Title of the invention: Dry vacuum pump

The present invention relates to a dry vacuum pump.

Dry vacuum pumps have one or more pumping stages in series in which a gas that is to be pumped circulates between an intake and a delivery. Among known vacuum pumps, a distinction is made between those with rotary lobes, also known by the name “Roots”, or those with claws, also known by the name “claw”. These vacuum pumps are referred to as “dry” because, during operation, the rotors turn inside a stator without any mechanical contact between one another or with the stator, this making it possible not to use oil in the pumping stages.

The rotors are supported by lubricated bearings located at the shaft end. In order to facilitate their installation and removal, certain rotors are installed in cantilever style, the shafts being supported solely by the bearings located by the motor.

Certain pumping applications require the ability to absorb significant gas flows at least intermittently. These transitional phenomena most often occur while chambers are being emptied at atmospheric pressure or while gas is entering suddenly. The pumping of these strong gas flows causes the vacuum pump to heat up considerably and leads to significant loads on the rotors. The accumulation of phenomena of thermal expansion and shaft deflection movements caused by these various transitional phases can give rise to radial contact between the rotors or between the rotors and the stators. Even though they are very infrequent, these transitional phases can be very damaging to the vacuum pump.

One object of the present invention is to at least partially resolve one of the abovementioned disadvantages.

To that end, the subject of the invention is a dry vacuum pump having: at least one pumping stage, two rotors configured to turn in the at least one pumping stage, the rotors being configured to be rotated by at least one motor of the vacuum pump, characterized in that the vacuum pump also has at least one pair of double bearings each having at least one permanent-magnet magnetic bearing and at least one plain bearing for supporting each of the two rotors.

The permanent-magnet magnetic bearings center the rotors in a steady-state regime, that is to say generating only very few loads on the shafts for the pumping of weak and moderate gas flows. The permanent-magnet magnetic bearings limit the phenomena of deflection of the rotors during normal operation. They also limit the vibrations of the rotors during normal operation that are caused by phenomena of resonance or balancing defects. The plain bearings form a stop for the rotors in the transitional modes, that is to say for the intermittent pumping of significant gas flows, by providing guidance in rotation by sliding only when the centering via the permanent-magnet magnetic bearings is not sufficient. The plain bearings thus provide a backup for the permanent-magnet magnetic bearings. The advantage of this device is that these bearings are contactless, thus do not have any friction or wear. They do not restrict the gas flows that are pumped and do not require lubrication or dilution gases to protect them, such that the pumping performance is not affected. In addition, these bearings can be made compatible with the corrosive environments. This solution likewise facilitates the disposition of a vacuum pump installed “vertically”, that is to say with a vertical axial direction, because the absence of lubricant means that there is no risk of oil or grease from the bearings migrating by gravity toward the dry pumping stages.

The vacuum pump may also have one or more of the features described below, taken alone or in combination.

The permanent-magnet magnetic bearings may each have a stator part that is fixed to the stator and a rotor part that rotates conjointly with the rotor.

The plain bearings of the at least one pair of double bearings may be installed with a respective clearance between the rotor and the stator that is less than the clearance between the rotor part and the stator part of the permanent-magnet magnetic bearings of the at least one pair of double bearings. This ensures that contact between the rotors and the stator occurs firstly in the plain bearings instead of between the stator parts and rotor parts of the permanent-magnet magnetic bearings.

The plain bearings may each have a ring that is installed clamped in a bore in the stator or in the rotor and/or a ring that is installed clamped on an axle of the stator and/or of the rotor. The plain bearings thus each have for example a single ring that is installed clamped in a bore or a single ring that is installed clamped on an axle or two rings, one that is installed clamped in a bore and one that is installed clamped on an axle.

The plain bearings may be coated or surface-treated at a bore in the stator or in the rotor and/or on an axle of the stator or of the rotor and/or on a ring that is installed clamped in a bore and/or on an axle. For example, each plain bearing is coated or surface-treated solely at the bore or coated or surface-treated solely on the axle or coated or surface-treated at the bore and on the axle, or coated or surface-treated on the ring that is installed clamped in the bore and/or on the axle.

The vacuum pump may have at least two pumping stages arranged in series, the permanent-magnet magnetic bearings of a pair of double bearings being arranged in a shaft passage between two successive pumping stages. The vacuum pump may have at least two pumping stages arranged in series, the plain bearings of a pair of double bearings being arranged in a shaft passage between two successive pumping stages.

The permanent-magnet magnetic bearings of a pair of double bearings may be located at the shaft end, the pumping stage(s) being interposed between the motor and the shaft ends.

The plain bearings of a pair of double bearings may be located at the shaft end, the at least one pumping stage being interposed between the motor and the shaft ends.

The permanent-magnet magnetic bearing of a double bearing may be arranged spaced apart from or next to the plain bearing along the rotor. Provision is made for example for a permanent-magnet magnetic bearing at the shaft end and a plain bearing arranged in a shaft passage, such as at the first shaft passage, that is to say between the first and the second pumping stage. This arrangement can improve the compactness of the vacuum pump.

According to one embodiment example, the stator parts of the permanent-magnet magnetic bearings of a pair of double bearings and/or the plain bearings of a pair of double bearings surround the rotor.

According to one embodiment example, the permanent-magnet magnetic bearings of a pair of double bearings and/or the plain bearings of a pair of double bearings are arranged inside a respective rotor.

The plain bearings may each have a silicon carbide coating or a nickel/PTFE coating.

The permanent-magnet magnetic bearings may each have a nickel/PTFE coating.

The vacuum pump may also have at least two roller-bearing devices configured to support a respective rotor in a driving part of the vacuum pump.

Other features and advantages of the invention will become apparent from the following description, given by way of example and without limitation, with reference to the appended drawings, in which:

[Fig. 1] Figure 1 shows a schematic view of a first embodiment example of a dry vacuum pump.

[Fig. 2] Figure 2 shows a sectional view of a detail of the dry vacuum pump of figure 1 at the shaft ends.

[Fig. 3] Figure 3 shows a sectional view of a detail of another dry vacuum pump variant at the shaft ends.

[Fig. 4] Figure 4 shows a schematic view of a detail of another dry vacuum pump variant at a shaft end.

[Fig. 5] Figure 5 shows a similar view to figure 1 for a second embodiment example of a dry vacuum pump. [Fig. 6] Figure 6 shows a similar view to figure 1 for a third embodiment example of a dry vacuum pump.

In these figures, identical elements bear the same reference numerals.

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 various embodiments may also be combined or interchanged to provide other embodiments.

“Upstream” is understood to mean an element that is positioned in front of another element with respect to the circulation direction of the gas that is to be pumped. Conversely, “downstream” is understood to mean an element that is positioned beyond another element with respect to the circulation direction of the gas that is to be pumped.

The axial direction is defined as the longitudinal direction of the vacuum pump in which the axes of rotation of the rotors extend.

The invention applies to any type of dry vacuum pump 1 having at least one pumping stage 3a-3e, such as comprising one to ten pumping stages, such as for example five pumping stages 3a-3e. This vacuum pump 1 may be a rough-vacuum pump configured to deliver the gases pumped at atmospheric pressure or a dry vacuum pump with one to three pumping stages that, during use, is coupled upstream of a rough-vacuum pump and the delivery pressure of which during operation is that obtained by the rough-vacuum pump.

The vacuum pump 1 has two rotors 7 configured to turn in the compression chamber(s) of the at least one pumping stage 3a-3e in order to convey a gas that is to be pumped from an intake orifice 4 toward a delivery orifice 5, in the circulation direction of the gases indicated schematically by arrows in figure 1.

The rotors 7 have mating profiles that can be assembled on the shafts 6a, 6b or made in one piece with the shafts 6a, 6b of the rotors 7 (referred to as integral rotors). The rotors 7 are for example of the “Roots” type with two lobes or more or of the “claw” type, or are based on another similar positive-displacement vacuum pump principle.

The vacuum pump 1 has for example at least two pumping stages 3a-3e arranged in series. Each pumping stage 3a-3e of the stator 2 is formed by a compression chamber that receives the two mating rotors 7, the compression chambers comprising a respective inlet and a respective outlet. During rotation, the gas drawn in from the inlet is trapped in the volume generated between the rotors 7 and the stator 2 and then conveyed toward the next stage by the rotors 7. The successive pumping stages 3a-3e are coupled in series one after another by respective inter-stage channels coupling the outlet of the preceding pumping stage to the inlet of the following pumping stage. The inlet of the first pumping stage 3a communicates with the intake orifice 4 of the vacuum pump 1. The outlet of the last pumping stage 3e communicates with the delivery orifice 5. The axial dimensions of the pumping stages are for example the same or decrease with the order of arrangement of the pumping stages 3a-3e, the pumping stage 3a located by the intake orifice 4 having the largest axial dimension.

These vacuum pumps are referred to as “dry” because, during operation, the rotors 7 turn inside the stator 2 without any mechanical contact between one another or with the stator 2, this making it possible not to use oil in the pumping stages 3a-3e.

The rotors 7 are configured to be rotated by at least one motor 9 in a driving part 8 of the vacuum pump 1. The vacuum pump 1 has for example a single motor 9 installed on one of the rotors 7, for example at one end of the vacuum pump 1, such as by the last pumping stage 3e of the vacuum pump 1.

In addition to the motor 9, the driving part 8 may have synchronized gears 10 and at least two rolling-bearing devices 11a, 11b for supporting a respective rotor 7 in the driving part 8.

The driving part 8 has for example multiple pairs of rolling-bearing devices 11a, for example three, that may be located on either side of the motor 9 for the rolling-bearing devices 11a of the drive shaft 6a. There are for example one rolling-bearing device 11a at the shaft end of the driving part 8 and two rolling-bearing devices 11a interposed between the motor 9 and the pumping stage(s) 3a-3e. The rolling-bearing devices 11a of the driven shaft 6b may be arranged symmetrically to the rolling-bearing devices 11a of the drive shaft 6a. The rolling-bearing devices 11a, 11b have ball bearings, for example.

The rolling-bearing devices 11a, 11b may be lubricated by a lubricant inside an oil sump 12 of the driving part 8 of the vacuum pump 1 , the oil sump 12 being interposed between the motor 9 and the pumping stage(s) 3a-3e. The lubricant lubricates the rolling bearings of the rolling-bearing devices 11a, 11b and the synchronized gears 10 of the rotors 7.

The vacuum pump 1 also has a device for sealing against lubricants (not shown) that is interposed between the driving part 8 and the dry pumping part of the pumping stages 3a-3e in which the gases circulate. The sealing device makes it possible to rotate the shafts 6a, 6b in the dry pumping part while limiting the transfer of lubricants.

The vacuum pump 1 also has at least one pair of double bearings 13a, 13b each having at least one permanent-magnet magnetic bearing 14a, 14b and at least one plain bearing 15a, 15b for supporting each of the two rotors 7. The rotors may turn contactlessly during “normal” operation in these bearings 13a, 13b which are arranged by the dry pumping part, that is to say by the pumping stage(s) 3a-3e. The permanent-magnet magnetic bearings 14a, 14b are bearings that support the rotors 7 via magnetic levitation without making contact with the rotating rotors 7. They each have for example a rotor part 17a that is configured to turn in a stator part 17b, the rotor part 17a rotating conjointly with the rotor 7 and bearing the magnets, the rotation of which generates magnetic fields ensuring that it is centered in the stator part 17b (figure 2).

The permanent-magnet magnetic bearings 14a, 14b may each have a nickel/PTFE coating, notably one that has been heat-treated to a temperature below the Curie point. The coating covers the rotor part 17a and/or the stator part 17b.

The plain bearings 15a, 15b are installed with a respective clearance d to the rotor 7 that is less than the operating clearance between the rotors 7 and less than the operating clearance between the rotors 7 and the stator 2. This clearance d, at the radius, is for example greater than 0.1 mm and/or less than 0.5 mm. The clearance between the rotor part 17a and the stator part 17b of the permanent-magnet magnetic bearings 14a, 14b is for example greater than d.

The plain bearings 15a, 15b each have for example a ring that is installed clamped in a bore in the stator 2 or in the rotor 7 and/or a ring that is installed clamped on an axle 23 of the stator 2 and/or on an axle 18 of the rotor 7. The plain bearings 15a, 15b may also be coated or surface-treated at a bore in the stator 2 or in the rotor 7 and/or on an axle 23, 18 of the stator 2 or of the rotor 7 and/or on a ring that is installed clamped in a bore and/or on an axle.

The plain bearings 15a, 15b may each have a silicon carbide (SiC) coating or a nickel/PTFE coating, notably one that has been heat-treated. The coating covers a ring or a bore or an axle, such as the shaft 6a of the rotor 7, or such as the axle 18, 23 of the plug- seal 19 as will be seen below.

The permanent-magnet magnetic bearings 14a, 14b center the rotors 7 in a steady-state regime, that is to say generating only very few loads on the rotors 7 for the pumping of weak and moderate gas flows. The permanent-magnet magnetic bearings 14a, 14b make it possible to limit the phenomena of deflection of the rotors 7 during normal operation. They also limit the vibrations of the rotors 7 during normal operation that are caused by phenomena of resonance or balancing defects. The plain bearings 15a, 15b form a stop for the rotors 7 in the transitional modes, that is to say for the intermittent pumping of significant gas flows, by providing guidance in rotation by sliding only when the centering via the permanent-magnet magnetic bearings 14a, 14b is not sufficient. The plain bearings 15a, 15b thus provide a backup for the permanent-magnet magnetic bearings 14a, 14b. The advantage of this device is that these bearings 13a, 13b are contactless, thus do not have any friction or wear. They do not restrict the gas flows that are pumped and do not require lubrication or dilution gases to protect them, such that the pumping performance is not affected. In addition, these bearings 13a, 13b can be made compatible with the corrosive environments. This solution likewise facilitates the disposition of a vacuum pump 1 installed “vertically”, that is to say with a vertical axial direction, because the absence of lubricant means that there is no risk of oil or grease from the bearings 13a, 13b migrating by gravity toward the dry pumping stages 3a-3e.

According to a first embodiment example shown in figure 1, the permanent-magnet magnetic bearings 14a, 14b and the plain bearings of a pair of double bearings 13a, 13b are located at the shaft end 16a, 16b, the pumping stage(s) 3a-3e being interposed between the motor 9 of the driving part 8 and the shaft ends 16a, 16b. This architecture is what is referred to as a cantilever architecture since there is no contact between the rotors 7 and the bearings 13a, 13b.

As can be seen in the illustrative and non-limiting example of figure 2, the rotor part 17a of the permanent-magnet magnetic bearings 14a, 14b has for example a ring that is fixed on an axle 18 of a plug-seal 19 installed in a central housing 22 of the rotor 7. The stator part 17b has for example an annulus that is fixed to the stator 2.

The plug-seal 19 has for example a main body 20 having a base which has a complementary shape to the central housing 22 of the rotor 7, for example cylindrical, and is surmounted by the axle 18 coaxial to the axis of rotation of the rotor 7. The main body 20 is made of steel, for example. The plug-seal 19 also has a toric seal 21 interposed between the main body 20 and the rotor 7 that is made of fluoroelastomer, for example. The plug-seal 19 is for example fixed to the rotor 7 by screwing.

The plug-seals 19 sealingly close the central housings 22 of the rotors 7 in order to prevent corrosive gases, powders or other substances from entering the central housing 22, which could cause the rotors 7 to corrode or become damaged.

The plain bearings 15a, 15b are installed here in the stator 2 with a clearance d to the axle 18 of the plug-seal 19.

The plain bearings 15a, 15b each have for example a ring that is installed clamped in a bore in the stator 2.

The axle 18 protruding at the shaft end of the rotor 7 may also be made in a single piece with the body of the rotor 7. This variant applies notably in the case of integral rotors 7 without plug-seals.

Figure 3 illustrates a variant embodiment of the vacuum pump 1, for which the permanent-magnet magnetic bearings 14a, 14b and/or the plain bearings 15a, 15b of the pair of double bearings 13a, 13b are arranged inside a respective rotor 7. More precisely, here the vacuum pump 1 has a permanent-magnet magnetic bearing 14a, 14b arranged inside a respective rotor 7 and a plain bearing 15a, 15b arranged inside a respective rotor 7.

In the example of figure 3, in which the pair of double bearings 13a, 13b is located at the shaft end 16a, 16b, the rotor part 17a of the permanent-magnet magnetic bearings 14a, 14b has for example a ring that is fixed in a housing of the plug-seal 19 facing a stator part 17b. The ring is installed on an axle 23 protruding from the stator 2 and is inserted in the housing of the plug-seal 19. In this example, the plug-seal 19 does not have an axle 18 but a housing, coaxial to the axis of rotation of the rotor.

The plain bearings 15a, 15b are installed here in the housing of a respective plug-seal 19, with a clearance d to the axle 23 of the stator 2.

It is also conceivable for the rotor part 17a of the permanent-magnet magnetic bearings 14a, 14b and the plain bearings 15a, 15b to be arranged directly in an axial cavity of the rotor 7 facing the axle 23 protruding from the stator 2. This variant applies notably in the case of integral rotors 7 without plug-seals.

Figure 4 illustrates another embodiment example for which the vacuum pump 1 has a pair of double bearings 13a, 13b located at the shaft end 16a, 16b and a pair of double bearings 13a, 13b surrounding the rotor 7.

In this example, the rotor parts 17a of the permanent-magnet magnetic bearings 14a, 14b are for example formed in the rotor 7. The stator part 17b of the permanent-magnet magnetic bearings 14a, 14b and the rings of the plain bearings 15a, 15b are formed in the stator 2 and respectively surround the rotor parts 17a of the rotors 7.

The vacuum pump 1 may have only one pair of double bearings 13a, 13b surrounding each rotor 7. These may be arranged at the shaft end 16a, 16b as in figure 4 or at other locations along the rotor 7.

Figures 5 and 6 thus show two examples in which the permanent-magnet magnetic bearings 14a, 14b of a pair of double bearings 13a, 13b are arranged in a shaft passage between two successive pumping stages 3a-3e and/or the plain bearings 15a, 15b of a pair of double bearings 13a, 13b are arranged in a shaft passage between two successive pumping stages 3a-3e.

The permanent-magnet magnetic bearing 14a, 14b of a pair of double bearings 13a, 13b may be arranged spaced apart from or next to the plain bearing 15a, 15b.

Provision is made, for example, for a permanent-magnet magnetic bearing 14a, 14b at the shaft end and a plain bearing 15a, 15b at the first shaft passage, that is to say between the first and the second pumping stage 3a, 3b. This arrangement can improve the compactness of the vacuum pump 1. In the illustrative examples of figures 5 and 6, the permanent-magnet magnetic bearings 14a, 14b and the plain bearings 15a, 15b of a pair of double bearings 13a, 13b are arranged in the shaft passages between two respective pumping stages 3a-3e, notably at the first shaft passage between the first and the second pumping stage 3a, 3b (figure 5) and at the second shaft passage between the second and the third pumping stage 3b, 3c (figure 6).

In the case in which the bearings 13a, 13b are located between two respective pumping stages 3a-3e, the shaft ends 16a, 16b may be left free, without any guiding means by the intake orifice 4 (figure 5) in a cantilever architecture, or the vacuum pump 1 may have traditional bearings at the rotor-shaft ends 16a, 16b, such as ball bearings 24a, 24b (figure 6). The ball bearings 24a, 24b are lubricated by grease, for example.