Rotating electrical machines with improved slot insulation.

Abstract

To provide a rotating electric machine having high power efficiency and high performance per unit mass and / or unit volume. The electric machine 1 includes a shaft 2, a rotor 4 attached to the shaft 2 and equipped with permanent magnets 23, a stator 5 having a magnetic core 6 consisting of a series of laminations made of ferromagnetic material and longitudinally crossed by a number of stator slots 7, and a number of rigid bars 9, the bars 9 being covered on the outside with an insulating coating 14 and having stator windings 8 inserted into the corresponding stator slots 7. Each stator slot 7 does not have any insulating element interposed between the ferromagnetic material constituting the laminations of the magnetic core 6 and the corresponding bar 9, so that the outer surface 18 of the corresponding bar 9 is in direct contact with the inner surface 19 of the stator slot 7 made of ferromagnetic material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Italian Patent Application No. 102020000002263, filed February 5, 2020, the entire disclosure of which is incorporated herein by reference. [Technical field]

[0002] The present invention relates to rotating electrical machines.

[0003] The invention has advantageous application to automotive rotating electric machines that are mounted on vehicles and can be used as motors (receiving electrical power and generating mechanical torque) or generators (converting mechanical power into electrical power). [Background technology]

[0004] A rotating electric machine for an automotive vehicle includes a shaft mounted for rotation about a central axis of rotation, a rotor, typically including permanent magnets, mounted on the shaft for rotation therewith, and a tubular, cylindrical stator disposed around and surrounding the rotor.

[0005] It has long been proposed to perform the stator windings with rigid bars, i.e. the rigid bars are initially shaped into a "U" shape and are thus inserted axially into a stator slot forming an inlet side where the cusps of the "U" shaped bar are located and an outlet side where the legs (i.e. straight portions) of the "U" shaped bar are located; once the bar is inserted into the stator slot, the outlet legs are bent and the free ends of the legs are connected together by welding to form the electrical paths of the stator windings.

[0006] US 2015 / 249372 A1 discloses a rotating electric machine in which each stator slot does not include any insulating element interposed between the ferromagnetic material constituting the laminations of the ferromagnetic core and the corresponding bar of the stator winding.

[0007] US 2016 / 365164 A1 discloses an electrical conductor having a rectangular cross section that is insulated on the outside by multiple resin layers superimposed on one another. Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to provide a rotating electric machine having higher power efficiency and greater specific performance (power and / or torque). [Means for solving the problem]

[0009] According to the invention there is provided a rotating electric machine according to the subject matter set out in the accompanying utility claims.

[0010] The claims describe preferred embodiments of the invention and form an integral part of this disclosure. [Brief description of the drawings]

[0011] The present invention will now be described with reference to the accompanying drawings, which show one non-limiting embodiment of the invention. [Figure 1] 1 is a schematic longitudinal section of a rotating electrical machine constructed in accordance with the present invention; [Diagram 2] FIG. 2 is a perspective view of a stator of the rotating electrical machine of FIG. 1; [Diagram 3] FIG. 3 is an enlarged view of a detail of FIG. 2. [Figure 4] FIG. 3 is a cross-sectional view of a stator slot of the stator of FIG. 2. [Diagram 5] FIG. 3 is a cross-sectional view of a bar of a stator winding of the stator of FIG. 2. [Figure 6] FIG. 2 is a perspective view of a rotor of the rotating electrical machine of FIG. 1; [Figure 7] FIG. 7 is a perspective view of the rotor of FIG. 6 with some parts removed for clarity. [Figure 8] FIG. 7 is a cross-sectional view of the rotor of FIG. 6. [Figure 9] FIG. 2 is a schematic longitudinal section of the rotating electrical machine of FIG. 1, highlighting the air flow paths during operation. [Figure 10] FIG. 2 is a schematic longitudinal section of a variant of the rotating electric machine of FIG. 1, highlighting the air flow path during operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In FIG. 1, a reversible (i.e., capable of operating both as an electric motor receiving electrical power to produce drive torque, and as a generator receiving mechanical power to produce electrical power) automotive synchronous electric machine is indicated generally at 1.

[0013] The electric machine 1 comprises a shaft 2 mounted to rotate about a central rotation axis 3, a rotor 4 having permanent magnets mounted on the shaft 2 to rotate together with the shaft 2, and a cylindrical tubular stator 5 arranged around the rotor 4 so as to surround the rotor 4.

[0014] Between the rotor 4 and the stator 5 an air gap is defined in the shape of an annulus having a small thickness (usually required to allow a sufficiently safe rotation of the rotor 4 inside the stator 5).

[0015] As shown in Figures 2 and 3, the stator 5 has a magnetic core 6 formed by closely packing (i.e. grouping together) a series of thin plates (made of a ferromagnetic material) and has a tubular shape with a central hole, and is longitudinally (axially) traversed by a number of stator slots 7 that house three-phase stator windings 8 evenly distributed along the inside of the magnetic core 6.

[0016] The three-phase stator winding 8 comprises a series of "U"-shaped copper rigid bars 9, each bar 9 comprising two legs 10 connected to each other by a cusp 11, the two legs 10 of the same bar 9 constituting two corresponding conductors of the stator winding 8. The "U"-shaped bars 9 are inserted into stator slots 7 that define an inlet side, where the cusps 11 of the "U"-shaped bars 9 are located, and an outlet side, where the legs 10 of the "U"-shaped bars 9 are located. In particular, as better shown in FIG. 4, in each stator slot 7, eight legs 10 belonging to eight corresponding "U"-shaped rigid bars 9 (i.e., eight conductors of the stator winding 8) are located. As shown in FIG. 2, the ends of the legs 10 of the "U"-shaped bars 9 are bent and thus electrically connected (welded) to each other to form the electrical paths of the stator winding 8. As a result, considering one single stator slot 7, each bar 9 has a straight central portion inserted into the corresponding stator slot 7 and two end portions bent relative to the central portion.

[0017] As shown in FIG. 5, each bar 9 has a rectangular cross section with long sides 12 and short sides 13 and is coated on the outside with an insulating coating 14 .

[0018] As shown in FIG. 4, each stator slot 7 has a rectangular cross-section with radially oriented longer sides 15 and circumferentially oriented shorter sides 16 .

[0019] As already mentioned and also shown in FIG. 4, each stator slot 7 houses eight bars 9 arranged in a row, each bar 9 having a rectangular cross section with a long side 12 parallel to the short side 16 of the corresponding stator slot 7 and a short side 13 parallel to the long side 15 of the corresponding stator slot 7. Furthermore, as better shown in FIG. 5, the ratio between the long side 12 and the short side 13 of the rectangular cross section of each bar 9 is greater than 2, preferably greater than 3, and in particular, according to a preferred embodiment, the ratio between the long side 12 and the short side 13 of the rectangular cross section of each bar 9 is between 3 and 3.7. This arrangement and this form of the interdigitated bars 9 allows a significant reduction of the power losses due to the skin effect in the bars 9, increasing the power efficiency and also the specific performance (power and / or torque).

[0020] According to the preferred embodiment shown in Figures 2 and 3, each bar 9 is bent about a short side 13 of the rectangular cross-section, i.e. each bar 9 is bent "latently", in other words each bar 9 is bent relative to (along) the short side 13 of the rectangular cross-section.

[0021] According to the embodiment shown in FIG. 4, in each stator slot 7, the legs 10 of the eight bars 9 are arranged in a row and a filling element 17 (optional) is arranged, which has a predetermined elastic deformation capacity and has the function of filling the remaining space inside the stator slot 7 and stabilizing the legs 10 of the eight bars 9.

[0022] As shown in Figure 4, each stator slot 7 does not have any insulating element interposed between the ferromagnetic material constituting the laminations of the magnetic core 6 and the corresponding bar 9, so that the outer surface 18 of the corresponding bar 9 is in direct contact with the inner surface 19 of the stator slot 7 made of the ferromagnetic material of the stator slot 7. This solution requires an increase in the thickness of the insulating coating 14 of each bar 9, but it makes it possible to increase the fill factor of the stator slot 7 as a whole (i.e. the ratio between the total area of ​​the copper cross section present in each stator slot 7 and the area of ​​the cross section of the stator slot 7) and thus the specific performance (power and / or torque).

[0023] As shown in Fig. 5, the insulating coating 14 covering the outside of each bar 9 has a thickness greater than 0.30 mm (for example, equal to 0.35-0.40 mm). Moreover, according to one possible embodiment (but not limited to this), the insulating coating 14 covering the outside of each bar 9 has an inner layer 20 in direct contact with the copper and having a thickness of about 0.20-0.25 mm, and an outer layer 21 arranged on the inner layer 20, having a thickness of about 0.10-0.15 mm, and in direct contact with the ferromagnetic material constituting the lamella of the magnetic core 6. The inner layer 20 is made of a first material (enamel or resin) and the outer layer 21 is made of a second material (enamel or resin) different from the first material. In particular, the second material is mechanically stronger but less electrically insulating than the first material, i.e. the inner layer 20 essentially has the function of ensuring electrical insulation, while the outer layer 21 essentially has the function of mechanically protecting the inner layer 20 from friction with the inner surface 19 of the stator slot 7 when the leg 10 of the bar 9 is inserted into the stator slot 7.

[0024] As shown in Figure 7, the rotor 4 comprises a number of rows 22 of permanent magnets, which are axially oriented and arranged side by side with one another around the axis of rotation 3 to form a closed ring. In the embodiment shown in Figure 7, twelve rows of permanent magnets 22 are provided, arranged to form a closed ring, however, according to other embodiments not shown, the total number of rows of permanent magnets 22 may be different, for example, there may be between 8 and 24 rows of permanent magnets 22.

[0025] Each row of permanent magnets 22 consists of a series of permanent magnets 23 arranged in a line, i.e., each row of permanent magnets 22 is composed of a plurality of permanent magnets 23 arranged in a line in the axial direction, and in particular, each row of permanent magnets 22 generally has 20 to 60 permanent magnets 23 arranged in a line.

[0026] Each permanent magnet row 22 is composed of a plurality of permanent magnets 23 arranged in the axial direction according to a Halbach array so as to radially nullify the inner magnetic field of the permanent magnets 23 and radially maximize the outer magnetic field of the permanent magnets 23. In other words, the permanent magnets 23 in each permanent magnet row 22 are arranged so as to radially nullify the inner magnetic field of the permanent magnets 23 (toward the shaft 2) and radially maximize the outer magnetic field of the permanent magnets 23 (toward the magnetic core 6 of the stator 5).

[0027] A Halbach array is a particular combination (arrangement) of permanent magnets 23 arranged to reinforce the magnetic field along one face of the array (in this embodiment, the radially outermost face) while simultaneously interfering with and eliminating (nullifying) the magnetic field on the opposite face (in this embodiment, the radially innermost face). As shown in Figure 7, according to the Halbach array, a group of four permanent magnets 23 is periodically repeated, i.e., one permanent magnet 23 has an SN orientation arranged axially to the right, a further permanent magnet 23 has an SN orientation arranged radially outward (i.e., away from the central rotation axis 3), a further permanent magnet 23 has an SN orientation arranged axially to the left, and a further permanent magnet 23 has an SN orientation arranged radially inward (i.e., closer to the central rotation axis 3).

[0028] In the embodiment shown in the accompanying drawings, the rows of permanent magnets 22 have a rectangular cross section and rectangular and isosceles trapezoidal rectangular cross sections, but according to another embodiment not shown, all of the rows of permanent magnets 22 have the same isosceles trapezoidal rectangular cross sections.

[0029] As better shown in FIG. 8, in the rotor 4, no ferromagnetic material is disposed on the outer surface (external to the permanent magnets 23) of the permanent magnets 23, i.e., in the rotor 4, there is neither a ferromagnetic material disposed radially outside the permanent magnets 23 (i.e., between the permanent magnets 23 and the magnetic core 6 of the stator 5) nor a ferromagnetic material disposed radially inside the permanent magnets 23 (i.e., between the permanent magnets 23 and the shaft 2).

[0030] As shown in Figures 6 and 8, the rotor 4 comprises a constraining element 24 (not shown in Figure 7) arranged around the permanent magnet row 22 to keep the permanent magnet row 22 in contact with the shaft 2, i.e. the constraining element 24 covers the outside of the permanent magnet row 22 and forms a radial constraint for the permanent magnet row 22 so that the permanent magnet row 22 is not pressed against the magnetic core 6 of the stator 5 by, for example, centrifugal forces. According to one possible embodiment, the constraining element 24 consists of a resin-treated filament wound in a spiral shape around the permanent magnet row 22, according to an alternative embodiment the constraining element 24 consists of a tubular element made of a composite material, a lightweight non-ferromagnetic metallic material (e.g. aluminium) or a ferromagnetic metallic material.

[0031] According to a preferred embodiment shown in Figure 7, in each row of permanent magnets 22, the individual permanent magnets 23 are adhered to one another by means of an adhesive 25, which is preferably an electrical insulator to reduce power losses due to eddy currents. In other words, each row of permanent magnets 22 is fabricated by adhering a single permanent magnet 23 to one another by means of an adhesive 25, which is preferably an electrical insulator.

[0032] According to a preferred embodiment shown in Figures 7 and 8, the permanent magnet rows 22 are attached directly to the outer wall of the shaft 2, in particular each permanent magnet row 22 being glued to the outer wall of the shaft 2 by an adhesive 26 (shown in Figure 8), which is preferably an electrical insulator (so that the various permanent magnets 23 of the same permanent magnet row 22 are not "short-circuited" to each other by the outer wall of the shaft 2). In other words, an electrically insulating layer of adhesive 26 is interposed between the outer wall of the shaft 2 and the permanent magnet row 22. According to another embodiment, the adhesive 26 may be an electrical insulator, i.e. it is not necessary that the adhesive 26 is an electrical insulator.

[0033] The adhesive 26 serves to electrically insulate the permanent magnet row 22 from the underlying outer wall of the shaft 2, and also serves to connect the permanent magnet row 22 to the outer wall of the shaft 2 during manufacture of the rotor 4 (mechanical retention of the permanent magnet row 22 is provided by the restraining element 24, as the adhesive 26 would not be able to withstand the centrifugal forces when the rotor 4 rotates at high speed).

[0034] According to a preferred embodiment shown in Figures 7 and 8, the outer wall of the shaft 2 has a plurality of seats 27, each of which is configured to accommodate a corresponding row of permanent magnets 22, i.e. each seat 27 is shaped to reproduce in the form of a recess the shape of the corresponding row of permanent magnets 22 so as to receive and accommodate the row of permanent magnets 22 with minimal clearance.

[0035] As shown in FIG. 8 , the shaft 2 has a hub 28 supported by bearings (not shown), a rim 29 disposed around the hub 28 at a given distance from the hub 28 and supporting the array of permanent magnets 22 (i.e., constituting the outer wall of the shaft 2), and a number of spokes 30 extending radially and connecting the hub 28 to the rim 29 such that there is some free space between the hub 28 and the rim 29.

[0036] As shown in Fig. 1, the electric machine 1 comprises a casing 31 housing a stator 5, the casing 31 having a cylindrical central body 32 arranged around the magnetic core 6 of the stator 5 and two cup-shaped caps 33 (which may be flat) closing the central body 32 on both sides. Between the outer surface 18 of the magnetic core 6 of the stator 5 and the inner surface 19 of the central body 32 of the casing 31, an annular hollow space 34 is obtained, configured to allow the circulation of an air flow. In the embodiment shown in Fig. 1, each cap 33 is associated with a liquid heat exchanger (i.e., inside which a cooling liquid circulates) or with an air heat exchanger 35 (i.e., against which a cold air flow impinges), according to another embodiment, only one heat exchanger 35 is provided, associated with only one cap 33 (as shown in Fig. 10) or no heat exchanger 35 is provided (variant not shown).

[0037] As shown in FIG. 9, the spokes 30 of the shaft 2 are shaped (e.g., as a spiral) to cause the air present inside the shaft 2 to have an axially directed component of motion, and therefore, when the shaft 2 rotates, the air inside the shaft 2 (i.e. in the empty gaps between the spokes 30) receives an axial thrust which causes an airflow axially across the shaft 2, and the airflow exiting the shaft 2 and impinging on the cap 33 (located on the left side of FIG. 9) is deflected outwardly until it enters the annular hollow space 34, through which it flows in a direction opposite to the direction of motion imparted by the spokes 30 of the shaft 2. This creates a continuous air current inside the casing 31, as the shaft 2 rotates, circulating in one direction inside the shaft 2 and in the opposite direction outside the stator 5, which removes heat from the inside of the shaft 2 and carries it to the casing 31 (i.e. towards the outside), in other words to both the cap 33 (which may be connected to a heat exchanger 35 more or less integrated into the cap 33) and the central body 32 (which may also be connected to a heat exchanger more or less integrated into the central body 32).

[0038] In the variant shown in FIG. 10, the annular hollow space 34 is not provided, and therefore the airflow leaving the shaft 2 and impinging on the cap 33 (located on the left side of FIG. 10) is deflected towards the gap existing between the rotor 4 and the stator 5, enters the gap and flows through it in a direction opposite to the movement imparted by the spokes 30 of the shaft 2.

[0039] This creates a continuous airflow inside the casing 31, when the shaft 2 rotates, circulating in one direction inside the shaft 2 and in the opposite direction inside the gap, which airflow carries heat away from the inside of the shaft 2 and from the outside of the rotor 4 and towards (i.e. out of) the cap 33 of the casing 31. Obviously, also in the embodiment shown in Figure 9, a small part of the airflow flows through the gap instead of the hollow space 34, but the majority of the airflow flows through the hollow space 34, which has a cross-section much larger than that of the gap.

[0040] Thanks to the continuous air flow inside the shaft 2, it is possible to effectively cool the entire shaft 2, and therefore the rotor 4, without the need for highly complex coolant cooling of the rotor 4, which would require continuous passage of coolant from fixed to rotating parts.

[0041] According to one possible embodiment, on the inside of the two caps 33, a number of fins are arranged which are shaped to direct the air flow from the centre to the periphery and vice versa, i.e. on the one hand directing the air flow from the shaft 2 towards the annular hollow space 34 and on the other hand directing the air flow from the annular hollow space 34 towards the shaft 2.

[0042] According to one preferred, but non-limiting embodiment, the spokes 30 are further shaped to generate a predetermined sound when the shaft 2 rotates, i.e., the shape of the spokes 30 is designed to generate a desired sound when the shaft 2 rotates.

[0043] The embodiments described in this specification can be combined with one another without departing from the scope of protection of the present invention.

[0044] The electric machine 1 described above has several advantages.

[0045] First, the electric machine 1 described above has a high power efficiency (ie, a high yield between the mechanical power or electrical power input and the mechanical power or electrical power output).

[0046] Furthermore, the above described electric machine 1 has a high specific performance (power and / or torque), ie a high performance (power and / or torque) per unit mass and / or unit volume.

[0047] Finally, the above described electric machine 1 can be easily and cheaply manufactured since it does not require substantially higher manufacturing costs than traditional electric machines with comparable performance. [Explanation of symbols]

[0048] 1 Electrical machinery 2 Shaft 3 Rotation Axis 4 Rotors 5 Stator 6 Magnetic Core 7. Status Slot 8 Stator Winding 9. Bar Leg 10 11 Cusp 12 Long side 13 Short side 14 Insulation Coating 15 Long side 16 Short Side 17 Filling Elements 18 Exterior 19 Inner 20 inner layer 21 Outer layer 22 Row of permanent magnets 23 Permanent Magnets 24 Constraints 25 Adhesive 26 Adhesive 27 seats 28 Hub 29 Rims 30 spokes 31 Casing 32 Central Body 33 Cap 34 Annular hollow space 35 Heat exchanger

Claims

1. a shaft (2) mounted for rotation about a central axis of rotation (3); a rotor (4) provided with a permanent magnet (23) and mounted on the shaft (2) for co-rotation therewith; a stator (5) having a tubular cylindrical shape, arranged around the rotor (4) so ​​as to surround the rotor (4) on the inside, and having a magnetic core (6) composed of a series of thin plates made of a ferromagnetic material and longitudinally crossed by a number of stator slots (7); The rotor comprises a number of copper rigid bars (9), the bars (9) being covered on the outside with an insulating coating (14) and stator windings (8) inserted into corresponding stator slots (7). It is equipped with An electric machine (1) in which each stator slot (7) does not have any insulating element interposed between the ferromagnetic material constituting the laminations of the magnetic core (6) and the corresponding bar (9), so that an outer surface (18) of the corresponding bar (9) is in direct contact with an inner surface (19) of the stator slot (7) made of the ferromagnetic material of the stator slot (7), the insulating coating (14) covering the outside of each of the bars (9) comprises an inner layer (20) in direct contact with the copper and an outer layer (21) disposed on the inner layer (20) in direct contact with the ferromagnetic material constituting the laminations of the magnetic core (6); The electric machine (1), characterized in that the inner layer (20) is made of a first material and the outer layer (21) is made of a second material different from the first material, the second material being mechanically stronger than the first material but less electrically insulating than the first material.

2. 2. The electric machine (1) according to claim 1, wherein the insulating coating (14) covering the outside of each of the bars (9) has a thickness greater than 0.30 mm.

3. 3. The electric machine (1) according to claim 1 or 2, wherein the first material is enamel.

4. The electric machine (1) according to claim 1 or 2, wherein the first material is a resin.

5. 5. The electric machine (1) according to claim 1, wherein the inner layer (20) essentially has the function of ensuring electrical insulation, whereas the outer layer (21) essentially has the function of mechanically protecting the inner layer (20) from friction against the inner surface (19) of the stator slot (7).

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