Patent Application
20140225373
This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/FI2012/050989, which was filed as an International Application on Oct. 16, 2012 designating the U.S., and which claims priority to European Application 11185420.4 filed in Europe on Oct. 17, 2011. The entire contents of these applications are hereby incorporated by reference in their entireties.
The present disclosure relates to suppression of vibrations in a rotating electric machine.
Vibrations of a rotating electric machine may have several different sources such as unbalance in a rotor, magnetic forces due to imperfect magnetic design, external excitation, or magnetic forces caused by air-gap anomalies due to overhang of an outer rotor of the rotating electric machine combined with gravitational pull.
Vibrations cause significant problems in known rotating electric machines. Vibrations may cause excessive noise. Vibrations may also shorten operating life of rotating electric machines.
The present disclosure utilizes a constrained-layer damping technique which is described, for example, in the following documents.
[1] Cremer, L. & Heckl, M. & Ungar, E. E., 1987. Structure-Borne Sound. 2nd ed. Berlin: Springer Verlag.
[2] Ewins, D. J., 2001. Modal Testing, Theory, Practice, and Application. 2nd ed. Hertfordshire, England: Research Studies Press ltd.
[3] Garibaldi, L. & Onah, H. N., 1996. Viscoelastic Material Damping Technology. Torino: Becchis Osiride.
There exist a great number of mathematical formulations to describe the dampening mechanisms of a material. Herein, a hysteretical damping model is used. The hysteretical damping model is also called as a structural damping model. For hysteretically damped isotropic material, the complex Young's modulus E* and Shear modulus G* are defined as
E*=E(1+jη)
G*=G(1+jη),
where E is the real Young's modulus, G is the real shear modulus and n is the material loss factor. The above definitions can be found in reference [3], on page 30.
An exemplary embodiment of the present disclosure provides an electric machine which includes a support frame, an outer rotor, a stator, and dampening means. The outer rotor and the stator are supported to the support frame. The dampening means is configured for dampening vibrations of the outer rotor. The outer rotor includes an annular end plate. The dampening means comprises a first damper having a first constraint element and a first visco-elastic layer provided on a surface of the first constraint element. The first constraint element is connected to the annular end plate through the first visco-elastic layer.
An exemplary embodiment of the present disclosure provides an electric machine which includes a support frame, an outer rotor, a stator, and dampening means. The outer rotor and the stator are supported to the support frame. The dampening means is configured for dampening vibrations of the outer rotor. The outer rotor includes an annular end plate. The dampening means comprises a first damper having a first constraint element and a first visco-elastic layer provided on a surface of the first constraint element. The first constraint element is connected to the annular end plate through the first visco-elastic layer. The outer rotor is supported to the support frame exclusively at one end by a bearing located at an opposed end of the outer rotor relative to the annular end plate.
Additional refinements, advantages and features of the present disclosure are described in more detail below with reference to exemplary embodiments illustrated in the drawings, in which:
Exemplary embodiments of the present disclosure provide an outer rotor electric machine which alleviates the above-described vibration problems associated with known techniques.
Exemplary embodiments of the present disclosure are based on the idea of providing an outer rotor of an electric machine with one or more dampers connected to an annular end plate of the outer rotor, where the one or more dampers utilize a constrained-layer damping technique.
An advantage of the present disclosure is that vibrations of an outer rotor electric machine may be suppressed thereby reducing noise and extending the operating life of the electric machine.
The outer rotor 2 includes an annular end plate 28, the first damper 10 being connected to the annular end plate 28. The annular end plate 28 may be made of steel or aluminium. A symmetry axis of the annular end plate 28 coincides with rotation axis of the outer rotor 2. Thus a plane defined by the annular end plate 28 extends perpendicular to the rotation axis of outer rotor 2.
The outer rotor 2 is supported to the support frame 6 exclusively at one end by a bearing 8 located at an opposed end of the outer rotor 2 relative to the annular end plate 28. The bearing 8 may comprise one or more bearing units. A bearing unit may comprise for example a ball bearing or a cylindrical bearing.
The annular end plate 28 and the bearing 8 are spaced apart in axial direction of the outer rotor machine. Active parts of the outer rotor 2 and the stator 4 are situated between the annular end plate 28 and the bearing 8 when seen in the axial direction, the active parts being the components configured to interact magnetically during operation of the machine.
The proper design method, also known as Master Curve Procedure using International Plot, for optimizing the damping capacity vs. temperature and frequency is explained thoroughly in reference [3], on pages 101-110. The reference [3], which is identified in section Background of the Disclosure, discloses that the material loss factor has a property of reaching a maximum value at certain temperature and frequency. In other words the material loss factor is a function on temperature and frequency.
To ensure an adequate damping capacity of the first damper 10 maximum loss factor ηfvel
In an alternative embodiment maximum loss factor of the first visco-elastic layer is greater than or equal to 0.9. Basically, the higher the maximum loss factor of a visco-elastic layer is the more effective the damping is.
In the embodiment shown in
Both the maximum loss factor ηfvel-2
According to an exemplary embodiment, the first damper 10″ is optimized for a first temperature T1 and a first frequency f1. The second damper 20″ is optimized for a second temperature T2 and a second frequency f2. The second temperature T2 is different from the first temperature T1, and the second frequency f2 is different from the first frequency f1. Herein, a damper is considered to be optimized for a certain temperature and a certain frequency if the material loss factor of the visco-elastic layer of the damper reaches its maximum value at said temperature and frequency.
Dampening means including a plurality of dampers may be configured such that each of the dampers is optimized for a different temperature-frequency pair than rest of the dampers. Thereby maximum dampening range of the dampening means may be widened.
In the exemplary embodiment of
An annular end plate of an outer rotor of a wind generator may be equipped with a brake disc for braking the outer rotor. The first damper may be located outer in radial direction than the brake disc. In some cases it is possible to retrofit a first damper according to present disclosure to an annular end plate of an outer rotor of an existing wind generator.
It will be obvious to a person skilled in the art that the inventive concept can be implemented in various ways. The present disclosure and its embodiments are not limited to the examples described above but may vary within the scope of the claims.
It will therefore be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein
| Number | Date | Country | Kind |
|---|---|---|---|
| 11185420.4 | Oct 2011 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/FI2012/050989 | Oct 2012 | US |
| Child | 14255644 | US |
