Rotor for an electric machine

Abstract

The present invention relates to a rotor stack (1, 1') for a rotor assembly comprising a stack of rotor laminations having an outer zone (2) with a plurality of magnet pockets (3) adapted to receive a plurality of permanent magnets (4), each magnet pocket (3) having a radial width W1, the outer zone (2) having a circumferential outer wall (5) and a circumferential inner wall (6) between which the magnet pockets (3) are radially arranged, a plurality of ribs (7) extending from the inner wall (6) to an inner zone (8) forming a hole-like zone (9) adapted to receive a shaft (11), the circumferential inner wall (6) having a thickness varying periodically and each rib (7) extending from the minimum radial thickness of the inner wall (6). The present invention also relates to a rotor assembly (10) and a method of manufacturing the rotor assembly (10). Figure for abstract: Figure 2

Description

Title of the invention: Rotor for an electric machine

[0001] The invention relates to a rotor for an electric machine, in particular an electric motor.

[0002] The rotor is particularly intended for use in an electric motor which drives a hydraulic pump, such as used in motor vehicles to provide a volumetric flow of hydraulic oil which is supplied to a clutch actuator, a gearbox actuator, a clutch cooling system, a gearbox lubrication system or the like.

[0003] Rotors are known having a stack of rotor laminations mounted on a metal shaft, in which permanent magnets are held. Such rotors require manufacturing effort, but are distinguished by a strong magnetic field strength.

[0004] One of the technical problems associated with these types of rotor is the fixing of the permanent magnets in the pockets.

[0005] It is known to hold these permanent magnets in their respective pockets with glue or by making complex shapes, which increases production costs.

[0006] The invention aims to provide a rotor comprising a stack of rotor laminations which can be produced with less effort and with good retention of the permanent magnets.

[0007] This object is achieved according to the invention by a stack of rotors for a rotor assembly comprising a stack of rotor laminations having an outer zone with a plurality of magnet pockets capable of receiving a plurality of permanent magnets, each magnet pocket having a radial width, the outer zone having a circumferential outer wall and a circumferential inner wall between which the magnet pockets are arranged radially, a plurality of ribs extending from the inner wall to an inner zone of the stack of rotor laminations forming a hole-like zone capable of receiving a shaft. According to the invention, the circumferential inner wall has a thickness varying periodically and each rib extends from the minimum radial thickness of the inner wall.

[0008] The invention is based on the basic concept of creating a preferential portion at the junction of the ribs and the circumferential inner wall where a thinner wall allows radial displacement of the ribs towards the magnet pockets when the shaft is inserted into the hole-like area.

[0009] The circumferential inner wall is defined between a first circle of radius R of which a tangent is the innermost wall of a magnet pocket and a second circle of which the radius r corresponds to the part of the inner wall closest to the center of the rotor stack.

[0010] The above-mentioned object is also achieved according to the invention by providing a rotor assembly for an electrical machine, in particular for an electric motor, comprising a stack of rotors, a plurality of permanent magnets and a shaft. The diameter of the hole-like area is smaller than the shaft diameter such that when the shaft is inserted into the hole-like area, the insertion force causes a radial displacement of the ribs reducing the radial width of the magnet pockets, thus radially compressing the permanent magnets in their magnet pockets.

[0011] The aforementioned object is also achieved according to the invention by providing a method for producing a rotor assembly for an electric machine, in particular for an electric motor, by means of the following steps: i. assembling a stack of rotor laminations having an outer zone with a plurality of magnet pockets having an initial radial width and an inner zone forming a hole-like zone with a diameter, the outer zone and the inner zone being connected by a plurality of ribs, ii. inserting a permanent magnet into each of the magnet pockets, iii. inserting a shaft with a diameter into the hole type area, the diameter of hole-like area being smaller than the shaft diameter causing radial displacement of the ribs reducing the radial width of the magnet pockets, thereby radially compressing the permanent magnets in their magnet pockets.

[0012] The invention is based on the basic principle of using the shaft insertion force to deform a portion of the contours of the magnet pockets, allowing the permanent magnets to be firmly held in their magnet pockets without additional components, complex shapes, or complex operations.

[0013] According to one configuration of the invention, the hole-like area has a substantially round shape. This provides a counter-shape for inserting the shaft.

[0014] According to one configuration of the invention, a plurality of bridges provide a connection between the ribs in the inner area. These bridges hold the ribs together during radial displacement. Preferably, the bridges are concentric with the hole-like area. Preferably, the bridges have a non-linear shape in order to allow radial displacement of the ribs while maintaining an equal distance between each rib.

[0015] According to one configuration of the invention, the direction of extension of the ribs is substantially perpendicular to the direction of extension of the magnet pockets. In other words, the ribs extend from the circumferential inner wall substantially in the middle of the magnet pocket in its direction of extension. This reduces the radial width of the magnet pocket in its center. The permanent magnet is thus pinched in its center.

[0016] According to one configuration of the invention, the ribs extend from the inner wall at a connection zone of two adjacent magnet pockets. This reduces the radial width of the magnet pocket at their ends. The permanent magnet is thus pinched at its ends.

[0017] According to one configuration of the invention, an area formed between the inner wall, two adjacent ribs and the bridge is free of material. This facilitates the radial displacement of the ribs.

[0018] The invention will be described below on the basis of two embodiments illustrated in the accompanying drawings. In the drawings:

[0019] [Fig. 1] illustrates a first embodiment of a stack of rotors in a top view according to the invention;

[0020] [Fig.2] illustrates a rotor assembly in a perspective view according to the invention;

[0021] [Fig.3] illustrates the mechanical behavior of the rotor stack according to [Fig.l] when inserting the tree;

[0022] [Fig.4] illustrates a magnet pocket of the rotor stack according to [Fig.l] before tree insertion;

[0023] [Fig.5] illustrates a magnet pocket of the rotor stack according to [Fig.l] after tree insertion;

[0024] [Fig.6] illustrates a second embodiment of a stack of rotors in a top view according to the invention;

[0025] [Fig.7] illustrates a step-by-step diagram of the process of producing an assembly rotor according to the invention.

[0026] [Fig.l] represents a stack of rotors 1 comprising a stack of metal rotor laminations. The stack of rotors 1 has an external zone 2 with a plurality of magnet pockets 3 capable of receiving a plurality of permanent magnets 4. The external zone 2 has a circumferential external wall 5 and a circumferential internal wall 6 between which the magnet pockets 3 are radially arranged.

[0027] A plurality of ribs 7 extend from the inner wall 6 to an inner zone 8 of the rotor stack 1 forming a hole-like zone 9 capable of receiving a shaft 11. The hole-like zone 9 has a substantially round shape of diameter DI. The inner ends of ribs 7 have a concave shape to correspond to the outer shape of shaft 11.

[0028] The circumferential inner wall 6 is defined between a first circle of radius R of which a tangent is the innermost wall of one of the magnet pockets 3 and a second circle of which the radius r corresponds to the part of the inner wall 6 closest to the center of rotation of the rotor stack 1. The circumferential inner wall 6 has a thickness varying periodically and each rib 7 extends from the thickness minimum radial displacement of the inner wall 6. This structure creates a preferential portion at the junction of the ribs 7 and the circumferential inner wall 6 where a thinner wall allows radial displacement of the ribs 7 towards the magnet pockets 3 when the shaft 11 is inserted into the hole-like area 9.

[0029] The rotor stack 1 comprises a plurality of bridges 12 providing a connection between the ribs 7 in the internal zone 8 of the rotor stack 1. The plurality of bridges 12 forms a concentric connection to the hole-like zone 9. The bridges 12 have a non-linear shape to allow radial displacement of the ribs 7 without the ribs 7 moving away from each other.

[0030] The direction of extension D of the ribs 7 is substantially perpendicular to the direction of extension d of the magnet pockets 3. In other words, the ribs 7 extend from the circumferential inner wall 6 substantially in the middle of the magnet pockets 4 in their direction of extension d. The permanent magnets 4 are thus pinched in their center.

[0031] An area 13 formed between the inner wall 6, two adjacent ribs 7 and the bridge 12 is free of material. The shape of the ribs 7 is thus created.

[0032] In [Fig. 2] is shown a rotor assembly 10 for an electrical machine, in particular for an electric motor of an electric oil pump. The rotor assembly 10 comprises a stack of rotors 1 as described above with the plurality of permanent magnets 4 and the shaft 11 extending along the axis X which is the axis of rotation of the rotor assembly 10. This rotor assembly 10 has the particularity that, before assembly, the diameter DI of the hole-like area is less than the diameter D2 of the shaft 11 so that when the shaft 11 is inserted into the hole-like area 9, the insertion force causes a radial displacement of the ribs 7 reducing the radial width W2 of the magnet pockets 3, thus radially compressing the permanent magnets 4 in their magnet pockets.

[0033] In [Fig. 3] is shown a simulation of the mechanical behavior of the rotor stack 1 according to [Fig. 1] during the insertion of shaft 11. Because the diameter D2 of the shaft 11 is greater than the diameter DI of the hole-like zone 9, this causes a radial displacement of the ribs 7 of the order of 0.028 mm at the end of the ribs 7 facing the shaft 11 and of the order of 0.02 mm in the region where the ribs 7 are connected to the inner wall 6. This simulation shows that the connection of each rib 7 at the minimum radial thickness of the inner wall 6 allows a reduction in the radial width of the magnet pockets 3.

[0034] The reduction in the radial width of the magnet pockets is shown in detail in [Fig.4] and [Fig.5]. [Fig.4] shows a permanent magnet 4 inserted into its magnet pocket 3 before the shaft 11 is inserted into the rotor stack 1. The magnet pocket 3 has a radial width W1 with a radial clearance between the permanent magnet 4 and the inner and outer walls of the magnet pocket 3 allowing the permanent magnet 4 to be inserted into the magnet pocket 3. [Fig.5] shows the magnet pocket 3 after the shaft 11 has been inserted into the rotor stack 1. The magnet pocket 3 has a radial width W2 less than W1 without radial clearance between the permanent magnet 4 and the inner and outer walls of the magnet pocket 3 allowing the permanent magnet 4 to be firmly held in the magnet pocket 3.

[0035] The rotor stack 1' shown in [Fig. 6] is an alternative to the rotor stack 1 shown in [Fig. 1]. Only the different appearance will be specified here, the rest of the structure being similar. The main difference concerns the connection area of the ribs 7 to the circumferential inner wall 6. In this embodiment, the ribs 7 extend from the inner wall 6 at a connection area of two adjacent magnet pockets 3. This reduces the radial width of the magnet pocket at their ends. The permanent magnets 4 are thus pinched at their ends.

[0036] [Fig.7] specifies the three steps of the method for manufacturing a rotor assembly 10 according to the characteristics mentioned above, in particular the rotor assembly 10 as shown in [Fig.2]. The method comprises the following steps: i. assembly of a stack 1, 1' of rotor laminations having an external zone 2 with a plurality of magnet pockets 3 having an initial radial width W1 and an internal zone 8 forming a hole-type zone 9 of diameter D1, the external zone 2 and the internal zone 8 are connected by a plurality of ribs 7, ii. insertion of a permanent magnet 4 into each of the magnet pockets 3, iii. insertion of a shaft 11 of diameter D2 into the hole type area 9, the diameter Dl of the hole-like area is less than the diameter D2 of the shaft causing a radial displacement of the ribs 7 reducing the radial width of the magnet pockets 3 from W1 to W2, thus radially compressing the permanent magnets 4 in their magnet pockets 3.

Claims

Claims

1. A stack of rotors (1, 1') for a rotor assembly comprising a stack of rotor laminations having an outer zone (2) with a plurality of magnet pockets (3) adapted to receive a plurality of permanent magnets (4), each magnet pocket (3) having a radial width W1, the outer zone (2) having a circumferential outer wall (5) and a circumferential inner wall (6) between which the magnet pockets (3) are radially arranged, a plurality of ribs (7) extending from the inner wall (6) to an inner zone (8) forming a hole-like zone (9) adapted to receive a shaft (11), characterized in that the circumferential inner wall (6) has a periodically varying thickness and each rib (7) extends from the minimum radial thickness of the inner wall (6).

2. Stack of rotors (1, 1') according to claim 1, characterized in that the hole-like zone (9) has a substantially round shape.

3. Stack of rotors (1, 1') according to claim 1 or 2, characterized in that it comprises a plurality of bridges (12) providing a connection between the ribs (7) in the internal zone (8).

4. Stack of rotors (1, 1') according to claim 3, characterized in that the bridges (12) are concentric with the hole-like zone (9).

5. Stack of rotors (1, 1') according to claim 3 or 4, characterized in that the bridges (12) have a non-linear shape.

6. Stack of rotors (1, 1') according to at least one of claims 1 to 5, characterized in that the direction of extension (D) of the ribs (7) is substantially perpendicular to the direction of extension (d) of the magnet pockets (3).

7. Stack of rotors (1, 1') according to at least one of claims 1 to 5, characterized in that the ribs (7) extend from the inner wall (6) at a connection zone of two adjacent magnet pockets (3).

8. Stack of rotors (1, 1') according to at least one of the preceding claims, characterized in that a zone (13) formed between the inner wall (6), two adjacent ribs (7) and the bridge (12) is free of material.

9. Rotor assembly (10) for an electric machine, in particular for an electric motor, comprising a rotor stack (1, 1') according to at least one of claims 1 to 8, a plurality of permanent magnets (4) and a shaft (11), characterized in that the diameter (Dl) of the rotor area hole type (9) is smaller than the diameter (D2) of the shaft (11) such that when the shaft (11) is inserted into the hole type area (9), the insertion force causes a radial displacement of the ribs (7) reducing the radial width of the magnet pockets (3) from W1 to W2, thereby radially compressing the permanent magnets (4) in their magnet pockets (3).

10. A method of manufacturing a rotor assembly (10) for an electric machine, in particular for an electric motor, by means of the following steps: i. assembly of a stack (1, 1') of rotor laminations having an external zone (2) with a plurality of magnet pockets (3) having an initial radial width W1 and an internal zone (8) forming a hole-like zone (9) of diameter (Dl), the external zone (2) and the internal zone (8) are connected by a plurality of ribs (7), ii. inserting a permanent magnet (4) into each of the magnet pockets (20), iii. inserting a shaft (11) of diameter (D2) into the hole-like area (9), the diameter (D1) of the hole-like area is smaller than the shaft diameter (D2), causing a radial displacement of the ribs (7) reducing the radial width of the magnet pockets (3) from W1 to W2, thus radially compressing the permanent magnets (4) in their magnet pockets (3).

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