EP1510697B1 - Vacuum pump - Google Patents

Abstract

The pump has a motor (7) that is inserted inside a cavity (5c) of a molecular rotor (5a) of a molecular pumping stage (5). The motor permits a rotation speed higher than 20000 revolutions per minute, such that electrical power density is high. An upstream end (8b) of a crank shaft (8) is coupled to the rotor and a downstream zone (8b) of the shaft is connected to the primary rotor (9a).

Description

The present invention relates to vacuum pumps for generating and maintaining an appropriate vacuum in a vacuum chamber or a vacuum line.

Vacuum pumps of different types are known which are generally each adapted to particular flow conditions and pumped gas pressure.

Thus, primary pumps have been designed which are required to repress at atmospheric pressure, which have a plurality of compression stages, and whose last stages produce a high compression under a relatively low volume flow. An example of such a primary pump is a kinematic pump formed of a disk-shaped rotor with concentric ribs equipped with individual radial blades engaged in corresponding communicating concentric annular grooves of the stator.

The primary pumps thus formed do not achieve sufficiently advanced voids for many vacuum applications. They are then associated in series with at least one secondary pump, for example a pump of molecular type or turbomolecular type, the discharge is connected aerauliquement to the suction of the primary pump.

A molecular or turbomolecular pump must be placed in the immediate vicinity of the vacuum chamber that it must evacuate, in order to benefit from the maximum pumping speed in the vacuum chamber.

However, usually, the size and weight of the single-axis primary pumping stage is incompatible with integration close to the vacuum chamber, and therefore the primary pump must be removed from the vacuum chamber, and the pumping performance are thus degraded.

It has already been imagined to mechanically couple the primary pump and the secondary pump, to drive them by the same motor on the same motor shaft. Thus, a composite pump has already been described in US Pat. No. 5,848,873 A or in US Pat. No. 6,135,709 A or in EP 1318309 A in which a radial vane kinematic pumping stage engaged in annular grooves of the stator is mounted. on the same rotor with a molecular pumping stage and optionally a turbomolecular pumping stage, the pumping stages being connected seriely in series, the rotors being mounted one after the other on the same motor shaft whose one end is coupled to a drive motor. The kinematic pumping stage has the advantage of providing the primary pump function, discharging at atmospheric pressure, while having a high rotation speed compatible with the usual rotational speeds of the molecular or turbomolecular stages.

The motor of such a composite pump must be able to provide sufficient power for driving the primary pump. The position of the motor at the end of the motor shaft leads to a space that prevents the integration of the composite pump in the immediate vicinity of the vacuum chamber that the pump must evacuate.

The solutions proposed in documents US Pat. No. 5,848,873 and 6,135,709 A are therefore not sufficient for vacuum applications in which it is desired to integrate the pumping system directly in the vicinity of the vacuum chamber.

The problem proposed by the present invention is to design a new composite pump structure which is compact enough to be integrated in close proximity to the vacuum chamber or process chamber, and which is capable of pumping from atmospheric pressure (1000 mbar). to the high vacuum usually required in some industries (10 ^-8 mbar).

The idea behind the invention is to both reduce the size of the motor itself that drives the pump, and to place the engine inside the pump to further reduce the total space of the motor-pump assembly.

According to another aspect of the invention, there is provided a primary stage pump structure which has improved and adjustable pumping properties, so as to achieve a satisfactory pumping with the aid of a pump of smaller volume.

• le rotor moléculaire comporte une cavité axiale borgne ouverte vers l'aval du corps de pompe,
• le moteur est logé au moins partiellement dans ladite cavité axiale borgne du rotor moléculaire,
• l'arbre-moteur est couplé par son extrémité amont au rotor moléculaire,
• l'arbre-moteur est couplé par sa portion aval au rotor primaire.

To achieve these and other aims, a vacuum pump according to the invention comprises, in a same pump body, at least one molecular pumping stage connected in series with at least one primary pumping stage at a compatible speed, the molecular pumping stage having a molecular rotor cooperating with a molecular stator provided in the pump body, the primary pumping stage having a primary rotor cooperating with a primary stator provided in the pump body, the molecular and primary rotors being driven in rotation by the same motor shaft coupled to a motor; according to the invention:

• the molecular rotor has a blind axial cavity open downstream of the pump body,
• the motor is housed at least partially in said blind axial cavity of the molecular rotor,
• the motor shaft is coupled by its upstream end to the molecular rotor,
• the motor shaft is coupled by its downstream portion to the primary rotor.

The speed-compatible primary pumping stage is a statically and statically viscous, viscous drive pumping structure which is able to discharge at atmospheric pressure and which operates correctly at the usual rotational speeds of the molecular or turbomolecular stages, ie say speeds of around 20,000 rpm.

In a practical embodiment, the motor shaft is rotated by an upstream bearing and a downstream bearing, the upstream bearing being located between the motor and the coupling zone to the molecular rotor, the downstream bearing being located between the motor and the coupling zone to the primary rotor.

• le rotor primaire est un rotor cinématique multiétagé à entraînement visqueux comprenant un disque dont une face transversale comporte une série de nervures annulaires concentriques ayant chacune des lames individuelles radiales,
• le stator primaire est un stator cinématique comprenant une face transversale correspondante ayant une série de gorges annulaires concentriques dans lesquelles s'engagent les lames individuelles radiales du rotor cinématique,
• les gorges annulaires concentriques du stator cinématique ont une section transversale plus grande que les lames individuelles radiales correspondantes du rotor cinématique, à l'exception d'une courte zone de gorge à section réduite dans laquelle les lames individuelles radiales s'engagent à faible jeu,
• les gorges annulaires concentriques successives sont reliées l'une à l'autre par un canal de communication prévu à l'extrémité aval de la zone de gorge à section réduite.

According to a first embodiment, a composite vacuum pump according to the invention is such that:

• the primary rotor is a multi-stage kinematic rotor with a viscous drive comprising a disk whose transverse face comprises a series of concentric annular ribs each having individual radial blades,
• the primary stator is a kinematic stator comprising a corresponding transverse face having a series of concentric annular grooves in which the individual radial blades of the kinematic rotor engage,
• the concentric annular grooves of the kinematic stator have a greater cross-section than the corresponding individual radial blades of the kinematic rotor, with the exception of a short region of reduced section groove in which the individual radial blades engage with low clearance,
• the successive concentric annular grooves are connected to each other by a communication channel provided at the downstream end of the reduced section groove area.

The areas of reduced section grooves have the role of providing a leak barrier between two distinct annular grooves, which are at different pressures.

According to a second embodiment, a vacuum pump according to the invention is such that the primary rotor is a multi-stage kinematic rotor with viscous drive comprising one or more disks whose transverse face comprises oblique centrifugal ribs which cooperate with a corresponding transverse face a multi-stage kinematic stator.

An improvement consists in providing that the primary pumping stage is furthermore such that the primary rotor comprises an upstream transverse face with oblique centrifugal ribs which cooperate with a corresponding transverse face of the pump body to constitute an additional kinematic pumping stage. Thus, without increasing the size of the pump, there is added a pumping stage which improves the pumping performance.

• les nervures centrifuges obliques de rotor coopèrent avec la face transversale correspondante du corps de pompe pour constituer un joint dynamique aval qui produit une aspiration protégeant le palier aval,
• un dernier étage moléculaire est inversé pour réaliser un joint dynamique amont qui produit une aspiration protégeant le palier amont,
• une purge de gaz neutre est adaptée pour amener un courant de gaz neutre dans le logement contenant le moteur, et pour produire ainsi un courant de gaz neutre à travers les paliers.

Alternatively, according to another variant, the primary pumping stage is further such that:

• the oblique centrifugal rotor ribs cooperate with the corresponding transverse face of the pump body to form a downstream dynamic seal which produces a suction protecting the downstream bearing,
• a last molecular stage is inverted to produce an upstream dynamic seal which produces a suction protecting the upstream bearing,
• a purge of neutral gas is adapted to bring a stream of neutral gas into the housing containing the engine, and thereby produce a neutral gas stream through the bearings.

Preferably, in the above embodiments, the composite vacuum pump according to the invention comprises a plurality of molecular pumping stages consisting of concentric cylindrical rotor elements connected to the motor shaft according to their upstream ends, and stator elements in the form of concentric cylinders with helical ribs connected to the pump body according to their downstream ends and engaged between the successive concentric rotor cylinders.

Also, to increase the pumping performance, it can be provided that the pump according to the invention further comprises at least one turbomolecular pumping stage connected aeraulically upstream of the molecular pumping stage or stages, the turbomolecular pumping stage comprising a rotor turbomolecular device having at least one stage of radial vanes and a turbomolecular stator having at least one annular groove in which are engaged the radial vanes of the turbomolecular rotor.

Preferably, there is provided a plurality of turbomolecular stages consisting of a rotor having a plurality of radial fin stages distributed along the motor shaft, and a plurality of corresponding annular grooves distributed over the stator.

In the embodiments defined above, the internal position of the motor preferably leads to providing means for increasing the overall efficiency of the engine, in order to reduce the losses and therefore the heating of the engine in operation. The goal is to provide the mechanical energy needed to drive the pump, with a smaller motor. For this, it is possible in particular to provide recessed cooling means in the stator of the engine, for example pipes in which is passed a cooling fluid.

• le moteur est adapté pour une vitesse de rotation élevée supérieure à 20 000 tours par minute en régime nominal,
• les gorges annulaires concentriques et les lames individuelles radiales correspondantes de l'étage primaire de type cinématique ont une taille plus réduite au voisinage du refoulement de l'étage de pompage cinématique.

Preferably, it is furthermore provided that:

• the engine is suitable for a high speed of rotation greater than 20 000 rpm in nominal speed,
• the concentric annular grooves and the corresponding individual radial blades of the kinematic-type primary stage have a smaller size in the vicinity of the discharge of the kinematic pump stage.

According to the invention, it is advantageous to provide a multi-stage kinematic type primary stator mounted displaceable in the axial direction relative to the pump body, and biased by displacement means for modifying its relative axial position with respect to the primary rotor, so that the pumping performance is adjustable. Note that this arrangement can be used in a kinematic stage pump regardless of the presence or absence of the other characteristics defined above, and thus constitutes an independent invention.

Furthermore, the motor shaft can advantageously be guided in rotation by magnetic bearings which allow an increase in the service life and a reduction of vibrations.

• la figure 1 est une vue schématique en coupe longitudinale d'une structure de pompe à vide composite selon un premier mode de réalisation de la présente invention ;
• la figure 2 illustre la face transversale principale aval du rotor cinématique de la pompe de la figure 1 ;
• la figure 3 illustre soit la face transversale amont du rotor cinématique de la pompe de la figure 1 selon un mode de réalisation avantageux, soit la face transversale principale aval d'un rotor cinématique selon un second mode de réalisation ;
• la figure 4 illustre la face transversale amont active du stator cinématique de la pompe de la figure 1 ;
• la figure 5 est une vue en coupe longitudinale de la pompe de la figure 1, avec le stator cinématique déplacé ; et
• la figure 6 est une vue en coupe longitudinale d'une pompe à vide composite selon un autre mode de réalisation de la présente invention.

Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, with reference to the accompanying figures, in which:

• Figure 1 is a schematic longitudinal sectional view of a composite vacuum pump structure according to a first embodiment of the present invention;
• FIG. 2 illustrates the main downstream transverse face of the kinematic rotor of the pump of FIG. 1;
• FIG. 3 illustrates either the upstream transverse face of the kinematic rotor of the pump of FIG. 1 according to an advantageous embodiment, or the main downstream transverse face of a kinematic rotor according to a second embodiment;
• FIG. 4 illustrates the active upstream transverse face of the kinematic stator of the pump of FIG. 1;
• Figure 5 is a longitudinal sectional view of the pump of Figure 1, with the kinematic stator displaced; and
• Figure 6 is a longitudinal sectional view of a composite vacuum pump according to another embodiment of the present invention.

In the embodiment illustrated in FIG. 1, a composite vacuum pump according to the invention comprises, in the same pump body 100 having a suction orifice 1 and a discharge orifice 2, at least one molecular pumping stage. 5 connected aerauliquement, by a transfer conduit 6, in series with at least one primary pump stage 9 kinematic type multi-stage viscous drive.

In the embodiment illustrated, the pump further comprises at least one turbomolecular pumping stage 4, connected aeromagnetically upstream of the molecular pumping stage (s) 5.

The molecular pumping stage 5 comprises a molecular rotor 5a which cooperates with a molecular stator 5b provided in the pump body 100.

The primary pumping stage 9 comprises a primary rotor 9a of kinematic type cooperating with a primary stator 9b kinematic type provided in the pump body 100.

The molecular rotor 5a and the primary rotor 9a are rotated by the same motor shaft 8 coupled to an electric motor 7.

The motor 7 comprises a motor rotor 7a, keyed on the central section of the motor shaft 8, and rotating in a motor stator 7b itself fixed in a housing 100b of the pump body 100.

The motor shaft 8 is rotated by an upstream bearing 15 and a downstream bearing 16, on either side of the motor rotor 7a. In the embodiment illustrated in FIG. 1, the bearings 15 and 16 are mechanical bearings with ball bearings. Alternatively, it can advantageously be provided that the bearings 15 and / or 16 are magnetic bearings, in a manner known per se.

The molecular rotor 5a has a blind axial cavity 5c, open downstream of the pump body 100, that is to say open towards the discharge orifice 2, and closed upstream, that is to say say towards the suction port 1, by a transverse wall 5d.

According to the invention, the motor 7 is housed at least partially in said blind axial cavity 5c of the molecular rotor 5a. Preferably, as shown in FIG. 1, the motor 7 is housed entirely in the blind axial cavity 5c of the molecular rotor 5a. For this, the motor shaft 8 is coupled by its end Upstream 8a to the molecular rotor 5a, and the motor shaft 8 is coupled by its downstream portion 8b to the primary rotor 9a.

In the illustrated example, the upstream end 8a of the motor shaft 8 passes through an axial hole provided in the transverse wall 5d of the molecular rotor 5a, and is fixed thereto by a nut 8c. Similarly, the downstream portion 8b of the motor shaft 8 passes through a hole in the primary rotor 9a and is fixed to it by a nut 13.

The upstream bearing 15 comprises, in the illustrated embodiment, an elastic washer 15a for pre-loading the ball bearing constituting said upstream bearing 15.

The upstream bearing 15 is located between the motor 7 and the upstream end 8a of the motor shaft 8 or coupling zone to the molecular rotor 5a.

The downstream bearing 16 is located between the motor 7 and the downstream portion 8b of the motor shaft 8 or coupling zone to the primary rotor 9a.

In the embodiment of FIG. 1, the primary rotor 9a is a kinematic rotor comprising a disk whose transverse face, for example the downstream transverse face in the illustrated embodiment, comprises a series of concentric annular ribs each having blades. individual radial. In this respect, reference can be made to FIG. 2, which illustrates in perspective an embodiment of such a transverse face 9c of a disk-shaped kinematic rotor 9a: the successive concentric annular ribs 9d, 9e, are distinguished 9f, 9g and 9h, which extend from the periphery to the center of the disc. Each concentric annular rib 9d-9h comprises individual radial blades such as the blade 10, protruding axially from the ridge of the corresponding concentric annular rib 9d and each oriented substantially in a radial direction relative to the disk forming the kinematic rotor 9a.

The kinematic stator 9b has a transverse wall integral with the pump body 100 and which comprises a corresponding transverse face, the upstream transverse face in the illustrated embodiment, which comprises a series of concentric annular grooves. In this regard, reference can be made to FIG. 4, which illustrates in perspective an embodiment of such a kinematic stator 9b, with concentric annular grooves 9j, 9k, 9l, 9m and 9n, which respectively correspond to the annular ribs. respective concentric 9d-9h of the kinematic rotor 9a. The individual radial blades such as the blade 10 of the kinematic rotor 9a engage in the concentric annular grooves 9j-9n, and for this the concentric annular grooves 9j-9n of the kinematic stator 9b have a larger cross-section than the individual radial blades 10 corresponding to the kinematic rotor 9a, with the exception of a short region of reduced section groove in which the individual radial blades 10 engage with little clearance. Thus, for example, for the groove 9k of FIG. a reduced section groove area 9o in which the groove 9k is not flared towards its bottom, unlike the other portions of the same groove 9k.

The successive concentric annular grooves 9j-9n are connected to each other by a communication channel provided at the downstream end of the corresponding groove area. Thus, for example, the channel 9p which connects the concentric annular grooves 9j and 9k.

In the embodiment of FIG. 1, an additional pumping stage 11 has also been represented, at the interface between the primary rotor 9a and the upstream portion of the pump body 100. In this case, the second transverse face or upstream transverse face of the kinematic rotor disk 9a may be as shown in perspective in FIG. 3 to constitute a rotor 11a, having oblique centrifugal ribs 11c, 11d, 11e and 11f, to cooperate with a corresponding transverse face 11b (FIG. 1) of the pump body 100 which constitutes a stator.

Referring again to FIG. 1, it can be seen that, in the illustrated embodiment, there is provided a plurality of molecular pumping stages 5, consisting of rotor elements in the form of concentric cylinders connected to the shaft. -moteur 8 according to their upstream ends, that is to say according to the transverse wall 5d, and stator elements in the form of concentric cylinders with helical ribs connected to the pump body 100 according to their downstream ends and engaged between the cylinders successive rotor concentrics. In the figure, there are three stator cylinders and two rotor cylinders interlocked into each other.

Also, in the figure, we distinguish the turbomolecular pumping stage 4 comprising a turbomolecular rotor 4a having at least one stage of radial fins, two stages of radial fins in the figure, and a turbomolecular stator 4b having annular rings, two rings in Figure 1, which engage between the radial fins of the turbomolecular rotor 4a. The rings may be inserts, stacked axially with appropriate spacers, in a manner known per se. Alternatively, in a manner also known per se, the stator may consist of the peripheral assembly of several shells reported radially around the rotor.

In order to reduce the volume of the assembly, it is sought to make a motor 7 of small size, allowing its insertion inside the cavity 5c of the molecular rotor 5a. For this, it is necessary in particular to improve the cooling of the motor 7, and can be provided for this purpose cooling means 17 embedded in the motor stator 7b, for example conduction ducts of a cooling fluid.

Alternatively or in addition, the motor 7 must be adapted to allow a high speed of rotation, greater than 20 000 revolutions per minute in nominal speed. The electric power density is, in this way, higher, which reduces the size of the engine.

In alternative or in addition, the concentric annular grooves 9j-9n and the corresponding individual radial blades 10 have a smaller size in the vicinity of the discharge of the kinematic stage. In practice, in Figures 2 and 4, the transverse dimension of the grooves and the blades is smaller and smaller when moving from the peripheral annular groove 9j to the central annular groove 9n, and the same is true of the ribs concentric 9d-9h and individual radial blades 10. In this way, the blades are reduced in the high pressure zone, that is to say in the vicinity of the axis of rotation, which reduces the viscous friction and allows to reduce the power that must develop the engine.

Alternatively or in addition, means are provided for reducing leakage between the kinematic pumping stages, providing a very small clearance between the individual radial blades 10 and the reduced section grooves areas 9o. This can be achieved by providing a high machining accuracy of the corresponding parts, but also by providing means for adjusting the axial position of the kinematic stator 9b with respect to the kinematic rotor 9a, as will be described below.

In the embodiment illustrated in FIGS. 1 and 5, the kinematic stator 9b can be displaced axially between a maximum approach position illustrated in FIG. 1 and a maximum position of displacement shown in FIG. 5. For this, the rotor kinematic 9a can slide axially in the pump body 100, with the interposition of an annular seal 100a, being guided by guide means 21 and biased by displacement means such as a jack not shown.

In the maximum approach position illustrated in FIG. 1, the individual radial blades 10 penetrate deeper into the corresponding grooves 9j-9n, which makes it possible to reduce the clearance between the individual radial blades 10 and the zones to the smallest possible size. of reduced section grooves 9o, as shown in Figure 1 in the right part of the kinematic rotor 9a. In the maximum recoil position as shown in FIG. 5, the clearance between the individual radial blades 10 and the kinematic stator 9b, increasing the internal leakage and thus reducing the pumping performance.

It is thus possible to modify at will the pumping performance of the kinematic pump, regardless of its speed, and quickly and efficiently by positioning at will the kinematic stator 9b in any position between its maximum approach and maximum retraction positions. At the same time, the axial position adjustment means make it possible to minimize internal leakage when it is in the maximum approaching position of FIG. 1, allowing the constitution of an improved performance kinematic pump.

It will be understood that the use of the position adjustment means of the kinematic stator 9b with respect to the kinematic rotor 9a is independent of the presence or absence of the other structural parts of the pump of FIG. 1, and in particular of the presence molecular stages and / or turbomolecular stages. This means thus constitutes an independent invention that can be used alone, for certain applications of kinematic pumps.

The embodiment is now considered as illustrated in FIG. 6. In this case, the composite pump takes up the essential means of the embodiment of FIG. 1, with the molecular pumping stages 5, possibly the turbomolecular pumping stages. 4, with the kinematic pump stage 9, and with the motor 7 engaged in the rear cavity 5c and mounted on the central section of the motor shaft 8, whose upstream end 8a is coupled to the molecular rotor 5a and whose downstream zone 8b is coupled to the kinematic rotor 9a.

In this second embodiment, the means are preferred to protect the bearings 15 and 16 against the harmful action of corrosive gases, powders and dust that the pump is often required to extract vacuum chambers. For this, a purge 19 is provided by which a purge neutral gas can be introduced into the housing 100b containing the engine 7, and means are provided for sucking up the neutral gas through the zones occupied by the bearings 15 and 16.

Thus, there is provided a suction duct 20 which goes directly from the discharge of the molecular pumping stage 5 to the kinematic pumping stage 9, at the periphery of the disk forming the kinematic rotor 9a, and the direction of the grooves is reversed. helical in the last stage of molecular pumping 5e so that it constitutes an upstream dynamic seal that sucks the gases from the upstream bearing 15 to drive back to the kinematic pumping stage 9. Simultaneously, it can be provided that the second transverse face upstream 11a of the kinematic rotor disk 9a, as illustrated in FIG. 3, comprises oblique centrifugal ribs 11c-11f for cooperating with a corresponding face 11b of the pump body 100 and constituting a downstream dynamic seal which draws the gases from the downstream bearing 16 to the primary pumping stage 9.

The motor 7 is powered by electrical conductors connected to a power supply connector 18.

According to the invention, it is possible to replace the downstream transverse primary kinematic primary rotor provided with radial individual blades engaged in concentric annular grooves of a kinematic stator, by any other kinematic multi-stage kinematic pump with viscous drive which operates satisfactorily. at the speed of rotation of molecular or turbomolecular pumps.

An example of another possible structure of such a suitable primary stage is illustrated in FIG. 3. It is then considered that the face 11a constitutes the main face of the rotor 9a, and that the oblique centrifugal ribs 11c-11f, cooperating with a corresponding transverse face of the stator or pump body, constitute a kinematic stage with viscous drive. One can then design a stack of several similar disks, a transverse face comprises the oblique centrifugal ribs which cooperate with a corresponding transverse face of a multi-stage kinematic stator.

This embodiment is also compatible with the presence of an additional kinematic pumping stage constituted by the upstream transverse face of the rotor with other oblique centrifugal ribs.

The embodiment is also compatible with a particular arrangement of dynamic seals and neutral gas purges in the bearing area.

In all cases, a plurality of molecular and / or turbomolecular pumping stages can be provided.

Claims (13)

1. A vacuum pump comprising, in a common pump body (100), at least one molecular drag pump stage (5) in series in air-flow connection with at least one primary pump stage (9) of compatible speed, the molecular drag pump stage (5) having a molecular drag rotor (5a) co-operating with a molecular drag stator (5b) provided in the pump body (100), the primary pump stage (9) having a primary rotor (9a) co-operating with a primary stator (9b) provided in the pump body (100), the molecular drag rotor (5a) and the primary rotor (9a) being rotated by a common drive shaft (8) coupled to a motor (7), the pump being characterized in that:

   · the molecular drag rotor (5a) includes a blind axial cavity (5c) that is open towards the downstream end of the pump body (100);

   · the motor (7) is housed at least in part in said blind axial cavity (5c) of the molecular drag rotor (5a);

   · the drive shaft (8) is coupled via its upstream end (8a) to the molecular drag rotor (5a); and

   · the drive shaft (8) is coupled via its downstream portion (8b) to the primary rotor (9a).
2. A vacuum pump according to claim 1, characterized in that the drive shaft (8) is carried to rotate by an upstream bearing (15) and a downstream bearing (16), the upstream bearing (15) being situated between the motor (7) and the zone (8a) for coupling to the molecular drag rotor (5a), the downstream bearing (16) being situated between the motor (7) and the zone (8b) for coupling to the primary rotor (9a).
3. A vacuum pump according to claim 1 or claim 2, characterized in that:

   · the primary rotor (9a) is a multistage regenerative rotor using viscous drag, comprising a disk having a transverse face (9c) carrying a series of concentric annular ribs (9d-9h) each carrying individual radial blades (10);

   · the primary stator (9b) is a regenerative stator including a corresponding transverse face having a series of concentric annular grooves (9j-9n) in which the individual radial blades (10) of the regenerative rotor (9a) are engaged;

   · the concentric annular grooves (9j-9n) of the regenerative stator (9b) are of cross-section that is greater than the cross-section of the corresponding individual radial blades (10) of the regenerative rotor (9a), with the exception of a short groove zone (9o) of small section in which the individual radial blades (10) engaged with little clearance; and

   · the successive concentric annular grooves (9j-9n) are connected to one another via respective communication channel (9p) provided at the downstream end of the corresponding small section groove zone (9o).
4. A vacuum pump according to claim 1 or claim 2, characterized in that the primary rotor (9a) is a multistage regenerative rotor using viscous drag comprising one or more disks, each having a transverse face carrying oblique centrifugal ribs which co-operate with a corresponding transverse face of a multistage regenerative stator.
5. A vacuum pump according to claim 3 or claim 4, characterized in that the primary pump stage (9) is also such that the primary rotor (9a) includes an upstream transverse face (11a) having oblique centrifugal ribs (11c-11f) which co-operate with a corresponding transverse face (11b) of the pump body (100) in order to constitute an additional regenerative pump stage (11).
6. A vacuum pump according to claim 5, characterized in that the primary pump stage (9) is further such that:

   · the oblique centrifugal ribs (11c-11f) of the rotor co-operate with the corresponding transverse face (11b) of the pump body (100) to constitute a downstream dynamic seal which produces suction protecting the downstream bearing (16);

   · a last molecular drag stage (5d) is reversed to constitute an upstream dynamic seal which produces suction protecting the upstream bearing (15); and

   · an inert gas inlet (19) is adapted to deliver a flow of inert gas into the housing (100b) containing the motor (7), thereby producing a flow of inert gas through the bearings (15, 16).
7. A vacuum pump according to any one of claims 1 to 6, characterized in that it comprises a plurality of molecular drag pump stages (5) constituted by rotor elements in the form of concentric cylinders connected to the drive shaft (8) at their upstream ends, and a plurality of stator elements in the form of concentric cylinders having helical ribs and connected to the pump body (100) at their downstream end, and engaged between successive concentric rotor cylinders.
8. A vacuum pump according to any one of claims 1 to 7, characterized in that it further comprises at least one turbomolecular pump stage (4) in gas-flow connection upstream from the molecular drag pump stage(s) (5), the turbomolecular pump stage (4) comprising a turbomolecular rotor (4a) having at least one stage with radial fins and a turbomolecular stator (4b) having at least one annular groove in which the radial fins of the turbomolecular rotor (4a) are engaged.
9. A vacuum pump according to claim 8, characterized in that it comprises a plurality of turbomolecular stages constituted by a rotor having a plurality of stages of radial fins distributed along the drive shaft (8) and a plurality of corresponding annular grooves distributed along the stator (4b).
10. A vacuum pump according to any one of claims 1 to 9, characterized in that the motor (7) includes cooling means (17) engaged in the stator (7b) of the motor.
11. A vacuum pump according to any one of claims 1 to 10, characterized in that:

    · the motor (7) is adapted for a high speed of rotation, greater than 20,000 rpm in nominal operating conditions; and

    · the concentric annular grooves (9j-9n) and the corresponding individual radial blades (10) are of a size that is smaller in the vicinity of the delivery from the regenerative pump stage (9).
12. A vacuum pump according to any one of claims 1 to 11, characterized in that the primary stage (9b) is mounted to be movable in the axial direction relative to the pump body (100) and is driven by displacement means enabling its axial position relative to the primary rotor (9a) to be modified, thereby enabling pumping performance to be adjusted.
13. A vacuum pump according to any one of claims 1 to 12, characterized in that the drive shaft (8) is guided in rotation by magnetic bearings (15, 16).

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