FR2651280A1 - PRIMARY VACUUM PUMP. - Google Patents

Abstract

The invention relates to a primary vacuum pump. It relates to a 1 primary vacuum pump comprising a stator (1) and at least one rotor (2) rotating in the stator while maintaining a predetermined leakage clearance with respect to the latter, characterized in that this clearance is rendered variable during pumping thanks to an elastically deformable part (4, 5,) of the wall of the rotor and / or of the stator and to a means for controlling this deformation. Application to primary vacuum pumps

Description

-1- Primary vacuum pump

  The present invention relates to a primary vacuum pump

  re, comprising a stator and at least one rotating rotor in the sta-

  tor by maintaining a predetermined escape game with respect thereto.

  Primary vacuum pumps, alone or in series, are

  to create total pressures of about 10-3 to 10 -4 mbar by repressing against atmospheric pressure. The oxygen and nitrogen molecules are entrained in such a pump under viscous and / or turbulent conditions. The flow / volume characteristic S / pressure P of such a pump is essentially a function of the clearance between the rotor and the stator. This function is shown in Figure 1 attached, taking the pressure p in mbar as abscissa and the flow S in m / h ordinate. Each of the five curves represented in solid lines corresponds to a given game, the game

  increasing from one curve to another in the direction of arrow j.

  During the pumping of a large volume, vis-à-vis the volume flow rate of the pump, the temperature of the rotor or rotors increases much faster than the stator temperature. In order to avoid any seizure, the manufacturer is led to impose the game

  largest stator-rotor, corresponding to the maximum of the dilat-

  differential This large game corresponds to a medium volume / pressure characteristic, which, moreover, evolves with the

  respective temperatures of the rotor and the stator.

  On the other hand, gases such as hydrogen, propane, pentane, etc., have absolute viscosities that are 10 times lower than air. Internal mass leaks are therefore much larger than with air, and therefore, the volume / pressure characteristic, constant clearance, is significantly lower than with air. It is therefore interesting to be able to adapt the game in

  depending on the viscosity of the pure gas or the pumped mixture.

  As a result, it is impossible to construct pumps with a low clearance and therefore excellent characteristics, that is to say - at atmospheric pressure, a high flow rate and a very low dS / dp derivative, - at zero flow, a low pressure and a derivative dS / dp as large as possible.

  In addition, in some applications (semiconductor

  as well as in mass spectrometry, leak detection by helium or neon tracer gas, in spatial simulation, etc.),

  wants to control the flow of the pump independently of the pressure.

  However, to do this, one skilled in the art has two possibilities to his

  provision, namely the series connection with the pump of a conductive

  variable speed, or the reduction of the rotational speed of the pump. The object of the invention is to design a pump which makes it possible to achieve a very low clearance and a rapid modification of

  the characteristic, even during pumping, in order to be able to

  the pressure variation as a function of time in a

  to which the pump is associated.

  According to the invention, this object is achieved by the fact that the

  clearance between stator and rotor is made variable during pumping. se-

  In a first embodiment, this variation is obtained thanks to an elastically deformable part of the wall of the rotor and / or the stator and to a means for controlling this deformation. Said control means acting on said elastically deformable part can

  comprise an adjustable pressure fluid which is applied to a cavity

  at least partially delimited by said elastically

  deformable rotor wall and / or stator.

  In an alternative embodiment, the change in clearance between the rotor and the stator is not obtained by an elastic deformation of a wall, but by a change in the position of the rotor in the stator. This applies in particular to a pump whose rotor has a frustoconical or hemispherical shape, and to any

  pump whose flow of gas is generally parallel to the axis.

  The invention will be described hereinafter in more detail in

  using some examples and drawings.

  Figure 1 shows the flow function

  volume / pressure for different game pumps.

  FIG. 2 schematically represents a pump according to the invention of the magnetically controlled type of the game. FIG. 3 shows a side channel pump according to

  the invention, whose game control means are hydraulic.

  FIG. 4 schematically shows a cylindrical pump

  than a helical groove whose control means is pneumatic.

  FIG. 5 schematically shows a frustoconical rotor pump whose clearance is modified by displacement of this rotor or

of the stator.

  Figure 6 shows a pump similar to the previous one,

whose rotor is hemispherical.

  Figure 7 shows a vane pump according to the invention.

  Figure 8 schematically shows a vacuum pump

  screw whose stator wall has several distinct zones.

deformation.

  Referring to FIG. 2, a primary vacuum pump comprising a stator i and a rotor 2 rotating about an axis 3 is shown schematically. The rotor is for example a disk and the stator comprises suction and discharge openings. suppression

  not represented. The pumping effect is entirely dependent on the game

  be the stator and the rotor. This game has been represented on this figure (and the following ones) in an exaggerated way. In fact, it is a distance of less than a tenth of a millimeter. As seen in Figure 2, the walls 4 and 5 of the ring-shaped stator, which are on either side of the rotor 2, are thin walls, which are plastically deformable. The deformation of these walls is obtained by magnetic control means constituted by

  two support rings 6 and 7 which are applied against the rear face

  4 or 5 respectively and can be slightly displaced by electromagnets, such as 8, which bear against the fixed part of the stator 1. By more or less deforming the elastically deformable portions 4 and 5 of the stator , one can thus modify the game between stator and rotor and thus modify the characteristics

  flow rate pump pressure.

  We can, for example. modify the clearance as a function of the pressure prevailing at the suction side of the pump, so that a characteristic is obtained as outlined in dashed lines

in Figure 1.

  The displacement of the elastically deformable parts can not only

  be provided by electromagnetic means, but also by

  by pneumatic or hydraulic or mechanical means. The

  FIG. 3 shows a side channel pump whose rotor 11 is

  on a shaft 12 and rotates in a stator 13. The two channels

  are each equipped with an inflatable torus 14 and 15 respectively.

  which is connected to a fluid source with adjustable pressure, not shown. The lateral distance between the blades of the rotor 11 and the face opposite the two tori constitutes the game which can be more

  or smaller depending on the pressure of the fluid applied to the cores.

  Another possibility of pneumatic control

  or hydraulic pump is shown in Figure 4. It is

  here is a cylindrical pump with a helical groove with a rotor

  16 rotating about an axis 17 inside a stator 18, also

  cylindrical. In comparison with the turns of the rotor 16, the stator is

  equipped with a tube 19, of synthetic elastomer, which is fixed frontally

  in both stator flanges. This tubular elastomer tube

  thetic delimits a cavity 20 with the stator which may be

  at a pressure of a fluid, such as air. The tube is thus more or less contracted and close to the rotor, according to the increase of

  the pressure prevailing in the cavity 20.

  In Figure 5, there is shown a pump, the rotor 21 and the stator 22 each have a frustoconical shape and symmetrical around the axis 23 of rotation. The clearance 24 between rotor and

  stator by moving the rotor axially in the stator, or reversing

  by an action that can be purely mechanical. It has been indicated in dashed lines in this figure another relative position

  rotor leading to a game 24 'smaller.

  The displacement of the rotor in the stator can be obtained by any suitable means of action, such as electromagnets, fluid pressures, an electric motor or a control system.

purely mechanical.

  This principle is not limited to a frustoconical shape, but also applies to other shapes, such as those represented on the

  Figure 6. This is a hemispherical shape, the rotor 25

  in the stator 26 about its axis 27 of symmetry.

  This example shows that it is not absolutely necessary to re-

  uniformly the game in question, and that it is enough to act on this game in areas where gas leaks are particularly

  important. When considering the application of the principle of gambling

  In particular, it is sufficient to modify the clearance in the area between the suction port and the discharge port, since the pressure difference is the highest. HE

  note that this is a deformed metal wall

  The diagram of FIG. 7 also shows a system for measuring the capacitive bridge clearance. The first electrode of a capacitor of said bridge (not shown) is the rotor 37, connected to ground, and the

  second electrode 35 is in a sensor fixed on the deformed wall

  36. The value of this game can be controlled by a loop of

  serving by acting on a setpoint potentiometer.

  Finally, FIG. 8 shows a twin screw pump having two rotors 28 and 29 rotating about two parallel axes 30 and 31. The stator of this pump is divided into a plurality of zones, each having a distinct cavity such as 32. Such

  cavities can not only be provided in the cylindrical part

  stator, but also in the frontal part (cavities 33 and

  34). By subjecting these different cavities to different pressures

  you can establish different games in the different areas between the stator and the two rotors. It is thus possible to design pumps of very variable characteristics. The same principle of a subdivision into several deformable zones can, of course, be applied to other pumps such as those of FIGS.

  4, to take into account the non-linear variation in mass flow rates

  gas leakage between the suction end and the end

pump discharge.

  The invention is not limited to the examples of

  outlined above. Instead of making the geometry of the stator variable, we can also apply the same principle to the rotor, which

  is particularly interesting in the case of two cooperating rotors.

  In this case, the variation of the geometry does not only concern the clearance between the rotors and the stator, but also the clearance between the two rotors. The invention is also not limited to the types of pumps mentioned above. On the contrary, it can be applied to any pump whose clearance between the rotor and the stator is decisive for the pumped mass flow rate. This is, for example, also the case for a pump of the Roots type or for a pump of the type with two tangential eccentric spirals, such as

  described in French Patent 2,141,402.

-7-

Claims (6)

  1 / primary vacuum pump comprising a stator (1, 26) and at least one rotor (2, 11, 16, 21, 25, 28, 29, 37) rotating in the stator while maintaining a predetermined clearance clearance with respect to it, characterized in that this game is made variable during pumping through a portion (4, 5, 14, 15, 19, 32, 33, 34, 36) elastically deformable of the wall of the rotor and / or the stator and a means of control of this deformation.   2 / primary vacuum pump according to claim 1, characterized in that the control means comprise at least one electromagnet (8) or a purely mechanical means whose movable part is fixed   on said resiliently deformable portion (4, 5) of the rock wall tor and / or stator.   3 / primary vacuum pump according to claim 1, characterized in   the control means comprise a pressure-controlled fluid   ble in a cavity (14, 15, 20, 32, 33, 34, 38) which is at least partially delimited by said elastically deformable portion   of the wall of the rotor and / or the stator.   4 / primary vacuum pump according to one of the preceding claims,   characterized in that it is the wall of the stator which comprises said elastically deformable portion.   Primary vacuum pump according to claims 3 and 4, comprising   a stator with a cylindrical wall of circular section, characterized in that said wall is constituted by an elastomeric tube synthetic or metal (19, 36).   6 / primary vacuum pump according to claims 3 and 4, characterized   characterized in that the wall is subdivided into slices (32 to 34) whose elastic deformations are individually controlled by distinct control means.   7 / Primary vacuum pump, comprising a stator and a rotating rotor   in the stator while retaining a predetermined set of leakage   port to it, characterized in that the rotor (21, 25) and the   tor (22, 26) being frustoconical or hemispherical, the clearance (24) is variable during the pumping due to a relative axial displacement of the rotor relative to the stator and that this displacement is obtained by a -8- control means.