FIELD

One or more aspects of embodiments according to the present disclosure relate to electric machines, and more particularly to electric machines including wound strip structures.

BACKGROUND

In the manufacturing of electric machines, such as electric motors, the cost of fabricating rotor cores and stator cores may be significant, and in the operation of such machines, heating due to various loss mechanisms may be a mechanism limiting the performance of the machine. As such there is a need for improvements in the design of rotor and stator cores for electric machines.

SUMMARY

Aspects of embodiments of the present disclosure are directed towards a system for cooling both induction and permanent magnet machines which enables specific power levels in excess of 10 kW/kg for machines in the range of 10 kW to 1000 kW. In addition to the enablement of high continuous specific power, the present disclosure also enables reduced cost, especially for high pole-count designs, by reducing material waste associated with the core structure, while enabling more rapid fabrication of the same.

In order to achieve these very high specific power levels, stator and rotor current densities may be maintained on the order of 1500 A/cm2. The resulting conductor and core specific losses are respectively on the order of 5 W/cm3and 1 W/cm3. In the case of permanent magnet machines, similar specific power levels can be achieved where stator current densities are maintained on the order of 1500 A/cm2and where gap peak flux densities are maintained on the order of 1 Tesla.

In order to handle these high specific levels of heat production, the specific heat transfer may be on the order of 0.1 W/cm3/C (averaged over the machine active volume). A technique has been developed, termed “capillary cooling”, which provides heat transfer from either laminated or strip-wound cores which is well in excess of 0.1 W/cm3/C. More specifically, repeating apertures are punched in the magnetic strip used for the stator core. When wound, these apertures partly align such that coolant paths are formed having a thickness dimension which is equal to the strip thickness or a multiple of the strip thickness. By applying this heat transfer technique to wound-strip stator cores, a variety of machine types can be implemented wherein material waste is reduced and power density is significantly increased.

The new stator core construction applies for both induction and permanent magnet type machines; stator designs are nearly identical for these two machine types. For each of these machine types, radial-gap and axial gap designs are identified which are based on the new strip-wound concept. Within the subset of radial-gap designs, both conventional and inside-out designs are provided. Furthermore, for both the conventional and inside-out radial gap designs, single piece and two-piece coaxial strip-wound core designs are identified. Finally, for axial gap designs, single piece and two-piece strip wound core designs are identified which include the capillary cooling technique. Inside-out machines may be useful as wheel motors and as propeller motors for electric aircraft.

In one embodiment of the present invention there is provided a radial-gap machine stator core formed from an edge-wound strip of ferromagnetic material. Prior to winding of the wound strip, repeating slots and repeating apertures are stamped into the strip, such that upon winding of the wound strip, a cylinder is formed which includes fully aligned winding slots (i.e., slots in the wound strip structure for accommodating a winding, e.g., a stator winding) which point radially inward, and partly aligned apertures which form coolant channels wherein a significant portion have a thickness dimension which is equal to the strip thickness or a multiple thereof. With the addition of coolant manifolds at both ends of the core, coolant can be introduced and collected from the coolant channels within the core. This constitutes a radial-gap stator core which may be used for induction or permanent magnet machines. For both the conventional and inside-out designs, high pole-count designs may be used since the back-iron thickness is then relatively small—thus simplifying the edge-bending process. Furthermore, with high pole-count stators, strip-wound designs typically incur less material waste than stator designs which use stacked laminations.

In another embodiment of the invention, a similar radial-gap stator core is formed from an edge-wound magnetic strip, but where the winding slots face radially outward, rather than inward. Cooling details and details of the stator winding may be similar for the two designs. With the slots facing radially outward, the core is suitable for an inside-out stator wherein the rotor is external to the stator and rotates about, rather than within the stator. For both the conventional and inside-out designs, high pole-count designs may be used since the back-iron thickness is relatively small—thus simplifying the edge-bending process.

In another embodiment of the invention, a radial-gap stator core is formed from two concentric edge-wound magnetic strips, where the inner strip includes winding slots which face radially outward, while the outer wound strip provides the back-iron and cooling functions. Repeating apertures included in the outer strip partly align such that cooling channels are formed as described earlier. With this design, winding slots are closed with respect to the bore. This has the advantage that tooth tip losses are reduced. Furthermore, since bending takes place on the thin “bridge” elements between adjacent teeth, edge-bending for the inner member is relatively simple. Winding of the wound strip is also simplified since the wire slots are fully open and face radially outward. As such, it is possible to apply a preformed winding to the wire slots—which may have further benefits such as improved packing factor and improved heat transfer within the winding. In turn the performed winding maybe formed from multiple strands which are compacted. This may be achieved through the use of a two piece die prior to the insertion of the winding. In some embodiments, the wire strands may also include a thermally set epoxy on them such that when current is applied the winding strands fuse together to form a busbar—like structure.

Non-oriented ferro-magnetic material may be used for both core sections. Alternatively, magnetic performance can be improved where grain-oriented ferro-magnetic materials are used. Back-iron performance is improved in the case where the grain orientation vector aligns with the direction of the back-iron strip—thus increasing permeability and magnetic saturation withstand, while reducing losses. Likewise magnetic performance of the tooth element is improved in the case where the grain orientation vector aligns with the radius vector.

In another embodiment, the two-piece radial-gap stator core design can be applied to an inside-out design. In this case, the inner edge-wound core element provides the functions of back-iron and cooling. The outer edge-wound core element includes inward facing slots. The periphery of the outer wound core faces the bore. Application of the winding is simplified in that the winding slots are fully open. Grain-oriented materials can again be used to improve magnetic performance—as mentioned above.

In another embodiment, an axial-gap stator core is formed from a tape-wound ferro-magnetic strip. Slots, punched along an edge, align when wound to form wire slots and teeth. Apertures punched within the back-iron region, partly align when wound to form cooling channels. Manifolds added at the O.D. and I.D. of the wound-strip complete the coolant flow circuit. A conventional or bus winding may be applied to the winding slots.

In another embodiment, a similar axial-gap stator core is formed from a tape-wound strip with the addition of O.D. and I.D. manifolds. Two partitions segregate the O.D. manifold into two 180 degree sectors such that inlet flow is constrained to the first sector, while outlet flow is constrained to the second sector. The I.D. manifold serves to redirect radially inward flow received from the first sector to radially outward flow into the second sector.

In another embodiment, a similar-axial gap stator core is formed from a tape-wound strip and only a single O.D. manifold is used in combination with a flow-director. The flow-director serves to separate inlet and outlet flow such that odd numbered apertures in the wound-strip O.D are contiguous with a fluid inlet, while even numbered apertures are contiguous with a fluid outlet. Flow between inlet and outlet channels is directed through multiple thin azimuthal or capillary channels such that efficient heat transfer between the core and coolant results.

In another embodiment, an axial-gap stator core is formed from two mating tape-wound strips, where one strip forms the back-iron element which includes the apertures which form cooling channels, and a second wound-strip which forms the tooth element. With this approach, the winding slots within the tooth element are fully open—thus allowing for the insertion of a pre-formed winding, which may have further benefits such as improved packing factor and improved heat transfer within the winding. In turn the performed winding maybe formed from multiple strands which are compacted. This may be achieved through the use of a two piece die prior to the insertion of the winding. The closed surface in the tooth strip faces the rotor gap and as such, tooth tip losses may be reduced as compared with conventional cases where wire slots exist between the teeth. The two core halves may be bonded together via a resin such as an epoxy resin. As with the redial-gap designs, the two core halves may be fabricated from grain-oriented materials such that the grain orientation vectors substantially align with the magnetic vectors.

In another embodiment, an axial-gap stator core is formed from two mating tape-wound strips, where one strip forms the back-iron element which includes edge notches such that a portion of the winding notches is included. The back-iron element also includes the cooling apertures which partly align to form the cooling channels. The second wound strip includes the remainder of the tooth and slot structures. The advantage of this design is that the mechanical bonding between the two core halves may be improved due to reinforcement caused by the winding. This is especially the case where bus windings are used.

According to an embodiment of the present disclosure, there is provided an electric machine including one or more face wound strips including a first strip, the one or more strips having a plurality of openings, the first strip having a plurality of turns, an opening of a turn of the first strip overlapping an opening of an adjacent turn, to form a portion of a fluid channel of a plurality of fluid channels, the turn and the adjacent turn abutting against each other at the overlapping openings.

In some embodiments, the electric machine is an axial gap electric machine.

In some embodiments, a subset of the openings are narrow and a subset of the openings are wide.

In some embodiments, the electric machine includes: a stator having a stator core including the one or more face wound strips, and a rotor, the rotor having a fluid passage.

In some embodiments, the electric machine further includes a manifold having a manifold channel in fluid communication with the fluid channel.

In some embodiments, the electric machine further includes a flow director.

In some embodiments, the electric machine includes the first strip and a second strip co-wound with the first strip.

In some embodiments: the one or more face wound strips further include a second strip, the first strip has a plurality of substantially identical openings, the second strip has a plurality of substantially identical openings, and an opening of the first strip differs in shape and/or size from an opening of the second strip.

In some embodiments, the electric machine further includes a sealant between the turn and the adjacent turn, and/or within a fluid channel of the plurality of fluid channels.

In some embodiments: the one or more face wound strips further include a second strip concentric with the first strip, wherein: the first strip is configured as a back-iron portion of a stator core of the electric machine; and the second strip has a plurality of teeth, and is configured as a tooth portion of the stator core.

In some embodiments, the electric machine further includes bonding agent and/or thermal interface agent, between the first strip and the second strip.

In some embodiments, the electric machine further includes an enclosure, wherein a portion of an interior surface of the enclosure forms a portion of wall of a fluid channel of the plurality of fluid channels.

In some embodiments, the electric machine further includes a winding, wherein a portion of the winding includes insulated conductors packed with a void fraction of less than 12%.

In some embodiments, the electric machine further includes a stator core including the one or more face wound strips, the electric machine further including a winding, and a potting compound, filling a void between the stator core and the winding, the potting compound having a thermal conductivity of at least 0.5 W/K/m.

In some embodiments, the first strip is composed of a non-isotropic magnetic material, and the first strip includes a tooth portion of a stator of the electric machine, and a magnetic permeability tensor of the first strip has, within a tooth of the stator, a substantially radial eigenvector, the substantially radial eigenvector corresponding to a greatest eigenvalue of the magnetic permeability tensor of the first strip; or the first strip includes a back-iron portion of a stator of the electric machine, and a magnetic permeability tensor of the first strip has, within the back-iron portion of the stator, a substantially azimuthal eigenvector, the substantially azimuthal eigenvector corresponding to a greatest eigenvalue of the magnetic permeability tensor of the first strip.

In some embodiments, the plurality of fluid channels includes: a first fluid channel, a second fluid channel, and a third fluid channel, the first fluid channel and the second fluid channel both being: substantially axial, or substantially radial, the third fluid channel connecting the first fluid channel and the second fluid channel, the third fluid channel being not parallel to the first fluid channel and the third fluid channel being not parallel to the second fluid channel.

In some embodiments: the first strip includes a back-iron portion of a stator of the electric machine, and a magnetic permeability tensor of the first strip has, within the back-iron portion of the stator, a substantially azimuthal eigenvector, the substantially azimuthal eigenvector corresponding to a greatest eigenvalue of the magnetic permeability tensor of the first strip; and the stator includes a tiled or multi-piece tooth portion, wherein a magnetic permeability tensor of the tooth portion has a substantially radial eigenvector, the substantially radial eigenvector corresponding to a greatest eigenvalue of the magnetic permeability tensor of the tooth.

In some embodiments, the electric machine further includes: a first manifold around the outside of a first face wound strip of the one or more face wound strips, and a second manifold inside the first face wound strip, the second manifold being in fluid communication with the first manifold.

In some embodiments, the electric machine further includes: a first manifold around a first portion of the outside of a first face wound strip of the one or more face wound strips, a second manifold around a second portion of the outside of the first face wound strip, and an interior flow cavity inside the first face wound strip, wherein the electric machine is configured to cause fluid flowing into an inlet port of the first manifold to flow: through the first face wound strip into the interior flow cavity, and from the interior flow cavity through the first face wound strip into the second manifold.

In some embodiments, the electric machine includes a magnetic core including: a first core portion including the one or more face wound strips; and a second core portion, coaxial with and abutting against the first core portion.

In some embodiments, the one or more face wound strips are configured to provide a specific heat transfer of between 0.02 W/cm3/C and 1 W/cm3/C.

In some embodiments, the electric machine further includes: a first manifold extending around the outside of a first face wound strip of the one or more face wound strips, a second manifold extending around the outside of the first face wound strip, and wherein: the openings form a plurality of feed passages and a plurality of cooling passages, the first manifold and the second manifold are configured to cause fluid flowing into an inlet port of the first manifold to flow: inward through a first subset of the feed passages, through the cooling passages to a second subset of the feed passages, and from the second subset of the feed passages to an outlet of the second manifold.

According to an embodiment of the present disclosure, there is provided an electric machine fluid cooling jacket including: one or more face wound strips, a plurality of fluid channels, and a manifold; the one or more face wound strips including a first strip, the one or more face wound strips having a plurality of openings, the first strip having a plurality of turns, an opening of a turn of the first strip overlapping an opening of an adjacent turn, to form a portion of a fluid channel of the plurality of fluid channels, the turn and the adjacent turn abutting against each other at the overlapping openings, and the manifold having a manifold channel in fluid communication with the plurality of fluid channels.

