Rim driven thruster having transverse flux motor

The present invention is directed generally to rim driven thrusters (RDT) used as propulsion systems for watercraft and the like. More particularly, the present invention relates to permanent magnet brushless motors for RDTs.

In rim driven thrusters, an electro-magnetic motor is integrated with propeller blade propulsors. In typical RDTs, a rotor assembly is integrated at outer diameter ends of the propeller blades and a stator assembly is integrated into a stationary annular housing surrounding the propeller blades. The stator assembly electro-magnetically causes the rotor assembly to rotate and generate propulsive thrust with the propeller blades. The housing is connected to the vessel through a pylon that rotates about a vertical axis so that the RDT is able to provide propulsion and steering in a single unit.

RDTs are advantageous for submerged operation because the electro-magnetic motor is removed from the center of the propulsor. In such a configuration, electrically active components of the stator assembly are positioned within the housing so as to be easily insulated. Moreover, the motor is positioned so as to minimize hydraulic drag. Specifically, the stator assembly is positioned within the annular housing and the rotor assembly is positioned in close proximity to the housing at the outer diameter of the blades. The stator and rotor assemblies are, however, still exposed to hydraulic drag when submerged. Thus, it becomes desirable to reduce the thickness of the rotor and stator assemblies to further minimize hydrodynamic losses.

Typical RDTs utilize conventional slotted stator cores in the stator assembly. In these designs, however, it is difficult to accommodate multiple windings in the narrow and shallow slots that are needed to achieve favorable thickness dimensions. Another proposal for reducing stator core thickness has included the use of a slot-less stator winding and spiral wound stator core laminations. This stator assembly design is expensive, difficult to manufacture and suitable only for small motors. There is, therefore, a need for a permanent magnet motor configuration having favorable hydraulic drag properties in an easily and inexpensively manufactured configuration.

The present invention is directed to a rim driven thruster having a transverse flux motor. The rim driven thruster comprises an annular housing, a propulsor assembly, a magnetic rotor assembly and a transverse flux stator assembly. The annular housing defines a flow path extending along an axis. The propulsor assembly is supported within the housing and comprises propeller blades extending radially from the axis of the flow path. The propeller blades are configured to rotate about the axis. The magnetic rotor assembly is mounted to radially outer ends of the propeller blades. The transverse flux stator assembly is mounted to the annular housing and is configured to provide electromagnetic torque to the magnetic rotor assembly.

FIG. 1 is a perspective view of a rim driven thruster (RDT) connected to a hull of a waterborne vessel.

FIG. 2 is an aft view of the rim driven thruster of FIG. 1 , as taken at section 2 - 2 , showing a rotor core and a stator core.

FIG. 3A is a side cross-sectional view of the rim driven thruster of FIG. 2 , as taken at section 3 - 3 , showing a propulsor assembly supported by rim bearings.

FIG. 3B is an alternate side cross-sectional view of the rim driven thruster of FIG. 2 , as taken at section 3 - 3 , showing the propulsor assembly supported by shaft bearings.

FIG. 4 is a partial perspective view of the rotor assembly and the stator assembly of FIGS. 1-3B .

FIG. 5A is a side cross-sectional view of a first embodiment of the stator assembly of FIG. 4 , as taken at section 5 - 5 , showing a stator core comprising a U-shaped core formed by laminations and a yoke.

FIG. 5B is a side cross-sectional view of a second embodiment of the stator assembly of FIG. 4 , as taken at section 5 - 5 , showing a stator core comprising a U-shaped core.

FIG. 5C is a cross-sectional view of FIG. 5B as taken as section 5 B- 5 B, showing lamination layers of the U-shaped core.

FIG. 1 is a perspective view of rim driven thruster (RDT) 10 connected to the stern of waterborne vessel 12 . Waterborne vessel 12 may comprise any conventional watercraft, such as a floating ship or underwater submarine. In the embodiment shown, vessel 12 comprises a hull of a ship having transom 14 and keel 16 . In operation, vessel 12 is positioned such that keel 16 is submerged and transom 14 is partially submerged in water, or any other fluid, so as to fully submerge RDT 10 . RDT 10 is mounted to the hull of vessel 12 by pylon 18 underneath transom 14 and aft of keel 16 . RDT 10 includes housing 20 , propellers 22 , hub 24 , rim 26 and forward and aft fairings 28 A and 28 B. RDT 10 may also be referred to as an integrated motor propeller (IMP).

RDT 10 provides propulsive power to vessel 12 by rotation of propellers 22 . RDT 10 swivels about pylon 18 behind keel 16 to steer vessel 12 . RDT 10 rotates on pylon 18 under an external power source such as provided from within vessel 12 . Propellers 22 are rotated by an electro-magnetic motor integrated into rim 26 and housing 20 . A stator core is mounted within housing 20 and receives electric power from vessel 12 through pylon 18 . Magnetic forces from the stator core are transmitted to a rotor core mounted on rim 26 . Rim 26 drives propellers to rotate on hub 24 within housing 20 . Forward fairing 28 A and aft fairing 28 B provide hydrodynamic shields for housing 20 , rim 26 , the stator core and the rotor core.

RDT 10 provides hydrodynamic advantages to vessel 12 because the electromagnetic motor is moved out of the flow path provided within housing 20 . As such, the effect of hub 24 on hydrodynamic drag is minimized and the length of propellers 22 can be increased, thereby improving thrust production. Operating performance of RDT 10 depends on the electromagnetic performance of the motor configuration. For example, large air gaps between the stator and rotor cores are required to provide corrosion protection. It is, however, also desirable to have a large motor diameter relative to the radial thickness of the stator core to provide better electro-magnetic torque transmission, such as by increasing the number of rotor poles. Furthermore, it is desirable to have radially thin stator and rotor cores to reduce the hydraulic drag of RDT 10 . RDT 10 of the present invention utilizes a transverse flux permanent magnet motor to achieve a thin stator core that is easy to manufacture and that transmits substantial torque to the stator core over a large gap.

FIG. 2 is an aft view of rim driven thruster (RDT) 10 of FIG. 1 , as taken at section 2 - 2 , showing stator assembly 30 and rotor assembly 32 . FIG. 2 corresponds to a view of RDT 10 with aft fairing 28 B removed. RDT 10 also includes housing 20 , propellers 22 , hub 24 and rim 26 . Housing 20 extends axially along centerline CL to form a flow path for water driven by propellers 22 . Rim 26 is supported within housing 20 by bearings in various configurations, as discussed with reference to FIGS. 3A and 3B . Hub 24 is supported by propellers 22 within rim 26 so as to be co-axial with centerline CL. Propellers 22 extend radially from hub 24 across the flow path to rim 26 . Propellers 22 comprise hydrofoils or blades shaped to accelerate water as they rotate about centerline CL, as is known in the art. Rim 26 comprises a continuous support ring integrally mounted to the tips, or radially outermost portion, of propellers 22 . Rotor assembly 32 is affixed to a radially outer surface of rim 26 and comprises an array of permanent magnet pole pairs and a ferromagnetic core. Stator assembly 30 is mounted to a radially inner surface of housing 20 and comprises an array of ferromagnetic cores and a coil winding. Forward fairing 28 A and aft fairing 28 B ( FIG. 1 ) are connected to forward and aft ends of housing 20 , respectively, to cover housing 20 , stator assembly 30 , rotor assembly 32 and rim 26 .

Stator assembly 30 is mounted so as to be a small distance away from rotor assembly 32 to provide gap G. The thicknesses of gap G, as well as rim 26 , rotor assembly 32 , stator assembly 30 and housing 20 are not drawn to proportion in FIG. 2 . In particular, it is desirable to minimize gap G to improve electro-magnetic performance. However, gap G must be provided to permit encapsulation of stator assembly 30 and rotor assembly 32 for corrosion resistance and water-proofing. Stator assembly 30 and rotor assembly 32 of the present invention are configured as a brushless, permanent magnet, transverse flux motor, as described in greater detail with reference to FIGS. 3A-5 .

FIG. 3A is a side cross-sectional view of rim driven thruster 10 of FIG. 2 , as taken at section 3 - 3 , showing bearings assemblies 34 A and 34 B supporting propulsor assembly 36 A at rim 26 . RDT 10 includes pylon 18 ; housing 20 ; forward fairing 28 A; aft fairing 28 B; stator assemblies 30 A, 30 B and 30 C; rotor assemblies 32 A, 32 B and 32 C; and propulsor assembly 36 A. Propulsor assembly 36 A comprises propellers 22 ; hub 24 ; rim 26 ; bearing assemblies 34 A and 34 B; bearing pads 38 A and 38 B; and bearing rims 40 A and 40 B. Rotor assemblies 32 A, 32 B and 32 C comprise rotor cores 42 A, 42 B and 42 C; permanent magnets 44 A, 44 B and 44 C; permanent magnets 46 A, 46 B and 46 C; and spacers 48 A, 48 B and 48 C, respectively. Stator assemblies 30 A, 30 B and 30 C comprise stator cores 50 A, 50 B and 50 C; and coil windings 52 A, 52 B and 52 C, respectively.

Annular housing 20 is connected to vessel 12 ( FIG. 1 ) by pylon 18 . Pylon 18 rotates about vertical axis VA, which causes RDT 10 to adjust the yaw of vessel 12 when propellers 22 are rotating. Annular housing 20 defines a cylindrical flow path through which center line CL axially extends. Propellers 22 extend radially with respect to center line CL between hub 24 and rim 26 . The center of hub 24 extends co-axially along center line CL such that rim 26 of propulsor assembly 36 A is supported concentrically within housing 20 by bearing assemblies 34 A and 34 B when mounted on bearing pads 38 A and 38 B, respectively.

Forward fairing 28 A and aft fairing 28 B are connected to housing 20 to provide hydrodynamic surfaces to RDT 10 . Forward fairing 28 A is connected to housing 20 at a forward end using any suitable attachment means, such as fasteners. Alternatively, forward fairing 28 A may be integrated with housing 20 . Forward fairing 28 A is shaped to smoothly direct flow of water over RDT 10 , while allowing water to enter housing 20 to engage propulsor assembly 36 A. Forward fairing 28 A includes bearing pad 38 B located at an aft end so as to be positioned near rim 26 . Aft fairing 28 A is connected to housing 20 at an aft end using any suitable attachment means, such as fasteners. Aft fairing 28 A is removable from housing 20 to provide access to stator assemblies 30 A- 30 C and rotor assemblies 32 A- 32 C. Although, in other embodiments, aft fairing 28 A may be integrated with housing 20 if access is provided elsewhere. Aft fairing 28 B includes bearing pad 38 A located at a forward end so as to be positioned near rim 26 . Aft fairing 28 B also includes shield 54 , which extends radially inward past bearing assembly 34 A and alongside bearing rim 40 A. Shield 54 protects bearing assembly 34 A and provides a hydrodynamic surface. In other embodiments, shield 54 may be omitted from aft fairing 28 B, as shown in FIG. 3B (which will be discussed later), to allow water to directly enter bearing assemblies 34 A and 34 B, stator assemblies 30 A- 30 C and rotor assemblies 32 A- 32 C for cooling purposes.

Rim 26 is supported by bearing assemblies 34 A and 34 B at bearing rims 40 A and 40 B. Bearing rims 40 A and 40 B comprise forward and aft axial extensions, respectively, of rim 26 . Bearing rims 40 A and 40 B may be integral with rim 26 or separate components fastened to rim 26 . Bearing rims 40 A and 40 B increase the available surface of rim 26 not used to support rotor assemblies 32 A- 32 C. Bearing rims 40 A and 40 B extend axially beyond stator assemblies 30 C and 30 A, respectively, such that a radially outer surface faces towards forward fairing 28 A and aft fairing 28 B, respectively. Bearing rims 40 A and 40 B thus comprise annular rings against which bearing assemblies 34 A and 34 B engage.

Forward fairing 28 A includes bearing pad 38 B, and aft fairing 28 B includes bearing pad 38 A. Bearing pad 38 B is integrally formed with forward fairing 28 A, and bearing pad 38 A is integrally formed with aft fairing 28 B. In other embodiments, bearing pads 38 A and 38 B may comprise separate components or may be formed as part of housing 20 . In any embodiment, bearing pads 38 A and 38 B comprise annular surfaces or lands against which bearing assemblies 34 A and 34 B engage. Thus, bearing assemblies 34 A and 34 B are positioned concentrically between rims 40 A and 40 B and pads 38 A and 38 B to permit propulsor assembly 36 A to rotate within housing 20 when rotor assemblies 32 A- 32 C are activated by stator assemblies 30 A- 30 C. Specifically, stator assemblies 30 A- 30 C apply an electro-magnetic force to rotor assemblies 32 A- 32 C, respectively, to produce rotational movement of propellers 22 about center line CL.

Stator assemblies 30 A- 30 C are mounted to a radially inward facing surface of housing 20 . Specifically, stator cores 50 A- 50 C are joined to housing 20 by any suitable means. Stator cores 50 A- 50 C comprise ferromagnetic material that is fashioned in the form of U-shaped bodies that open toward rim 26 . Stator cores 50 A- 50 C each comprise a plurality of U-shaped bodies spaced around centerline CL in a ring-like configuration, as is shown more clearly in FIG. 4 . In the axial direction, stator cores 50 A- 50 C are spaced equally along housing 20 with spacers 56 A and 56 B fitted between. Spacers 56 A and 56 B comprise rings of non-conducting and non-magnetic material that maintain spaces 57 . Coil windings 52 A- 52 C are disposed within the U-shaped bodies formed by stator cores 50 A- 50 C, respectively. Coil windings 52 A- 52 C comprise single toroidal coils that form continuous rings of conducting material.

Rotor assemblies 32 A- 32 C are mounted to a radially outward facing surface of rim 26 . Specifically, rotor cores 42 A- 42 C are joined to rim 26 by any suitable means. Rotor cores 42 A- 42 C comprise ferromagnetic material that is fashioned in the form of annular rings that circumscribe rim 26 . Rotor cores 42 A- 42 C are spaced equally along rim 26 to align with stator cores 50 A- 50 C. Permanent magnets 44 A- 44 C, permanent magnets 46 A- 46 C and spacers 48 A- 48 C are mounted to radially outward faces of rotor cores 42 A- 42 C, respectively, in a surface-mount configuration. In other embodiments, permanent magnets 44 A- 44 C, 46 A- 46 C and spacers 48 A- 48 C may be mounted in a buried configuration. In yet another embodiment, rim 26 is omitted from propulsor assembly 36 A and rotor cores 42 A- 42 C are mounted directly to tips of propellers 22 . As shown in the cross-section of FIG. 3A , permanent magnets 44 A- 44 C are mounted to axially forward ends of rotor cores 42 A- 42 C, and permanent magnets 46 A- 46 C are mounted to axially aft ends of rotor cores 42 A- 42 C. However, as shown in FIG. 4 , permanent magnets 44 A- 44 C and permanent magnets 46 A- 46 C have opposite magnetic pole orientations and alternate being positioned at forward and aft ends of their respective rotor cores 42 A- 42 C. Spacers 48 A- 48 C comprise non-magnetic material and are disposed on rotor cores 42 A- 42 C between permanent magnets 44 A- 44 C and permanent magnets 46 A- 46 C, respectively, to magnetically isolate rotor cores 32 A- 32 C from each other.

Rotor assemblies 32 A- 32 C and stator assemblies 30 A- 30 C are easily mounted in configurations advantageous to operation of RDT 10 . For example, the axial length of stator assemblies 30 A- 30 C is shortened in transverse flux motors as compared to conventional magneto-electric motors having parallel flux lines. The shortened size of stator assemblies 30 A- 30 C permit easy integration of spacers 56 A and 56 B, which spread stator assemblies 30 A- 30 C along housing 20 to produce spaces 57 . Spaces 57 permit water, or other fluid in which RDT 10 is submerged, to cool stator assemblies 30 A- 30 C. Also, rotor assemblies 32 A- 32 C are maintained at a gap-distance from stator assemblies 32 A- 32 C, respectively. The gap-distance is suitable to permit propulsor assembly 36 A to rotate and to permit incorporation of corrosion protection coatings on stator assemblies 30 A- 30 C and rotor assemblies 32 A- 32 C. For example, rotor assemblies 32 A- 32 C and stator assemblies 30 A- 30 C may be encapsulated in an epoxy or some other material that is non-insulating and water resistant. In other embodiments, rotor assemblies 32 A- 32 C and stator assemblies 30 A- 30 C may be incorporated into structural members. For example, stator assemblies 30 A- 30 C may be positioned within housing 20 to provide environmental protection. The gap-distance between rotor assemblies 32 A- 32 C and stator assemblies 30 A- 30 C is maintained as small as possible to accommodate encapsulation while also permitting rotor cores 32 A- 32 C to maintain efficient electro-magnetic interaction with stator cores 30 A- 30 C.

Arranged as such within RDT 10 , stator assemblies 30 A- 30 C and rotor assemblies 32 A- 32 C form a three-phase, single-sided magneto-electric motor. In a three-phase motor, alternating current is applied to stator cores 52 A- 52 C one-hundred-twenty degrees out of phase, as is known in the art. In other embodiments, other multi-phase configurations can be used, rather than three-phase. In a single-sided motor, current from a single stator core is applied to each rotor core. In other embodiments, double-sided motors can be used wherein current from a pair of stator cores is applied to each rotor core, one from the outside and one from the inside. Alternating electrical current is supplied directly to coil windings 52 A- 52 C such as from a power source in vessel 12 ( FIG. 1 ). A conventional solid-state, three-phase inverter may be used. Current within coil windings 52 A- 52 C causes magnetic flux to flow through stator cores 50 A- 50 C. The oppositely oriented magnetic poles of permanent magnets 44 A- 44 C and permanent magnets 46 A- 46 C cause magnetic flux to travel through rotor assemblies 32 A- 32 C. Spacers 56 A and 56 B isolate magnetic flux in each pair of permanent magnets 44 A- 44 C and 46 A- 46 C, respectively, causing the flux path within rotor cores 32 A- 32 C to travel through rotor cores 42 A- 42 C. The magnetic flux of stator cores 30 A- 30 C interacts with the magnetic flux of permanent magnets 44 A- 44 C and permanent magnets 46 A- 46 C to apply a torque to rim 26 . Bearing assemblies 34 A and 34 B permit rim 26 and rotor assembly 36 A to rotate smoothly about center line CL.

FIG. 3B is an alternate side cross-sectional view of rim driven thruster 10 of FIG. 2 , as taken at section 3 - 3 , showing bearing assemblies 34 C and 34 D supporting propulsor assembly 36 B at shaft 58 . RDT 10 includes stator assemblies 30 A- 30 C and rotor assemblies 32 A- 32 C, which comprise the same structures as described with reference to FIG. 3A . As such, discussion of stator assemblies 30 A- 30 C and rotor assemblies 32 A- 32 C is omitted with reference to FIG. 3B for brevity. RDT 10 also includes pylon 18 , housing 20 , propellers 22 , hub 24 , rim 26 , forward fairing 28 A and aft fairing 28 B, as was discussed with reference to propulsor assembly 36 A of FIG. 3A . Propulsor assembly 36 B includes support brackets 60 A, 60 B, 60 C and 60 D. Support brackets 60 A and 60 B extend radially inward from aft fairing 28 B straight towards support ring 62 A. Support brackets 60 A and 60 B comprise two of three support brackets (the third not seen in the cross-section of FIG. 3B ) spaced one-hundred-twenty degrees apart within aft fairing 28 B. Support brackets 60 C and 60 D extend radially inward from forward fairing 28 A straight towards support ring 62 B. Support brackets 60 C and 60 D comprise two of three support brackets (the third not seen in the cross-section of FIG. 3B ) spaced one-hundred-twenty degrees apart within forward fairing 28 A. In other embodiments, support brackets 60 A- 60 D extend directly from housing 20 , rather than fairings 28 A and 28 B. Support brackets 60 A- 60 D provide structure for supporting shaft 58 with support rings 62 A and 62 B. Bearing assemblies 34 C and 34 D are fitted within support rings 62 A and 62 B, respectively. Bearing assemblies 34 C and 34 D receive opposite ends of shaft 58 . Shaft 58 extends from bearing assembly 34 C, through hub 24 and into bearing assembly 34 D. Hub 24 is fitted around shaft 58 , such as with a force fit, so that hub 24 and shaft 58 rotate in unison. As such, propellers 22 are permitted to rotate about centerline CL as shaft 58 rotates in bearing assemblies 34 C and 34 D when torque is applied to rotor assemblies 32 A- 32 C by stator assemblies 30 A- 30 C.

FIG. 4 is a partial perspective view of stator assembly 30 A and rotor assembly 32 A of FIGS. 1-3B . Stator assembly 30 A includes stator core 50 A and coil winding 52 A. Stator core 50 A includes U-shaped cores 64 . In the embodiment shown, stator core 50 A is comprised of twenty-eight U-shaped cores 64 , as FIG. 4 shows a quarter section of stator assembly 30 A. Rotor assembly 30 A includes rotor core 42 A, spacer 48 A and a plurality of permanent magnets 44 A and 46 A. As shown in FIG. 4 , permanent magnets 44 A are configured to have magnetic pole orientations that extend radially outward, and permanent magnets 46 A are configured to have magnetic pole orientations that extend radially inward. Permanent magnets 44 A and permanent magnets 46 A are disposed along forward and aft surfaces of spacer 48 A in an alternating fashion such that a permanent magnet 44 A at the forward surface is axially aligned with a permanent magnet 46 A at the aft surface.

When operating as an electric motor, stator core 30 A and rotor core 32 A interact magnetically to cause rotation of rotor assembly 30 A about centerline CL. Alternating electric current is applied to coil winding 52 A, which causes magnetic flux MF to flow through U-shaped cores 64 . Magnetic flux MF reverses direction as the applied current alternates. Magnetic flux MF travels through the plane formed by each U-shaped core 64 , and the electric current travels perpendicular to this plane in coil winding 52 A. Magnetic flux MF induced in U-shaped cores 64 interact with the pole orientations of permanent magnets 44 A and 46 A, generating force vector F. Force vector F is aligned in a direction that is tangential to rotor assembly 32 A. Specifically, force vector F is perpendicular to the plane of magnetic flux MF, which causes torque to be applied to rotor core 42 A and the rest of propulsor assembly 36 A or 36 B.

Performance of RDT 10 benefits from the construction of stator assembly 30 A and rotor assembly 32 A. Stator assembly 30 A only requires a single coil provided by coil winding 52 A. Also, the size of stator assembly 30 A can be increased in the axial direction, such that the height can be decreased. These configurations permit stator assembly 30 A to be radially thin. The diameter of RDT 10 is increased by the thin construction of stator assembly 30 A, which allows the diameter of rotor core 42 A to be increased to include a greater number of permanent magnets 44 A and 46 A. The increased number of magnetic poles present from permanent magnets 44 A and 46 B allows for better torque transmission, among other things.

FIG. 5 is a side cross-sectional view of a second embodiment of stator assembly 30 A of FIG. 4 , as taken at section 5 - 5 , showing stator core 50 A comprising U-shaped core 64 formed by laminations 66 A, laminations 66 B and yoke 68 . Coil winding 52 A extends through U-shaped cored 64 between laminations 66 A and 66 B. Yoke 68 is attached to an interior surface of housing 20 ( FIG. 2 ) such that U-shaped core 64 opens towards rotor assembly 32 A ( FIG. 4 ). Yoke 68 extends axially from a first end, where laminations 66 A are attached, to a second end, where laminations 66 B are attached. Laminations 66 A and 66 B extend radially from yoke 68 . Laminations 66 A together form arm 70 A, and laminations 66 B together form arm 70 B. Yoke 68 , laminations 66 A and laminations 66 B form a U-shaped channel that forms a magnetic path. The U-shaped channel forms a planar magnetic circuit through which magnetic flux flows when current is applied to coil winding 52 A. Arm 70 A, arm 70 B and yoke 68 are assembled together in any suitable fashion. Encapsulation layer 72 surrounds exposed surfaces of stator core 50 A to protect arm 70 A, arm 70 B and yoke 68 from corrosion and the operating environment of RDT 10 .

Laminations 66 A and 66 B extend radially from yoke 68 so that they are parallel to magnetic flux MF ( FIG. 4 ) within U-shaped core 64 , which preserves the transverse flux nature of stator assembly 30 A. Laminations 66 A and 66 B and yoke 68 are comprised of ferromagnetic material, such as cobalt alloy, silicon steel, nickel, iron or other similar materials. Laminations 66 A and 66 B comprise thin plates of solid ferromagnetic material that can be easily stamped or cut from stock materials to facilitate easy manufacturing. Yoke 68 is comprised of a solid piece of material machined to the appropriate shape. Yoke 68 may also be formed of laminations extending in the axial direction (between first arm 70 A and second arm 70 B) that are stacked in the tangential direction (in the plane of the paper of FIG. 5 ) to avoid laminations extending perpendicular to magnetic flux MF in yoke 68 . Yoke 68 may also be comprised of a sintered powder. Likewise, arms 70 A and 70 B may be comprised of a sintered powder in embodiments not using laminations. U-shaped cores suitable for use in the present invention are described in greater detail in U.S. Patent Application No. 2010/0052467 A1 to Gieras and assigned to Hamilton Sundstrand Corporation, Rockford, Ill., which is incorporated herein by reference.

FIG. 5B is a side cross-sectional view of a second embodiment of stator assembly 30 A of FIG. 4 , as taken at section 5 - 5 , showing stator core 50 A comprising U-shaped core 64 . FIG. 5C , which is discussed concurrently with FIG. 5B , is a cross-sectional view of FIG. 5B as taken as section 5 B- 5 B, showing lamination layers 72 A- 72 F of U-shaped core 64 . Stator assembly 30 A also includes coil winding 52 A as discussed with reference to FIG. 5A . Laminations 72 A- 72 F comprise U-shaped laminations mounted to housing 20 . Laminations 72 A- 72 F each include a pair of longitudinally extending portions that connect a transversely extending portion. The longitudinal and transverse portions are stacked in the tangential direction (in the plane of the paper of FIG. 5B ) to form a magnetic flux path similar to that of arms 70 A, 70 B and yoke 68 of FIG. 5A . As with the previously described embodiment, laminations 72 A- 72 F are comprised of easily formed pieces of ferromagnetic material, such as cobalt alloy, silicon steel, nickel, iron or other similar materials.

Transverse flux motors provide advantages to rim driven thrusters and integrated motor propellers. Specifically, transverse flux motors provide built-in step down of electromagnetic transmission, such that high frequency input current, such as may be provided from a gas turbine engine, is transformed into low shaft speed. Higher frequency input current allows for smaller motors having higher power density. Higher power density is further achieved by increased numbers of permanent magnet poles enabled by transverse flux machines. Transverse flux machines also permit increased size of gap G ( FIG. 2 ), which allows for better sealing and encapsulation of the stator and rotor assemblies. Construction of the transverse flux machines described is simple, comprising only a single stator winding and simple rotor core laminations. Additionally, each stator and rotor assembly in multi-phase configurations are identical, reducing the number of components and associated manufacturing costs. Rim driven thrusters using transverse flux machines can provide power output in the range of kilowatts up to megawatts.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.