EP0626516B1 - Lubricant-free vacuum pump arrangement - Google Patents

Description

The invention relates to a lubricant-free vacuum pump device with a turbo-molecular pump, which is followed by a hybrid pump in the flow path.

Double piston pumps are already known, in which the two pistons are connected to one another via a piston rod and are driven by a linear drive (see brochure "LABOVAC linear diaphragm pumps and piston pumps" from SASKIA, Hochvakuum-und Labortechnik GmbH, O-6300 Ilmenau). It is also mentioned there that hermetic sealing of the pistons can be achieved in special models by installing a separating membrane. However, piston pumps of this type with or without a separating membrane have several disadvantages: With the piston, which causes it to be pushed out, for example outdoors, condensate can form if the fluid handled is suitably humid. This leads to increased wear and leaks in the piston seals. This means a drop in performance of the entire pump unit.
A piston pump is also already known, in which the piston-cylinder chamber is closed off from the crank chamber with a sealing membrane. This prevents, for example, atmospheric air from getting past the piston rings or a lip seal of the piston can and thereby the vacuum generated in the piston pump deteriorates somewhat. The disadvantage is also prevented that the actual delivery medium itself is contaminated by air which may or may not be contaminated, coming from the crank chamber. It should also be noted that you cannot achieve tightness in the long run when the crankshaft passes and that lubrication is necessary in the crankcase due to the mechanical movements. This also contributes to undesirable contamination of the actual delivery medium if the piston-cylinder chamber is not sealed off from the crank chamber.
The "LABOVAC D65 - D1600" brochure from SASKIA Hochvakuum-und Labortechnik GmbH, O-6300 Ilmenau, has already made known the suggestion to use a linearly working double piston pump with two sliding pistons as described above as a backing pump for one Use turbo molecular pump. However, this also has several disadvantages. On the one hand, the previously known double piston pump with linear drive has the already mentioned disadvantage of the formation of condensate. On the other hand, it does not have a mass balance with regard to the piston movements or a complex, additional mass balance must be created. When such a known double linear piston pump works together with a turbo-molecular pump, the usual vibrations lead to undesirable movements in the turbo-molecular pump, which is usually combined with the double-piston pump in a single frame or even designed as a common pump block. However, the turbo molecular pump is extremely sensitive to vibrations. As is known, turbomolecular pumps of a type known per se have speeds of, for example, 30,000 rpm, but also much higher speeds. The rotors of such turbo-molecular pumps are therefore usually also stored in magnetic bearings and are accordingly sensitive to shocks.

From GB 2 126 665 a piston pump is already known, the piston of which is blocked off from the crank chamber by means of a sealing sleeve which bears against the pump cylinder. In order to be able to separate the parts that come into contact with the pumped medium absolutely leak-free from the mechanical pump drive area, a sealing membrane is provided in the known piston pump, which is operated as a dry-running pump, which is arranged between the sealing sleeve and the crank chamber. The intermediate space between the sealing sleeve and the sealing membrane is connected to a suction line, which discharges the pumping medium that passes through the sealing sleeve into the intermediate space and conveys it back to the suction side of the pump. This known piston pump is primarily intended as a separate feed pump.

In contrast, one knows from FR-21 75 507 a vacuum pump, which is designed as a double-acting diaphragm pump and has two oppositely symmetrical diaphragms. In order to promote high vacuum formation, the pumping chambers of the previously known vacuum pump are connected in series. However, due to the reduced Schöpf volume of such diaphragm pumps, the performance of the known vacuum pump is still in need of improvement.

A pump device is known from the brochure "Vacuum chemistry hybrid pump RC 5" from VACUUBRAND, D-97877 Wertheim, in which a diaphragm pump is connected downstream of a two-stage rotary lobe pump. While the rotary lobe pump sealed by an oil in an oil reservoir forms a first pumping stage, the diaphragm pump is connected downstream of this as an oil-free, condensation and corrosion-insensitive second pumping stage.

However, by using the oil-sealed rotary lobe pump, it cannot be completely ruled out that at least small amounts of the lubricant are carried away and carried outside, where they lead to contamination in the work area, which may possibly have to be avoided. The area of application of the known vacuum pump device is therefore limited.

It is therefore the task of creating a versatile and particularly powerful vacuum pump device of the type mentioned at the beginning.

The solution to this problem according to the invention consists in the features of claim 1 in the vacuum pump device of the type mentioned at the outset.

In the vacuum pump device according to the invention, the turbomolecular pump is followed by a dual displacement pump designed as a hybrid pump in the flow path. This gives a relatively large suction volume without having to accept the disadvantages of two piston pumps connected in series. In particular, the harmful effects of a possible formation of condensate in the diaphragm pump expelling the pumped medium are largely avoided, since the diaphragm pump is practically insensitive to the formation of condensate. On the other hand, with the aid of the piston pump arranged in the way of the delivery medium between the turbomolecular pump and the diaphragm pump, a relatively large delivery volume can be achieved and the piston pump can be designed with respect to its volume so that the piston pump volume compressed by it matches the intake volume of the diaphragm pump. This combination of piston pump and diaphragm pump can avoid the disadvantage that can occur when using two diaphragm pumps:

The diaphragm pump directly connected to the turbomolecular pump must because of the different suction volumes of the two pumps connected in series have relatively large dimensions, which leads to large masses to be moved and also has certain disadvantages with regard to the membrane formation in the membrane pump adjacent to the turbomolecular pump. In contrast, optimal conditions are achieved with the hybrid pump provided in the vacuum pump device according to the invention, that is to say when a piston pump is combined with a membrane pump connected downstream of this piston pump. Above certain performance limits, backing pumps with two diaphragms - as I said - are no longer optimally efficient. In contrast, tests have shown that backing pumps, which are to work together with turbo-molecular pumps, are of a magnitude where two diaphragm pumps connected in series can no longer be optimally designed. The vacuum pump device according to the invention is thus characterized by its high performance even with a compact design.

The reciprocating piston pump having a pendulum piston, in conjunction with the associated sealing membrane, ensures that the delivery paths for the medium do not come into contact with any lubricated parts. For example, no lubricated parts are required in the area of the piston pump close to the pump, because a piston pin is avoided with the pendulum piston. The double displacement pump downstream of the turbo-molecular pump in the vacuum pump device according to the invention therefore allows absolute freedom from lubricants and the like. This is particularly advantageous if the vacuum pump device according to the invention is used, for example, in the field of electronics component production. This is where absolute cleanliness is important, for example when chips are vapor-deposited. The production process which is to be kept under vacuum here by the vacuum pump device according to the invention usually takes place under the influence of protective gas. Even very minor impurities have considerable disadvantages. Such contamination can be largely avoided by the double-displacement pump connected downstream of the turbo-molecular pump. The invention Vacuum pump equipment is therefore, for example, also in the field of electronics component manufacture and is accordingly versatile.

Since the reciprocating pump and the diaphragm pump are driven by a common crankshaft, a mass compensation of the parts moved back and forth is possible in the vacuum pump device according to the invention, which is particularly valuable with the turbo-molecular pump sensitive to vibrations and a high performance of the vacuum according to the invention -Pump device benefits.

The sealing membrane provided in the vacuum pump device according to the invention not only counteracts any contamination of the conveying paths by any lubricated parts; rather, the space provided between the pendulum piston or its associated sealing collar on the one hand and the sealing membrane on the other hand, especially when the vacuum pump device according to the invention starts up, can be evacuated via the provided suction line to such an extent that the suction process is accelerated and the operating vacuum is reached more quickly. The vacuum pump device consisting of the turbomolecular pump and the downstream double displacement pump is thus ready for operation faster when starting, which further increases the performance of this pump device according to the invention.

Additional developments of the invention are listed in further subclaims. The features of claims 3 and 4 give particularly favorable conditions with regard to the suction capacity of the double displacement pump provided in the vacuum pump device according to the invention.

The measures of claim 5 have the advantage that a minimal dead space is achieved.

Due to the combination of the turbo-molecular pump with a piston pump sealed against the crank chamber and with a diaphragm pump connected thereafter, the piston pump and the diaphragm pump volume can be designed accordingly, taking into account the needs of the turbomolecular pump, and optimal conditions of such a one Create overall device.

Tests have shown that the configuration according to claim 7 is particularly advantageous and also simple in construction.

The measures of claim 8 simplify mass balancing of the parts moved back and forth, which favors the smooth running of the double displacement pump provided in the vacuum pump device according to the invention. You can design the pump device taking into account all the masses to be moved and achieve a largely quiet running, which is particularly important if the turbo-molecular pump and the double displacement pump are accommodated in a common frame or even in a common housing.

Fig.1

eine im wesentlichen im Schnitt gehaltene Seitenansicht einer Zweifach-Verdrängerpumpe, die mit einer Turbo-Molekularpumpe in Verbindung steht, und

Fig.2

ein schematisiertes Diagramm, in dem für zwei unterschiedliche Pumpentypen deren Saugvermögen über den Ansaugdruck aufgetragen ist.

Further features of the invention result from the following description of an exemplary embodiment in conjunction with the claims and the drawing. The individual features can be implemented individually or in groups in one embodiment of the invention. It shows, more schematically:

Fig. 1

an essentially sectional side view of a double positive displacement pump, which is connected to a turbo-molecular pump, and

Fig. 2

a schematic diagram in which the pumping speed is plotted against the suction pressure for two different pump types.

1 shows a double positive displacement pump 1 below a turbo-molecular pump 2 connected to it. It is part of the invention that the double positive displacement pump 1 is designed as a hybrid pump 3, the piston 4 on the medium inlet side being a comparatively large piston pump 5 Has displacement 6, the piston-cylinder chamber 7 is sealed off from the crank chamber 8 of the hybrid pump 3 by means of a sealing membrane 9. It is also part of the invention that, in the hybrid pump 3, the piston pump 5 is followed by a diaphragm pump 10, the displacement 11 of which is noticeably smaller than that of the piston pump 5. According to a particularly advantageous embodiment, the displacements 6 and 11 of the hybrid pump 3 are at least approximately matched to one another in such a way that the extension volume of the piston pump 5 is equal to the suction volume of the diaphragm pump 10 at a certain operating vacuum. If necessary, intake and extension volumes can also be coordinated for an operating area in the sense of optimization.

In the vacuum pump device shown in FIGS. 1 and 2, the double displacement pump 1 is the turbo-molecular pump

2 downstream in the flow path such that the intake port 12 of the piston pump 5 is connected to the outlet 15 of the turbo-molecular pump 2. It is expedient if the turbomolecular pump 2 and the double displacement pump 1 are connected to one another with respect to their housings 16 and 17, for example by means of a frame 31 only indicated schematically in FIG. The turbo molecular pump 2 and the double displacement pump 1 can of course also be accommodated in a common housing (not shown). Both pumps 5 and 10 of the double displacement pump 1 are provided with pendulum pistons 18 and 19, and in the piston pump 5 of the double displacement pump 1 a disk-like sealing sleeve 20 is attached to the piston head 21 thereof. This sealing sleeve 20 seals the piston head 21 against the piston-cylinder space 7 of the piston pump 5. Because the double positive displacement pump 1 on the one hand has a piston pump 5 and on the other hand has a diaphragm pump 10, one speaks of a “hybrid pump 3”. The diaphragm pump 10 of this hybrid pump 3 has a shaped membrane 22, the upper side 24 of the adjacent pump chamber wall 23 which is adapted to it, so that there is only a practically minimal dead space in the dead center position (lower in FIG. 1).

The piston pump 5 and the diaphragm pump 10 of the hybrid pump 3 are driven via a common crankshaft 26. The two pumps 5 and 10 are arranged opposite one another in the direction of the longitudinal axis L of the pump. Because of this and because of the common drive via the crankshaft 26, mass balancing with regard to the pumping movement of the piston pump 5 and the diaphragm pump 10 is readily possible. This results in a particularly smooth running of the hybrid pump if a mass balance of all moving masses is provided with respect to the piston and diaphragm pumps 5 and 10.

In FIG. 1, one can also see a suction line 33, which extends from the connecting line 32, which leads from the turbomolecular pump 2 of the piston pump suction point 12, and from there to the intermediate space 30 which, on the one hand, extends between the piston head 21 of the piston pump 5 and the associated sealing membrane 9 is located. The intermediate space 30 is also evacuated by this suction line 33, in particular when the hybrid pump 3 starts up. Leakages on the associated sealing collar 20 are not significant and do not have a long-term effect, so that the piston pump 5 brings about a corresponding reduction in pressure soon after the hybrid pump 3 starts up with the desired large suction volume. From the outlet port 34, the pumping medium indicated in FIG. 1 for pump 1 by points 35 is passed via the pump line 36 to the inlet 37 of the diaphragm pump 10. This diaphragm pump then ejects the medium conveyed by the hybrid pump 3 or the combined turbo-molecular and hybrid pump 2, 3, for example into the open, at its outlet connection 38.

The mode of operation of the combined turbo-molecular and hybrid pump 2, 3 can be explained particularly well during the start-up process. This is done as follows:

In the housing 16 of the turbomolecular pump 2 there is an impeller 40, which is connected to a motor M, which is only indicated schematically, and paddle wheels 41 of known construction having. In the housing 16 there are, adjacent to the impeller wheels 41, guide disks 42 or the like. The impeller 40 of the turbomolecular pump runs at, for example, 30,000 revolutions per minute, but possibly also much faster, for example at around 60,000 revolutions per minute. Because of this high rotational speed, it is usually stored in magnetic bearings 43, one of which is drawn on the right side of FIG. 44 is a space, container or the like which is to be evacuated by the turbo-molecular and hybrid pump 2, 3. This can be, for example, an area in which absolute cleanliness is important, for example the area of a production process in which sensitive work processes are carried out under the influence of vacuum and / or protective gas, for example vapor deposition on chips. A turbomolecular pump inlet 45 leads from space 44 into this turbomolecular pump 2. When such a turbomolecular pump 2, known per se, starts up, it initially does little in the start-up stage. Its pressure-side outlet 15 leads via the connecting line 32 into the displacement 6 of the piston pump 5. The piston pump 5, as well as the diaphragm pump 10, on the inlet and outlet sides of the medium is equipped with known vacuum valves 27, which are only indicated schematically in FIG. In a conventional manner, vacuum is generated by the movement of the pendulum piston 18 in the displacement 6. Via the outlet valve 27 of the displacement 6, the medium, as described above, which is usually air, but also other gases, is then conducted via the pump line 36 to the inlet port 37 of the diaphragm pump 10. This sucks in gas, air or the like medium in the usual working cycle and pushes it out at its outlet connection 38. The sealing membrane 9 attached to the rear of the pendulum piston 18 of the piston pump 5 prevents impurities from penetrating into the medium area. The suction line 33 leads from the intermediate space 30 to the connecting line 32, which connects the turbomolecular pump to the piston pump 5. Any leaks on the sealing collar 20 of the pendulum piston 5 and thus the medium that has penetrated into the intermediate space 30 can be eliminated with the aid of this suction line again before the suction valve 27 of the piston pump 5 are performed. This speeds up the suction process in order to achieve an operating vacuum.

The turbomolecular pump 2 only begins to be practically effective when a certain minimum vacuum has been reached by the hydride pump 3, which practically represents a backing pump for the turbomolecular pump 2. Then it works in combination with the hybrid pump 3 as follows: Due to the high speed of the impeller wheels 41 of the turbomolecular pump 2, molecules in their housing 16 receive correspondingly high impulses and are moved from the turbomolecular pump inlet 45 to their outlet 15 , which leads to the desired increase in the vacuum known per se in turbomolecular pumps. To a certain extent, the molecules are mechanically transported by these impulses in the direction of the outlet 15 of the turbomolecular pump, which results in an increase in the vacuum.

Significant advantages of the invention are that the double positive displacement pump 1 serving as the backing pump for the turbo-molecular pump 2 is designed as a hybrid pump 3, the piston pump 5 of which, in the sense of the medium flow, adjacent to the turbo-molecular pump 2 produces a relatively large suction volume and is nevertheless protected against contamination and leaks, but works in combination with the outlet-side diaphragm pump 10, which in turn is insensitive to condensate.

The differences in the suction capacity of a normal two-stage diaphragm pump compared to a two-stage hybrid pump 3 can still be clearly seen from FIG. 2. Curve 46 shows the suction capacity, plotted against the suction pressure, for a normal, two-stage diaphragm pump. Curve 47 shows the course of the pumping speed of a two-stage hybrid pump 3 with a piston pump on the suction side and a diaphragm pump 5 and 10 on the outlet side. In a relatively simple manner, the pumping speed is increased considerably under the same conditions Conditions (suction pressure) if a two-stage hybrid pump with a larger-volume displacement 6 on the inlet side is connected in the manner described above to a diaphragm pump 10, the disadvantages of the piston pump 5 being avoided by the sealing diaphragm 9.

All of the features described above and / or listed in the claims can be essential to the invention alone or in any combination.

Claims (8)

1. A lubricant-free vacuum pump arrangement with a turbomolecular pump (2) downstream of which (2) in the flow route is a two-stage positive displacement pump (1) in the form of a hybrid pump (3), said two-stage positive displacement pump (1) having on the medium-entry side a reciprocating pump (5) which has a pendulum piston (18) and downstream of which (5) is a diaphragm pump (10) expelling the pumping medium, which reciprocating pump and diaphragm pump (5, 10) are driven by a common crankshaft (26), whereby the piston-cylinder space (7) is sealed off with respect to the crank area (8) by means of a sealing diaphragm (9) and whereby the intermediate space (30) provided between the piston (18) on the one hand and the sealing diaphragm (30) on the other hand is connected to an extraction line (33).
2. A vacuum pump arrangement as claimed in claim 1, characterized in that in the direction of delivery flow the extraction line (33) ends ahead of a suction valve (27) of the reciprocating pump (5).
3. A vacuum pump arrangement as claimed in claim 1 or claim 2, characterized in that the displacement area (11) of the diaphragm pump (10) is appreciably smaller in comparison to that of the reciprocating pump (5).
4. A vacuum pump arrangement as claimed in any one of claims 1 to 3, characterized in that the displacement areas (6, 11) of the two positive displacement pumps (5, 10) are approximately matched to each other in such a way that, at a given operating vacuum, the reciprocating pump (5) has an expulsion volume which is at least approximately equal to the suction volume of the diaphragm pump (10).
5. A vacuum pump arrangement as claimed in any one of claims 1 to 4, characterized in that the diaphragm pump (10) has a shaped diaphragm (22) whose front side (24) is adapted to the adjacent pumping area wall (23) of the diaphragm pump (10).
6. A vacuum pump arrangement as claimed in any one of claims 1 to 5, characterized in that the intake port (12) of the reciprocating pump (5) is connected with the outlet (15) of the turbomolecular pump (2), that the turbomolecular pump (2) and the two positive displacement pumps (5, 10) are interconnected with respect to their housings (16, 17), and that a mass balance of all moved masses is provided, at least nearly, preferably with respect to the reciprocating pump and diaphragm pump (5, 10).
7. A vacuum pump arrangement as claimed in any one of claims 1 to 6, characterized in that the reciprocating pump (5) has a piston head with a disk-like sealing collar which, upon insertion into the piston-cylinder space (7), takes on a U-shaped cross section.
8. A vacuum pump arrangement as claimed in any one of claims 1 to 7, characterized in that the reciprocating pump (5) and the diaphragm pump (10) are arranged in the direction of a common pump longitudinal axis (L).

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