Stator for electric machine with multi-part conductor assembly

A winding assembly for a stator has a plurality of bridges each including an arcuate center section extending circumferentially over an end surface of a core at a first axial level relative thereto, first and second necks contiguous with respective first and second ends of the center section and extending therefrom axially away from the end surface, and first and second blocks contiguous with the respective necks and connected to the respective terminals of a pair of conductors at a second axial level farther from the end surface than the first axial level.

TECHNICAL FIELD

This disclosure relates to the field of electric machines. More particularly, it pertains to a stator having a winding that comprises two or more separately fabricated sub-assemblies.

BACKGROUND

Electric machines (motors, generators, etc.) are comprised of several fundamental components that are common to many different types of machines: one or more current carrying components (the conductors or winding); a magnetic path component (the core); and a magnetic field source (one or more coils or magnets). In typical motors, including those currently employed in most electric vehicles, the stator includes windings comprising a plurality of straight portions extending axially through the core (usually passing through slots defined by the core), and a plurality of portions outside of and at each axial end of the core, generally referred to as end-turns. The end-turns electrically connect the axially oriented conductors inside slots defined by the core thereby completing the electrical circuit and creating the desired/required number of electric phases. Although necessary for the correct functioning of the machine, the end-turn region contributes to electrical losses, weight, cost, and volume but not to torque. It is therefore desirable to reduce the length and electrical resistance of the end-turns.

It is conventionally known to manufacture the stator of an electric machine by inserting U-shaped “hairpin conductors” into axially-extending slots formed in the stator from a first axial end of the stator and subsequently inter-connecting the ends of the hairpins projecting from the opposite second axial end of the stator as necessary to achieve the desired circuit path. Each hairpin conductor is conventionally fabricated by bending a copper rod or bar with rectangular cross section. As a result, the shape and area of the conductor cross section remains the same throughout the machine. The end-turns must cross axially over one another at both ends of the stator, and this adds to the overall length of the windings. The end-turns may therefore comprise a significant portion of the total winding length that in short stack machines (defined as machines where the radius is much larger that the axial length) can reach 50% of the total copper content.

Configurations have been suggested that allow electrical machine components to be produced by additive manufacturing, also commonly known as three-dimensional (3D) printing.

SUMMARY

An electric machine includes a core defining a plurality of slots extending parallel to a longitudinal axis of the core, and a first winding assembly comprising a plurality of conductors each disposed in a different one of the slots. Ends of the conductors define terminals projecting axially beyond an end surface of the core. The electric machine also includes a second winding assembly comprising a plurality of bridges. Each bridge includes an arcuate center section extending circumferentially over the end surface at a first axial level relative thereto, first and second necks contiguous with respective first and second ends of the center section and extending therefrom axially away from the end surface, and first and second welding blocks contiguous with the respective necks and welded to the respective terminals of a pair of the conductors at a second axial level farther from the end surface than the first axial level.

A stator for an electric machine includes a winding assembly comprising a plurality of bridges each including an arcuate center section extending circumferentially over an end surface of a core at a first axial level relative thereto, first and second necks contiguous with respective first and second ends of the center section and extending therefrom axially away from the end surface, and first and second blocks contiguous with the respective necks and connected to the respective terminals of a pair of conductors at a second axial level farther from the end surface than the first axial level. The bridges are arranged in mutually radially-nested relationship to each other without overlapping one another.

A stator for an electric machine includes a core defining a plurality of slots extending parallel to a longitudinal axis of the core, and a plurality of U-shaped hairpins each including a first and a second conductor disposed in a respective one of the plurality of slots. First ends of the conductors define terminals projecting axially beyond a first end surface of the core, and second ends of the conductors adjacent a second axial end of the core being interconnected by end-turns with the conductors of others of the plurality of hairpins. The stator further includes a plurality of bridges, each including an arcuate center section extending circumferentially over the first end surface at a first axial level relative thereto, first and second necks contiguous with respective first and second ends of the center section and extending therefrom axially away from the first end surface, and first and second welding blocks contiguous with the respective necks and welded to the respective terminals of a pair of the conductors at a second axial level farther from the end surface than the first axial level.

DETAILED DESCRIPTION

As seen in the exploded view ofFIG.1, a stator10comprises a first winding assembly (FWA)20, a second winding assembly (SWA)30, and a core40. Longitudinal or central axis A indicates the axis of radial symmetry of stator10and is also the axis-of-rotation of a generally cylindrical rotor (not shown) that, in an assembled electric machine, is supported within the stator for rotation relative thereto

Stator core40is generally conventional in configuration and defines a plurality of axially extending slots42separated by teeth44. Core40is composed of a ferrous material such as iron or steel and may be fabricated as a unitary component or as a stack of thin layers.

FWA20comprises a plurality of U-conductors24(which may alternatively be referred to as “hairpins” by persons of skill in the art) each of which comprises two parallel uprights24a,24band an end-turn24cextending between, connecting, and formed integrally with the uprights. U-conductors24are arranged such that radially-adjacent pairs of end-turns24care in a radially-nested relationship with one another to form an annular disk or ring20alaying in the x-y plane indicated inFIG.1and uprights24a,24bextend parallel to central axis A and to the z-axis. The free ends of uprights24a,24bdistal from their respective end-turns24ccomprise terminals26as further described below.

To enable the radially-nested relationship of U-conductors24, end-turns24cand the portions of uprights24a,24bimmediately adjacent thereto may be configured as shown inFIG.2. A first end of end-turn24ais connected to a radially inner portion of first upright24asuch that the junction between the end-turn and the first upright is configured to define a radially outward-facing ledge27, and a second end of the end-turn is connected to a radially outer portion of the second upright24bsuch that the junction between the end-turn and the second upright is configured to define a radially inward-facing ledge28. Upright24ais relatively more radially inward in comparison to upright24b. Consequently end-turn24csteps radially outward as it extends clockwise, as viewed inFIG.2, about the central axis A of SWA30.

The nested relationship between radially-adjacent U-conductors is best seen inFIG.3, in which two representative U-conductors124,224are shown isolated from the rest of conductors making up FWA20. The two representative U-conductors shown may be any pair of radially-adjacent U-conductors which compose FWA20. As shown, the following relationships exist: 1) The end-turn of a radially outer U-conductor124lies in and passes over the outward-facing ledge227of a radially inner conductor224; and 2) The end-turn of the radially inner conductor224passes over and lies in the inward-facing ledge128of the radially outer conductor124. As this closely-nested relationship between each pair of radially-adjacent U-conductors124,224is repeated around the circumference and across the radius of ring20a, the requirement for end-turns of the U-conductor to cross axially over one another is avoided.

As compared with a conventionally-known stator in which the end-turns of conductors cross over (overlap) one another at the axial ends of the core, the disclosed radially-nested configuration allows for conductors to be shorter in total length and therefore use less material and produce less electrical resistance. Further, the disclosed stator (and hence the electrical machine overall) may be more axially compact than is known in the prior art.

As best seen ifFIG.4, the distal ends of uprights immediately adjacent to terminals26are configured to form outward-facing ledges127and inward-facing ledges128similar to the ledges27,28shown inFIGS.3and4. Ledges127,128allow elements of SWA30to mate with terminals26in an axially-nested fashion, as described further below.

U-conductors24are formed of material having a high electrical conductivity (such as copper) and are covered by a non-conductive coating so as to be electrically insulated from one another (and from core40when assembled therewith). Because the insulating coating is very thin relative to the size of the conductors it is not shown in the figures or identified by a reference number.

FWA20may advantageously be formed using an additive manufacturing process (also known as three-dimensional or 3D printing) wherein stratified layers of material are deposited in sequence on top of one another. Such a process may allow U-conductors24to be printed simultaneously with one another and in the nested relationship shown. The 3D printing process further allows the fabrication of end-turns that vary in cross-sectional shape and/or are over their respective lengths. A thin insulating layer (not shown) surrounding the U-conductors24may also be formed simultaneously by such a process.

SWA30(seeFIG.5) comprises a plurality of electrically conductive bridges32configured substantially similar to end-turns24cand arranged in a mutually nested relationship substantially similar to that of ring20a. When in the nested arrangement, bridges32are electrically insulated from one another, for example by thin dielectric coatings, as described above in relation to U-conductors24.

A representative one of the bridges32is shown inFIG.6to have opposite ends defining respective second terminals32a,32bthat are configured for mating electrical connection to respective first terminals26. In the embodiment ofFIG.6, second terminals32a,32bdefine generally rectangular openings34adapted to receive first terminals26therein.

SWA30may further comprise a casing36partially enclosing the ring formed by nested bridges32and holding the bridges together in a unitary, rigid disk. In the embodiment shown, casing36encloses the ring of nested bridges32on the circumferentially outer surface and on the radially inner surface thereof. Casing36is formed of an electrically non-conductive material such as epoxy and may be formed by an over-molding process after bridges32have been arranged in their ring-shaped, mutually nested relationship. Casing36may fill any gaps or spaces that may exist between adjacent bridges32.

As also shown inFIG.6, bridges32may vary in width along their circumferential lengths/spans. Specifically, the portions of the bridge that (when SWA30is assembled with FWA20and core40, as described below) pass over (directly axially above) the teeth44separating slots42are greater in radial width than the adjacent portions of the bridge passing over the slots. This length-wise variation of the radial widths of the bridges is also enabled by a 3D printing process. This width variation may also be present in end-turns24c.

Referring now toFIG.7, in a first stator assembly step, FWA20is inserted axially into core40such that ring20aformed by end-turns24cis closely adjacent to or contacting a first end surface of the core (the far end of the core, not visible inFIG.7) and uprights24a,24bare disposed in respective slots42. First terminals26at the distal ends of the uprights project axially beyond a second end surface40bof the core.

The uprights24a,24bof each U-conductor are disposed in respective slots separated by one or more intervening slots which are spanned by end-turns24c. The number of intervening slots spanned by an end-turn24cis dictated by several design features of the electrical machine (the number of electrical phases and the number of slots-per-pole, for example). In the depicted embodiment, a three-phase, three slots-per-pole stator is shown, wherein each end-turn24cspans two intervening slots. The disclosed design concepts may be applied to electric machines having configurations different from this embodiment.

In a second assembly step, SWA30is positioned in axial alignment with the combined FWA20and core30and moved relative to those components along axis A so that first terminals26a,26bof each U-connector are brought into engagement with their respective second terminals32a,32b(FIG.8). ComparingFIGS.5and7with one another, it is apparent that this engagement is enabled by the number and locations of first terminals26corresponding to the number and locations of openings34defined by each of bridges32. At the conclusion of the second assembly step, bridges32are closely adjacent to or contacting (but, due to their dielectric coatings, electrically insulated from) core40.

In an alternative embodiment of a second assembly step, the bridges32may be placed in engagement with their respective first terminal26a,26bindividually or in a plurality of groups, rather than first being formed into a unitary SWA as described above. In this care, each group may comprise any number of bridges less than the total number included in SWA30. In this embodiment, the casing may be dispensed with completely or the casing may be over-molded onto the ring-shaped array of bridges after it is assembled to the FWA. In another alternative, groups of any number of bridges32may be enclosed by insulating casings to form multiple sub-units that are then assembled to the FWA.

First terminals26a,26band second terminals32a,32bmay take a variety of complementary shapes designed to minimize electrical resistance to current passing through the junction therebetween. In a first exemplary embodiment shown inFIGS.9A-B, a first terminal26comprises a generally rectangular tenon and a second terminal32adefines a mortise34configured to matingly receive the tenon to thereby form a mortise-and-tenon joint. In a second exemplary embodiment shown inFIGS.9C-D, a first terminal626defines a groove626aand a second terminal632acomprises a V-shaped tongue634which fits into the groove to thereby form a tongue-and-groove joint635. In a third exemplary embodiment shown inFIGS.9E-F, a first terminal comprises a generally rectangular peg726and a second terminal732acomprises a butt end734. Butt end734presses against a generally flat surface of peg726to thereby form a butt-type joint735.

The second assembly step may further include heating of the junctions between the mating first and second terminals, for example by laser welding, to improve the quality, durability, and reliability of the electrical connection.

As will be apparent to persons of skill in the art, additional components and/or connections (terminals, neutral connections, jumpers, etc.) needed to complete the electrical circuits formed by the windings disclosed herein may be incorporated at either axial end of the core.

FIGS.10-17show components of a second embodiment of a stator having three-phases and six slots-per-pole (two slots-per-pole for each phase). In this design the number of end-turns and bridges that must span the intervening slots is twice that of the three slots-per-pole design in the first embodiment described above. To achieve this, the end-turns of the U-conductors at a first end of the core and the corresponding bridges at the second end of the core are arranged in two layers: an inner layer immediately adjacent to the end surfaces of the core (substantially similar to the previously described end-turns and bridges) and an outer layer spanning over and passing axially above the inner layer.

FIG.10shows a stator core240along with portions of an inner U-conductor424and an outer U-conductor524(both of which belong to a common electrical phase of the electrical machine) that are components of a dual-layer first winding assembly (DL-FWA)220. The depicted inner/outer pair of U-conductors424,524depicted is representative of any such pair comprising DL-FWA220, and the rest of the component U-conductors are not shown inFIG.10for clarity.

Inner U-conductor424comprises uprights424a,424b(shown disposed in respective slot242defined by core240) and inner end-turn424cconnecting the uprights. Inner U-conductors424are substantially identical to U-conductors24making up FWA20of the first disclosed embodiment, except that end-turns424cspan four intervening slots242between the uprights424a,424b.

Outer U-conductor524comprises uprights524a,524bconnected by outer end-turn524c. As depicted inFIG.10, uprights424band524bare positioned more radially inboard than uprights424a,524aand therefore both inner and outer end-turns424c,524cstep radially outward as then extend in a generally counterclockwise circumferential direction over end surface240a. Outer end-turn524cspans six intervening slots (two of which are occupied by inner uprights424a-b) and extends immediately axially above and parallel with inner end-turn424c. Outer uprights524a-bare disposed in slots immediately adjacent to and circumferentially outboard (relative to inner end-turn424c) of the slots containing inboard uprights424a-b. The junctions between outer uprights524a-band the respective opposite ends of outer end-turn524cform inward-facing and outward-facing ledges528,527disposed even with (located at the same axial position as) the corresponding inner end-turn ledges428,427. This configuration allows a mutual nesting of radially-adjacent end-turns, substantially identical to that described in relation to the single-layer end-turns of the previous embodiment. In this dual-layer embodiment, the end-turns of the inner layer nest radially against one another, and the end-turns of the outer layer nest radially against one another directly above those of the inner layer. DL-FWA220may advantageously be fabricated by a 3D printing process, as described above.

FIGS.1I and12show DL-FWA220fully inserted into core240after a first assembly step. It should be noted that the end surface240bvisible inFIG.10is the axially opposite end from end surface240ashown inFIG.11. The distal ends of outer U-conductor uprights524a-b(distal from end-turns524c) comprise terminals526that project a relatively short distance beyond (above, in the depicted orientation) core end surface240b. The distal ends of inner uprights424a,424b(distal from end-turns424c) comprise terminals426that project a relatively longer (compared with the projection distance of terminals526) distance beyond core end surface240b. In this six slots-per-pole embodiment, each slot242contains two inner U-conductor uprights424a,424bterminating in terminals426, and further contains two outer U-conductor uprights524a,524bterminating in terminals526.

A dual-layer second winding assembly (DL-SWA)430(FIG.13) comprises a plurality of electrically conductive inner bridges432configured substantially similar to inner end-turns424c(and to bridges32of the single layer FWA previously described) and arranged in a mutually nested relationship substantially similar to that of the ring20aof the first disclosed embodiment. Inner bridges432are electrically insulated from one another when in the mutually nested arrangement, for example by thin dielectric coatings, as described above in relation to U-conductors24.

Opposite ends of inner bridges432comprise respective second terminals432a,432bthat are configured for mating electrical connection with respective terminals526of the outer U-connectors. In the embodiment ofFIG.13, second terminals432a,432bdefine generally rectangular mortises434adapted to receive terminals526therein, similar to the configuration shown inFIGS.9A-B.

DL-SWA430may further comprise a casing436partially enclosing the ring-shaped army of nested inner bridges432. In the embodiment shown, casing436encloses the ring of bridges432on the circumferentially outer surface and on the radially inner surface thereof. As in the first embodiment disclosed herein, casing436is formed of an electrically non-conductive material such as epoxy and may be formed by an over-molding process after inner bridges432have been arranged in their ring-shaped, mutually nested relationship.

A plurality of holes or pass-throughs438are defined in casing436, the pass-throughs being located in radial alignment with mortices434. Pass-throughs438are thus positioned to allow terminals426at the distal ends of inner U-conductor uprights424a,424bto extend therethrough when, in a second assembly step (seeFIG.14), DL-SWA430is placed onto core240such that outer conductor first terminals326are placed into engagement with respective inner bridge second terminals432a,432b.

A third dual-layer winding assembly (DL-TWA)530(FIG.15) comprises a plurality of electrically conductive outer bridges532configured substantially similar to outer end-turns524c(and, aside from spanning a greater number of intervening slots, to inner bridges432) and arranged in a mutually nested relationship substantially similar to that of DL-SWA430. Outer bridges532are electrically insulated from one another when arrayed as shown inFIG.15, for example by thin dielectric coatings, as described above.

Opposite ends of outer bridges532comprise respective second terminals532a,532bconfigured for mating physical and electrical connection with respective first terminals426of the inner U-connectors. In the embodiment ofFIG.15, second terminals532a,532bdefine generally rectangular mortises534adapted to receive terminals426therein.

DL-TWA530may further comprise a casing536partially enclosing the ring formed by the nested outer bridges532. In the embodiment shown, casing536encloses the ring of nested bridges532on the circumferentially outer surface and on the radially inner surface thereof. Similar to the first embodiment disclosed herein, casing536is formed of an electrically non-conductive material such as epoxy and may be formed by an over-molding process after outer bridges532have been arranged in their ring-shaped, mutually nested relationship.

In a third assembly step, DL-TWA530is placed in axial alignment with the core/DL-FWA/DL-SWA combination ofFIG.14and moved relative thereto along axis A so that terminals532a,532bat opposite ends of outer bridges532are placed in engagement with respective inner U-connector terminals426(FIG.16). As best shown inFIG.17, only the tips of inner U-connector terminals426are visible when engaged with their respective bridge terminals532a,532b. Inner and outer casings436,536are thus in an axially stacked relationship with one another and the circuits formed by the stator windings are completed.

FIGS.18and19show a core840that defines a plurality of slots842extending parallel to a longitudinal axis of the core840, and a plurality of conductors824each disposed in a different one of the slots842. Ends of the conductors842define terminals826that project axially beyond an end surface827of the core840. Some are longer than others.

FIGS.18and19also show a plurality bridges832,833. Each of the bridges832has an arcuate center section860that extends circumferentially over the end surface at a first axial level relative thereto, first and second necks862contiguous with respective first and second ends of the center section860and extending therefrom axially away from the end surface827, and first and second welding blocks864contiguous with the respective necks862and welded to the respective terminals826of a pair of the conductors824at a second axial level farther from the end surface than the first axial level. Each of the bridges833, which is axially over the bridges832, has an arcuate center section866that extends circumferentially over the end surface827at a third axial level relative to the end surface827, first and second necks868contiguous with respective first and second ends of the center section866and extending therefrom axially away from the end surface827, and first and second welding blocks870contiguous with the respective necks868and welded to the respective terminals826of a pair of the conductors824at a fourth axial level farther from the end surface827than the third axial level.

The bridges832are disposed in a ring, and the bridges833are disposed in a ring. Each of the rings has an electrically non-conductive casing836enclosing the ring on a circumferentially outer surface thereof and on a radially inner surface thereof.

FIG.20shows an alternative welding block configuration. Welding block970extends from neck968and contacts only two sides of terminal926.FIG.21likewise shows welding block1070extending from neck1068and contacting one side of terminal1026. Other arrangements are also contemplated.