WO2020128888A1

WO2020128888A1 - Rotor for an electric machine and method for making said rotor

Info

Publication number: WO2020128888A1
Application number: PCT/IB2019/061004
Authority: WO
Inventors: Fabio MARIGLIANO; Pasquale Forte
Original assignee: Eldor Corporation S.P.A.
Priority date: 2018-12-20
Filing date: 2019-12-18
Publication date: 2020-06-25
Also published as: IT201800020491A1

Abstract

A rotor for an electric machine comprises a main body (2) made of a ferromagnetic material, provided with a central core (3) extending around its own axis of rotation (A) and with a plurality of poles (4) radially projecting from said central core (3) ad suitable for being wrapped by multiple of turns of a winding (6) made of a current conducting material. The rotor comprises guiding means (7) for the multiple turns comprising a plurality of radial sleeves (8) made of an electrically insulating material, each extending around a respective pole (4), wherein the guiding means (7) and the main body (2) are co-moulded.

Description

ROTOR FOR AN ELECTRIC MACHINE AND METHOD FOR MAKING SAID ROTOR

The present invention relates to a rotor for an electric machine and a method for making said rotor.

The present invention therefore applies to the field of high-speed electric machines and in particular refers to devices for fixing coils of electrically conductive wires to the rotors of such machines.

A wound-rotor electric motor, such as electric machines used in the automotive field, is made by winding a plurality of turns of electrically conducting cables around the salient "poles" of a rotor core, typically made of iron.

Such windings, due to the strong mechanical stresses they are subjected to at the machine's working speeds, are wound around the poles with considerable strength and tension, which are required for such windings to keep their position firm even in the presence of high centrifugal thrusts.

To overcome such drawbacks, in the prior art plastic inserts (or in any case made of an insulating material) are used, which are anchored to the various poles of the rotor so as to define axial shoulders which prevent the axial sliding of the wires.

However, in addition to the significant installation complexity, whereby a complex balancing step is needed, such inserts do not prevent the direct contact of the wires in the winding area, which as a result of several stresses can also lead to breakage or damage of the wires.

Further prior art solutions, aimed at overcoming such drawbacks, provide for coupling to the rotor core a pair of plastic supports, abutted against the two axial ends of the rotor.

Generally, such supports are defined by a central body made of an electrically insulating material and provided with a central through opening for accommodating a rotation shaft of the rotor, from which a plurality of arms radially departs, being angularly equally spaced apart and provided with a flat face configured to mate with a respective rotor pole. An example of such elements is known from document US2014/368068.

However, disadvantageously, while partially solving the problems concerning the possible breakage of the windings, such solution introduces both a procedural complication, related to the assembly, and an issue related to the mechanical sealing of the support element on the rotor core.

Therefore, it is an object of the present invention to provide a rotor for an electric machine and a method for making said rotor allowing to overcome the prior art drawbacks mentioned above.

More precisely, the object of the present invention is to provide a rotor for an electric machine having improved strength and quality.

Furthermore, it is an object of the present invention to provide a method for making a high quality and efficient rotor for an electric machine.

Said objects are achieved by a rotor for an electric machine having the features of one or more of the following claims 1 to 7, as well as by a method for making said rotor according to claim 8.

In particular, the rotor comprises a main body made of a ferromagnetic material.

Preferably, the main body is provided with a central core extending around its own axis of rotation and a plurality of poles radially projecting from said central core.

Said poles are suitable for being wound by a plurality of turns of a winding made of a current conducting material.

Preferably, a conductive (multi-phase) winding equipped with multiple turns wound around each pole is provided.

According to an aspect of the invention, the rotor comprises guiding means for said multiple turns.

Said guiding means preferably comprise a plurality of radial sleeves made of an electrically insulating material, each extending (or being fitted) around a respective pole. Preferably, said guiding means and said main body are co-moulded.

Advantageously, it is thereby possible to have a guiding member perfectly constrained to the main body and capable of facilitating the positioning of the winding.

Such solution proves to be highly efficient from both a mechanical (optimal balancing and fixing) and a procedural point of view (the moulding step being easy to be automated).

It should be noted that, preferably, each pole of the main body extends along a radial direction between a narrow portion proximal to the central core and wound by said turns of the winding and an enlarged terminal portion distal from the central core.

Preferably, the radial sleeves each comprise a corresponding narrow portion and a corresponding enlarged terminal portion for housing said narrow portion and enlarged terminal portion of the main body, respectively.

According to an aspect of the invention, the enlarged terminal portion of each sleeve comprises a radial end edge defining an internal undercut in which a peripheral edge of the enlarged terminal portion of the respective pole is constrained.

Advantageously, such peculiarity (achievable by co-moulding) maximizes the constraint of the guiding member to the main body and reduces its exposed area, thus resulting in advantages in terms of electrical performance.

Another object of the present invention is a method for making a rotor for an electric machine, preferably but not exclusively, for the rotor described hitherto.

Such method preferably involves arranging a main body made of a ferromagnetic material, provided with a central core extending around its own axis of rotation and a plurality of poles radially projecting from said central core.

Preferably, a mould equipped with a cavity conformed to accommodate said main body is to be arranged.

Preferably, the cavity is provided with a central opening for accommodating said central core and a plurality of radial channels for accommodating said poles.

Preferably, the main body is positioned in the mould so that a side edge of each pole is spaced apart from and facing the side edge of the corresponding channel, thus defining a free annular volume around the pole.

An electrically insulating material is then injected into the cavity of the mould so as to fill said free annular volume around the poles and, once the material has solidified, the main body is extracted from the mould.

Advantageously, by operating this way, the rotor proves to be extremely robust and efficient, being moreover easy to make by means of a totally automated process.

These and further features, as well as the related benefits, will become more apparent from the following exemplary, and therefore non-limiting, description of a preferred, and therefore not exclusive, embodiment of a rotor for an electric machine and of a method for making said rotor having the features illustrated in the attached drawings, wherein:

- Figure 1 shows a perspective front view of a rotor of an electric machine according to the present invention;

- Figure 2 shows an exploded perspective view of the rotor in Figure 1 .

With reference to the attached figures, number 1 indicates a rotor for an electric machine according to the present invention.

As said, the rotor 1 according to the present invention mainly applies to an electric machine (not shown) for motor vehicles or automotive use in general, therefore suitable for generating traction.

It is therefore understood that the term "vehicle" or other similar term, as used herein, generally includes motor vehicles such as passenger cars including sports vehicles (SUVs), buses, trucks, various commercial vehicles, (including hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen vehicles and other alternative fuel vehicles ( e.g . fuels derived from resources other than oil). As indicated herein, a hybrid vehicle is a vehicle with two or more power sources, e.g. both petrol- fuelled vehicles and electric vehicles.

The electric machine or electric motor generally comprises a stator casing extending around its own central axis and comprising a stator winding. Within the stator casing, the rotor 1 is rotatably housed, the rotation of which is allowed by the presence of a rotation shaft 3 located coaxially with the central axis of the stator casing.

The rotor 1 therefore comprises a main body 2 which is integrally made or, preferably, constrained to a rotation shaft (not shown).

The main body 2 is made of a ferromagnetic material and extends along an axis of rotation "A" which, in the assembled condition, corresponds to the central axis of the stator casing.

In the preferred embodiment, the main body 2 has a lamellar structure, i.e. defined by a plurality of planar plates, each extending in a plane orthogonal to the axis of rotation, axially constrained to each other (packed).

Preferably, the main body 2 has a central core 3 extending around its own axis of rotation "A" and a plurality of poles 4 radially projecting from said central core 3.

It should be noted that the rotor 1 according to the present invention is of the salient pole type; therefore, the term "poles" herein is meant to define a plurality of radial teeth which depart from the central core 3 of the main body 2 in a radial direction.

Preferably, each pole 4 extends along a radial direction between a narrow portion 4a and an enlarged terminal portion 4b distal from the central core 3.

More precisely, the enlarged terminal portion 4b of each pole 4 defines two shoulders 5 with the respective narrow portion 4a. In detail, the enlarged terminal portion 4b extends transversely to the narrow portion 4a symmetrically with respect to a radial centre line "B" of the narrow portion 4a itself.

The expression "radial centre line" herein is meant to define a median line of the narrow portion 4a (and generally of the pole 4) which extends along a radial direction from the axis of rotation "A".

Therefore, each pole 4 has a "T" (or mushroom) shape, in which the top of the T is defined by the enlarged portion 4b while the stem of the T is defined by the narrow portion.

Preferably, the top (or radially outer surface) of each pole 4 has a convex conformation, such that along a radial centre line portion each pole has a greater radial extension than at the respective peripheral edge 4c.

Multiple turns of a conductive winding 6 are wound around the narrow portion 4a (or stem) of each pole 4.

This winding 6 is defined by one or more wires made of copper or a similar conductive material and wound around the poles 4.

More precisely, the winding 6 is composed of a plurality of separate strands 6a, each being wound like a coil around a respective narrow portion of one or more poles 4.

The strands 6a are as many as the phases of the electric machine (e.g. three-phase = three, six-phase = six, etc.).

Therefore, each strand 6a is wound with multiple turns around one or more respective poles 4.

Advantageously, the mushroom shape of the poles allows the windings to be held radially, avoiding that the centrifugal force generated by the rotation of the rotor leads to sliding or displacement thereof.

According to an aspect of the invention, the rotor 1 comprises guiding means 7 for the turns of the winding 6.

Such guiding means 7 comprise a plurality of radial sleeves 8 made of an electrically insulating material, each extending around a respective pole 4.

Electrically insulating material herein is meant to define, for example, Poliparaphenylene sulfide (PPS), alternatively Polybutylene Terephthalate (PBT).

Preferably, such guiding means 7, in particular the sleeves 8, are co moulded with said main body 2.

Preferably, the radial sleeves 8 each comprising a corresponding narrow portion 8a and a corresponding enlarged terminal portion 8b arranged sequentially along the radial direction.

The narrow portion 8a is conformed to house (to size) the narrow portion 4a of the pole 4.

The enlarged portion 8b is conformed to house (to size and partially) the enlarged terminal portion 4b of the pole 4.

In the preferred embodiment, the enlarged terminal portion 8b of each sleeve 8 comprises a radial end edge 9 defining an internal undercut in which a peripheral edge 4c of the enlarged terminal portion 4b of the respective pole 4 is constrained.

In other words, the radial end edge 9 of the sleeve 8 is conformed to surmount the peripheral edge 4c of the enlarged terminal portion 4b of the respective pole 4, thus acting as an axial constraint element.

In this respect, in fact, the radial centre line portion of each pole 4 has a greater radial extension than the corresponding sleeve 8.

In addition, preferably, the narrow portion 8a of each sleeve has a cross section counter-shaped to the cross section of the respective pole 4, preferably quadrilateral.

Therefore, preferably, each narrow portion 8a is defined by a plurality of walls 10 angle one with respect to another.

Preferably, at each junction corner between two adjacent walls 10, guiding grooves 11 are formed externally, which facilitate the positioning of the turns and reduce the mechanical stress on the strand 6a.

In addition, preferably, at least two of said sleeves 8 comprise, at said enlarged terminal portion 8b, at least one axial fastening pin or hole 13 for a locking ring (not illustrated). More preferably, the axial fastening pins or holes are two, departing from opposite faces of the sleeve 8 in order to allow two locking rings (a front and a rear one) to be secured.

It should be noted that the term "axial" herein is meant to define the extension of an element or component parallel, but not necessarily coaxial, to the axis of rotation "A".

Preferably, the sleeves 8 of the guiding means 7 are connected to each other by a central body 12.

The guiding means 7 therefore comprise said central body 12, which is conformed to cover at least part of the central core 5 of the main body 2. Advantageously, this makes the assembly more stable.

Furthermore, a plurality of anchoring pins 12a for the extremities of each phase (i.e. strand 6a) of the winding 6 preferably projects axially from this central body.

Another object of the present invention is a method for making a rotor 1 for an electric machine, preferably, but not necessarily, corresponding to the rotor 1 described hitherto.

Therefore, where appropriate, the features described hitherto in relation to the device will be applicable mutatis mutandis to the method illustrated below and reference numbers will be used in a similar way.

The method involves the provision of a main body 2 made of a ferromagnetic material, provided with a central core 3 extending around its own axis of rotation "A" and a plurality of poles 4 radially projecting from said central core 3.

The main body 2 preferably has the features described hitherto.

Preferably, a mould (not shown) equipped with a cavity conformed to accommodate said main body is then arranged.

The cavity is provided with a central opening for accommodating said central core 3 and with a plurality of radial channels for accommodating said poles 4.

Thereafter, the main body 2 is positioned in the mould, so that a side edge of each pole 4 is spaced apart from and facing the side edge of the corresponding channel, thus defining a free annular volume around the pole 4.

In the preferred embodiment, each channel ends with a radial end wall which is abutted against, or in contact with, the centre line portion of the enlarged portion of the respective pole.

At this stage, an electrically insulating material is injected into the mould cavity, so as to fill said free annular volume around the poles.

Once the plastic material has cooled, then the main body is extracted from the mould and then wrapped with the strands 6a.

The invention achieves the intended objects and offers important advantages.

In fact, the presence of a rotor in which the central body and the guiding means are co-moulded allows to optimize the structure thereof both from a mechanical and electrical point of view.

In addition, this way, a complete coating of the pole is possible, with considerable advantages in the sealing and positioning of the winding.

Claims

1. A rotor for an electric machine, comprising:

- a main body (2) made of a ferromagnetic material, provided with a central core (3) extending around its own axis of rotation (A) and a plurality of poles (4) radially projecting from said central core (3) ad suitable for being wrapped by a plurality of turns of a winding (6) made of a current conducting material,

- a conductive winding (6) provided with multiple turns wound around each pole (4);

characterized in that it comprises guiding means (7) for said multiple turns comprising a plurality of radial sleeves (8) made of an electrically insulating material, each extending around a respective pole (4), wherein said guiding means (7) and said main body (2) are co-moulded.

2. The rotor according to claim 1 , wherein each pole (4) of the main body (2) extends along a radial direction between a narrow portion (4a), proximal to the central core (3) and wrapped by said turns of the winding (6), and an enlarged terminal portion (4b) distal from the central core (3); said radial sleeves (8) each comprising a corresponding narrow portion (8a) and a corresponding enlarged terminal portion (8b) for housing said narrow portion (4a) and enlarged terminal portion (4b) of the pole (4), respectively.

3. The rotor according to claim 2, characterized in that said enlarged terminal portion of each sleeve (8) comprises a radial end edge (9) defining an internal undercut in which a peripheral edge (4c) of the enlarged terminal portion (4b) of the respective pole (4) is constrained.

4. The rotor according to any one of claims 1 to 3, wherein a radial centre line portion of each pole (4) has a greater radial extension than the corresponding sleeve (8).

5. The rotor according to any one of the preceding claims, wherein the guiding means (7) comprise a central body (12) for joining the sleeves (8), which is conformed to cover at least part of the central core (3) of the main body (2).

6. The rotor according to claim 5, wherein said central body (12) of the guiding means (7) comprises a plurality of anchoring pins (12a) for the extremities of each phase of the winding (6).

7. The rotor according to any one of the preceding claims, wherein at least two of said sleeves (8) comprise, at said enlarged terminal portion (8b), at least one axial fastening pin or hole 13 for a locking ring.

8. A method for making a rotor (1 ) for an electric machine, comprising the following steps:

- provision of a main body (2) made of a ferromagnetic material, provided with a central core (3) extending around its own axis of rotation (A) and a plurality of poles (4) radially projecting from said central core (3);

- provision of a mould equipped with a cavity conformed to accommodate said main body (2) and provided with:

a central opening for accommodating said central core (3), a plurality of radial channels for accommodating said poles (4); - positioning of said main body (2) in the mould so that a side edge of each pole is spaced from and facing the side edge of the corresponding channel, thus defining a free annular volume around the pole (4);

- injection of an electrically insulating material inside the mould cavity so as to fill said free annular volume around the poles (4);

- extraction of the main body (2) from the mould.