WO2010070405A2

WO2010070405A2 - Slotted stator section of an axial flux electric machine and process for making the slotted stator section of an axial flux electric machine.

Info

Publication number: WO2010070405A2
Application number: PCT/IB2009/007578
Authority: WO
Inventors: Fabio Lucchi
Original assignee: Fabio Lucchi
Priority date: 2008-12-19
Filing date: 2009-11-25
Publication date: 2010-06-24
Also published as: WO2010070405A3; IT1392358B1; ITRN20080062A1

Abstract

To make the slotted stator section (1) of an axial flux electric machine, a toroidal core (2), extending in a ring around a reference axis (20), comprises a central ring (21) in turn extending lengthways along the annular centre line (200) of the core (2) and defines a profile (210) transversal to the annular centre line of the core (2). At least one interruption (211) in the central ring (21) is used for fitting to the central ring both a plurality of toroidal coils (3), each by- means of its central through-hole (300) whose shape matches the transversal profile (210), and a plurality of toroidal elements (22) made of magnetic material, each by means of a respective central through-hole (220) whose shape matches the profile (210). Coils (3) and toroidal elements (22) are alternated and adjacent to each other along the annular centre line (200) of the core (2).

Description

Slotted stator section of an axial flux electric machine and process for making the slotted stator section of an axial flux electric machine

Technical Field

This invention relates to a slotted stator section of an axial flux electric machine.

This invention also relates to a process for making a slotted stator section of an axial flux electric machine .

Background Art

Generally speaking an electric machine comprises a stationary part, commonly referred to as "stator section" (or simply "stator"), and a mobile part, both equipped with windings of electrical conductor and/or sources of a magnetic and/or electromagnetic field. Together with the machine structure, these windings and sources always form both an electric circuit (defined as an assembly of structures and materials with an electric current and/or an electric field flowing through it) and a magnetic circuit (defined as an assembly of structures and materials with a magnetic field flowing through it) . In order to operate, the electric machine uses electromagnetic induction (produced by the concatenation of magnetic field fluxes with the electric windings) and/or electromagnetic forces (generated by the magnetic/electromagnetic field sources on the electric windings with current flowing through them and/or on the other magnetic/electromagnetic field sources) . Some electric machines (for example, electric motors) can convert the electric current circulating in the electric windings into movement of the mobile part relative to the stator section. Other electric machines (for example, generators) can generate electric current and/or electromagnetic force in the electric windings using the motion of the mobile part relative to the stator section. An electric machine of this kind can normally be used in both ways (that is, as a generator and as a motor) . The windings can be made around a core of magnetic material in order to optimise the effect of magnetic flux concatenation with the electric windings themselves .

In one type of electric machine, the mobile part is a rotating member, also known as "rotor section" (or simply "rotor") . The axis of rotation of the rotor section is particularly important and is usually used as the reference and/or symmetry axis for the structure of the electric machine. As the rotor section moves relative to the stator section, portions of the magnetic field sources and portions of the electric windings face each other at a certain distance defining a gap between the rotor section and the stator section. There is a geometrical relation between the axis of rotation of the rotor section and the pattern of the flux lines of the magnetic field, generated by the sources, in the gap between the stator section and the rotor section. Based on this geometrical relation, machines of this kind can be broadly divided into two categories: radial flux electric machines and axial flux electric machines .

Of these two types of electric machines, radial flux electric machines are the most widespread and well known .

In this specification, the term radial flux electric machine is used to mean: an electric machine where the pattern of the magnetic field sources and of the electric windings with which the magnetic field is concatenated, is such that in the gap between the stator section and the rotor section (where source portions face winding portions during rotor section movement) the magnetic field flux lines can be likened to line segments perpendicular to the axis of rotation of the rotor section and arranged radially with respect to the axis of rotation itself.

The term axial flux electric machine, on the other hand, is used to mean: an electric machine where the pattern of the magnetic field sources and of the electric windings with which the magnetic field is concatenated, is such that in the gap between the stator section and the rotor section (where source portions face winding portions during rotor section movement) the magnetic field flux lines can be likened to line segments parallel with the axis of rotation. The most common type of axial flux electric machine comprises: a generally toroidally-shaped stator section and at least one disc-shaped rotor section facing one of the two bases of the toroid constituting the stator section. In some cases, the machine has two rotor sections, each facing one of the bases of the stator section. Some electric machines may comprise two or more toroidal stator sections, alternated with respective disc-shaped rotor sections. Stator section and rotor section are coaxial along the axis of rotation of the rotor section. The rotational shaft of the rotor section generally passes through the central hole in the toroid constituting the stator section. Usually, the rotor section mounts the magnetic field sources, preferably in the form of permanent magnets, while the stator section mounts the electric windings with which the magnetic field is concatenated. The magnetic field sources are normally distributed in a circular crown of the rotor disc that faces one of the bases of the toroid constituting the stator section. The stator section of an axial flux electric machine usually comprises a toroidal core, which mounts the electric windings of the stator section. The toroid formed by the core extends in a ring around a central axis coinciding with the axis of rotation of the rotor section. The electric windings are in the form of a plurality of coils (which are also usually toroidal) , spaced apart from each other, one after the other along the annular centre line of the core, and electrically connected to each other in various ways. In a slotted stator section of an axial flux electric machine, the core has projections (also called "teeth") extending transversally to the annular centre line of the core. Said projections (or "teeth") alternate with the coils along the annular centre line of the core and form grooves (or "slots") housing at least part of each coil. In this case, the core of the electric machine is said to be "slotted".

The core therefore has a structure in which there is a central ring (or "yoke") from which the teeth extend, between which the slots housing parts of the coils are made. Usually, the teeth are made as a single part with the core yoke. The core (and therefore also the teeth) is made of a magnetic (preferably ferromagnetic) material .

The presence of the teeth (and the slots) maximises the efficiency of the electric machine, since it allows the magnetic reluctance of the space between one coil and the next in the active region of the machine to be minimised. The "active region of the machine" is the region of the "active faces" of the coils, that is to say, the faces which, in the case of a motor, when crossed by current, are subject to magnetic forces that rotationally drive the rotor section.

To reduce eddy currents in the core (these currents, which reduce the efficiency of the electric machine, tend to be generated in the core along rings that surround the magnetic field lines) , the core is usually made by winding a metal strip spirally on itself around the shared axis of the lateral cylindrical surfaces of the core itself. In this way, the interfaces between one strip and the next are distributed crossways relative to the path that would be followed by the eddy current rings, thus tending to break it and to reduce its effect. To make the teeth as a single part with the core, the strip, before being wound on itself or during the winding operation, is punched in such a way that slots and teeth are automatically formed when it is wound on itself.

The electric machine also comprises a casing (or enclosure) which the stator section is usually fixed to and which surrounds at least the latter around its axis .

Prior art axial flux electric machines with a slotted stator section have several disadvantages. In particular, the presence of the teeth makes the task of making the electric windings particularly troublesome. In particular, it is very difficult to insert each coil in the respective slot. On the traditional core the teeth are made as a single part with the core yoke (or central ring) . Therefore, it is not possible to fit a ready-formed coil in the slots. The only solution is to take a length of electrical conductor (usually in the form of a band) long enough to form the coil and wind it on the yoke in a slot between two consecutive teeth. The process of winding the coils on the yoke is complex and must be carried out with precision and without damaging the electrical conductor coating. Said coating is usually made by enamelling or covering with a material suitable for electrically insulating one turn of the coil from another. Damage to the electrical conductor insulating coating could therefore compromise the electrical insulation between the turns of the coil. When it is wound around the core yoke, the turn of the coil may be damaged by rubbing against the strip forming the teeth and yoke. Disclosure of the Invention

This invention is intended for axial flux electric machines with a slotted stator section and in this context the technical purpose which forms the basis of this invention is to propose a slotted stator section of an axial flux electric machine and a process for making a slotted stator section of an axial flux electric machine which overcome the above-mentioned disadvantages of the prior art.

In particular, this invention has for an aim to provide a slotted stator section of an axial flux electric machine and a process for making a slotted stator section of an axial flux electric machine able to render assembly of the stator section particularly simple and effective.

The stated technical purpose and specified aims, as well as other aims which are more apparent in the description which follows, are achieved, in accordance with the invention, by a slotted stator section of an axial flux electric machine and a process for making a slotted stator section of an axial flux electric machine having the structural and functional features described in the appended independent claims, further embodiments of the same being described in the dependent claims .

Brief Description of the Drawings

Other characteristics and advantages of the invention are more apparent in the description which follows, with reference to a preferred, non-limiting, embodiment of a slotted stator section of an axial flux electric machine and a process for making a slotted stator section of an axial flux electric machine, as illustrated in the accompanying drawings, in which: Figure 1 is a plan view of a stator section of an axial flux electric machine made in accordance with the invention, with some parts cut away (in particular the casing) to better illustrate some details of the invention (in particular the core equipped with coils) ; Figure 2 is a plan view of half of a central ring of the core of a stator section of an electric machine made in accordance with the invention, in particular forming a segment of the central ring, on which several toroidal elements made of magnetic material and several electrical conductor coils are inserted, both arranged correctly relative to each other and about to be put in position;

Figure 3 is a schematic perspective view of the half of the central ring of Figure 2;

Figure 4 is a perspective view of an embodiment of an electrical conductor coil having the shape of a toroidal solid and designed to be inserted on the central ring of the core of the stator section made in accordance with the invention;

Figure 5 is a perspective view of an embodiment of a toroidal element made of magnetic material designed to be inserted on the central ring of the core of the stator section made in accordance with the invention; Figure 5a is a schematic view of the connection between the toroidal elements and the coils in an embodiment of the invention;

Figure 6 is a view of a complete central ring of a core of a stator section made in accordance with the invention, on which several toroidal elements made of magnetic material and several electrical conductor coils are already inserted, both arranged correctly relative to each other and about to be put in position; Figure 7 is a plan view of two segments of a central ring, each in particular forming one half of a central ring in the same way as the segment of Figure 1; the two segments of central ring being shown near each other but a certain distance apart, the arrows indicating a possible assembly movement for the two segments to form the complete central ring; Figure 8 is a plan view of a central ring similar to that of Figure 6, with an alternative embodiment of the interruption;

Figure 9 is a view similar to that of Figure 1, of a stator section of an axial flux electric machine made in accordance with the invention, showing a plurality of segments (in the case illustrated there are 4) forming the central ring, the corresponding plurality of coils and toroidal elements, alternating with each other, being fitted on each segment.

Detailed Description of the Preferred Embodiments of the Invention

With reference to the accompanying drawings, the numeral 1 denotes a slotted stator section of an axial flux electric machine.

The slotted stator section 1 of an axial flux electric machine comprises a toroidal core 2, extending along an annular centre line 200 around a reference axis 20. The reference axis 20 is designed to coincide with an axis of rotation of a rotor section of an axial flux electric machine. Therefore, when the stator section 1 according to the invention is assembled with the relative rotor section, the reference axis 20 coincides with the axis of rotation of the rotor section. The slotted stator section 1 of an axial flux electric machine also comprises a plurality of electrical conductor coils 3 spaced apart from each other one after another along the annular centre line 200 of the core 2.

The core 2 comprises a central ring 21 which extends lengthways along the annular centre line 200 of the core 2. The central ring 21 forms a profile 210 which is transversal to the annular extension of the core 2. The profile 210 is transversal to the annular centre line 200 of the core 2. At the point of the annular centre line 200 considered, the transversal profile 210 forms a section of the central ring 21 of the core 2 which is transversal to the annular centre line 200 of the core 2.

The core 2 also comprises a plurality of toroidal elements 22 made of magnetic material, fitted to the central ring 21 by means of a respective central through-hole 220 whose shape matches the transversal profile 210 of the central ring 21. The toroidal elements 22 are spaced apart one after another along the annular centre line 200 of the core 2. The central ring 21 and the plurality of toroidal elements 22 together form the core 2 teeth and slots. The core 2 is completed by the combination of the central ring 21 with the toroidal elements 22.

Each coil 3 has the shape of a toroidal solid 30 having a respective central through-hole 300 whose shape matches the transversal profile 210 of the central ring

21. Each coil 3 is also fitted to the central ring 21 by means of its central through-hole 300.

Along the annular centre line 200 of the core 2, the central ring 21 has at least one interruption 211, allowing the toroidal elements 22 and coils 3 to be fitted

The coils 3 and toroidal elements 22 are alternated and adjacent to each other along at least one stretch, or along at least a plurality of stretches, of the annular centre line 200 of the core 2.

The stator section 1 of an electric machine according to the invention is easy to assemble.

The invention also relates to a process for making a slotted stator section 1 of an axial flux electric machine. The process according to the invention is used to make a stator section of an electric machine in accordance with the invention. The process comprises the following steps:

- taking the central ring 21;

- taking the plurality of toroidal elements 22; - taking the plurality of coils 3 which are in the form of toroidal solids 30; using the at least one interruption 211 in the central ring 21, fitting to the central ring^' 21, alternating them with one another, a coil 3 and a toroidal element 22 by means of their respective central through-holes 220, 300 and repeating the operation a plurality of times until at least one portion, or at least a plurality of portions of the central ring 21 is full of coils 3 alternated with toroidal elements 22 and adjacent to these. All of the elements for making the stator section 1 according to the invention can be made separately. In particular, the coils 3 can be made in a very simple way by winding the conductor cable (for example a copper band) already covered with an insulating sheath, until the toroidal solid 30 is obtained. Before being inserted on the central ring 21, the coil 3 obtained in this way can be covered with insulating material (for example by resin-coating) . The coil 3 which can be obtained is very sturdy and the simplicity of the operation required to apply it to the central ring 21 makes the likelihood of damaging it negligible. The toroidal elements 22 made of magnetic material can also be easily fitted to the central ring 21 and, by alternating them with the coils 3 during fitting, it is possible to reconstruct (easily and without the risk of damaging the conductor insulating sheaths) the structure of a core 2 having slots in which the coils 3 are inserted.

The toroidal elements 22 made of magnetic material may be made in various shapes and/or sizes, depending on requirements. Even the shape of the cross-section of the ring which defines the geometry of the toroidal element 22 may vary as appropriate and/or according to constraints and requirements relative to the stator section to be made. Figures 3, 5, 6 show toroidal elements 22 with a substantially rectangular outer edge. In particular, the toroidal elements 22 may comprise two longitudinal teeth 225, 226, joined together by two transversal jumpers 227, 228 (see Figure 5) .

The toroidal elements 22 may be made by packing together thin strips and making the strips integral with each other using adhesives or suitable fixing means obvious to experts in the field. This solution could be preferable in the case of large axial flux electric machines, which need a large stator section 1 to be made. The plane in which the packed strips lie should preferably be such that they are angled to minimise eddy currents in the core 2 (similarly to what is done in the case of the central ring 21, if the latter is made by winding on itself, around the reference axis 20, a metal strip of suitable length, width and thickness) .

The magnetic material of which the toroidal element 22 is made may be selected from: iron, iron-silicon alloys, iron-nickel alloys, iron-cobalt alloys, Somaloy and combinations of them.

Each toroidal element 22 may be made of microcrystalline sintered magnetic material. The magnetic material is preferably Somaloy. The term "Somaloy" indicates a commercial product consisting of micro-granules of iron-based magnetic material, covered with an insulating film and sintered together. The structure of "Somaloy" allows toroidal elements 22 to be made with a structure which minimises eddy currents. Thanks to the invention, a slotted stator section 1 of an axial flux electric machine which is optimised from a magnetic viewpoint is easily obtained. In general, the term "heads" is used to refer to the portions of a coil 3 which, when the coil is applied to the central ring 21, are located on opposite sides of the central ring 21 along a radius of the latter centred in the reference axis 20.

In general, the term "active faces" is used to refer to the portions of a coil 3 which, when the coil is applied to the central ring 21, are located on opposite sides of the central ring 21 along a straight line parallel with the reference axis 20.

Once the stator section 1 has been installed in an axial flux electric machine, the reference axis 20 coincides with the axis of rotation of a rotor section of the electric machine. Referring to what was said in the introduction to axial flux electric machines, the active faces are therefore located in a position in which they pass through the magnetic field (generated by the sources positioned on the rotor section) in a region in which the magnetic field has flux lines parallel with the axis of rotation.

One head (outer head 33) is on the outside of the central ring 21 relative to the reference axis 20. The other head (inner head 34) is on the inside of the central ring 21 relative to the reference axis 20. As shown in the accompanying drawings, the outer heads 33 project radially outside the central ring 21 beyond the radial dimensions of the toroidal elements 22. Between two consecutive outer heads 33 along the annular centre line 200 of the core 2 there is therefore an empty space which can be used for cooling the heads and/or for anchoring the stator section 1 either to its casing or to parts outside the stator section 1. The transversal profile 210 may have various shapes and/or sizes depending on the constraints and/or requirements .

The transversal profile 210 of the central ring 21 illustrated in the accompanying drawings is rectangular. The central through-hole 220 of the toroidal elements 22 illustrated in the accompanying drawings is rectangular. The accompanying drawings show by way of example that the central through-hole 300 of the toroidal solids 30 forming the geometry of the coils 3 is rectangular. The central through-holes 220, 300 of the toroidal elements 22 and/or of the toroidal solids 30 are preferably rectangular when the transversal profile 210 of the central ring 21 is also rectangular.

In general, when referring to rectangular or polygonal shapes they are shapes which may have rounded corners (as shown in Figure 4 in the case of the central through-hole 300 of the toroidal solid 30 defining the shape of a coil 3) . In particular, in the case of the central through-holes 220, 300 of the toroidal elements 22 and/or of the toroidal solids 30, there may be widened portions of the hole (preferably having a rounded shape) at the corners of the rectangle or polygon forming the hole (as shown in Figure 5, in the case of the central through-hole 220 of a toroidal element 22) .

Along the annular centre line 200 of the core 2 groups of coils 3 and toroidal elements 22 may be alternated with stretches which have no coils 3 and toroidal elements 22. Said alternation may be regular or irregular. The stretches with no coils 3 and toroidal elements 22 may be located at particular points of the annular centre line 200 of the core 2.

The central ring 21 may be a single part comprising, at a predetermined point of the annular centre line 200 of the core 2, a transversal cut in the annular centre line 200 forming the at least one interruption 211. This type of embodiment is illustrated in Figure 6 (on the right-hand side, where the interruption 211 is indicated with a continuous line) and in Figure 8 (also on the right, where the interruption 211 is indicated with a continuous line) . The transversal cut in the annular centre line 200 has a predetermined width L along the annular centre line 200. The predetermined width L of the transversal cut may be less than (or equal to) the maximum value between the thickness of a coil 3 and the thickness of a toroidal element 22. The former case is illustrated in Figures 6 and 8 on the right in both, where the transversal cut is indicated with a continuous line. In this configuration, the predetermined width L of the transversal cut allows insertion of the coils 3 and the toroidal elements 22 on the central ring 21 by means of an elastic deformation of the central ring 21 which widens the transversal cut. The predetermined width L of the transversal cut may be greater than the maximum value between the thickness of a coil 3 and the thickness of a toroidal element 22. This latter case is illustrated in Figure 8 on the right-hand side, where the transversal cut is indicated with a dashed line. In this configuration, the predetermined width L of the transversal cut allows direct insertion of the coils 3 and the toroidal elements 22 on the central ring 21 without the need for an elastic deformation of the central ring 21 to widen the transversal cut. As is also shown with a dashed line in Figure 8, once insertion of the coils 3 and the toroidal elements 22 is complete, the central ring 21 may be completed using a filling element 216. The filling element 216 may be constrained to the rest of the central ring 21 by suitable fixing means obvious to experts in the field and/or, for example, by applying to the core 2 a casing or outer enclosure of the stator section 1 of the electric machine (not illustrated) .

The central ring 21 may have cuts transversal to the annular centre line 200 at a plurality of predetermined points (that is to say, at two or more points) of the annular centre line 200 of the core 2, each transversal cut forming a respective interruption 211. Said embodiment is illustrated, with only two transversal cuts, in Figures 6 and 8 (also considering the interruption 211 indicated with a dashed line on the Left-hand side of the figures) .

To obtain a plurality (that is to say, two or more than two) of interruptions 211, the central ring 21 may be directly made in separate parts, as illustrated in Figures 2, 3, 7 (by way of example illustrating the case of two separate parts) , Figure 9 (by way of example illustrating the case of four separate parts) . In Figure 1 the dashed line r indicates the possibility of the central ring 21 of the core 2 of this embodiment being divided into at least two parts, which are connected to each other. The central ring 21 comprises at least two consecutive segments 212, 213, 212a, 212b which can be separated from each other. Fitted to each segment 212, 213, 212a, 213a there is a respective plurality of coils 3 and a respective plurality of toroidal elements 22.

The segments 212, 213, 212a, 213a of the central ring 21 can be connected to each other by suitable connecting means obvious to experts in the field. The segments 212, 213, 212a, 213a of the central ring 21 may also be held together by applying to the core 2 a stator section 1 casing or enclosure (not illustrated) . In the case of a central ring 21 which is divided into two or more parts, that is to say, comprising at least two consecutive segments 212, 213, 212a, 212b which can be separated from each other, the process for making a slotted stator section 1 of an axial flux electric machine according to the invention comprises: - fitting to each of the segments 212, 213, 212a, 213a of the central ring 21, alternating them with one another, a coil 3 and a toroidal element 22 by means of their respective central through-holes 220, 300 and repeating the operation a plurality of times until at least one portion, or at least a plurality of portions of each of the segments 212, 213, 212a, 213a of the central ring 21 is full of coils 3 alternated with toroidal elements 22 and adjacent to these; - joining the segments 212, 213, 212a, 213a of the central ring 21 to each other.

Each of the segments 212, 213, 212a, 213a of the central ring 21 may be filled with coils 3 alternated with toroidal elements 22 and adjacent to these (see in particular the segments labelled 212a and 213a in Figure 9 and those completed with the part shown using dashed lines, also in Figure 9, labelled 212 and 213) . However, in some or all of the segments 212, 213, 212a, 213a of the central ring 21, in said completely full configuration it is possible to leave empty the end portions 215 of the segments 212, 213, 212a, 213a of the central ring 21 (this latter configuration is shown, in particular, in Figure 9 by the elements labelled 212 and 213 if only the part drawn with continuous lines is considered) .

In an embodiment of the stator section 1 of an electric machine according to the invention the coils 3 and the toroidal elements 22 are alternated, being adjacent to each other along the entire annular centre line 200 of the core 2. This configuration is illustrated in particular in Figures 1 and 9 (also considering the part of the drawing shown with dashed lines) . Again in this configuration at least one predetermined portion of the annular centre line 200 of the core 2 may have no toroidal elements 22 and coils 3. In particular, this may occur at least at an interruption 211 (either if the one or more interruptions 211 are made with one or more transversal cuts in the central ring 21, or if the one or more interruptions 211 are made using the end faces of the segments forming the central ring 21) . Correspondingly, in the process for making a slotted stator section 1 of an axial flux electric machine according to the invention, the coils 3 and the toroidal elements 22 are fitted, alternating them and placing them adjacent to each other, along the entire annular centre line 200 of the core 2. As already indicated, at least one predetermined portion of the annular centre line 200 of the core 2 may have no toroidal elements 22 and coils 3.

As illustrated in detail in particular in Figure 5, each toroidal element 22 has on its outer edge 221 a first and a second widened portion 222, 223. The first and the second widened portions 222, 223 are located on diametrically opposed sides of an axis 224 of the central through-hole 220 of the toroidal element 22 and are each designed to cover a respective outer edge portion 31, 32 of the coils 3 adjacent to the toroidal element 22 (see also Figures 3 and β, showing the connection between the first widened portions 222 and the respective coils 3, the connection between the second widened portions 223 and the respective coils 3 being identical - and not illustrated because it is hidden in the drawing. However, Figures 1, 2, 8 and 9 may identically represent either one face of the core 2 or the opposite face, thus representing both the connection between the first widened portions 222 and the respective coils 3, and the connection between the second widened portions 223 and the respective coils 3) .

The parts which are diametrically opposed relative to the axis 224 of the central through-hole 220 of the toroidal element 22 correspond to parts 214, 217 of the transversal profile 210 which are opposite each other along a direction parallel with the reference axis 20. In one embodiment, the first and second widened portions 222, 223 of each toroidal element 22 extend cantilever-style from the toroidal element 22 for a width which is less than or equal to the thickness of a coil 3 measured along an axis of symmetry of the toroidal solid 30 defining the shape of the coil 3. In this case, schematically illustrated in Figure 5a, the widened portions 222, 223 of a toroidal element 22 cover only the outer edge portions 31, 32 of the coil 3 located on one side of the toroidal element 22, the outer edge portions 31, 32 of the coil 3 located on the opposite side being covered by the widened portions 222 and 223 of another toroidal element 22 consecutive to the previous one.

In another embodiment, illustrated in Figures 1, 2, 3, 5, 6, 8 and 9, the first and second widened portions 222, 223 of each toroidal element 22 project cantilever-style from the toroidal element 22, towards each of the two directions of the axis 224 of the central through-hole 220 of the toroidal element 22, for a width which is less than or equal to half of the thickness of a coil 3 measured along the axis of symmetry of the toroidal solid 30 defining the shape of the coil 3. In this way, the outer edge portions 31, 32 of each coil 3 are each covered respectively by the part of the first and second widened portions 222, 223 of two consecutive toroidal elements located immediately at the sides of the coil 3 considered. The widened portions 222, 223 allow optimisation of magnetic flux concatenation in the core 2. The invention brings important advantages. First, the structure of the stator section according to the invention is easy to assemble. The process according to the invention is simple and easy to industrialise. The coils can be made separately, saving on production costs and reducing the risks of damage during their fitting to the core. The toroidal elements can be made separately and independently. Moreover, the structure of the stator section according to the invention allows easy maintenance and substitution of components in the stator section, where the components are removable.

The invention described may be modified and adapted in several ways without thereby departing from the scope of the inventive concept. Moreover, all of the details of the invention may be substituted by other technically equivalent elements. In practice, the embodiments of the invention may be made from any material, and in any size, depending on requirements.

Claims

1. A slotted stator section (1) of an axial flux electric machine, comprising:

- a toroidal core (2), extending along an annular centre line (200) around a reference axis (20) designed to coincide with an axis of rotation of a rotor section of an axial flux electric machine;

- a plurality of electrical conductor coils (3) , spaced apart from each other one after another along the annular centre line (200) of the core (2) ; the stator section being characterised in that the core (2) comprises:

- a central ring (21) extending lengthways along the annular centre line (200) of the core (2) and forming a profile (210) which is transversal to the annular centre line of the core (2); a plurality of toroidal elements (22) made of magnetic material, fitted to the central ring (21) by means of a respective central through-hole (220) having a shape matching the transversal profile (210) of the central ring (21) and spaced apart from each other one after another along the annular centre line (200) of the core (2), the central ring (21) and the plurality of toroidal elements (22) together forming the teeth and slots of the core (2) ; and also being characterized in that:

- each coil (3) has the shape of a toroidal solid (30) having a respective central through-hole (300) whose shape matches the transversal profile (210) of the central ring (21) ;

- each coil (3) is fitted to the central ring (21) by means of its respective central through-hole (300) ; the coils (3) and toroidal elements (22) are alternated and adjacent to each other along at least one stretch, or along at least a plurality of stretches, of the annular centre line (200) of the core

(2);

- the central ring (21) having, along the annular centre line (200) of the core (2) , at least one interruption (211) to allow the toroidal elements (22) and the coils (3) to be fitted.

2. The stator section (1) of an electric machine according to claim 1, characterised in that the coils (3) and the toroidal elements (22) are alternated, being adjacent to each other, along the entire annular centre line (200) of the core (2) .

3. The stator section (1) of an electric machine according to claim 1 or 2, characterised in that the central ring (21) comprises at least two consecutive segments (212, 213; 212a, 213a) which can be separated from each other, a respective plurality of coils (3) and a respective plurality of toroidal elements (22) being fitted to each segment (212, 213; 212a, 213a) .

4. The stator section (1) of an electric machine according to claim 1 or 2 or 3, characterised in that the transversal profile (210) of the central ring (21) is rectangular.

5. The stator section (1) of an electric machine according to any of the foregoing claims, characterised in that each toroidal element (22) has on its outer edge (221) a first and a second widened portion (222, 223) , located on diametrically opposed sides of an axis (224) of the central through-hole (220) of the toroidal element (22) and each designed to cover a respective outer edge portion (31, 32) of the coils (3) adjacent to the toroidal element (22) .

6. The stator section (1) of an electric machine according to claim 5, characterised in that the parts which are diametrically opposed relative to the axis

(224) of the central through-hole (220) of the toroidal element (22) correspond to parts (214, 217) of the transversal profile (210) which are opposite each other along a direction parallel with the reference axis (20) .

7. The stator section (1) of an electric machine according to claim 6, characterised in that the first and second widened portions (222, 223) of each toroidal element (22) extend cantilever-style from the toroidal element (22) for a width which is less than or equal to the thickness of a coil (3) measured along an axis of symmetry of the toroidal solid (30) defining the shape of the coil (3) .

8. The stator section (1) of an electric machine according to claim 7, characterised in that the first and second widened portions (222, 223) of each toroidal element (22) extend cantilever-style from the toroidal element (22) towards each of the two directions of the axis (224) of the central through-hole (220) of the toroidal element (22), for a width which is less than or equal to half of the thickness of a coil (3) measured along the axis of symmetry of the toroidal solid (30) defining the shape of the coil (3) .

9. The stator section (1) of an electric machine according to any of the foregoing claims, characterised in that each toroidal element (22) is made of microcrystalline sintered magnetic material.

10. A process for making a slotted stator section (1) of an axial flux electric machine, characterised in that the stator section (1) to be made is as described in any of the claims from 1 to 9 and the process comprises the following steps:

- taking the central ring (21) ;

- taking the plurality of toroidal elements (22);

- taking the plurality of coils (3) which are in the form of toroidal solids (30);

- using the at least one interruption (211) in the central ring (21) , fitting to the central ring (21) , alternating them with one another, a coil (3) and a toroidal element (22) by means of their respective central through-holes (220, 300) and repeating the operation a plurality of times until at least one portion, or at least a plurality of portions of the central ring (21) is full of coils (3) alternated with toroidal elements (22) and adjacent to these.

11. The process for making a slotted stator section (1) of an axial flux electric machine according to claim 10, characterised in that the coils (3) and the toroidal elements (22) are fitted, alternating them and placing them adjacent to each other, along the entire annular centre line (200) of the core (2) .

12. The process for making a slotted stator section (1) of an axial flux electric machine according _, to claim 10 or 11, characterised in that the stator section (1) to be made is as described in claim 3, or any of the claims from 3 to 9 when dependent on claim 2, and the process comprises:

- fitting to each of the segments (212, 213; 212a, 213a) of the central ring (21) , alternating them with one another, a coil (3) and a toroidal element (22) by means of their respective central through-holes (220, 300) and repeating the operation a plurality of times until at least one portion, or at least a plurality of portions of each of the segments (212, 213; 212a, 213a) of the central ring (21) is full of coils (3) alternated with toroidal elements (22) and adjacent to these;

- joining the segments (212, 213; 212a, 213a) of the central ring (21) to each other.

13. The process for making a slotted stator section (1) of an axial flux electric machine according to claim 12, characterised in that each of the segments (212, 213; 212a, 213a) of the central ring (21) is filled with coils (3) alternated with toroidal elements (22) and adjacent to these.