Rotor unit for an electrical machine

Abstract

Rotor arrangement for an electrical machine with a rotor and a shaft with a support area which forms a stop for the rotor, wherein the rotor is preloaded against the support area.

Description

[0001] The application relates to a rotor arrangement for an electrical machine, comprising a rotor and a shaft with a support region which forms an abutment for axially supporting the rotor, wherein the rotor is prestressed against the support region.

[0002] Such rotor arrangements, in which sheet metal laminations arranged on a shaft form the rotor, are known. To ensure a reliable connection for transmitting torque between the lamination packs and the shaft, various elements are used, such as axial tie rods or positive locking devices.

[0003] US 2017 / 117766 A1 relates to a method for mounting laminations on the shaft of a rotor for an electrical machine, wherein the laminations are pushed onto the shaft and clamped between two support areas connected to the shaft in a rotationally fixed manner. However, the axial preload of the rotor assembly leads to increased structural stress and impacts costs.

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

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

[0006] The rotor assembly for an electric machine comprises a rotor and a shaft with a support region that forms an abutment for axially supporting the rotor, wherein the rotor is axially preloaded against the support region. A friction-increasing means is arranged between a contact surface of the support region that abuts the rotor and a contact surface of the rotor.

[0007] Increasing the friction between the contact surface of the support area adjacent to the rotor and the contact surface of the rotor advantageously allows for a reduction in the axial preload force without reducing the transmittable torque. Depending on the degree to which the axial preload force is to be reduced, the transmittable torque can even be increased.

[0008] Furthermore, an electrical machine is excited to vibrate during operation. If the vibration frequencies and a natural frequency of the electrical machine are the same or close to each other, resonance occurs, which can cause significant deflections of electrical machine components. Such deflections cause acoustic noise, which is disruptive and can impair the service life of the electrical machine. The resonance range can be shifted into an acceptable frequency range by axially preloading the rotor assembly. However, high preloads typically lead to structural stresses and higher costs.The rotor arrangement with increased friction between the contact surface of the support area adjacent to the rotor and the contact surface of the rotor therefore has the further advantage of offering a favorable compromise between a reduction of noise, vibration, and harshness (NVH), torque transmission and structural load.

[0009] The rotor and the shaft are mounted for rotation about a longitudinal axis, where axial refers to a direction parallel to the longitudinal axis. Electric machines may have a stator provided with permanent magnets or stator coils and a rotor provided with permanent magnets or rotor coils. The stator may be housed in and secured to a housing. The housing may further include bearings to keep the rotor assembly rotatable about the longitudinal axis. The support portion may be an integral part of the shaft or connected to the shaft.

[0010] The friction-increasing agent can be provided in the form of a surface treatment of the contact surface of the support area that abuts the rotor and / or the contact surface of the rotor. The friction-increasing agent can also be considered a friction-increasing element.

[0011] According to one embodiment, the friction-increasing means or element is a friction disc with a coating on both sides. The friction disc can be disc-shaped, round, with a central bore for supporting the shaft, and arranged between the support area and the rotor so that one side of the friction disc faces the contact surface of the support area that abuts the rotor, and the other side of the friction disc faces the corresponding contact surface of the rotor. An outer diameter of the friction disc can be adapted to an outer diameter of the support area.

[0012] According to one embodiment, the coating comprises particles embedded in a matrix. The particles can be diamond particles with an average particle size between 10 and 35 micrometers. The matrix can be an electroless nickel-phosphorus coating with a thickness between 5 and 25 micrometers. The friction disc can be made of a tempered high-carbon steel with a thickness between 0.12 and 0.20 millimeters. The friction disc can have a surface roughness (Rz) in a range between 4 and 17 micrometers, where Rz is the mean of the absolute values of the heights of the five highest profile peaks and the depths of the five deepest grooves within an evaluation length along the surface of the friction disc.

[0013] According to a further embodiment, the shaft has a preloading disk to exert an axial preload force on the rotor at an axial end opposite the support region.

[0014] According to a further embodiment, a dry static friction coefficient (µ_th) of the friction disc between the contact surface of the support region and the contact surface of the rotor is at least twice as large as a dry static friction coefficient (µ_pr) of the preload disc between a contact surface of the preload disc and an opposite contact surface of the rotor, if the friction-increasing agent is arranged between the contact surface of the support region and the contact surface of the rotor and not between the contact surface of the preload disc and the opposite contact surface of the rotor. In particular, the dry static friction coefficient of the friction disc (µ_th) is at least three times as large as the dry static friction coefficient of the preload disc (µ_pr).

[0015] The axial preload force (Fp) multiplied by the dry static friction coefficient (µ_th) of the friction disc and a mean radius (Rm_th) of the contact surface of the support area adjacent to the rotor plus the axial preload force (Fp) multiplied by the dry static friction coefficient (µ_pr) of the preload disc and a mean radius (Rm_pr) of the contact surface of the preload disc exceeds a maximum torque (Tmax) of the electric machine: Fp⋅μ_th⋅Rm_th+Fp⋅μ_pr⋅Rm_pr>Tmax.

[0016] Fulfilling the above condition prevents the rotor from slipping relative to the shaft. Assuming that the mean radius (Rm_th) of the contact surface of the support area adjacent to the rotor is equal to the mean radius (Rm_pr) of the contact surface of the preload disc adjacent to the opposite end of the rotor (Rm_th = Rm_pr), and that the dry static friction coefficient of the friction disc (µ_th) is three times higher than the dry static friction coefficient of the preload disc (µ_th = 3 µ_pr), a reduction in the axial preload force (Fp) of, for example, 75% is possible while maintaining the same torque. The axial preload force (Fp) can range between 20 kN and 150 kN.

[0017] The rotor may be provided with an end cap at its axial end facing the friction-increasing means and / or at its axial end facing the preloading disc. The rotor may consist of stacks of sheet metal laminations.

[0018] According to a further embodiment, the friction-increasing means or element is positively connected to the shaft. The shaft may have at least one axially extending groove that interacts with a tongue on the friction disc to secure the friction disc circumferentially on the shaft.

[0019] An exemplary embodiment and further advantages of the rotor arrangement are presented below with reference to the accompanying drawings, wherein Fig. 1 shows an exemplary embodiment of the rotor assembly in an exploded perspective view; Fig. 2 the embodiment of Fig. 1 in another perspective view, partially assembled; Fig. 3 a detail of the embodiment of Fig. 1 in assembled state in a schematic representation.

[0020] An exemplary embodiment is shown in the Fig. 1 and Fig. 2, which show the rotor assembly in an exploded perspective view and in another perspective view, partially assembled. Fig. 1 and Fig. 2 are described together. The rotor arrangement for an electrical machine consists of a rotor 2 and a shaft 1 with a support region 3, which forms an abutment for axially supporting the rotor 2. The rotor 2 and the shaft 1 are rotatably mounted about a longitudinal axis L. The rotor 2 is axially preloaded against the support region 3 by means of a preload disk 5 in order to exert an axial preload force on the rotor 2 at an end opposite the support region 3. The rotor 2 comprises an end cap 10 at each axial distal end. The rotor 2 also comprises stacks of laminations stacked between the end caps 10.

[0021] As a friction-increasing means, a friction disc 4 is arranged between a contact surface of the support area 3 resting on the rotor 2 and a contact surface of the rotor 2. In this embodiment, the friction disc 4 is formed on the surface of the respective end cap 10. The friction disc 4 is positively connected to the shaft 2. The shaft 1 has two axially extending grooves 6, which interact with corresponding tongues 7 on the friction disc 4 to secure the friction disc 4 in the circumferential direction on the shaft 1.

[0022] Fig. 3 shows a detail of the embodiment of Fig. 1. Shown is a schematic representation of the support region 3 and the rotor 2 or its end cap 10 in the assembled state with the friction disc 4 arranged between the contact surface of the support region 3 lying against the rotor 2 and a contact surface of the rotor 2. The person skilled in the art will recognize that the rotor 2 and the support region 3 are the abutting parts of the rotor arrangement, not the friction disc 4 between the abutting parts, since the thickness of the friction disc is insignificantly small, for example in the range between 0.1 and 0.2 millimeters. The representation in Fig. 4 is therefore not to scale, since the thickness of the support area 3 in the axial direction is, for example, at least 25 times the thickness of the friction disc 4.

[0023] The friction disc 4 has a coating on each side consisting of particles 9 embedded in a matrix 8. The particles 9 can be diamond particles with an average particle size between 10 and 35 micrometers. The matrix 8 can be an electroless nickel-phosphorus coating with a thickness between 5 and 25 micrometers. The friction disc 4 can be made of a tempered steel with a high carbon content and a thickness between 0.12 and 0.20 millimeters including the coatings. The friction disc 4 has a surface roughness Rz in the range between 4 and 17 micrometers. The resulting dry static friction coefficient (µ_th) between the contact surface of the support area 3 and the contact surface of the rotor 2 can be at least 0.5, for example more than 0.7.The dry static friction coefficient (µ_th) of the friction disc 4 between the contact surface of the support area 3 and the contact surface of the rotor 2 is at least twice as large as the dry static friction coefficient (µ_pr) of the preload disc 5 between a contact surface of the preload disc 5 and an opposite contact surface of the rotor 2, if the friction-increasing agent is arranged between the contact surface of the support area 3 and the contact surface of the rotor 2 and not between the contact surface of the preload disc 5 and the opposite contact surface of the rotor 2.

[0024] To prevent the rotor from slipping relative to the shaft, the axial preload force (Fp) multiplied by the dry static friction coefficient (µ_th) of the friction disc and a mean radius (Rm_th) of the contact surface of the support area 3 lying on the rotor 2 plus the axial preload force (Fp) multiplied by the dry static friction coefficient (µ_pr) of the preload disc and a mean radius (Rm_pr) of the contact surface of the preload disc exceeds a maximum torque (Tmax) of the electric machine: Fp⋅μ_th⋅Rm_th+Fp⋅μ_pr⋅Rm_pr>Tmax.

[0025] Assuming that the mean radius (Rm_th) of the contact surface of the support area 3 lying on the rotor 2 is equal to the mean radius (Rm_pr) of the contact surface of the preload disc lying on the opposite end of the rotor 2 (Rm_th = Rm_pr), and that the dry static friction coefficient of the friction disc (µ_th) is three times as high as the dry static friction coefficient of the preload disc (µ_th = 3 µ_pr), for example, a reduction of the axial preload force (Fp) by 75% is possible while maintaining the same torque. Reference symbol 1 wave 2 rotors 3 Support area 4 friction disc 5 preload washer 6 grooves 7 Tongue 8 Matrix 9 particles 10 end cap L Longitudinal axis. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2017 / 117766 A1

[0003]

Claims

[1] Rotor arrangement for an electrical machine, comprising a rotor (2) and a shaft (1) with a support region (3) which forms an abutment for axially supporting the rotor (2), wherein the rotor (2) is prestressed against the support region (3), and wherein a friction-increasing means is arranged between a contact surface of the support region (3) lying against the rotor (2) and a contact surface of the rotor (2). [2] Rotor arrangement according to claim 1, characterized by that the friction-increasing means is a friction disc (4). [3] Rotor arrangement according to claim 2, characterized by that the friction disc (4) has a coating on each side. [4] Rotor arrangement according to claim 3, characterized by that the coating comprises particles (9) embedded in a matrix (8). [5] Rotor arrangement according to claim 4, characterized bythat the particles (9) are diamond particles with an average particle size between 10 and 35 micrometers. [6] Rotor arrangement according to one of claims 4 or 5, characterized by that the matrix (8) is an electroless nickel-phosphorus coating with a thickness between 5 and 25 micrometers. [7] Rotor arrangement according to one of claims 2 to 6, characterized by that the friction disc (4) is made of a tempered steel with a high carbon content and a thickness between 0.12 and 0.20 millimetres. [8] Rotor arrangement according to one of claims 2 to 7, characterized by that the friction disc (4) has a surface roughness (Rz) in the range between 4 and 17 micrometers. [9] Rotor arrangement according to one of claims 1 to 8, characterized by that the shaft (1) has a preloading disk (5) at an end opposite the support region (3) for exerting an axial preload force on the rotor (2). [10] Rotor arrangement according to one of claims 1 to 9, characterized by that a dry static friction coefficient (µ_th) of the friction disc between the contact surface of the support region (3) and the contact surface of the rotor (2) is at least twice as high as a dry static friction coefficient (µ_pr) of the preload disc between a contact surface of the preload disc (5) and an opposite contact surface of the rotor (2), in particular the dry static friction coefficient of the friction disc (µ_th) is at least three times as high as the dry static friction coefficient of the preload disc (µ_pr). [11] Rotor arrangement according to claims 9 and 10, characterized bythat the axial preload force (Fp) multiplied by the dry static friction coefficient (µ_th) of the friction disc and a mean radius (Rm_th) of the contact surface of the support area 3 lying on the rotor 2 plus the axial preload force (Fp) multiplied by the dry static friction coefficient (µ_pr) of the preload disc and a mean radius (Rm_pr) of the contact surface of the preload disc exceeds a maximum torque (Tmax) of the electrical machine: Fp · µ_th · Rm_th + Fp · µ_pr · Rm_pr > Tmax. [12] Rotor arrangement according to one of claims 1 to 11, characterized by that the friction means is positively connected to the shaft (1). [13] Rotor arrangement according to one of claims 2 to 11, characterized by that the shaft (1) has at least one axially extending groove (6) which cooperates with a tongue (7) on the friction disc (4) in order to secure the friction disc (4) on the shaft (1) in the circumferential direction. [14] Rotor arrangement according to one of claims 1 to 13, characterized by that the rotor (2) has an end cap (10) at its axial end facing the friction-increasing means. [15] Rotor arrangement according to one of claims 1 to 14, characterized by that the rotor (2) consists of stacks of sheet metal laminations.

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