Multi-stage vacuum pump

Abstract

Multi-stage vacuum pump The invention relates to a multi-stage vacuum pump (1) comprising a plurality of pumping stages (3a, 3b, 3c) respectively comprising an inlet (E) and an outlet (S), the pumping stages (3a, 3b, 3c) being connected in series between a suction (4) and a discharge (5) of the vacuum pump (1), a stator (2) comprising at least one stator element produced by the assembly of two complementary half-shells (2A, 2B) which meet along an assembly surface (8), at least one discharge channel (11) connected to the outlet (S) of a pumping stage (3a, 3b) and in fluid communication with the discharge (5), and at least one valve (13) associated with the discharge channel (11).According to the invention, the discharge channel (11) is arranged in one of the half-shells (2A, 2B) opening out at least at one mouth in the assembly surface (8) and the associated valve (13) is arranged between the two half-shells (2A, 2B) being at least partly movable so as to close or release the mouth of the discharge channel (11), depending on a pressure difference on either side of the valve (13). Figure for the abstract: Fig. 2.

Description

Title of the invention: Multi-stage vacuum pump

[0001] The present invention relates to a multi-stage vacuum pump. The invention applies in particular to a dry type vacuum pump.

[0002] Multi-stage vacuum pumps comprise several pumping stages in series in which a gas to be pumped circulates between a suction and a discharge. Among the known vacuum pumps, a distinction is made between those with rotary lobes, also known as "Roots" with two or three lobes, or those with double nozzles, also known as "Claw" or even those with screws. Rotary lobe 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 free space between the rotors and the stator, and is driven by the rotors to the next stage or after the last stage at the discharge outlet. These vacuum pumps are called "dry" because in operation, the rotors rotate inside a stator without any mechanical contact between the rotors and the stator, which makes it possible not to use oil in the pumping stages.

[0003] A constant objective is to facilitate the assembly of such vacuum pumps while reducing costs. To this end, the stators can be made in several parts. According to a known solution, the stator is formed by the assembly of at least two complementary half-shells. Such a half-shell architecture makes it possible to reduce the assembly time and also makes it possible to reduce the risks of accumulation of alignment defects.

[0004] Furthermore, to reduce their energy consumption, the last pumping stages, on the discharge side, can have a generated volume, i.e. a volume of pumped gas, smaller than that of the first pumping stages, on the suction side.

[0005] In some applications, for example for pumping loading / unloading airlocks (or "load lock" in English), the airlock enclosures are evacuated from atmospheric pressure, in order to be able to transfer a substrate into a process chamber maintained at low pressure. To reduce the pressure in the enclosure from atmospheric pressure, the vacuum pump must absorb large initial gas flows, which are difficult to accommodate by the last pumping stages on the discharge side. However, all pumping stages are required at low pressure, in order to be able to reach the desired limit vacuum pressures.

[0006] This same situation where the last stages can limit the overall pumping rate of the vacuum pump, can occur for pumping the process chambers. Even if the process chamber is normally continuously under vacuum, the pump vacuum must be able to absorb a large pumping flow at the first vacuum.

[0007] It is therefore essential to shorten these pressure reduction times so as not to slow down the manufacturing processes taking place in the process chamber, with high added value.

[0008] Some vacuum pumps therefore provide a load shedding device connecting the outlet of a pumping stage to be unloaded to the discharge. The load shedding device makes it possible to evacuate the excess gas flow coming from the outlet of the pumping stage to be unloaded directly to the discharge of the vacuum pump.

[0009] To do this, a housing external to the vacuum pump is generally arranged below the stator comprising pumping stages. Such a housing comprises, for each pumping stage to be relieved, a channel connecting the outlet of this pumping stage to be relieved to the discharge of the vacuum pump.

[0010] However, the assembly of the housing to the stator of the vacuum pump requires an additional operation, increases the cost of the vacuum pump and increases the size, in particular the height, of the vacuum pump. In addition, the channels for connecting the pumping stages to the discharge can be complicated to produce and involve as many additional seals to manage.

[0011] An aim of the present invention is to propose an improved vacuum pump making it possible to at least partially resolve one of the aforementioned drawbacks of the state of the art.

[0012] To this end, the invention relates to a multi-stage vacuum pump comprising a plurality of pumping stages comprising respectively an inlet and an outlet, the pumping stages being mounted in series between a suction and a discharge of the vacuum pump, a stator comprising at least one stator element produced by the assembly of two complementary half-shells which join along an assembly surface, at least one discharge channel connected to the outlet of a pumping stage and in fluid communication with the discharge, and at least one valve associated with the discharge channel.

[0013] According to the invention, the discharge channel is arranged in one of the half-shells, opening into at least one mouth in the assembly surface. The associated valve is arranged between the two half-shells, being at least partly movable so as to close or release the mouth of the discharge channel, depending on a pressure difference on either side of the valve.

[0014] The arrangement of the valve between the half-shells makes it possible to avoid the assembly of an additional housing to the stator of the vacuum pump, for example to perform a load shedding and / or discharge function. This makes it possible to reduce the cost and size of the vacuum pump. In addition, the discharge channel is made in such a way that simple within one of the half-shells. Finally, in the absence of an additional box, such a solution makes it possible to minimize the sealing to be managed with the exterior.

[0015] The vacuum pump may further comprise one or more of the following features described below, taken separately or in combination.

[0016] The discharge channel or one of the discharge channels may be a relief channel connected to the outlet of a pumping stage to be relieved and in fluid communication with the discharge.

[0017] According to one embodiment, the successive pumping stages are connected in series by a respective inter-stage channel connecting the output of a previous pumping stage to the input of a following pumping stage.

[0018] A common channel can be connected to the output of the pumping stage to be unloaded. This common channel can be connected to at least two bypass portions, a first portion of which forms with the common channel an inter-stage channel connected to the input of the following pumping stage and a second portion forms with the common channel the unloading channel.

[0019] The discharge channel or one of the discharge channels may be a discharge channel connected to the outlet of the last pumping stage and in fluid communication with the discharge.

[0020] The vacuum pump may comprise at least two valves respectively associated with a pumping stage. The valves may be sized differently depending on the associated pumping stage. The valves may be sized differently depending on the set pressures.

[0021] The valve is mounted at least partly movable in a cavity formed in the half-shell opposite the half-shell comprising the discharge channel, the valve being arranged opposite the mouth of the discharge channel in the assembly surface.

[0022] The vacuum pump may comprise at least one outlet channel fluidly connecting the cavity to the discharge. This outlet channel may be provided in one of the half-shells.

[0023] According to an exemplary embodiment, the valve or at least one of the valves comprises a ball.

[0024] At least one annular seal may be arranged in the mouth of the discharge channel associated with the valve.

[0025] The seal has, for example, a base received in a first groove of the mouth of the discharge channel. The base may be of a generally toric shape. The first groove has, for example, a generally cylindrical shape.

[0026] The base may be surmounted by a portion delimiting a valve seat by example for the ball, and received in a second groove of the mouth of the discharge channel formed above the first groove. The portion delimiting the valve seat may be frustoconical. The second groove may have a general frustoconical shape complementary to the frustoconical portion of the sealing gasket.

[0027] The vacuum pump may comprise at least one injection channel opening through at least one injection orifice configured to inject a purge gas onto the valve and / or onto a bearing face of a valve seat.

[0028] The vacuum pump may comprise a discharge pipe arranged to connect the outlet of the last pumping stage to the discharge and fluidically connected to the discharge channel. This discharge pipe has, for example, a housing for receiving a silencer of the vacuum pump interposed between the outlet of the last pumping stage and the discharge.

[0029] The discharge pipe can be attached to either of the half-shells.

[0030] Furthermore, the vacuum pump comprises, for example, two rotor shafts configured to rotate synchronously in opposite directions in the pumping stages to drive a gas to be pumped between suction and discharge.

[0031] The stator may comprise at least one end piece. The stator element is axially assembled with the end piece or with another stator element.

[0032] The invention also relates to a pumping group comprising at least one vacuum pump. This vacuum pump may for example be as defined above.

[0033] The pumping group may further comprise at least one additional pump upstream of the vacuum pump depending on the direction of gas circulation.

[0034] Advantageously, the pumping group may comprise at least one other valve arranged movably between the stators of the additional pump and the vacuum pump. It is configured to close or release a mouth of a pipe connected to the discharge of the vacuum pump, depending on a pressure difference on either side of the valve.

[0035] The stator of the vacuum pump defines for example a seat for the valve.

[0036] The valve may be received in a cavity provided in the stator of the addi pump tional.

[0037] Other advantages and characteristics of the invention will appear more clearly on reading the following description given by way of illustrative and non-limiting example, and the appended drawings among which:

[0038] [Fig-1] is a perspective view showing in part a stator of a multi-stage vacuum pump according to a first exemplary embodiment.

[0039] [Fig.2] is a schematic representation of elements of a vacuum pump according to a second example of realization.

[0040] [Fig.3] is a cross-sectional view of the stator of [Fig.l] showing a valve of a device for unloading the vacuum pump in the closed position.

[0041] [Fig.4] is a longitudinal sectional view of a portion of the stator of [Fig.l] showing two vacuum pump relief device valves in the closed position.

[0042] [Fig.5] is a schematic representation of elements of a vacuum pump according to a third example of realization.

[0043] [Fig.6] is a schematic representation of elements of a vacuum pump according to a fourth example of realization.

[0044] [Fig.7] is a schematic representation of elements of a vacuum pump according to a fifth example of realization.

[0045] [Fig.8a] is a schematic representation of elements of a vacuum pump according to a sixth embodiment.

[0046] [Fig.8b] is a schematic representation of elements of a vacuum pump according to a seventh exemplary embodiment.

[0047] [Fig.9] is a schematic representation of elements of a vacuum pump according to a eighth example of realization.

[0048] [Fig. 10] is a schematic representation of a pumping group comprising the vacuum pump of [Fig.7] and an additional pump.

[0049] In these figures, identical or similar elements have the same reference numbers. The figures have been simplified for the sake of clarity. Only the elements necessary for understanding the invention are shown.

[0050] 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 to only one embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0051] [Fig.l] illustrates an exemplary embodiment of a multi-stage vacuum pump 1, i.e. comprising several stages (at least two). The vacuum pump 1 is in particular of the dry type.

[0052] This vacuum pump 1 may be a primary vacuum pump that can be started at atmospheric pressure. Such a primary vacuum pump is configured to suck, transfer, and then discharge the pumped gases at atmospheric pressure.

[0053] The vacuum pump 1 comprises a stator 2 forming at least two pumping stages connected in series between a suction 4 and a discharge 5, and in which a gas to be pumped can circulate.

[0054] In the example illustrated in [Fig.l], the vacuum pump 1 comprises, for example, five pumping stages. Of course, this number is not limiting. [Fig.2] shows a another example of the embodiment of a multi-stage vacuum pump 1, comprising for example three pumping stages 3a-3c.

[0055] The vacuum pump 1 further comprises two rotor shafts 6 configured to rotate synchronously in opposite directions in the pumping stages 3a-3c so that the rotors 6 drive a gas to be pumped between the suction 4 and the discharge 5.

[0056] The rotors 6 have, for example, rotating lobes with identical profiles, for example of the “Roots” type. Alternatively, they may be lobes of the “Claw” type or of the screw type or of another similar vacuum pump principle. The rotor shafts are driven in rotation by at least one motor (not shown) of the vacuum pump 1. The motor is located, for example, at one end of the vacuum pump 1.

[0057] Each pumping stage 3a, 3b, 3c, is formed by a compression chamber receiving the rotors 6. The compression chambers comprise a respective inlet E and outlet S. During rotation, the gas sucked from the inlet E is trapped in the volume generated by the rotors 6 and the stator 2, then is transferred by the rotors 6 to the next stage and so on until the discharge 5.

[0058] The vacuum pump 1 is called “dry” because in operation, the rotors 6 rotate inside the stator 2 of the vacuum pump 1 in opposite directions without any mechanical contact between them or with the stator 2, which makes it possible not to use oil in the pumping stages 3a-3c.

[0059] The successive pumping stages 3a-3c are connected in series one after the other by respective inter-stage channels 7 connecting the output S of the preceding pumping stage 3a-3b to the inlet E of the following pumping stage 3b-3c. The inlet E of the first pumping stage 3a, also called the “suction stage”, communicates with the suction 4 of the vacuum pump 1. The output S of the last pumping stage 3c, also called the “discharge stage”, communicates with the discharge 5. The pumping stage(s) connected in series between the suction stage 3a and the discharge stage 3c are also called intermediate stages.

[0060] Furthermore, the stator 2 comprises, for example, at least one stator element produced by assembling a first and a second complementary half-shells 2A, 2B. A stator casing (not shown) may optionally surround the assembled half-shells 2A, 2B. The stator 2 may further comprise at least one end piece (not shown), for example two end pieces on either side of the two half-shells 2A, 2B. The end piece(s) form, for example, supports for the bearings of the rotor shafts 6. The half-shells 2A, 2B and the possible end pieces are assembled together, for example by axial assembly. The axial direction is defined as the longitudinal direction of the vacuum pump 1 in which the axes of the rotor shafts 6 extend. The assembly can be carried out by any known suitable fastening means, for example by means of a curable glue and / or by screwing. One or more sealing gaskets (not shown) may be provided to ensure sealing between the various assembled elements of the vacuum pump 1.

[0061] The two half-shells 2A, 2B, when assembled, join along an assembly surface 8, to form the compression chambers of the pumping stages 3a-3c. The compression chambers and the inter-stage channels 7 are partly formed in the first half-shell 2A and partly in the second half-shell 2B. The inter-stage channels 7 are for example arranged on the sides of the compression chambers, in the half-shells 2A, 2B. They can extend on the same side of the compression chambers or on both sides of the compression chambers. There is for example an inter-stage channel 7 between two successive pumping stages 3a, 3b, 3c mounted in series or two inter-stage channels 7 mounted in parallel between these two pumping stages 3a, 3b, 3c on each side of the compression chamber.

[0062] The assembly surface 8 may be flat. It passes for example through a median plane of the dry primary vacuum pump 1. This assembly surface 8 may be strictly flat or may have for example complementary relief shapes or grooves or grooves for example for seals between the half-shells 2A, 2B. In the assembled state of the half-shells 2A, 2B, the axes of the rotor shafts 6 are for example contained between the half-shells 2A, 2B at the level of the assembly surface 8.

[0063] In a known manner, orifices are provided in transverse walls of the half-shells 2A, 2B separating the compression chambers, and possibly in the end pieces for the passage of the rotor shafts 6.

[0064] The stator 2 may comprise several stator elements and at least one end piece, for example two end pieces on either side of the stator elements (not shown). Each stator element is assembled axially (i.e. in a direction parallel to the axis of the rotor shafts 6) with another stator element or with an end piece of the stator 2, to form the compression chambers of the pumping stages 3a-3c receiving the rotors 6. At least one, or even each, of the stator elements may be produced by assembling two complementary half-shells which join along an assembly surface.

[0065] The vacuum pump 1 further comprises at least one channel, also referred to as a discharge channel, and a valve, associated with a pumping stage 3a, 3b, 3c to be connected to the discharge 5. Particular examples of such associated channels and valves are detailed below. In particular, it may be a discharge channel and valve and / or a relief channel and valve.

[0066] The evacuation channel is arranged in one of the half-shells 2A or 2B in closing at least one mouth in the assembly surface 8. This mouth can be closed or released by the associated valve. Thus, the discharge channel ends at the assembly surface 8. In particular, the discharge channel is connected by a first end to the outlet S of the associated pumping stage 3a-3c. Its second end is the mouth in the assembly surface 8 which can be closed or released by the associated valve.

[0067] The associated valve is notably metallic. This associated valve is arranged between the two half-shells 2A, 2B. It is arranged opposite the mouth (or second end) of the associated discharge channel in the assembly surface 8. The valve is at least partly movable so as to be able to release or close the mouth of the associated discharge channel. Such a valve is configured to open according to pressure differentials on either side of the valve, more precisely when the pressure difference is greater than a predefined threshold. The valve can be mounted movable in a cavity formed in the other half-shell 2B, 2A. When the valve releases the mouth (or second end), the discharge channel then opens into the cavity.

[0068] In a non-limiting manner, the valve may comprise a ball, for example made of steel. The valve may be configured to move in translation, in rotation or even in a combined movement.

[0069] By arranging the valve between the half-shells 2A, 2B, the assembly of an additional housing to the stator of the vacuum pump is avoided, which reduces the cost and size of the vacuum pump. In addition, the discharge channel and the sealing are simple to produce.

[0070] According to one embodiment, the vacuum pump 1 comprises at least one channel 11 and a relief valve 13, associated with a pumping stage 3a, 3b, to be connected to the discharge 5.

[0071] Indeed, to reduce the energy consumption of the vacuum pump 1, the discharge stage 3c, or even at least some of the last intermediate stages, have a generated volume, i.e. a volume of pumped gas, smaller than that of the first stage(s). To absorb the strong gas flows originating in particular from the start of a vacuum of an enclosure at atmospheric pressure, the vacuum pump 1 may comprise at least one load-shedding device 9 for a pumping stage 3a, 3b.

[0072] The unloading device 9 makes it possible to evacuate any excess gas flow coming from the outlet S of a pumping stage to be unloaded to the discharge 5 of the vacuum pump 1. The choice of the pumping stage to be unloaded depends on the geometry of the vacuum pump 1 and more particularly, on the volume generated in the pumping stages. Generally, the pumping stage having the highest compression ratio is unloaded. Since the generated volume decreases with increasing pressure, the pumping stages to be unloaded are most often the low-pressure pumping stages such as the first or second pumping stage. It is also possible to unload several pumping stages, for example the first two pumping stages.

[0073] The or each load shedding device 9 comprises the load shedding channel 11 and the load shedding valve 13.

[0074] The unloading channel 11 is connected to the outlet S of the pumping stage to be unloaded 3a, 3b and is in fluid communication with the discharge 5 of the vacuum pump 1. It is in particular connected by a first end to the pumping stage to be unloaded 3a, 3b.

[0075] The relief channel 11 forms an evacuation channel arranged in one of the half-shells 2A or 2B. In the illustrated examples, the relief channel 11 is arranged in the lower half-shell 2B with reference to the orientation of the vacuum pump 1 in the assembled state.

[0076] This load shedding channel 11 may be separate from the inter-stage channel 7 at the outlet of the pumping stage to be unloaded 3a, 3b. According to an alternative not shown, a common channel connected to the outlet S of the pumping stage to be unloaded 3a, 3b, may be connected to two bypass portions, a first portion of which forms an inter-stage channel 7 connected to the inlet E of the following pumping stage and a second portion forms the load shedding channel 11 opening onto the assembly surface 8.

[0077] Depending on the dimensions and / or pumping capacities of the vacuum pump 1, the latter may comprise only a single unloading device 9 with a single mouth of the unloading channel 11 and an associated unloading valve 13. Alternatively, several unloading devices 9 mounted in a bypass may be provided to unload a larger gas flow while maintaining a reduced footprint. For example, two unloading channels and two associated valves may be provided to unload a single pumping stage. Furthermore, several unloading devices 9 may be provided to unload several pumping stages.

[0078] When several load-shedding devices 9 are provided to unload several pumping stages, the different unloading valves 13 can be sized differently depending on the associated pumping stage to be unloaded and / or as a function of setting pressures.

[0079] The or each relief valve 13 is arranged so as to be able to release or close the mouth (or second end) of the associated relief channel 11.

[0080] More precisely, such a relief valve 13 is arranged at least partially in a cavity 15 formed in the other half-shell, that is to say in the half-shell opposite the relief channel 11, being opposite the mouth (or second end) of the associated relief channel 11. In the examples illustrated, the cavity 15 is provided in the upper half-shell 2A.

[0081] A single relief valve 13 may be arranged per cavity 15 or, on the contrary, several relief valves 13 may be arranged in a common cavity 15. In the latter case, the cavity 15 may have its own housing in which each relief valve 13 can move.

[0082] The unloading valve 13 functions as a valve that opens to prevent undesirable overpressures in the vacuum pump 1. Thus, in normal operation of the vacuum pump 1, i.e. for pumping a gas flow sized for the pumping capacity of the vacuum pump 1, the mouth (or second end) of the or each unloading channel 11 is closed by the associated unloading valve 13. And in the event of an overpressure in the associated pumping stage 3a, 3b, the unloading valve 13 is configured to open.

[0083] In particular, when the pressure difference is lower than the calibration threshold of the relief valve 13, the latter is in a closed position, preventing the passage of gases towards the discharge 5. This prevents the pumped gases from short-circuiting the following pumping stages. The pumped gas follows the path represented by the arrows F1 in solid lines. It is sucked in by all the pumping stages 3a-3c and leaves at the outlet S of the discharge stage 3c. Then, the gas circulates to the discharge 5 of the vacuum pump 1.

[0084] When the pressure difference is greater than the calibration threshold of the relief valve 13, the latter releases the passage of the gas to be pumped which can be evacuated from the relieved pumping stage 3a, 3b towards the discharge 5. This makes it possible to short-circuit the last pumping stage(s) 3c of the vacuum pump 1 which could limit the overall flow rate generated. The relieved gas follows the path represented by the white arrows F2 whose outline is shown in broken lines.

[0085] Generally, in the closed position, the relief valve 13 is in contact with a bearing face of an associated valve seat. Such a valve seat has a passage or an opening in fluid communication with the relief channel 11. When the relief valve 13 is in the closed position, it closes the opening of the valve seat. On the contrary, when it opens, the relief valve 13 is for example away from the valve seat and releases the passage of gases.

[0086] According to the example of the relief valve 13 comprising a ball, the opening of such a valve 13 can be done according to a translational movement of the ball towards a bottom 16 of corresponding cavity 15. For example, an excess of gas lifts the ball(s) from their respective valve seat.

[0087] Furthermore, the relief valve 13 is configured to close in a sealed manner. For this purpose, as seen in Figures 3 and 4, the relief device 9 can comprise at least one annular seal 17 arranged in the mouth (or second end) of the relief channel 11. Such a seal 17 defines the valve seat.

[0088] When the relief valve 13, for example in the form of a ball, rests on the seat formed by the seal 17, and is partially housed in the cavity 15 opposite the mouth (or second end) of the relief channel 11, it closes the mouth of the relief channel 11 in a sealed manner.

[0089] The shape of the seal 17 is complementary to the shape of the relief valve 13 and to the shape of the mouth (or second end) of the relief channel 11.

[0090] According to a particular embodiment, the sealing joint 17 may be of generally frustoconical shape, which allows self-centering of the ball forming the relief valve 13.

[0091] The seal 17 also makes it possible to guide by cushioning the fall of the ball when it falls back onto the valve seat, for example when the gas flow decreases and can again be absorbed by the vacuum pump 1.

[0092] By way of example, the seal 17 has a base 17a surmounted by a portion 17b defining the valve seat. Such a seal 17 is preferably made in one piece, for example by molding. The seal 17 comprises at least one material chosen from an elastomer material, a silicone material, which makes it possible to improve its mechanical strength and its resistance to high temperatures of the vacuum pump 1.

[0093] The base 17a is housed in a first groove 21 complementary to the mouth of the relief channel 11. This makes it possible to secure the seal 17 in the relief channel 11. The base 17a has, for example, a toric shape. The first groove 21 has, for example, a generally cylindrical shape, which makes it possible to leave a clearance around the toric base 17a of the seal 17 allowing it to fit elastically in the first groove 21.

[0094] According to one embodiment, the portion 17b delimiting the valve seat may have a frustoconical external shape. It is received in a second groove 23 complementary to the mouth of the relief channel 11 which is formed above the first groove 21. Complementarily, the second groove 23 may be of frustoconical shape. Thus, the external frustoconical portion 17b of the seal 17 matches the complementary shape of the frustoconical portion of the mouth of the relief channel 11. The reinforcement provided by the frustoconical mouth of the channel 5 makes it possible to improve the mechanical strength of the annular seal 17 and its fixing in the mouth.

[0095] As shown diagrammatically in [Fig.5], an elastic return member 25 can be arranged and configured to urge an associated relief valve 13 towards the position for closing the mouth of the relief channel 11 opposite. The elastic return member 25 comprises for example a spring, such as a helical spring, interposed between the relief valve 13 and the half-shell, here the half-shell 2A, of the stator 2 opposite the relief channel 11. In particular, the spring may be integral with a bottom 16 of cavity 15. This spring also makes it possible to guide the movement of the relief valve 13.

[0096] Alternatively, it is also possible not to use such an elastic return. In this case, the relief valve 13 is urged into the closed position by the force of gravity.

[0097] Advantageously, an injection of a purge gas may be provided to clean the relief valve 13 or the valve seat. The purge gas is, for example, nitrogen. The injection of purge gas, which may be continuous or discontinuous and targeted in time, makes it possible to prevent the presence of deposits and to avoid contamination at the relief valve 13, which could impair the operation of the relief valve 13 and generate a leak. This cleaning allows the sealing function in the closed position and the opening function of the relief valve 13 in the event of overpressure to be ensured for longer between two maintenance periods.

[0098] For this purpose, the vacuum pump 1 may comprise at least one injection channel 27 shown in broken lines in [Fig. 6], opening out via at least one injection orifice (not visible in the figures). According to an exemplary embodiment, such an injection channel 27 may be provided in one of the half-shells; this is the lower half-shell 2B in the illustrated example. The injection orifice may, for example, be obstructed by the relief valve 13 when it closes and closes the mouth of the relief channel 11, and released when the relief valve 13 opens and releases the mouth.

[0099] The purge gas can be injected onto a bearing face of the valve seat. Alternatively or additionally, the purge gas can be injected onto the relief valve 13, in particular the part bearing on the valve seat in the position for closing the mouth of the relief channel 11. The injection of the purge gas can be done for example when the relief valve 13 is open and frees the mouth (or second end) of the relief channel 11. Alternatively or additionally, the injection of the purge gas can be done when the relief valve 13 is closed, and closes the mouth (or second end) of the relief channel 11. In this case, the injection orifice opens out of the valve seat.

[0100] In the example of [Fig.6], only one injection channel 27 is shown. This number is not limiting. Several injection channels 27 can be arranged to clean the same relief valve 13 and / or associated valve seat. Alternatively, several injection channels 27 may be provided for different relief valves 13 and / or valve seats.

[0101] Furthermore, the vacuum pump 1 further comprises at least one outlet channel 29 fluidly connecting the or each cavity 15 to the discharge 5. Such an outlet channel 29 can be provided in the half-shell (for example here 2B) comprising the relief channel 11, as shown in FIGS. 2 and 5. Alternatively, the outlet channel 29 can be provided in the half-shell (for example 2A) comprising the cavity 15, as shown in FIGS. 7 to 8b.

[0102] Thus, when the or one of the relief valves 13 opens, the gas at the outlet S of a relieved pumping stage 3a, 3b passes under the relief valve 13 into the cavity 15 before entering the outlet channel 29 and then joining the discharge 5 of the vacuum pump 1 (arrows F2).

[0103] Finally, the vacuum pump 1 generally comprises a discharge valve 31 (also called a non-return valve) arranged at the outlet of the last pumping stage 3c ([Fig.2]). As previously described, such a valve 31 is configured to open as a function of pressure differentials on either side of the valve 31. It can be urged into the closed position by an elastic return member such as a spring 33 or by the force of gravity. The discharge valve 31 makes it possible to prevent the pumped gases from returning to the vacuum pump 1.

[0104] In the examples of Figures 2, 5 and 6, the discharge valve 31 is mounted in a discharge pipe 35 arranged to connect the outlet S of the last pumping stage 3c to the discharge 5 of the vacuum pump 1. The discharge pipe 35 can be arranged under the pumping stages 3a-3c and be fixed to the lower half-shell 2B by any suitable fixing means. Alternatively, the discharge pipe 35 can be arranged above the pumping stages 3a-3c by being fixed to the upper half-shell 2A as in the examples of Figures 8a, 8b. The discharge gases are generally hotter than those of the first stages (due to the compression ratios and the pressure rise in the so-called high-pressure stages, i.e. the last pumping stage(s)).In the case of a vacuum pump used for pumping process gases, such as those used in semiconductor manufacturing processes in particular, it may be desirable to control the temperature of the discharge gases. For this purpose, the discharge line 35 may be insulated and / or heated in order to maintain the discharge gases at a high temperature. The discharge line 35 attached to one or other of the half-shells 2A, 2B thus makes it possible to achieve the required temperatures in the vacuum pump 1 by using the heat of the discharge gases to heat the stator 2.

[0105] In particular, the discharge line 35 may extend above or below the first pumping stage(s). When the discharge line 35 is located above the pumping stages 3a-3c, it can be extended so as to be crossed by an inlet pipe connecting the suction 4 to the inlet of the first stage 3a as shown in the example of [Fig.8b]. The heat of the discharge gases thus makes it possible to heat the pumping stages, in particular the so-called low pressure stages, i.e. the first pumping stage(s), or even to heat the inlet pipe connected to the suction 4.

[0106] Furthermore, the or each outlet channel 29 fluidically connected to at least one relief channel 11 opens into this discharge pipe 35.

[0107] In addition, the discharge pipe 35 may have a housing for receiving a silencer of the vacuum pump 1, interposed between the outlet S of the last pumping stage 3c and the discharge 5. The silencer is therefore fluidically connected to the outlets of the or each outlet channel 29 as well as to the outlet S of the last pumping stage 3c. The discharge valve 31 is generally arranged upstream of the silencer according to the direction of circulation of the gas.

[0108] Alternatively, as shown in Figures 7 to 9, the discharge valve 31 is arranged between the two half-shells 2A, 2B in a similar manner to the unloading valves 13, as previously described. According to this embodiment, the discharge channel associated with the discharge valve 31 is a discharge channel 37 connected to the outlet S of the last pumping stage 3c. The discharge channel 37 is arranged in one of the half-shells, opening into at least one mouth in the assembly surface 8. This discharge channel 37 can be arranged in the same half-shell as the unloading channel(s) 11. In the illustrated examples, it is arranged in the lower half-shell 2B.

[0109] In addition, the discharge valve 31 is mounted at least partly movable in a cavity 39 fluidly connected to the discharge 5 of the vacuum pump 1. This cavity 39 is also designated as a discharge cavity. Such a cavity 39 is provided in the half-shell opposite the discharge channel 37, for example the upper half-shell 2A. This discharge cavity 39 may be provided in the same half-shell as the cavities 15 housing the relief valves 13.

[0110] As shown in [Fig.7], the discharge cavity 39 can be arranged in the same half-shell as the outlet channel 29 and open into this outlet channel 29. Thus, all the discharged or discharged gas can be evacuated from the half-shell via the outlet channel 29. In this case, a silencer can be interposed between the discharge 5 and the outlet of the outlet channel 29. Such a silencer can be simplified compared to the embodiments with several outlets connected to the silencer. The vacuum pump 1 is all the more compact.

[0111] It is also conceivable that the discharge cavity 39 and the outlet channel(s) 29 open into a common discharge pipe 35 connected to the re 5. The discharge pipe 35 can be fixed on the first half-shell 2A ([Fig.8a] or 8b) or under the second half-shell 2B ([Fig.9]). In particular, when the discharge pipe 35 is fixed on the first half-shell 2A, this discharge pipe 35 can stop before the suction 4 ([Fig.8a]), or on the contrary the inlet pipe connecting the suction 4 to the inlet of the first stage 3a can pass through this discharge pipe 35 ([Fig.8b]). As previously described, these configurations make it possible to reach the required temperatures in the vacuum pump 1, or even to heat the inlet pipe connected to the suction 4 ([Fig.8b]).

[0112] Similar to the operation of the relief valves 13, the discharge valve 31 is arranged to close or release the mouth of the discharge channel 37 connected to the outlet of the last pumping stage 3c. When closed, the discharge valve 31, such as a ball, may rest on a valve seat and when it opens it may move away from it. The valve seat may be defined by a seal 17 as described with reference to FIGS. 3 and 4. The discharge valve 31 may be urged towards the closed position closing the mouth of the channel 37 by the force of gravity or by means of an elastic return member, such as a spring 25, as described with reference to [Fig. 5].

[0113] Furthermore, in the examples of Figures 7 to 9, the half-shells 2A, 2B house between them both a discharge valve 31 and relief valves 13. According to another embodiment, the discharge valve 31 can be arranged between the half-shells 2A, 2B without further providing for the interposition of relief valves 13 between the latter.

[0114] [Fig. 10] shows an exemplary embodiment of a pumping group 100 comprising a vacuum pump 1 and at least one additional pump 200. The additional pump 200 is in this example arranged upstream of the vacuum pump 1, according to the direction of circulation of the gas. This additional pump 200 can complement the vacuum pump 1 according to one or other of the embodiments previously described with reference to FIGS. 1 to 9.

[0115] Such an additional pump 200 also called a “booster” in English makes it possible to increase the pumping speed. It may in particular be a Roots depressor or compressor also called a “Roots blower” in English, which may comprise one stage or be multi-stage. Each pump comprises a drive motor configured to drive the rotors in rotation.

[0116] The pumping group 100 may further comprise one or more pipes 41, 43 between the additional pump called “booster” 200 and the vacuum pump 1.

[0117] In such a pumping group 100, when a valve (not shown) is opened, the pumps 1, 200 are subjected to a pressure wave which can force the mechanical parts caniques. In order to occasionally absorb large pumping flows at the inlet of the additional pump called “booster” 200, the pumping group 100 comprises at least one valve 45, also called a relief valve.

[0118] This valve 45 can be arranged between the additional pump called “booster” 200 and the vacuum pump 1. The unloading valve 45 can be arranged between the stators of the additional pump called “booster” 200 and the vacuum pump 1. More precisely, the unloading valve 45 is arranged so as to short-circuit the stages 3a-3c of the vacuum pump 1. The unloading valve 45 can be fluidically connected to the discharge 5 of the vacuum pump 1. For this, the valve 45 is arranged to move between the stators of the two pumps 1, 200, so as to close or release a mouth of a pipe 43, depending on a pressure difference on either side of the valve 45.

[0119] The relief valve 45 can be made in a similar manner to the relief valve 13 or the discharge valve 35 of the vacuum pump 1.

[0120] A pipe 41 can be connected to the outlet of the additional pump called “booster” 200. This pipe 41 can comprise at least two bypass portions, a first portion of which is connected to the inlet of the first pumping stage 3a of the vacuum pump 1 and a second portion is connected to the relief valve 45. The other pipe 43 can be connected to the outlet of the relief valve 45 and to the discharge 5 of the vacuum pump 1.

[0121] In the example illustrated in [Fig. 10], the pipe 43 at the outlet of the relief valve 45 opens into the outlet channel 29 formed in one of the half-shells 2A of the vacuum pump 1. According to a variant not shown, this pipe 43 can open into a discharge pipe 35 of the vacuum pump 1 as previously described.

[0122] The relief valve 45 makes it possible to bypass the pumping stages 3a-3c of the vacuum pump 1 in the event of overpressure. When the pressure difference is lower than the setting threshold of the relief valve 45, the pumped gas follows the path represented by the arrows F1 in solid lines and is sucked in by the first pumping stage 3a. On the contrary, when the pressure difference is higher than the setting threshold of the relief valve 45, the gas leaving the additional pump 200 follows the path represented by the white arrows F2', the outline of which is shown in solid lines, so as to "short-circuit the vacuum pump" and be evacuated to the discharge 5 of the vacuum pump 1.

[0123] In addition, one or more of the pipes 41, 43 between the additional pump or “booster” 200 and the vacuum pump 1 may be provided in the stator of one or both pumps 1, 200. In particular, the pipe 43 at the outlet of the relief valve 45 and connected to the discharge 5 of the vacuum pump 1 may pass through the stator 2 of the vacuum pump 1.

[0124] In particular, it is conceivable that the stator of one of the pumps, for example the stator 2 of the vacuum pump 1, serves as a seat for the unloading valve 45. In this case, the unloading valve 45 can be arranged to move in a cavity formed in the stator of the additional pump called “booster” 200. The valve seat 45 is defined opposite the cavity.

[0125] Thus, according to one or other of the previously described embodiment variants, one or more valves 13, 31 can be integrated directly into the functional pumping block, between the half-shells 2A, 2B, without it being necessary to provide an external housing to be attached to the vacuum pump 1. The assembly surface 8, that is to say the joint plane of the half-shells 2A, 2B, is used and shaped to receive such valves 13, 31. For each valve 13, 31, an associated discharge channel 11, 37 for the connection of at least one pumping stage 3a, 3b, 3c to the discharge of the vacuum pump 1, can be provided in a simple manner in one of the half-shells by opening onto the assembly surface 8.

[0126] This can be implemented both to unload a pumping stage, such as the first pumping stage 3a and / or an intermediate pumping stage 3b, and for the discharge at the outlet of the last pumping stage 3c. It is therefore no longer necessary to assemble an external housing to perform these unloading / discharge functions. The vacuum pump 1 thus becomes more compact (particularly in height). In addition, there is less sealing to manage with the exterior of the vacuum pump 1, compared to known state-of-the-art solutions with an external housing added for unloading and / or discharge.

[0127] Finally, all the discharged and / or relieved gas can be evacuated from a half-shell by a single channel connected to the discharge 5 of the vacuum pump 1 and into which the cavity or cavities 15, 39 housing a respective valve 13, 31 and fluidically connected to the outlet of a pumping stage 3a-3c open. When the vacuum pump 1 comprises a silencer, the latter can then be produced in a very simple manner.

[0128] Furthermore, a discharge pipe 35 can be integrated into the vacuum pump 1, being fixed to one of the half-shells 2A, 2B, so that the discharge gases circulate in the parts of the pumping cell. This is advantageous for heating, using these discharge gases, the parts of the pumping cell, in particular the first low-pressure stages, or even the inlet pipe connected to the suction 4.

Claims

Claims

1. Multi-stage vacuum pump (1) comprising: - a plurality of pumping stages (3a, 3b, 3c) respectively comprising an inlet (E) and an outlet (S), the pumping stages (3a, 3b, 3c) being mounted in series between a suction (4) and a discharge (5) of the vacuum pump (1), - a stator (2) comprising at least one stator element produced by the assembly of two complementary half-shells (2A, 2B) which join along an assembly surface (8), - at least one discharge channel (11, 37) connected to the outlet (S) of a pumping stage (3a, 3b, 3c) and in fluid communication with the discharge (5), and - at least one valve (13, 31) associated with the discharge channel (11, 37), characterized in that: - the channel evacuation (11, 37) is arranged in one of the half-shells (2A, 2B) opening into at least one mouth in the assembly surface (8) and in that - the valve (13,31) associated is arranged between the two half-shells (2A, 2B) while being at least partly movable so as to close or release the mouth of the evacuation channel (11, 37), depending on a pressure difference on either side of the valve (13, 31).,

2. Vacuum pump (1) according to the preceding claim, in which at least one discharge channel is a relief channel (11) connected to the outlet (S) of a pumping stage (3a, 3b) to be relieved and in fluid communication with the discharge (5).

3. Vacuum pump (1) according to the preceding claim, in which: - the successive pumping stages (3a, 3b, 3c) are connected in series by a respective inter-stage channel (7) connecting the output (S) of a preceding pumping stage (3a, 3b) to the inlet (E) of a following pumping stage (3b, 3c), and in which - a common channel is connected to the output (S) of the pumping stage (3a, 3b) to be relieved, the common channel being connected to at least two bypass portions, a first of which portion forms with the common channel an inter-stage channel (7) connected to the inlet (E) of the following pumping stage (3b, 3c) and a second portion forms with the common channel the unloading channel (11).

4. Vacuum pump (1) according to one of the preceding claims, in which at least one discharge channel is a discharge channel (37) connected to the outlet (S) of the last pumping stage (3c) and in fluid communication with the discharge (5).

5. Vacuum pump (1) according to one of the preceding claims, comprising at least two valves (13, 31) respectively associated with a pumping stage (3a, 3b, 3c), and in which the valves (13, 31) are dimensioned differently depending on the associated pumping stage (3a, 3b, 3c).

6. Vacuum pump (1) according to one of the preceding claims, in which the valve (13, 31) is mounted at least partly movable in a cavity (15, 39) formed in the half-shell (2B) opposite the half-shell (2A) comprising the discharge channel (11, 37), the valve (13, 31) being arranged opposite the mouth of the discharge channel (11, 37) in the assembly surface (8).

7. Vacuum pump (1) according to the preceding claim, comprising at least one outlet channel (29) fluidly connecting the cavity (15, 39) to the discharge (5), and arranged in one of the half-shells (2A, 2B).

8. Vacuum pump (1) according to one of the preceding claims, in which: - the valve (13, 31) comprises a ball, and - at least one annular seal (17) is arranged in the mouth of the associated discharge channel (11, 37), such that: • the seal (17) has a base (17a) of generally toric shape received in a first groove (21) of the mouth of the discharge channel (11, 37) having a generally cylindrical shape, and such that • the base (17a) is surmounted by a frustoconical portion (17b) delimiting a valve seat for the ball, the frustoconical portion (17b) being received in a second groove (23) of the mouth of the channel evacuation (11, 37) arranged above the first groove (21) and having a general truncated cone shape complementary to the truncated cone portion (17b) of the sealing joint (17).

9. Vacuum pump (1) according to one of the preceding claims, comprising at least one injection channel (27) opening through at least one injection orifice configured to inject a purge gas onto the valve (13, 31) and / or onto a bearing face of a valve seat.

10. Vacuum pump (1) according to one of the preceding claims, comprising a discharge pipe (35) arranged to connect the outlet (S) of the last pumping stage (3c) to the discharge (5) and fluidically connected to the discharge channel (11, 37), the discharge pipe (35) having a housing for receiving a silencer of the vacuum pump (1) interposed between the outlet (S) of the last pumping stage (3c) and the discharge (5).

11. Vacuum pump (1) according to the preceding claim, wherein the discharge pipe (35) is fixed to one or other of the half-shells (2A, 2B).

12. Vacuum pump (1) according to one of the preceding claims, comprising two rotor shafts (6) configured to rotate synchronously in opposite directions in the pumping stages (3a, 3b, 3c) to drive a gas to be pumped between the suction (4) and the discharge (5).

13. Vacuum pump (1) according to one of the preceding claims, wherein the stator (2) comprises at least one end piece, and wherein the stator element is axially assembled with the end piece or with another stator element.

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