WO2011065893A1

WO2011065893A1 - Rotating electrical machine with improved rotor bearing

Info

Publication number: WO2011065893A1
Application number: PCT/SE2010/051244
Authority: WO
Inventors: Vilmos TÖRÖK
Original assignee: Toeroek Vilmos
Priority date: 2009-11-25
Filing date: 2010-11-12
Publication date: 2011-06-03
Also published as: SE0950897A1; SE533879C2

Abstract

An electrical machine comprises a stator (10) with an opening (14), and an essentially circular rotor (20) mounted in the opening of the stator. The rotor is rotatably journalled to the stator by means of wheels (32). The rotor comprises at least four rotor sections (30), each rotor section having at least one pair of wheels. By providing pivotal interconnection of adjacent rotor sections in the peripheral direction of the rotor, a very small air gap between stator and rotor can be maintained. (FIG. 1)

Description

Rotating Electrical Machine with Improved Rotor Bearing

HELD OF INVENTION

[0001] The present invention relates generally to electrical irachines and more particulariy to a rotating electrical rmchine with improved rotor bearing.

BACKGROUND

[0002] In prior art electrical machines, regardless whether the rmchine has been intended for use as a motor or as a generator, the rotor traditionally has been built around a central shaft rotatably joumalled to the stator, also for very large diameter machines.

[0003] In generators driven by wind turbines in the multi-MW -class the use of gearboxes to increase the speed of the generator is widely used. However, due to breakdown of these gearboxes, particulariy in off-ehore plants, the use of low speed generators is being looked at as a preferred solution.

[0004] Such low speed multi pole generators preferably have rotors provided with permanent magnets, but permanent magnets are very expensive. This in turn leads to high costs for these permanent magnets, particulariy in large generators having a diameter of four meters or more, where the air gap for mechanical reasons must be large.

[0005] In a typical electric machine, the radial forces acting on the rotor surface are an order of magnitude larger than the tangential forces acting thereon. This means that the air gap between stator and rotor must be made large to accommodate for varying stator and rotor diameter due to exerted forces etc.

[0006] However, a large air gap requires large permanent magnets and furthermore prevents efficient use of the so called MixedRrie principle, described in the international patent publication No. WO 98/ 25330 A2, incorporated herein by reference. In short, the Mixedlble principle teaches the use of poles with a pushing edge in the form of a permanent magnet part and a sparsely laminated pulling edge. This leads to several advantages, such as savings of permanent magnet material, low induced voltage when currentless, reduced short circuit currents and easy field weafening.

[0007] The international patent publication WO 2004/ 068678 Al discloses a rotating electrical rmchine, wherein the rotor is rotatably joumalled to the stator by means of bearing devices arranged in or adjacent to an air gap between the rotor and the stator. In the embodiment with an inner rotor, the rotor is an annular body with high stiffness.

SUMMA OF THE INVENTION

[0008] An object of the present invention is to provide a rotating electrical rmchine, wherein the air gap between the stator and the rotor can be kept considerably shorter than in prior art machines.

[0009] According to the invention, there is provided an electrical machine comprising a stator with an opening, an essentially circular rotor mounted in the opening of the stator, wherein the rotor is rotatably joumalled to the statorby means of wheels, the electrical machine being characterized in that the rotor comprises at least four rotor sections, each rotor section having at least one pair of wheels, wherein adjacent rotor sections are pivo tally interconnected in the peripheral direction of the rotor.

[0010] Ey providing the rotor with a plurality of pivotally interconnected rotor sections, the rotor easily follows the curvature of the stator, thereby keeping the air gap between the stator and the rotor small. [0011] a preferred embodiment, each rotor section is provided witii a rotor yoke, which allows closed magnetic flow paths between the stator and the respective rotor section.

[0012] In a preferred embodiment, the rotor of the electrical machine comprises a plurality of spokes interconnecting each of the rotor sections and a shaft lis preferred that the plurality of spokes is resilient so as to accommodate for variations in the diameter of the stator and for the possible eccentric position of the turbine shaft This also relieves the shaft bearing from possible unbalanced radial magnetic forces acting on the rotor, particularly in connection with permanent magnets.

[0013] In another preferred embodiment, the stator comprises rails, preferably affixed to the stator housing, wherein the wheels are adapted to roll on the rails. This ensures smooth movement of the rotor sections.

[0014] Further preferred embodiments are defined in the dependent claims. BHEF DESCRIPTION OF DRAWINGS

[0015] The invention is now described, by way of example, with reference to the acconpanying drawings, in which;

[0016] Jig. 1 is a schematic side view of an electrical machine according to the invention,

[0017] Jig. 2 is a detailed sectional view showing some of the rotor sections making up the rotor shown in Jig. 1 ,

[0018] Jigs. 3a-c are a side view, a top view, and a front view, respectively, of a rotor section comprised in the electrical machine of Jig. 1. DEMED DESCRIPTION OF A HEFERRED EMBODIMENT

[0019] In the following, a detailed description of a preferred embodiment of an electrical machine according to the invention will be given.

[0020] In this description reference is made to "electrical machine". This expression is to be interpreted to cover electrical rmchines acting both as

generators and as motors.

[0021] Jig. 1 is a schematic side view of an electrical machine 1 with a stator, generally designated 10, and an essentially circular rotor, generally designated 20. Tne stator 10 comprises a stator housing, laminations and windings, as will be further explained below. Tne play or air gap between the stator 10 and the rotor 20 is designated 12 in the figure.

[0022] Tne stator 10 exhibits an opening 14 in which the rotor 20 is rotatably provided. To Ibis end, the wall of the opening 14, i.e., the radially inner portion of the stator 10, is provided with atleasttwo rails 16, one of which is shown in Jig. 1, which extend circumferentially 360 degrees all around the periphery of the opening 14.

[0023] Tne rotor 20 comprises at least four rotor sections 30, in the

embodiment of Jig. 1 15 rotor sections, wherein adjacent rotor sections are pivo tally interconnected in the peripheral direction of the rotor 20. Tne rotor sections 30 comprise wheels 32, which roll on the rails 16. Thereby the rotor sections 30 together form an endless train, which is pulled towards the rails 16 by magnetic forces which typically amount to 20 tons / m² of the air gap surface. These rotor sections thereby replace the permanent magnet rotor found in conventional rotating machines.

[0024] Tne rotor may optionally comprise a plurality of elastic elements in the form of spokes 22, which transfer the turning force of a shaft 24 to the endless train of rotor sections 30. Due to tiie magnetic forces pulling tiie rotor sections 30 to tiie stator, no or almost no force is needed from t e spokes to maintain tiie wheels 32 in contact with tiie rails 16. Instead, tiie spokes 22 are preferably resilient so as to accommodate for variations in tiie diameter of tiie stator 10. In other words, if a rotor section 30 is forced radially inward due to decreasing diameter of tiie stator, tiie length of tiie corresponding spoke should decrease, such as by spring action. Conversely, if a rotor section 30 is forced radially outward due to increasing diameter of the stator, the length of the corresponding spoke should increase, preferably also by spring action.

[0025] The elastic elements 22 may be in the form of rubber elements, which are resilient in a radial direction and also to a certain extent in a tangential direction.

[0026] Jig. 2 shows a detailed sectional view of the four lowermost rotor sections 30 of Jig. 1. lis here seen that each rotor section 30 is provided with a pair of wheels 32 (of which one in each pair is shown in the figure) and that adjacent rotor sections are pivo tally interconnected at the wheel axle 36.

[0027] Jigs. 3a-c show one of the above mentioned rotor sections 30, which are all identical. Each rotor section comprises a chassis or frame 34 to which the pair of wheels 32 is rotatably joumalled by means of a wheel axle 36 extending through bearing boxes 44, see Hgs. 3b and 3c.

[0028] Again with reference to E.g. 3a, a rotor yoke 38 is attached to a curved lower surface of the frame 34. The curvature of the curved lower surface is adapted to the curvature ofthe stator inner surface. On the rotoryoke 38, a plurality of rotor poles 40 are attached. These rotor poles can be conventional permanent magnet poles but are preferably of the above mentioned Mixedfble kind. [0029] The frame 34 is provided with an attachment hook 42, which is adapted to engage an engagement portion 46 of an adjacent rotor section 30. the embodiment shown in the figures, this engagement portion is part of the frame 34 surrounding the central portion of the wheel axle 36.

[0030] Tlirning now to Jig. 3c, it is shown a cross-section through the stator 10 with a stator housing 19 and a stator package 18. lis here seen that the air gap 12 between the stator package 18 and the rotor poles 40 can be keptto a minimum thanks to the rotor poles being provided on a rotor section 30, which is pivotally connected to the adjacent rotor sections.

[0031] A preferred embodiment of an electrical machine according to the invention has been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea. Thus, the elastic elements interconnecting the rotor sections and the shaft may take any suitable form, as long as they take up variations in the rotor diameter and transfer the movement of the rotor sections into turning of the shaft

Claims

CIAJMS

1. An electrical machine comprising: a stator (10) with an opening (14), an essentially circular rotor (20) mounted in the opening of the stator, wherein the rotor is rotatably joumalled to the statorby means of wheels (32), characteriz ed in that the rotor comprises atleastfour rotor sections (30), each rotor secuon having at least one pair of wheels, wherein adjacent rotor sections are pivo tally interconnected in the peripheral direction of the rotor.

2. The electrical rmchine according to claim 1, wherein each of the rotor sections is provided with atleastone rotor pole (40).

3. The electrical rmchine according to claim 2, wherein each of the poles (40) comprises a pushing edge in the form of a permanent magnet part and a sparsely laminated pulling edge.

4. The electrical machine according to claim 2 or 3, wherein each of the rotor sections is provided with a rotor yoke (38).

5. The electrical machine according to any of claims 14, wherein the rotor comprises a plurality of elastic elements (22) interconnecting each of the rotor sections (30) and a shaft (24).

6. The electrical machine according to claim 5, wherein the plurality of elastic elements (22) is resilient so as to accommodate for variations in the diameter of the stator (10).

7. The electrical machine according to claim 5 or 6, wherein the plurality of elastic elements comprises rubber elements (22).

8. The electrical machine according to any of claims 1-7, wherein each of the rotor sections (30) comprises an attachment hook (42) and an engagement portion (46), and wherein the attachment hook is adapted to engage the engagement portion (46) of an adjacent rotor section (30).

9. The electrical machine according to any of claims 1-8, wherein the stator comprises rails (16) and wherein the wheels (32) are adapted to roll on the rails.

10. The electrical machine according to claim 9, wherein the stator (10) comprises a stator housing (19), wherein the rails are affixed to the stator housing.