Rotor for an electrical machine and electrical machine comprising such a rotor

Abstract

The invention relates to a rotor for an electric machine, the rotor comprising: - a shaft intended to be driven in rotation about an axis X; - a body which is rotationally fixed to the shaft and comprises n slots (7) distributed around the axis X and defining n teeth (8, 9) extending radially outwards; where n is an even number greater than or equal to 2; - coils of wire (10) which are wound around the teeth (8, 9) and inserted into the slots (7), said coils of wire (10) being configured to impart to the teeth (8, 9) opposite polarities alternately about the axis X; and - at least one permanent magnet (19) disposed in one of the slots (7) and oriented such that a first pole and a second pole of opposite polarities are each adjacent to a tooth (8, 9) having a corresponding polarity. Figure to be published with the abstract: Fig. 3

Description

Title of the invention: Rotor for an electrical machine and electrical machine comprising such a rotor Scope of the invention

[0001] The invention relates to the field of rotating electrical machines, in particular for motor vehicles.

[0002] The invention relates to a rotor for a rotating electrical machine, and more specifically a wound rotor, that is to say a rotor having a body made up of a stack of sheets having notches separated by teeth and accommodating coils of wire. Technological background

[0003] A wound rotor consists of a body formed by a stack of steel laminations. These laminations have notches that define the rotor teeth. The teeth extend radially outwards and are arranged circumferentially around the rotor's axis of rotation. Coils of wire are placed in the notches, and the winding is designed so that the current flows in opposite directions around adjacent teeth. Thus, neighboring teeth have opposite magnetic polarities, which creates an alternating magnetic field, essential for producing motion in a rotating electrical machine.

[0004] However, wound rotors have significant limitations. Their low-speed efficiency is often compromised due to magnetic flux diffusion. Furthermore, the peak torque, i.e., the maximum torque the machine can produce, is limited. Rotating electrical machines with such rotors therefore require a large footprint to achieve the desired performance. Summary

[0005] Also, a problem which arises and which the present invention aims to solve is to propose a wound rotor having better performance without increasing its size.

[0006] In order to solve this problem, and according to a first object, a rotor for an electrical machine is proposed, the rotor comprising: - a shaft intended to be driven in rotation around an X axis; - a body which is rotationally fixed to the shaft and comprises n notches distributed around the X axis and defining n teeth extending radially outwards; where n is an even number greater than or equal to 2; - coils of wire which are wound around the teeth and inserted into the slots, said coils of wire being configured to impart opposite polarities to the teeth alternately around the X-axis; and - at least one permanent magnet arranged in one of the notches and oriented so that a first pole and a second pole of opposite polarities are each adjacent to a tooth having a corresponding polarity.

[0007] Thus, the permanent magnet helps to concentrate the magnetic fluxes further, which improves the efficiency of the electric machine, particularly at low speeds. In addition, the permanent magnet provides an extra magnetic flux, which increases the peak torque. Such a rotor therefore allows for better performance without increasing the motor's size.

[0008] According to embodiments, such a rotor may include one or more of the following characteristics.

[0009] According to one embodiment, each tooth has a radially external end which is equipped with a head comprising two retention zones projecting circumferentially on either side of said tooth, at least one permanent magnet being held radially outwards by one of the retention zones of each tooth which borders said notch.

[0010] According to one embodiment, the retention zones each have a notch, with at least one permanent magnet being received in said notch.

[0011] According to one embodiment, at least one permanent magnet extends along the entire length of the notch. Thus, said permanent magnet has a dual function since it replaces the closing wedge that covers the notch and, in particular, reduces the coefficient of rotational friction with the cooling fluid contained in the housing.

[0012] According to one embodiment, only some of the slots house a permanent magnet. According to another embodiment, the rotor has at least one permanent magnet in each slot. This ensures homogeneity of the magnetic fluxes and thus limits torque fluctuations.

[0013] According to one embodiment, the at least one permanent magnet comprises only one permanent magnet housed per notch, which simplifies the manufacture and assembly of the rotor.

[0014] According to another embodiment, the at least one permanent magnet comprises several permanent magnets which are housed in the notch and are aligned one after the other parallel to the X axis and / or arranged successively circumferentially around the X axis.

[0015] According to one embodiment, each tooth carries a single coil of wire. The winding is therefore concentrated. Such a winding is simpler to manufacture and ensures a greater power density, that is to say, greater power for a given volume.

[0016] According to another embodiment, the coil windings are distributed, that is to say that each winding is distributed over at least two of the teeth.

[0017] According to one embodiment, the body consists of a plurality of sheets stacked along the X axis.

[0018] According to a second object, the invention relates to an electrical machine comprising a casing as well as a rotor of the aforementioned type and a stator which are housed in said casing, the rotor shaft being mounted for rotation about the X axis on the casing. Brief description of the figures

[0019] Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of example but not limitation, with reference to the accompanying drawings in which:

[0020] [Fig-1] is a schematic axial cross-sectional view of a rotating machine.

[0021] [Fig.2] is a perspective view of a rotor according to one embodiment.

[0022] [Fig.3] is a partial schematic cross-sectional view of the rotor of the [Fig.2] and representing in detail a permanent magnet received in a notch between two teeth. Description of the implementation methods

[0023] In the description and claims, the terms "external" and "internal," as well as the orientations "axial" and "radial," shall be used to designate, according to the definitions given in the description, elements of the electric machine. By convention, the X-axis of rotation of the rotor defines the "axial" orientation. The terms "external" and "internal" are used to define the relative position of one element with respect to another, with reference to the X-axis; an element close to the X-axis is thus described as internal, as opposed to an external element located radially on the periphery. The "circumferential" orientation is directed orthogonally to the X-axis and orthogonally to the radial direction.

[0024] The electric machine 1 is a synchronous machine. It can in particular be used as a motor intended to provide propulsion for an electric or hybrid vehicle and / or as a generator for such a vehicle.

[0025] As shown in [Fig.1], the electric machine 1 comprises a case 2, as well as a rotor 3 and a stator 4 which are housed in said case 2.

[0026] The stator 4 comprises a frame fixed inside the housing 2 and which carries coils. The frame is made of steel sheets stacked axially against each other. The frame has grooves in which coils of wire are housed.

[0027] The rotor 3 is mounted for rotation inside the housing 2 and is positioned radially inside the stator 4. It comprises a rotor shaft 5 and a body 6 which is fixed to said rotor shaft 5. The rotor shaft 5 is guided in rotation by means of a pair of bearings 21, 22.

[0028] The body 6 is formed by a stack of laminations, for example, made of steel. These laminations are provided with notches 7, distributed circumferentially around the axis X and defining teeth 8, 9 which extend radially outwards, in an even number. Coils of wire 10 are placed in the notches 7 and are arranged so that the current flows in opposite directions around adjacent teeth 8, 9. Thus, each tooth 8, 9 has a polarity and constitutes a pole of the rotor 3, the polarities of said teeth 8, 9 being alternated around the axis of rotation X of the rotor 3.

[0029] As illustrated, for example, in [Fig. 2], each tooth 8, 9, when viewed in cross-section in a plane perpendicular to the X-axis, has a base 12 around which the wires of one or more of the wire spools 10 are wound, and a head 11 positioned at an external end of said tooth 8, 9. The head 11 has a width, measured in said transverse plane, that is greater than the width of the base 12. The head 11 thus has two retention zones 13, 14, which project circumferentially on either side of the tooth 8, 9 and thus allow the wires to be held radially in the notches 7 under the effect of centrifugal force. Thus, the teeth 8, 9 adopt a T-shaped or mushroom-shaped form.

[0030] Each tooth 8, 9 is equipped with an insulating support 15, visible in [Fig. 3], which provides electrical insulation between the wires and the body 6 of the stator 4. The insulating support 15 has a sleeve 16 which is arranged around the base 12 of the teeth 8, 9 and two rims, namely an external rim 17 and an internal rim 18. The external rim 17 is arranged radially between the wires and one of the retention areas 13, 14 of the teeth 8, 9, while the internal rim 18 is arranged between the wires and the central part of the body 6 of the stator 4.

[0031] In the embodiment shown, the winding is of the concentrated type. Thus, each tooth 8, 9 carries exactly one of the wire coils 10. However, in another embodiment, not shown, the winding is of the distributed type, that is to say that each wire coil 10 is distributed over at least two of the teeth 8, 9 of the rotor 3.

[0032] The wire coils 10 are impregnated with a resin which helps to keep them properly in place during the rotation of the rotor 3.

[0033] The ends of the wires of the wire coils 10 are fixed to a rotating collector, not shown. The current collector has two slip rings, each mounted on one end of the rotor shaft 5, insulated from each other, and in contact with fixed brushes.

[0034] The rotor 3 further comprises permanent magnets 19, shown in Figures 2 and 3, each of which is disposed in one of the notches 7 formed between two teeth 8, 9. In the embodiment shown, a single permanent magnet 19 is placed in each notch 7. The permanent magnet 19 extends circumferentially between two adjacent teeth 8, 9 and is held radially outwards by the retention zones 13, 14 of the adjacent teeth 8, 9. For this purpose, each retention zone 13, 14 has a notch 20 receiving one of the lateral edges of the permanent magnet 19, said notch 20 having a shape complementary to that of the lateral edges of the permanent magnet 19.

[0035] The permanent magnet 19 can be retained radially inward by various means. In one embodiment, the resin fills the notch 7 so as to hold said permanent magnet 19 between the resin and the retention areas 13, 14 of two adjacent teeth 8, 9. In another embodiment, the longitudinal ends of the permanent magnet 19 are each fixed in a recess provided in a wedge which is press-fitted into said notch 7.

[0036] The permanent magnet 19 is oriented such that its magnetic axis, that is, the axis connecting its poles, is directed circumferentially. In other words, the neutral plane passing through the center of the permanent magnet 19 is oriented radially. Furthermore, each pole of the permanent magnet 19 is adjacent to a tooth 8, 9 of the same polarity. Thus, as shown in [Fig. 3], the south pole of the permanent magnet 19 is held by the head 11 of the south-polarized tooth 9, while the north pole of the permanent magnet 19 is held by the head 11 of the north-polarized tooth 8.

[0037] Advantageously, the permanent magnet 19 extends over substantially the entire length of the notch. Thus, the permanent magnet provides a dual function since, in addition to generating a magnetic flux, it allows a notch 7 to be closed, thereby reducing the coefficient of rotational friction of the rotor 3 with the cooling fluid, such as oil, which is present in the housing 2.

[0038] The permanent magnets 19 are, for example, made of an alloy chosen from: Neodymium-iron-boron (NdFeB), samarium-cobalt (SmCo) and Ferrite (iron oxide).

[0039] In other embodiments not illustrated, the rotor 3 includes several permanent magnets 19 housed in each notch 7. Thus, it is possible to align several permanent magnets one behind the other, parallel to the X axis and / or to arrange an odd number of permanent magnets successively on the periphery, with an alternation of polarities.

[0040] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention, as defined by the claims.

[0041] The use of the verb "comprise", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0042] In the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Demands

1. Rotor (3) for an electric machine (1), the rotor (3) comprising: - a shaft (5) intended to be driven in rotation about an axis X; - a body (6) which is rotationally fixed to the shaft (5) and comprising n slots (7) distributed around the axis X and defining n teeth (8, 9) extending radially outwards; where n is an even number greater than or equal to 2; - coils of wire (10) which are wound around the teeth (8, 9) and inserted into the slots (7), said coils of wire (10) being configured to impart to the teeth (8, 9) opposite polarities alternately around the axis X; and - at least one permanent magnet (19) disposed in one of the notches (7) and oriented so that a first pole and a second pole of opposite polarities are each adjacent to a tooth (8, 9) having a corresponding polarity.

2. Rotor (3) according to claim 1, wherein each tooth (8, 9) has a radially external end which is equipped with a head (11) comprising two retention zones (13, 14) projecting circumferentially on either side of said tooth (8, 9) and wherein at least one permanent magnet (19) is held radially outwards by one of the retention zones (13, 14) of each tooth (8, 9) which borders said notch (7).

3. Rotor (3) according to claim 2, wherein the retention zones (13, 14) each have a notch (20) and wherein at least one permanent magnet (19) is received in said notch (20).

4. Rotor (3) according to any one of claims 1 to 3, wherein at least one permanent magnet (19) extends over a whole length of the slot (7).

5. Rotor (3) according to any one of claims 1 to 4, comprising at least one permanent magnet (19) in each slot (7).

6. Rotor (3) according to any one of claims 1 to 5, wherein the at least one permanent magnet (19) comprises only one permanent magnet (19) housed in the notch (7).

7. Rotor (3) according to any one of claims 1 to 5, wherein at least one permanent magnet (19) comprises several permanent magnets (19) which are housed in the notch (7) and are aligned one after the other parallel to the X axis and / or arranged successively circumferentially around the X axis.

8. Rotor (3) according to any one of claims 1 to 6, wherein each tooth (8, 9) carries a single coil of wire (10).

9. Rotor (3) according to any one of claims 1 to 8, wherein the body (6) is made up of a plurality of sheets stacked along the X axis.

10. Electric machine (1) comprising a housing (2) and a rotor (3) according to any one of claims 1 to 9 and a stator (4) which are housed in said housing (2), the shaft (5) of the rotor (3) being mounted for rotation about the X-axis on the housing.

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