EP2402613B1 - Dry type vacuum pump - Google Patents

Description

The present invention relates to a dry type vacuum pump comprising a lubricant seal device mounted between a lubricated bearing and a pumping stage. The invention applies in particular to a dry type vacuum pump comprising two rotary lobes type "Roots" or "Claw", or type spiral or screw or another similar principle.

Generally, these pumps comprise one or more series pumping stages in which circulates a gas to be pumped between an intake inlet and a discharge outlet. There are known vacuum pumps, rotary lobes also known as "Roots" with two or three lobes or double-billed, also known as "Claw".

The rotary lobe pumps comprise two rotors of 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 rotor to the next stage or after the last stage discharge outlet. The operation is carried out without any mechanical contact between the rotors and the stator, which allows the total absence of oil in the pumping stages.

The rotors are carried by rotary shafts supported by lubricated bearings of a motor drive compartment at the end of the shaft. This motor drive compartment is isolated from the pumping stages by a lubricant sealing device through which the rotating shafts are always rotatable.

In operation, the rotation of the shafts in the lubricated bearings generates a mist of lubricant which, when subjected to pressure variations, may migrate to the pumping stages. However, it is essential that no trace of oil or grease is found in the pump stages for so-called "dry" applications, such as semiconductor substrate manufacturing processes.

Lubricant sealing devices are already known comprising a lubricant baffle and a so-called rubbing annular seal. The lubricant baffle is mounted on the rotating shaft between the lubricated bearings and the friction ring seal, and rotates solidarily with the rotating shaft in operation. The deflector deflects the lubricant by the effect of centrifugal force and returns it to the bottom of the engine drive compartment via a small pipe whose inlet is disposed opposite the end of the lubricant baffle and the outlet opens to the bottom of the compartment motor drive. This device keeps the lubricant confined in the engine drive compartment. The rubbing annular seal forms a second safety in the event that lubricant residues still pass through the lubricant baffle. However, this security measure may not be sufficient. The intensification of the production rates increases the operating temperatures of the vacuum pumps, which can weaken the rubbing ring seal. In addition, the increase in the repetition of pressure variations on either side of the rubbing annular seal, which may be associated with the aggressiveness of lubricant having passed through the lubricant baffle, may cause premature wear of the rubbing ring seal. and require closer maintenance intervals, each intervention involving the shutdown of the semiconductor manufacturing facilities and the vacuum pump, which is very expensive.

Document is also known FR 2 920 207 , a sealing device that uses the effect of centrifugal force to separate the lubricating fluids from the pumped gas.

In addition, the document WO 2008/142437 discloses a dry type vacuum pump whose lubricated bearing includes a first lubricant reservoir and a lubricant gap. The vacuum pump also has a second reservoir for recovering the lubricant projected by the spark gap. This second tank has an outlet connected to a lubricant return channel in the first tank.

A similar vacuum pump is also described in the document DE 197 36 017 .

One of the aims of the present invention is to provide a dry type vacuum pump comprising a lubricant seal device mounted between a lubricated bearing and a pumping stage whose life is increased.

• au moins un étage de pompage,
• au moins un arbre rotatif supporté par un palier lubrifié,
• un éclateur de lubrifiant, monté sur l'arbre rotatif dans le premier réservoir, une extrémité de l'éclateur de lubrifiant baignant dans la première réserve de lubrifiant liquide.

For this purpose, the subject of the invention is a dry type vacuum pump comprising:

• at least one pumping stage,
• at least one rotary shaft supported by a lubricated bearing,
• a lubricant gap, mounted on the rotary shaft in the first reservoir, an end of the lubricant gap bathed in the first supply of liquid lubricant.

The vacuum pump includes a second reservoir having a second supply of liquid lubricant, the second reservoir being separated from the first reservoir by a partition wall having a communication hole communicating the first and second reserves of liquid lubricant. A lubricant return channel having an inlet facing said lubricant baffle, opens into the second volume of the second reservoir, above the second reserve of liquid lubricant.

In operation, the first volume, containing the lubricated bearing and the lubricant gap, has a scrambled internal atmosphere of a mixture of gas and lubricant, created in particular by the rotation of the lubricant gap which allows the lubrication of the bearings of the vacuum pump. This environment is separated by the partition wall, the atmosphere of the second tank, into which the lubricant return channel. The second tank does not contain a lubricant gap, nor any other rotating element in operation during operation of the vacuum pump, has a calm gas atmosphere above the liquid lubricant, without lubricant mist, the liquid and gaseous phases being well separated from each other.

Thus, when lubricant mist is drawn from the lubricated bearing to the pumping stage, the lubricant is deflected by the lubricant baffle into the lubricant return channel by the effect of the centrifugal force until it flows into the liquid lubricant reserve of the second insulated tank. Then, during pressure balancing phases where the pressure of the lubricated bearing is greater than the pressure of the pumping stage, the lubricant dropped to the bottom of the reservoir in the second reserve of lubricant at a level lower than the mouth lubricant return channel, can not go up in it. On the contrary, "dry" gas, that is to say, free of lubricant, located in the second tank above the level of lubricating liquid, will fill the lubricant return channel and restore the balancing of the pressures of both sides of the sealing device. The separation of the second tank thus makes it possible to avoid that the scrambled air of lubricant contained in the oiled environment of the lubricated bearing in operation, enters the lubricant return channel.

Said second reservoir and said lubricant return channel are for example formed in the housing of a motor drive compartment of said vacuum pump.

The conductance of the shaft passage of said partition wall and the conductance at the mouth of the lubricant return channel are calibrated to direct a flow of gas in the lubricant return channel from the second volume to the lubricant baffle. .

With this calibration of the conductances, when the pressure falls in the pumping stage, it falls more rapidly in the first volume comprising the lubricated bearing than in the second volume of the second isolated tank. The second volume then retains a slight overpressure compared to the first volume. The dry gas will then rush through the lubricant return channel to be accelerated to the inlet of the lubricant return channel, thereby forming a dry gas barrier at the lubricant baffle. This promotes an acceleration of the gas flow in the lubricant return channel from the second volume to the lubricant baffle rather than from the first volume to the second volume.

For example, it is provided that the difference between the diameter of the shaft passage of the partition wall and the diameter of the rotary shaft is less than 3 millimeters, preferably of the order of 2 millimeters. And, it is also possible that the dimension of the internal diameter of the mouth of the lubricant return channel is less than 5 millimeters, preferably of the order of 4 millimeters.

An annular groove may be provided in the housing facing a peripheral end of the lubricant baffle, said annular groove communicating with the inlet of said lubricant return channel.

According to one embodiment, the vacuum pump comprises two rotary shafts supported by a respective lubricated bearing. Said lubricant return channel may then comprise a first channel portion associated with a first lubricated bearing, a second channel portion associated with a second lubricated bearing and a channel portion common to said first and second channel portion, to maintain a lubricant balance on the two lubricated bearings.

For example, the lubricant return channel comprises a groove communicating between said first channel portion and said second channel portion and said lubricant return channel comprises a connecting member assembling on said communicating groove and opening with a tube of junction. Said connecting member may comprise a plate closing said communicating groove and an eccentric junction tube projecting perpendicularly from said wafer.

• la figure 1 est une vue en coupe longitudinale d'une partie de pompe à vide,
• la figure 2 est une vue en perspective du stator moteur et du carter d'huile (vu du côté moteur) du compartiment d'entraînement moteur d'une pompe à vide à l'état désassemblé,
• la figure 3 est une vue du recto du carter d'huile de la figure 2 (vu du côté engrenage),
• la figure 4 est une vue similaire du carter d'huile vu du côté engrenage de la figure 3 dans lequel on a disposé un organe de raccordement,
• la figure 5 est une vue en perspective des éléments du palier lubrifié, et
• la figure 6 est une vue schématique des éléments de la figure 5 à l'état assemblé.

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

• the figure 1 is a longitudinal sectional view of a vacuum pump part,
• the figure 2 is a perspective view of the engine stator and the oil sump (as seen from the engine side) of the engine drive compartment of a vacuum pump in the disassembled state,
• the figure 3 is a front view of the oil pan of the figure 2 (seen from the gear side),
• the figure 4 is a similar view of the oil sump seen from the gear side of the figure 3 in which a connecting member has been arranged,
• the figure 5 is a perspective view of the elements of the lubricated bearing, and
• the figure 6 is a schematic view of the elements of the figure 5 in the assembled state.

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

The Figures 1 to 6 illustrate an example embodiment of a dry type vacuum pump comprising two rotary lobe shafts of "Roots" type. Of course, the invention is also applicable to other types of dry type vacuum pumps, such as "Claw" type, or such as spiral or screw type dry vacuum pumps or a another similar principle.

The vacuum pump 1 comprises one or more series pumping stages 2 in which circulates a gas to be pumped from an intake inlet to a discharge outlet (not visible). Rotating shafts 3 (only one is visible on the figure 1 ) extend into the pumping stage 2 by rotary lobe rotors 4, and are driven on the discharge stage side into a motor drive compartment 5 of the vacuum pump 1. The pumping stage 2 is called "dry" because in operation, the rotors 4 rotate inside the housing 6 in opposite directions without any mechanical contact between the rotors 4 and the casing 6 of the vacuum pump 1, which allows the total absence of lubricant.

The vacuum pump runs horizontally as shown on the figure 1 , that is to say that in operation of the vacuum pump, the rotating shafts 3 are substantially parallel to the ground plane.

The rotary shafts 3 are supported at the end of the shaft by two lubricated bearings, for example by grease at the suction stage (not visible) and two lubricated bearings 7a, 7b of the motor drive compartment 5 of the side of the discharge stage, for example lubricated with a liquid lubricant, such as oil. The lubricated bearings 7a, 7b are provided with bearings 9 for guiding and supporting the rotary shafts 3.

The vacuum pump 1 comprises a motor (not shown), housed in the engine drive compartment 5, as well as gears (not shown) mounted on the respective rotary shafts 3 for synchronously driving a driving shaft and a driven shaft. .

The vacuum pump 1 comprises a first reservoir 28 having a first reserve of liquid lubricant 16a. The first reservoir 28 is in communication with the lubricated bearing 7a in a first volume V1 (dashed on the figure 1 ).

The vacuum pump 1 also includes a lubricant gap 11, mounted on the driving rotary shaft 3 in the first reservoir 28, one end of the lubricant gap 11 immersed in the first supply of liquid lubricant 16a. The lubricant gap 11 is for example in the form of a disc mounted coaxially with the rotary shaft 3. In operation, the rotation of the driving shaft 3 causes the rotation of the lubricant gap 11, thereby generating a lubricant mist in the bearings 7a, 7b, which allows the lubrication of the bearings 9 of the vacuum pump 1.

The vacuum pump 1 further comprises a lubricant sealing device for blocking the passage of lubricants from the engine drive compartment 5 to the pump stages 2. The sealing device comprises a lubricant baffle 12 ( figures 1 and 5 ) and an annular seal 13 mounted on the respective rotary shaft 3, the annular seal 13 being mounted between the lubricant baffle 12 and the pumping stage 2 and the lubricant baffle 12 being mounted between the annular seal 13 and the bearing lubricated 7a, 7b.

The annular seal 13 is for example a double-lip rubbing annular seal.

The lubricant baffle 12 rotates integrally with the rotary shaft 3, which allows the lubricant and the particles coming from the lubricated bearing 7a, 7b to be deflected by centrifugation, for example towards an annular groove 14 formed in the body of the engine drive compartment. 5 facing the peripheral end of the lubricant baffle 12 (see more specifically the figures 1 and 5 ). The lubricant deflector 12 is for example in the form of a disc mounted coaxially with the rotary shaft 3.

The vacuum pump 1 comprises a second reservoir 15 formed in the casing 6 of the vacuum pump 1, comprising a second reserve of liquid lubricant 16b, such as oil. The second tank 15 is separated from the first tank 28 by a partition wall 20 having a communication hole 34 communicating the first and the second reserve of liquid lubricant 16a, 16b. A lubricant return channel 17 of the vacuum pump 1 has an inlet 18 facing the lubricant deflector 12, for example in the annular groove 14. The lubricant return channel 17 extends into the body casing of the motor drive compartment 5, under the lubricated bearings 7a, 7b, and opens through a mouth 19, in the second volume V2 of the second reservoir 15, above the second reserve of liquid lubricant 16b.

In operation, the first volume V1, containing the lubricated bearings 7a, 7b and the lubricant gap 11, has a scrambled internal atmosphere of a mixture of gas and lubricant, generally air lubricated with oil, created in particular by the rotation of the lubricant gap 11. This environment is separated by the partition wall 20, the atmosphere of the second volume V2 of the second reservoir 15, into which the lubricant return channel 17 opens. The second reservoir 15 does not contain a lubricant gap or any other rotating element in operation during operation of the pump vacuum 1, has a calm gas atmosphere above the liquid lubricant 16b, without lubricant mist, the liquid and gaseous phases being well separated from one another.

Thus, when lubricant mist is attracted lubricated bearings 7a, 7b to the pumping stage 2, the lubricant is deflected by the lubricant baffle 12 into the annular groove 14, then into the lubricant return channel 17 by the effect of the centrifugal force until it flows into the second reserve of liquid lubricant 16b of the second reservoir 15.

Then, during the pressure balancing phases where the pressure in the lubricated bearings 7a, 7b is greater than the pressure of the pumping stage 2, the liquid lubricant dropped to the bottom of the second reservoir 15 in the second liquid lubricant reservoir 16b, at a level lower than the mouth 19 of the lubricant return channel 17, can not go up therein. In contrast, "dry", i.e., lubricant-free, gas in the second reservoir 15 above the liquid lubricant level will fill the lubricant return channel 17 and restore the balance of the lubricant. pressures on both sides of the sealing device. The separation of the second reservoir 15 thus makes it possible to prevent the scrambled air of lubricant contained in the lubricated environment of the lubricated bearings 7a, 7b during operation from entering the lubricant return channel 17.

For this, and according to the embodiment shown on the Figures 1 to 6 , the housing of the motor drive compartment 5 comprises for example a motor stator 21, an oil sump 22, and an end plate 23 (or support HP (high pressure)) for example cast iron, flocking together and a partition wall separating the second volume V2 (filled with dotted lines on the figure 1 ) of the second tank 15 of the first volume V1 having the first reservoir 28 and the lubricated bearings 7a, 7b.

Better visible on the figure 2 , the partition wall 20 is for example integral with the oil sump 22 which assembles with the motor stator 21. The assembly of the motor stator 21 and the oil sump 22 forms the second volume V2 having at the bottom the second reserve of liquid lubricant 16b. The assembly is conventionally performed with an O-ring 24 and fixing means. The motor stator 21 further comprises means 26 for cooling the motor with a refrigerant fluid. These means are partly concealed by a resin in which an axial housing 27 is formed in the axis of rotation of the drive shaft to accommodate the motor rotor (not shown).

The bottom of the first volume V1 formed by the oil sump 22 and the end flange 23 assembled comprises the first reserve of liquid lubricant 16a, for lubricating the rotary elements of the lubricated bearings 7a, 7b ( figures 3 and 5 ).

On the reverse side of the oil sump 22 is figure 3 , a filling orifice 30 at the top right of the oil sump, communicating with the first volume V1. The filling orifice 30 is closed by a plug 31. There is also a mark at the bottom right of the oil sump 22 for the set point N of the liquid lubricant. This mark corresponds to a transparent portion of the oil pan 22 formed on the wafer (not visible on the figure 3 ) to guide the set point N of the liquid lubricant filling 16a by the user. The oil sump 22 also comprises a purge port 32 which is obstructed and communicates with the bottom 28 and an obstructed tank portion 33 for emptying the vacuum pump 1.

As can be seen on the figure 2 the partition wall 20 has a communication hole 34 below the set point N of the liquid lubricant for leveling the lubricating liquids of the first and second liquid lubricant reserves 16a, 16b. The communication hole 34 is thus located below the mouth 19 of the lubricant fluid return channel 17. This ensures the level of liquid lubricant of the second reserve 16b at the same time as the level of liquid lubricant. the first reserve 16a by the filling means, purging, draining the oil sump 22.

Furthermore, the conductance of the shaft passage 35 of the partition wall 20 and the conductance at the mouth 19 of the lubricant return channel 17 are calibrated to direct a flow of gas in the lubricant return channel 17 from the second volume V2 to the lubricant baffle 12.

With this calibration of the conductances, when the pressure is lowered in the pumping stage 2, it falls more rapidly in the first volume V1 comprising the lubricated bearings 7a, 7b, than in the second volume V2 of the second reservoir 15. The second volume V2 then retains a slight overpressure with respect to the first volume V1 of about 2 bar. The dry gas will then rush through the lubricant return channel 17, and be accelerated to the inlet 18 of the lubricant return channel 17, forming a dry gas barrier at the lubricant baffle 12 This promotes an acceleration of the gas flow in the lubricant return channel 17 since the second volume V2 to the lubricant deflector 12 rather than from the first volume V1 to the second volume V2.

The conductance between the first V1 and the second volume V2 is defined by the space provided between the driving shaft 3 and the shaft passage 35 of the partition wall 20. For example, it is expected that the difference between the diameter of the shaft passage 35 and the diameter of the rotary shaft 3 is less than 3 millimeters, preferably of the order of 2 millimeters. And, it is also possible that the dimension of the internal diameter of the mouth 19 of the lubricant return channel 17 is less than 5 millimeters, preferably of the order of 4 millimeters.

Thus, the small space at the shaft passage 35 promotes an overpressure in the second volume V2 with respect to the first volume V1 and the low conductance of the lubricant return channel 17 promotes the acceleration of the dry gas in the return channel lubricating fluid 17, which allows the formation of the gas barrier at the lubricant baffle 12.

In addition, provision can be made for the lubricant return channel 17 to comprise a first channel portion 17a associated with the first lubricated bearing 7a, a second channel portion 17b associated with the second lubricated bearing 7b and a common channel portion 17c with the first and second channel portion 17a, 17b. Each channel portion 17a, and 17b has an inlet located in the annular groove 14 facing the lubricant baffle 12 associated with the lubricated bearing 7a, 7b respective. The lubricant fluid return channel 17 thus communicates between the first and second lubricated bearings 7a, 7b in order to maintain a lubricant balance on the two lubricated bearings 7a, 7b.

For this, and as visible on the figure 5 , the lubricant return channel 17 has a communicating groove 36 between the first channel portion 17a and the second channel portion 17b. The lubricant return channel 17 further comprises a connecting member 37 assembled on the communicating groove 36 and opening through a connecting tube 38. Once the connecting member 37 assembled between the oil sump 22 and the end flange 23, the connecting tube 38 opens out of the partition wall 20 in the second volume V2 through the mouth 19.

The connecting member 37 comprises for example a wafer 39 closing the communicating groove 36 and a junction tube 38 eccentric from the middle of the wafer 39. protruding perpendicularly from the wafer 39. The connecting tube 38 is eccentric to allow rotation of the rotating elements, such as the lubricant gap 11 of the lubricated bearing 7a of the driving shaft 3.

This limits the migration of the lubricant to the sealing device through the lubricant return channel 17 and by the lubricated bearings 7a, 7b, by ensuring that the lubricant does not short-circuit the lubricated bearings 7a, 7b of the compartment. 5 to drive directly to the annular seal 13 without being treated by the lubricant baffle 12, which increases the life of the annular seal 13.

Although there has been described a sealing device and liquid lubricant reservoirs arranged on the discharge side of the vacuum pump, the sealing device and the liquid lubricant reservoirs can be arranged on the suction side as well. end of the lower pressure stage, replacing lubrication with grease.

Claims (8)

1. Dry-type vacuum pump comprising:

   - at least one pumping stage (2),

   - at least one rotary shaft (3) supported by a lubricated support bearing (7a, 7b)

   - at least one ring seal (13) mounted on the rotary shaft (3),

   - a first reservoir (28) containing a first reserve of liquid lubricant (16a), said first reservoir (28) being in communication with the lubricated support bearing (7a, 7b) in a first volume (V1),

   - a lubricant splashing unit, mounted on the rotary shaft (3) in the first reservoir (28), one end of the lubricant splashing unit being bathed in the first reserve of liquid lubricant (16a),

   - a second reservoir (15) comprising a second reserve of liquid lubricant (16b), and

   - a lubricant return channel (17) opens into the second volume (V2) of the second reservoir (15),

   - at least one lubricant deflector (12) mounted on the rotary shaft (3), the ring seal (13) being mounted between the lubricant deflector (12) and the pumping stage (2), the lubricant deflector (12) being mounted between the lubricated support bearing (7a, 7b) and the ring seal (13), the second reservoir (15) being separated from the first reservoir (28) by a separation wall (20) having a communication aperture (34) that puts the first and the second reserves of liquid lubricant (16a, 16b) into communication

   - characterized in that said lubricant return channel (17) having one inlet (18) situated so as to be facing said lubricant deflector (12) opens above the second reserve of liquid lubricant (16b) of the second volume (V2) of the second reservoir (15).
2. Vacuum pump according to claim 1, wherein the second reservoir (15) and said lubricant return channel (17) are made in the casing (6) of a motor drive compartment (5) of said vacuum pump (1).
3. Vacuum pump according to one of the previous claims, wherein the size of the internal diameter of the opening (19) of the lubricant return channel (17) is smaller than 5 millimeters.
4. Vacuum pump according to one of the previous claims, wherein the gap between the diameter of the shaft passage (35) in the separation wall (20) and the diameter of the rotary shaft (3) is smaller than three millimeters.
5. Vacuum pump according to one of claims 1 to 4, wherein an annular groove (14) is made in the casing (6) in front of a peripheral end of the lubricant deflector (12) and communicates with the inlet (18) of said lubricant return channel (17).
6. Vacuum pump according to one of claims 1 to 5, comprising two rotary shafts (3), said rotary shafts (3) being each supported by a respective lubricated support bearing (7a, 7b) and wherein said lubricant return channel (17) comprises a first channel portion (17a) associated with a first lubricated support bearing (7a), a second channel portion (17b) associated with a second lubricant support bearing (7b) and a channel portion common (17c) to said first and second channel portions (17a, 17b).
7. Vacuum pump according to claim 6, wherein the lubricant return channel (17) has a communicating groove (36) between said first channel portion (17a) and said second channel portion (17b) and said lubricant return channel (17) comprises a connection element (37) that gets joined with said communicating groove (36) and opens into a junction tube (38).
8. Vacuum pump according to claim 7, wherein said connection element (37) comprises a plate (39) closing said communicating groove (36) and an off-centered junction tube (38) projecting perpendicularly from said plate (39).

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