Electric machine with asymmetric hairpin crown

An electric machine is disclosed that includes a rotor, a stator and a plurality of pins. The stator is received inside the rotor and defines a plurality of slots for receiving the pins. The pins are conductors that are each joined with a circumferentially adjacent pins to form a conductive path for each power phase. The pins each have a first axial leg and a second axial leg that are each disposed in one of the plurality of slots. The first and second axial legs are joined by an asymmetric crown portion of the pin conductors. The crown portion includes a long arm and a short arm that are joined at an apex that is radially and circumferentially offset to be closer to the second leg than the first leg.

TECHNICAL FIELD

This disclosure relates to conductors for electric machines that provide propulsion for electric vehicles.

BACKGROUND

Electric vehicles, for example hybrid vehicles, partial hybrid vehicles, plug-in vehicles and the like, may have an electric machine for propelling the vehicle and for storing energy from regenerative braking. The electric machine receives power from a high voltage traction battery that provides direct current (DC) to a variable voltage inverter that supplies multi-phase alternating current (AC) to the electric machine.

Electric machines are known that use shaped wire pins, also known as “hairpins” (hereinafter “pins”) in place of windings on the stator of the electric machine. Pins are thin wire-like members that are received in receptacles, or axially extending slots, on the stator that are arranged in a nested circumferential array on the stator core. The pins have spaced legs that are welded together to create a conductor path. One path may be is provided for each phase of the alternating current. Two parallel conductor paths may be provided to increase the efficiency of the electric machine. The pins form a crown at one axial end of the stator. The crown end protrudes several millimeters out of the stator core.

Pin geometry is created by bending a metal rod or pin in a precise pattern to create separate conductor paths. The pins are coated with enamel that insulates the pin from adjacent pins that are not in the same conductor path.

The pins are inserted into axially extending slots in the stator core that are adapted to receive a plurality of pins (e.g. six or eight pins per slot). The pins are stacked in the slots from an inner diameter of the slot to the outer diameter of the slot and may be assigned numeric location identifiers (e.g. L1being at the ID of each slot and L8being at the OD of each slot with the intervening locations being identified as L2to L7). The number of pins received in the slots may be a number other than eight.

In the locations in the slots adjacent to the ID and OD (e.g. L1and L8in an eight location slot) the pins are inserted in the slots at locations at the same radius from the central axis of the stator core. (L1to L1and L8to L8). Symmetrical pins are normally bent to form an apex at the center of the crown that is formed by two equal arms that meet at the apex. Symmetrical pins that are inserted different ranks (e.g. L2to L3; L4to L5; L6to L7) require only one sharp bend to avoid interference with adjacent pins because they do not return to the same radius ring. In a multi-phase electric machine, the pins from the other phases must be circumvented that are in intervening slots. Circumventing the intervening pins with a symmetrical pin in locations L1and L8necessitates sharply bending the pin adjacent one end of an arm of the pin that extends from a leg received in one of the slots to the apex. Symmetrical pins in L1and L8require sharper bends in the area of the crown to avoid interference with intervening pins. Bend sharpness is typically more severe compared to the intermediate pins (e.g. pins inserted between L2to L3, L4to L5) The sharper bends may create stress fractures in the enamel that may reduce the effectiveness of the enamel.

One previously proposed approach to reducing the need for a sharp bend is to increase the height of the crown in the locations adjacent the ID and OD of the stator core where the pins are inserted in the same radius slot locations. However, increasing the height of the crown suffers from the disadvantage of increasing the space requirements for the electric machine.

This disclosure is directed to solving the above problems and other problems as summarized below.

SUMMARY

According to one aspect of this disclosure, a pin conductor is disclosed for a stator of an electric machine. The pin conductor, or pin, comprises a wire segment having first and second connector portions, first and second axial legs, and a crown portion, wherein the crown portion has an apex, formed at the intersection of a short arm that extends from the apex to the first axial leg and a long arm that extends from the apex to the second axial leg.

According to another aspect of this disclosure, a stator is disclosed for an electric machine of an electric vehicle. The stator comprises a stator core defining a plurality of slots that are arrayed circumferentially around a central axis of the stator. A plurality of pins are joined together with adjacent pins in conductive paths for each AC power phase, wherein the pins have a first axial leg and a second axial leg that are received in two of the slots, wherein each of the first and second legs are joined together by a crown portion, the crown portion including a long arm and a short arm that are joined together at an apex that is radially and circumferentially offset to be closer to the second leg than the first leg.

According to yet another aspect of this disclosure, an electric machine having a plurality of AC power phases is disclosed that includes a rotor, a stator and a plurality of pins. The stator defines a plurality of slots that receive the pins. The pins are conductors that are each joined with a circumferentially adjacent pin conductor to form a conductive path for each power phase. The pin conductors each have a first axial leg and a second axial leg that are each disposed in one of the plurality of slots. The first and second axial legs are joined by a crown portion of the pin conductors. The crown portion includes a long arm and a short arm that are joined at an apex that is radially and circumferentially offset to be closer to the second leg than the first leg.

The above aspects of this disclosure and other aspects will be described below with reference to the attached drawings.

DETAILED DESCRIPTION

Various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more of the other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure could be used in particular applications or implementations.

FIG.1is a schematic diagram illustrating an example of an electric machine for an electric vehicle. The electric machine10is diagrammatically illustrated that may be used in a vehicle10such as a fully electric vehicle or a hybrid-electric vehicle. The electric machine10may be referred to as an electric motor, a traction motor, a generator, or the like. The electric machine10may be a permanent magnet machine, an induction machine, a synchronous machine, or the like. The electric machine10acts as both a motor to propel the vehicle and as a generator during regenerative braking.

The electric machine10may be powered by the traction battery (not shown) of the vehicle (not shown). The traction battery provides high-voltage direct current (DC) from one or more battery-cell arrays, sometimes referred to as battery-cell stacks, within the traction battery. The battery-cell arrays may include one or more battery cells that convert stored chemical energy to electrical energy. The cells may include a housing, a positive electrode (cathode), and a negative electrode (anode). An electrolyte allows ions to move between the anode and cathode during discharge, and then return during recharge. Terminals allow current to flow out of the cells for use by the vehicle.

The traction battery may be electrically connected to one or more power electronics modules. The power electronics modules may be electrically connected to the electric machine10and may provide the ability to bi-directionally transfer electrical energy between the traction battery and the electric machine10. For example, a typical traction battery provides DC voltage while the electric machine10may require a multi-phase alternating current (AC) voltage. The power electronics module may include an inverter that converts the DC voltage to a multi-phase AC voltage as required by the electric machine10. In a regenerative mode, the power electronics module may convert the multi-phase AC voltage from the electric machine10acting as a generator to the DC voltage required by the traction battery.

Referring toFIGS.1and2, the electric machine12includes a housing12that encloses a stator14and a rotor16. The stator14is fixed to the housing12and includes a cylindrical stator core18having an inner diameter20that defines a hole22in which the rotor16is received and an outer diameter23. The rotor16may include windings or permanent magnets that interact with conductor of the stator14to rotate the rotor16when the electric machine12is energized by the traction battery. The rotor16is supported on a driveshaft24that extends through the housing12. The driveshaft24is configured to be coupled with a drivetrain of the vehicle.

The stator core18defines slots26(shown inFIGS.10and11) circumferentially arranged around the core18that extend radially outward from the inner diameter20. The slots26are equally spaced around the circumference of the stator core and extend axially from a first end28, or crown end, of the core18to a second end30, or connection end. In the illustrated embodiment, the core18defines thirty-six slots and has three poles (one for each phase), but the core18may include more or fewer slots and/or poles in other embodiments. For example, the core18may define forty-eight slots and have four poles.

The electric machine10includes pin conductors32, or hairpins, assembled into the slots26of the core18. Pin conductors32improve efficiency by providing a greater number of stator conductors that reduces the resistance of the conductor32without encroaching into the space required for the electrical steel and the magnetic flux path. The pin conductors32are wave conductors that weave pole to pole in a wave-like pattern.

For example, while the possible number of poles, slots per pole, and layers may vary, it is not practical in a pin conductor to have as many turns per coil as in a stranded winding. Each pin needs to be connected at the connection end30to the next pin by welding, soldering or the like, and needs to be bent according to a specific shape in order to make the connection possible. Another challenge is creating parallel circuits that are balanced (i.e., not causing large circulating currents in the loop formed by the parallel circuits due do dissymmetry) and have robust connections.

The electric machine12may be a three-phase machine in which the pin conductors32are arranged to have a U phase, a V phase, and a W phase. In one embodiment, each phase includes associated pins conductors32(also known as pins, pins, or bar conductors) arranged in a parallel path including two parallel conductive paths. In a three-phase system three of the parallel conductive paths are provided, one for each of the three phases. A set of three terminals33are shown inFIG.2with each of the three parallel conduction paths being connected to one of the terminals33. A neutral terminal35is connected to all of the parallel conduction paths.

Referring toFIG.3, a seven-pitch pin conductor32afor the outer diameter (OD) ring of the stator14is shown that includes a crown end portion34athat has a maximum height (the height is measured from the crown end of the stator core) at a non-symmetrical peak36a. The conductor32aincludes first and second axial legs38aand40athat extend linearly through the stator from the crown end28to the connection end30. First and second connection segments42aand44aare provided at the connection end30and are configured to be welded to other pin conductors32arranged in a parallel conduction path (seeFIG.10). The conduction path extends from a terminal provided either on the ID or on the OD of the stator14to a neutral terminal provided either on the ID or on the OD of the stator14.

The crown end portion34aextends from the first axial leg38ato the second axial leg40a. A non-symmetrical peak36aof the crown end portion34ais offset to be spaced from the first axial leg38ato a greater extent than the non-symmetrical peak36ais spaced from the second axial leg40. By offsetting the non-symmetrical peak36a, the crown end portion34ais reduced in height. The non-symmetrical peak36ais formed at the intersection of a short arm37athat extends from the non-symmetrical peak36ato the first axial leg and a long arm39athat extends from the non-symmetrical peak36ato the second axial leg39a.

Referring toFIG.4, a five-pitch pin conductor32bfor the outer diameter (OD) ring of the stator14is shown that includes a crown end portion34bthat has a maximum height at a non-symmetrical peak36b. The conductor32bincludes first and second axial legs38band40bthat extend linearly through the stator from the crown end28bto the connection end30b. First and second weld segments42band44bare provided at the connection end30band are configured to be welded to other pin conductors32barranged in a conduction path (seeFIG.10) that extends from a terminal provided either on the ID or on the OD of the stator14to a neutral terminal provided either on the ID or on the OD of the stator14.

The crown end portion34bextends from the first axial leg38bto the second axial leg40b. The non-symmetrical peak36bof the crown end portion34bis offset to be spaced from the first axial leg38bto a greater extent than the non-symmetrical peak36bis spaced from the second axial leg40. By offsetting the non-symmetrical peak36b, the height of the crown end portion34bis reduced in height. The non-symmetrical peak36bis formed at the intersection of a short arm37bthat extends from the non-symmetrical peak36bto the first axial leg and a long arm39bthat extends from the non-symmetrical peak36bto the second axial leg39b.

Referring toFIG.5, a seven-pitch pin conductor32cfor the ID ring of the stator14is shown that includes a crown end portion34cthat has a maximum height at a non-symmetrical peak36c. The conductor32cincludes first and second axial legs38cand40cthat extend linearly through the stator14from the crown end28cto the connection end30c. First and second weld segments42cand44care provided at the connection end30cand are configured to be welded to other pin conductors32carranged in a conduction path (seeFIG.10) that extends from a terminal provided either on the ID or on the OD of the stator14to a neutral terminal provided either on the ID or on the OD of the stator14.

The crown end portion34cextends from the first axial leg38cto the second axial leg40cc. The non-symmetrical peak36cof the crown end portion34cis offset to be spaced from the first axial leg38cto a greater extent than the non-symmetrical peak36cis spaced from the second axial leg40. By offsetting the non-symmetrical peak36c, the height of the crown end portion34cis reduced in height. The non-symmetrical peak36cis formed at the intersection of a short arm37cthat extends from the non-symmetrical peak36cto the first axial leg and a long arm39cthat extends from the non-symmetrical peak36cto the second axial leg39c.

Referring toFIG.6, a five-pitch pin conductor32dfor the ID ring of the stator14is shown that includes a crown end portion34dthat has a maximum height at a non-symmetrical peak36d. The conductor32dincludes first and second axial legs38dand40dthat extend linearly through the stator14from the crown end28to the connection end30. First and second weld segments42dand44dare provided at the connection end30and are configured to be welded to other pin conductors32arranged in a conduction path (seeFIG.10) that extends from a terminal provided either on the ID or on the OD of the stator14to a neutral terminal provided either on the ID or on the OD of the stator14.

The crown end portion34dextends from the first axial leg38dto the second axial leg40d. The non-symmetrical peak36dof the crown end portion34dis offset to be spaced from the first axial leg38dto a greater extent than the non-symmetrical peak36dis spaced from the second axial leg40. By offsetting the non-symmetrical peak36d, the height of the crown end portion34dis reduced in height. The non-symmetrical peak36dis formed at the intersection of a short arm37dthat extends from the non-symmetrical peak36dto the first axial leg and a long arm39dthat extends from the non-symmetrical peak36dto the second axial leg39d.

FIGS.7-9illustrate conventional symmetrical middle pins46for the middle layers of the stator14that are inserted in other rings at different radial distances from the central axis of the stator (L1to L2or L5to L6). The middle pins46do not face the same problem as the pins connected in the rings adjacent the ID and OD wherein both legs are inserted in the same ring because they don't interfere with the adjacent pins. The middle pin46shown inFIG.7is a six-pitch conductor that is inserted in two slots that are spaced apart by six slots. The middle pin may have a centered symmetrical peak48. The middle pin50shown inFIG.8is a five-pitch conductor that may have a centered symmetrical peak52. The middle pin54shown inFIG.9is a five-pitch conductor that has a centered symmetrical peak56.

FIGS.10and11illustrate in cross section the structure of the stator14with slots46that receive the first and second axial legs38and40. The slots46are arranged 1 through 36 in the counterclockwise direction with only the odd number slots being labeled for convenience. The slots46may include an inner radial layer58of pins, a middle radial layer60of pins, and an outer radial layer62of pins. Each of the layers includes at least two radial positions that are adjacent to each other. In the illustrated embodiment, each slot46has six positions with the inner layer58including an inner position58aand an outer position58b; the middle layer60including an inner position60aand an outer position60b; and the outer layer62including an inner position62aand outer position62b. The positions extend radially outward with the inner position58abeing adjacent to the inner diameter20of the stator core18and the outer position62bof the outer layer62being nearest to an outer diameter23of the core18. The positions are sequential and in a one-by-six linear arrangement.

Referring toFIG.12, a sample wiring diagram is provided for a single phase of the electric machine10. The diagram identifies the levels of the slots46from L1to L8with L1being the location closest to the ID and L8being the location closest to the OD. The slots46are numbered from 1 to 48 and are arranged circumferentially around the stator14. The pin conductors shown inFIGS.3and4are inserted into the location L8and the pin conductors shown inFIGS.5and6are inserted into the location L1. The middle pin conductors shown inFIGS.7-9are inserted in the locations L2to L7and are inserted in adjacent radial layers (between L2and L3; L4and L5; etc.).

The pin conductors inFIGS.3and4are inserted in the L1to reduce the height of the crown end. The pin conductors inFIGS.5and6are inserted in the L8to also reduce the height of the crown end. The middle pin conductors46,50, and54shown inFIGS.7-9are used to jump between layers.

One portion of a conduction path is described beginning with a seven-pitch conductor at L1slot32-39. One of the middle pins jumps from L1slot38to L2slot32. Another middle pin jumps from L1slot39to L2slot33. Insertion of the middle pins54continues linking the middle pins in rows L1to L8with one leg of the middle pins in L1or L8and asymmetric pins with both legs in either rows L1or L8.

Referring toFIG.13, several five pitch pins32band seven pitch pins32aare shown with an area66being indicated by brackets to show where reduced bending is required compared to symmetric pins shown inFIGS.7-9.

The embodiments described above are specific examples that do not describe all possible forms of the disclosure. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts. The words used in the specification are words of description rather than limitation. The scope of the following claims is broader than the specifically disclosed embodiments and also includes modifications of the illustrated embodiments.