Abstract:
A system includes an azimuthing pod configured to be attached to the hull of a ship, a superconducting motor positioned within the azimuthing pod, a refrigeration system including a compressor and a cryogenic refrigeration module coupled to the compressor. The system further comprises a transfer system configured to circulate a coolant between the cryogenic refrigeration module and the superconducting machine, at least one of the compressor and the cryogenic refrigeration module being positioned within the hull of the ship.

Description:
BACKGROUND  
       [0001]     Large shipping vessels including cruise ships, naval vessels and tankers are often propelled with pod propulsion systems. Such systems generally include an electric motor enclosed within a hydrodynamically optimized body, which can be rotated through 360 degrees to provide the required thrust in any direction. These systems, often called azimuthing pods eliminate the need for stem tunnel thrusters and maximize maneuverability. Thus, even large vessels with azimuthing pods can maneuver into relatively small ports without the need for tug assistance. Azimuthing pods also save space, are more easily installed and are efficient, relative to conventional stem thrusters. 360° azimuthing propulsion can provide power at levels as high as 30 megawatts.  
       SUMMARY  
       [0002]     In a general aspect of the invention, a system comprises an azimuthing pod configured to be attached to the hull of a ship, a superconducting motor positioned within the azimuthing pod, a refrigeration system including a compressor and a cryogenic refrigeration module coupled to the compressor. The system further comprises a transfer system configured to circulate a coolant between the cryogenic refrigeration module and the superconducting machine, at least one of the compressor and the cryogenic refrigeration module being positioned within the hull of the ship.  
         [0003]     Embodiments of this aspect of the invention may include one or more of the following features.  
         [0004]     The system includes a rotatable support member configured to interface a stationary reference frame in the hull to a rotating reference frame in the azimuthing pod. The transfer system includes transfer lines extending through the rotatable support member and between the module and superconducting motor. The transfer lines extend through a center axis of the rotatable support member.  
         [0005]     The position of the compressor and module relative to the pod can vary depending upon the available space on the rotatable support member as well as within the pod. For example, n certain embodiments, both the compressor and module are positioned within the hull, while in others the module is positioned in the pod.  
         [0006]     In some embodiments, neither the compressor nor the module is on the rotatable support member, while in other embodiments, the module is on the rotatable support member while the compressor is not on the rotatable support member, while still in other embodiments, both the compressor and the module are on the rotatable support member.  
         [0007]     The rotatable support member is configured to rotate 360°. The coolant circulated by the transfer system is selected from a group consisting of helium, hydrogen, oxygen, nitrogen, argon, neon, and mixtures thereof. The superconducting motor includes high temperature superconducting windings.  
         [0008]     In another aspect of the invention, a system comprises a superconducting machine disposed in a rotatable reference frame; a refrigeration system including a compressor and a cryogenic refrigeration module coupled to the compressor; and a transfer system configured to circulate a coolant between the cryogenic refrigeration module and the superconducting machine, at least one of the compressor and the cryogenic refrigeration module being positioned in a stationary reference frame.  
         [0009]     In certain embodiments, the system can include a housing in the rotatable reference frame for enclosing the superconducting machine. The rotatable reference frame has an axis about which the superconducting machine rotates and the superconducting machine includes a rotor assembly which, in operation, rotates about an axis of the superconducting machine that is substantially perpendicular to the axis of the rotatable reference frame. The rotatable reference frame is configured to rotate without limit around an axis of rotation.  
         [0010]     Among other advantages, the systems described above offer the possibility of a smaller, more efficient pod propulsion system for use, in particular, with large shipping vessels. A superconducting motor is generally smaller than its non-superconducting motor for a given output power rating. Thus, the overall volume of the pod for enclosing the motor can be smaller. However, unlike it&#39;s non-superconducting counterpart, a superconducting motor requires a system for cryogenically cooling the superconducting components (e.g., windings) of the motor. Positioning the cryogenic cooling system in the pod eliminates the reduced size advantage of the superconducting motor. However, the reduced size advantage can be maintained by positioning the cooling system external to the pod (e.g., within the hull). That said, because the pod rotates, the cooling must be provided in a manner that does not interfere with other mechanical systems (e.g., lubrication systems) needed for the motor. The systems described above provide various configurations in which cooling can be provided to the superconducting motor, while maintaining the overall size advantages associated with using a superconducting motor.  
         [0011]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0012]      FIG. 1  is a cross-sectional side view schematic representation of an azimuthing pod including a cryogenic cooling system.  
         [0013]      FIG. 2  is a block diagram of the cooling system of  FIG. 1 .  
         [0014]      FIG. 3  is an alternative embodiment of an azimuthing pod including a cryogenic cooling system.  
         [0015]      FIG. 4  is a further embodiment of an azimuthing pod including a cryogenic cooling system.  
         [0016]      FIG. 5  is a cross-sectional side view of a transfer coupling used in conjunction with the cryogenic cooling systems of  FIGS. 3 and 4 .  
         [0017]      FIG. 6  is a still another embodiment of an azimuthing pod including a cryogenic cooling system. 
     
    
     DETAILED DESCRIPTION  
       [0018]     Referring to  FIG. 1 , a pod propulsion system  10  includes an azimuthing pod  12  attached to the hull  14  of a ship through a pod seating  16 . Azimuthing pod  12  includes a superconducting electric motor  18  which drives a propeller  20  through a thrust bearing mechanism  22  and sealing system  24 . The electric motor  18 , thrust bearing mechanism  22  and sealing system  24  are enclosed within an outer shell  26  of the azimuthing pod  12 .  
         [0019]     Positioned within the hull  14  and upon the pod seating  16  is a turntable assembly  28  which supports, among other components, a steering system  30  and a power transmission/control system  32  for rotating and steering the azimuthing pod  12 . Steering system  30  and transmission/control system  32  allow azimuthing pod to spin continuously and without limit about an axis of rotation  52 .  
         [0020]     Superconducting electric motor  18  includes a rotor assembly  19  surrounded by a stator assembly  21  and having a number high temperature superconductive (HTS) windings (not shown) mounted, for example in a multi-pole topology. Superconducting electric motors suitable for use in azimuthing pod  12  are described, for example, in U.S. Pat. No. 6,489,701 and U.S. Pat. No. 6,597,082, both of which are incorporated herein by reference. The HTS windings are required to be cryogenically cooled to temperatures about 108° K. The overall size of the azimuthing pod  12  can be minimized by limiting the number of components within the pod.  
         [0021]     For example, as shown in the embodiment of  FIG. 1 , the turntable assembly  28  within the hull also supports the primary components of the cryogenic system for cooling the HTS windings. Cryogenic cooling systems suitable for use in cooling the HTS windings of superconducting electric motor  18  are described in U.S. Pat. No. 6,347,522 and U.S. Pat. No. 6,376,943, both of which are incorporated herein by reference. In particular, turntable assembly  28  supports an HTS refrigeration module  34  and its associated compressor  36 , which is connected to refrigeration module  34  via a pressurized gas line  38 . Pressurized gas line is flexible, are 30 mm in diameter, have a minimum bend radius of 100 mm and can easily be run over lengths up to 20 meters.  
         [0022]     Referring to  FIG. 2 , refrigerant from HTS refrigeration module  34  is circulated through rotor assembly  19  through a supply transfer line  40  and return transfer line  42 . Supply transfer line  40  and return transfer line  42  are in the form of vacuum insulated lines. In one configuration, the transfer lines are formed as concentric streams in vacuum jacketed plumbing. The diameter of the vacuum jacket for this configuration is approximately 4 inches and can assume a bend radius of 6 inches. In an alternate configuration, the insulated cold gas inner supply and return lines are independent from each other, 0.75 inches in diameter and run in parallel inside the vacuum jacket. For separate streams the vacuum jacket diameter would be 2 inches and the bend radius would be 4 inches. These separate lines are lighter and can be easier to install than a larger single line. The refrigerant is supplied and returned to rotor assembly  19  through a transfer coupling  44  for interfacing the stationary reference frame of the hull to the rotating reference frame of the azimuthing pod  12 . Details relating to the structure of transfer coupling  44  can be found in U.S. Pat. No. 6,489,701. Other approaches for interfacing a stationary reference frame to a rotating reference frame are described in U.S. Pat. No. 6,347,522 and U.S. Pat. No. 6,376,943.  
         [0023]     In this embodiment, the cryogenic fluid is helium and, therefore, cooling system  10  includes a source  45  of helium, which, if necessary, may be required to replenish helium to the system. Preferentially, the cryogen circulates through the cooling system in a gaseous state. HTS refrigeration module  34  may be in the form of any of a wide variety of configurations including perforated plate or coiled tube heat exchangers.  
         [0024]     In this embodiment, HTS refrigeration module  34  includes six cryocoolers  46 , each of which may be any of a wide variety of cryocooling refrigerators designed to operate according to one of several thermodynamic cycles including Gifford-McMahon, Stirling and pulse-tube cycle, such as those described in U.S. Pat. No. 5,482,919, which is incorporated herein by reference. Each cryocooler  46  is associated with a compressor  36 , however, in other embodiments, a single compressor may be used with the multiple cryocoolers. Each cryocooler provides a cryogenically cooled surface for cooling the helium. One example of a cryocooler appropriate for use in HTS refrigeration module  34  is Model No. RGS 120-T, manufactured by Leybold, Inc., Cologne, Germany.  
         [0025]     Cryocoolers  46  are connected in a series arrangement through conduit lines  49  that include valves  47  to allow each cryocooler to be isolated from remaining ones of the cryocoolers while allowing continued operation of the system. In particular, bypass conduits (not shown) for each cryocooler  46  are used to allow continued flow of the cryogenic fluid so that the isolated cryocooler can be, for example, repaired or replaced. Valves  47  may be any of a wide variety of valves capable of operating at cryogenic temperatures including control or solenoidal valves. Valcor Scientific, Inc., Springfield, N.J. provides valves (e.g., on/off type) which are appropriate for use as valve  47 .  
         [0026]     HTS refrigeration module  34  also includes, in this embodiment, a pair of redundant high-speed (10,000-30,000 rpm) fans  48  disposed within the HTS refrigeration module  34  for circulating the helium through the cooling system. In essence, fans  48  serve as a mechanical mechanism positioned within the cryogenic environment for providing the necessary force to move the helium past cryocoolers  46  and on to rotor assembly  19 . With that in mind, other mechanical devices capable of supplying such forces and operating in a cryogenic environment including diaphragms, piston-operated devices or blowers can serve as fluid transfer device(s). Thus, unlike many conventional cooling arrangements the helium (or other cryogenic fluid) need not undergo a phase change to be re-cooled after being heated by the load. As was the case with the multiple cryocoolers  46 , a pair of fans  48  is used to provide redundancy and facilitate maintenance in the event that one of the fans requires maintenance or replacement. Of course, appropriate valve and bypass conduits are required to allow each of fans  48  to be isolated from the other while allowing continuous operation of the system. A fan determined well-suited for operation in a cryogenic environment is a Model A20 fan, available from Stirling Cryogenics and Refrigeration BV, The Netherlands.  
         [0027]     Because the HTS refrigeration module  34  and associated compressor  36  are both supported by turntable assembly  28 , these components of the system are advantageously part of the rotatable reference frame and rotate with the turntable assembly. Thus, as shown in  FIG. 1 , a conduit line  40 ,  42  between the refrigeration module  34  and transfer coupling  44  of the superconducting motor  18  can be introduced at almost any point between the pod seating and azimuthing pod  12 . More particularly, conduit line  40 ,  42  need not be introduced into the azimuthing pod  12  along the axis of rotation  52  about which turntable assembly  28  rotates. This feature is particularly advantageous because much of the electrical wiring and lubrication lines (e.g., bearing lubrication) required between power transmission/control system  32  lies along axis of rotation  52 . Moreover, because refrigeration module  34  and compressor  36  are mounted within hull  14 , access to these components of the pod propulsion system  10  is easier, for example, for maintenance purposes.  
         [0028]     In certain other embodiments, space on the turntable assembly  28  or around pod seating  16  may be limited. In other embodiments, components of the cooling system may necessarily be positioned at an area of the ship remote from pod, seating  16 . In such embodiments, it may be necessary to move one or more of the components of the cryogenic cooling system off of turntable assembly  28 .  
         [0029]     For example, referring to  FIG. 3 , while refrigeration module  34  is mounted on turntable assembly  28  and, therefore, rotates with the turntable assembly, a compressor  36   a  is mounted off of the turntable assembly. Gas lines  54 , at ambient temperatures, couple HTS refrigeration module  34  with compressor  36   a  through a transfer coupling  55  including a gas seal assembly. Transfer coupling  55  is mounted along axis of rotation  52  and includes a standard gas seal with O-rings. Transfer coupling  55  is at ambient temperature and transfers the ambient temperature high pressure gas between the stationary reference on the hull side of pod seating  16  and the rotating reference frame of the azimuthing pod  12 . Like the embodiment discussed above in conjunction with  FIG. 1 , the conduit line  40 ,  42  between HTS refrigeration module  34  and superconducting motor  18  need not be introduced into the azimuthing pod  12  along an axis of rotation  52  about which turntable assembly  28  rotates.  
         [0030]     Similarly, as shown in  FIG. 4 , where space on turntable assembly  28  is further limited, a refrigeration module  34   b  and compressor  36   b  are not supported by turntable assembly  28 . Thus, unlike the embodiment of  FIG. 3 , because both refrigeration module  34   b  and compressor  36   b  are not supported by turntable assembly  28 , a conduit line  38   b , like that used in the embodiment of  FIG. 1 , is used to couple the two components of the cryogenic cooling system. This topology requires a cooling conduit  54   b  between refrigeration module  34   b  and a transfer coupling  57  mounted at the interface between turntable assembly  28  and pod seating  16 . Furthermore, supply and return transfer lines  40   b ,  42   b  connect transfer coupling  57  to transfer coupling  44   b  of superconducting motor  18 . In this embodiment, the refrigeration module  34   b  and compressor  36   b  are not supported by turntable assembly  28  and therefore these components are stationary relative to the rotatable turntable assembly. To avoid winding of the cooling conduit  56  about the components mounted on the turntable assembly  28 , transfer coupling  57  is located on the axis of rotation  52 . Thus, this topology, unlike the embodiments of  FIGS. 1 and 3 , has the advantage of a smaller turntable assembly with the disadvantage of requiring use of the axis of rotation  52 . Referring to  FIG. 5 , an example of a transfer coupling suitable for use as transfer couplings  44   b ,  57  in  FIG. 4  is shown. The transfer coupling includes a bayonet connection  59  between the stationary reference and rotating reference frames. In particular, the bayonet connection  59  includes a center conduit  60  surrounded by a coaxial outer jacket  62 . Center conduit  60  is supported within coaxial outer jacket  62  with a slip seal  64 . The transfer coupling also includes a ferrofluidic seal  66  positioned between a stationary vacuum flange  68  and a rotor vacuum flange  70 . Cryogenically-cooled gas from fans  48  is provided through center conduit  60  to the rotor assembly  19  and returned to the HTS refrigeration module  34 ,  34   b  along a path between center conduit and coaxial outer jacket  62 .  
         [0031]     Referring to  FIG. 6 , in a further embodiment, a HTS refrigeration module  34   c  is shown positioned with azimuthing pod  12  with the associated compressor  36   c  mounted on turntable assembly  28 . Similar to the embodiment discussed above in conjunction with  FIG. 1 , a conduit line  40   c ,  42   c  extending between the stationary and rotating reference frames (i.e., between compressor  36   c  and refrigeration module  34   c ) need not be introduced into the azimuthing pod  12  along an axis of rotation  52  about which turntable assembly  28  rotates. A simple conduit  72  connects refrigeration module  34   c  and transfer coupling  44  of the superconducting motor  18 . In this topology, space within azimuthing pod  12  is occupied by HTS refrigeration module  34   c  and access to it is more limited (e.g., for maintenance purposes). However, this topology advantageously, provides more space along the axis of rotation for other mechanical systems (e.g., bearing lubrication, etc.).  
         [0032]     Other embodiments are within the scope of the claims.