WO2021148525A1

WO2021148525A1 - Dry vacuum pump

Info

Publication number: WO2021148525A1
Application number: PCT/EP2021/051318
Authority: WO
Inventors: Yann Olivier; Thierry Neel; Lucas REY
Original assignee: Pfeiffer Vacuum
Priority date: 2020-01-24
Filing date: 2021-01-21
Publication date: 2021-07-29
Also published as: FR3106630A1; FR3106630B1; KR20220127266A

Abstract

Dry vacuum pump (1) in which the at least two pumping stages (1a-1f) each have an inlet (7) and an outlet (8) emerging from a respective half-shell (9, 10), the stator (2) also having a stator casing (15) surrounding the joined half-shells (9, 10), at least one groove (20) being provided in the stator casing (15) or in an external surface of the half-shells (9, 10) so as to form at least one transfer channel (21) by joining the stator casing (15) to the half-shells (9, 10), the at least one transfer channel (21) placing the outlet (8) of a pumping stage (1a-1e) in communication with the inlet (7) of the following pumping stage (1b-1f).

Description

Title of the invention: Dry vacuum pump

[1] The present invention relates to a dry vacuum pump, in particular a multistage dry vacuum pump, such as a pump of the Roots type or of the claw type.

[2] Multistage vacuum pumps have a plurality of pumping stages mounted in series, in which a gas to be pumped circulates between an intake and a delivery. Among known rough-vacuum pumps, a distinction is made between those with rotary lobes, also known as “Roots” pumps, with two or three lobes, or those with double claws, also known as “claw” pumps.

[3] Dry vacuum pumps comprise two rotors with identical profiles, rotating inside a stator in opposite directions. During rotation, the gas to be pumped is trapped in the volume created by the rotors and the stator, and is driven by the rotors towards the following stage and then progressively as far as the delivery of the vacuum pump.

[4] The successive pumping stages are connected in series one after another by transfer channels connecting the outlet of the preceding pumping stage to the inlet of the following stage. These transfer channels are generally integrated in the stator. They are provided in the walls interposed between the compression chambers or are arranged on either side of the compression chambers.

[5] Furthermore, in order to make both the machining and the assembly of the multistage vacuum pump easier, the stators are sometimes composed of two half-shells joined at a longitudinal joining surface that is generally parallel to the axes of the rotors, as described for example in the document US6572351. The stator made of half-shells allows one-piece shaft- rotors to be used. The assembly time can then be reduced on account of the smaller number of interfaces to be aligned. This architecture also makes it possible to reduce the risk of accumulation of alignment defects.

[6] A drawback of this embodiment is that it may prove difficult to realize a good seal between the half-shells. Specifically, the compression chambers and the transfer channels integrated in the stator are in two parts, a first part being provided in a first half-shell and a second part being provided in the second half-shell. This entails the need to mutually seal these two parts at the longitudinal joining surface.

[7] One solution consists in adhesively bonding the half-shells together via a hardenable seal. However, the material of hardenable seals may not be sufficiently resistant, notably to the corrosive gases in certain applications.

[8] Another solution consists in using three-dimensional seals that realize the seal between the outside and the pumping stages and between the outside and the transfer channels. Such seals can, however, generate additional costs that are not insignificant, notably on account of their complex shape that is expensive to produce and on account of the additional need to coat them with corrosion-resistant materials, which are likewise expensive.

[9] Another drawback of the production of half-shells with transfer channels integrated in the stator is that the inside of the channels is difficult to access, thereby complicating both the production of the half-shells and the cleaning thereof in a maintenance phase.

[10] An aim of the present invention is to propose a multistage dry vacuum pump that at least partially solves one of the abovementioned drawbacks.

[11] To this end, the subject of the invention is a dry vacuum pump having:

- a stator having two complementary half-shells that meet at a joining surface so as to form at least two pumping stages mounted in series between an intake and a delivery of the vacuum pump,

- two rotor shafts configured to rotate synchronously in opposite directions in the pumping stages so as to drive a gas to be pumped between the intake and the delivery, characterized in that:

- the at least two pumping stages each have an inlet and an outlet emerging from a respective half-shell,

- the stator also has a stator casing surrounding the joined half-shells, at least one groove being provided in the stator casing or in an external surface of the half-shells so as to form at least one transfer channel by joining the stator casing to the half-shells, the at least one transfer channel placing the outlet of a pumping stage in communication with the inlet of the following pumping stage.

[12] The at least one transfer channel thus extends in the stator, on the sides of the pumping stages, on the outside of the half-shells. The inside of the transfer channels is therefore accessible when the stator casing is removed from the half-shells. The transfer channels are thus easily accessible when the vacuum pump is disassembled, thereby making them easier to produce and clean. The transfer channels are furthermore in one piece, thereby making it possible to avoid having to seal the transfer channels at the joining surface.

[13] The vacuum pump may also have one or more of the features described below, considered on their own or in combination.

[14] The outlet of a pumping stage may be placed in communication with the inlet of the following pumping stage by two transfer channels arranged respectively on either side of the pumping stages.

[15] The stator casing may have a cross section of oblong or cylindrical overall shape. [16] The at least one groove may have a portion of helical shape. The helical shape allows the outlet of a pumping stage to be placed in communication with the inlet of the following pumping stage, without sharp angles but smoothly. The lack of an abrupt deviation in the transfer channel makes it possible to limit pressure drops, thereby making it possible to avoid an increase in the power consumed and heating of the pumped gases and of the vacuum pump. Controlling the pressure drops in the transfer channels also makes it possible to avoid the creation of dead zones that are conducive to deposits of condensable entities, and makes it easier for powders to be carried along, if appropriate.

[17] The two portions of helical shape of the two transfer channels may be connected to one another by a first and a second straight portion of the transfer channels, the first straight portion communicating with an inlet and the second straight portion communicating with an outlet.

[18] The inlets of the pumping stages may be provided in a first flat surface of a first half shell and outlets may be provided in a second flat surface of a second half-shell, the first and second flat surfaces being parallel to one another.

[19] The stator may have a first and a second end plate joined to the axial ends of the stator casing, the vacuum pump being able to have at least one first annular seal interposed between the stator casing and the first end plate and at least one second annular seal interposed between the stator casing and the second end plate. The annular seals are thus compressed between flat and fixed surfaces that are positioned facing one another. As a result, these seals can be conventional annular seals, i.e. flat O-ring seals, and can therefore be of simple technology and, consequently, low cost.

[20] A delivery channel communicating between the outlet of the last pumping stage and the delivery may be provided in an end flange of the stator, said end flange being joined to the first end plate of the stator.

[21] According to a first example, the vacuum pump does not have a seal, for the one part, between the half-shells and, for the other part, between the half-shells and the stator casing. In this case there is neither a flat or three-dimensional O-ring seal, nor a hardenable seal, between the half-shells and between the half-shells and the stator casing. The seal between the pumping stages is ensured by the fastening together of the half-shells. The seal between the transfer channels is realized by precise fitting of the stator casing on the half-shells. This is made possible notably by the fact that the stator casing can contain any leaks of gas from the pumping stages or from the transfer channels. The seal between the pumped gases and the outside of the vacuum pump can be realized by the use of the at least two conventional annular seals disposed at the two axial ends of the stator casing. [22] According to a second example, the vacuum pump has at least one annular seal interposed, for the one part, between the half-shells and the stator casing and, for the other part, between two successive pumping stages.

[23] When the at least one groove is provided in the stator casing, the vacuum pump may have at least one bypass channel interposed between two inlets or between an inlet and an outlet, the at least one bypass channel being provided in the stator casing, and a valve arranged in the bypass channel so as to open or close the bypass channel depending on the difference in pressure on either side of the valve.

[24] When the at least one groove is provided in the stator casing, at least one fluid circulation channel may be provided in the stator casing in order to thermalize the stator or in order to distribute a fluid in the pumping stages.

[25] When the at least one groove is provided in an external surface of the half-shells, the stator may have an additional stator casing, surrounding the stator casing, the vacuum pump being configured to cause a fluid to circulate in the gap situated between the stator casing and the additional stator casing, in order to thermalize the stator.

[26] The joining surface of the half-shells may pass through a median plane of the vacuum pump, such as the plane containing the axes of the rotor shafts.

[27] Presentation of the drawings

[28] Other advantages and features will become apparent on studying the following description of a particular, but in no way limiting, embodiment of the invention, and also the appended drawings, in which:

[29] [Fig.1] Figure 1 shows a perspective view of a pumping part of a dry vacuum pump according to a first embodiment.

[30] [Fig.2] Figure 2 shows a cross-sectional view of the pumping part of the vacuum pump in Figure 1, on a vertical median plane passing between the rotor shafts.

[31] [Fig.3] Figure 3 shows a perspective view of the joined half-shells and of the rotor shafts of the vacuum pump in Figure 1.

[32] [Fig.4A] Figure 4A shows an upper half-shell of the stator in Figure 3.

[33] [Fig.4B] Figure 4B shows a lower half-shell of the stator in Figure 3.

[34] [Fig.5] Figure 5 shows a stator casing, an end flange and an end plate of the stator of the vacuum pump in Figure 1.

[35] [Fig.6] Figure 6 shows a view in longitudinal and vertical cross section of the stator casing in Figure 5.

[36] [Fig.7] Figure 7 is a depiction of two transfer channels of the vacuum pump in Figure 1 , placing the outlet of a pumping stage in communication with the inlet of the following pumping stage. [37] [Fig.8] Figure 8 shows an exploded view of a variant embodiment of the pumping part.

[38] [Fig.9] Figure 9 shows a schematic side view of a pumping part of a dry vacuum pump according to a second embodiment, the stator casing being viewed in longitudinal section.

[39] [Fig.10] Figure 10 shows a schematic view in cross section of the pumping part in Figure 9.

[40] [Fig.11] Figure 11 shows a schematic bottom view of the pumping part in Figure 9, the stator casing being viewed in longitudinal section.

[41] [Fig.12] Figure 12 shows a view similar to Figure 10 for a variant embodiment.

[42] In these figures, identical or similar elements bear the same reference numerals.

[43] The figures have been simplified for the sake of clarity. Only the elements necessary for understanding the invention are shown.

[44] The following embodiments 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 apply only to a single embodiment. Individual features of different embodiments can also be combined or interchanged to provide other embodiments.

[45] The longitudinal direction is defined as the direction in which the axes of the rotor shafts extend.

[46] Figures 1 and 2 show a first exemplary embodiment of a multistage dry vacuum pump 1 , having a stator 2 (or pump body) that forms at least two pumping stages 1 a-1 f, such as between two and ten pumping stages, in this case six 1 a-1 f, mounted in series between an intake 3 and a delivery 4 of the vacuum pump 1 and in which a gas to be pumped can circulate.

[47] The pumping stage 1a that communicates with the intake 3 of the vacuum pump 1 is the first pumping stage or the stage with the lowest pressure and the pumping stage 1f that communicates with the delivery 4 is the last pumping stage or the stage with the highest pressure.

[48] The vacuum pump 1 also has two rotor shafts 5, 6 (Figures 2 and 3) configured to rotate synchronously in opposite directions in the pumping stages 1 a-1 f so as to drive a gas to be pumped between the intake 3 and the delivery 4.

[49] The shafts bear rotors that have for example lobes with identical profiles, for example of the “Roots” type with two lobes (Figure 8), three lobes (Figure 3) or more, or of the “claw” type or based on another similar positive-displacement vacuum pump principle.

[50] These rotor shafts 5, 6 are advantageously in one piece. [51] The stator 2 has two complementary half-shells 9, 10 that meet at a joining surface 11 so as to form the at least two pumping stages 1a-1f. The joining surface 11 of the half shells 9, 10 passes for example through a median plane of the vacuum pump 1, such as the plane containing the axes of the rotor shafts 5, 6. The joining surface 11 is for example substantially flat or has shapes that are complementary between the half-shells.

[52] Each pumping stage 1 a-1 f defines a compression chamber of the stator 2 accommodating two mating rotors of the vacuum pump 1. The at least two pumping stages 1a-1f each have an inlet 7 and an outlet 8 emerging from a respective half-shell 9, 10.

[53] During rotation, the gas drawn in through the inlet 7 is trapped in the volume created by the rotors and the stator 2 of the pumping stage 1 a-1 f, and is then compressed and driven towards the outlet 8 and towards the following stage.

[54] The pumping stages 1a-1f have a swept volume, i.e. a volume of pumped gas, that decreases (or remains the same) with the pumping stages 1 a- 1 f , the first pumping stage 1a having the highest swept-volume output and the last pumping stage 1f having the lowest swept-volume output. The axial dimensions of the rotors are for example the same or decrease with the pumping stages, the pumping stage 1a situated on the intake 3 side accommodating the rotors of largest axial dimension.

[55] In operation, the rotor shafts 5, 6 are driven in rotation by a driving part (not shown) comprising a motor for driving the rotors, gears for synchronizing the rotors, and bearings supporting the shafts of the rotors. The motor of the vacuum pump 1 is mounted on one of the shafts 5, 6, for example at one end of the vacuum pump 1 , such as on the delivery 4 side of the vacuum pump 1. The vacuum pump 1 is called “dry” since, in operation, the rotor shafts 5, 6 rotate inside the stator 2 without any mechanical contact between them or with the stator 2 but via very small clearances, this making it possible for there to be no oil in the compression chambers.

[56] The joined half-shells 9, 10 have for example a cross section of oblong shape (Figures 3, 4A, 4B). The inlets 7 of the pumping stages are for example provided in a first flat surface 12 of a first half-shell 9, such as the upper half-shell. The outlets 8 are for example provided in a second flat surface 13 of a second half-shell 10, such as the lower half-shell, with the exception in this case of the outlet 8 of the last pumping stage 1f. The first and second flat surfaces 12, 13 are parallel to one another.

[57] The inlets 7 and outlets 8, with the exception of that of the last pumping stage 1 f, have for example sections of oblong shape. The inlet 7 and the outlet 8 of the first pumping stage 1a have for example the largest sections. [58] The half-shells 9, 10 are fastened to one another for example by means of two series of screws that are regularly tightened in holes 14 provided in the half-shells 9, 10, on each side of the joining surface 11.

[59] The stator 2 also has a stator casing 15 surrounding the joined half-shells 9, 10. The stator casing 15 is complementary to the half-shells 9, 10.

[60] The stator 2 can also have a first and a second end plate 16, 17 joined to the axial ends of the stator casing 15 for example by means of screws (Figure 1). The end plates thus extend perpendicular to the longitudinal direction of the rotor shafts 5, 6.

[61] Likewise, the stator 2 can have an end flange 18 bearing for example means for sealing with respect to lubricants, interposed between the driving part (not shown) and the dry pumping part, at the shaft passages. The end flange 18 has a flat face that is for example fastened to the first end plate 16 by means of screws. Shaft passages are of course provided in the end plates 16, 17 and the compression chambers of the pumping stages for the rotor shafts 5, 6 to pass through.

[62] According to one exemplary embodiment, the outlet 8 of the last pumping stage 1f does not emerge from the flat surface 13 of the lower half-shell 10, but communicates with a delivery channel 19 provided in the end flange 18, communicating with the delivery 4 (Figure 2). This arrangement makes it easier to manufacture a delivery having an orifice of standard diameter, conventionally used in the field of vacuum technology.

[63] According to a first exemplary embodiment of the invention, at least one groove 20 is provided in the stator casing 15 so as to form at least one transfer channel 21 by joining the stator casing 15 to the half-shells 9, 10 (Figure 5). The at least one transfer channel 21 places the outlet 8 of a pumping stage 1a-1e in communication with the inlet 7 of the following pumping stage 1 b- 1 f . The at least one transfer channel 21 thus extends in the stator 2, on the sides of the pumping stages 1a-1f, on the outside of the half-shells 9, 10, and on the inside of the stator casing 15. The inside of the transfer channels 21 is therefore accessible from the inner side of the stator casing 15 when the stator casing 15 is removed from the half-shells 9, 10. The transfer channels 21 are thus easily accessible when the vacuum pump 1 is disassembled, thereby making them easier to produce and clean. The transfer channels 21 are furthermore in one piece, thereby making it possible to avoid having to seal the transfer channels 21 at the joining surface 11.

[64] There are at least N-1 transfer channels 21 for placing N pumping stages 1a-1f in communication.

[65] In the case of a vacuum pump 1 having more than two pumping stages, the widths of the transfer channels 21 may be the same or decrease with the pumping stages 1a-1f, the first transfer channel 21, which connects the first pumping stage 1a to the second pumping stage 1b, having the largest width.

[66] The stator casing 15 has for example a cross section of oblong overall shape complementary to the joined half-shells 9, 10. The same oblong section extends for example in the longitudinal direction so as to form an oblong right cylinder.

[67] As can be seen more clearly in Figures 6 and 7, the at least one groove 20 has for example a portion 20a of helical shape. The helical shape allows the outlet 8, which is in this case at the bottom, of a pumping stage to be placed in communication with the inlet 7, which is in this case at the top, of the following pumping stage, without sharp angles but smoothly. The lack of an abrupt deviation in the transfer channel 21 makes it possible to limit pressure drops, thereby making it possible to avoid an increase in the power consumed and heating of the pumped gases and of the vacuum pump. Controlling the pressure drops in the transfer channels 21 also makes it possible to avoid the creation of dead zones that are conducive to deposits of condensable entities, and makes it easier for powders to be carried along, if appropriate.

[68] Provision is made for example for the outlet 8 of a pumping stage 1a-1e to be placed in communication with the inlet 7 of the following pumping stage 1b-1f by two transfer channels 21 arranged respectively on either side of the pumping stages. The gas thus flows in parallel in the two transfer channels 21 surrounding the pumping stages, making it possible to improve the efficiency of the transfer of gas (Figures 5 and 7). Each pumping stage 1a-1e can thus be placed in communication with the following pumping stage 1b-1f by two transfer channels 21, the two portions 20a of helical shape being in this case connected to one another by a first and a second straight portion 20b of the transfer channels 21 , the first straight portion 20b communicating with an inlet 7 and the second straight portion 20b communicating with an outlet 8 (Figure 7).

[69] It will be understood from what has just been described that the stator casing 15 with the integrated transfer channels 21 that can have different depths or widths does not pose any particular problem in terms of its production, and can be produced easily for example by casting, at an economical cost.

[70] According to a first exemplary embodiment, the vacuum pump 1 does not have a seal, for the one part, between the half-shells 9, 10 and, for the other part, between the half shells 9, 10 and the stator casing 15. In this case there is neither a flat or three-dimensional O-ring seal, nor a hardenable seal, between the half-shells 9, 10 and between the half-shells 9, 10 and the stator casing 15. The seal between the pumping stages 1a-1f is ensured by the fastening together of the half-shells 9, 10. The seal between the transfer channels 21 is realized by precise fitting of the stator casing 15 on the half-shells 9, 10. This is made possible notably by the fact that the stator casing 15 can contain any leaks of gas from the pumping stages 1a-1f or from the transfer channels 21. The seal between the pumped gases and the outside of the vacuum pump 1 can be realized by the use of at least two conventional annular seals 22 disposed at the two axial ends of the stator casing 15.

[71] Thus for example, and as can be seen in Figure 2, the vacuum pump 1 has at least one first annular seal 22 interposed between the edge face of the stator casing 15 and the first end plate 16 and at least one second annular seal 22 interposed between the edge face of the stator casing 15 and the second end plate 17. There is for example an additional annular seal 22 that is interposed between the half-shells 9, 10 and the second end plate 17 situated on the side with the lowest pressures, in series with the annular seal 22 interposed between the stator casing 15 and the half-shells 9, 10.

[72] The annular seals 22 are thus compressed between flat and fixed surfaces positioned facing one another. As a result, these seals 22 can be conventional annular seals, i.e. flat O-ring seals, and can therefore be of simple technology and, consequently, low cost. The annular seals 22 are for example made of relatively economical fluoroelastomer material (FKM). They can be coated with a material of the PFA (perfluoroalkoxy) type, for example. This material is resistant to most aggressive chemicals.

[73] Figure 8 shows a variant embodiment in which the vacuum pump 1 also has at least one annular seal 23 interposed, for the one part, between the half-shells 9, 10 and the stator casing 15 and, for the other part, between two successive pumping stages 1a-1f.

[74] More specifically for example, at least one sealing half-slot 24 is provided in the outer surface of each half-shell 9, 10 so as to form a peripheral annular slot when the two half shells 9, 10 are joined. The peripheral annular slot is interposed between two inlets 7 and two outlets 8 of two successive pumping stages so as to accommodate the annular seal 23. There are thus N-1 peripheral annular slots and associated annular seals 23 for N pumping stages. The annular seals 23 can, as described above, be conventional seals. They are flat and mutually parallel, the annulus being inscribed in a plane parallel to the planes of the end plates 16, 17. These annular seals 23 make it possible to reinforce the relative seal between the compression chambers and between the transfer channels 21.

[75] Furthermore, in the embodiments described, provision can be made to arrange conventional functionalities of the stator in the stator casing 15.

[76] Thus, provision can be made for at least one fluid circulation channel to be provided in the stator casing 15 in order to thermalize the stator 2, notably to heat or cool it by circulation of water.

[77] Likewise, provision can be made for at least one fluid circulation channel to be provided in the stator casing 15 for the distribution of a gas in the pumping stages 1 a-1 f, such as a neutral gas, notably to dilute the pumped gases, or such as a reactive gas, for example to react with the pumped gases.

[78] These fluid circulation channels can be realized simply in the stator casing 15, for example by drilling.

[79] Furthermore, at least one bypass channel interposed between two inlets 7 or between an inlet 7 and an outlet 8 can be provided in the stator casing 15, and the vacuum pump 1 can have a valve arranged in the bypass channel so as to open or close the bypass channel depending on the difference in pressure on either side of the valve (not shown).

[80] In a manner known per se, the valve has a seat and a mobile shutter, the valve being able to adopt a closed position in which the mobile shutter closes a passage of the seat and an open position in which the mobile shutter opens up the passage, the difference in pressure on either side of the mobile shutter being able to open the valve. The mobile shutter may be urged to close by means of a spring.

[81] The valve can be a relief valve arranged at the outlet of the first or second pumping stage, communicating with the delivery 4 of the vacuum pump 1. In the open position, the relief valve makes it possible to short-circuit the last pumping stages of the vacuum pump, which could limit the overall swept-volume output in the event of a strong gas flow being pumped.

[82] The valve can be a delivery valve arranged at the outlet of the last pumping stage. The delivery valve makes it possible to prevent the pumped gases from returning into the vacuum pump.

[83] The valve can be a recirculation valve connected between an outlet and an inlet of a first pumping stage. Opening the valve makes it possible to cause the gases to be pumped to be recirculated into the same pumping stage in the event of a strong gas flow being pumped.

[84] The very light mechanical stresses at the stator casing 15 easily allow these various configurations to be realized. Likewise, these lower stresses allow the stator casing 15 to be made from a material different from that of the half-shells 9, 10, which are generally made of cast iron. For example, the stator casing 15 can be made of aluminium. This material is less heavy, less expensive and easier to machine. In the latter case, however, it is preferred to arrange annular seals 23 between the stator casing 15 and the half-shells 9, 10 in order to make up for the possible clearances between the stator casing 15 and the half-shells 9, 10 on account of the variations in coefficient of thermal expansion between the various materials.

[85] Figures 9 to 12 show a second embodiment of a multistage dry vacuum pump 1. [86] This embodiment differs from the preceding ones by the fact that in this case the at least one groove 20 is provided in an external surface of the half-shells 9, 10 so as to form at least one transfer channel 21 by joining the stator casing 25; 26 to the half-shells 9, 10, the transfer channel 21 placing the outlet 8 of a pumping stage 1a-1e in communication with the inlet 7 of the following pumping stage 1b-1f.

[87] The at least one transfer channel 21 thus extends on the external surfaces of the half-shells 9, 10, on the sides of the pumping stages. The inside of the transfer channels 21 is therefore accessible when the stator casing 25; 26 is removed from the half-shells 9, 10. The transfer channels 21 are thus easily accessible when the vacuum pump 1 is disassembled, thereby making them easier to produce and clean. The transfer channels 21 are furthermore in one piece, thereby making it possible to avoid having to seal the transfer channels at the joining surface 11.

[88] For example, the stator casing 25; 26 may be made by a profiled section, such as a tube. [89] The stator casing 25 may have a cross section of oblong overall shape (Figure 10).

The stator casing 25 of oblong cross section may be complementary to two half-shells 9, 10, which themselves have a cross section of oblong shape in the assembled state.

[90] It is possible for the vacuum pump 1 not to have a seal, for the one part, between the half-shells 9, 10 and, for the other part, between the half-shells 9, 10 and the stator casing 25; 26. The stator casing 25; 26 is for example interference fitted on the half-shells 9, 10, for example at the axial ends of the stator casing 25; 26.

[91] Figure 12 shows a variant embodiment in which the stator casing 26 has a cross section of cylindrical overall shape. This stator casing 26 may be complementary to two half shells 9, 10 having a cross section of oblong shape in the assembled state. [92] Furthermore in this example, the stator 2 has an additional stator casing 28, surrounding the stator casing 26, the two stator casings 26, 28 being in this case cylindrical and coaxial, the vacuum pump 1 being configured to cause a fluid to circulate in the gap 29 situated between the stator casing 26 and the additional stator casing 28, in order to thermalize the stator 2, notably to heat or cool it by circulation of water.

Claims

[Claim 1] Dry vacuum pump (1) having:

- a stator (2) having two complementary half-shells (9, 10) that meet at a joining surface (11) so as to form at least two pumping stages (1 a-1 f) mounted in series between an intake (3) and a delivery (4) of the vacuum pump (1),

- two rotor shafts (5, 6) configured to rotate synchronously in opposite directions in the pumping stages (1a-1f) so as to drive a gas to be pumped between the intake (3) and the delivery (4), characterized in that:

- the at least two pumping stages (1 a-1 f) each have an inlet (7) and an outlet (8) emerging from a respective half-shell (9, 10),

- the stator (2) also has a stator casing (15, 25, 26) surrounding the joined half-shells (9, 10), at least one groove (20) being provided in the stator casing (15, 25, 26) or in an external surface of the half-shells (9, 10) so as to form at least one transfer channel (21) by joining the stator casing (15, 25, 26) to the half-shells (9, 10), the at least one transfer channel (21) placing the outlet (8) of a pumping stage (1a-1e) in communication with the inlet (7) of the following pumping stage (1 b-1 f).

[Claim 2] Vacuum pump (1) according to the preceding claim, characterized in that the outlet (8) of a pumping stage (1a-1e) is placed in communication with the inlet (7) of the following pumping stage (1 b-1 f) by two transfer channels (21) arranged respectively on either side of the pumping stages.

[Claim 3] Vacuum pump (1) according to either of the preceding claims, characterized in that the stator casing (15, 25, 26) has a cross section of oblong or cylindrical overall shape.

[Claim 4] Vacuum pump (1) according to one of the preceding claims, characterized in that the at least one groove (20) has a portion (20a) of helical shape.

[Claim 5] Vacuum pump (1) according to Claims 2 to 4, characterized in that the two portions (20a) of helical shape of the two transfer channels (21) are connected to one another by a first and a second straight portion (20b) of the transfer channels (21), the first straight portion (20b) communicating with an inlet (7) and the second straight portion (20b) communicating with an outlet (8).

[Claim 6] Vacuum pump (1) according to one of the preceding claims, characterized in that the inlets (7) of the pumping stages are provided in a first flat surface (12) of a first half-shell (9) and outlets (8) are provided in a second flat surface (13) of a second half-shell (10), the first and second flat surfaces (12, 13) being parallel to one another.

[Claim 7] Vacuum pump (1) according to one of the preceding claims, characterized in that the stator (2) has a first and a second end plate (16, 17) joined to the axial ends of the stator casing (15, 25, 26), the vacuum pump (1) having at least one first annular seal (22) interposed between the stator casing (15, 25, 26) and the first end plate (16) and at least one second annular seal (22) interposed between the stator casing (15, 25, 26) and the second end plate (17).

[Claim 8] Vacuum pump (1) according to the preceding claim, characterized in that a delivery channel (19) communicating between the outlet (8) of the last pumping stage (1f) and the delivery (4) is provided in an end flange (18) of the stator (2), said end flange (18) being joined to the first end plate (16) of the stator (2).

[Claim 9] Vacuum pump (1) according to one of the preceding claims, characterized in that it does not have a seal, for the one part, between the half-shells (9, 10) and, for the other part, between the half-shells (9, 10) and the stator casing (15, 25, 26).

[Claim 10] Vacuum pump (1) according to one of Claims 1 to 8, characterized in that it has at least one annular seal (23) interposed, for the one part, between the half shells (9, 10) and the stator casing (15, 25, 26) and, for the other part, between two successive pumping stages (1 a-1 f).

[Claim 11] Vacuum pump (1) according to one of the preceding claims, wherein the at least one groove (20) is provided in the stator casing (15), characterized in that it has at least one bypass channel interposed between two inlets (7) or between an inlet (7) and an outlet (8) provided in the stator casing (15), and a valve arranged in the bypass channel so as to open or close the bypass channel depending on the difference in pressure on either side of the valve.

[Claim 12] Vacuum pump (1) according to one of the preceding claims, wherein the at least one groove (20) is provided in the stator casing (15, 25, 26), characterized in that at least one fluid circulation channel is provided in the stator casing (15) in order to thermalize the stator (2) or in order to distribute a fluid in the pumping stages (1a- 1f).

[Claim 13] Vacuum pump (1) according to one of Claims 1 to 10, wherein the at least one groove (20) is provided in an external surface of the half-shells (9, 10), characterized in that the stator (2) has an additional stator casing (28), surrounding the stator casing (26), the vacuum pump (1) being configured to cause a fluid to circulate in the gap (29) situated between the stator casing (26) and the additional stator casing (28), in order to thermalize the stator (2).

[Claim 14] Vacuum pump (1) according to one of the preceding claims, characterized in that the joining surface (11) of the half-shells (9, 10) passes through a median plane of the vacuum pump (1), such as the plane containing the axes of the rotor shafts (5, 6).