Abstract:
A magnetic bearing assembly for a rotary machine, having a rotor circuit and a stator magnetic circuit secured to a stationary support element having at least one body of ferromagnetic material and at least one coil, both being fitted in a protective annular housing leaving uncovered a surface of revolution of said ferromagnetic body and a surface of revolution of said one coil facing a surface of revolution of the rotor circuit. The bearing assembly comprises at least one row of blades secured on the rotor circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under35 U.S.C. § 371(c) of prior filed, co-pending PCT application Ser. No. PCT/EP2014/060640, filed on May 23, 2014, which claims priority to EP Patent Application Ser. No. 13169387.1, titled “MAGNETIC BEARING ASSEMBLY HAVING INNER VENTILATION” filed May 27, 2013. The above-listed applications are herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Embodiments of the invention relate to bearings, in particular magnetic bearings used in rotary machines having a rotor. 
         [0003]    In particular, the embodiments of the invention relate to active magnetic bearings having electromagnetic elements arranged in the radial direction and adapted to cooperate with a rotor circuit secured to the rotor. 
         [0004]    Axial magnetic bearings use electromagnetic forces pulling in opposition on the thrust collar secured to the rotor shaft to maintain relative position of a rotating assembly (rotor) to a stationary component (stator). A thrust collar is generally a flat, solid, ferromagnetic disc secured to the rotor. Disc-shaped electromagnetic elements are located on either side of the thrust collar and bolted to the rotary machine housing, forming the active axial magnetic bearing. 
         [0005]    Use of magnetic bearings in rotary machines is becoming more and more widespread, in particular in case of corrosive or hot fluid. The inner ventilation of the magnetic bearing is thus important to increase the service-life of the bearing. 
         [0006]    The friction generated by the relative movement of the thrust collar with respect to the electromagnetic elements creates a radial flow of fluid which leads to the cooling of the magnetic bearing. 
         [0007]    However, such flow is dependent of the friction between two components and the rotational speed of the rotor, and is thus not reliable. Furthermore, because of uncertainty in the pressure distribution, a back flow could appear which would lead to a lack of flow of cooling fluid. 
         [0008]    Current magnetic bearings do not provide enough inner ventilation, so that the flow of fluid becomes insufficient to cool the axial magnetic bearing. 
       SUMMARY OF THE INVENTION 
       [0009]    An object of embodiments of the invention is to remedy the above drawbacks. 
         [0010]    It is a particular object of embodiments of the invention to provide a magnetic bearing assembly having enhanced cooling flow, while being easy to manufacture. 
         [0011]    It is another object of embodiments of the invention to ensure recirculation of the flow of cooling fluid even in case of poor differential pressure inside the bearing. 
         [0012]    In one embodiment, a magnetic bearing assembly for a rotary machine, comprises a rotor circuit and a stator magnetic circuit secured to a stationary support element and comprising at least one body of ferromagnetic material and at least one coil, both being fitted in a protective annular housing leaving uncovered a surface of revolution of the ferromagnetic body and a surface of revolution of the one coil facing a surface of revolution of the rotor circuit. 
         [0013]    The bearing assembly comprises at least one row of blades secured on the rotor circuit. Such row of blades facilitates the pumping of the flow of cooling fluid enhancing the cooling of the magnetic bearing. In an embodiment, the one row of blades comprises a plurality of blades extending from the rotor circuit. 
         [0014]    In an embodiment, the rotor circuit comprises an annular thrust collar having an axial portion secured to a rotor shaft and radially extending towards the stator magnetic circuit by a radial portion, the radial portion facing the uncovered surfaces of the ferromagnetic body and the one coil. The row of blades is, for example, secured to the annular thrust collar and extends radially from the annular thrust collar towards the stator magnetic circuit. 
         [0015]    In an embodiment, the bearing is an axial magnetic bearing. 
         [0016]    In another embodiment the bearing is a radial magnetic bearing. 
         [0017]    The one row of blades may comprise a plurality of axial blades or a plurality of radial blades or a combination of the radial and axial type of blades. 
         [0018]    In an embodiment, the bearing assembly comprises two rows of blades. 
         [0019]    The radial magnetic bearing can be axially located between the two rows of blades. 
         [0020]    In an embodiment, the stator magnetic circuit comprises two bodies of ferromagnetic material, each facing the radial lateral surface of the radial portion of the annular thrust collar, each row of blades being secured on the axial portion of the collar and radially located between the annular thrust collar and each stator magnetic circuits. 
         [0021]    According to another aspect of the invention, a turbo machine comprises a stator, a rotor mounted in rotation in the stator, and at least one magnetic bearing assembly as described above radially arranged between the rotor and the stator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Embodiments of the invention will be better understood from studying the detailed description of a number of embodiments considered by way of entirely non-limiting examples and illustrated by the attached drawings in which: 
           [0023]      FIG. 1  is an axial half-section of the magnetic bearing assembly according to a first embodiment of the invention; 
           [0024]      FIG. 2  is an axial half-section of the magnetic bearing assembly according to a second embodiment of the invention; and 
           [0025]      FIG. 3  is a cross-section according to the line III-III of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. 
         [0027]    As illustrated on  FIG. 1 , a magnetic bearing assembly, designed by general reference number  10 , is designed to be mounted in a rotary machine (not shown) comprising a casing or housing, a rotating shaft  12  extending along an axis X-X and adapted to support a rotor part (not shown). For example, if the rotating machine is a centrifugal compressor, the rotor part comprises impellers. 
         [0028]    As illustrated on  FIG. 1 , the magnetic bearing  10  is of the axial type and is designed to support the rotor shaft  12  inside the stator casing. 
         [0029]    The active magnetic bearing  10  comprises a stator armature  14  fixed to the stator casing and a rotor armature  16  or annular thrust collar having the shape of a disk secured to the rotating shaft  12 . 
         [0030]    The annular thrust collar  16  and the rotor shaft  12  form the rotor circuit  17 . The annular thrust collar  16  extend s radially from an axial plate  16   a  secured to the rotor shaft  12  towards the stator magnetic circuit  18  by a radial portion  16   b  having an outer cylindrical surface  16   c  and two lateral surfaces  16   d,    16   e.    
         [0031]    The stator armature  14  comprises a stator magnetic circuit  18  including, in conventional manner, one or more annular coils  20  and two ferromagnetic bodies  22  which may be massive or laminated locally. In the example of  FIG. 1 , each ferromagnetic body  22  encloses two annular coils  20 . The stator armature  14  also comprises a protective annular support or annular housing  24  into which is placed the stator magnetic circuit  18 , leaving uncovered a surface of revolution  22   a  of the ferromagnetic bodies  22  and a surface  20   a  of revolution of each coils  20 . The support  24  is secured to a stationary support element  26  that is itself fixed to the casing. As illustrated, the surfaces of revolution  20   a,    22   a  are the axial lateral surface. 
         [0032]    As illustrated, the radial portion  16   b  of the thrust collar  16  faces the uncovered surfaces  20   a,    22   a  respectively of each ferromagnetic bodies  22  and each coils  20 . In other words, the stator magnetic circuit  18  is placed axially facing one of the radial lateral surface  16   d,    16   e  of the radial portion  16   b  of the annular thrust collar  16  with no mechanical contact, leaving an axial gap  28  between the annular thrust collar  16  and the stator magnetic circuit  18 . 
         [0033]    The rotation shaft  12  may be provided with a stepped profile  12   a  for an axial positioning of the thrust collar  16 . Alternatively, the annular thrust collar  16  could, for example, be made integrally with the rotor shaft  12 . 
         [0034]    As illustrated on  FIG. 1 , the bearing assembly  10  comprises two rows of blades  30 ,  32  comprising a plurality of blades (not shown) which can be axial or radial or a combination thereof, secured on the axial plate  16   a  of the thrust collar  16 . The blade s  30 ,  32  extend radially from the annular thrust collar  16  towards the stator magnetic circuit  18 . Alternatively, the rows of blades  30 ,  32  can be secured directly to the rotor shaft  12 . As illustrated, each row of blades  30 ,  32  can be radially located between the annular thrust collar  16  and each annular housing  24  of the stator magnetic circuits  18 , leaving a radial air gap  34  between the annular housing  24  and one of the rows of blades  30 ,  32 . 
         [0035]    Such row s of blades  30 ,  32  increase the ventilation inside the magnetic bearing and allow the magnetic bearing to be cooled. 
         [0036]    The embodiment shown in  FIGS. 2 and 3 , in which identical parts bear the same reference, differs from the embodiment of  FIG. 1  in the type of magnetic bearing. 
         [0037]    As illustrated on  FIGS. 2 and 3 , the magnetic bearing  40  is of the radial type and is designed to support radially the rotor shaft  12  inside the stator casing. 
         [0038]    The radial magnetic bearing  40  comprises a stator armature  42  fixed to the stator casing and the rotating shaft  12  forming the rotor circuit  17 . Alternatively, an additional rotor armature may be secured to rotor shaft  12  facing the stator armature  42 . 
         [0039]    The stator armature  42  comprises a stator magnetic circuit  44  including, in conventional manner, one or more coils  46  and one annular ferromagnetic body  48  which may be massive or laminated locally. As shown in  FIG. 3 , the ferromagnetic body  48  encloses four circumferentially equally spaced coils  46 . The stator armature  42  also comprises a protective annular support or annular housing  50  into which is placed the stator magnetic circuit  44 , leaving uncovered a surface of revolution  48  of the ferromagnetic body  48  and a surface  46   a  of revolution of each coils  46 . The protective annular support  50  is secured to a stationary support element  52  that is itself fixed to the casing. 
         [0040]    As illustrated, the outer cylindrical surface  12   b  of the rotor shaft  12  faces the uncovered surfaces  46   a ,  48   a  respectively of ferromagnetic body  48  and each coils  46 , In other words, the stator magnetic circuit  44  is placed radially facing the outer cylindrical surface  12   b  of the rotor shaft  12 , leaving a radial gap  54  between the rotor shaft  12  and the stator magnetic circuit  44 . 
         [0041]    As illustrated on  FIG. 2 , the bearing assembly  40  comprises two rows of blades  56 ,  58  comprising a plurality of blades (not shown) which can be axial or radial or a combination thereof, secured on the outer cylindrical surface  12   b  of the rotor shaft  12 . The blades  56 ,  58  extend axially from the rotor shaft  12  towards the stator magnetic circuit  44 . As illustrated, the stator magnetic circuit  44  is located axially between the two rows of blades  56 ,  58 , leaving an axial air gap  59  between the annular housing  50  and each of the rows of blades  56 ,  58 . 
         [0042]    As an example, a magnetic bearing assembly may comprise the combination of a radial type magnetic bearing  40  as shown on  FIG. 2  associated to the axial type magnetic bearing  10  as shown on  FIG. 1  to support the rotating shaft  12 . 
         [0043]    The each magnetic bearing assembly has enhanced cooling flow. 
         [0044]    Indeed, the rows of blades facilitate the pumping of the flow of fluid enhancing the cooling of the active magnetic bearing. The magnetic bearing is thus provided with inner ventilation. 
         [0045]    This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.