Title of the invention: Dry vacuum pump

Technical field of the invention

[0001] The present invention relates to a dry vacuum pump.

Technical background

[0002] Vacuum pumps of the dry type have one or more pumping stages in series in which a gas to be pumped circulates between a suction inlet and a delivery outlet. Among known vacuum pumps, a distinction is made between those with rotary lobes, also known as “Roots” pumps, with two or more lobes, or those with claws, also known as “claw” pumps, or else those of the screw type.

[0003] These vacuum pumps are referred to as “dry” since, in operation, the rotors rotate inside the stator without any mechanical contact with each another or with the stator, thus making it possible to not use oil in the pumping stage(s).

[0004] In operation, the compression of gases leads to significant heating of the vacuum pump. This rise in temperature makes it possible to avoid condensing or solidification into a powder of pollutant gaseous species inside the vacuum pump. However, in certain applications, the stator temperature has to be controlled so that it does not exceed a predefined maximum beyond which the gaseous species being pumped could agglomerate in the pump and cause the pump to seize. It may also be necessary to cool the bearings or the motor of the vacuum pumps in order to avoid any malfunctioning.

[0005] In current vacuum pumps, the cooling is generally achieved by circulating water through aluminium blocks in thermal contact with the stator. It is furthermore possible for the temperature of specific locations of the pump to be differentiated by using several branches through which different water flow rates circulate. The cooling circuit thus generally has two to four branches distributing the water to different specific points of the vacuum pump, for example into the pump body at a first temperature and into the bearings at the two ends of the vacuum pump at a second temperature.

[0006] The flow rates in each branch are generally fixed by means of nozzles, the conductance of which is chosen so as to obtain the desired cooling. However, this assumes a constant water feed pressure upstream of all the branches of the circuit. Specifically, the water flow rate through a nozzle is proportional to the pressure prevailing upstream of the nozzle. However, this pressure may not be the same at all times, for example due to the water network being used simultaneously for different applications. This results in a certain degree of uncertainty about the flow rates actually circulating in the cooling circuit of the vacuum pump. [0007] Also, in this type of installation, the distribution of the flow rate among the different branches is generally measured only upon first entry of the vacuum pump into service. However, this distribution may change over time such that it no longer corresponds to the initial specifications after a certain duration of use. Furthermore, the distribution of the flow rates may not be exactly the same from one vacuum pump to another as a function of the geometrical tolerances of the conductances and of the water circuit.

[0008] This all has the result that the vacuum pump may not be continuously correctly cooled.

[0009] It is possible for the water feed rate to be overdimensioned, but this solution is not economical. Another solution may be to provide regulating valves and temperature sensors or flowmeters making it possible to control the different water flow rates. However, this other solution is also costly and is, moreover, bulky.

Summary of the invention

[0010] One of the aims of the present invention is to propose a dry vacuum pump which at least partially solves one drawback of the prior art.

[0011] To that end, a subject of the invention is a dry vacuum pump having a stator, at least two rotors configured to rotate in the stator, and a cooling device configured to cool the stator, the cooling device having a fluidic circuit and at least one flow rate regulator arranged in a regulation duct of the fluidic circuit, characterized in that:

- the regulation duct has at least one first duct and a second duct of smaller section than the first duct,

- the flow rate regulator has an orifice plate traversed by an orifice, and a flexible membrane having a central opening which is smaller than said orifice, the orifice plate and the flexible membrane being positioned in the first duct, the flexible membrane being positioned upstream of the orifice plate in the flow direction of the cooling fluid, said flexible membrane being able to be deflected towards said orifice plate in response to a pressure differential on both sides of said flexible membrane between a position of maximum deflection, in which said flexible membrane comes into abutment against said orifice plate, closing circumferential orifices of the flexible membrane, the flow of fluid being limited by said central opening, and positions in which said flexible membrane is spaced apart from said orifice plate, thus permitting the flow of fluid through said circumferential orifices, so as to maintain a constant flow rate of the fluid downstream of the orifice plate.

[0012] In operation, a decrease in differential pressure leads to an increase in the size of the openings, and an increase in differential pressure leads to a reduction in the dimensions of these same openings, thus making it possible to stabilize the flow rate in an automatic manner. The structure is simple and reliable because there are no wearing parts. It is compact and economical in terms of energy because it is a mechanical solution, without an electrical power supply. Moreover, the mounting is simple.

[0013] The dry vacuum pump may also have one or more of the features that are described below, considered on their own or in combination.

[0014] The flexible membrane has, for example, at least one elastic blade in the shape of a star, such as a star with four arms.

[0015] The flexible membrane may have two elastic blades mounted in a cross shape and fastened to one another in the circumferential zone of the central opening.

[0016] The orifice plate may have a conical set-back portion (set back with respect to the flexible membrane).

[0017] The fluidic circuit has, for example, a common duct connected to several parallel branches which are each configured to cool a different element of the stator, such as a bearing support, a driving part or a pumping stage stator.

[0018] The common duct is intended to be connected to a fluid supply.

[0019] The pipes of the branches may be at least partially internal or external to the stator elements. They are, for example, provided inside the stator elements or in respective, for example metallic, conductive blocks, such as made of aluminium, in thermal contact with a respective stator element.

[0020] The fluid is for example a liquid, such as liquid water, for example at ambient temperature.

[0021] At least one regulation duct may be arranged in a common duct connected to at least two branches of the parallel fluidic circuit, each branch being configured to cool a different element of the stator.

[0022] At least one regulation duct may be arranged in a branch of the fluidic circuit, said branch being configured to cool an element of the stator. A sufficient water flow rate can then be ensured at all times for cooling the branch of the fluidic circuit, without the influence of variations in fluid feed pressure. Moreover, with this solution, it is possible to ensure minimum cooling on a branch, thus making it possible to have more fluid available for promoting the cooling by the other branches of the fluidic circuit.

[0023] The fluidic circuit has, for example, several branches respectively configured to cool a different element of the stator, the cooling device comprising a regulation duct arranged in at least two of said branches. The distribution of the water flow rates in the branches cooling the stator elements can thus be ensured, without the influence of variations in fluid feed pressure. [0024] At least two flow rate regulators arranged in the different regulation ducts may be configured to deliver different constant respective flow rates.

[0025] An element to be cooled of the stator may be a bearing support, a pumping stage stator or a driving part of the vacuum pump.

[0026] The at least one regulation duct is for example provided in a connection unit of the cooling device, the at least one first duct being open to the outside of the connection unit.

[0027] When the cooling device has several regulation ducts, it may be particularly advantageous to make provision for the regulation ducts to be provided in a connection unit of the cooling device, the first ducts being open to the outside of the connection unit. This facilitates the assembly of the flow rate regulators in the first ducts and reduces the size of the fluidic circuit.

[0028] The connection unit has, for example:

- at least one regulation duct arranged in a common duct of the fluidic circuit through which the fluid is intended to enter, and

- at least two regulation ducts arranged in respective branches of the fluidic circuit, through which branches the fluid is intended to exit, the common duct being connected to said branches by pipes provided in said connection unit.

[0029] This embodiment is particularly compact since it does not require fluidic connectors between the different regulation ducts.

[0030] An annular groove may be provided in the first duct of a regulation duct so as to receive a circlip of the cooling device in order to clamp the outer edges of the flow rate regulator.

[0031] A tapped part may be provided in the first duct of a regulation duct and receives a threaded ring of the cooling device, so as to clamp the outer edges of the flow rate regulator.

Brief description of the figures

[0032] 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:

[0033] [Fig. 1 ] Figure 1 is a schematic depiction of a vacuum pump according to a first exemplary embodiment.

[0034] [Fig. 2] Figure 2 shows a schematic front view of a flow rate regulator arranged in a regulation duct of a cooling device of the vacuum pump in Figure 1 .

[0035] [Fig. 3] Figure 3 shows a side view in section of the elements in Figure 2. [0036] [Fig. 4] Figure 4 is a graph showing the outlet flow rate for a flow rate regulator (curve A) and for a regulating valve of the prior art (curve B) as a function of the fluid feed pressure.

[0037] [Fig. 5] Figure 5 shows a diagram similar to Figure 3 for a first embodiment variant.

[0038] [Fig. 6] Figure 6 shows a diagram similar to Figure 3 for a second embodiment variant.

[0039] [Fig. 7] Figure 7 is a schematic depiction of a vacuum pump according to a second exemplary embodiment.

[0040] [Fig. 8] Figure 8 is a schematic depiction of a vacuum pump according to a third exemplary embodiment.

[0041] [Fig. 9] Figure 9 is a schematic depiction of a connection unit of the cooling device.

[0042] In these figures, identical elements bear the same reference numbers.

Detailed description

[0043] 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.

[0044] “Upstream” means that an element comes before another with respect to the circulation direction of the pumped gases F1 or with respect to the flow direction of the cooling fluid, such as water f2. By contrast, “downstream” means that an element comes after another with respect to the circulation direction of the pumped gases F1 or with respect to the flow direction of the cooling fluid f2.

[0045] The invention applies to any type of dry vacuum pump 1 having a stator 2 and at least two rotors configured to rotate in the stator 2. The invention applies to any type of single-stage or multi-stage dry vacuum pump, that is to say comprising one or more stages, such as comprising one to ten pumping stages. This vacuum pump may be a multi-stage rough-vacuum pump configured to deliver gases pumped at atmospheric pressure or a dry vacuum pump with one to three pumping stages which, in use, is connected upstream of a rough-vacuum pump and whose delivery pressure is that obtained by the rough-vacuum pump.

[0046] Figure 1 shows a first example of a dry vacuum pump 1 . [0047] The vacuum pump 1 has at least one pumping stage, such as several pumping stages T1 -T5, which are mounted in series between a suction orifice 4 and a delivery orifice 5.

[0048] The vacuum pump 1 also has two shafts parallel to the axial direction, which are configured to drive the rotors in rotation in the respective compression chambers of the pumping stages T1 -T5 about a respective axis of rotation. The shafts are configured to be driven in rotation by at least one motor in a driving part 3 of the vacuum pump 1 (Figure 1 ).

[0049] During rotation, the gas drawn in through the inlet of the compression chamber is trapped in the volume created by the rotors and the pumping stage stator, and is then driven by the rotors towards the outlet and then towards the following stage. The arrows F1 in Figure 1 show the circulation direction of the gases to be pumped.

[0050] The successive pumping stages T1 -T5 are connected in series one after another by respective inter-stage channels connecting the outlet of the preceding pumping stage to the inlet of the following pumping stage.

[0051] The inlet of the first pumping stage T 1 communicates with the suction orifice 4 of the vacuum pump 1. The outlet of the last pumping stage T5 communicates with the delivery orifice 5 by way of an outlet pipe.

[0052] The axial and/or radial dimensions and flow rates created by the pumping stages T1 -T5 decrease or are the same with the order of arrangement of the pumping stages, the pumping stage T1 situated on the side of the suction orifice 4 having the greatest axial or radial dimension, creating the greatest pumping flow rate.

[0053] The vacuum pump 1 may also have a non-return valve 6 and a silencer 7 which are arranged in series upstream of the delivery orifice 5 in the outlet pipe. The silencer 7 may be mounted in series and upstream of the non-return valve 6 of the vacuum pump 1 , at the outlet of the last compression chamber.

[0054] The vacuum pump 1 also has synchronizing gearings for synchronizing the rotors and lubricated bearings, lubricated by a lubricant, such as oil or grease, contained in at least one oil sump of the vacuum pump 1 . The stator 2 has, for example, a bearing support 8 at each end of the vacuum pump 1. A lubricant-tight sealing device is interposed between the bearing supports 8 and the dry pumping part in which the gases circulate. The sealing device allows the rotation of the shafts in the dry pumping part while limiting the transfers of lubricants. The at least one pumping stage stator, the at least one bearing support 8 and the driving part 3 form different elements of the stator 2 of the vacuum pump 1. [0055] These vacuum pumps are referred to as “dry” since, in operation, the rotors rotate inside the stator 2 without any mechanical contact with each another or with the stator 2, thus making it possible to not use oil in the pumping stage(s) T1 -T5.

[0056] The vacuum pump 1 also has a cooling device 10 configured to cool the stator 2. The cooling device 10 has a fluidic circuit 1 1 and at least one flow rate regulator 12 arranged in a regulation duct 15 of the fluidic circuit 1 1 in order to regulate the fluid flow rate.

[0057] The fluidic circuit 11 has, for example, a common duct 18 connected to several parallel branches 18a, 18b, 18c which are each configured to cool a different element of the stator 2, such as a bearing support 8, a driving part 3 or a pumping stage stator.

[0058] The common duct 18 is intended to be connected to a fluid supply.

[0059] The pipes of the branches 18a, 18b, 18c may be at least partially internal or external to the elements of the stator 2. They are, for example, provided inside the elements of the stator 2 or in respective, for example metallic, conductive blocks, such as made of aluminium, in thermal contact with a respective element of the stator 2.

[0060] The fluid is for example a liquid, such as liquid water, for example at ambient temperature.

[0061] According to a first exemplary embodiment depicted in Figure 1 , the regulation duct 15 is arranged in a common duct 18 of the fluidic circuit 1 1 , said common duct 18 being connected to at least two branches 18a, 18b, 18c of the parallel fluidic circuit 11 .

[0062] As can be seen in Figures 2 and 3, the regulation duct 15 has at least one first duct 15a and a second duct 15b of smaller section than the first duct 15a. The first and second ducts 15a, 15b are, for example, cylindrical.

[0063] The regulation duct 15 is situated upstream of the element to be cooled in the flow direction of the fluid f2 in order to deliver the desired fluid flow rate for cooling said element.

[0064] The flow rate regulator 12 has an orifice plate 17 and a flexible membrane 20 (Figure 3). The orifice plate 17 and the flexible membrane 20 are, for example, metallic, such as made of stainless steel.

[0065] The orifice plate 17 is positioned inside the first duct 15a, while being adjacent to the second duct 15b in this case. The orifice plate 17 is traversed by an orifice 26. The diameter of the orifice 26 corresponds, for example, substantially to the diameter of the second duct 15b. The orifice plate 17 has, for example, a for example conical set-back portion (set back with respect to the flexible membrane 20), in which the orifice 26 is provided, the conical set-back portion being adjacent to the outlet duct 15b in this case. [0066] The flexible membrane 20 is positioned inside the first duct 15a, upstream of the orifice plate 17 in the flow direction of the cooling fluid f2. The flexible membrane 20 has a central opening 14 of smaller dimensions than the orifice 26 of the orifice plate 17 (Figure 2).

[0067] The flexible membrane 20 has at least one elastic blade 13a, 13b. Circumferential openings 16 are formed between the adjacent branches of the elastic blade 13a, 13b and the first duct 15a.

[0068] According to an exemplary embodiment visible in Figure 2, the elastic blade 13a, 13b has the shape of a star, such as a star with four arms, the arms of the star with four arms being spaced apart from one another by 90°. The arms have, for example, triangular or trapezoidal shapes.

[0069] According to one exemplary embodiment, the flexible membrane 20 has several elastic blades 13a, 13b disposed one above the other, such as two elastic blades 13a, 13b mounted in a cross shape and fastened, for example riveted, to one another in the circumferential zone of the central opening 14. The two elastic blades 13a, 13b have, for example, a respective star shape. The two elastic blades 13a, 13b are for example offset from one another by 45°.

[0070] The cooling device 10 may have several flow rate regulators 12 arranged in the same regulation duct 15 of the fluidic circuit 1 1 in order to regulate the fluid flow rate, the regulation duct 15 then having several first ducts 15a and second ducts 15b.

[0071] Furthermore, other forms of embodiment of the flexible membrane 20 are possible as described in document US4708166A.

[0072] In this first exemplary embodiment, the fluid enters the first duct 15a and exits through the second duct 15b. The orifice plate 17 is interposed between the flexible membrane 20 and the second duct 15b.

[0073] According to one exemplary embodiment visible in Figure 3, the regulation duct 15 is provided in a connection unit 19 of the cooling device 10, said connection unit for example being metallic, such as made of aluminium. The first larger-diameter duct 15a is open to the outside of the connection unit 19. A for example flexible tube fluidically connects the first duct 15a to the branches 18a, 18b, 18c of the fluidic circuit 11 in order to deliver the fluid into the branches 18a, 18b, 18c for cooling the elements of the stator 2.

[0074] An annular groove 21 may be provided in the first duct 15a so as to receive a circlip 22 of the cooling device 10 in order to clamp the outer edges of the flow rate regulator 12, and more specifically the flexible membrane 20, thus blocking the flexible membrane 20 and the orifice plate 17 in the first duct 15. [0075] The mounting is therefore facilitated and does not require connectors or sealing adhesive, thus reducing the mounting time and the costs.

[0076] The flexible membrane 20 can be deflected towards the orifice plate 17 in response to a pressure differential on both sides of the flexible membrane 20 between a position of maximum deflection, in which said flexible membrane 20 comes into abutment against said orifice plate 17, closing the circumferential orifices 16 of the flexible membrane 20, the flow of fluid then being limited by said central opening 14, and positions in which said flexible membrane 20 is spaced apart from said orifice plate 17, thus permitting the flow of fluid through said circumferential orifices 16, so as to maintain a constant flow rate of the fluid downstream of the orifice plate 17.

[0077] Consequently, in operation, a decrease in differential pressure leads to an increase in the size of the openings 16, and an increase in differential pressure leads to a reduction in the dimensions of these same openings 16, thus making it possible to stabilize the flow rate in an automatic manner.

[0078] Figure 4 shows an example of the outlet flow rate obtained for a flow rate regulator 12 (curve A) and for a regulating valve of the prior art (curve B) as a function of the fluid feed pressure.

[0079] In the system of the prior art, the water flow rate through a nozzle is proportional to the pressure prevailing upstream of the nozzle (curve B). This has the result that the water flow rate in the vacuum pump 1 is not controlled if the feed pressure varies.

[0080] By contrast, for the curve A of a flow rate regulator 12, it is noted that beyond a minimum fluid feed pressure, for example greater than 2 bar (2.10 ⁵ Pa), the flow rate regulator 12 ensures a more or less constant outlet flow rate.

[0081] The flow rate through the flow rate regulator 12 is determined by the pressure difference on both sides of the flow rate regulator and by the dimensions of the circumferential orifices 16 and the central opening 14.

[0082] The structure is simple and reliable because there are no wearing parts. It is compact and economical in terms of energy because it is a mechanical solution, without an electrical power supply. Moreover, the mounting is simple.

[0083] Figure 5 shows another exemplary embodiment of the mounting of the flow rate regulator 12 in the regulation duct 15.

[0084] In the example illustrated, the fluid is intended to enter the second duct 15b and to exit through the first duct 15a. The flexible membrane 20 is interposed between the orifice plate 17 and the second duct 15b. The orifice plate 17 has a conical set-back portion (set back with respect to the flexible membrane 20). [0085] A tapped part 24 is provided in the first duct 15a and receives a threaded ring 25 of the cooling device 10, so as to clamp the outer edges of the flow rate regulator 12, in this case of the set-back portion of the orifice plate 17 in which the orifice 26 is provided, thus blocking the flexible membrane 20 and the orifice plate 17 in the first duct 15.

[0086] The mounting is simple and the fluidic connection is easy to produce.

[0087] This embodiment can also be implemented for the case in which the fluid is intended to enter the first duct 15a and to exit through the second duct 15b (Figure 6).

[0088] In that case, the flow rate regulator 12 is mounted in the opposite direction in the first duct 15a. The orifice plate 17 is interposed between the flexible membrane 20 and the second duct 15b. The conical set-back portion of the orifice plate 17 is adjacent to the second duct 15b.

[0089] The tapped part 24 is provided in the first duct 15a and receives a threaded ring 25 of the cooling device 10, so as to clamp the outer edges of the flow rate regulator 12, in this case of the flexible membrane 20, thus blocking the flexible membrane 20 and the orifice plate 17 in the first duct 15.

[0090] Figure 7 shows another exemplary embodiment for which the regulation duct 15 is arranged in a branch 18c of the fluidic circuit 1 1 , said branch being configured to cool an element of the stator 2, such as a bearing support 8 or a pumping stage stator or the driving part 3, in this case the driving part 3. The other branches of the fluidic circuit 1 1 may have a nozzle or a regulating valve 23 or may not have a particular element for controlling the flow rate.

[0091] A sufficient water flow rate can then be ensured at all times for cooling the driving part 3 in the branch 18c of the fluidic circuit 11 , without the influence of variations in fluid feed pressure.

[0092] The same result can be obtained to regulate the temperature of a bearing support 8 or of a pumping stage stator.

[0093] Moreover, with this solution, it is possible to ensure minimum cooling on a branch 18c, thus making it possible to have more fluid available for promoting the cooling by the other branches 18a, 18b of the fluidic circuit 1 1 .

[0094] Figure 8 shows another exemplary embodiment.

[0095] In this example, the cooling device 10 comprises a regulation duct 15 arranged in at least two of the branches 18a, 18b, 18c, such as in each of the branches 18a, 18b, 18c of the fluidic circuit 11 .

[0096] The flow rate regulators 12 arranged in the regulation ducts 15 may be configured to deliver different constant respective flow rates. [0097] The distribution of the water flow rates in the branches 18a, 18b, 18c cooling the elements of the stator 2 can thus be ensured, without the influence of variations in fluid feed pressure.

[0098] When the cooling device 10 has several regulation ducts 15, it may be particularly advantageous to make provision for the regulation ducts 15 to be provided in a connection unit 19 of the cooling device 10 (Figure 9), the first ducts 15a being open to the outside of the connection unit 19. This facilitates the assembly of the flow rate regulators 12 in the first ducts 15 and reduces the size of the fluidic circuit 11 .

[0099] This is the case for example when the fluidic circuit 11 has several branches 18a, 18b, 18c of which at least two are respectively provided with regulation ducts 15 for cooling a respective element of the stator 2 and/or when the cooling device 10 has a regulation duct 15 arranged in the common duct 18 and at least one regulation duct 15 arranged in a branch 18a, 18b, 18c.

[0100] For example, the connection unit 19 has at least one regulation duct 15 arranged in the common duct 18 through which the fluid is intended to enter, and at least two regulation ducts 15 arranged in respective branches 18a, 18b, 18c through which the fluid is intended to exit (Figure 9).

[0101] The first duct 15a of the regulation duct 15 arranged in the common duct 18 through which the fluid is intended to enter is open to the outside of the connection unit 19. The at least two first ducts 15a of the regulation ducts 15 which are arranged in respective branches 18a, 18b, 18c through which the fluid is intended to exit are also open to the outside of the connection unit 19.

[0102] In addition, the common duct 18 is connected to the branches 18a, 18b, 18c by pipes which are also provided in said connection unit 19. More specifically, these pipes connect the second duct 15b of the regulation duct 15 arranged in the common duct 18 to the second ducts 15b of the regulation ducts 15 which are arranged in the respective branches 18a, 18b, 18c.

[0103] Tubes, for example flexible tubes, fluidically connect the first ducts 15a of the regulation ducts 15 to the pipes of the branches 18a, 18b, 18c in thermal contact with the respective elements to be cooled of the stator 2.

[0104] The first duct 15a of the regulation duct 15 arranged in the common duct 18 is intended to be connected to a fluid source.

[0105] This embodiment making use of a connection unit 19 is particularly compact since it does not require fluidic connectors between the different regulation ducts 15. [0106] According to another example, the regulation ducts 15 arranged in the respective branches 18a, 18b, 18c are produced directly, for example by machining, in the stator 2 of the vacuum pump 1 , for example in the pumping stage stators.

[0107] The first larger-diameter ducts 15a of these regulation ducts 15 are then open to the outside of the stator 2. The flow rate regulators 12 can be mounted directly in the stator 2. The second ducts 15b of these regulation ducts 15 are connected to pipes of the branches 18a, 18b, 18c in thermal contact with the respective elements to be cooled of the stator 2, such as internal channels of the stator 2.

[0108] Tubes, for example flexible tubes, may fluidically connect the first ducts 15a of the regulation ducts 15 to a first duct 15a of a regulation duct 15 arranged in a common duct 18.