part of the stanchion. In other implementations, the fairing support may be separate from the stanchion and attached directly to the hull  215 . Typically, the fairing  610  is shaped so as to improve hydrodynamic performance. 
     A number of exemplary implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the steps of described techniques are performed in a different order and/or if components in a described component, system, architecture, or devices are combined in a different manner and/or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the following claims.