VENTILATION

The present invention relates to bearings, in particular magnetic bearings used in rotary machines having a rotor. In particular, the present invention relates to axial thrust active magnetic bearings having electromagnetic elements arranged in the radial direction and adapted to cooperate with a thrust co llar secured to the rotor.

Axial magnetic bearings use electromagnetic forces pulling in opposition on the thrust co llar to maintain relative position o f a rotating assembly (rotor) to a stationary component (stator) . A thrust co llar is generally a flat, so lid, ferromagnetic disc secured to the rotor. Disc-shaped electromagnetic elements are located on either side of the thrust co llar and bo lted to the rotary machine housing, forming the active axial magnetic bearing.

Use o f magnetic bearings in rotary machines is becoming more and more widespread, in particular in case o f corrosive or hot fluid. The inner ventilation of the magnetic bearing is thus important to increase the service-life o f the bearing. The friction generated by the relative movement of the thrust co llar with respect to the electromagnetic elements creates a radial flow o f fluid which leads to the cooling of the magnetic bearing.

However, such flow is dependant of the friction between two components and the rotational speed o f 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 o f radial flow of fluid.

Current axial magnetic bearings do not provide enough inner ventilation, so that the flow o f fluid becomes insufficient to cool the axial magnetic bearing. An obj ect of the present invention is to remedy the above drawbacks .

It is a particular obj ect of the present invention to provide an axial magnetic bearing assembly having enhanced cooling flow, while being easy to manufacture.

It is another obj ect of the present invention to ensure recirculation o f the flow o f cooling fluid even in case of poor differential pressure inside the bearing.

In one embodiment, a magnetic bearing assembly for a rotary machine having a rotor shaft, comprises a stator magnetic circuit secured to a stationary support element and comprising at least one body o f ferromagnetic material and at least one coil, both being fitted in a protective annular housing leaving uncovered a surface o f revo lution of said ferromagnetic body and a surface o f revo lution o f said one coil, the magnetic bearing assembly comprising an annular thrust co llar secured to the rotor shaft and radially extending towards the stator magnetic circuit by a radial portion, said radial portion facing the uncovered surfaces of said ferromagnetic body and said one coil.

The annular thrust collar comprises at least one flow channel.

Such flow channels facilitate the pumping o f the flow o f cooling fluid enhancing the cooling of the magnetic bearing.

Advantageously, said one flow channel extends from the outer cylindrical surface of the radial portion towards the rotor shaft.

In an embodiment, said one flow channel is a groove provided on at least one o f the lateral surfaces o f the radial portion o f the annular thrust collar.

In another embodiment, said one flow channel is a groove provided inside the radial portion of the annular thrust collar.

For example, said groove is oblique and/or radial and can open on the outer cylindrical surface of the rotor shaft. Advantageously, said groove can be radially and tangentially shaped.

In an embodiment, the bearing assembly comprises a plurality o f flow channels .

Advantageously, the stator magnetic circuit comprises two bodies o f ferromagnetic material, each facing one lateral surface o f the radial portion of said annular thrust collar.

The bearing is, for example, an axial magnetic bearing.

According to another aspect of the invention, a turbo machine comprises a stator, a rotor mounted in rotation in said stator, and at least one magnetic bearing assembly as described above radially arranged between the rotor and the stator.

The present invention will be better understood from studying the detailed description o f a number o f embo diments considered by way of entirely non-limiting examples and illustrated by the attached drawings in which:

Figure 1 is an axial half-section o f the axial magnetic bearing assembly according to a first embodiment of the invention mounted between two components of a motor;

Figure 2 is an axial half-section of a thrust collar along line II-II o f Figure 1 according to a first embodiment of the invention;

Figure 3 is an half view o f the thrust co llar o f figure 1 mounted on a rotor according to the first embodiment of the invention;

Figure 4 is an axial half-section o f a thrust co llar according to a second embodiment of the invention; Figure 5 is an half view o f the thrust co llar o f figure 4 mounted on a rotor according to the second embodiment of the invention.

The fo llowing detailed description o f the exemp lary 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 .

As illustrated on Figure 1 , a magnetic bearing, 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 . The rotating shaft 12 and the associated rotor part form a rotor assembly. As illustrated on Figure 1 , the magnetic bearing 10 is o f the axial type and is designed to support said rotor shaft 12 inside the stator casing. A radial type magnetic bearing (not shown) may also be associated to the axial magnetic bearing 10 to support the rotating shaft 12. The active magnetic bearing 10 comprises a stator armature 14 fixed to the stator casing and a rotor armature 16 or annular thrust co llar having the shape o f a disk secured to the rotating shaft 12. The annular thrust co llar 16 extends radially from an axial plate 1 6a secured to the rotor shaft 12 towards the stator magnetic circuit 1 8 by a radial portion 16b having an outer cylindrical surface 16c and two lateral surfaces 1 6d, 16e.

The stator armature 14 comprises a stator magnetic circuit 1 8 including, in conventional manner, one or more annular coils 20 and two ferromagnetic bodes 22 which may be massive or laminated lo cally. In the examp le of figure 1 , each ferromagnetic body 22 enclo ses 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 1 8 , leaving uncovered a surface o f revo lution 22a of said ferromagnetic bodes 22 and a surface 20a o f revo lution o f each coils 20. The support 24 is secured to a stationary support element 26 that is itself fixed to the casing.

As illustrated, the radial portion 1 6b o f the thrust collar 1 6 faces the uncovered surfaces 20a, 22a respectively o f each ferromagnetic bodies 22 and each coils 20. In other words, the stator magnetic circuit 1 8 is placed axially facing the annular thrust co llar 1 6 with no mechanical contact, leaving an axial gap 28 between the annular thrust collar 16 and the stator magnetic circuit 1 8. The rotation shaft 12 may be provided with a stepped profile 12a for an axial positioning o f the thrust collar 1 6. The annular thrust co llar 16 could, for example, be made integrally with the rotor shaft 12.

As illustrated on figures 2 and 3 , the annular thrust collar 1 6 comprises a plurality o f grooves 30 on each radial lateral surface 16d, 16e o f the radial portion 16b . Said grooves 30 act as flow channels for the flow o f the fluid. The flow channels 30 extend from the outer cylindrical surface 16c of the radial portion 16b towards the rotor shaft 12 and are inclined grooves directed radially towards the shaft 12 and are provided on the lateral surface 16d o f the radial portion 16b o f the thrust co llar 16. As illustrated, said grooves 30 are shaped radially and tangentially to the outer cylindrical surface 16c of the radial portion 1 6b.

As illustrated on Figure 3 , the flow channels 30 are be provided on both lateral surfaces 16d, 16e of the radial portion 16b of the thrust co llar 16. Alternatively, flow channels can be provided only on one lateral surface of the thrust collar 16.

As illustrated, the flow channels 30 opens on the axial plate 16a o f the thrust collar 1 6. Alternatively, the flow channels can open on the outer cylindrical surface 12b o f the rotor shaft 12. The fluid inside the turbomachine flows through the air gap 28 and inside the flow channels 30. The direction of flow is shown by the arrow F .

Such flow channels 30 increase the ventilation inside the magnetic bearing and allow the magnetic bearing to be cooled.

The embodiment shown in Figures 4 and 5 , in which identical parts bear the same reference, is substantially different from the embodiment of Figures 2 and 3 in the location o f the flow channels . As illustrated on Figures 4 and 5 , the thrust collar 16 is provided with a plurality o f grooves 32 provided inside the radial portion 16b . Said grooves 32 act as flow channels for the fluid and open only at the outer cylindrical surface 16c o f the radial portion 16b . Alternatively, the flow channels can open on the outer cylindrical surface 12b of the rotor shaft 12.

The groove 32 are inclined and radially directed towards the shaft 12. As illustrated, said grooves 32 are shaped radially and tangentially to the outer cylindrical surface 16c o f the radial portion 16b.

Thanks to the invention, the axial magnetic bearing assembly has enhanced cooling flow.

Indeed, the flow channels facilitate the pumping o f the flow o f fluid enhancing the cooling o f the active magnetic bearing. The magnetic bearing is thus provided with inner ventilation.