IT202200025740A1 - ROTOR FOR A ROTATING ELECTRIC MACHINE - Google Patents

Description

DESCRIPTION

of the patent for Industrial Invention entitled:

?ROTOR FOR A ROTATING ELECTRIC MACHINE?

TECHNICAL SECTOR

The present invention relates to a rotor for a rotating electrical machine.

The present invention finds advantageous application in a rotating electric machine for automotive traction which is installed on board a vehicle and can be used as a motor (absorbing electrical energy and generating a mechanical driving torque) or as a generator (converting mechanical energy into electrical energy).

EARLY ART

A rotating electric machine for automotive use comprises a shaft, which is rotatably mounted to rotate about a central axis of rotation, a rotor, usually with permanent magnets, keyed to the shaft to rotate with the shaft itself, and a stator arranged around the rotor to enclose the rotor within itself.

DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a rotor for a rotating electrical machine which has a particularly low mass and rotational inertia.

According to the present invention, a rotor for a rotating electric machine is provided, as claimed in the appended claims.

The claims describe preferred embodiments of the present invention and form an integral part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of its implementation:

? Figure 1 is a schematic and longitudinal sectional view of a rotating electrical machine provided with a rotor made in accordance with the present invention;

? Figure 2 is a perspective view of the rotor of Figure 1;

? Figure 3 is a longitudinal sectional view of the rotor of Figure 1; and

? Figure 4 is a longitudinal sectional view of a variant of the rotor of Figure 1.

PREFERRED FORMS OF EMBODIMENT OF THE INVENTION

In figure 1, the number 1 indicates as a whole a reversible synchronous electric machine for automotive traction (i.e. one that can function both as an electric motor, absorbing electrical energy and generating a mechanical driving torque, and as an electric generator, absorbing mechanical energy and generating electrical energy).

Electric machine 1 is intended to be installed in a vehicle with electric or hybrid traction comprising at least two drive wheels (i.e. in a vehicle with electric or hybrid traction with two or four drive wheels). In particular, electric machine 1 can be connected to the drive wheels (directly or via a transmission possibly equipped with a clutch); i.e. between electric machine 1 and the drive wheels there may be a direct connection, there may be a simple speed reducer, or there may also be a clutch.

The electric machine 1 comprises a shaft 2, which is rotatably mounted to rotate around a central rotation axis 3, a permanent magnet rotor 4 keyed to the shaft 2 to rotate together with the shaft 2 itself, and a stator 5 of cylindrical tubular shape arranged around the rotor 4 to enclose the rotor 4 itself within itself.

Between the rotor 4 and the stator 5 there is an annular air gap of reduced thickness (normally the minimum necessary to allow the rotation of the rotor 4 inside the stator 5 in complete safety).

As illustrated in figure 3, the rotor 4 comprises a plurality of permanent magnets 6, which are axially oriented and are arranged next to each other around the rotation axis 3 to form a closed ring. The permanent magnets 6 have a surface arrangement, that is, they are arranged in correspondence with the external surface of the rotor 4 and are not inserted in slots obtained in the rotor 4.

The sequence of 6 permanent magnets that constitutes the closed ring provides a circumferential arrangement according to a Halbach array to cancel the magnetic field radially inside the 6 permanent magnets and to maximize the magnetic field radially outside the 6 permanent magnets. In other words, the 6 permanent magnets are arranged to cancel the magnetic field radially inside the 6 permanent magnets (towards the shaft 2) and to maximize the magnetic field radially outside the 6 permanent magnets (towards the magnetic core of the stator 5). That is, the 6 permanent magnets are arranged circumferentially one after the other according to a Halbach array to cancel the magnetic field radially inside the 6 permanent magnets and to maximize the magnetic field radially outside the 6 permanent magnets.

A Halbach array is a particular union (arrangement) of permanent magnets 6 that are positioned so as to strengthen the magnetic field along one face of the array (the radially outermost face in the present embodiment) while simultaneously canceling (canceling) by interference the magnetic field on the opposite face (the radially innermost face in the present embodiment). The Halbach array involves cyclically repeating sequences of at least 6 permanent magnets (i.e. at least four): a permanent magnet 6 having a South-North orientation arranged circumferentially in a clockwise direction, a subsequent permanent magnet 6 having a South-North orientation arranged radially outwards (i.e. moving away from the central rotation axis 3), a subsequent permanent magnet 6 having a South-North orientation circumferentially in a counterclockwise direction, and a subsequent permanent magnet 6 having a South-North orientation arranged radially inwards (i.e. moving closer to the central rotation axis 3).

According to a different embodiment, the 6 permanent magnets are not arranged in a Halbach array.

According to a preferred embodiment, each permanent magnet 6 is not monolithic (i.e. constituted from the beginning by a single piece of undivided and indivisible magnetic material), but is formed by an axial succession of (smaller) permanent magnets 7 arranged axially in a single file one after the other, or each permanent magnet 6 is formed by a plurality of (smaller) permanent magnets 7 that are arranged axially one after the other; according to a possible (but not limiting) embodiment, each permanent magnet 6 is generally provided for example with between twenty and sixty permanent magnets 7 arranged axially in a single file one after the other.

In each permanent magnet 6, all the permanent magnets 7 that make up the permanent magnet 6 have the exact same orientation, that is, they are all equi-oriented from the point of view of the magnetic field; in other words, in the same permanent magnet 6, the permanent magnets 7 that make up the permanent magnet 6 have the magnetic field oriented in the same way.

In the embodiment illustrated in the attached figures, the 6 permanent magnets alternatively have a rectangular cross-section and an isosceles trapezoidal cross-section; according to a different embodiment not illustrated, the 6 permanent magnets all have an isosceles trapezoidal cross-section (obviously with alternate orientations to compose the ring).

As illustrated in figure 3, the rotor 4 comprises a support cylinder 8 which houses the permanent magnets 6; in particular, the support cylinder 8 has an external surface 9 on which the permanent magnets 6 rest. In other words, the permanent magnets 6 are arranged superficially on the outside of the support cylinder 8. According to a preferred embodiment, the external surface 9 of the support cylinder 8 is faceted, that is, it is composed of a plurality of flat faces, each of which provides a flat support for a corresponding permanent magnet 6.

The support cylinder 8 is coupled (i.e. constrained to be angularly integral) with the shaft 2 in such a way as to form a single cohesive block together. According to a preferred embodiment, the shaft 2 is made up of two half-shafts 10 and 11, each of which is separate and distant from the other and is individually coupled (fixed) to the support cylinder 8; that is, each half-shaft 10 or 11 is independent and separate from the other half-shaft 11 or 10 and is coupled (fixed) to the support cylinder 8 independently of the other half-shaft 11 or 10 (the two half-shafts 10 and 11 do not touch each other as they are arranged at a certain distance from each other). In particular, the support cylinder 8 is internally hollow and has a cavity 12 central through-hole into which the two half-shafts 10 and 11 are inserted. According to a preferred embodiment, each half-shaft 10 or 11 is interference-fitted (in particular by means of a hot-cold coupling to obtain a high clamping force) inside the support cylinder 8 (i.e. inside the central cavity 12 of the support cylinder 8).

According to a preferred embodiment, two annular shoulders 13 are formed inside the central cavity 12 of the support cylinder 8 and at the two ends, against which the corresponding half-shafts 10 and 11 rest; that is, the two annular shoulders 13 constitute limit switches (seats) for the insertion of the half-shafts 10 and 11 inside the central cavity 12 of the support cylinder 8. In particular, each half-shaft 10 or 11 ends internally with a mounting ring 14 which is driven by interference into the central cavity 12 of the support cylinder 8 and rests on the corresponding annular shoulder 13.

The half-shaft 10 is shaped to be mounted on a support bearing; furthermore, the half-shaft 10 is also shaped to be connected to a motion transmission and therefore has a serrated finish. The half-shaft 11 is shaped to be mounted on another support bearing; furthermore, the half-shaft 11 is also shaped to be connected to an angular position sensor (in particular to a resolver).

As illustrated in Figure 3, the rotor 4 comprises a pair of end discs 15 (also called balancing discs), which are arranged around the shaft 2 at the two opposite ends of the support cylinder 8 and are adapted (among other things) to contain and possibly keep the permanent magnets 6 tightly packed. In other words, the two end discs 15 constitute the two opposite ends of the rotor 4 and can keep the permanent magnets 6 compressed axially to keep the permanent magnets 6 tightly packed.

According to a possible embodiment, the end discs 15 are designed to have balancing openings that balance the rotor 4 around the rotation axis 3 and are made by cylindrical drilling or by milling. To allow the rotor 4 to operate at high rotation speeds while ensuring, at the same time, a long operating life, it is necessary to minimize the vibrations that are generated during operation and that must be absorbed by the bearings that support the shaft 2. For this purpose, it is often necessary to proceed with fine balancing of the rotor 4 in such a way as to reduce the imbalances (due to the inevitable construction tolerances) that generate vibrations during rotation. To allow the balancing of the rotor 4, the two end discs 15 are used which act as balancers thanks to calibrated asymmetries in their mass generated by the balancing openings (which can be blind or through and can be arranged radially or axially). In general, the calibrated asymmetries in the two end discs 15 can be obtained either by removing material (i.e. by creating the balancing openings) or by adding material (i.e. by fixing balancing masses to the end discs 15).

Obviously, the presence, number, arrangement and depth of the balancing holes are completely random and can vary completely from rotor 4 to rotor 4 as they depend on the actual imbalance (due to the construction tolerances) of rotor 4 at the end of its production. In theory, it is also possible that rotor 4 is completely devoid of balancing holes as, due to a fortunate combination of construction tolerances, at the end of its production it has an imbalance around the rotation axis 3 so small that it does not require corrections.

Each end disc 15 forms a single monolithic and indivisible body (piece) with the support cylinder 8, or is an integral and indivisible part of the support cylinder 8. Consequently, the support cylinder 8 and the end discs 15 are made of exactly the same material, being two parts of the same single undivided and indivisible body from the beginning. The two end discs 15 constitute the external edges of the support cylinder 8 which project from the external surface 9 of the support cylinder 8 and delimit the external surface 9 itself on both sides.

The rotor 4 comprises a cylindrical and internally hollow containment element 16 which is arranged around the permanent magnets 6 to keep the permanent magnets 6 in contact with the support cylinder 8; that is, the containment element 16 externally covers the permanent magnets 6 to provide radial containment of the permanent magnets 6 themselves so as to prevent centrifugal force from pushing the permanent magnets 6 against the magnetic core of the stator 5. According to a preferred embodiment, the containment element 16 is made of a tubular element made of composite material which is interference-fitted around the permanent magnets 6. Alternatively, the containment element 14 is made of plastic material or of light non-ferromagnetic metallic material (for example, aluminium, titanium or magnesium); less likely, the containment element 14 is made of ferromagnetic metallic material. As a further alternative, the containment element 16 is made of a composite material which is interference-fitted around the permanent magnets 6. consisting of a resinated filament wrapped in a spiral around 6 permanent magnets.

According to a possible embodiment, the containment element 16 is made from a single monolithic piece (i.e. without interruption). Alternatively, the containment element 16 is made from two or more pieces that are separate and independent from each other and are arranged next to each other; in this embodiment, the various pieces that make up the containment element 16 are individually fitted around the permanent magnets 6, reducing the overall force required for the operation (which, as previously stated, occurs with a certain interference).

Generally, the half-shaft 10 is made of high-strength steel (or other material with equivalent mechanical characteristics) as it must be able to transmit the torque generated or absorbed by the rotor 4; on the other hand, the half-shaft 11 is made of steel or other metallic material with lower resistance than the steel of the half-shaft 10 as the half-shaft 11 does not transmit the torque generated or absorbed by the rotor 4.

In the embodiment illustrated in figure 3, the support cylinder 8 (which integrates the two end discs 15 which are made of the exact same material as the support cylinder 8) is preferably made of a non-magnetic material which can be metallic (for example stainless steel, aluminium, titanium or magnesium) or even non-metallic (typically composite material such as carbon fibre to have the necessary resistance). As previously stated, the magnetic field inside the permanent magnets 6 is zero due to the Halbach arrangement of the permanent magnets 6 and therefore the support cylinder 8 is not affected by an appreciable magnetic field; consequently, the support cylinder 8 does not necessarily have to have ferromagnetic properties.

In the embodiment illustrated in figure 4, the support cylinder 8 (which integrates the two end disks 15 which are made of the exact same material as the support cylinder 8) is preferably made of ferromagnetic (i.e. metallic) material. The support cylinder 8 made of ferromagnetic metallic material simplifies the assembly of the rotor 4, since the permanent magnets 6 adhere by magnetic attraction to the external surface 9 of the support cylinder 8 and are therefore easier to arrange on the external surface 9 of the support cylinder 8 during assembly. When the support cylinder 8 (and therefore the end disks 15 which are integrated into the support cylinder 8) is made of ferromagnetic metallic material, the rotor 4 is easier to assemble. made of ferromagnetic material, two separation disks 17 can be provided which are placed between the permanent magnets 6 and the end disks 15, they are made of non-magnetic material (metallic or non-metallic), and have the function of creating an air gap (therefore a "barrier" to the magnetic flux) which reduces the dispersed magnetic flux which is generated by the permanent magnets 6 and closes through the end disks 15 without affecting the stator 5.

According to a possible embodiment, in each permanent magnet 6 the individual permanent magnets 7 are glued to each other by means of the interposition of a mounting glue (which constitutes an electrical insulator) in order to reduce energy losses due to eddy currents. In other words, each permanent magnet 6 is made by gluing the individual permanent magnets 7 to each other by means of the mounting glue (which constitutes an electrical insulator).

According to a preferred embodiment, the permanent magnets 6 are directly mounted on the external surface 9 of the support cylinder 8; in particular, each permanent magnet 6 is glued to the external wall 9 of the support cylinder 8 by means of a mounting glue which is preferably an electrical insulator (to avoid "short-circuiting" the various permanent magnets 7 of the same permanent magnet 6 through the external wall 9 of the support cylinder 8). In other words, an electrically insulating layer consisting of the mounting glue is interposed between the external wall 9 of the support cylinder 8 and the permanent magnets 6.

The assembly glue has the function of electrically isolating the permanent magnets 6 from the underlying external wall 9 of the support cylinder 8 and above all has the function of connecting the permanent magnets 6 to the external wall 9 of the support cylinder 8 during the construction of the rotor 4 (the mechanical retention of the permanent magnets 6 is achieved by the containment element 16 since the assembly glue is not able to resist the centrifugal force when the rotor 4 rotates at high speed).

The embodiments described herein may be combined with each other without departing from the scope of protection of the present invention.

The rotor 4 described above has several advantages. First of all, the rotor 4 described above has both a low mass and a low rotational inertia, which is beneficial for performance (in particular, the low rotational inertia allows for a reduction in dynamic stresses along the entire transmission line).

Furthermore, the rotor 4 described above allows the use of innovative materials (in particular composite materials) which allow for a performance/mass ratio never achieved before. In particular, the rotor 4 described above allows the use of different materials for the main parts (support cylinder 8 integrating the end discs 15, half-shaft 10, half-shaft 11) which make up the rotor 4 itself; in this way each main part (support cylinder 8 integrating the end discs 15, half-shaft 10, half-shaft 11) can be made from the best material to withstand the mechanical stresses generated in use and to optimise the performance/mass ratio.

The rotor 4 described above features a significant reduction in mass and inertia also thanks to the integration of the end discs 15 into the support cylinder 8 as all additional mechanical connections (such as, for example, welding) of the two end discs 15 to the support cylinder 8 are eliminated.

In the rotor 4 described above, the mechanical connection between the end discs 15 and the support cylinder 8 is optimal, since the end discs 15 are directly integrated seamlessly into the support cylinder 8 and therefore the rotor 4 described above can withstand high centrifugal forces. Consequently, this construction method is particularly suitable for the construction of large-diameter rotors 4 in which the centrifugal force acting on the end discs 15 reaches particularly high values.

The rotor 4 described above allows for high energy efficiency (i.e. a high efficiency between the mechanical or electrical power input and the electrical or mechanical power output); in this regard, it is important to note that the presence of the containment element 16, ensuring high precision in radial positioning and circularity, allows for the air gap between the rotor 4 and the stator 5 to be reduced to a minimum.

Finally, the rotor 4 described above is easy to manufacture as it is composed of a small number of pieces of simple shape that can be quickly combined with each other even in automatic processes.

LIST OF FIGURE REFERENCE NUMBERS

1 electric machine

2 tree

3 axis of rotation

4 rotor

5 stator

6 permanent magnets

7 permanent magnets

8 support cylinder

9 external surface

10 half shafts

11 half shaft

12 central cavities

13 annular shoulders

14 mounting ring

15 end disc?

16 containment element 17 separation disc

Claims (14)

CLAIM S 1) Rotor (4) for an electric machine (1) rotating and comprising: a support cylinder (8) which has an external surface (9) and a central cavity (12); a plurality of main permanent magnets (6), which are axially oriented, are supported on the external surface (9) of the supporting cylinder (8), and are arranged next to each other around a rotation axis (3) to form a closed ring; and two end discs (15) which are fixed to the axially opposite ends of the supporting cylinder (8); the rotor (4) is characterised by the fact that each end disc (15) is integrated into the support cylinder (8) and is therefore a seamless part of the support cylinder (8) and is made of the same material as the support cylinder (8). 2) Rotor (4) according to claim 1, wherein the two end discs (15) axially contain the permanent magnets (6). 3) Rotor (4) according to claim 1 or 2, wherein the end discs (15) have respective balancing openings which balance the rotor (4) around the rotation axis (3). 4) Rotor (4) according to claim 1, 2 or 3, wherein the two end discs (15) constitute external edges of the support cylinder (8) which protrude from the external surface (9) of the support cylinder (8) and delimit the external surface (9) itself on both sides. 5) Rotor (4) according to one of claims 1 to 4, wherein the support cylinder (8) and the two end discs (15) are made of non-magnetic material. 6) Rotor (4) according to one of claims 1 to 4, wherein the support cylinder (8) and the two end discs (15) are made of ferromagnetic material. 7) Rotor (4) according to claim 6 and comprising two separation discs (17) which are interposed between the main permanent magnets (6) and the end discs (15) and are made of non-magnetic material. 8) Rotor (4) according to one of claims 1 to 7 and comprising two half-shafts (10, 11) which are independent and separate from each other and are inserted individually into opposite ends of the central cavity (12) of the support cylinder (8) in such a way as to form a single cohesive block with the support cylinder (8) itself. 9) Rotor (4) according to claim 8, wherein each half-shaft (10, 11) is interference-fitted into the central cavity (12) of the support cylinder (8). 10) Rotor (4) according to claim 8 or 9, wherein a first half-shaft (10) is made of a material other than a material constituting a second half-shaft (11). 11) Rotor (4) according to claim 8, 9 or 10, wherein the support cylinder (8) is made of a material different from the materials constituting the two half-shafts (10, 11). 12) Rotor (4) according to one of claims 1 to 11, wherein each main permanent magnet (6) is formed by a plurality of smaller secondary permanent magnets (7) which are arranged axially one after the other. 13) Rotor (4) according to one of claims 1 to 12, wherein the main permanent magnets (6) are arranged circumferentially one after the other in a Halbach array to cancel the magnetic field radially inside the main permanent magnets (6) and to maximize the magnetic field radially outside the main permanent magnets (6). 14) Rotor (4) according to claim 13, wherein the Halbach array provides for cyclically repeating sequences each of at least four main permanent magnets (6): a main permanent magnet (6) having a South-North orientation arranged circumferentially in a clockwise direction, a subsequent main permanent magnet (6) having a South-North orientation arranged radially towards the outside, a subsequent main permanent magnet (6) having a South-North orientation arranged circumferentially in a counterclockwise direction, and a subsequent main permanent magnet (6) having a South-North orientation arranged radially towards the inside.