WO2023232353A1

WO2023232353A1 - Vacuum pump and mounting method

Info

Publication number: WO2023232353A1
Application number: PCT/EP2023/060726
Authority: WO
Inventors: Laurent BIZET; Lucas REY
Original assignee: Pfeiffer Vacuum
Priority date: 2022-06-03
Filing date: 2023-04-25
Publication date: 2023-12-07
Also published as: FR3136262A1

Abstract

The invention relates to a vacuum pump (1) comprising a stator (2) and two shafts (4) of rotors (5) that are configured to rotate in at least one pumping stage (T1-T7) of the stator (2). The invention is characterised in that, for each shaft (4), the vacuum pump (1) further comprises a stationary rolling device (10) having a bearing (12) which is mounted on the shaft (4) and a first housing (13) which is screwed into the stator (2), the bearing (12) being accommodated in the first housing (13), the first housing (13) forming an axial stop for an outer ring (12b) of the bearing (12), and/or a movable rolling device (11) having a bearing (20) which is mounted on the shaft (4) and a second housing (21) which is screwed into the stator (2), the bearing (20) being accommodated in the second housing (21), an annular resilient element (22) being inserted between an outer ring (20b) of the bearing (20) and the second housing (21).

Description

Title of the invention: Vacuum pump and assembly method

Technical field of the invention

[0001] The present invention relates to a vacuum pump, in particular a dry vacuum pump. The invention relates more particularly to a vacuum pump requiring means for adjusting the axial positioning of the rotors in the stator and preloading the bearings. The invention also relates to a method of mounting such a vacuum pump.

Technical background

[0002] Dry vacuum pumps comprise one or more pumping stages in series in which a gas to be pumped circulates between suction and discharge. Among the known vacuum pumps, we distinguish those with rotating lobes, also known under the name "Roots", comprising two or more lobes, or those with a nozzle, also known under the name "Claw". These vacuum pumps are called “dry” because in operation, the rotors rotate inside the stator without any mechanical contact between them or with the stator, which allows no oil to be used in the pumping stages.

[0003] In order to guarantee the proper functioning of dry vacuum pumps, it is necessary to achieve precise positioning of the rotors relative to the stator. This positioning can be obtained by means of axial adjustment of the rotor shafts carried out for example by means of shims arranged at the level of each lobe in the case of vacuum pumps having rotor lobes attached to the shaft or to the level of the flange of the last pumping stage in the case of one-piece rotor shafts.

[0004] Furthermore, the rotor shafts are respectively supported and positioned, axially and radially, by at least two respective ball bearings, of which a single bearing, called a bearing or fixed bearing, ensures the axial position of the shaft and the The other bearing, called a bearing or mobile bearing, takes its place by itself. [0005] This assembly has the advantage of being simple but requires pre-assembly of all the components of the shaft lines (shaft, rotors, bearings) in the stator to measure the axial clearances in order to be able to determine the thickness necessary shims, then disassemble the pre-assembled components to add or remove shims if necessary. These operations are therefore long and costly.

[0006] Furthermore, in certain cases, it may be necessary to ensure axial preloading of the bearings in order to guarantee their optimal operation. This preload is generally ensured by means of an elastic washer interposed between the stator and the outer ring of the mobile bearing.

[0007] The preload of the bearings influences the radial and axial load seen by them. The greater the radial and axial loads, the more limited the life of the bearing. The preload also has an influence on the phenomenon of alveolar excursion (relative movement of the ball in relation to the cage). The greater the preload, the less the alveolar excursion phenomena. The dimensioning of the preload must therefore make it possible both to guarantee a sufficient lifespan of the bearing but also to limit the phenomenon of alveolar excursion. The preload value window is often small because the two criteria are inversely related.

[0008] It is more difficult to achieve this preload finely. Indeed, there can be a fairly significant dispersion of stiffness for the same batch of spring washers. This dispersion of washer stiffness can in certain cases lead to premature wear of the bearings or the cage.

[0009] It is possible to adjust this preload by adding shims, but this operation is tedious and difficult to implement in the context of efficient production.

[0010] In certain vacuum pumps, an additional elastic washer is also axially interposed between the stator and the outer ring of the fixed bearing to reduce the phenomena of fretting corrosion or wear by friction between the surfaces metal and to allow the addition or removal of axial positioning blocks. However, the insertion of these elements tends to complicate the assembly of the shaft lines.

[0011] Another drawback linked to these assemblies comes from the current trend towards an increasingly significant reduction in the dimensions of vacuum pumps. Bearings are becoming smaller and smaller and therefore more and more difficult to assemble and disassemble. Special tools must be developed to allow the assembly of bearings and their disassembly during maintenance operations.

Summary of the invention

[0012] An aim of the present invention is to propose a vacuum pump resolving at least one of the drawbacks described above, in particular making it easier to adjust the axial positioning of the rotors in the stator and/or to adjust the preload of the bearings and facilitating the assembly and disassembly of bearings. [0013] For this purpose, the subject of the invention is a vacuum pump comprising a stator and two rotor shafts configured to rotate in at least one pumping stage of the stator, characterized in that for each shaft, the vacuum pump further comprises: a fixed rolling device comprising: a bearing mounted on the shaft,

- a first housing screwed into the stator, the bearing being received in the first housing, the first housing forming an axial stop for an external ring of the bearing, and/or a mobile rolling device comprising: a bearing mounted on the shaft,

- a second box screwed into the stator, the bearing being received in the second box,

- an annular elastic element interposed between an outer ring of the bearing and the second housing.

[0014] The fixed rolling device ensures on the one hand the radial guidance of the rotor shaft and on the other hand, forms a means of adjusting the axial positioning of the rotor shaft by screwing/unscrewing it in the stator , thus making it possible to optimize the operating clearances. This means of adjusting the axial positioning makes it possible to avoid the use of adjustment shims as in the architecture of the prior art, which constitutes a certain advantage in terms of ease of assembly. It is also possible to have fine adjustment of the clearance. Another advantage is that this makes it possible to limit the machining precision on certain parts: screwing/unscrewing the housing frees up adjustment latitude.

The mobile rolling device forms a means of adjusting the preload of the bearing by screwing/unscrewing it into the stator. The preload adjustment can thus be precise. This preload also prevents possible thread play movements between the threaded portion of the housings and the stator threads. The advantage of having the possibility of adjusting the loading of the bearing preload is to make the operation of the vacuum pump more reliable. Indeed, it is possible to have, in a simple way, the same preload on each vacuum pump because we decorrelate the preload values, the machining dispersions of the parts entering the dimension chain concerned as well as the possible dispersion stiffness of the spring washers.

[0016] The vacuum pump may comprise two fixed rolling devices and two conventional movable bearings (that is to say not include movable rolling devices) for adjusting the axial positioning of the rotor shafts. [0017] The vacuum pump may comprise two mobile rolling devices and two conventional fixed bearings (i.e. not include fixed rolling devices) for adjusting the preload of the bearings, adjusting the axial positioning rotor shafts which can be conventionally produced by means of positioning blocks.

[0018] The vacuum pump may comprise two movable bearing devices and two fixed bearing devices to be able to adjust, on the one hand, the axial positioning of the rotor shafts by means of the fixed bearing devices and, on the other hand, the preload bearings by means of mobile rolling devices. These devices are for example arranged on each shaft on either side of the dry pumping part of the pumping stages in which the gases circulate, that is to say on either side of at least one stage of pumping.

[0019] Mounting the devices by screwing also makes it easier to automate the assembly. It is then particularly easy to control the preload force of the bearings and to adjust it by tightening/loosening the second housings.

[0020] It is also possible to keep the part of the stator supporting the fixed and mobile bearing devices after maintenance because it is not damaged by contact corrosion phenomena as can be the case with pumps. void of the prior art.

The vacuum pump may also include one or more of the characteristics which are described below, taken alone or in combination.

The first and/or the second housing has a cylindrical shape having an external threaded portion allowing the housings to be screwed/unscrewed into a respective thread formed in a housing of the stator (or bore). The thread pitch of the threaded portions of the first boxes and/or the second boxes is for example between 0.5mm and 4mm, such as 1 mm.

[0023] The cylindrical parts of the housings ensure the radial positioning and guiding of the housings. The quality of the guidance is ensured by the adjustment between the cylindrical part of the housing and the housing opposite the stator. It is possible to introduce a slightly greater clearance between the thread and the tapping so that radial positioning is only achieved by the cylindrical guide. This avoids possible over-stresses in the event of a thread machining defect, the preload of the mobile rolling devices ensuring axial contact between the thread flanks.

The annular elastic element is for example an elastic washer, for example metallic. The bearings respectively comprise two coaxial rings, an internal ring secured in rotation to the shaft and an external ring secured to the housing, as well as rotating elements interposed between the internal and external rings, such as balls. Axial stops can axially block the internal rings of the bearings on either side of the internal rings.

The vacuum pump may include fixed bearing devices and mobile rolling devices, the bearings of the fixed rolling devices and the bearings of the mobile rolling devices being able to be mounted in an “O” shape. The annular elastic element then biases an outer ring of the bearing of the mobile rolling device in the direction going from the pumping cell towards the mobile rolling device. The assembly/disassembly of the bearings is simplified since it is enough to screw/unscrew the housings to remove the bearings from the shafts. This is an advantage both for original equipment due to the saving of time and reliability in production, but also for assembly/disassembly during subsequent maintenance. In fact, to dismantle the bearings during a service operation, simply unscrew the housings.

Likewise, when the vacuum pump comprises fixed rolling devices and conventional movable bearings, the bearings of the fixed rolling devices and the movable bearings can be mounted in an “O” shape.

Also, when the vacuum pump comprises mobile rolling devices and conventional fixed bearings, the fixed bearings and the bearings of the mobile rolling devices can be mounted in an “O” shape.

[0029] According to another example, the vacuum pump may include fixed rolling devices and mobile rolling devices, the bearings of the fixed rolling devices and the bearings of the mobile rolling devices being mounted in an “X”. The annular elastic element then biases the outer ring of the bearing of the movable rolling device in the direction going from the pumping cell towards the fixed rolling device.

Likewise, when the vacuum pump comprises fixed rolling devices and conventional movable bearings, the bearings of the fixed rolling devices and the movable bearings can be mounted in an “X”.

[0031] Also, when the vacuum pump includes mobile rolling devices and conventional fixed bearings, the fixed bearings and the bearings of the mobile rolling devices can be mounted in an "X".

[0032] According to an exemplary embodiment, the fixed rolling devices comprise a respective anti-rotation device configured to block the rotation of the first housings in the stator and/or the mobile rolling devices comprise a respective anti-rotation device configured to block the rotation of the second housings in the stator. [0033] The anti-rotation devices are for example formed by at least one cavity provided in the first housings and/or the second housings, cooperating with a respective locking tab fixed to the stator in a radial locking position.

[0034] The first housings and/or the second housings respectively have, for example, several regularly distributed cavities, the locking tabs being able to take different radial locking positions.

[0035] The anti-rotation devices comprise for example at least one respective fixing screw passing through an opening, for example oblong, of a respective locking tab to fix the locking tab in a thread of the stator. The stator may have several tappings in an arc around the first and/or second housings.

[0036] According to another exemplary embodiment, the anti-rotation devices configured to block the rotation of the first and/or second boxes in the stator are produced by gluing the threads of the boxes in the respective housings of the stator or by inserting elements for threaded connections between the threads of the housings and those of the stator housings, such as a sealing tape made of polytetrafluoroethylene material. The fixed bearing devices can respectively comprise a first O-ring arranged between the first housing and the stator housing in which the first housing is received.

The fixed bearing devices can respectively include a second O-ring arranged between the first housing and the bearing.

The mobile rolling devices can respectively comprise a first O-ring arranged between the second housing and the stator housing in which the second housing is received.

The movable bearing devices can respectively include a second O-ring arranged between the second housing and the bearing.

[0041] The invention also relates to a method of mounting a vacuum pump as described above in which the fixed and/or mobile bearing devices are screwed onto the shafts by robotic means.

[0042] For example, for adjusting the preload force of the bearings of an “O” assembly, the robotic means can press axially on the shaft on the side of the mobile bearing devices by measuring the force exerted. As soon as the tree moves, the force exerted cancels the preload force and therefore the measured force corresponds to the preload force.

This adjustment method is simple to carry out and makes it possible to easily adjust the same bearing preload force on all vacuum pumps produced.

Brief description of the figures

[0044] Other advantages and characteristics will appear on reading the following description of a particular embodiment of the invention, but in no way limiting, as well as the appended drawings in which:

[0045] [Fig. 1] Figure 1 is a schematic representation of an example of a vacuum pump.

[0046] [Fig. 2] Figure 2 is an enlarged sectional view of elements of a fixed bearing device mounted on a shaft of the vacuum pump of Figure 1.

[0047] [Fig. 3] Figure 3 is an enlarged sectional view of elements of a movable rolling device mounted on the shaft.

[0048] [Fig. 4] Figure 4 is a perspective view of a second housing of a mobile rolling device.

[0049] [Fig. 5] Figure 5 is a front view of the mobile rolling devices with second housings and anti-rotation devices in a first radial locking position.

[0050] [Fig. 6] Figure 6 is a view similar to Figure 5 with second housings and anti-rotation devices in a second radial locking position.

[0051] [Fig. 7] Figure 7 is a schematic view of a variation in mounting the bearings of fixed bearing devices and mobile bearing devices.

[0052] [Fig.8] Figure 8 shows a view similar to Figure 7 for another embodiment.

[0053] [Fig.9] Figure 9 shows a view similar to Figure 7 for another embodiment.

[0054] In these figures, identical elements bear the same reference numbers.

detailed description

[0055] The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features only apply to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments without departing from the scope of the invention, as defined by the claims.

[0056] A primary vacuum pump is defined as a volumetric vacuum pump, which is configured to suck up, transfer, then discharge a gas to be pumped at atmospheric pressure or beyond. The rotors of the primary vacuum pump can be Roots or Claw type or another similar principle of positive displacement vacuum pump. The rotors are carried by two shafts driven in rotation by a primary vacuum pump motor. A primary vacuum pump is also configured to be able to be started at atmospheric pressure.

[0057] Roots vacuum pump (also called “Roots Blower” in English or Roots compressor or “Booster” in English) is defined as a volumetric vacuum pump configured to, using two Roots rotors, suck up, transfer then deliver a gas to be pumped. The Roots vacuum pump is mounted upstream and in series with a primary vacuum pump. The rotors are carried by two shafts rotated by a Roots vacuum pump motor.

“Upstream” means an element which is placed before another with respect to the direction of circulation of the pumped gases. Conversely, “downstream” means an element placed after another in relation to the direction of circulation of the pumped gases. The axial direction is defined as the longitudinal direction of the vacuum pump in which the axes of rotation of the rotors extend.

By stator we define all the stator parts assembled together and defining in particular the pumping chamber(s) and the stator parts supporting the joints or bearings, also called joint supports or bearing supports.

[0061] The invention applies to any type of dry vacuum pump 1 comprising a stator 2 comprising at least one pumping stage T 1 -T7, such as comprising one to ten pumping stages, such as for example seven stages of pumping (figure 1). This vacuum pump 1 can be a primary vacuum pump configured to discharge the pumped gases at atmospheric pressure or a dry vacuum pump with one to three pumping stages which, in use, is connected upstream of a primary vacuum pump and whose delivery pressure in operation is that obtained by the primary vacuum pump.

[0062] The vacuum pump 1 comprises two shafts 4 of rotors 5 configured to rotate in at least one pumping stage T1-T7 to drive a gas to be pumped from a suction port towards a discharge port, in the direction gas circulation. The rotors 5 have combined profiles which can be assembled on the shafts 4 or made in one piece with shafts 4 (called one-piece rotors). The rotors 5 are for example of the “Roots” type with two or more lobes or of the “Claw” type or another similar principle of positive displacement vacuum pump.

The vacuum pump 1 comprises for example at least two pumping stages T 1 -T7 arranged in series. Each pumping stage T 1 -T7 comprises a pumping chamber receiving the two combined rotors 5, the pumping chambers comprising a respective inlet and an outlet. During rotation, the gas sucked in from the inlet is trapped in the volume generated by the rotors 5 and the stator 2, then is driven by the rotors 5 towards the next stage. The successive pumping stages T1-T7 are connected in series one after the other by respective interstage channels connecting the output of the preceding pumping stage to the inlet of the following pumping stage.

The inlet of the first pumping stage T1 communicates with the suction port of the vacuum pump 1. The outlet of the last pumping stage T7 communicates with the discharge port. The axial dimensions of the pumping stages are for example equal or decreasing with the order of arrangement of the pumping stages T 1 -T7, the pumping stage T 1 located on the side of the suction orifice having the largest axial dimension.

[0066] These vacuum pumps are called “dry” because in operation, the rotors 5 rotate inside the stator 2 without any mechanical contact with each other or with the stator 2, which makes it possible not to use oil in the pumping stages T 1 -T7. The shafts 4 of rotors 5 are configured to be rotated by at least one motor 6 of the vacuum pump 1. The vacuum pump 1 comprises for example a single motor 6 driving a shaft 4, for example at one end of the vacuum pump 1, such as on the side of the first or last pumping stage T1, T7 of the vacuum pump 1 . The vacuum pump 1 also has synchronization gears 7 mounted on the shafts 4 to synchronize the rotation of the rotors 5.

[0068] For each shaft 4, the vacuum pump 1 further comprises a fixed rolling device 10 and/or a mobile rolling device 11. There are therefore two fixed rolling devices 10 and/or two mobile rolling devices 11 in a vacuum pump 1.

The vacuum pump 1 illustrated in Figure 1 comprises two fixed bearing devices 10 and two mobile bearing devices 11. These devices 10, 11 are for example arranged on each shaft 4 on either side of the dry pumping part of the pumping stages T1-T7 in which the gases also circulate. called “pumping cell”, that is to say on either side of at least one pumping stage T1-T7.

[0070] The fixed bearing devices 10 are arranged on the same side of the vacuum pump 1, here on the side of the last pumping stage T7 (on the left in Figure 1), at each end of the shaft, and the movable rolling devices 11 are arranged on the other side of the vacuum pump 1, here on the side of the first pumping stage T 1 (on the right in Figure 1), one being arranged at one end of the shaft (at the top on the right in Figure 1) and the other interposed between the first pumping stage T1 and the motor 6 (bottom right in Figure 1).

[0071] Although the fixed rolling devices 10 are shown on the side of the last pumping stage T7 (on the left in FIG. 1) and the mobile rolling devices 11 on the side of the first pumping stage T 1 (on the right on the Figure 1), the reverse is of course possible without departing from the present invention.

[0072] Better visible in Figure 2, the fixed bearing device 10 comprises a bearing 12 mounted on the shaft 4 and a first housing 13 screwed into the stator 2, the bearing 12 being received in a housing 14 of the first housing 13 .

[0073] More precisely, the first housing 13 has a cylindrical shape comprising an external threaded portion 13a allowing the first housing 13 to be screwed/unscrewed into a thread formed in a housing of the stator 2. The screw pitch of the threaded portion 13a of the first housing 13 is for example between 0.5mm and 4mm, such as 1 mm.

The internal housing 14 is cylindrical and includes an opening opposite a bottom 15 in which a hole 16 is provided for the passage of a shaft.

[0075] The cylindrical part of the first housing 13 ensures the radial positioning and guidance of the housing 13. The quality of the guidance is ensured by the adjustment between the cylindrical part of the housing 13 and the housing opposite of stator 2.

The first housing 13 is for example metallic, such as steel.

The first box 13 is simple to produce and therefore inexpensive.

The bearing 12 comprises two coaxial rings, an internal ring 12a secured in rotation to the shaft 4 and an external ring 12b secured to the first housing 13, as well as rotating elements 12c interposed between the internal and external rings 12a, 12b , such as marbles.

[0079] The first housing 13 forms an axial stop for an outer ring 12b of the bearing 12. It is more precisely here the bottom 15 of the housing 14 of the first housing 13 which forms an axial stop for the outer ring 12b of the bearing 12 side interior in relation to the pumping cell. This axial stop prevents the bearing 12 from moving axially towards the mobile rolling device 11.

[0080] Axial stops also block axially the internal rings 12a of the bearings 12 on either side of the internal rings 12a.

[0081] An axial stop of the internal ring 12a of the bearing 12 on the interior side is for example formed by a ring 17 of the fixed bearing device 10 mounted on the shaft 4 or by a shoulder of the shaft 4 (not shown). The ring 17 passes for example through the shaft passage hole 16 of the first housing 13 so as to be inserted radially between the first housing 13 and the shaft 4 at the level of the hole 16.

[0082] Opposite the axial stop of the internal ring 12a of the bearing 12, on the exterior side, the bearing 12 can also be blocked axially, for example by means of a nut 18 screwed onto the shaft 4.

The fixed rolling device 10 ensures on the one hand the radial guidance of the shaft 4 of rotors 5 and on the other hand, forms a means for adjusting the axial positioning of the shaft 4 of rotors 5 by its screwing / unscrewing in stator 2, thus making it possible to optimize the operating clearances. This means of adjusting the axial positioning makes it possible to avoid the use of adjustment shims as in the architecture of the prior art, which constitutes a certain advantage in terms of ease of assembly. It is also possible to have fine adjustment of the clearance. Another advantage is that this makes it possible to limit the machining precision on certain parts: screwing/unscrewing the housing frees up adjustment latitude. With a screw pitch of the first housing 13 of 1 mm, the adjustment to 0.01 mm is achieved by a rotation of 3.6° of the first housing 13. The adjustment of the axial play can therefore be precise.

[0084] The fixed rolling device 10 may include a first O-ring 19a arranged between the first housing 13 and the housing of the stator 2 in which the first housing 13 is received. The first O-ring 19a is for example mounted in an annular groove external 26 provided on the periphery of the first housing 13. The fixed bearing device 10 may include a second O-ring 19b arranged between the first housing 13 and the bearing 12. The second O-ring 19b is for example mounted in an internal annular groove 27 provided in the housing 14 of the first housing 13 receiving the bearing 12. The O-rings 19a, 19b make it possible to limit the phenomena of contact corrosion between the bearing 12 and the first housing 13 and between the first housing 13 and the stator 2. They also help to dampen vibrations and contribute to the centering of the different parts.

[0085] As will be described in more detail later, the fixed rolling devices 10 may include a respective anti-rotation device 30 configured to block the rotation of the first boxes 13 in the stator 2 in order to prevent possible unscrewing of the first boxes 13 in the stator 2 due for example to vibrations of the stator 2.

[0086] Better visible in Figure 3, the mobile rolling device 11 comprises a bearing 20 mounted on the shaft 4, a second housing 21 screwed into the stator 2, and an annular elastic element 22. The bearing 20 and the annular elastic element 22 are received in a housing 23 of the second housing 21.

[0087] More precisely, the second housing 21 has a cylindrical shape comprising an external threaded portion 21 a allowing the second housing 21 to be screwed/unscrewed into a thread formed in a housing of the stator 2. The thread of the portion threaded 21 a of the second housing 21 is for example between 0.5mm and 4mm, such as 1 mm.

The internal housing 23 is cylindrical and has an opening opposite a bottom 24. A hole 16 is provided in the bottom 24 for the passage of the shaft. The housing 23 of the second housing 21 is deeper than that of the first housing 13 in order to accommodate the annular elastic element 22.

[0089] The cylindrical part of the second housing 21 ensures the radial positioning and guiding of the housing 21. The quality of the guidance is ensured by the adjustment between the cylindrical part of the housing 21 and the housing opposite the stator 2.

[0090] The second housing 21 is for example metallic, such as steel.

The second box 21 is simple to produce and therefore inexpensive.

The bearing 20 comprises two coaxial rings, an inner ring 20a secured in rotation to the shaft 4 and an outer ring 20b secured to the second housing 21, as well as rotating elements 20c interposed between the inner and outer rings 20a, 20b , such as marbles.

The bearings 12, 20 of the fixed rolling devices 10 and the mobile rolling devices 11 may all be the same or may be different. They are for example with oblique or radial contact.

The annular elastic element 22 is interposed between an external ring 20b of the bearing 20 of the mobile rolling device 11 and the second housing 21. More precisely here, the annular elastic element 22 is interposed between the bearing 20 and the bottom 24 of the housing 23 of the second housing 21 and biases the outer ring 20b of the bearing 20 of the mobile rolling device 11 in the direction going towards the device. movable bearing 11.

The annular elastic element 22 is for example an elastic washer, for example metallic. [0096] Axial stops axially block the internal rings 20a of the bearings 20 on either side of the internal rings 20a.

[0097] An axial stop of the internal ring 20a of the bearing 20 on the interior side relative to the pumping cell is for example formed by a ring 17 of the mobile rolling device 11 mounted on the shaft 4 or by a shoulder of the shaft 4 (not shown). The ring 17 passes for example through the shaft passage hole 16 of the second housing 21 so as to be inserted radially between the second housing 21 and the shaft 4 at the level of the hole 16.

[0098] Opposite this axial stop, the internal ring 20a of the bearing 20, on the exterior side relative to the pumping cell, can also be blocked axially, for example by means of a nut 18 screwed onto the shaft 4.

[0099] In this configuration, the bearings 12 of the fixed rolling devices 10 and the bearings 20 of the mobile rolling devices 11 are mounted in an “O” shape. [0100] For each shaft 4, the bearings 12 of the fixed rolling devices 10 have axial stops on either side of the internal ring 12a and an axial stop on the interior side of the external rings 12b relative to the pumping cell of the made the first 13 boxes.

[0101] The bearings 20 of the mobile rolling devices 11 have axial stops on either side of the internal ring 20a. They are elastically biased on the inside of the pumping cell towards the mobile rolling device 11 by the annular elastic element 22.

[0102] The mobile rolling device 11 forms a means of adjusting the preload of the bearing 20 by its screwing/unscrewing in the stator 2. Unscrewing the second housing 21 increases the stress on the annular elastic element 22 and therefore increases the preload. On the contrary, tightening the second box 21 reduces the preload. With a screw pitch of the second housing 21 of 1 mm, the adjustment to 0.01 mm is achieved by a rotation of 3.6° of the second housing 21. The preload adjustment can therefore be precise. This preload also prevents possible thread clearance movements between the threaded portions 13a, 21a of the housings 13, 21 and the threads of the stator 2. The advantage of having the possibility of adjusting the loading of the preload of the bearings 20 is to make the operation of the vacuum pump 1 more reliable. Indeed, it is possible to have, in a simple way, the same preload on each vacuum pump because we decorrelate the preload values, the machining dispersions of the parts entering the dimension chain concerned as well as the possible dispersion stiffness of the spring washers. [0103] As for the fixed rolling device 10, the mobile rolling device 11 may include a first O-ring 19a arranged between the second housing 21 and the housing of the stator 2, for example mounted in an external annular groove 26 formed on the periphery of the second housing 21 (figure 4) and a second O-ring 19b arranged between the second housing 21 and the bearing 20 for example mounted in an internal annular groove 27 formed in the housing 23 of the second housing 21 receiving the bearing 20.

[0104] Like the fixed rolling devices 10, the mobile rolling devices 11 may include a respective anti-rotation device 30 configured to block the rotation of the second housings 21 in the stator 2 in order to prevent possible unscrewing of the second housings 21 in stator 2 due for example to vibrations of stator 2.

[0105] The bearings 12, 20 can be lubricated by a lubricant such as oil contained in at least one oil pan or by grease. The lubricant can also lubricate the timing gears 7.

[0106] The vacuum pump 1 may further comprise a lubricant sealing device 25 interposed between the fixed bearing device 10 and the dry pumping part of the pumping stages T1 -T7 in which the gases circulate and a device for sealing 25 to lubricants interposed between the mobile rolling device 11 and the dry pumping part. The sealing device 25 allows the rotation of the shafts 4 in the dry pumping part while limiting the transfer of lubricants and the pollution of the oil sump by the pumped gases. The sealing device 25 may comprise at least one annular seal, for example a “dynamic” seal, that is to say non-rubbing, such as a segment seal, a labyrinth or “wall” seal. gas, or a rubbing annular seal, such as a lip seal or a combination of these embodiments. The rubbing annular seal is for example in contact with the ring 17 mounted on the shaft 4.

[0107] We will now describe an exemplary embodiment of the anti-rotation devices 30 of the fixed and mobile rolling devices 11 with reference to Figures 5 and 6. Although these figures illustrate anti-rotation devices 30 of a mobile rolling device 11 , the same embodiment can apply to the fixed rolling device 10.

[0108] In this exemplary embodiment, the anti-rotation devices 30 are formed by at least one cavity 31 provided in the first and second housings 13, 21 cooperating with one end 32a of a respective locking tab 32 fixed to the stator 2 in a radial blocking position. [0109] The first and second housings 13, 21 can have several respective cavities 31 regularly distributed, for example around the periphery of the opening of the housings 14, 23. The first and second housings 13, 21 thus have crenellated shapes (figure 4).

[0110] Furthermore, the locking tabs 32 can take different respective radial locking positions for which the end 32a can engage in a cavity 31 and block the rotation of the first and second boxes 13, 21.

[0111] For this, for example, the anti-rotation device 30 comprises at least one fixing screw 34, here two, passing through an opening 35 of the locking tongue 32 to fix the locking tongue 32 in a tapping 36 of the stator 2, the stator 2 presenting several threads 36 arranged in an arc around the second housing 21, here five (figure 5). The opening 35 can be oblong. The oblong opening 35 and the arcuate tappings 36 allow the locking tongue 32 to block the rotation of the second housing 21 for all the possible angular positions that can be taken by the second housing 21 due to its screwing into the stator housing 2.

[0112] Figure 5 shows an example of radial locking positions of the locking tabs 32 for a first angular position of the second housings 21 in which the ends 32a of the locking tabs 32 are engaged in a cavity 31 of a second housing 21 respective. These positions of the locking tabs 32 allow the engagement of the end 32a in a cavity 31 for the angular position of the second housing 21 obtained by tightening for adjusting the preload of the bearing 20. It can be seen that two distinct radial locking positions locking tabs 32 make it possible to lock in rotation as can be seen in the right and left views of Figure 5 for which the two second boxes 21 have the same angular position.

[0113] In Figure 6, the adjustment of the preload has generated an angular position of the second housing 21 different from that of Figure 5 and consequently, another radial locking position of the locking tabs 32 allowing the engagement of the ends 32a in a cavity 31 of the second housing 21. It can be seen that one and the same radial locking position of the locking tabs 32 makes it possible to lock in rotation as can be seen in the right and left views of FIG. 6 for which the two second boxes 21 have the same angular position. [0114] When mounting the vacuum pump 1, the fixed bearing devices 10 and/or mobile 11 are screwed onto the shafts 4, for example by robotic means. In fact, mounting the devices 10, 11 by screwing makes it easier to automate the assembly.

[0115] The degree of tightening of the first housings 13 of the fixed rolling devices 10 makes it possible to adjust the axial positioning of the shafts 4 of rotors 5 and the degree of tightening of the second housings 21 of the mobile rolling devices 11 makes it possible to adjust the force of bearing preload 20.

[0116] To adjust the preload force of the bearings 20, the robotic means can press axially on the shaft 4 on the side of the mobile bearing devices 11 by measuring the force exerted. As soon as shaft 4 moves, the force exerted cancels the preload force and therefore the measured force corresponds to the preload force. This method is simple to carry out and makes it possible to easily adjust the same preload force of the bearings 20 on all the vacuum pumps 1 produced.

[0117] Once the tightening of the boxes 13, 21 has been adjusted, the boxes 13, 21 are angularly correctly positioned and the locking tabs 32 can be fixed to the stator 2 in the respective radial locking position making it possible to cooperate as best as possible with a cavity 31 of the boxes 13, 21.

[0118] The assembly/disassembly of the bearings is therefore simplified since it is enough to screw/unscrew the housings 13, 21 to remove the bearings from the shafts. This is an advantage both for original equipment due to the saving of time and reliability in production, but also for assembly/disassembly during subsequent maintenance. In fact, to dismantle the bearings 12, 20 during a service operation, simply unscrew the housings 13, 21.

[0119] It is also possible to retain the part of the stator 2 supporting the fixed and mobile bearing devices 10, 11 also called bearing support, after maintenance because it is not damaged by contact corrosion phenomena. as may be the case with vacuum pumps of the prior art. Indeed, if these phenomena appear, it is sufficient to change the fixed bearing device 10 and/or the mobile bearing device 11 rather than changing the entire bearing support.

[0120] Other embodiments of the anti-rotation devices are possible to block the rotation of the boxes 13, 21 in the stator 2. For example, the anti-rotation devices can be produced by gluing the threads of the boxes 13, 21 in the respective housings of the stator 2 or by inserting elements for threaded connections between the threads of the housings 13, 21 and those of the housing of the stator 2, such as a sealing tape made of polytetrafluoroethylene material.

[0121] Figure 7 illustrates a variant embodiment in which the bearings 12 of the fixed rolling devices 10 and the bearings 20 of the mobile rolling devices 11 are mounted in an “X”.

[0122] This configuration differs from the previous one in that for each shaft 4, the bearings 12 of the fixed rolling devices 10 have axial stops on either side of the internal ring 12a and an axial stop on the outer side of the rings external 12b relative to the pumping cell due to the first housings 13. [0123] It is more precisely here the bottom 15 of the housing 14 of the first housing 13 which forms an axial stop for the external ring 12b of the bearing 12 on the exterior side relative to the pumping cell.

The bearings 20 of the mobile rolling devices 11 have axial stops on either side of the internal ring 20a and an axial elastic stress on the exterior side relative to the pumping cell exerted by the annular elastic element on the external rings 20b.

[0125] More precisely here, the annular elastic element 22 is interposed between the bearing 20 and a shoulder of the second housing 21. The annular elastic element 22 biases the outer ring 20b of the bearing 20 of the mobile rolling device 11 in the direction going from the pumping cell towards the fixed rolling device 10. [0126] With this assembly, unscrewing the second housing 21 reduces the stress on the annular elastic element 22 and therefore reduces the preload. On the contrary, tightening the second housing 21 increases the preload.

The other elements are similar to those of the previous embodiment described.

[0128] Furthermore, although the vacuum pumps 1 which have just been described respectively comprise two mobile rolling devices 11 and two fixed rolling devices 10 to be able to adjust, on the one hand, the axial positioning of the rotor shafts 4 5 by means of the fixed rolling devices 10 and on the other hand, the preloading of the bearings 20 by means of the mobile rolling devices 11, other configurations are possible.

[0129] In particular, the vacuum pump 1 may comprise two fixed rolling devices 10 and two conventional mobile bearings 37 (that is to say no mobile rolling devices 11) (figure 8).

[0130] The movable bearing 37 comprises a bearing 20 mounted on the shaft 4 and an elastic washer 38. The bearing 20 and the elastic washer 38 are received in a housing of the stator 2. The elastic washer 38 is interposed between an external ring 20b of the bearing 20 and the housing of the stator 2.

[0131] The fixed bearing devices 10 allow the axial positioning of the shafts 4 of rotors 5 to be adjusted, but there is no simple way to adjust the preload of the bearing.

[0132] In the configuration illustrated in Figure 8, the bearings 12 of the fixed rolling devices 10 and the movable bearings 37 are mounted in an “O” shape but they can also be mounted in an “X” shape (not shown).

[0133] According to another exemplary embodiment, the vacuum pump 1 comprises two mobile rolling devices 11 and two conventional fixed bearings 39 (that is to say no fixed rolling devices 10) (figure 9).

[0134] The fixed bearing 39 comprises a bearing 12 mounted on the shaft 4 and an elastic washer 40. The bearing 12 and the elastic washer 40 are received in a housing of the stator 2. The elastic washer 40 is interposed between an external ring 12b of the bearing 12 and the housing of the stator 2.

[0135] The mobile bearing devices 11 allow the preload of the bearings to be adjusted. The adjustment of the axial positioning of the shafts 4 of rotor 5 can be carried out by means of axial positioning wedges 41.

[0136] In the configuration illustrated in Figure 9, the fixed bearings 39 and the bearings 20 of the mobile rolling devices 11 are mounted in “O” but they can also be mounted in “X” (not shown).

Claims

[Claim 1] Vacuum pump (1) comprising a stator (2) and two shafts (4) of rotors (5) configured to rotate in at least one pumping stage (T1-T7) of the stator (2), characterized in what for each shaft (4), the vacuum pump (1) further comprises:

- a fixed bearing device (10) comprising: a bearing (12) mounted on the shaft (4),

- a first housing (13) screwed into the stator (2), the bearing (12) being received in the first housing (13), the first housing (13) forming an axial stop for an external ring (12b) of the bearing ( 12), and/or

- a mobile rolling device (11) comprising: a bearing (20) mounted on the shaft (4),

- a second housing (21) screwed into the stator (2), the bearing (20) being received in the second housing (21),

- an annular elastic element (22) interposed between an outer ring (20b) of the bearing (20) and the second housing (21).

[Claim 2] Vacuum pump (1) according to the preceding claim, characterized in that the first housings (13) and/or the second housings (21) have threaded portions (13a, 21a) whose screw pitch is included between 0.5mm and 4mm, such as 1mm.

[Claim 3] Vacuum pump (1) according to one of the preceding claims, characterized in that it comprises fixed rolling devices (10) and movable rolling devices (11), the bearings (12) of the devices fixed bearing (10) and the bearings (20) of the movable rolling devices (11) being mounted in an “O”.

[Claim 4] Vacuum pump (1) according to one of claims 1 or 2, characterized in that it comprises fixed rolling devices (10) and movable rolling devices (11), the bearings (12) fixed rolling devices (10) and the bearings (20) of the movable rolling devices (11) being mounted in an “X”.

[Claim 5] Vacuum pump (1) according to one of the preceding claims, characterized in that the fixed bearing devices (10) comprise a respective anti-rotation device (30) configured to block the rotation of the first housings (13). ) in the stator (2) and/or the movable rolling devices (11) comprise a device respective anti-rotation (30) configured to block the rotation of the second boxes (21) in the stator (2).

[Claim 6] Vacuum pump (1) according to the preceding claim, characterized in that the anti-rotation devices (30) are formed by at least one cavity (31) formed in the first housings (13) and/or the second housings (21), cooperating with a respective locking tab (32) fixed to the stator (2) in a radial locking position.

[Claim 7] Vacuum pump (1) according to the preceding claim, characterized in that the first housings (13) and/or the second housings (21) respectively have several regularly distributed cavities (31), the locking tabs (32 ) which can take different radial blocking positions.

[Claim 8] Vacuum pump (1) according to the preceding claim, characterized in that the anti-rotation devices (30) comprise at least one respective fixing screw (34) passing through an oblong opening (35) of a tongue of respective locking (32) for fixing the locking tongue (32) in a thread (36) of the stator (2), the stator (2) having several threads (36) in an arc around the first and/or second housings ( 13, 21).

[Claim 9] Vacuum pump (1) according to one of the preceding claims, characterized in that the fixed bearing devices (10) respectively comprise a first O-ring (19a) arranged between the first housing (13) and the housing of the stator (2) in which is received the first housing (13) and a second O-ring (19b) arranged between the first housing (13) and the bearing (12).

[Claim 10] Vacuum pump (1) according to one of the preceding claims, characterized in that the movable rolling devices (11) respectively comprise a first O-ring (19a) arranged between the second housing (21) and the housing of the stator (2) in which the second housing (21) is received and a second O-ring (19b) arranged between the second housing (21) and the bearing (20).

[Claim 11] Vacuum pump (1) according to one of the preceding claims, characterized in that axial stops axially block the internal rings (12a, 20a) of the bearings (12, 20) on either side of the rings internal (12a, 20a). [Claim 12] Method of mounting a vacuum pump (1) according to one of the preceding claims, characterized in that the fixed (10) and/or mobile (11) bearing devices are screwed onto the shafts ( 4) by robotic means.