CN114830497A

CN114830497A - Stator assembly for an electric motor

Info

Publication number: CN114830497A
Application number: CN202080087180.5A
Authority: CN
Inventors: 陈宇; A.贝斯里; D.史密斯
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2019-10-18
Filing date: 2020-09-10
Publication date: 2022-07-29
Also published as: WO2021074563A1; GB2588388A; GB201915072D0; GB2588388B

Abstract

A stator assembly (10) for an electric motor (100) has a stator body (12), a plurality of slots (14) formed in the stator body (12), and a phase winding having a plurality of hairpin windings (24) electrically connected together. The phase winding has a first phase winding leg (50) and a second phase winding leg (52). The plurality of slots (14) form at least one slot pair (19) around the stator body (12). Each slot (14) of the slot pair (19) includes N radial slot locations (16, 18, 20, 22). N is an even number. Each radial slot location (16, 18, 20, 22) has an arm of a hairpin winding (24) located therein. The first phase winding leg (50) and the second phase winding leg (52) each include an equal number of hairpin arms distributed between the first slot (15) and the second slot (17) of the slot pair (19). Each hairpin arm of a first phase winding branch (50) in the first slot (15) is in a radial position corresponding to the hairpin arm of a second phase winding branch (52) in the second slot (17). The first phase winding leg (50) and the second phase winding leg (52) are electrically connected in parallel.

Description

Stator assembly for an electric motor

Technical Field

The present invention relates to a stator assembly for an electric motor, an electric motor comprising such a stator assembly, and an electric vehicle comprising such an electric motor.

Background

Electric motors having stator assemblies utilizing hairpin windings are known to provide benefits including increased slot fill factor. However, it has been found that conventional electric motors using hairpin windings suffer from a number of problems including, but not limited to, large back EMF values generated in use, increased AC losses, and unbalanced back EMF, resistive and inductive paths, all of which result in increased copper losses due to circulating currents.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a stator assembly for an electric motor, the stator assembly comprising a stator body, a plurality of slots formed in the stator body, and a phase winding comprising a plurality of hairpin windings electrically connected together, the phase winding comprising a first phase winding limb and a second phase winding limb, wherein the plurality of slots form at least one slot pair around the stator body, each slot of the slot pair comprising N radial slot locations, N being an even number, and each radial slot location having an arm of a hairpin winding located therein, wherein the first and second phase winding legs each comprise an equal number of hairpin arms distributed between the first and second slots of the slot pair, each hairpin arm of the first phase winding leg in the first slot being in a radial position corresponding to the hairpin arm of the second phase winding leg in the second slot, and the first and second phase winding legs are electrically connected in parallel.

The stator assembly according to the first aspect of the invention may be primarily advantageous in that the first and second phase winding legs each comprise an equal number of hairpin arms distributed between the first and second slots of the slot pair, each hairpin arm of the first phase winding leg in the first slot being in a radial position corresponding to the hairpin arm of the second phase winding leg in the second slot, and the first and second phase winding legs being electrically connected in parallel.

In particular, by splitting the phase winding into first and second phase winding branches electrically connected in parallel, the level of induced voltage in the phase winding is reduced due to back EMF and armature reactance, so that operation is compatible with the available supply voltage. However, in the case where an unequal number of hairpin arms are arranged in a slot pair of each parallel branch, for example where the first parallel branch comprises more or fewer hairpin arms than the second parallel branch in a slot pair, there may be a phase and/or amplitude difference in the induced operating voltage between the first and second parallel branches.

By including an equal number of hairpin arms for each parallel leg in the slot pair, the phase and/or amplitude differences in back EMF and armature reaction generated by current flowing in the parallel paths in the first and second slots may be reduced or eliminated.

However, in arrangements in which the first phase winding leg includes arms of hairpin windings located only in the first subset of radial slot locations and the second phase winding leg includes arms of hairpin windings located only in the second subset of radial slot locations, there may be uneven current flow through the first and second phase winding legs. In particular, radial slot locations located closer to the motor rotor in use may have additional induced voltages caused by additional leakage flux. This may result in unbalanced resistance and inductance, for example in arrangements where the first phase winding leg includes only arms at certain, e.g., inner, radial slot locations and the second phase winding leg includes only arms at certain other, e.g., outer, radial slot locations. This may result in additional circulating currents or AC losses due to current imbalance in each path.

By having an arrangement in which each hairpin arm of a first phase winding leg in a first slot is at a corresponding radial position to the hairpin arm of a second phase winding leg in a second slot (i.e. by including an equal number of hairpin arms in the first and second phase winding legs distributed between the corresponding radial slot positions of the first and second slots), the first and second phase winding legs may have a more balanced resistance and inductance and thus may reduce circulating currents and AC losses.

Reducing circulating currents and AC losses in the windings for a given input current may improve motor efficiency and/or thermal performance.

The first and second slots of the slot pair may be circumferentially spaced from each other around the stator body, for example with at least one further slot between the first and second slots. The first and second slots may be spaced apart at a slot pitch around the stator body.

The phase windings may be located in a plurality of slots disposed around the stator body. For example, a phase winding may be located in a first channel of adjacent slots and a second channel of adjacent slots, with a plurality of intermediate slots located between the first and second channels. Each channel may include a plurality of adjacent slots. The stator assembly may include a plurality of slot pairs. Each channel may include at least one slot of a pair of slots as previously described. For example, the first channel may include a plurality of first slots of a plurality of slot pairs and the second channel may include a plurality of second slots of the plurality of slot pairs.

Each slot may include an equal number of hairpin arms distributed between the first and second phase winding legs. For example, each slot may include N hairpin arms in a first phase winding leg and N hairpin arms in a second phase winding leg.

Each channel may include an equal number of hairpin arms distributed between respective radial slot positions of the slots within the channel. For example, each slot may include N hairpin arms of a first phase winding leg distributed over each of N radial slot positions, and each slot may include N hairpin arms of a second phase winding leg distributed over each of N radial slot positions. This may provide a uniform current distribution within each slot in use.

The hairpin arms of the first phase winding leg may be disposed within a first subset of radial slot positions within the first slot, and the hairpin arms of the second phase winding leg may be disposed within a second subset of radial slot positions within the second slot, the radial slot positions of the first subset corresponding to the radial slot positions of the second subset. For example, in the case where the winding hairpin arm of the first phase winding leg is located at the first radial slot position of the first slot, the winding hairpin arm of the second phase winding leg may be located at the first radial slot position of the second slot.

The hairpin arms of the first phase winding leg may be disposed in a first pattern within the first slot, the hairpin arms of the first phase winding leg may be disposed in a second pattern within the second slot, and the second pattern may be opposite the first pattern.

The plurality of hairpin windings may include a first set of hairpin windings having a first cross-sectional area and a second set of hairpin windings having a second cross-sectional area, wherein the first cross-sectional area is greater than the second cross-sectional area. The first set of hairpin windings may be located radially outward of the second set of hairpin windings. This may be beneficial because locating arms of smaller cross-sectional area at the radially inner slot locations may reduce the AC losses induced in those hairpin arms that are caused by slot leakage flux that is more concentrated at the radially inner slot locations. The hairpin arm with the smaller cross-sectional area is connected with a smaller magnetic flux ratio and less induced AC loss. The consequent splitting of these smaller cross-sectional area arms can be used to reduce or eliminate the possibility of circulating currents and losses within the phase path.

The first slot of the slot pair may include N/2 hairpin arms of the first phase winding leg and N/2 hairpin arms of the second phase winding leg. The second slot of the slot pair may include N/2 hairpin arms of the first phase winding leg and N/2 hairpin arms of the second phase winding leg.

The hairpin arms at odd-numbered radial slot positions of the first slot may be electrically connected in series with the hairpin arms at even-numbered radial slot positions of the second slot of the pair of slots to form a first phase winding leg, and the hairpin arms at even-numbered radial slot positions of the first slot may be electrically connected in series with the hairpin arms at odd-numbered radial slot positions of the second slot to form a second phase winding leg.

According to a second aspect of the invention, there is provided an electric motor comprising a stator according to the first aspect of the invention.

According to a third aspect of the invention, there is provided an electric vehicle comprising an electric motor according to the second aspect of the invention.

According to a fourth aspect of the present invention, there is provided a stator assembly for an electric motor, the stator assembly comprising a stator body, a plurality of slots formed in the stator body, and a phase winding comprising a plurality of hairpin windings electrically connected together, the phase winding comprising a first phase winding leg and a second phase winding leg, wherein the plurality of slots form at least one slot pair around the stator body, each slot of the slot pair comprising N radial slot positions, N being an even number, and wherein arms of a hairpin winding located in an odd number of radial slot positions of a first slot of the slot pair are electrically connected in series with arms of a hairpin winding located in an even number of radial slot positions of a second slot of the slot pair to form first phase winding legs, arms of a hairpin winding located in an even number of radial slot positions of the first slot being electrically connected in series with arms of a hairpin winding located in an odd number of radial slot positions of the second slot, to form a second phase winding branch, and the first and second phase winding branches are electrically connected in parallel.

The stator assembly according to the first aspect of the invention may be primarily advantageous in that the arms of the hairpin windings located at odd-numbered radial slot positions of a first slot of a slot pair are electrically connected in series with the arms of the hairpin windings located at even-numbered radial slot positions of a second slot of the slot pair to form a first phase winding leg, the arms of the hairpin windings located at even-numbered radial slot positions of the first slot are electrically connected in series with the arms of the hairpin windings located at odd-numbered radial slot positions of the second slot to form a second phase winding leg, and the first and second phase winding legs are electrically connected in parallel.

In particular, by splitting the phase winding into first and second phase winding branches electrically connected in parallel, the level of induced voltage in the phase winding is reduced due to back EMF and armature reactance, so that operation is compatible with the available supply voltage. However, in the case where the first phase winding leg includes all of the arms disposed in the first slot of the slot pair and the second phase winding leg includes all of the arms disposed in the second slot of the slot pair, there may be a phase difference in the induced operating voltages between the first and second slots.

By including arms of the hairpin windings in the first and second slots of each phase winding leg, the phase difference of the induced operating voltage between the first and second slots may be reduced or eliminated. However, in arrangements in which the first phase winding leg includes arms of hairpin windings in a first subset of radial slot locations and the second phase winding leg includes arms of hairpin windings in a second subset of radial slot locations, there may be uneven current flow through the first and second phase winding legs. In particular, radial slot locations located closer to the motor rotor in use may have additional induced voltages caused by additional leakage flux. This may result in unbalanced resistance and inductance, for example in arrangements where the first phase winding leg includes only arms at certain, e.g., inner, radial slot locations and the second phase winding leg includes only arms at certain other, e.g., outer, radial slot locations. This may result in additional circulating currents or AC losses due to current imbalance in each path.

By including arms of hairpin windings disposed at odd and even radial slot locations in the first and second phase winding legs, the first and second phase winding legs may have more balanced back EMF, resistance and inductance, and thus may reduce circulating copper losses.

Each of the first and second phase winding legs may include a hairpin winding having arms located at N/2 radial slot locations of the first slot and N/2 radial slot locations of the second slot. Each of the first and second phase winding legs may include a hairpin winding having an arm located at each of the N radial slot locations, e.g., spanning each of the first and second slots simultaneously. The N/2 arms in the first slot may be electrically connected in a first phase winding leg and the N/2 arms in the first slot may be electrically connected in a second phase winding leg. The N/2 arms in the second slot may be electrically connected in the first phase winding leg and the N/2 arms in the second slot may be electrically connected in the second phase winding leg.

Each of the first and second slots may have N arms of the hairpin winding located in N radial slot locations, e.g., such that a single arm of the hairpin winding is disposed in a single radial slot location.

The first subset of arms located in the first slot may include arms having a first cross-sectional area. The first subset of arms may be distributed over odd and even radial slot positions of the first slot. The second subset of arms located in the first slot may comprise arms having a second cross-sectional area. The second subset of arms may be distributed over the odd and even radial slot positions of the first slot. The third subset of arms located in the second slot may comprise arms of the first cross-sectional area. The third subset of arms may be distributed over the odd and even radial slot positions of the second slot. The fourth subset of arms located in the second slot may comprise arms of the second cross-sectional area. The fourth subset of arms may be distributed over the odd and even radial slot positions of the second slot. The first cross-sectional area may be greater than the second cross-sectional area.

This may be beneficial because each of the first and second phase winding branches may be formed by arms of first and second cross-sectional areas. Arms of different cross-sectional areas may have different resistances, and thus utilizing arms of different cross-sectional areas may reduce AC losses by placing an arm of a particular cross-sectional area at a particular radial slot location.

The first and third subsets of arms may be located at the first through N/2 radial slot positions of their respective slots, and the second and fourth subsets of arms may be located at the (N/2) +1 through N radial slot positions of their respective slots.

This may be beneficial where the first through N/2 radial slot positions of each slot comprise the radially outer slot position, and the (N/2) +1 through N radial slot positions of each slot comprise the radially inner slot position. In particular, in use, radially inner slot locations may be more susceptible to flux leakage. Locating the smaller cross-sectional area arms at the radially inner slot locations may reduce the induced AC losses in these arms that are caused by slot leakage flux that is more concentrated at the radially inner slot locations. An arm with a smaller cross-sectional area proportionally links less flux and has less induced AC losses. The consequent splitting of these smaller cross-sectional area arms can be used to reduce or eliminate the possibility of circulating currents and losses within the phase path. Here, the radially outer slot position may be considered to be a slot position located at a greater radial distance from the center of the stator assembly than the radially inner slot position.

The N radial slot locations may extend from a radially outer slot location to a radially inner slot location, e.g., such that a first radial slot location comprises a radially outermost slot location and an nth radial slot location comprises a radially innermost slot location.

N may comprise an even number greater than or equal to 4. N may comprise a multiple of 4.

The first and second slots may be adjacent to each other, for example such that there is no further slot between the first and second slots.

The plurality of slots may form a plurality of slot pairs around the stator body. Adjacent slot pairs may be spaced apart around the stator body, for example circumferentially around the stator body, with at least one intermediate slot pair located therebetween, the at least one intermediate slot pair corresponding to at least one further phase winding.

The stator assembly may include at least one additional phase winding. At least one additional phase winding may be disposed in at least one additional slot pair and may include a similar structure as the phase winding. For example, the arms of the hairpin windings located at odd radial slot positions of a first further slot of a further slot pair may be electrically connected in series with the arms of the hairpin windings located at even radial slot positions of a second further slot of the further slot pair to form a first further phase winding leg, the arms of the hairpin windings located at even radial slot positions of the first further slot may be electrically connected in series with the arms of the hairpin windings located at odd radial slot positions of the second further slot to form a second further phase winding leg, and the first and second further phase winding legs may be electrically connected in parallel.

The stator assembly may include first, second, and third pluralities of slot pairs disposed about the stator body, the first plurality of slot pairs may have a first phase winding disposed therein, the second plurality of slot pairs may have a second phase winding disposed therein, and the third plurality of slot pairs may have a third phase winding disposed therein. The first, second and third phase windings may comprise the same structure, for example with the first and second phase winding branches electrically connected in the manner described above.

The first, second and third plurality of slot pairs may be arranged in a repeating pattern around the stator body, for example such that the first plurality of slot pairs is followed by the second plurality of slot pairs, followed by the third plurality of slot pairs, followed by the first plurality of slot pairs, and so on.

According to a fifth aspect of the invention, there is provided an electric motor comprising a stator assembly according to the first aspect of the invention.

According to a sixth aspect of the present invention, there is provided an electric vehicle comprising an electric motor according to the second aspect of the present invention.

Preferred features of each aspect of the invention may be equally applicable to other aspects of the invention where appropriate.

Drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the following drawings in which:

figure 1 is a schematic perspective view showing a stator assembly according to the present invention;

figure 2a is a schematic plan view of the stator assembly of figure 1;

FIG. 2b is an enlarged view of section X of FIG. 2 a;

figure 2c is a schematic plan view of the stator assembly of figure 2 as wound;

FIG. 3 is a schematic perspective view of hairpin pre-bending for use with the stator assembly of FIG. 1;

FIG. 4 is a table showing the positioning of pre-bent hairpin windings within slots of the stator assembly of FIG. 1;

FIG. 5 is a schematic perspective view of a hairpin winding used with the stator assembly of FIG. 1 after bending;

fig. 6a is a schematic view of the stator assembly of fig. 1, wherein the hairpin windings are inserted and bent to define radial rows;

FIG. 6b is an enlarged view of portion X of FIG. 6 a;

fig. 7 is a table showing the positioning of the connecting portions of the hairpin windings in radial rows after bending;

fig. 8 is a table showing the positioning of the hairpin winding arms relative to their respective connection portions;

fig. 9 is a first schematic diagram illustrating electrical connections of phase windings of the stator assembly of fig. 1;

figure 10 is a second schematic diagram illustrating electrical connections of phase windings of the stator assembly of figure 1;

FIG. 11 is a first schematic view showing the mechanical and electrical connections of the windings used with the stator assembly of FIG. 1;

fig. 12 is a schematic diagram illustrating the radial position of the connecting portion of the hairpin winding arm relative to the slots of the stator assembly of fig. 1;

FIG. 13 is a schematic view of a hairpin arm disposed in a slot pair of the stator assembly of FIG. 1;

FIG. 14 is a schematic diagram showing the electrical connection of the arms in the single slot of FIG. 13;

FIG. 15a is a schematic diagram showing the electrical connection of the arms of the slot pair of FIG. 13;

fig. 15b is a schematic diagram illustrating the physical location of the hairpin arm in the electrical connection scheme of fig. 15 a;

FIG. 16 is a schematic view illustrating a fully wound stator assembly according to the present invention;

FIG. 17 is a schematic diagram illustrating complete electrical connections of the stator assembly of FIG. 16;

fig. 18 is a schematic view showing a first further embodiment of a hairpin arm disposed within a stator of the invention;

FIG. 19 is a schematic view illustrating a second additional embodiment of a hairpin arm disposed within a stator of the invention;

fig. 20 is a schematic view showing a third additional embodiment of a hairpin arm disposed within a stator of the invention;

FIG. 21 is a schematic view of an electric motor including the stator assembly of FIG. 1; and

fig. 22 is a schematic diagram of an electric vehicle including the motor of fig. 17.

Detailed Description

In fig. 1 and 2a-c, a stator assembly 10 according to an embodiment of the invention is shown in isolation without any windings.

The stator assembly 10 has a generally cylindrical stator body 12 and a plurality of slots 14 formed in the stator body 12. The plurality of slots 14 are generally rectangular, each slot 14 having four

radial slot locations

16, 18, 20, 22, a limited number of slots 14 being schematically illustrated in fig. 2a and 2b, aligned from a radially outer side of the stator body 12 to a radially inner side of the stator body 12. In this embodiment, there are 60 slots.

The stator assembly 10 is intended to be a stator assembly for a three-phase electric motor. Thus, the windings of the stator assembly 10 are electrically connected to form three phase windings, commonly referred to as A, B and C. The slots 14 are arranged in channels 13 surrounding the stator body, each channel 13 corresponding to a particular phase. The channels 13 circulate circumferentially around the stator body 12 such that a first channel 13 corresponds to phase a, a second channel 13 adjacent to the first channel 13 corresponds to phase B, a third channel 13 adjacent to the second channel 13 corresponds to phase C, a fourth channel 13 adjacent to the third channel 13 corresponds to phase a, and so on.

The stator assembly 10 is wound using hairpin windings 24, the hairpin windings 24 being of the general form shown in figure 3. Each hairpin winding 24 has a first arm 26 and a second arm 28, the first arm 26 and the second arm 28 being connected by a generally u-shaped or v-shaped portion 30. Each hairpin winding 24 has first and

second connection portions

32, 34 located at the ends of the respective first and

second arms

26, 28. The connecting

portions

32, 34 are bent portions of the

arms

26, 28 to form an electrical connection between the hairpin windings 24, the ends of the connecting

portions

32, 34 being free of an electrically insulating coating. In the present embodiment, 120 hairpin windings 24 are used to wind the stator assembly 10 in the manner described below.

Each hairpin winding 24 is inserted into the stator assembly 10 such that a first arm 26 of the hairpin winding 24 is located in the first slot 14 and a second arm 28 of the hairpin winding 24 is located in the second slot 14, the second slot 14 being circumferentially spaced from the first slot 14 around the stator body 10. In the illustrated embodiment, the slot pitch 14 of the hairpin winding is 6, for example such that a hairpin winding 24 having a first arm 26 located in a nominal slot 14, designated "1", has a corresponding second arm 28 located in a nominal slot 14, designated "7". It will be appreciated here that the numbering of the slots is such that the numbering increases in a counter-clockwise direction when viewed from the end of the stator assembly, as shown in figure 2 a.

The hairpin winding 24 is inserted into the stator assembly 10 such that the hairpin winding 24 forms an outer winding layer 36 and an inner winding layer 38, as schematically shown in fig. 2 c. In this embodiment, the hairpin windings 24 of the outer layer 36 have

arms

26, 28 with a larger cross-sectional area than the hairpin windings 24 of the inner layer 38 for reasons that will be discussed below. It should be understood, however, that hairpin windings having arms of equal cross-sectional area for the outer winding layer 36 and the inner winding layer 38 may also be used within the scope of the invention.

In the outer winding layer 36, the hairpin winding 24 is located in the slot 14 such that the first arm 26 is located at the first radial slot location 16 and the second arm 28 is located at the second radial slot location 18. In the inner winding layer 38, the hairpin winding 24 is located in the slot 14 such that the first arm 26 is located at the third radial slot position 20 and the second arm 28 is located at the fourth radial slot position 22. Thus, the outer winding layer 36 occupies the first and second radial slot positions 16, 18, while the inner winding layer 38 occupies the third and fourth radial slot positions 20, 22. The position of the

arms

26, 28 of the hairpin winding 24 within the slot 14 can be seen in fig. 4, S denoting the slot number and L the radial slot position.

When the hairpin windings 24 are positioned in the slots 14, the

connection portions

32, 34 of the hairpin windings extend axially outward from the stator body 12 of the stator assembly 10. To enable connection of the hairpin windings 24, the

connection portions

32, 34 of the hairpin windings are twisted/bent such that the

connection portions

32, 34 extend circumferentially around the stator body 12 relative to the

respective arms

26, 28 before being twisted such that the

connection portions

32, 34 extend in the axial direction of the stator assembly 10. Such a twisted hairpin winding is shown separately in fig. 5, and the positioning of the bent connecting portion is shown in fig. 2b and 6 to 8. The first connection portion 32 and the second connection portion 34 are twisted in opposite directions, i.e., the first connection portion 32 is twisted in a clockwise direction when viewed from the terminal end of the stator assembly 10, and the second connection portion 34 is twisted in a counterclockwise direction when viewed from the terminal end of the stator assembly 10.

Assuming that the first and

second arms

26, 28 of each hairpin winding 24 are located at different radial slot positions of different slots, this causes the connecting

portions

32, 34 to sequentially twist in different directions depending on the radial slot positions of their

respective arms

26, 28. Thus, the first connection portion 32 of the outer winding layer 36 having the first arm 26 located at the first radial slot position 16 is twisted in a clockwise direction. The second connection portion 34 of the outer winding layer 36 with the second arm 28 at the second radial slot position 18 twists in the counterclockwise direction. The first connection portion 32 of the inner winding layer 38 having the first arm 26 located at the third radial slot position 20 is twisted in a clockwise direction. The second connection portion 34 of the inner winding layer 38 having the second arm 28 located at the fourth radial slot position 22 is twisted in a counter-clockwise direction.

The connecting

portions

32, 34 of each hairpin winding 24 are twisted to the same extent. This gives an arrangement in which the connecting

portions

32, 34 are aligned in radial rows 40, each radial row 40 having four

radial positions

42, 44, 46, 48, as shown schematically in fig. 6a, 6b and 11. It should be understood that the radial position of the radial rows 44 forming the circuit connections may be slightly different from the radial position of the radial rows 44 not forming the circuit connections. For example, the input and output connections of each phase winding may be at a first radial position 42, the first radial position 42 being radially offset from the first radial positions 42 of the other radial rows 40.

In the present embodiment, the degree of twist is such that each radial row 40 covers a respective slot 14, although those skilled in the art will appreciate that arrangements in which radial rows 40 are not aligned with slots 14 are also contemplated.

In the present embodiment, the connecting

portions

32, 34 are twisted at a pitch of 3 grooves. This results in an arrangement in which, for example, the first connection portion 32 of the hairpin winding 24 has the first arm 26 located at the first radial slot position 16 of the slot 14 labeled "1" at the first radial position 42 corresponding to the radial row 40 of slots 14 labeled "58". The second connection portion 34 of the same hairpin winding 24, having the second arm 28 located at the second radial slot position 18 of the slot 14, labeled "7", is located at a second radial position 44 corresponding to the radial row 40 of slots, labeled "10".

Similarly, the second connection portion 34 of the hairpin winding 24, having the second arm 28 located at the second radial slot position 18 of the slot 14 labeled "55", is located at the second radial position 44 corresponding to the radial row 40 of slots 14 labeled "58". From a comparison of fig. 5 and 7, it can be seen that the radial position of the connecting

portions

32, 34 with respect to the radial slot position of the

respective arms

26, 28, where R represents the number of radial rows (corresponding to the number of slots S) and P represents the radial position (corresponding to the radial slot position L), as can also be seen in fig. 8.

Given the positioning of the

connection portions

32, 34, the hairpin winding 24 forms an electrical connection for the three-phase winding as will be discussed below with reference to fig. 9 to 16.

As can be seen in fig. 9 and 10, each phase winding A, B, C has a first phase winding leg 50 and a second phase winding leg 52 electrically connected in parallel. The structure of phase winding a will be discussed below, although those skilled in the art will appreciate that phase windings B and C have similar structures.

Each

phase winding leg

50, 52 is made up of a series of four loops electrically connected together in series. Each loop is formed by a plurality of hairpin windings 24 and includes the hairpin windings 24, the hairpin windings 24 forming a loop around the stator body 12 when connected together. It is considered herein that a loop is formed in which an electrical path may be traced from a first connection portion 32 at a first radial position 42 of a given radial row 40 to a second connection portion 34 at a second radial position 44 of the same radial row, and vice versa, and in which an electrical path may be traced from a first connection portion 32 at a third radial position 46 of a given radial row 40 to a second connection portion 34 at a fourth radial position 48 of the same radial row, and vice versa. The circuit is schematically represented in fig. 12 by line shading, which will be described later.

The

loops

54, 56, 58, 60 of the first phase winding branch 50 will be described below, although it will be clear later that the loops of the second phase winding branch 52 have a similar structure.

The first loop 54 of the sequence of first phase winding legs 50 utilizes the hairpin winding 24 of the outer winding layer 36. As briefly mentioned above, the first connection portion 32 of the hairpin winding 24, having the first arm 26 located at the first radial slot position 16 of the slot 14 labeled "1", is located at the first radial position 42 corresponding to the radial row 40 of slots 14 labeled "58". This first connection portion 32 serves as a starting point for the first circuit 54 and may in particular serve as an input connection through which, in use, current is input into the first circuit 54, for example from an inverter (not shown) of the electric motor. The arm positions of the start and end of the loop can be seen in fig. 10, while the radial positions of the connecting portions can be seen in fig. 11 and 12. Fig. 12 shows in particular the radial position of the

connection portions

32, 34 with respect to the respective slot 14. The line hatching of fig. 12 shows the connecting

portions

32, 34 having the

arms

26, 28 in the same slot 14, while the dot hatching shows the connecting

portions

32, 34 having the

arms

26, 28 in the other slot 14.

The second connection portion 34 of the same hairpin winding 24, having the second arm 28 located at the second radial slot position 18 of the slot 14, labeled "7", is located at a second radial position 44 corresponding to the radial row 40 of slots, labeled "10". The first connection portion 32 of the next hairpin winding 24 in the first loop 54 has a first arm 26 located at a first radial slot position 16 of the slot 14 labeled "13", located at a first radial position 42 corresponding to the radial row of slots labeled "10".

This arrangement of the hair clip is similarly repeated around the stator body 12 until the first loop 54 terminates at the second connection portion 34 of the hairpin winding 24 having the second arm 28 located at the second radial slot location 18 of the slot 14 labeled "55", the second connection portion 34 located at the second radial location 44 corresponding to the radial row 40 of slots 14 labeled "58".

Thus, first loop 54 begins at first radial position 42 corresponding to radial row 40 of slots 14 labeled "58" and ends at second radial position 44 corresponding to radial row 40 of slots 14 labeled "58".

It will be appreciated that this gives an arrangement in which the first and

second connection portions

32, 34 of the sequential hairpin windings 24 defining the first loop 54 are adjacent to one another at the first radial position 42 and the second radial position 44 of the radial row 40 around the stator body 12. This adjacent arrangement of

connection portions

32, 34 enables direct welding between hairpin windings 24 within first circuit 54, thereby mechanically and electrically connecting hairpin windings 24 within first circuit 54 in series. Such a direct weld is a relatively direct connection compared to, for example, arrangements requiring an intermediate electrical conductor.

The second loop 56 of the sequence utilizes the hairpin winding 24 of the inner winding layer 38. The first connection portion 32 of the hairpin winding 24 has the first arm 26 located at the third radial slot position 20 of the slot 14 labeled "1" at a third radial position 46 corresponding to the radial row 40 of slots 14 labeled "58". The first connection portion 32 is used as a starting point for the second circuit 56. The second loop 56 is then constructed in a manner similar to the first loop 54 until the second loop 56 terminates in the second connection portion 34 of the hairpin winding 24 having the second arm 28 located at the fourth radial slot position 22 of the slot 14 labeled "55" and located at the fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "58".

As can be seen from the above, the end of first loop 54 is located at second radial position 44 corresponding to radial row 40 of slots 14 labeled "58", and the start of second loop 56 is located at third radial position 46 corresponding to radial row 40 of slots 14 labeled "58". Because the ends of first loop 54 and the beginning of second loop 56 are located at adjacent radial positions of the same radial row 40, first loop 54 and second loop 56 may be welded directly to each other, thereby mechanically and electrically connecting first loop 54 and second loop 56 in series. Such a direct weld is a relatively direct connection compared to, for example, arrangements requiring an intermediate electrical conductor. The connections between the loops can be seen relative to the

connections

32, 34 in fig. 11 and 12.

The third loop 58 of the sequence utilizes the hairpin winding 24 of the inner winding layer 38. The second connection portion 34 of the hairpin winding 24 has the second arm 28 located at the fourth radial slot position 22 of the slot 14 labeled "2" and at a fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "5". The second connecting portion 34 is used as a starting point of the third loop 58. The third loop 58 is then constructed in a manner similar to the first and

second loops

54, 56 until the third loop 58 terminates at the first connection portion 32 of the hairpin winding 24, having the first arm 26 located at the third radial slot position 20 of the slot 14 labeled "8", at the third radial position 46 corresponding to the radial row 40 of slots 14 labeled "5".

As can be seen from the above, the end of the second circuit 56 is located at the fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "58", and the start of the third circuit 58 is located at the fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "5". Since the ends of second loop 56 and the beginning of third loop 58 are located in spaced radial rows 40, a direct weld cannot be made between second loop 56 and third loop 58. An electrical conductor 62, commonly referred to as a jumper, is used to bridge the gap, thereby providing an indirect connection between the second and

third circuits

56, 58, mechanically and electrically connecting the second and

third circuits

56, 58 in series.

Although indirect connections may be considered less beneficial than direct connections, it should be noted that the end of the second circuit 56 and the beginning of the third circuit 58 are located at the fourth radial position 48 of their respective radial rows 40. This may enable a relatively direct indirect connection between second circuit 56 and third circuit 58.

The fourth loop 60 of the sequence utilizes the hairpin winding 24 of the outer winding layer 36. The second connection portion 34 of the hairpin winding 24 has a second arm 28 located at a second radial slot position 18 of the slot 14 labeled "2" and located at a second radial position 44 corresponding to the radial row 40 of slots 14 labeled "5". The second connecting portion 34 is used as a starting point of the fourth circuit 60. The fourth circuit 60 is then configured in a manner similar to the first, second and

third circuits

54, 56, 58 until the fourth circuit 60 terminates in the first connection portion 32 of the hairpin winding 24 having the first arm 26 located at the first radial slot position 16 of the slot 14 labeled "8", the first arm 26 being located at the first radial position 42 corresponding to the radial row 40 of slots 14 labeled "5".

As can be seen from the above, the end of the third circuit 58 is located at the third radial position 46 corresponding to the radial row 40 of slots 14 labeled "5", and the start of the fourth circuit 60 is located at the second radial position 44 corresponding to the radial row 40 of slots 14 labeled "5". Third circuit 58 and fourth circuit 60 may be directly welded to each other, thereby mechanically and electrically connecting third circuit 58 and fourth circuit 60 in series, since the end of third circuit 58 and the beginning of fourth circuit 60 are located at adjacent radial positions of the same radial row 40. Such a direct weld is a relatively direct connection compared to, for example, arrangements requiring an intermediate electrical conductor.

Furthermore, since the start of the first loop 54 and the end of the fourth loop 60 are both located at the first radial position 42 of the respective radial row 40, the input and output connections of the sequence, i.e. the input and output connections of the first phase winding branch 50, may be formed at the same radial position, which may enable a relatively simple connection arrangement. The beginning of first loop 54 and the end of fourth loop 60 are located in radial rows 40 that are spaced apart from one another, which may further facilitate ease of connection.

As noted above, the second phase winding branch 52 is constructed in a manner generally similar to the construction of the first phase winding branch 50. In particular, the second phase winding branch 52 is a sequence of four

loops

64, 66, 68, 70 electrically connected together in series. However, as will be appreciated, the

loops

64, 66, 68, 70 of the second phase winding limb have different starting and end positions than the

loops

54, 56, 58, 60 of the first phase winding limb 50, and have

arms

26, 28 of the hairpin winding 24 located in different slots 14.

The first loop 64 of the sequence of second phase winding legs 52 utilizes the hairpin winding 24 of the outer winding layer 36. The first connection portion 32 of the hairpin winding 24, having the first arm 26 located at the first radial slot position 16 of the slot 14 labeled "2", is located at a first radial position 42 corresponding to the radial row 40 of slots 14 labeled "59". The first connecting portion 32 is used as a starting point for the first loop 64. The first loop 64 is then constructed in a similar manner to the first loop 54 of the sequence of first phase winding legs 50 until the first loop 64 terminates in the second connection portion 34 of the hairpin winding 24 having the second arm 28 located in the second radial slot position 18 of the slot 14 labeled "56" in the second radial position 44 corresponding to the radial row 40 of slots 14 labeled "59".

It is thus clear that the start of the first loop 54 of the sequence of first phase winding legs 50 and the start of the first loop 64 of the sequence of second phase winding legs 52 are adjacent to each other at the first radial position 42 of their respective adjacent radial rows 40. This enables a relatively direct input connection to be made for the first phase winding branch 50 and the second phase winding branch 52.

The second loop 66 of the sequence of second phase winding legs 52 utilizes the hairpin winding 24 of the inner winding layer 38. The first connection portion 32 of the hairpin winding 24 has the first arm 26 located at the third radial slot position 20 of the slot 14 labeled "2" at a third radial position 46 corresponding to the radial row 40 of slots 14 labeled "59". The first connection portion 32 is used as a starting point for the second loop 66. The second loop 66 is then constructed in a manner similar to the first loop 64 until the second loop 66 terminates in the second connection portion 34 of the hairpin winding 24 having the second arm 28 located at the fourth radial slot position 22, labeled "56", of the slot 14, at the fourth radial position 48 corresponding to the radial row 40 of slots 14, labeled "59".

As can be seen from the above, the end of the first loop 64 is located at the second radial position 44 corresponding to the radial row 40 of slots 14 labeled "59", and the start of the second loop 66 is located at the third radial position 46 corresponding to the radial row 40 of slots 14 labeled "59". Because the ends of first loop 64 and the beginning of second loop 66 are located at adjacent radial positions of the same radial row 40, first loop 64 and second loop 66 may be welded directly to each other, thereby mechanically and electrically connecting first loop 64 and second loop 66 in series. Such a direct weld is a relatively direct connection compared to, for example, arrangements requiring an intermediate electrical conductor.

The third loop 68 of the sequence utilizes the hairpin winding 24 of the inner winding layer 38. The second connection portion 34 of the hairpin winding 24 has the second arm 28 located at the fourth radial slot position 22 of the slot 14 labeled "1" at a fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "4". The second connecting portion 34 is used as a starting point for the third circuit 68. The third loop 68 is then constructed in a manner similar to the first and

second loops

64, 66 until the third loop 68 terminates at the first connection portion 32 of the hairpin winding 24 having the first arm 26 located at the third radial slot position 20 of the slot 14 labeled "7" and located at the third radial position 46 corresponding to the radial row 40 of slots 14 labeled "4".

As can be seen from the above, the end of the second circuit 66 is located at the fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "59", and the start of the third circuit 68 is located at the fourth radial position 48 corresponding to the radial row 40 of slots 14 labeled "4". Since the ends of the second circuit 66 and the beginning of the third circuit 68 are located in the spaced radial rows 40, no direct weld can be made between the second circuit 66 and the third circuit 68. An electrical conductor 72, commonly referred to as a jumper, is used to bridge the gap, thereby providing an indirect connection between the second loop 66 and the third loop 68, mechanically and electrically connecting the second loop 66 and the third loop 68 in series.

Although indirect connections may be considered less beneficial than direct connections, it should be noted that the ends of the second circuits 66 and the beginning of the third circuits 68 are located at the fourth radial position 48 of their respective radial rows 40. This may enable a relatively direct indirect connection between second circuit 66 and third circuit 68.

It will also be noted here that the end of the second loop 66 and the start of the third loop 68 of the sequence of second phase winding branches 52 are located between the end of the second loop 56 and the start of the third loop 58 of the first phase winding branch 52. For example, it can be said that the radial rows of the beginning and end of the loops having the sequence of second phase winding legs 52 are nested within the radial rows of the beginning and end of the loops having the sequence of first phase winding legs 50. This arrangement may enable the electrical conductors 72 connecting the second and

third loops

66, 68 of the second phase winding branch 52 to nest within the electrical conductors 62 connecting the second and

third loops

56, 58 of the first phase winding branch 50. This may enable a connection arrangement with a relatively small axial height.

The fourth loop 70 of the sequence utilizes the hairpin winding 24 of the outer winding layer 36. The second connection portion 34 of the hairpin winding 24, having the second arm 28 located at the second radial slot position 18 of the slot 14 labeled "1", is located at a second radial position 44 corresponding to the radial row 40 of slots 14 labeled "4". The second connecting portion 34 is used as a starting point of the fourth loop 70. A fourth loop 70 is then constructed in a manner similar to the first, second and

third loops

64, 66, 68 until the fourth loop 70 terminates at the first connection portion 32 of the hairpin winding 24 having the first arm 26 located at the first radial slot position 16 of the slot 14 labeled "7" at the first radial position 42 corresponding to the radial row 40 of slots 14 labeled "4".

As can be seen from the above, the end of the third loop 68 is located at the third radial position 46 corresponding to the radial row 40 of slots 14 labeled "4", and the start of the fourth loop 70 is located at the second radial position 44 corresponding to the radial row 40 of slots 14 labeled "4". Since the end of the third loop 68 and the start of the fourth loop 70 are located at adjacent radial positions of the same radial row 40, the third loop 68 and the fourth loop 70 may be directly welded to each other, thereby mechanically and electrically connecting the third loop 68 and the fourth loop 70 in series. Such a direct weld is a relatively direct connection compared to, for example, arrangements requiring an intermediate electrical conductor.

Furthermore, since the start of the first loop 64 and the end of the fourth loop 70 are both located at the first radial position 42 of the respective radial row 40, the input and output connections of the sequence, i.e. the input and output connections of the second phase winding branch 52, may be formed at the same radial position, which may enable a relatively simple connection arrangement. The beginning of the first loop 64 and the end of the fourth loop 70 are located in radial rows 40 that are spaced apart from one another, which may further aid in ease of connection.

It can also be seen that the end of the fourth loop 60 of the sequence of first phase winding branches 50 and the end of the fourth loop 70 of the sequence of second phase winding branches 52 are adjacent to each other at the first radial position 42 of their respective adjacent radial rows 40. This enables a relatively direct output connection to be made for the first phase winding branch 50 and the second phase winding branch 52.

As can be seen from the above discussion, the first phase winding leg 50 and the second phase winding leg 52 are each formed by a hairpin winding 24, the hairpin winding 24 having

arms

26, 28 disposed in both slots 14 of a given slot pair 19 around the stator body 12. Here, the pair of grooves 19 are considered to be grooves spaced at a groove pitch of six, although it is equally understood for the particular embodiment shown that the pair of grooves 19 can be considered to be a pair of adjacent grooves 14 in the channel 13, as shown in fig. 15 b. If we consider the slots labeled "1" and "7", as shown in fig. 13, the first phase winding leg 50 has a first arm 26 disposed in the first 16 and third 20 radial slot positions of the slot 14 labeled "1", and a second arm 28 disposed in the second 18 and fourth 22 radial slot positions of the slot 14 labeled "7". Similarly, the second phase winding leg 52 has a first arm 26 disposed in the first and third radial slot positions 16, 20 of the slot 14 labeled "7", and a second arm 28 disposed in the second and fourth radial slot positions 18, 22 of the slot 14 labeled "1". In fig. 13-15, for clarity, the

arms

26, 28 in slot "1" are labeled a1-a4, while the

arms

26, 28 in slot "7" are labeled b1-b 4.

This electrical connection can be seen more clearly in fig. 15 a. It will be appreciated that the electrical connections shown in figures 14 and 15a are not complete electrical connections of the phase windings, but are schematic diagrams intended to show the electrical connections between the arms disposed in the slots of the slot pair 19.

Thus, and in more general terms, the arms in the first and third radial slot positions 16, 20 of the first slot 15 of the slot pair 19 are electrically connected in series with the arms in the second and fourth radial slot positions 18, 22 of the second slot 17 of the slot pair 19 to define part of the first phase winding leg 50, the slot pair 19 being two circumferentially spaced slots 14 carrying the same phase current. The arms in the first and third radial slot positions 16, 20 of the second slot 17 of the slot pair 19 are then electrically connected in series with the arms in the second and fourth radial slot positions 18, 22 of the first slot 15 of the slot pair 19 to define a portion of the second phase winding leg 52. This arrangement is repeated for all slot pairs 19 around the stator body 12 to form a three-phase winding A, B, C.

It can be seen that this electrical connection provides an equal number of arms of the hairpin windings 24 of the first and second

phase winding legs

50, 52 distributed between the first and

second slots

15, 17 of the slot pair 19, while the first and second

phase winding legs

50, 52 each also have an equal number of hairpin arms distributed between the respective radial slot positions 16, 18, 20, 22 of the first and

second slots

15, 17 of the slot pair 19. Such an electrical connection may provide several benefits. In particular, by splitting each phase winding into two parallel branches, the induced voltage level in the phase winding is reduced due to the back EMF and armature reactance, so that operation is compatible with the available supply voltage. Then forming each parallel branch of the phase winding from the mixed arms of adjacent slots 14 of the slot pair 13 around the stator body 12 may reduce or eliminate any phase difference in the induced operating voltage between the slots 14. Each parallel leg is formed not only by the mixing arms from the slots of each slot pair 19, but also by the mixing arms at each

radial slot position

16, 18, 20, 22. This may reduce or eliminate any variation in inductance and/or resistance between adjacent slots of the slot pair 19, and thus may reduce circulating currents and/or AC losses within the stator assembly 10 in use.

As mentioned briefly above, the reduction in circulating current and/or AC losses may be further enhanced by forming the outer winding layer 36 and the inner winding layer 38 from hairpin windings having different arm thicknesses.

In an embodiment of the invention, the outer winding layer 36 is formed by a hairpin winding 24, the hairpin winding 24 having a larger arm cross-sectional area than the hairpin winding 24 forming the inner winding layer 38. This results in the arrangement of a given slot pair 19 as shown in figure 13. It should be understood that fig. 13 depicts the physical location of the

arms

26, 28 within the slot 14, and that the slots are depicted in increasing numerical order from left to right for clarity.

It can be seen that for a given slot 14 of a slot pair 19, the arms at the first and second

radial slot locations

16, 18 have a greater cross-sectional area than the arms at the third and fourth

radial slot locations

20, 22. As shown in fig. 14 and 15, the arms of a given slot are then electrically connected such that one of the arms of greater cross-sectional area is electrically connected in series with one of the arms of lesser cross-sectional area to form a first subset of slots 74 and the other arm of greater cross-sectional area is electrically connected in series with the other arm of lesser cross-sectional area to form a second subset of slots 76. Then, the first cell group 74 and the second cell group 76 are electrically connected in parallel.

Repeating this structure for each slot of a given phase gives the aforementioned arrangement, in which each phase winding limb is formed by a mixing arm of an adjacent slot of the slot pair, each phase winding limb is formed by a mixing arm at each radial slot location, and each phase winding limb is also formed by a mixing arm of a different cross-sectional area.

This arrangement may further reduce circulating currents within the stator assembly 10 in use and thus reduce the AC losses experienced.

Positioning a smaller cross-sectional area arm at a radially inner slot location may result in a reduction in AC losses in that arm. The AC loss is proportional to the magnitude of the cross slot leakage flux surrounded by the physical boundaries of the arms, which in turn are proportional to their cross-sectional area given the slot boundaries. The AC losses in the arms may be mainly reactive eddy currents to the leakage flux. The strength of the cross-slot leakage flux increases towards the rotor side of the stator, so maximum loss minimization can be achieved by placing a smaller cross-sectional area closer to the rotor. Thus, by careful selection of the relative cross-sectional areas, AC losses can be minimized. It is further concluded that the resistance and inductance of any hairpin is proportional to its position and cross-sectional area in the slot. The connection of these hairpins in parallel paths may cause additional circulation and unbalanced current to flow between the paths, which may result in additional losses. To minimize this additional loss, it may be beneficial to ensure that each parallel path has an equal share of hairpins at each cross-sectional area and slot location.

Fig. 17 schematically illustrates the electrical connections of the stator assembly 10, wherein the isolated numbers show the hairpin winding numbers according to fig. 4, SXLY indicating the slot number and radial slot position of a given

hairpin arm

26, 28 corresponding to the hairpin winding 24. It can be seen that each loop is made up of five hairpin windings 24, such that each loop has five turns, with 20 turns per phase A, B, C of the stator assembly 10.

Further examples of arrangements of the hairpin arms can be seen in fig. 18 to 20, which result in an equal number of hairpin arms being distributed between the first and second slots of a slot pair, and each of the first and second phase winding legs comprises an equal number of hairpin arms distributed between the respective radial slot positions of the first and second slots.

In the arrangement of fig. 18, the slots 14 are provided in channels 300 around the stator body 12, each channel 300 having three slots. For example, first channel 302 has slots "55", "56", and "57", while second channel 304 has slots "1", "2", and "3".

Here, each of the slots within the first channel 302 and the second channel 304 may be considered to form a slot pair 19. For example, in the embodiment of fig. 18, there are three slot pairs 19, slots "55" and "1", slots "56" and "2", and slots "57" and "3" in the first channel 302 and the second channel 304. Considering each slot pair 19, it can be seen that an equal number of hairpin arms are distributed between the slots of the slot pair, the hatched arms representing the first phase winding branches and the hatched arms representing the second phase winding branches. It can also be seen that in the slot pairs, the arms are evenly distributed between the radial slot positions 16, 18, 20, 22.

For example, considering slot pair 19 of slots "55" and "1", it can be seen that in slot "55", there is an arm in the first phase winding leg 50 at the fourth radial slot location 22 and an arm in the second phase winding leg 52 at the third radial slot location 20. Then in slot "1" there is an arm in the first phase winding leg 50 at the third radial slot location 20 and an arm in the second phase winding leg 52 at the fourth radial slot location 22.

Considering the slot pair 19 of slots "56" and "2", it can be seen that in slot "56", there are arms in the first phase winding leg 50 at the second and third radial slot positions 18 and 20, and there are arms in the second phase winding leg 52 at the first and fourth radial slot positions 16 and 22. In slot "2", there are arms in the first phase winding leg 50 at the first and fourth radial slot positions 16 and 22 and arms in the second phase winding leg 52 at the second and third radial slot positions 18 and 20.

Considering the slot pair 19 of slots "57" and "3", it can be seen that in slot "57", there is an arm in the first phase winding leg 50 at the first radial slot location 16 and an arm in the second phase winding leg 52 at the second radial slot location 18. Then in slot "3" there is an arm in the first phase winding leg 50 at the second radial slot location 18 and an arm in the second phase winding leg 52 at the first radial slot location 16.

Thus, each groove 14 of a pair 19 is actually an inverse pattern of the other groove 14 of the pair 19. As can be seen from the arrangement of the third channels 306 of slots "7", "8" and "9" shown in fig. 18, which is the same as the arrangement of slots "55", "56" and "57", is repeated for successive channels 300 around the body.

Fig. 18 also shows schematically how the hairpin arms are arranged in the circuit forming the phase winding branches according to the previous embodiments.

Those skilled in the art will appreciate that an arrangement such as that shown in fig. 18 may in practice require the use of hairpin windings 24 having arms of different lengths. For example, a hairpin arm at the second radial slot location 18 of slot "56" may need to be connected to a hairpin arm at the third radial slot location 20 of slot "1". This connection is typically made above slot "58", requiring a different, i.e., shorter, connection extension for slot "56" than the longer connection extension required for slot "1". This arrangement is similar to what is known in the art as "short pitch".

A similar alternative embodiment can be seen in fig. 19 and 20, with three slots 14 per channel. Those skilled in the art will appreciate that an arrangement such as that shown in figure 19 may in practice require the use of hairpin windings 24 having arms of the same length.

Fig. 21 schematically illustrates a motor 100 including the stator assembly 10, the motor 100 including a rotor 102, the rotor 102 rotating relative to the stator assembly 10 when, in use, current flows through the phase windings A, B, C. Further details of the motor 100 are not relevant to the present invention and therefore, for the sake of brevity, will not be described here, but will be well known and understood by those skilled in the art.

Fig. 22 schematically shows an electric vehicle 200 including the motor 100. Likewise, further details of the vehicle 200 are not relevant to the present invention and, therefore, are not described herein for the sake of brevity, but are well known and understood by those of ordinary skill in the art.

Claims

1. A stator assembly for an electric motor, the stator assembly comprising a stator body, a plurality of slots formed in the stator body, and a phase winding comprising a plurality of hairpin windings electrically connected together, the phase winding comprising a first phase winding leg and a second phase winding leg, wherein the plurality of slots form at least one slot pair around the stator body, each slot of the slot pair comprising N radial slot locations, N being an even number, and each radial slot location having an arm of a hairpin winding located therein, wherein the first and second phase winding legs each comprise an equal number of hairpin arms distributed between the first and second slots of the slot pair, each hairpin arm of the first phase winding leg in the first slot being in a radial position corresponding to the hairpin arm of the second phase winding leg in the second slot, and the first and second phase winding legs are electrically connected in parallel.

2. The stator assembly of claim 1 wherein the first and second slots of the slot pair are circumferentially spaced from each other about the stator body, and at least one additional slot is located between the first and second slots.

3. The stator assembly of claim 1 or 2, wherein the hairpin arms of the first phase winding leg are disposed in a first subset of radial slot positions in the first slot, and the hairpin arms of the second phase winding leg are disposed in a second subset of radial slot positions in the second slot, the first subset of radial slot positions corresponding to the second subset of radial slot positions.

4. The stator assembly according to any of the preceding claims, wherein the hairpin arms of the first phase winding branch are disposed in a first pattern within a first slot, the hairpin arms of the first phase winding branch are disposed in a second pattern within a second slot, and the second pattern is opposite the first pattern.

5. The stator assembly of any of the preceding claims, wherein the phase windings are located within a plurality of slots disposed about the stator body, each slot comprising a plurality of adjacent slots, the stator assembly comprises a plurality of slot pairs, and each slot comprises at least one slot of a slot pair.

6. The stator assembly of claim 5, wherein each slot comprises an equal number of hairpin arms distributed between a first phase winding leg and a second phase winding leg.

7. The stator assembly of claim 5 or claim 6, wherein each slot comprises N hairpin arms in a first phase winding branch and N hairpin arms in a second phase winding branch.

8. The stator assembly of any of claims 5-7, wherein each slot includes an equal number of hairpin arms distributed between respective radial slot positions of slots within the slot.

9. The stator assembly of claim 8, wherein each slot comprises N hairpin arms of a first phase winding leg distributed over each of N radial slot positions, and each slot comprises N hairpin arms of a second phase winding leg distributed over each of N radial slot positions.

10. The stator assembly of any of the preceding claims, wherein the plurality of hairpin windings includes a first set of hairpin windings having a first cross-sectional area and a second set of hairpin windings having a second cross-sectional area, wherein the first cross-sectional area is greater than the second cross-sectional area.

11. The stator assembly of claim 10, wherein the first set of hairpin windings are located radially outward of the second set of hairpin windings.

12. The stator assembly according to any of the preceding claims, wherein a first slot of the slot pair comprises N/2 hairpin arms of a first phase winding branch and N/2 hairpin arms of a second phase winding branch, and a second slot of the slot pair comprises N/2 hairpin arms of the first phase winding branch and N/2 hairpin arms of the second phase winding branch.

13. The stator assembly according to any of the preceding claims, wherein the hairpin arms at odd-numbered radial slot positions of a first slot are electrically connected in series with the hairpin arms at even-numbered radial slot positions of a second slot of a pair of slots to form a first phase winding leg, and the hairpin arms at even-numbered radial slot positions of the first slot are electrically connected in series with the hairpin arms at odd-numbered radial slot positions of the second slot to form a second phase winding leg.

14. An electric motor comprising a stator assembly according to any of the preceding claims.

15. An electric vehicle comprising an electric motor according to claim 14.

16. A stator assembly for an electric motor, the stator assembly comprising a stator body, a plurality of slots formed in the stator body, and a phase winding comprising a plurality of hairpin windings electrically connected together, the phase winding comprising a first phase winding leg and a second phase winding leg, wherein the plurality of slots form at least one slot pair around the stator body, each slot of the slot pair comprising N radial slot locations, N being an even number, each radial slot location having a wall of the hairpin winding located therein, and wherein arms of the hairpin windings located in odd radial slot locations of a first slot of the slot pair are electrically connected in series with arms of the hairpin windings located in even radial slot locations of a second slot of the slot pair to form a first phase winding leg, arms of the hairpin windings located in even radial slot locations of the first slot being electrically connected in series with arms of the hairpin windings located in odd radial slot locations of the second slot, to form a second phase winding branch and the first and second phase winding branches are electrically connected in parallel.

17. The stator assembly of claim 16, wherein a first subset of the arms in the first slot comprise arms of a first cross-sectional area, a second subset of the arms in the first slot comprise arms of a second cross-sectional area, a third subset of the arms in the second slot comprise arms of the first cross-sectional area, and a fourth subset of the arms in the second slot comprise arms of the second cross-sectional area.

18. The stator assembly of claim 17, wherein the first subset of arms and the third subset of arms are located at first through N/2 radial slot positions of their respective slots, and the second subset of arms and the fourth subset of arms are located at (N/2) +1 through N radial slot positions of their respective slots.

19. The stator assembly of any of claims 16-18, wherein the N radial slot positions extend from a radially outer slot position to a radially inner slot position such that a first radial slot position comprises a radially outermost slot position and an nth radial slot position comprises a radially innermost slot position.

20. The stator assembly of any of claims 16-19, wherein N comprises an even number greater than or equal to 4.

21. The stator assembly of any of claims 16-20, wherein the first and second slots are adjacent to each other.

22. The stator assembly of any of claims 16-21, wherein the plurality of slots form a plurality of slot pairs around the stator body, and adjacent slot pairs are spaced around the stator body, at least one intermediate slot pair being located between adjacent slot pairs.

23. The stator assembly of any of claims 16-22, wherein the stator assembly comprises at least one additional phase winding disposed in at least one additional slot pair.

24. The stator assembly of any of claims 16-23, wherein the stator assembly comprises a first plurality of slot pairs disposed about the stator body, the first plurality of slot pairs having a first phase winding disposed therein, a second plurality of slot pairs having a second phase winding disposed therein, and a third plurality of slot pairs having a third phase winding disposed therein.

25. The stator assembly of claim 24, wherein the first, second, and third pluralities of slot pairs are arranged in a repeating pattern around the stator body.

26. An electric motor comprising a stator assembly according to any of claims 16 to 25.

27. An electric vehicle comprising an electric motor according to claim 26.