Rotor assembly for electric machine

Abstract

A rotor assembly for an electric machine includes a rotor and a shaft having a thrust portion forming a support of the rotor, where the rotor is preloaded against the thrust portion.

Description

[0001] The present application relates to a rotor assembly for an electric machine, the rotor assembly comprising a rotor and a shaft having a thrust portion forming a rotor seat, wherein the rotor is preloaded against the thrust portion.

[0002] Such rotor assemblies are known to have laminated sheets forming a rotor arranged on a shaft. Various elements, such as axial tie rods or positive locking devices, are used to provide a secure connection for transmitting torque between the laminated stack assembly and the shaft.

[0003] US2017 / 117766A1 relates to a method for mounting a laminate on the shaft of an electric machine rotor, wherein the laminate is slid onto the shaft and supported in a rotationally rigid manner between two thrust parts connected to the shaft. However, axially preloading the rotor assembly means increased structural stress and cost impact.

[0004] The aim is to reduce the axial preload force without reducing the transmittable torque of the rotor assembly.

[0005] This object is achieved by a rotor assembly according to claim 1. Further embodiments are subject to the dependent claims.

[0006] The rotor assembly of the electric machine comprises a rotor and a shaft, the shaft having a thrust portion, the thrust portion forming a seat for axially supporting the rotor, wherein the rotor is axially preloaded against the thrust portion. The friction increasing device is arranged between a contact surface of the thrust portion adjacent to the rotor and a contact surface of the rotor.

[0007] Increasing the friction between the contact surface of the thrust portion adjoining the rotor and the contact surface of the rotor advantageously allows reducing the axial preload force without reducing the transmittable torque. Depending on the desired reduction in the axial preload force, it may even be possible to increase the transmittable torque.

[0008] Furthermore, during operation of the motor, the motor is excited to vibrate. If the frequency of the vibration and the natural frequency of the motor are the same or close to each other, resonance occurs and components of the motor may be strongly deflected due to the resonance. This deflection causes audible noise, which is disturbing and may damage the service life of the motor. By axial preloading of the rotor assembly, the resonance area can be shifted to an acceptable frequency range. However, high preloads generally lead to structural stresses and cost impacts. Therefore, a rotor assembly having increased friction between the contact surface of the thrust section adjoining the rotor and the contact surface of the rotor has a further advantage, thereby providing a beneficial compromise between noise, vibration, harshness (NVH) reduction, torque transmission and structural stress.

[0009] The rotor and the shaft are rotatably mounted to rotate about a longitudinal axis, wherein the axial direction refers to a direction parallel to the longitudinal axis. The electric machine may have a stator and a rotor, the stator being provided with permanent magnets or stator coils, and the rotor being provided with permanent magnets or rotor coils. The stator may be located within a housing and fixed to the housing. The housing may also include bearings for supporting the rotor assembly for rotation about the longitudinal axis. The thrust portion may be an integral part of the shaft or connected to the shaft.

[0010] The friction increasing means may be provided in the form of a surface treatment of a contact surface of the thrust portion adjoining the rotor and / or of a contact surface of the rotor.The friction increasing means may also be regarded as a friction increasing element.

[0011] According to one embodiment, the friction increasing device or element is a friction pad, which has a coating on both sides. The friction pad may be disc-shaped and circular, with a central hole, for being supported on the shaft, arranged between the thrust part and the rotor, so that one side of the friction pad faces the contact surface of the thrust part adjacent to the rotor, and the other side of the friction pad faces the corresponding contact surface of the rotor. The outer diameter of the friction pad may be adapted to the outer diameter of the thrust shoulder.

[0012] According to one embodiment, the coating comprises particles embedded in a matrix. The particles may be diamond-shaped particles having an average particle size between 10 and 35 microns. The matrix may be an electroless nickel-phosphorus coating having a thickness between 5 and 25 microns. The friction pad may be made of quenched and tempered high carbon steel having a thickness between 0.12 and 0.20 mm. The surface roughness (Rz) of the friction pad may be in the range of 4 to 17 microns, where Rz is the average of the absolute values ​​of the height of the five highest profile peaks and the depth of the five deepest routes within the evaluation length along the friction pad surface.

[0013] According to another embodiment, the shaft has a preload washer for applying an axial preload force to the rotor at an axially distal end opposite to the thrust portion.

[0014] According to another embodiment, the dry static friction coefficient (μ_th) of the shim between the contact surface of the thrust portion and the contact surface of the rotor is at least twice the dry static friction coefficient (μ_pr) of the shim between the contact surface of the preload washer and the opposing contact surface of the rotor, wherein the friction increasing means is applied between the contact surface of the thrust portion and the contact surface of the rotor and not between the contact surface of the preload washer and the opposing contact surface of the rotor. In particular, the dry static friction coefficient (μ_th) of the shim is at least three times the dry static friction coefficient (μ_pr) of the shim.

[0015] The axial preload force (Fp) multiplied by the dry static friction coefficient of the gasket (μ_th), the average radius of the contact surface of the thrust part adjacent to the rotor (Rm_th), plus the axial preload force (Fp) multiplied by the dry static friction coefficient of the gasket (μ_pr), the average radius of the contact surface of the preload gasket (Rm_pr) exceeds the maximum torque (Tmax) of the motor:

[0016] Fp·μ_th·Rm_th+Fp·μ_pr·Rm_pr>Tmax.

[0017] Meeting the above conditions prevents the rotor from sliding relative to the shaft. Assuming that the average radius of the contact surface of the thrust portion adjacent to the rotor (Rm_th) is equal to the average radius of the contact surface of the preload washer adjacent to the opposite end of the rotor (Rm_pr) (Rm_th = Rm_pr), the dry static friction coefficient of the washer (μ_th) is three times the dry static friction coefficient of the washer (μ_th = 3 μ_pr), allowing, for example, a 75% reduction in the axial preload force (Fd) while still resisting the same torque. The axial preload force (Fp) can be in the range of 20kN to 150kN.

[0018] The rotor may comprise an end cap at its axially distal end facing the friction increasing means and / or at its axially distal end facing the preload washer.The rotor may comprise a stacked assembly of laminated metal plates.

[0019] According to another embodiment, the friction increasing device or element is connected to the shaft in a form-locking manner. The shaft may have at least one axially extending groove that cooperates with a tongue at the friction pad to fix the friction pad circumferentially on the shaft.

[0020] Exemplary embodiments and further advantages of the rotor assembly will be described below with reference to the accompanying drawings, in which

[0021] Figure 1 An exemplary embodiment of a rotor assembly is shown in a perspective exploded view;

[0022] Figure 2 Another perspective view of the partially assembled Figure 1 Embodiments of

[0023] Figure 3 The schematic diagram shows Figure 1 Details of the assembled state of the embodiment.

[0024] refer to Figure 1 and 2 An exemplary embodiment is described showing a rotor assembly in a perspective exploded view and in another perspective view partially assembled. Figure 1 and 2Described together. The rotor assembly of the electric machine includes a rotor 2 and a shaft 1, the shaft 1 having a thrust portion 3, the thrust portion 3 forming a seat for axially supporting the rotor 2. The rotor 2 and the shaft 1 are rotatably mounted to rotate about a longitudinal axis L. The rotor 2 is axially preloaded against the thrust portion by a preload washer 5, which is used to apply an axial preload force to the rotor 2 at the end opposite to the thrust portion 3. The rotor 2 includes an end cover 10 at each axial distal end. The rotor 2 also includes a stacked assembly of laminated metal plates stacked between the end covers 10.

[0025] As friction increasing means, a friction pad 4 is arranged between a contact surface of the thrust portion 3 adjoining the rotor 2 and a contact surface of the rotor 2, which contact surface of the rotor 2 is formed on the surface of the corresponding end cover 10 in this embodiment. The friction pad 4 is connected to the shaft 2 in a form-locking manner. The shaft 1 has two axially extending grooves 6, which cooperate with corresponding tongues 7 at the friction pad 4 to fix the friction pad 4 circumferentially on the shaft 1.

[0026] exist Figure 3 The picture shows Figure 1 Details of an embodiment of the present invention. A schematic diagram of the thrust portion 3 and the rotor 2 or, respectively, its end cover 10 is depicted in an assembled state, wherein the friction pad 4 is arranged between the contact surface of the thrust portion 3 adjacent to the rotor 2 and the contact surface of the rotor 2. A person skilled in the art knows that the rotor 2 and the thrust portion 3 are adjacent parts of the rotor assembly, rather than the friction pad 4 between the adjacent parts, because the thickness of the friction pad is very small, for example in the range of 0.1 to 0.2 mm. Therefore, the illustration of FIG. 4 is not drawn to scale, because the thickness of the thrust portion 3 in the axial direction is, for example, at least 25 times the thickness of the friction pad 4.

[0027] Each side of the friction pad 4 has a coating, the coating comprising particles 9 embedded in a matrix 8. The particles 9 may be rhombic particles with an average particle size between 10 and 35 microns. The matrix 8 may be an electroless nickel-phosphorus coating with a thickness between 5 and 25 microns. The pad 4 may be made of hardened and tempered high carbon steel with a thickness between 0.12 and 0.20 mm (including the coating). The surface roughness Rz of the friction pad 4 is in the range of 4 to 17 microns. The dry static friction coefficient (μ_th) of the pad generated between the contact surface of the thrust portion 3 and the contact surface of the rotor 2 may be at least 0.5, for example higher than 0.7. The dry static friction coefficient of the gasket (μ_th) between the contact surface of the thrust portion 3 and the contact surface of the rotor (2) can, for example, be three times the dry static friction coefficient of the gasket (μ_pr) between the contact surface of the preload gasket 3 and the relative contact surface of the rotor 2, wherein the friction increasing device is applied between the contact surface of the thrust portion 3 and the contact surface of the rotor 2, and not between the contact surface of the preload gasket 3 and the relative contact surface of the rotor 2.

[0028] In order to prevent the rotor from sliding relative to the shaft, the axial preload force (Fp) multiplied by the dry static friction coefficient of the gasket (μ_th), the average radius of the contact surface of the thrust portion 3 adjacent to the rotor 2 (Rm_th), plus the axial preload force (Fp) multiplied by the dry static friction coefficient of the washer (μ_pr), the average radius of the contact surface of the preloaded washer (Rm_pr) exceeds the maximum torque (Tmax) of the motor:

[0029] Fp·μ_th·Rm_th+Fp·μ_pr·Rm_pr>Tmax.

[0030] Assuming that the average radius (Rm_th) of the contact surface of the thrust portion 3 adjacent to the rotor 2 is equal to the average radius (Rm_pr) of the contact surface of the preload washer adjacent to the opposite end of the rotor 2 (Rm_th=Rm_pr), the dry static friction coefficient of the gasket (μ_th) is, for example, three times the dry static friction coefficient of the gasket (μ_th=3·μ_pr), allowing the axial preload force (Fd) to be reduced by 75% while still resisting the same torque.

[0031] Reference numerals

[0032] 1 axis

[0033] 2 rotors

[0034] 3Thrust part

[0035] 4 Friction pads

[0036] 5 Preload washers

[0037] 6 grooves

[0038] 7 Tongue

[0039] 8 Matrix

[0040] 9 pellets

[0041] 10 End cap

[0042] L longitudinal axis

Claims

1. A rotor assembly for a motor, comprising: a rotor (2), and A shaft (1) having a thrust portion (3) forming a seat for axially supporting the rotor (2), wherein the rotor (2) is preloaded against the thrust portion (3), and The friction increasing device is arranged between a contact surface of the thrust portion (3) adjacent to the rotor (2) and a contact surface of the rotor (2).

2. The rotor assembly according to claim 1, characterized in that The friction increasing device is a friction pad (4).

3. The rotor assembly according to claim 2, characterized in that The friction pad (4) has a coating on each side.

4. The rotor assembly according to claim 3, characterized in that The coating comprises particles (9) embedded in a matrix (8).

5. The rotor assembly according to claim 4, characterized in that The particles (9) are rhombus-shaped particles with an average particle size between 10 and 35 microns.

6. The rotor assembly according to any one of claims 4 or 5, characterized in that The substrate (8) is a chemical nickel phosphorus coating with a thickness between 5 and 25 microns.

7. A rotor assembly according to any one of claims 2 to 6, characterized in that The friction pad (4) is made of quenched and tempered high carbon steel with a thickness between 0.12 and 0.20 mm.

8. A rotor assembly according to any one of claims 2 to 7, characterized in that The surface roughness (Rz) of the friction pad (4) is in the range of 4 to 17 micrometers.

9. The rotor assembly according to any one of claims 1 to 8, characterized in that The shaft (1) has a preload washer (5) for applying an axial preload force to the rotor (2) at an end opposite to the thrust portion (3).

10. The rotor assembly according to any one of claims 1 to 9, characterized in that The gasket dry static friction coefficient (μ_th) between the contact surface of the thrust portion (3) and the contact surface of the rotor (2) is at least twice the gasket dry static friction coefficient (μ_pr) between the contact surface of the preload gasket (3) and the relative contact surface of the rotor (2), and in particular, the gasket dry static friction coefficient (μ_th) is at least three times the gasket dry static friction coefficient (μ_pr).

11. A rotor assembly according to claims 9 and 10, characterised in that The axial preload force (Fp) multiplied by the dry static friction coefficient of the gasket (μ_th), the average radius of the contact surface of the thrust portion 3 adjacent to the rotor 2 (Rm_th), plus the axial preload force (Fp) multiplied by the dry static friction coefficient of the gasket (μ_pr), the average radius of the contact surface of the preload gasket (Rm_pr) exceeds the maximum torque (Tmax) of the motor: Fp·μ_th·Rm_th+Fp·μ_pr·Rm_pr>Tmax.

12. A rotor assembly according to any one of claims 1 to 11, characterized in that The friction device is connected to the shaft (1) in a form-locking manner.

13. A rotor assembly according to any one of claims 2 to 11, characterised in that The shaft (1) has at least one axially extending groove (6), and the groove (6) cooperates with a tongue (7) at the friction pad (4) to fix the friction pad (4) on the shaft (1) along the circumference.

14. A rotor assembly according to any one of claims 1 to 13, characterised in that The rotor (2) comprises, at its axial distal end, an end cover (10) facing the friction increasing device.

15. A rotor assembly according to any one of claims 1 to 14, characterised in that The rotor (2) comprises a stacked assembly of laminated metal plates.

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