FR2826076A1 - Emergency bearing for rotary machine with magnetic bearings comprises ball bearing attached intermediate component which has large surface of contact with component attached to stator - Google Patents

Abstract

The emergency bearing for a rotary machine with magnetic bearings comprises a ball bearing (1 -3) mounted so that the axial play between it and the rotor (6) is half the air gap of the magnetic bearing. The emergency support system comprises an intermediate component (9) which has a large surface of contact with a component (10) attached to the stator (15). A radial damper (13) is mounted between the two components (9, 10) and there are low friction linings (14) on their axial surfaces of contact. Spring clips (12) hold the ball bearing and intermediate component together.

Description

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 The subject of the present invention is an emergency bearing insensitive to the axial load for a rotary machine with magnetic bearings having a mean radial air gap Er relative to a rotor, the emergency bearing comprising at least one rolling member such as a set. radial whose thickness Er / 2 is of the order of half of the mean radial air gap Er of the magnetic bearings is formed between the rolling member and the rotor, and axial clearances sa are provided on both sides other of the rolling member between the latter and first and second axial stop elements.

 All equipment of rotating machines with active magnetic bearings requires, in the event of overloading of the said bearings or in the event of failure of the electrical or electronic control device or even during a stop or overload of the suspension, a backup device commonly known as the emergency landing. This device, which acts as mechanical redundancy, must be defined and dimensioned correctly so as to guarantee the total integrity of the machine and the possibility of immediate recovery of the equipment after disappearance of the overload or failure of the servo-control. These emergency bearings are generally dry lubricated bearings, but other types of dry bearings can be used. They have a play with the rotor and are not in rotation during normal operation. This clearance is generally equal to half the air gap but can be reduced if necessary. These bearings which are described for example in French patent document 2613791 are ball bearings or smooth rings usually mounted relative to the stator, on shock absorbers and having a radial clearance.

 Rotors mounted on magnetic bearings often have very high nominal rotational speeds. In this case, during a

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 landing on the emergency bearings in the event of failure of the servo or of its power supply, the rotor presents swirling movements at its speed of rotation with an eccentricity which is then defined by the play of the emergency landing. This swirling movement is called a radial whip or (whirl. In this case, the unbalance can be very important and can cause the destruction of the bearings or a deformation of the rotor.

 It is therefore particularly important that the functioning of the shock absorber is guaranteed, its function being on the one hand to avoid the departure in radial whip or whirl of the rotor in the event of contact with the emergency landing or to limit the frequency of this radial whip movement at a frequency low enough not to damage the ball bearings or plain rings used. Typically this frequency is between a quarter and a third of the frequency corresponding to the nominal speed of rotation of the machine. As long as the radial freedom of movement of the bearings is ensured, the radial crushing of the assembly allows the stressing of the damping metallic strip or of any viscoelastic equivalent and therefore satisfies the preceding condition.

 In certain turbomachinery, the axial load in action may be considerable. As long as the axial magnetic bearing functions correctly, nothing disturbs the correct functioning of the emergency bearing for a radial failure. On the other hand, in the event of a strong axial load, not controlled by the magnetic bearing, the emergency bearing device must also cope with this strong axial load.

 Figure 1 shows the effect of an axial load 100 transmitted from the rotor to the stator through a bearing of an emergency bearing of the prior art. The contact surface being quite small, it is difficult to organize a very low coefficient of friction there or to avoid a too high Hertz pressure. These two restrictions can lead, in the event of a high axial load, to a radial blockage of the emergency landing in its housing and to the non-stressing of the damping device 130. In this case,

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 the radial or whirl whip is synchronous at the speed of rotation and therefore leads to considerable and sometimes destructive radial loads for ball bearings or plain rings if they are used in place of ball bearings, even if stopping the machine intervenes quickly, usually after a few seconds thanks to braking from the operating process or the drive machine.

This situation can become prejudicial to the equipment and consequently to the technology of the magnetic bearing.

 The present invention aims to remedy the aforementioned drawbacks and to provide an emergency landing having high operational safety and limited wear, in particular in the event of failure or stopping of the supply of the magnetic bearings.

 These aims are achieved by means of an emergency bearing insensitive to the axial load for a rotating machine with magnetic bearings having a mean radial air gap cr with respect to a rotor, the emergency bearing comprising at least one rolling member such as a set. radial whose value c,. / 2 is of the order of half of the mean radial air gap cr of the magnetic bearings is provided between the rolling member and the rotor, and axial clearances Sa are provided on both sides and d 'other of the rolling member between it and first and second axial stop elements; said emergency landing being characterized in that it further comprises an emergency landing device comprising an intermediate element having a large contact surface with a stator element, said intermediate element being interposed between the rolling member and said fixed stator element to the stator with a radial clearance with respect to this stator element, a damping means in the radial direction interposed between the intermediate element and the stator element, and a very low friction contact means produced between the intermediate element and the stator element to reduce friction during rotational movements between these two elements.

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 According to one aspect of the invention, the emergency landing further comprises preload means interposed between the intermediate element and the rolling member and acting axially on the latter.

 Preferably, the preload means are springs fixed on the two extreme sides of the intermediate element, thus exerting a bidirectional preload on the rolling member.

 According to a particular embodiment, the rolling member comprises a stator cage, a rotor cage and rolling elements arranged between the stator and rotor cages.

 According to another particular possible embodiment, the rolling member comprises a smooth ring.

 The value ber / 2 of the radial clearance may advantageously be between approximately 0.15 mm and 0.3 mm, but may also have other values depending on the application and the dimensions of the bearing.

 In the same way, the value Sa of the axial clearance can advantageously be between approximately 0.2mm and 0.5mm, but can also have other values depending on the application and the dimensions of the bearing.

 According to a particular embodiment, the intermediate element is an annular female part with flanges and the stator element is a male part adapted to the female intermediate element.

 In this case, the intermediate element can be a part in two parts.

 According to another particular embodiment, the stator element is an annular female part with flanges and the intermediate element is a male part adapted to the female stator element.

 According to a possible alternative embodiment, the stator element is a part in two parts.

 According to a first aspect of the invention, the very low friction contact means comprises depositing a material with a low coefficient of

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 friction, on the opposite faces perpendicular to the axis of rotation, of the intermediate and stator elements.

 In this case, the material with a low coefficient of friction, can comprise PTFE or MOS2.

 According to a second particular aspect of the invention, the very low friction contact means is produced by surface treatment of the opposite faces perpendicular to the axis of rotation, of the intermediate and stator elements.

 According to a third particular aspect of the invention, the very low friction contact means is a ball plate introduced between the opposite faces perpendicular to the axis of rotation, intermediate and stator elements.

 According to a particular embodiment, the damping means is constituted by a corrugated metal strip interposed between the opposite annular faces parallel to the axis of rotation, of the internal part of the intermediate and stator elements.

 According to another embodiment, the damping means is constituted by a visco-elastic ring interposed between the opposite annular faces parallel to the axis of rotation, of the internal part of the intermediate and stator elements.

 Other characteristics and advantages of the invention will emerge from the description of particular embodiments, given by way of examples, with reference to the appended drawings in which: - Figure 1 is a view in axial half-section, schematically showing a axial load transmitted from the rotor to the stator through a bearing of an emergency landing of the prior art, - Figure 2 is a half-section view, in an axial plane, of an emergency landing according to a first mode of the invention, and where the rolling member comprises a set of rolling elements held between two cages,

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 - Figure 3 is a view similar to that of Figure 2, but without preloading means and with a rolling member comprising a smooth ring, - Figure 4 is a half-sectional view, in an axial plane, of an emergency landing according to another embodiment of the invention, FIG. 5 is a half-section view, in an axial plane, of an emergency landing according to yet another embodiment of the invention, - Figure 6 is a view along line VI-VI of Figure 2, - Figure 7 is a view along arrow F of Figure 2 with cutaway showing the stator element in two parts.

 Figures 2 to 5 correspond to different alternative embodiments of emergency bearings which each comprise a series of constituent elements whose geometry may be different from one alternative embodiment to another, but whose function is the same. The elements whose structure remains essentially the same have the same reference numbers in the different embodiments while the elements of different configuration having essentially the same function bear different reference numbers but whose last two digits are the same.

 FIG. 2 shows an emergency bearing insensitive to the axial load intended to be used in combination with an active magnetic bearing not shown in the drawing. The proper functioning of the bearing is ensured whatever the arrangement of the rotor 6 relative to the stator 15, in other words the rotor 6 can be either inside or outside the stator 15.

 The emergency landing essentially comprises at least one rolling member, represented here by a double bearing comprising for each bearing a stator cage 1, a rotor cage 2 and rolling elements 3 disposed between the stator cages 1 and rotor 2.

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 In Figure 2 the emergency bearing is shown in a position in which the radial magnetic bearings are in normal service. The rotor cages 2 of the rolling member are then separated from the rotor 6 by a radial clearance 4 whose value ber / 2 is of the order of half that of the air gap Br of the magnetic bearings. The value of the radial clearance on / 2 may advantageously be between 0.15 mm and 0.3 mm, but may also lie outside these values depending on the application. The rotor cages 2 are also separated from the first, 7, and second, 8, axial abutment elements by axial clearances 5, the value of which is advantageously between approximately 0.2 mm and 0.5 mm, but may also lie outside these values depending on the application. These axial clearances allow the rolling member to have an axial movement in both directions during an axial load.

 The emergency landing also comprises an emergency landing device comprising an annular female intermediate element with flanges 9 having a large contact surface with a male stator element in two parts 10 adapted to the female intermediate element 9. The intermediate element 9 is interposed between the stator cage 1 and the stator element 10, with a radial clearance 11,13 relative to this stator element which is fixed to the stator 15. The large contact surface between the intermediate 9 and stator 10 elements avoids pressure too high when a large axial load is applied to this surface. Springs 12 fixed on the two extreme sides of the intermediate element 9 act axially on the rolling member by exerting a bidirectional preload. To promote an internal rolling movement, it is indeed important that the bearings are not unloaded, which otherwise could lead to internal slippages detrimental to the proper functioning of the system and its longevity. A damping means in the radial direction is interposed in the clearance 13 between the opposite annular faces parallel to the axis of rotation, of the part

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 internal of the intermediate 9 and stator 10 elements. This damping means can be constituted by a corrugated metal strip or by a visco-elastic ring. On the other hand, a very low friction contact means 14 is produced between the opposite faces perpendicular to the axis of rotation, of the intermediate 9 and stator elements 10. This contact can be produced by a surface treatment of the faces in contact , by a polytetrafluoroethylene (PTFE) or MOS2 type deposit or by any other similar lubricant deposit.

 When the magnetic bearings no longer ensure their normal support function, the rotor 6 lands on the rotor cages 2 with a high speed of rotation close to the nominal speed of rotation. Then, the rotor 6 gradually slows down while exhibiting a whirl type swirling movement at a limited frequency advantageously between a quarter and a third of the frequency corresponding to the nominal rotation speed of the machine, thanks to the damping system. Consequently, the centrifugal force exerted on the rotor 6 is reduced to a much lower fraction of the value that the centrifugal force would have in the absence of the damping means.

 The damping device is not placed directly on the outer cages 1 of the bearings, but at a larger diameter of the intermediate element 9 in direct relation with the intermediate 9 and stator 10 elements with low friction.

 Thanks to this device, it is guaranteed that whatever the axial load applied to the emergency bearing system, the resulting radial force coming from this axial load via the large contact surface with low coefficient of friction 14, can in no case oppose the free radial movement of this system. Consequently, this allows the damping system 13 to keep its efficiency and to ensure the function described above, which is the desired objective of the emergency bearing system. It should be noted that the proper functioning of the system is ensured

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 whatever the direction of this axial load, thanks on the one hand to the springs 12 which exert a bidirectional preload on the rolling member and on the other hand to the axial clearances 5.

 The emergency landing in FIG. 3 differs from that in FIG. 2 only in the arrangement of certain elements. The rolling member is a smooth ring 101 therefore having no internal bearing. Consequently, springs fixed on the two extreme sides of the intermediate element 9 are no longer necessary.

 In FIG. 4, the intermediate element 109 comprises a female annular element with flanges in two parts 109A, 109B. On the other hand, the stator element 110 is a part of revolution which can be produced in a single part. Furthermore, the very low friction contact means comprises a ball plate 114 introduced between the opposite faces perpendicular to the axis of rotation, intermediate 109 and stator 110 elements. In this case, the load is distributed over a large number balls which also guarantee a very low coefficient of friction.

 The ball plate 114 thus constitutes an alternative embodiment to the contact coating 14 with a very low coefficient of friction.

 FIG. 5 corresponds to another embodiment of the invention, in which the stator element 210 is an annular female part with flanges in two parts 210A, 210B and the intermediate element 209 is a male part of revolution in one part adapted to the female stator element 210.

 Figure 6 is a view along the plane VI-VI of Figure 2 showing the case where the rotor 6 is internal and the rolling member comprising a stator cage 1, a rotor cage 2 and rolling elements 3 disposed between the stator 1 and rotor 2 cages, is mounted on the rotor 6. We can also see the springs 12 fixed on the intermediate element 9 thus exerting a preload on the stator cage 1.

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 Figure 7 is a view along arrow F of Figure 2 with cutaway showing the stator element 10 in two parts 10A, 10B.

The fact that this stator element 10 is in two parts is necessary for the assembly of the device as soon as the intermediate element 9 is itself produced in a single part.

 Various modifications can be made to the various embodiments which have just been described without departing from the scope of the invention. In particular, the different embodiments can be combined with one another. For example, the ball plate 114 of FIGS. 4 and 5 could be interchanged with the contact coating 14 of FIGS. 2 and 3. The smooth ring 101 could also be integrated into the embodiment of FIGS. 4 and 5 in place of the rolling member 1,2, 3.

Claims (17)

1. Emergency bearing insensitive to the axial load for a rotary machine with magnetic bearings having a mean radial air gap Gr relative to a rotor (6), the emergency bearing comprising at least one rolling member (1,2, 3; 101) such that a radial clearance (4) whose value c ,, / 2 is of the order of half of the mean radial air gap Gr of the magnetic bearings is formed between the rolling member (1,2, 3; 101) and the rotor (6), and axial clearances c, (5) are provided on either side of the rolling member (1,2, 3; 101) between the latter and first and second axial stop elements (7, 8); characterized in that it further comprises an emergency landing device comprising an intermediate element (9; 109; 209) having a large contact surface with a stator element (10; 110; 210), said intermediate element (9; 109 ; 209) being interposed between the rolling member (1,2, 3; 101) and said stator element (10; 110; 210) fixed to the stator (15) with a radial clearance (11,13) relative to this stator element (10; 110; 210), a damping means (13) in the radial direction interposed between the intermediate element (9; 109; 209) and the stator element (10; 110; 210), and a very low friction contact means (14; 114) produced between the intermediate element (9; 109; 209) and the stator element (10; 110; 210) to reduce friction during rotational movements between these two elements .  2. Emergency bearing insensitive to axial load according to claim 1, characterized in that it further comprises preload means (12) interposed between the intermediate element (9; 109; 209) and the rolling member (1,2, 3) and acting axially on the latter. <Desc / Clms Page number 12>  3. Emergency bearing insensitive to axial load according to claim 2, characterized in that the preload means are springs (12) fixed on the two extreme sides of the intermediate element (9; 109; 209) thus exerting a preload bidirectional on the rolling member (1,2, 3).  4. Emergency bearing insensitive to the axial load according to any one of claims 2 and 3, characterized in that the rolling member (1,2, 3) comprises a stator cage (1), a rotor cage (2 ) and rolling elements (3) arranged between the stator (1) and rotor (2) cages.  5. Emergency bearing insensitive to the axial load according to claim 1, characterized in that the rolling member (101) comprises a smooth ring (101).  6. Emergency bearing insensitive to the axial load according to any one of claims 1 to 5, characterized in that the value 2 of the radial clearance (4) is between approximately 0.15mm and 0.3mm.  7. Emergency bearing insensitive to the axial load according to any one of claims 1 to 5, characterized in that the value c, of the axial clearance (5) is between approximately 0.2mm and 0.5mm.  8. Emergency bearing insensitive to axial load according to any one of claims 1 to 7, characterized in that the intermediate element is an annular female part with flanges (9; 109) and the stator element is a male part (10; 110) adapted to the female intermediate element (9; 109). <Desc / Clms Page number 13>  9. Emergency bearing insensitive to axial load according to any one of claims 1 to 7, characterized in that the stator element is an annular female part with flanges (210) and the intermediate element is a male part (209 ) adapted to the female stator element (210).  10. Emergency bearing insensitive to the axial load according to claim 8, characterized in that the intermediate element is a part in two parts (109).  11. Emergency bearing insensitive to axial load according to claim 8 or claim 9, characterized in that the stator element is a part in two parts (10; 210).  12. Emergency bearing insensitive to axial load according to any one of claims 1 to 11, characterized in that the contact means with very low friction comprises depositing a material with low coefficient of friction (14) on opposite faces perpendicular to

 the axis of rotation, intermediate (9; 109; 209) and stator (10; 110; 210) elements. 13. Emergency bearing insensitive to axial load according to claim 12, characterized in that the material with a low coefficient of friction (14) comprises PTFE or MOS2.  14. Emergency bearing insensitive to axial load according to any one of claims 1 to 11, characterized in that the contact means with very low friction is produced by a surface treatment of the opposite faces perpendicular to the axis of rotation. , intermediate (9; 109; 209) and stator (10; 110; 210) elements. <Desc / Clms Page number 14>  15. Emergency bearing insensitive to axial load according to any one of claims 1 to 11, characterized in that the very low friction contact means is a ball plate (114) introduced between the opposite faces perpendicular to the axis of rotation, intermediate (9; 109; 209) and stator (10; 110; 210) elements.  16. Emergency bearing insensitive to axial load according to any one of claims 1 to 15, characterized in that the damping means (13) consists of a corrugated metal strip interposed between the opposite annular faces parallel to the axis of rotation, of the internal part of the intermediate (9; 109; 209) and stator (10; 110; 210) elements.  17. Emergency bearing insensitive to axial load according to any one of claims 1 to 15, characterized in that the damping means (13) consists of a visco-elastic ring interposed between the opposite annular faces parallel to the 'axis of rotation, of the internal part of the intermediate (9; 109; 209) and stator (10; 110; 210) elements.