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(11) | EP 0 445 855 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Improved turbomolecular pump Verbesserte Turbomolekularpumpe Pompe turbomoléculaire améliorée |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention refers to an improved turbomolecular pump, especially to a turbomolecular pump of increased compression ratio, capable of extending the operating range towards higher pressures. Conventional turbomolecular pumps usually have operating ranges from about 10̸⁻⁷ to 10̸⁻¹ or 1 Pascal, i.e. they cannot exhaust directly to atmosphere. This means that they need to be teamed up to a forepump which produces the necessary fore vacuum and discharges the pumped gases at atmospheric pressure. However, contamination of the turbomolecular pump with lubrication oil of the forepump may occur, which prevents pumping at the lower operating range. This may be avoided by maintenance at short intervals, which raises the costs of operation, in addition to a higher initial cost of the vacuum system. Moreover, the combination of a turbomolecular pump with a forepump is cumbersome, which is a disadvantage in most applications.
[0002] So-called hybrid turbomolecular pumps have also been developed to reduce the necessity of these backing pumps. U.S. Patent No. 4,732,529, U.S. Patent No. 4,826,393 and U.S.Patent No. 4,797,0̸68 disclose turbomolecular pumps including a compression ratio raising section consisting of rotors formed with spiral grooves, or screw rotors, which guide gas from the high vacuum section to a simpler exhaustion system, e.g. to a membrane pump. Although such hybrid turbomolecular pumps do not need complex exhaustion systems consisting of a number of auxiliary vacuum pumps, they still require a forepump, because they are incapable of discharging gases at atmospheric pressure. A new type of roughing pump which can reach a low ultimate pressure (3·10̸⁻² Pascal) has also been developed. As reported in J.Vac.Sci.Technol.,A, Vol.6,No.4, 2518-2521, Jul/Aug 1988 , this pump is a turbo vacuum roughing pump comprising radial flow pumping stages consisting of impellers rotating into channels with grooves which direct radially the flow of the pumped gases, and a peripheral flow pumping stage at the exhaust side, which raises the pressure so that the pump can discharge at atmospheric pressure. However, this pump is only a roughing pump that can by no way replace a turbomolecular pump, the ultimate pressure of which is lower of several orders of magnitudes (10̸⁻⁷ Pascal) than the ultimate pressure of this roughing pump (10̸⁻² Pascal).
[0003] A first object of the present invention is to provide a turbomolecular pump with a high compression ratio. Another object of the present invention is to provide a turbomolecolar pump which is capable of discharging gases at atmospheric pressure, without being combined with forepumps.
[0004] A further object of the present invention is to provide a turbomolecular pump which is relatively not cumbersome in comparison with previous vacuum systems having similar operating range.
[0005] For attaining the foregoing objects, an improved turbomolecular pump according to the invention comprises at the suction side a plurality of pumping stages consisting of alternately arranged rotors and stators provided with inclined blades, the rotor blades being inclined in the inverse direction to the stator blades, for pumping gases along an axial flow through said pumping stages and comprising at least one pumping stage at the exhaust side consisting of a rotor disk and a coplanar stator, characterized in that a unique free annular channel is defined between the lateral surface or the rotor and the lateral inner surface of the stator, the stator further comprising an upper plate and a lower plate respectively provided with suction port and discharge port, said unique free annular channel being in communication with said suction port and said discharge port for pumping gases with a flow tangential to the lateral surface of said rotor from said suction port to said discharge port, said channel being delimited at its ends by a baffle arranged between said discharge port and said suction port.
[0006] According to another feature of the invention, to enhance the pumping effect in the viscous flow range, a tangential flow pumping stage may be added in which the rotor consists of a disk provided with blades. Illustrative embodiments of the invention are hereinafter described in conjunction with the drawings, where:
- FIG.1 is a schematic view in axial section of a part of a turbomolecular pump according to the invention;
- FIG.2 is a perspective view of part of the pump of FIG.1, with a partially broken first embodiment of a tangential flow pumping stage;
- FIG.3 is a partially broken plane view of a pumping stage of FIG.2; and
- FIG.4 is a perspective view of of a partially broken second embodiment of a tangential flow pumping stage.
[0007] With reference to FIG.1, a turbomolecular pump according to the invention comprises a certain number of axial flow pumping stages, each consisting of a rotor 1 or 1a, and of a stator 2 or 2a, contained in a cylindrical pump body 3, as known in the art. The pumping stage consisting of rotor 1a and stator 2a is also shown in FIG. 2. Each rotor consists of a disk 5 mounted on a rotatable shaft 6, and carrying at its periphery an array of radially protruding inclined blades 7, 7a, 7b. Each stator consists of a similar disk with a central hole for the shaft 6 of the rotors. Each stator is fixed to the pump body 3, and consists of a disk 8 provided with blades 9, 9a, 9b, which are inclined in a direction that is inverse to the direction of the rotor blades 7, 7a, 7b.
[0008] Gases coming from the suction side, not shown but indicated by arrow A, are pumped by the described stages along directions parallel to the axis of the cylindrical body 3, i.e. an axial flow of gases is produced through the alternate rotors and stators, as indicated by the arrow B of Fig. 1.
[0009] According to the invention, one or more pumping stages of different conception are added downstream the axial flow pumping stages.
[0010] In FIG.1 two of such pumping stages are shown, indicated globally with the reference numerals 10̸ and 30̸.
[0011] Each of the pumping stage 10̸ and 30̸ still comprises a rotor mounted on shaft 6, and a stator fixed to the the pump body 3. Constructional details of these pumping stages are also illustrated in FIGURES 2 to 4.
[0012] With reference to FIGURES 1, 2 and 3, pumping stage 10̸ comprises a rotor consisting of a plane disk 12 secured to shaft 6. Rotor 12 is encompassed by a substantially coplanar stator having the shape of a ring 13 spaced apart from the rotor disk 12, so that a free annular channel 14 is defined between rotor and stator. A baffle 15 closes channel 14 between a suction port 17 and a discharge port 18, provided in an upper closure plate 21 and in a lower closure plate 23, respectively. Closure plates 21 and 23 are joined together by suitable means, e.g. by connection of downwardly extending edge 22 of plate 21, so as to form a closed casing containing the pumping stage. Central holes are provided in both plate 21 and 23, for the passage of the shaft 6. The baffle 15 may be a radial projection of the stator 13, as shown in FIGURES 2 and 3, or a separate element tightly secured to the stator ring 13. The operation of the pumping stage above described is the following.
[0013] Gases pumped by the axial flow pumping stages come to suction hole 17, as indicated by arrow D in FIGURES 1 and 2, and enter into channel 14. Here, the gas molecules strike the rotating disk 12 and keep a speed with a component tangential to the disk 12, as indicated by arrow E. By this process the molecules are transferred within free channel 14 from the suction port 17 to the discharge port 18 according to a tangential flow, and leave channel 14 through discharge port 18, as indicated by arrow F. The flow of gases that is produced in the free channel 14 is referred to as "tangential flow" because it parallel to the direction of the velocity of the rotor, which is a tangent to the rotor.
[0014] This tangential flow pumping stage is effective in a molecular or transient flow pressure range, and permits to raise the outlet pressure from about 1 Pascal, that is the usual outlet pressure of conventional turbomolecular pumps, to 10̸³ Pascal and even more. At higher pressure ranges, i.e. in the viscous flow range, pumping stages with plane rotor disks are no more effective. It has been found that a different rotor design, such as shown in detail in FIG. 4, can produce a further raise of the outlet pressure, up to the atmospheric pressure.
[0015] With reference also to FIG.1, the pumping stage effective in the viscous flow range is indicated with 30̸. Pumping stage 30̸ is arranged in series, downstream pumping stage 10̸. As pumping stage 10̸, it comprises a closed casing consisting of an upper plate 31 with a downwardly extending edge 32 connected to a lower plate 33. Shaft 6 extends axially in the casing, and carries a rotor disk 35 with peripheral vanes such as 37, 37a, 37b, lying on planes perpendicular to the plane of disk 35. A coplanar stator ring 36 encompasses rotor 35 but is spaced apart from it, so that a free annular channel 38 is defined between the periphery of the vanes of the rotor and the stator. A baffle 39 obstructs the free channel 38 between a suction port 40̸ made in upper plate 30̸ and a discharge port 41 made in lower plate 33.
[0016] As shown in FIG. 1, gases discharged from port 18 of pumping stage 10̸ come to the suction port 40̸ of the pumping stage 30̸, as indicated by arrow G, and enter into channel 38 between rotor and stator. Here, gases molecules get kinetic energy by striking the rotor, a circular flow with a tangential speed component is produced in free channel 38, and gases are pumped from suction port 40̸ to discharge port 41. In this last stage the pressure is raised to about 10̸⁵ Pascal, so that the pump can exhaust directly to the atmosphere through port 43 in the pump body 3, as indicated by arrow I in FIG. 1.
[0017] The peripheral velocity of the rotor of this turbomolecular pump, including both axial and tangential stages, is usually not less than 250̸ m/s, preferably from 350̸ to 40̸0̸ m/s. For example, in a small pump equipped with a rotor having a diameter of 10̸0̸ mm (0̸.0̸1 m), the angular velocity of the rotor is of 50̸,0̸0̸0̸ r.p.m. to obtain a peripheral velocity of 260̸ m/s (
). For larger diameters of the rotor, the angular velocity may be lower, provided that the peripheral velocity does not drop below about 250̸ m/s. It is apparent from the above description that the number of both the axial flow and the tangential flow pumping stages, either of the type with plane rotor or of the type with vanes rotor, may be varied according to the specific applcations, without departing from the scope of the invention.
1. Turbomolecular pump comprising at the suction side a plurality of pumping stages consisting
of alternately arranged rotors (1,1a) and stators (2,2a) provided with inclined blades,
the rotor blades (7,7a,7b) being inclined in the inverse direction to the stator blades
(9,9a,9b), for pumping gases along an axial flow through said pumping stages and comprising
at least one pumping stage (10̸) at the exhaust side consisting of a rotor disk (12)
and a coplanar stator (13), characterized in that a unique free annular channel (14) is defined between the lateral surface of the
rotor (12) and the lateral inner surface of the stator (13), the stator (13) further
comprising an upper plate (21;31) and a lower plate (23;33) respectively provided
with suction port (17;40̸) and discharge port (18;41), said unique free annular channel
being in communication with said suction port (17;40̸) and said discharge port (18;41)
for pumping gases with a flow tangential to the lateral surface of said rotor (12)
from said suction port (17) to said discharge port (18), said channel (14) being delimited
at its ends by a baffle (15) arranged between said discharge port (18) and said suction
port (17).
2. Turbomolecular pump according to claim 1, characterized in that it comprises an additional
pumping stage (30̸) at the exhaust side, arranged downstream said discharge port (18),
said additional pumping stage (30̸) consisting of a rotor (35) with vanes (37,37a,37b)
and a coplanar stator (36), a free annular channel (38) being defined between the
periphery of said vanes (37,37a,37b) and said stator (36) along a part of the circumferences
of said rotor (35) and stator (36), said annular channel being in communication with
a suction port (40̸) and a discharge port (41) for pumping gases with a flow tangential
to said rotor (35) from said suction port (40̸) to said discharge port (41) and being
delimited at its ends by a baffle (39) arranged between said discharge port (41) and
said suction port (40̸).
3. Turbomolecular pump according to claim 2, characterized in that said vanes (37,37a,37b)
are perpendicular to the plane of said rotor (35).
4. Turbomolecular pump according to claim 1, characterized in that said rotors (1,1a)
of said pumping stages for pumping gases along an axial flow, and said rotor (12)
of said pumping stage (10̸) for pumping gases with a flow tangential to said rotor
(12) are mounted on a same rotatable shaft (6).
5. Turbomolecular pump according to claim 1,2, and 4 characterized in that also said
rotor (35) of said additional flow pumping stage (30̸) is mounted on said rotatable
shaft (6).
6. Turbomolecular pump according to claim 4 or 5, characterized in that said rotors (1,1a;12;35)
of said axial and tangential flow pumping stages are rotated, in operation, at a peripheral
velocity of at least 250̸ m/s.
7. Turbomolecular pump according to claim 1, characterized in that said upper plate (21;31)
and said lower plate (23;33) are joined together by connection of downwardly extending
edge (22;32) so as to form a closed casing containing the pumping stage (10̸;30̸).
1. Turbomolekularpumpe, umfassend eine Vielzahl von Pumpstufen an der Ansaugseite, bestehend
aus alternierend angeordneten Rotoren (1, 1a) und Statoren (2, 2a), die mit schräggestellten
Schaufeln ausgerüstet sind, wobei die Rotorschaufeln (7, 7a, 7b) in entgegengesetzer
Richtung zu den Statorschaufeln (9, 9a, 9b) geneigt sind, zum Pumpen von Gasen in
axialer Strömungsrichtung durch diese Pumpstufen und umfassend zumindest eine Pumpstufe
(10) an der Ausströmseite, bestehend aus einer Rotorscheibe (12) und einem in derselben
Ebene liegenden Stator (13), dadurch gekennzeichnet, daß zwischen der Seitenfläche
des Rotors (12) und der seitlichen Innenfläche des Stators (13) ein einziger, freier
ringförmiger Kanal definiert ist, der Stator (13) des weiteren eine obere Platte (21,
31) und eine untere Platte (23, 33) umfaßt, die mit einer Ansaugöffnung (17, 40) respektive
einer Ausströmöffnung (18, 41) versehen sind, wobei der freie, ringförmige Kanal mit
der Ansaugöffnung (17, 40) und der Ausströmöffnung (18, 41) in Verbindung steht, um
die Gase in tangentialer Strömungsrichtung zur Seitenfläche des Rotors (12) von der
Ansaugöffnung (17) zur Ausströmöffnung (18) zu pumpen, wobei der Kanal (14) an seinen
Enden durch ein Leitblech (15) begrenzt ist, das zwischen der Ausströmöffnung (18)
und der Ansaugöffnung (17) angeordnet ist.
2. Turbomolekularpumpe nach Anspruch 1, dadurch gekennzeichnet, daß sie eine zusätzliche
Pumpstufe (30) an der Ausströmseite umfaßt, die, bezogen auf die Ausströmöffnung (18),
stromabwärts angeordnet ist, wobei diese zusätzliche Pumpstufe (30) aus einem Rotor
(35) mit Schaufeln (37, 37a, 37b) und einem in derselben Ebene liegenden Stator (36)
besteht, wobei ein freier, ringförmiger Kanal (38) zwischen dem Umkreis der Schaufeln
(37, 37a, 37b) und dem Stator (36) entlang eines Teils des Umkreises des Rotors (35)
und des Stators (36) definiert ist, wobei dieser ringförmige Kanal eine Verbindung
mit der Ansaugöffnung (40) und der Ausströmöffnung (41) aufweist zum Pumpen von Gasen
in tangentialer Strömungsrichtung zum Rotor (35) von der Ansaugöffnung (40) zur Ausströmöffnung
(41) und dieser an seinen Enden durch ein Leitblech (39) begrenzt ist, das zwischen
der Ausströmöffnung (41) und der Ansaugöffnung (40) angeordnet ist.
3. Turbomolekularpumpe nach Anspruch 2, dadurch gekennzeichnet, daß die Schaufeln (37,
37a, 37b) rechtwinkelig zur Ebene des Rotors (35) angeordnet sind.
4. Turbomolekularpumpe nach Anspruch 1, dadurch gekennzeichnet, daß die Rotoren (1, 1a)
der Pumpstufen zum Pumpen von Gasen in axialer Strömungsrichtung und der Rotor (12)
der Pumpstufe (10) zum Pumpen von Gasen in tangentialer Strömungsrichtung zum Rotor
(12) auf derselben Drehwelle (6) montiert sind.
5. Turbomolekularpumpe nach Anspruch 1, 2 und 4, dadurch gekennzeichnet, daß auch der
Rotor (35) der zusätzlichen Pumpstufe (30) auf dieser Drehwelle (6) montiert ist.
6. Turbomolekularpumpe nach Anspruch 4 oder 5, dadurch gekennzeichnet, daß die Rotoren
(1, 1a, 12, 35) der Pumpstufen für die axiale und die tangentiale Strömungsrichtung
bei Betrieb mit einer Umfangsgeschwindigkeit von mindestens 250 m/s rotieren.
7. Turbomolekularpumpe nach Anspruch 1, dadurch gekennzeichnet, daß die obere Platte
(21, 31) und die untere Platte (23, 33) zur Bildung eines geschlossenen, die Pumpstufe
(10, 30) beinhaltendes Gehäuse über den nach unten sich erstreckenden Rand (22, 32)
miteinander verbunden sind.
1. Pompe turbomoléculaire comprenant, du côté de l'aspiration, un ensemble d'étages de
pompage consistant en rotors (1, 1a) et en stators (2, 2a) disposés en alternance,
comportant des ailettes inclinées, les ailettes de rotor (7, 7a, 7b) étant inclinées
en sens inverse des ailettes de stator (9, 9a, 9b), pour pomper des gaz en leur communiquant
un écoulement axial à travers les étages de pompage, et comprenant au moins un étage
de pompage (10) du côté de l'évacuation qui consiste en un disque de rotor (12) et
en un stator coplanaire (13), caractérisée en ce qu'un canal annulaire libre particulier
(14) est défini entre la surface latérale du rotor (12) et la surface latérale intérieure
du stator (13), le stator (13) comprenant en outre une plaque supérieure (21; 31)
et une plaque inférieure (23; 33) munies respectivement d'un orifice d'aspiration
(17; 40) et d'un orifice d'évacuation (18; 41), le canal annulaire libre particulier
étant en communication avec l'orifice d'aspiration (17; 40) et avec l'orifice d'évacuation
(18; 41) pour pomper des gaz avec un écoulement tangentiel vers la surface latérale
du rotor (12), à partir de l'orifice d'aspiration (17) vers l'orifice d'évacuation
(18), le canal (14) étant délimité à ses extrémités par un déflecteur (15) qui est
disposé entre l'orifice d'évacuation (18) et l'orifice d'aspiration (17).
2. Pompe turbomoléculaire selon la revendication 1, caractérisée en ce qu'elle comprend
un étage de pompage supplémentaire (39) du côté de l'évacuation, disposé en aval de
l'orifice d'évacuation (18), cet étage de pompage supplémentaire (30) consistant en
un rotor (35) avec des aubes (37, 37a, 37b) et en un stator coplanaire (36), un canal
annulaire libre (38) étant défini entre la périphérie des aubes (37, 37a, 37b) et
le stator (36) le long d'une partie des circonférences du rotor (35) et du stator
(36), ce canal annulaire étant en communication avec un orifice d'aspiration (40)
et un orifice d'évacuation (41) pour pomper des gaz avec un écoulement tangentiel
vers le rotor (35), à partir de l'orifice d'aspiration (40) vers l'orifice d'évacuation
(41), et étant délimité à ses extrémités par un déflecteur (39) qui est disposé entre
l'orifice d'évacuation (41) et l'orifice d'aspiration (40).
3. Pompe turbomoléculaire selon la revendication 2, caractérisée en ce que les aubes
(37, 37a, 37b) sont perpendiculaires au plan du rotor (35).
4. Pompe turbomoléculaire selon la revendication 1, caractérisée en ce que les rotors
(1, 1a) des étages de pompage destinés à pomper des gaz avec un écoulement axial et
le rotor (12) de l'étage de pompage (10) destiné à pomper des gaz avec un écoulement
tangentiel vers le rotor (12) sont montés sur le même arbre tournant (6).
5. Pompe turbomoléculaire selon les revendications 1, 2 et 4, caractérisée en ce que
le rotor (35) de l'étage de pompage supplémentaire (30) est également monté sur l'arbre
tournant précité (6).
6. Pompe turbomoléculaire selon la revendication 4 ou 5, caractérisée en ce que les rotors
(1, 1a; 12; 35) des étages de pompage à écoulement axial et à écoulement tangentiel
tournent, pendant le fonctionnement, avec une vitesse périphérique d'au moins 250
m/s.
7. Pompe turbomoléculaire selon la revendication 1, caractérisée en ce que la plaque
supérieure (21; 31) et la plaque inférieure (23; 33) sont réunies ensemble par la
jonction d'un rebord s'étendant vers le bas (22; 32), de façon à former un carter
fermé contenant l'étage de pompage (10; 30).