WO2016078691A1

WO2016078691A1 - Air-gap winding

Info

Publication number: WO2016078691A1
Application number: PCT/EP2014/074781
Authority: WO
Inventors: David Ramon; Luca Ferrario
Original assignee: Faulhaber Minimotor Sa
Priority date: 2014-11-17
Filing date: 2014-11-17
Publication date: 2016-05-26
Also published as: TW201622307A; EP3248272A1; CN107078579A

Abstract

A cylindrical multiphase coreless winding with hexagonal loops (2) is disclosed, preferably comprising two sections for each phase and having a symmetrical layout, said layout being such that a cross section of the winding according to a plane perpendicular to the main axis away from crossing regions of the loops comprises one or more concentric layers of cross-sectional areas (7) containing the loops of different phases, and that a cross section of the winding according to at least a second plane located in a crossing region of loops comprises one or more concentric layers of areas (8)containing a uniform distribution of loops of two phases.

Description

AIR-GAP WINDING

DESCRIPTION

Field of the invention

The invention relates to the field of coreless windings for electric motors.

Prior art

Electric motors including a coreless winding are known in the art. Coreless windings are also termed ironless or air-cored or self-standing windings. One of the main advantages of a coreless winding over a conventional winding is the reduced weight and low inertia, for example to provide a rotor with a fast acceleration and response. Another advantage is the low inductance due to the absence of a magnetic core, reducing the related drawbacks such as electrical disturbances and progressive wear of the brushes, and increasing life of the motor.

Various techniques of making coreless windings are known. Generally speaking, the goals of a coreless winding include: maximum power density; maximum of magnetic flux collected by the coils or loops of the winding; the achievement of a high torque or speed for a given size or, similarly, a smaller size for a required torque or speed. Another important issue is to simplify the manufacturing process and in particular the winding process of the wires. Still another problem is the avoidance or at least reduction of crossing between the wires. Wire crossing introduces drawbacks including a higher risk of failure of the insulation and the need to reduce the number of loops in order to leave the necessary room between the wires and avoid their damage. Reducing the number of loops, however, will reduce the performance of the winding, e.g. the torque delivered by a rotor comprising the winding.

The prior art coreless cylindrical windings of electric motors have typically triangular, hexagonal or rhombic coils. An overview of said known embodiments can be found in DE 2931725. The triangular iron-free armature winding originally introduced by Dr. Faulhaber is disclosed in US 3 360 668.

The early technique of coreless, self-standing windings is being continuously developed, for example a recent example of improved coreless winding with rhombic coils is disclosed in EP 2 642 636. In fact, there is an ongoing incentive to improve the performance of coreless windings for electric motors. In particular, there is a strong incentive to provide electric motors with coreless rotors of a small diameter but able to deliver a high torque and/or reach a considerable speed, especially in technical fields such as medical equipment, robotics, aerospace and aviation industries. Reducing the weight is another challenge, especially in the field of aeronautics. One of the technical problems in connection with coreless cylindrical windings, especially of a small diameter, is the arrangement of the wires which compose each single coil of the windings. More in detail, a drawback of the prior art multiphase coreless windings is asymmetrical layout of the loops of wire. The conventional process of making coreless winding provides that loops of each phase are wound sequentially one at a time, forming several concentric layers around a cylinder. A disadvantage of this technique is that each loop must be arranged on previously formed loops. This causes deviation from the symmetrical layout and deviation from the symmetry will result in the winding being electrically unbalanced. This drawback of the prior art can be better understood with the help of Fig. 20 and Fig. 21 .

Fig. 20 shows a cross section of a conventional three-phase wave winding according to a plane perpendicular to its main axis and situated at half height of the winding. The cross section is composed of regions 100, 101 and 102 which are traversed by the loops of a single phase each, for example the region 100 contain the loops of a phase U, the region 101 contain the loops of a phase V, the region 102 contain the loops of a phase W. As illustrated in the figure, the regions 100, 101 and 102 have a different shape and dimension. One reason is that, for example, the loops of phase U are arranged first around a cylindrical surface, leaving no sufficient room for the loops of the subsequent phase V which necessarily pass on an outer layer (that is at a greater distance from the axis); then the loops of the third phase W are accommodated in the remaining space. As above discussed, however, this technique leads to undesirable lack of symmetry and electrical unbalance.

Fig. 21 shows the typical appearance of the cross section of a conventional non-symmetric lap winding.

Another problem of the prior art is the difficult control of the position of the electrically conductive wire during formation of coils. The wire is normally wound around pins to obtain the desired cylindrical winding. In a conventional triangular winding, there is a relatively long straight portion of wire between two adjoining pins. This portion of wire may deviate from the ideal straight line between the two pins, thus introducing another source of asymmetry.

Still another problem is given by the crossing regions. In a multiphase cylindrical coil, the coils of different phases cross at certain regions, usually at around one third and two thirds of the height of the cylinder. In a crossing regions, wire of one phase of the system, e.g. directed downward, cross with wires of another phase, e.g. directed upward. As a result, the wires are densely interleaved and more exposed to mechanical stress which may deteriorate their insulation layer. Summary of the invention

The aim of the invention is to improve the above described prior art and solve the above problems.

A purpose of the invention is to provide a novel arrangement of a coreless cylindrical winding for electric motors, with a high power density and the capability to deliver a high torque or speed relative to the size (diameter) of the winding. Another aim of the invention is to simplify the winding technique avoiding in particular the crossing (overlapping) between the wires of the various coils of the winding. Another aim of the invention is to reduce the asymmetry of the winding thus having a better electrical balance.

These aims are reached with a coreless winding according to the attached claims.

A first embodiment of the invention is a multiphase coreless winding, having a cylindrical shape, characterized by comprising loops having at least six sides and wound with a wave winding.

In a preferred embodiment, the winding comprises a plurality of sections, including two sections for connection with each phase, the two sections of winding of each phase being opposite by 180 electrical degrees, and the angular distance (offset) between two adjoining sections of the winding, connected to two different phases, being 360 / (2 n) electrical degrees, where n is the number of phases.

For example in a three-phase winding said offset between the phases is 60 electrical degrees and said two sections of the winding are opposed by 180 electrical degrees. Accordingly, the winding may be named a 60° three phase winding. In a winding with 5 phases, for example, said offset is 36° (el).

All references to angles (degrees) in this description shall be understood to electrical angles unless otherwise indicated. In a rotating electrical machine, mechanical angles 9_m and corresponding electrical angles θ_βι follow the equation 9_m = 6_ei / np where np is the number of pairs of magnetic poles. For example, in a motor having a stator, a rotor and two pairs of poles (four poles), one mechanical turn of the rotor relative to the stator equals two electrical turns. A winding according to the invention may have two poles or a greater number of poles, e.g. four poles or more. The symbol (el) will be used for notation of electrical degrees, e.g. 60°(el) denotes 60 electrical degrees. Each section is made of several loops (also named turns) of wire of a conductive material, possibly grouped into coils. A coil is understood as a group of elementary loops of wire. For example a section of a winding (pertaining to one phase) may comprise one or more coils, and each coil is made of several loops of wire. Each loop can be regarded as a number of wire sections having different spatial orientation. Said wire sections are briefly referred to as sides or wires of the loop.

The winding includes crossing regions where sides of loops connected to two different phases cross each other. According to another preferred feature, said winding has a symmetrical layout relative to a main axis. The symmetrical layout, according to the invention, fulfils the following conditions.

First, a cross section of the winding according to a first plane, which is perpendicular to said main axis and intersects the axis away from said crossing regions, comprises one or more concentric layers which are formed by a symmetrical distribution, relative to said main axis, of cross- sectional areas containing the loops of different phases, each of said cross sectional areas containing loops of only one phase. Second, a cross section of the winding according to a second plane, which is perpendicular to said main axis and intersects the axis in a crossing region, comprises one or more concentric layers which are formed by contiguous cross-regional areas, each area containing a uniform distribution of loops of two phases.

As a consequence of the first condition above, the different phases appear symmetrically distributed in a cross section of the winding, relative to the axis of the winding, and angularly spaced by 360° / n. For example the cross section of a three-phase winding will show three regions substantially identical, one for each phase, spaced by 120°. Also in the crossing regions, the loops of the phases are uniformly distributed in accordance with the second condition above.

Preferably, all phases are wound simultaneously, instead of sequentially, to form said symmetrical coreless winding. This is in contrast with the prior art, where coils of different phases are wound sequentially, causing the above mentioned disadvantages.

The applicant has found that the combination of a wave winding and loops with at least six sides is of a particular advantage in terms of correct positioning of the wires and reduced asymmetry. This combination has not been proposed so far.

The loops of wire with at least six sides have the advantage of a better control of the position of wire, during the manufacturing process, because the wire is wound around pins positioned at a shorter distance. Hence the length of straight portions of wire, which is a source of deviation from the theoretical shape of the loops, is reduced.

The loops with six sides, preferably hexagonal, have also the advantage of a larger surface than conventional (e.g. rhombic) loops. As a consequence, each loop collects a larger amount of magnetic flux. This means that a in a rotor according to the invention, for example, each loop will deliver more torque. Hence the combination of hexagonal loops and wave winding is particularly suited when a high torque is desired.

The provision of two opposite sections of winding for each phase (60°- winding for three-phase system), according to a preferred feature, has the advantage of a small angle between a centre line of the winding section and a magnetic pole. Hence the arrangement of the single loops of wire relative to the magnetic field is more efficient, and a greater torque is produced for a given current.

The above described symmetrical layout has the additional advantage of a better electrical balance of the phases of the system, since all phases are evenly distributed around the axis of the winding. Hence the related distribution of the electromotive forces is also symmetrical. An advantage of the symmetrical layout is given by low losses, which is of particular importance in hi-speed applications. Hence the symmetrical layout is preferred, in particular, for application to the stator and/or rotor of a hi- speed motor.

In a preferred embodiment, the loops comprise two axially extended active sides which may be parallel or near-parallel to the axis of the winding, or inclined by a suitable angle. Said axially extended active sides are extended through a central band or region of the cylindrical winding. They are termed active wires since in most cases they collect a greater amount of magnetic flux (50% or more of the available flux) and produce most of the output torque. Further to said axially extended sides, a loop comprises a number of shorter connection legs, for example a hexagonal loop will comprise two active sides and two pairs of upper and lower connection legs.

A preferred shape of the loops is hexagonal. An aspect of the invention is the combination of hexagonal loops and symmetrical winding with opposite sections for each phase, as above defined. The applicant has found that said combination of features reduces the loss of magnetic flux and delivers more torque or more speed for a given size (diameter) of the winding, compared to the prior art arrangements.

In the embodiments with active sides of loops arranged parallel or nearly parallel to the axis, the angle of inclination of the active sides relative to the axis of the winding is preferably a small angle, more preferably said angle is not greater than 10° (mechanical degrees).

Embodiments with axially or near-axially oriented active wires may be preferred for maximizing the magnetic flux collected by each loop. An inclination of the active sides reduces the amount of magnetic flux collected by each loop while, on the other hand, allows room for accommodation of more loops. Hence, despite a deviation from the theoretical best embodiment, said inclination may provide an overall benefit in terms of the performance, for example in terms of the torque delivered by a rotor vs. intensity of current flowing in the loops. Furthermore, the inclination of the active sides of loops renders the manufacturing process easier.

Another embodiment of the invention is a winding according to the attached claim 1 1 . In this further embodiment, the winding comprises loops having at least six sides, preferably of hexagonal shape, and has the above described features of two sections for each phase (60°-winding for a three phase system) and symmetrical layout.

The above preferred features of axial or inclined active sides of loops are also applicable. In this embodiment, the loops may be wound with a wave winding or a lap winding. A lap winding is also termed imbricated winding. Lap and wave windings are known to a skilled person and described in the literature.

In a preferred embodiment, the turns are wound with a lap winding and have a reduced pitch (also termed opening width) of less than 180 electrical degrees. The pitch is a known feature and may be defined as the angular distance (measured in electrical degrees) between axial sides of a loop, or between the median loops of a coil made of several loops. Reducing the pitch of imbricated coils gives a significant advantage in terms of the manufacturing process, since it reduces the crossing and overlapping of single loops. Hence the manufacturing method is easier and the risk of damage of wires is reduced. A short pitch also causes a loss of the magnetic flux collected by each loop; this drawback however is overcompensated by the above positive effects.

More preferably, the pitch of the imbricated loops is comprised between 360 / (2-n) and 360 / n, wherein the number n of phases is 2 or greater. Even more preferably, in a three-phase embodiment (n=3), said pitch is around 100° (el), for example between 90 and 1 10° (el). In all the embodiments of the invention, the three phases can be connected in a star (wye) or delta fashion. Furthermore, in all the embodiments the loops may have more than six sides, e.g. eight sides.

The winding of the invention can be used in both the rotor and the stator of an electric motor. A preferred use is directed to the manufacturing of the stator of a brushless motor.

The features and the advantages of the invention will be elucidated with the help of the figures, which relate to preferred and non-limiting embodiments.

Description of figures Fig. 1 is a view of a wave winding according to an embodiment of the invention.

Fig. 2 is a plane view of the winding of Fig. 1 . Fig. 3 is a plane view which illustrates a variant of the winding of Fig. 1 , wherein the axial sides of the loops of wire are inclined.

Fig. 4 is another illustration of the winding of Fig. 1 , showing only three loops and also showing two section planes. Figs. 5 and 6 are cross sections of the winding according to the two planes illustrated in Fig. 4.

Figs. 7 and 8 illustrate a typical arrangement of a loop of a wave winding and of a lap (imbricated) winding.

Fig. 9 is a view of a lap winding according to another embodiment of the invention.

Fig. 10 is a view of a detail of lap winding according to still another embodiment of the invention, namely a variant of Fig. 9 where the opening pitch of the loops is reduced.

Fig. 1 1 and 12 illustrate, in a plane view, the arrangement of the loops of wire and coils of a lap winding according to the variant of Fig. 10.

Figs. 13 and 14 are exemplary cross sections of a lap winding according to an embodiment of the invention, and according to the planes illustrated in Fig. 9.

Fig. 15 is a view of a 5-phase winding according to another embodiment of the invention.

Figs. 16 and 17 are cross sectional views of the winding of Fig. 15.

Figs. 18, 19 show examples of star and delta connections.

Figs. 20, 21 relate to the prior art.

Detailed description of preferred embodiments The figures show various embodiments of the invention. In the figures, the letters U, V, W denote the phases of a three-phase system; letters A to F denote terminals of connection of the windings.

In the figures, a coordinate system x, y, z and angular coordinate Q_ei (theta) are also used to describe the winding, as illustrated for example Fig. 1 . Said angular coordinate Q_ei is expressed in electrical degrees. The letter h denotes the height of a winding measured in the axial direction z. The axis z as shown can be regarded as the main axis of the cylindrical winding.

Fig. 1 shows a two-pole three-phase coreless winding 1 according to a first embodiment of the invention. The winding 1 is a wave winding composed of hexagonal loops of wire. More in detail, the winding 1 is made of hexagonal loops 2. Each hexagonal loop 2 comprises two axially-oriented sides 3 extending in a central band of the winding 1 and two pairs of connection legs 4.

The region of sides 3 is also named coaxial portion of the winding 1 while the regions of the legs 4 can be named non-coaxial portions of the winding.

The letters Ai , A₂, Bi , B₂, ... to F₂ denote the terminals of the winding. Examples of a star and delta connections are given in Figs. 18 and 19. The symbol N of Fig. 18 denotes the neutral point. Since the winding 1 has two poles, mechanical degrees and electrical angles in this case coincide. In the following description, anyway, the references to degrees shall be intended to electrical degrees unless otherwise stated.

The winding 1 may comprise one section or two sections for each phase. In the first case, each section extends over 120° (el) and the winding can be termed 1 20° three-phase winding. In the second case, the two sections of each phase are opposite by 180° (el) and extends over 60° (el); hence the winding can be termed a 60° three-phase winding. Said extension of 120° or 60° corresponds to the angular distance (offset) between two phases. More generally, in a multiphase winding with n phases said extension or distance is 360 / n or 360 / (2 n), respectively.

In the 60° embodiment, the three-phase winding 1 requires twelve connections, namely two connections for each section and hence four connections for each phase. Said two sections have opposite sense of winding.

Fig. 2 shows the wave winding 1 in a plane view according to coordinates θβΐ (radians) and z. In Fig. 2, the sides 3 of the hexagonal loops 2 are parallel or substantially parallel to the axis z while Fig. 3 illustrates another embodiment where the axially-oriented sides 3 are inclined relative to the axis z by an angle β.

According to another preferred feature of the invention, the winding 1 has a symmetrical layout. This feature can be better understood with reference to Figs. 4 to 6.

In Fig. 4, showing only some of the loops for ease of graphical representation, it can be seen that the winding 1 comprises crossing regions 5 when the loops of two phases, e.g. of a first phase U and second phase W, cross each other. The symmetrical layout fulfils two conditions which can be defined making reference to the cross section of winding 1 according to at least two planes P1 and P2. The first plane P1 is perpendicular to the main axis z and intercepts said axis z away from the crossing regions 5, for example in the axially extended sides 3 of the loops 2. The second plane P2 is also perpendicular to the main axis z but intercepts said axis z in correspondence of the crossing regions 5. The dotted line 20 is the intersection between the first plane P1 and the winding 1 and the dotted line 21 is the intersection with the second plane P2. As seen in the Fig. 4, the intersection line 21 passes through the crossing regions 5 of loops 2. Preferably the plane P1 is at half height of the winding. The location of the crossing regions depend on the number of poles and phases. In a two- pole, three-phase winding the crossing regions 5 are at about 1/3 and 2/3 of the height of the winding. Accordingly in such a winding the aforesaid plain P2 is preferably at 1 /3 or 2/3 of the height h.

More generally, a winding having n phases and a number np of pair of poles will show several crossing regions in the non-coaxial portion.

The cross section of planes P1 and P2, in the symmetrical embodiments of the invention, appear as in Figs. 5 and 6, respectively. In a cross section according to the plane P1 (Fig. 5), six cross sectional areas, globally denoted by numeral 7, can be recognized. Each area 7 contains wires connected to one phase U or V or W. In the example the areas 7u and 7'u contain loops of phase U, and similarly the areas 7_V, 7'_v and 7w, 7'_w contain loops of phases V and W. As shown in Fig. 5, said areas 7 are substantially identical, they are symmetrically distributed relative to said axis z and they are evenly spaced. By comparison, this condition is not met by a prior-art winding as represented in Figs. 20, 21 .

In a cross section according to plane P2 located in the crossing regions 5 (Fig. 6), only three areas, globally denoted by numeral 8, can be recognized. More in detail each area 8uv, 8uw or 8vw contain a uniform distribution of wires connected to two different phases, namely U and V or U and W or V and W.

The terms of substantially identical areas and symmetrical distribution shall be interpreted taking into account the tolerances of fabrication. It shall be noted that Figs. 5 and 6 shows one layer for simplicity; several concentric layers of loops may be provided.

Referring back to Figs. 2 and 3, Fig. 2 shows an embodiment where sides 3 are parallel to the axis z. It should be noted that even in a "parallel" embodiment, a slight (negligible) inclination of sides 3 may be caused by the tolerances of fabrication process and winding machine. A more significant inclination of sides 3, as shown in Fig. 3 by angle β, may be preferred despite a loss in the magnetic flux collected by each loop 2, because the density of connection legs 4 will be increased and hence more loops will be accommodated and the overall output torque, for a given intensity of current, will be increased.

The angle β is preferably not greater than 10 mechanical degrees.

In a second embodiment of the invention, a multiphase winding has the above described symmetrical layout in combination with loops having at least six sides and the above described feature of sections of winding covering 360/2n degrees (60° winding for three-phase).

In this second embodiment, the loops may have a wave winding or a lap winding as well. The wave winding and lap winding are known to a skilled person. A typical arrangement of a loop 2 with a wave winding is shown in Fig. 7 and a typical arrangement of a loop 2 with a lap winding is shown in Fig. 8. A wave loop typically turns around the axis of the winding (z axis) as shown in Fig. 7.

A three-phase imbricated 60° winding 10 with hexagonal loops according to other embodiments of the invention is illustrated with reference to Figs. 9 to 13.

Fig. 9 illustrates the winding 10 in a manner similar to Fig. 4, and using the same numerals, showing in particular some of the loops 2 and their crossing regions 5. Fig. 10 shows a detail of a preferred embodiment where the pitch of the loops is reduced.

The winding 10 comprises two sections for each phase U, V, W. Said two sections of each phase are opposite by 180° (el). Each of said sections comprises one or more coils and each coil comprises a plurality of single loops of wire. The structure of the winding 10 can be better understood by means of Figs. 1 1 and 12.

Fig. 1 1 illustrates, in a planar view, the spatial arrangement of the hexagonal loops 2 of wire, showing only one loop for each coil. The pitch p of a single loop is also shown in the figure.

Fig. 12 illustrates the structure of the winding 10 wherein each section 1 1 comprises for example two coils 12 and each coil 12 is composed of a plurality of loops 2. The coils of phases U, V, W are conventionally denoted in the figure with symbols A, B, C. A minus sign is used in Fig. 12 to denote the opposite sense of winding of the wire. In practice, each section 1 1 may comprise a higher number of coils 12.

The two sections 1 1 of each phase are opposite by 180° as shown in the figure between the connections A and -A of phase U. The figure illustrates also the angular distance (offset) w between consecutive phases, which is 60° in this example and more generally is 360 / (2n) for n-phase winding, and the opening p of the coils of the lap winding. The distance w is taken between the centres of coils 12 or of groups of coils.

The pitch (or opening width) p of a coil 12 can be defined as the distance between the axial sides of a median loop 13, illustrated by the dotted line of Fig. 12.

According to a preferred feature of the invention, the pitch p is reduced to less than 180° (el), preferably around 100° (el). The advantage of a shorter pitch is a corresponding reduction of the crossing between the loops, as illustrated in Fig. 10.

The cross sections of the winding 10 according to planes P1 and P2, as above defined, is illustrated in Figs. 13 and 14.

Fig. 13 shows the plurality of concentric layers of coils forming the winding 10. A first (innermost) layer comprises the areas 7u, 7_V, 7_W, a second layer comprises areas 7'u, 7'_v, 7'_w and so on.

Fig. 14 illustrates the cross-sectional areas 8, namely 8uv, 8uw and 8vw, of crossing regions 5. Fig. 15 shows an example of the invention in a multiphase coreless winding comprising five phases, which may be used for example in a DC motor. When the phases comprise two opposite coils each, the offset is 36° (el) in this case.

Fig. 16 shows a cross section (first layer) of the winding of Fig. 15 according to a plane located in the coaxial region of the sides 3 and Fig. 17 shows a cross section according to a plane passing through one of the crossing regions 5. The cross sections show the areas 7, 8 as above described.

Claims

1 ) A cylindrical multiphase coreless winding, characterized by comprising loops (2) having at least six sides (3, 4) and wound with a wave winding.

2) A winding according to claim 1 , the winding comprising a plurality of sections (1 1 ), including two sections for connection with each phase, the two sections of winding of each phase being opposite by 180 electrical degrees, and the angular distance between two adjoining sections of the winding, connected to two different phases, is 360 / (2 n) electrical degrees, where n is the number of phases.

3) A winding according to claim 2, wherein each section (1 1 ) comprises a plurality of coils (12) and each coil is made of a plurality of loops.

4) A winding according to any of claims 1 to 3, having a symmetrical layout wherein:

- the winding has a main axis and comprises crossing regions (5) where the loops connected to two different phases cross each other;

- a cross section of the winding according to at least a first plane (P1 ), which is perpendicular to said main axis and intersects the axis away from said crossing regions, comprises one or more concentric layers which are formed by a symmetrical distribution, relative to said main axis, of cross-sectional areas (7) containing the loops of different phases, each of said cross sectional areas containing loops of only one phase, and

- a cross section of the winding according to at least a second plane (P2), which is perpendicular to said main axis and intersects the axis in a crossing region, comprises one or more concentric layers which are formed by contiguous cross-regional areas (8), each area containing a uniform distribution of loops of two phases.

5) A winding according to claim 4, wherein the loops of each phase are wound simultaneously.

6) A winding according to any of the previous claim, wherein each loop comprises two axially extended active sides (3).

7) A winding according to claim 6, said active sides being parallel or substantially parallel to a main axis of the winding.

8) A winding according to claim 7, said active sides being inclined relative to said axis.

9) A winding according to claim 8, said active sides being inclined relative to the axis by a small angle which is preferably not greater than 10 mechanical degrees.

10) A winding according to any of the previous claims, said loops having hexagonal shape.

1 1 ) A cylindrical multiphase coreless winding, characterized in that: the winding comprises a plurality of sections (1 1 ), including two sections for connection with each phase, the two sections of winding of each phase being opposite by 180 electrical degrees, and the angular distance between two adjoining sections of the winding, connected to two different phases, is 360 / (2 n) electrical degrees, where n is the number of phases; each of said sections comprises a plurality of loops (2) of wire, and the loops have at least six sides; the winding has a main axis and comprises crossing regions where the loops connected to two different phases cross each other; and the winding has a symmetrical layout wherein:

- a cross section of the winding according to at least a second plane, which is perpendicular to said main axis and intersects the axis in a crossing region, comprises one or more concentric layers which are formed by contiguous cross-regional areas (8), each area containing a uniform distribution of loops of two phases.

12) A winding according to claim 1 1 , wherein the loops of each phase are wound simultaneously.

13) A winding according to claim 1 1 or 12, wherein each section comprises a plurality of coils and each coil is made of a plurality of loops.

14) A winding according to any of claims 1 1 to 13, wherein each loop comprises two axially extended active sides.

15) A winding according to claim 14, said active sides being parallel or substantially parallel to a main axis of the winding.

16) A winding according to claim 15, said active sides being inclined relative to said axis.

17) A winding according to claim 16, said active sides being inclined relative to the axis by a small angle which is preferably not greater than 10 mechanical degrees.

18) A winding according to any of claims 1 1 to 17, said loops having hexagonal shape. 19) A winding according to any of claims 1 1 to 18, said loops being wound with a wave winding.

20) A winding according to any of claims 1 1 to 18, said loops being wound with a lap winding.

21 ) A winding according to claim 20, wherein the loops have a pitch of less than 180 electrical degrees.

22) A winding according to claim 21 , said pitch being comprised between 360 / (2-n) and 360 / n, wherein the number n of phases is 2 or greater.

23) A winding according to claim 21 , wherein the number of n phases is equal to 3 and said pitch is around 100 electrical degrees.

24) A motor comprising at least one of a rotor and a stator having a coreless winding according to any of the previous claims.