Vertical vacuum pump

[0001] The present invention relates to a vacuum pump, in particular of the dry type, arranged vertically.

[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 the known vacuum pumps, a distinction is made between rotary lobe pumps, also known as “Roots” pumps, with two or more lobes, or pumps with claws, also known as “Claw” pumps, or screw-type pumps. These vacuum pumps are referred to as “dry” since, during operation, the rotors rotate inside the stator without any mechanical contact with one another or with the stator, this making it possible to not use oil in the pumping stages.

[0003] The rotation of the rotors is supported by bearings which can be lubricated by grease or oil.

[0004] In the case of horizontally arranged vacuum pumps, an oil stirrer disc can be used to create a misted atmosphere of air and lubricants in an oil sump, facilitating the lubrication of the bearings. In general, the oil sump is shared by two corresponding bearings at each of the shafts of a vacuum pump. The oil stirrer is fastened to one of the rotor shafts of the vacuum pump, a lower end of the stirrer dipping into the liquid oil in the sump. The rotation of the rotor shaft supporting the oil stirrer forms an oil mist, spraying droplets of lubricant onto the walls of the sump which then trickle down under the effects of gravity to the components to be lubricated.

[0005] In certain configurations, vacuum pumps with a vertical pumping architecture require the use of bearings located close to their suction inlet. Using oil to lubricate an element such as a bearing that is mounted on a vertical rotor shaft notably close to the suction inlet is more complex than for a horizontal architecture, owing to the need to provide an ancillary oil pump. The oil pump is intended to force a liquid lubricant present in an oil sump to rise towards the elements to be lubricated, such as the bearings. The oil pump moreover makes it possible to maintain constant lubrication in spite of the possible pressure variations in the oil sump. [0006] Another difficulty of vertical vacuum pumps is that it is no longer possible to make effective use of oil stirrer discs.

[0007] An aim of the present invention is to propose an improved vacuum pump that makes it possible to at least partially resolve one or more drawbacks of the prior art that were specified, enabling simplified and constant lubrication of a bearing mounted on a vertical rotor shaft of the vacuum pump.

[0008] To that end, a subject of the invention is a vacuum pump having a stator having at least one pumping chamber, two rotors which are configured to rotate in the pumping chamber about a respective axis of rotation extending in a vertical direction and respectively have an end provided with a cavity, at least two bearings mounted in a respective cavity, and at least two support spindles for supporting a respective bearing, which are secured to the stator and each of which has at least one portion protruding into one of the cavities, the bearings being respectively arranged between the protruding portion of one of the support spindles and a wall delimiting one of the cavities.

[0009] According to the invention, the vacuum pump has at least one reservoir which is located in the bottom of at least one of the cavities, facing the bearing and below it along the axis of rotation. The reservoir is configured to receive a liquid lubricant intended to be entrained towards the bearing by a centrifugal force generated by the rotation of the rotor.

[0010] The vertical direction corresponds to the direction of gravity when the vacuum pump is placed on the ground or on a frame.

[0011] As a result, when the rotor rotates, the liquid lubricant is entrained upwards by the centrifugal force and rises up to the bearing, enabling lubrication of the latter. When the rotation ends, the liquid lubricant drops back down into the reservoir under the effect of gravity. Such a reservoir thus enables lubrication of a vertical bearing without using an ancillary device such as an oil pump. The lubrication can be done constantly.

[0012] The vacuum pump may also have one or more of the following features described below, considered separately or in combination.

[0013] The liquid lubricant is, for example, oil or includes oil. [0014] The bearing is preferably mounted in a cavity at an upper end of the rotor along the axis of rotation. The upper end is arranged on the side of a suction intake of the vacuum pump.

[0015] The reservoir may be produced by machining the end of the rotor.

[0016] In a variant, the reservoir may be produced by an added part inserted into the bottom of the cavity.

[0017] The reservoir may have a shape selected from a bowl shape, a cup shape, a rounded shape, a concave shape, a convex shape, a shape exhibiting symmetry of revolution about the axis of rotation, a shape which is cylindrical about the axis of rotation.

[0018] The reservoir is, for example, centred in relation to the axis of rotation.

[0019] In particular, the reservoir may have a bottom wall with a shape selected from a circular shape, a disc shape, a rounded shape, a shape having a dome in the centre of at least one annular recess, a wavy shape, a curved shape with a peak oriented towards the support spindle, a curved shape with a peak oriented away from the support spindle, a convex shape, a concave shape, a planar shape. The profile of the bottom wall may correspond to the equation of a parabola.

[0020] According to one example, the reservoir may have at least one fin extending from a peripheral wall of the reservoir towards the centre of the reservoir and in the direction of the support spindle.

[0021] The fin may have a shape that tapers between a base located on the peripheral wall of the reservoir and a free end.

[0022] According to another example, the reservoir may have a shape which is cylindrical about the axis of rotation and comprise a helical rib on the internal surface of the peripheral wall of the reservoir.

[0023] According to yet another example, the reservoir may have a shape which is cylindrical about the axis of rotation and comprise a helical groove on the internal surface of the peripheral wall of the reservoir.

[0024] The reservoir may have a planar bottom wall and a raised section in relation to the planar bottom wall. [0025] A respective reservoir may be provided in the bottom of the two cavities. The reservoirs in each cavity are independent of one another. The lubrication is thus provided independently for the two bearings.

[0026] The support spindle may comprise a through-passage for filling with liquid lubricant that leads into the reservoir.

[0027] The vacuum pump may comprise at least one indicator for the level of liquid lubricant in the reservoir.

[0028] The support spindle may comprise at least one viewing window, which is intended for viewing the level of liquid lubricant in the reservoir, is made from a transparent or translucent material, and is arranged at least partially facing the reservoir.

[0029] The support spindle may comprise at least one through-orifice configured for the passage of a sensor configured to be dipped into the reservoir so as to measure the level of liquid lubricant in the reservoir.

[0030] The support spindle may have a sensor which leads into the reservoir and is configured to measure the level of liquid lubricant in the reservoir.

[0031] The support spindle may be realized by a lug fastened to the stator.

[0032] The vacuum pump is, for example, of the dry type.

[0033] Other advantages and features of the invention will become more clearly apparent on reading the following description, which is given by way of illustrative and nonlimiting example, and the appended drawings, in which:

[0034] [Fig. 1] shows a cross-sectional view of a multistage vacuum pump with a vertical architecture according to one embodiment example.

[0035] [Fig. 2a] is an enlarged view of an upper end of a rotor of the vacuum pump, comprising a cavity which comprises a reservoir according to a first embodiment example and receives a support spindle for a bearing according to a first embodiment.

[0036] [Fig. 2b] is a view similar to Figure 2a, showing a support spindle for a bearing according to a second embodiment.

[0037] [Fig. 3] is a view similar to Figure 2a, showing a support spindle for a bearing according to a third embodiment. [0038] [Fig. 4] is a view similar to Figure 2a, showing a reservoir according to a second embodiment example.

[0039] [Fig. 5] is a view similar to Figure 2a, showing a reservoir according to a third embodiment example.

[0040] [Fig. 6a] is a view similar to Figure 2a, showing a reservoir according to a fourth embodiment example.

[0041] [Fig. 6b] is a top view of the reservoir from Figure 6a.

[0042] [Fig. 7] is a view similar to Figure 2a, showing a reservoir according to a fifth embodiment example.

[0043] [Fig. 8] is a view similar to Figure 2a, showing a reservoir according to a sixth embodiment example.

[0044] In these figures, identical or similar elements bear the same reference numerals. The figures have been simplified for the sake of clarity. Only the elements necessary for understanding the invention are shown.

[0045] 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 a single embodiment. Individual features of different embodiments can also be combined or interchanged to provide other embodiments.

[0046] In the description, it is possible for certain elements to be indexed, for example first element or second element. In this case, this is simple indexing for differentiating and denoting elements which are similar but not identical. This indexing does not imply that one element takes priority over another and such denominations can easily be interchanged without departing from the scope of the present invention. This indexing does not imply an order in time, either.

[0047] Figure 1 illustrates an embodiment example of a vacuum pump 1. The vacuum pump 1 is in particular of the dry type.

[0048] The invention applies to any type of single-stage or multistage dry vacuum pump, that is to say having one or more stages. This vacuum pump 1 may be a rough- vacuum pump that is able to be started up at atmospheric pressure. Such a rough-vacuum pump is configured to draw in, transfer and then deliver the pumped gases at atmospheric pressure. This vacuum pump 1 may also be of the “Blower” type, or Roots compressor or “Booster” type, arranged in series and upstream of a primary vacuum pump.

[0049] The vacuum pump 1 has a stator 2. The stator 2 has at least one pumping chamber 3. A stator is defined as all of the stator portions or stationary portions that are assembled together and notably define the one or more pumping chambers 3.

[0050] More specifically, the stator 2 forms one or more pumping stages, between a suction inlet and a delivery outlet (these not being visible in the figures), in which a gas to be pumped can circulate. The vacuum pump 1 may have multiple pumping stages arranged in series. Each pumping stage comprises a pumping chamber 3. The pumping chambers 3 comprise a respective inlet and outlet. The inlet of the first pumping stage, also referred to as suction stage, is in fluidic communication with the suction inlet of the vacuum pump 1. The outlet of the last pumping stage, also referred to as delivery stage, is in fluidic communication with the delivery outlet.

[0051] The vacuum pump 1 has two rotors 6 configured to rotate in the one or more pumping chambers 3 of the stator 2 about a respective axis of rotation Al, A2. The axes of rotation Al, A2 are parallel.

[0052] The vacuum pump 1 is configured to be installed, that is to say for example placed on the ground or on a frame, with the axes of rotation Al, A2 extending in a vertical direction. The vertical direction corresponds to the direction of gravity when the vacuum pump is placed on the ground or on a frame. The vertical arrangement of the vacuum pump 1 makes it possible to significantly reduce the footprint on the ground.

[0053] In the remainder of the description, the axial direction is parallel to the axes of rotation Al, A2 and corresponds to the vertical direction, or direction of gravity. The radial direction is the direction perpendicular to the axial direction. Similarly, the terms “above”, “below”, “top”, “bottom”, “upper” and “lower” are defined in the present case along the vertical direction, or direction of gravity, in relation to the orientation of the vacuum pump 1 placed on the ground or on a frame.

[0054] The rotors 6 have a respective rotor shaft. The rotors 6 may have mating profiles that can be assembled on the rotor shafts or they can be made in one piece with the rotor shafts (they are referred to as monobloc rotors). [0055] The rotors 6 have, for example, rotary lobes with identical profiles, for example of the “Roots” type, for example which are straight or have a helical twist (first pumping stage in Figure 1). In a variant, they may be lobes of the “Claw” type or of the screw type or be based on another similar vacuum pump principle. The rotor shafts are intended to be driven in rotation by at least one motor 9 of the vacuum pump 1 that is located, for example, at one end of the vacuum pump 1.

[0056] The rotor shafts are configured to rotate in synchronized fashion and in opposite directions in the pumping stages, such that the rotors entrain a gas to be pumped between the suction inlet and the delivery outlet. During rotation, the gas drawn in through the inlet is trapped in the free space present in a pumping chamber 3, between the rotors 6 and the interior of the stator 2, and then is entrained by the rotors 6 towards the next stage. The successive pumping stages may be connected one after another in series via respective passages between stages that connect the outlet of the preceding pumping stage to the inlet of the following pumping stage, and so on to the delivery outlet of the vacuum pump 1.

[0057] The vacuum pump 1 is referred to as “dry” since, during operation, the rotors 6 rotate inside the stator 2 of the vacuum pump 1 without any mechanical contact with one another or with the stator 2, this making it possible to not use oil in the pumping chambers 3.

[0058] The rotors 6 each have an end 11, also referred to as upper end, which is arranged on the side of the suction inlet. The rotors 6 each have another end 13, also referred to as lower end, which is arranged on the side of the delivery outlet.

[0059] The rotors 6, and more specifically the rotor shafts, are rotationally guided by at least one bearing 15 located at one end 11 of the vacuum pump 1. The rotors 6 may each be rotationally guided by at least two bearings 15, 17, located at the ends 11, 13, of the vacuum pump 1.

[0060] For that purpose, at an end 11, notably the upper end, the rotors 6 have a cavity 19 in which a bearing 15 is mounted. Such a bearing 15 mounted at the upper end 11 of a rotor 6 is referred to as upper bearing 15 below. [0061] The cavity 19 may have an overall shape which is cylindrical or substantially cylindrical, with an axis corresponding to the axis of rotation Al, A2. This cavity 19 may be realized by a bore.

[0062] The cavity 19, which can be seen better in Figure 2a, has a cavity bottom 19a. A reservoir 20 is located in the cavity bottom 19a of at least one of the cavities, and preferably of the two cavities 19. The reservoir 20 is configured to receive a liquid lubricant, such as oil. The reservoir 20 thus faces towards the upper bearing 15 and is below it along the axis of rotation Al, A2. Such a reservoir 20 is described in more detail below.

[0063] During operation, the liquid lubricant is intended to be entrained towards the upper bearing 15 by a centrifugal force generated by the rotation of the rotors 6. More specifically, the motor 9 drives the rotation of the rotors 6 in the pumping chambers 3 and, when the rotors 6 rotate, the liquid lubricant present in the reservoir 20 is entrained radially by the centrifugal force and is deflected upwards owing to the cylindrical shape of the cavity. In other words, the liquid lubricant rises to the level of the upper bearing 15 above the reservoir 20, enabling lubrication of the latter. The liquid lubricant then drops back down into the reservoir 20 under the effect of gravity. Such a reservoir 20 thus enables lubrication of a vertical bearing without using an ancillary device such as an oil pump. The lubrication can be done constantly.

[0064] The cavity 19 may also comprise a circumferential wall 19b. The circumferential wall 19b extends upwards from the cavity bottom 19a, with reference to the orientation of the vacuum pump 1 once it has been installed, as illustrated in Figure 1.

[0065] According to one embodiment example, the circumferential wall 19b comprises a shoulder 19c which may be intended to form a stop, notably a lower stop, against which the upper bearing 15 bears.

[0066] In particular, a cavity 19 may be provided at the end, notably the upper end 11, of each of the two rotors 6. The two cavities 19 are independent of one another. More specifically, the reservoirs 20 in the cavity bottoms 19a are independent of one another and do not communicate with one another. In other words, the liquid lubricant is not decanted from one reservoir 20 to another. The vacuum pump 1 thus incorporates at least two separate reservoirs 20 in the respective rotors 6. [0067] The vacuum pump 1 has a support spindle 21 which is intended for supporting the upper bearing 15 and is secured to the stator 2. The stator 2 may have a support spindle 21 for each upper bearing 15 rotationally guiding a rotor 6. The support spindle 21 may extend parallel to the axis of rotation Al, A2 and to the vertical direction.

[0068] The support spindle 21 may be realized by a part which is separate from the stator 2 and fastened to the stator 2. This is, for example, a lug which may extend vertically. In a variant, this may be a spindle made in one piece with the stator 2.

[0069] The support spindle 21 has at least one portion that protrudes into the cavity 19. The upper bearing 15 is arranged around the protruding portion of the support spindle 21, and against the circumferential wall 19b of the cavity 19.

[0070] In general, the support spindle 21 may have a cylindrical or an at least partially cylindrical shape. Embodiment variants of the support spindle 21 will be specified below.

[0071] A friction ring 23, intended to facilitate the friction of a friction seal, such as a lip seal, as described below, may be arranged around the protruding portion of the support spindle 21. This may be a fixed friction ring 23 secured to the support spindle 21. The friction ring 23 may be interposed between the upper bearing 15 and the shoulder 21b of the support spindle 21 along the axis of rotation Al, A2.

[0072] The upper bearing 15 may comprise at least one rolling bearing. According to one embodiment example, the rolling bearing 15 comprises an internal ring 15a secured to the support spindle 21 and an external ring 15b secured to the rotor 6 for conjoint rotation therewith. Rotary elements, such as ball bearings 15c, which ensure the rotation of the external ring 15b in relation to the internal ring 15a, travel between the internal ring 15a and the external ring 15b.

[0073] As an alternative, the upper bearing 15 may be a slide bearing.

[0074] It is also conceivable for the bearing 15 to be at least partially formed by the rotor 6 and/or the support spindle 21. In addition, a coating may be provided on the rotor 6 and/or the support spindle 21, to limit friction. In a variant or in addition, the liquid lubricant, such as oil, can ensure hydrodynamic bearing operation. [0075] At the other end 13, the lower end, the rotors 6 may have a bearing 17, also referred to as lower bearing 17. The lower bearings 17, which are not described in more detail below, may be similar to the upper bearing 15, or not.

[0076] The vacuum pump 1 advantageously has at least one seal 25 arranged above the upper bearing 15 along the axis of rotation Al, A2. This seal 25 may be interposed between the circumferential wall 19b of the cavity 19, for the one part, and the friction ring 23 or alternatively the support spindle 21, for the other part.

[0077] The seal 25 may be a seal with contact of the mechanical packing type. In a variant, this may be a seal 25 referred to as friction seal, such as a lip seal.

[0078] According to one example, the seal 25 is mounted so as to rotate conjointly with the stator 6, more specifically with the rotor shaft. In the case of a friction seal 25, it is configured to rub against the support spindle 21 or the friction ring 23 that is secured to the support spindle 21 while the rotor 6 is rotating.

[0079] According to another example (not shown), the seal 25 is secured to the stator 2 or to a stationary portion, such as the support spindle 21. In the case of a friction seal 25, it is configured to rub against the rotor 6 as it rotates or against a stationary portion, such as a friction ring secured to the rotor 6.

[0080] In a variant, the seal 25 may be a dynamic contactless seal, for example of the labyrinth type.

[0081] The seal 25 above the upper bearing 15 makes it possible to protect the liquid lubricant in the reservoir 20 by avoiding powder or other particles reaching the reservoir 20. The seal 25 also makes it possible to avoid the liquid lubricant entering the pumping cell to the greatest possible extent.

[0082] In a variant or in addition, a line for injecting purging gas, such as nitrogen, may be formed in the stator 2 so as to lead into the cavity 19 above the seal 25. This purging gas injection line (not shown) is attached to a purging gas inlet. It may, for example, be formed in the support spindle 21. As a result, the purging gas can be injected into the cavity 19 above the seal 25 to limit the entry of solid particles, powders, or other things into the reservoir 20. [0083] A first embodiment of the support spindle 21 is shown in Figure 2a. It has a cylindrical body which protrudes into the cavity 19. This cylindrical body thus forms the protruding portion of the support spindle 21. The cylindrical body has a free end 21a which faces towards the cavity bottom 19a and the reservoir 20 and is above them.

[0084] The support spindle 21 may have a shoulder 21b formed on the lateral wall of the cylindrical body. The cylindrical body 21 may have an upper portion above the shoulder 21b that has a first diameter DI and a lower portion below the shoulder 21b that has a second diameter D2 less than the first diameter DI. It is this lower part which is arranged facing towards the reservoir 20 and above it, and which terminates in the free end 21a.

[0085] In addition, opposite to the free end 21a, the support spindle 21 may have a base 21c for fastening to the stator 2, when it is realized by a part that is separate from the stator 2. This base 21c may possibly have a diameter which is greater than the first diameter DI.

[0086] The friction ring 23 may be arranged around the cylindrical body of the support spindle 21, and notably the lower portion of the cylindrical body. It may be arranged axially between the upper bearing 15 and the shoulder 21b of the support spindle 21. In this example, the friction ring 23 has an inside diameter equal to or slightly greater than the second diameter D2 of the cylindrical body, and an outside diameter of the friction ring 23 which may be equal to the first diameter DI of the cylindrical body.

[0087] The upper bearing 15 may be clamped between the circumferential wall 19b of the cavity 19 and the cylindrical body of the support spindle 21, along the radial direction.

[0088] In particular, if the upper bearing 15 is a rolling bearing comprising an internal ring 15a and an external ring 15b, the internal ring 15a may be mounted freely or clamped on the support spindle 21. Similarly, the external ring 15b may be mounted freely or clamped in the cavity 19 or bore of the rotor 6.

[0089] As a result, various arrangements can be envisaged. In a first arrangement, the internal ring 15a may be clamped on the support spindle 21, and the external ring 15b may be clamped in the cavity 19. In a second arrangement, the internal ring 15a may be mounted freely on the support spindle 21, and the external ring 15b may be clamped in the cavity 19. In a third arrangement, the internal ring 15a may be clamped on the support spindle 21, and the external ring 15b may be mounted freely in the cavity 19. In a fourth arrangement, the internal ring 15a may be mounted freely on the support spindle 21, and the external ring 15b may be mounted freely in the cavity 19.

[0090] In addition, the upper bearing 15 may be axially locked between the shoulder 19c of the cavity 19, for the one part, and the friction ring 23 or the shoulder 21b of the support spindle 21, for the other part.

[0091] By way of example, in the case of a rolling bearing, the internal ring may have an inside diameter equal or substantially equal to the second diameter D2 of the cylindrical body, and the external ring may have an outside diameter equal or substantially equal to the diameter of the cavity 19 above the shoulder 19c.

[0092] A second embodiment of the support spindle 21, which is shown in Figure 2b, differs from the embodiment of Figure 2a in that the support spindle 21 has a through -pas sage 27 which leads into the reservoir 20. This passage 27 can be used to fill the reservoir 20 with liquid lubricant and is referred to as filling passage 27 below. The filling passage 27 may have an inlet 27a. The filling passage 27 extends, for example, from this inlet 27a in the vertical direction, along the support axis 21, to an outlet 27b in the free end 21a of the cylindrical body of the support spindle 21 facing the reservoir 20. This is, for example, a through-orifice, for example central through-orifice, formed in the support spindle 21.

[0093] Furthermore, the vacuum pump 1 may comprise at least one indicator for the level of liquid lubricant in the reservoir 20. Such an indicator may be integrated in the support spindle 21. To do this, the support axis 21 comprises, for example, at least one window or porthole 29 for viewing the level of liquid lubricant in the reservoir 20. This viewing window 29 is advantageously made from a transparent or translucent material, and is arranged at least partially facing the reservoir 20. The viewing window 29 is, for example, formed in a cover or stopper which is intended for closing the filling passage 27 and is made at least partially, or even completely, transparent or translucent.

[0094] In a variant or in addition, a sensor or a probe may be intended to be dipped into the reservoir 20 so as to measure the level of liquid lubricant in the reservoir 20.

[0095] Various technologies can be used to measure the level of liquid lubricant in the reservoir 20. By way of nonlimiting example, this may be a capacitive technology, or in a variant an ultrasonic technology, involving or not involving contact of the sensor with the liquid lubricant. [0096] In the example of Figure 3, the support spindle 21 bears such a sensor 22. The sensor 22 may, for example, pass through the filling passage 27 visible in Figure 2b, or another through-orifice in the support spindle 21 that leads into the reservoir 20.

[0097] The sensor 22 may be long enough to dip into the reservoir 20 so as to be immersed in the liquid lubricant. This sensor 22 makes it possible to indicate the level of liquid lubricant when the rotor 6 is stationary, but also when it is rotating and the liquid lubricant is sprayed towards the upper bearing 15 by the centrifugal force.

[0098] The reservoir 20 of liquid lubricant is described in more detail below, with reference to Figures 1 to 8.

[0099] The reservoir 20 may be machined directly into the rotor 6. In a variant, the reservoir 20 may be produced by an added part inserted into the bottom 19a of the cavity 19. The storage capacity of the reservoir 20 is defined as a function of the quantity of liquid lubricant that it must receive depending on the application.

[0100] Moreover, the reservoir 20 may have various shapes, various profiles, in order to optimize the volume and flow rate of liquid lubricant sprayed onto the upper bearing 15, notably as a function of the rotational speed.

[0101] In theory, and notably when the shape of the reservoir 20 does not influence the surface flow, for example when it is a disc or another planar shape, the inertial forces can give the liquid lubricant, such as oil, a parabolic shape during rotation. The equation of the movement of the liquid lubricant in this case is the equation of a parabolic trajectory:

Q ² r ² h(r) = h ₀ -I - , where h corresponds to the height of the trajectory, r corresponds to the distance from the centre of rotation, ho corresponds to the initial height, Q corresponds to the rotational speed, and g corresponds to gravity. The height h is directly proportional to the square of the rotational speed Q and to the square of the distance from the centre of rotation r, and is inversely proportional to the acceleration due to gravity g. The density or the viscosity of the liquid lubricant does not affect the curvature of the parabola, or affects it only a little.

[0102] The reservoir 20 is preferably centred around the axis of rotation Al, A2. [0103] The reservoir 20 may have a bowl shape, a cup shape, a rounded shape, a concave shape, a convex shape, a shape exhibiting symmetry of revolution about the axis of rotation Al, A2, a shape which is cylindrical about the axis of rotation Al, A2.

[0104] As can be seen better in Figures 2a to 8, the reservoir 20 may have a bottom wall 20a that extends facing the upper bearing 15 and a peripheral wall 20b that extends upwards from the bottom wall 20a.

[0105] The bottom wall 20a may extend radially in relation to the axis of rotation Al, A2. The peripheral wall 20b may extend axially.

[0106] By way of example, the bottom wall 20a may take a shape selected from a circular or substantially circular shape, a disc shape, a planar, substantially planar or strictly planar shape, a rounded shape, a shape having a dome in the centre of at least one annular recess, a wavy shape, a curved shape with a peak oriented towards the support spindle 21, a curved shape with a peak oriented away from the support spindle 21, a convex shape, a concave shape. The profile of the bottom wall 20a may correspond to the equation of a parabola.

[0107] As an alternative or in addition, one or more structures may be provided in the bottom of the reservoir 20 and/or on the peripheral wall 20b. Such structures may be baffles, fins, ribs, channels, at least one raised section or overthickness, at least one deformation, or any other structure or shape making it possible, for example, to optimize the lubrication flow rate of the upper bearing 15, this list not being exhaustive.

[0108] Various embodiment examples of the reservoir 20 are described in more detail below. These various examples can apply irrespective of the embodiment of the support spindle 21.

[0109] According to a first embodiment example of the reservoir 20 shown in Figures 2a to 3, it has a bowl shape centred about the axis of rotation Al, A2, with a bottom wall 20a which is concave, that is to say forming a recess. As a result, the bottom wall 20a takes a curved shape, the peak of which is oriented away from the support spindle 21. The depth or height of the recess is selected as a function of the desired storage capacity. In addition, the peripheral wall 20b extends upwards from the bottom wall 20a, along the axis of rotation Al, A2, in the direction of the upper bearing 15. The peripheral wall 20b of the reservoir 20 has an internal surface which is planar or substantially planar. The internal surfaces of the bottom wall 20a and of the peripheral wall 20b are those that delimit the interior of the reservoir 20.

[0110] A second embodiment example of the reservoir 20 is shown in Figure 4. Only the differences in relation to the first embodiment example are specified below. The reservoir 20 has an overall shape which is cylindrical about the axis of rotation Al, A2, with a bottom wall 20a having a central dome in the centre of at least one annular recess. In the example illustrated, the wavy bottom wall 20a has a dome, the peak of which is oriented towards the support spindle 21, in the centre of an annular recess. A third embodiment example shown in Figure 5 differs from the preceding embodiment examples in that all of the bottom wall 20a has a convex shape, that is to say a curved shape, the peak of which is oriented towards the support spindle 21.

[0111] According to another, fourth embodiment example shown in Figures 6a and 6b, the reservoir 20 differs from the preceding examples in that it has an overall shape which is cylindrical about the axis of rotation Al, A2, with a bottom wall 20a extending radially without exhibiting a curve or wave. The bottom wall 20a has an internal surface which is planar or substantially planar. The internal surface of the bottom wall 20a is the surface facing the upper bearing 15. It also faces the protruding portion of the support spindle 21, such as the free end 21a of the cylindrical body in the example illustrated.

[0112] In addition, according to this fourth example, the reservoir 20 has at least one structure, such as a fin 31, on the peripheral wall 20b. More specifically, such a fin 31 extends from the peripheral wall 20b, for example from a low portion of the peripheral wall 20b, towards the inside of the reservoir 21, notably towards the centre of the reservoir 20, and also in the direction of the support spindle 21. Such a fin 31 is oriented upwards.

[0113] The fin 31 may have a shape that tapers between a base 31a located on the peripheral wall 20b of the reservoir 20 and a free end 3 lb. The shape of such a fin 31 may, for example, be triangular or substantially triangular.

[0114] Between its base 31a and its end 3 lb, the fin may have a length less than the radius of the bottom wall 20a, when the latter has a circular or disc shape or has a circular outline.

[0115] The reservoir 20 may comprise multiple fins 31. In the example of Figure 6b, four fins 31 are shown. These fins 31 may be spaced apart from one another at a regular angle. In the example illustrated, the four fins 31 are evenly distributed over the circumference of the peripheral wall 20b of the reservoir 20.

[0116] The fins 31 may be arranged at the same level along the axis of rotation Al, A2.

[0117] In addition, the fins 31 may be arranged symmetrically in relation to the axis of rotation Al, A2.

[0118] Figure 7 shows a fifth embodiment example which differs from the example of Figures 6a and 6b in that the reservoir 20 no longer has fins but has a helical rib 33 on the internal surface of the peripheral wall 20b. The axis of the helical rib 33 is the axis of rotation Al, A2.

[0119] According to an alternative (not shown), the reservoir 20 may have a groove, for example a helical groove, instead of a helical rib 33. The axis of the helical groove may be the axis of rotation Al, A2. This groove extends over the internal surface of the peripheral wall 20b. The groove may be formed, for example, by extrusion.

[0120] A sixth embodiment example of the reservoir 20 is shown in Figure 8 and differs from the embodiment examples of Figures 6a to 7 in that the reservoir 20 has a raised section 35, along the axis of rotation Al, A2, in relation to the bottom wall 20a which is planar or substantially planar. It has, for example, a parallelepipedal shape. This raised section 35 may be made in the centre of the bottom wall 20a.

[0121] The reservoir 20 or, more specifically, the peripheral wall 20b may extend axially over a first height Hl and the raised section 35 may extend axially over a second height h2 which is less than the first height Hl.

[0122] This raised section 35 may also have a radial dimension, for example, less than or equal to the diameter of the cylindrical body of the support spindle 21.

[0123] In the example illustrated, the internal surface of the peripheral wall 20b no longer has a structure, such as fins or a rib.

[0124] As a result, the reservoir 20 according to one or the other of the embodiment examples is directly incorporated in the vertically mounted rotor 6, without increasing the size of the vacuum pump 1. The reservoir 20 is preferably arranged at the upper end 11 of the rotor 6 on the side of the suction inlet. A reservoir 20 may be provided for each rotor 6 and the various reservoirs 20 are independent of one another. [0125] When the rotors 6 are rotating, the liquid lubricant in each reservoir 20 is entrained by the centrifugal force and rises up to the notably upper bearings 15, and then drops back down into the corresponding reservoir 20. The upper bearings 15 can be lubricated with a permanent flow without the need for any external element such as an oil pump to make the liquid lubricant circulate. The reservoirs 20 may take specific shapes depending on the vacuum pumps so as to cause the liquid lubricant to move centrifugally in a manner adapted to the flow rate necessary to lubricate the upper bearing 15.

[0126] The support spindle 21, such as a lug, can make it possible, notably by virtue of a through-hole, to fill the reservoir 20 and/or to pass through a liquid lubricant level sensor. The support spindle 21 may also incorporate a window 29 for viewing the level of liquid lubricant or a liquid lubricant level sensor.

[0127] The incorporation of the reservoirs 20 in the rotors 6 with associated seals 25 moreover makes it possible to limit the migration of liquid lubricant into the vacuum pump 1 and/or the deposition of particles in the reservoir.

[0128] These reservoirs 20 have smaller volumes than an oil sump of the prior art. These small reservoirs 20 that are independent of one another make it possible to facilitate the pressure equalizing operations above the lubricant bath.

[0129] This design thus makes it possible to remain very compact, to minimize the amount of liquid lubricant required, to make the reservoirs 20 independent, and to lubricate the bearings 15 with the desired flow rate, without an ancillary device such as an oil pump.