DESCRIPTION

[001] The present description refers to the technical field of reluctance electric machines, such as reluctance electric motors or generators, and more in particular it concerns a reluctance electric machine as defined in the preamble of claim 1.

[002] As known, reluctance electric machines are electric machines which are particularly interesting in terms of versatility, strength, relative structural simplicity and cost-effectiveness. On the other hand, such types of electric machines have some drawbacks that to this day have contributed towards preventing them from becoming widespread in some fields, like for example, and not for limiting purposes, its application in electric and/or hybrid traction vehicles. Despite the aforementioned advantages, reluctance electric machines normally have, for example, "torque ripple" values (i.e. the variation of the torque in outlet as the position of the rotor varies) that are relatively high which make such motors not very suitable for some types of application. Moreover, in particular, concerning reluctance electric motors, the values of the outlet torque, and more in general of the efficiency of the motor, can be improved with respect to the solutions of the prior art.

[003] One general purpose of the present description is that of providing a reluctance electric machine that is capable of at least partially solving or avoiding the drawbacks described above with reference to the prior art .

[004] This and other purposes are achieved with a reluctance electric machine as defined in claim ^" 1 in its most general form, and in the claims that are dependent on this one, in some particular embodiments.

[005] Concerning this, it should be noted that the fact that the reluctance machine according to the present invention has a stator with a bar winding, makes it possible to advantageously increase the number of stator slots, for the same inner diameter of the stator, thanks to the fact of being able to use a greater slot filling coefficient with respect to the case of a stator that is provided with a winding having a round wire (i.e. a winding made by means of electrically conducting wires having a circular cross- section) of the type that is normally used in known reluctance electric machines. Thanks to the possibility of increasing the number of slots of the stator it is possible to make the rotor of the reluctance machine by increasing the number of flux barriers, which leads to a reduction of torque ripple and, in the case of a motor, also an increase in the outlet torque. Moreover, the possibility of increasing the number of stator slots, advantageously makes it possible to improve the waveform of the flux at the air gap.

[006] Other objects of the present invention are also a wheel with an in-wheel motor and a traction motor as defined in claim 11. Another object of the present invention is also an auxiliary device for a vehicle as defined in claim 12.

[007] The invention shall become clearer from the following detailed description of its embodiments, given as an example and therefore in a non-limiting manner in relation to the attached drawings, in which: ^• Fig.l is a flat cross-section view of a reluctance machine in accordance with a currently preferred embodiment;

^■ Fig. 2 is a perspective view of the stator of the reluctance machine of Fig. 1;

^■ Fig. 3 is a partially flat section view, such a view being a section that is perpendicular with respect to the rotation axis of the rotor of the reluctance machine of Fig. 1; and

Fig. 4, is a flat section view showing an enlarged detail of Fig. 3, such a detail, in Fig. 3, being delimited by two broken lines.

[008] In the attached figures same or similar elements shall be indicated with the same reference numerals. It should be moreover noted that in the following description, the expression "radial" or other similar expressions used to describe a part of a reluctance machine should be intended referred to the rotation axis of the rotor of such a machine.

[009] Figure 1 shows a section view of a reluctance machine in accordance with a currently preferred embodiment, which is wholly indicated with reference numeral 1. In accordance with a preferred embodiment, the reluctance machine 1 is preferably a reluctance motor 1 and more preferably a synchronous switched reluctance motor (SRM) . Even more preferably, the reluctance machine 1 is a three-phase AC Brushless synchronous switched reluctance motor. In accordance with one preferred embodiment the reluctance motor 1 is designed to be used as a traction motor, for example in an electric wheel with an in-wheel motor (not represented) of an electric and/or hybrid traction vehicle, like for example an electric traction vehicle for agricultural use, for example a so-called "e- sprayer". It should be noted, in any case, that an electric motor in accordance with the present description is not limited to the application in a vehicle for agricultural use but it can be used in general, for example and not for limiting purposes as a traction motor, in any type of electric and/or hybrid traction vehicle. It should be further noted in general, as shall be described later in the description, that a reluctance electric machine according to the present description is not limited to the application as a traction motor for a vehicle.

[0010] The motor 1 comprises a stator 2 and a rotor 3, which are preferably housed inside a housing 4. The rotor 3, which is mounted coaxially with respect to the stator 2, comprises a motor shaft 5 which is rotatably mounted to rotate around a rotation axis XI.

[0011] Fig. 2 shows an axonometric view of the stator 2 of the motor 1. The stator 2 is provided with a stator winding which is wholly indicated with reference numeral _. 6. Advantageously, the winding 6 is a so-called bar winding 6. In a per se known manner, the bar winding 6 is a winding that is made by means of a plurality of electric bar conductors having a rectangular cross-section. In the example the stator 2 comprises a plurality of electric bar conductors having a "flat" rectangular section, that is to say a section having a rectangular shape in which two sides of the section have dimensions that are smaller with respect to the other two. In other words the bar conductors of the winding 6 are preferably flat conductors, since they have a pair of opposite faces that are spread apart from one another by a distance that is greater than the distance between the remaining two opposite faces. In any case, it should be noted that the teachings of the present description are not limited to a bar winding with flat conductors. In other words, in general the bar winding 6 can comprise bar conductors having a generally rectangular section, where by rectangular we mean both the "flat" section and the square section that represents a particular case of a rectangular section. It should be further noted that a conductor having a rectangular section can also be obtained starting from a so-called round wire, that is to say a conductor having a circular cross-section. This could be obtained for example by pressing a round wire on four sides so that such a wire has a generally rectangular cross-section.

[0012] In accordance with one embodiment, the stator 2 is a stator of the type that is analogous to the stator described in the international patent application published with number WO2013/005238 to the Applicant. In other words, by using the terminology used in such a patent application, Fig. 2 shows the stator 2 seen from the "welding side" and it comprises a plurality of "basic conductors" 7 and a plurality of "special conductors" 8, 9, 10 which are interconnected with one another so as to obtain the bar winding 6. The basic conductors 7 are obtained starting from preformed "U" and/or "P"-shaped conductors, also known in the field as "basic preformed conductors", which typically have two legs alongside one another with different lengths each having an end portion that is joined through a connection portion to the other one of the two legs and an opposite free end portion. The special conductors 8, 9, 10 are, on the other hand, conductors that are used for finishing off the winding 6 and comprise for example jumpers 8, phase terminals 9, and at least one neutral point 10. In a per se known manner the basic conductors 7 have the respective legs that are housed in stator slots 12 that are provided in a stator core 13 of the stator 2. In the example the stator 2 comprises a plurality of slots 12. More in particular the stator 2 comprises a circular array of slots 12 each of which receives a plurality of portions 14 (Fig. 3) of electric bar conductors 7-10 which are radially aligned with one another. In accordance with a preferred embodiment, each slot 12 houses four portions 14. More in particular such radially aligned longitudinal portions 14 can all consist of leg portions of the basic conductors 7 or of a plurality of legs of basic conductors 7 and of portions of the phase terminals 9. In the non-limiting example, the stator 2 comprises fifty-four slots 12.

[0013] Since a stator with bar winding and electric bar conductors with a rectangular section are widely known to a man skilled in the art, the stator 2 shall not be described any further in the present description.

[0014] Returning now to Fig. 1, the rotor 3 is preferably made from a plurality of laminations, which are preferably made in ferromagnetic material, which are stacked on top of one another so as to form the rotor 3. In accordance with a preferred embodiment, the rotor 3 is in particular a rotor of the so-called "skewed" type. In other words the rotor 3 is preferably divided into a plurality of rotor segments 15, 16, 17, 18 with a generally cylindrical shape, in which each segment is rotated around the rotation axis XI of the rotor by a predetermined angle with respect to the adjacent segment. In accordance with one preferred embodiment, the rotor 3 is divided into four rotor segments 15, 16, 17, 18. It should in any case be noted that the skewed rotor 3 can generally also be made in a different manner. For example, in accordance with one embodiment, the skewed rotor 3 can be obtained by rotating the single laminations that form the rotor with respect to one another in a substantially continuous manner rather than rotating rotor segments, having a relatively greater thickness with respect to that of the single lamination, with respect to one another .

[0015] With reference to Fig. 3, such a figure shows a section view of the stator 2 and the rotor 3. In particular in Fig. 3 the stator 2 and the rotor 3 are partially represented, since, for example, the motor shaft 5 is not represented. More in particular, in the example in which both the stator 2 and the rotor 3 are obtained through a plurality of laminations that are stacked on one another, the view of Fig. 3 shows in practice a lamination of the stator 2 and a lamination of the rotor 3.

[0016] As can be noted in Fig. 3, in accordance with a preferred embodiment the rotor 3 seen in section comprises a plurality of groups of flux barriers, in the example there are six groups of flux barriers, each of which comprises a plurality of flux barriers 19, 20, 21, 22. As known, the flux barriers are slots or air spaces that are provided on a lamination of the rotor lamination and that are obtained for example through shearing of the laminations of the rotor. The flux barriers are practically regions having a magnetic permeability value that is relatively low with respect to the magnetic permeability value of the parts of the lamination of the rotor that separate the flux barriers from one another and that are typically called "flux guides". In the example each group of flux barriers of the lamination of the rotor of Fig. 3 preferably comprises four flux barriers 19, 20, 21, 22. In general, in the example, all the small rotor plates have a structure that is the same as that of the small rotor plate of Fig. 3. The aforementioned groups of flux barriers are distributed around the rotation axis XI of the rotor. In accordance with a preferred embodiment such groups of flux barriers are the same as one another and are preferably angularly spaced in an even manner around the shaft 5 or around the rotation axis XI. The flux barriers 19-22 of each group are preferably separated from one another in the radial direction. Preferably, the flux barriers of each group have decreasing dimensions going from the radially innermost flux barrier 19 to the radially outermost flux barrier 22. In other words, for each group of flux barriers, the flux barrier 19, which is the closest to the shaft 5, (or that is closest to a shaft hole 23 which is intended to receive the shaft 5) is the biggest flux barrier, whereas the flux barrier 22, which is the flux barrier that is farthest from the shaft 5 or from the shaft hole 23, is the smallest flux barrier .

[0017] Again with reference to Fig. 3, in accordance with a preferred embodiment each flux barrier 19-22 has a shape that is substantially that of an isosceles trapezium without a greater base.

[0018] With reference to Fig. 4, in accordance with a preferred embodiment the rotor seen in section, or the small rotor plate, comprises a plurality of peripheral bridges 25, 26, 27, 28 each of which is defined between one end 29, 30, 31, 32 of one of the flux barriers 19- 22 and the radially external edge 33 of the section of the rotor 3. In the example, the outer edge 33 in particular has a generally circular shape. In accordance with one preferred embodiment two peripheral bridges 25-28 respectively are associated with the two opposite ends of each flux barrier of each of the aforementioned groups of flux barriers. In the example two bridges 25 are associated with each barrier 19, two bridges 26 are associated with each barrier 20, two bridges 27 are associated with each barrier 21 and two bridges 28 are associated with each barrier 22. It should be noted that in accordance with an advantageous embodiment, considering a group of flux barriers, the peripheral bridges 25-28 have a decreasing width going from the radially innermost flux barrier to the radially outermost flux barrier. By "width" of each bridge 25-28 we mean in particular a distance of the relative end 29-32 of the flux barrier from the edge 33 radially outside the rotor. Preferably, such a width is a radial or substantially radial width in the sense that such a distance is measured in the radial or substantially radial direction. In other words, in accordance with one advantageous embodiment the peripheral bridges 25-28 have a decreasing dimension going from the largest flux barrier 19 to the smallest flux barrier 22. For example, in accordance with a preferred embodiment, the bridges 25 have a width dl=2mm, the bridges 26 have a width d2=1.8mm, the bridges 27 have a width d3=1.6mm and the bridges 28 have a width d4=1.5mm. It should be noted that in accordance with one embodiment the peripheral bridges 25-28 can also be designed in a different manner from that which is described above, in which each peripheral bridge 25-28 has a constant width or section and in which the widths or sections of the peripheral bridges 25-28 radially decrease from the innermost flux barrier to the outermost flux barrier. For example, in accordance with one embodiment each peripheral bridge 25-28 can in turn have a width that varies instead of a constant width or section or the bridges 25-28 can each have a constant width or section but the dimensions of the bridges 25-28 do not vary in a decreasing manner going from the radially innermost flux barrier to the radially outermost flux barrier. In other words, the teachings forming the basis of the present description can be applied in general to any type of variation of the width or section of the peripheral bridges.

[0019] The Applicant has observed that having peripheral bridges, having a width that can vary, in the rotor, advantageously makes it possible on one hand to not use inner bridges that divide the flux barriers in the rotors of the reluctance machines of the prior art and on the other hand, at the same time, makes it possible to ensure a particularly strong structure of the rotor that makes it possible for the latter to handle even high number of revolutions, for example 7000-8000 rpm. Moreover, thanks to the possibility of not providing the aforementioned inner bridges, it is possible to improve the magnetic flux in the rotor allowing there to be an improvement in the performance of the reluctance electric machine with respect to the solutions of the prior art in which inner and peripheral bridges are provided. In particular, the Applicant has observed that a switched reluctance electric machine with a rotor in which there are peripheral bridges having a width that can vary, as described above, makes it possible to obtain an optimal compromise between good performance of the motor (greater than 95%), a good torque ripple and satisfactory mechanical strength of the rotor.

[0020] According to what is described above, it is in any case possible therefore to understand how a reluctance machine of the type described above makes it possible to achieve the purposes mentioned above with reference to the state of the art.

[0021] As indicated above, the fact of having a stator provided with a bar winding in a reluctance machine according to the present description, advantageously makes it possible to increase the number of stator slots, for the same inner diameter of the stator, thanks to the fact that it is possible to use a greater slot filling coefficient with respect to the case of a stator that is provided with a winding with a round wire (that is to say a winding that is made by means of electrically conductive wires having a circular cross- section) of the type that is normally used in known reluctance electric machines. Thanks to the possibility of increasing the number of slots in the stator it is possible to make the rotor of the reluctance machine by increasing the number of flux barriers, which leads to a reduction of the torque ripple and, in the case of a motor, also an increase in the outlet torque. Moreover, the possibility of increasing the number of stator slots, advantageously makes it possible to improve the wave form of the flux at the air gap.

[0022] It is clear that numerous modifications and/or variants can be carried out on a reluctance electric machine according to the present description.

[0023] For example, although a switched reluctance motor (SRM) has been described, it is clear that the teachings of the present description can be applied to any reluctance motor, like for example an assisted reluctance motor, that is to say a reluctance motor in which the magnets, like for example permanent magnets, for example ferrite magnets or other types of magnets, are fixed inside the flux barriers of the rotor. In particular, the teachings of the present description can be applied to a permanent magnet assisted synchronous reluctance motor (PMa-SynRM) .

[0024] It should further be noted that although an electric reluctance motor has been described, the teachings forming the basis of the present description can be applied to any reluctance electric machine, and in particular to any electric reluctance generator, like for example a switched reluctance electric generator or an assisted reluctance electric generator. A man skilled in the art, who knows the structure of an electric reluctance generator, can easily apply the teachings of the present description to such a type of electric generator. In order to keep the description brief the structure of a reluctance electric generator is not therefore described in the present description.

[0025] It should furthermore be noted that the applications of a reluctance motor according to the present description are not limited to a use as a traction motor in an electric and/or hybrid traction vehicle. Indeed, a reluctance motor and more in general a reluctance electric machine according to the present description can for example be used in general in an auxiliary device for a vehicle, like for example a water pump, an oil pump, a conditioner, a power steering, a servo-brake, an electric actuator, etc.. Even more in general, it should be noted that the main principles forming the basis of the present description can be extended to any application in which a reluctance electric machine can be used provided with a stator comprising a bar winding.

[0026] It should be understood that the number and the type of special conductors used, just like the number of basic conductors, can vary in general according to the specific design requirements.

[0027] Furthermore, it should be noted that a reluctance machine according to the present description is not limited to a stator in which each slot receives four portions of radially aligned bar conductors. For example, in accordance with a variant embodiment each stator slot can receive only two portions of radially aligned bar conductors. It should be noted that the number of portions of radially aligned bar conductors that are received in each stator slot, can vary in general according to the specific design requirements and can thus also be in a number other than two or four as indicated above.

[0028] Without affecting the principle of the invention, the embodiments and the manufacturing details can be widely varied with respect to what has been described and illustrated purely as an example and not for limiting purposes, without for this reason departing from the invention as defined in the attached claims.