DESCRIPTION

[001] The present description refers to the technical field of reluctance electric machines, such as for example an electric generator or motor, and more in particular it concerns a rotor of a switched or assisted reluctance machine as defined in the preamble of claim 1.

[002] As known, reluctance electric machines are electric machines which are particularly interesting for their characteristics 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 advantages listed above, 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 machines 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] Among reluctance electric machines so-called switched reluctance electric machines are in particular known. A switched reluctance electric machine normally has a rotor obtained through a plurality of stacked laminations of the rotor. Each of such laminations of the rotor is provided with a plurality of groups of flux barriers which are distributed around the rotation axis of the rotor. As known, such flux barriers are basically slots that are obtained in the laminations of the rotor for example through shearing of the laminations of the rotor themselves. Each group of flux barriers normally comprises a plurality of flux barriers which are separated from one another in the radial direction. It is provided for there to be one or more internal bridges that divide each flux barrier into two or more parts. Moreover, for each group of flux barriers, the rotor comprises a plurality of peripheral bridges each of which is defined between one end of one of the flux barriers and the radially external edge of the lamination of the rotor. Such peripheral bridges are typically all the same as one another, in the sense that the width of the bridges situated at the end of each flux barrier remains constant from the radially innermost flux barrier to the radially outermost flux barrier of each group of flux barriers. Ideally it would be desirable for the inner and peripheral bridges to not be present in the rotor. Indeed, such bridges have a distortion effect on the flux paths of the magnetic field inside the rotor. On the other hand, the aforementioned inner and peripheral bridges are considered necessary for ensuring that the rotor is sufficiently strong. Normally, such bridges are therefore designed in a way such as to have a width that is as small as possible.

[004] In addition to the switched reluctance electric machines discussed above there are also reluctance electric machines called assisted reluctance electric machines. Such assisted reluctance machines are provided with a rotor that differs from the rotor described above with reference to a switched reluctance motor essentially for the fact that it has magnets, like for example permanent magnets, which are fixed inside the flux barriers of the rotor.

[005] One drawback of the rotors of switched or assisted reluctance electric machines of the prior art described above is given by the fact that, in particular when the rotor rotates at a relatively high number of revolutions, like for example at between 7000 and 8000 rpm, it becomes particularly important to have the aforementioned inner and peripheral bridges in order to ensure that the rotor is sufficiently strong. In such a case, if for example the inner bridges were not provided, the peripheral bridges would break due to the inertia and magnetic pressure that act on the rotor in the operative conditions of the machine. Moreover, the fact of providing both the aforementioned inner and peripheral bridges worsens the performance of the reluctance electric machine and determines an increase in the torque "ripple".

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

[007] This and other purposes are achieved with a rotor as defined in claim 1 in its most general form, and in the claims that are dependent on it in some particular embodiments .

[008] One object of the present invention is also a switched or assisted reluctance machine as defined in claim 5. Further objects of the present invention are a wheel with an in-wheel motor and a traction motor as defined in claim 6. Another object of the present invention is an auxiliary device for a vehicle as defined in claim 7.

[009] The applicant has observed that the fact of providing peripheral bridges having a variable width in the rotor advantageously makes it possible on one hand to avoid using inner bridges that divide the flux barriers in the rotor of the prior art discussed above and on the other hand to simultaneously ensure a structure that the rotor has a particularly strong structure that allows the latter to also support high revs. Moreover, thanks to the possibility of not having inner bridges, it is possible to improve the magnetic flux inside the rotor making it possible for there to be improvements in the efficiency of the reluctance electric machine with respect to solutions of the prior art discussed above in which it is provided for there to be inner and peripheral bridges. In particular, the Applicant has observed that a switched reluctance electric machine with a rotor in which it is provided for there to be peripheral bridges with a variable width as described above, makes it possible to obtain an optimal compromise between having good efficiency of the motor (greater than 95%) , good torque ripple and a satisfactory mechanical strength of the rotor. [0010] The invention shall become clearer from the following detailed description of embodiments thereof, given as an example and therefore not with limiting purposes 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 flat partial section view, such a view being an orthogonal section view 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 being delimited in Fig. 3 by two broken lines.

[0011] In the attached figures same or similar elements are indicated with the same reference numerals. It should be noted moreover 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.

[0012] Figure 1 shows a section view of a reluctance machine in accordance with a currently preferred embodiment, which has been 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 a 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". In any case it should be noted that an electric motor in accordance with the present description is not limited to the application in an agricultural vehicle but it can also be used in general, for example and not for limiting purposes as a traction motor, in any type of electric and/or hybrid vehicle. It should be moreover noted that in general, as shall be described further in the description, a reluctance electric machine according to the present description is not limited to being used as a traction motor for a vehicle. [0013] 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 so as to rotate around a rotation axis XI.

[0014] Fig. 2 shows an axonometric view of the stator 2 of the motor 1. The stator 2 is provided with a stator winding which has been 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 obtained with 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 separated from one another by a distance that is greater than the distance between the remaining 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 rectangular section. It should be moreover noted that a conductor with a rectangular section can also be obtained 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 at the end such a wire has a generally rectangular cross/section.

[0015] 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 the number WO2013/005238 to the Applicant. In other words, by using the terminology that is used in such a patent application, in Fig. 2 the stator 2 is 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 make the bar winding 6. The basic conductors 7 are obtained starting from preformed "U" and/or "P"-shaped conductors, which are 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 basic conductors 7 have the respective legs that are housed in stator slots 12 which 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 houses 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 portions of the legs of basic conductors 7 or of a plurality of legs of basic conductors 7 and of portions of the phase terminals 9. In the example, the stator 2 comprises, in a non- limiting manner, fifty-four slots 12.

[0016] 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 in further detail.

[0017] Returning now to Fig. 1, the rotor 3 is preferably made with a plurality of laminations, preferably made in ferromagnetic material, which are stacked on one another so as to form the rotor 3. In accordance with one 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, where 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 a preferred embodiment, the rotor 3 is divided into four rotor segments 15, 16, 17, 18. It should be noted in any case that in general the skewed rotor 3 can also be made in a different manner. For example, in accordance with one embodiment, the skewed rotor 3 can be made by rotating the single laminations that form the rotor with respect to one another in a substantially continuous manner instead of rotating segments of rotor, having a relatively large thickness with respect to that of the single lamination, with respect to one another.

[0018] 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 shown, since, for example, the motor shaft 5 is not shown. More in particular, in the example in which both the stator 2 and the rotor 3 are made through a plurality of laminations that are stacked on one another, in the view of Fig. 3, in practice, a small stator plate 2 and a lamination of the rotor 3 are shown.

[0019] As can be seen in Fig. 3, in accordance with one preferred embodiment, the rotor 3 seen in section comprises a plurality of groups of flux barriers, in the example 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 and that are obtained for example through shearing of the laminations of the rotor. Flux barriers are in practice 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 laminations of the rotor have a structure have a structure that is the same as that of the lamination of the rotor of Fig. 3. The aforementioned groups of flux barriers are distributed around the rotation axis XI of the rotor. In accordance with one preferred embodiment such groups of flux barriers are the same as one another and are preferably angularly spaced in a homogeneous manner around the shaft 5 or the rotation axis XI. Preferably, the flux barriers 19-22 of each group are separated from one another in the radial direction. Preferably, the flux barriers of each group have decreasing dimensions 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 the 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.

[0020] Again with reference to Fig. 3, in accordance with one preferred embodiment each flux barrier 19-22 has a substantially isosceles trapezium shape without a greater base.

[0021] With reference to Fig. 4, in accordance with one preferred embodiment the rotor seen in section, or the lamination of the rotor, 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 generally has a 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 radially outside edge 33 of 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 or section 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 .

[0022] Based upon what has been described above, it is possible to understand how a rotor for a switched reluctance electric machine of the type described above makes it possible to achieve the purposes mentioned above with reference to the prior art.

[0023] As indicated above the Applicant has observed that the fact of providing peripheral bridges having a variable width in the rotor advantageously makes it possible, on one hand, to avoid using inner bridges that divide the flux barriers in the rotors of the prior art discussed above, and on the other hand, makes it possible to simultaneously ensure that the structure of the rotor is particularly strong allowing the structure to withstand even high number of relovutions. Moreover, thanks to the possibility of not having inner bridges, it is possible to improve the magnetic flux in the rotor making it possible to improve the efficiency of the reluctance electric machine with respect to solutions of the prior art discussed above in which there were inner and peripheral bridges. In particular, the Applicant has observed that a switched reluctance electric machine with a rotor in which peripheral bridges are provided with a variable width as described above, makes it possible to obtain an optimal compromise between good efficiency of the motor (greater than 95%), good torque ripple and satisfactory strength of the rotor.

[0024] It should be further noted that the Applicant has observed that the fact of providing a stator that is 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 of being able to use a greater slot filling coefficient with respect to the case in which there is a stator provided with a round wire winding

(that is to say a winding 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.

[0025] It is clear that numerous modifications and/or variants can be carried out on a reluctance motor according to the present description.

[0026] 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 other type of 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) .

[0027] Furthermore, it should 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.

[0028] 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 principles forming the basis of the present description can be extended to any application in which a switched or assisted reluctance electric machine can be used.

[0029] Moreover, it should be understood that the number of special conductors used, just like the number of basic conductors, can vary in general according to the specific design requirements.

[0030] 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.

[0031] It should be moreover noted that a reluctance electric machine according to the present description is not limited to a stator provided with a bar winding. Indeed, it is clear that the teachings of the present description can be applied also to the case of a switched or assisted reluctance machine in which the stator is provided with a round wire stator winding

(i.e. a winding obtained by means of electrically conducting wires having a circular cross-section) of the type normally used in known reluctance electric machines .

[0032] 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 .