EP3133290B1 - Vacuum pump - Google Patents

Description

The present invention relates to a vacuum pump, in particular a turbo molecular pump, with at least one rotor which has a rotor shaft and a plurality of rotor sections arranged on the rotor shaft, axially spaced along the rotor shaft, each comprising a plurality of rotor blades distributed in the circumferential direction, and at least one of the rotor associated stator, which has a plurality of stator sections each with a plurality of stator blades distributed in the circumferential direction, wherein a respective stator section is arranged in the axial direction between a first and a second rotor section and adjacent to these two rotor sections, and wherein between the first rotor section and a a first axial distance is provided for each stator section and a second axial distance is provided between the respective stator section and the second rotor section.

Typically, a plurality of rotor sections and a plurality of stator sections are provided, which are arranged alternately in the axial direction, a respective stator section being located centrally between two respectively adjacent rotor sections. The rotor sections can each either be designed in one piece with the rotor shaft or be provided in the form of a separately manufactured rotor disk that is connected to the rotor shaft in a rotationally fixed manner.

In the JP 2000 257586 A a vacuum pump of the type mentioned is described in which the rotor can be adjusted in the axial direction via electromagnetic control means so that the axial distance of a respective rotor section to the stator section on one side is smaller than the axial distance of the respective Rotor section to the stator section on the other hand to adjust the distance on the one hand to a desired value. It remains open in which direction the rotor should be adjusted. In addition, not all stator sections are each arranged between two adjacent rotor sections. The stator sections are each fixed directly to the pump housing or integrated in it.

With one of the EP 2 757 266 A1 Known vacuum pumps of the type mentioned at the beginning, the stator sections are separated from one another by spacer rings and are each arranged between two rotor sections, from which they are at least substantially the same distance apart.

It is an object of the invention to improve the performance of such a vacuum pump.

The object is achieved by a vacuum pump according to claim 1, and in particular in that the second axial distance is different from the first axial distance, the first rotor section being arranged in front of a respective stator section in the pumping direction and the second rotor section being arranged after the respective rotor section in the pumping direction is arranged, the first axial distance is smaller than the second distance and less than 0.7 times the second axial distance, and the two different distances of a respective stator section to the two adjacent rotor sections are defined by corresponding spacer rings between the individual stator sections .

The invention allows the arrangement of the rotor and stator sections to be adapted to the movement of the molecules to be conveyed, so that the pumping effect is improved. The mode of operation of the invention is described below in particular with reference to FIG Fig. 2 explained in more detail.

In addition, the invention allows an existing construction of a vacuum pump to be improved by merely changing the position of the stator sections relative to the rotor sections. This can be achieved in a particularly simple way, e.g. by changing spacer rings between individual stator sections. The invention thus improves the performance of a vacuum pump using particularly simple means, without the need to change the overall construction of the vacuum pump.

A respective stator section is arranged between two rotor sections adjacent to it. In other words, a respective stator section and each of the two rotor sections adjacent to it are arranged directly one after the other in the respective axial direction. No further stator or rotor sections are arranged between a respective stator section and a respective adjacent rotor section. The respective stator section has an adjacent rotor section in both axial directions.

In the prior art, it is assumed that optimum performance of the vacuum pump is achieved when the stator section is arranged exactly in the middle between two adjacent rotor sections. According to the invention, however, it was recognized that the first axial distance and the second axial distance can have a different influence on the pumping action, so that the pumping action can advantageously be influenced by different choices of the two distances.

The first rotor section is arranged in front of a respective stator section in the pumping direction, while the second rotor section is arranged after the stator section in the pumping direction. The first axial distance is smaller than that second axial distance. In other words, the first axial distance in the pumping direction is smaller than the second axial distance in the pumping direction. The first axial distance can be made as small as possible. A certain minimum distance greater than zero is maintained between a respective stator section and an adjacent rotor section. Although the second axial distance can become relatively large by reducing the first axial distance, it has been shown that the second axial distance does not have such a strong influence on the pump output, so that the pump output is improved overall when the first axial distance is reduced.

According to the invention, the first axial distance is less than 0.7 times the second axial distance. In this embodiment, a particularly good pump performance has resulted. Even better pump capacities can result if, according to one embodiment, the first axial distance is less than or equal to half the second axial distance.

In a further embodiment, the rotor shaft is mounted on the inlet side, in particular in a high vacuum area, by a lubrication-free bearing, in particular a magnetic bearing. As a result, the storage on the inlet side can not only be carried out maintenance-free, but contamination of the vacuum by the storage is also prevented due to the lack of lubricants.

The rotor shaft can alternatively or additionally on the outlet side, in particular in a medium or low vacuum range, by a lubricated bearing, in particular a roller bearing such as a ball bearing. This allows inexpensive storage with relatively little play, while the contamination problem on the outlet side is eliminated.

In one embodiment, at least one rotor section is formed in one piece with the rotor shaft. In particular, all rotor sections are designed in one piece with the rotor shaft. A rotor configured in this way is also referred to as a full rotor. In contrast to this, at least one rotor section can be formed by a rotor disk produced separately from the rotor shaft and fastened to the rotor shaft. In particular, all rotor sections can be formed by separately produced rotor disks. This is also referred to as a disk rotor.

In a further embodiment, at least one stator section is designed as a stator disk made from sheet metal. As a result, the production of the stator disk and thus also that of the vacuum pump is technically simplified and more cost-effective. In particular, the stator disk is stamped from sheet metal, which further simplifies the manufacturing process.

The rotor blades and the stator blades can each be inclined to a plane running at least essentially perpendicular to an axis of rotation, the rotor blades having an angle of attack and the stator blades having an angle of attack and the sum of the angle of attack of the stator blades and the angle of attack of the rotor blades at least substantially 90 ° is. In other words, a respective stator blade, in particular with a radially outer area, can be aligned at least substantially perpendicular to a respective rotor blade, in particular to its radially outer area. The molecules to be conveyed move away primarily perpendicularly from a respective blade surface of the rotor in the direction of the stator section, as shown below with reference to FIG Fig. 2 explained in more detail. So if the stator blades are parallel to If the molecules are aligned in this direction of movement, they offer minimal resistance to the molecules and the pump performance is optimized.

In one embodiment of the invention, the angle of incidence of the rotor blades is at least substantially 45 °, as a result of which the performance of the pump can be further improved.

Further embodiments of the invention are specified in the dependent claims, the description and the figures.

Fig. 1

zeigt eine erfindungsgemäße Anordnung zweier Rotorscheiben mit einer dazwischenliegenden Statorscheibe, und

Fig. 2

zeigt Rotor- und Statorschaufeln zur Veranschaulichung der Wirkungsweise der Erfindung.

The invention is explained below by way of example only with reference to the schematic drawing.

Fig. 1

shows an arrangement according to the invention of two rotor disks with a stator disk in between, and

Fig. 2

shows rotor and stator blades to illustrate the mode of operation of the invention.

An exemplary vacuum pump designed as a turbo molecular pump (not shown), which can be further developed by the invention and also by at least one of the embodiments disclosed here, comprises an inlet surrounded by an inlet flange and several pump stages for conveying the gas present at the inlet to an outlet . The turbo molecular pump can have a side tap. The turbomolecular pump comprises a stator with a static housing and a rotor, which is arranged in the housing and has a rotor shaft which is rotatably mounted about an axis of rotation.

The turbomolecular pump comprises several turbomolecular pump stages connected in series with one another for effective pumping, with several rotor sections connected to the rotor shaft, designed as turbomolecular rotor disks and with several stator sections arranged in the axial direction between the rotor disks and fixed in the housing, designed as turbomolecular stator disks, which are formed by spacer rings in one desired axial distance from each other are kept. The rotor disks and stator disks provide an axial pumping action directed in the pumping direction in a pumping area.

The turbomolecular pump also comprises three Holweck pump stages which are arranged one inside the other in the radial direction and are connected in series with one another for effective pumping. The rotor-side part of the Holweck pump stages comprises two cylinder-jacket-shaped Holweck rotor sleeves fastened to the rotor shaft and carried by the latter, which are oriented coaxially to the axis of rotation and are nested in one another. Furthermore, two cylinder jacket-shaped Holweck stator sleeves are provided, which are also oriented coaxially to the axis of rotation and nested one inside the other. The active pumping surfaces of the Holweck pump stages are each formed by the radial jacket surfaces lying opposite one another with the formation of a narrow radial Holweck gap, namely a Holweck rotor sleeve and a Holweck stator sleeve. One of the active pumping surfaces is smooth, in the present case, for example, that of the Holweck rotor sleeve, the opposite, active pumping surface of the respective Holweck stator sleeve having a structure with grooves running helically around the axis of rotation in the axial direction, in which the rotation of the rotor, the gas is propelled and thereby pumped.

The rotatable mounting of the rotor shaft is brought about by a roller bearing in the area of the outlet and a permanent magnetic bearing in the area of the inlet.

The permanent magnetic bearing comprises a rotor-side bearing half and a stator-side bearing half, each of which comprises a ring stack of several permanent magnetic rings stacked on top of one another in the axial direction, the magnetic rings being opposite one another to form a radial bearing gap.

Inside the permanent magnetic bearing, an emergency or safety bearing is provided, which is designed as an unlubricated roller bearing and runs empty during normal operation of the vacuum pump without contact and only comes into engagement with an excessive radial deflection of the rotor relative to the stator to create a radial stop for the rotor to form, which prevents a collision of the rotor-side structures with the stator-side structures.

In the area of the roller bearing, a conical injection nut with an outer diameter that increases towards the roller bearing is provided on the rotor shaft, which is in sliding contact with a scraper of a plurality of absorbent disks soaked with an operating medium such as a lubricant. During operation, the operating medium is transferred from the operating medium storage via the scraper to the rotating injection nut by capillary action and, as a result of the centrifugal force, is conveyed along the injection nut in the direction of the increasing outer diameter of the injection nut to the roller bearing, where it has a lubricating function, for example.

The turbo molecular pump comprises a drive motor for rotatingly driving the rotor, the rotor of which is formed by the rotor shaft. A control unit controls the drive motor.

Fig. 1 shows a rotor shaft 14 of a rotor of a turbomolecular pump according to the invention, shown here only partially, with two rotor sections designed as rotor disks 16 being connected to the rotor shaft 14 in a rotationally fixed manner. A The respective rotor disk 16 has a plurality of rotor blades (not shown) which are arranged spaced apart in the circumferential direction.

Arranged between the rotor disks 16 is a stator section designed as a stator disk 22, which is not connected to the rotor shaft 14, but statically to a housing of the turbo molecular pump, not shown. The stator disk 22 has a plurality of stator blades, likewise not shown, which are arranged spaced apart in the circumferential direction.

There is a first axial distance A1 between the upper rotor disk 16 and the stator disk 22, and there is a second axial distance A2 between the stator disk 22 and the lower rotor disk 16. The first axial distance A1 is smaller than the second axial distance A2. Here, the axial distance A1 is approximately 0.4 times the second axial distance A2. According to the invention, this distance ratio must be less than 0.7.

In other words, the stator section is here arranged outside an axial center between the first rotor section, here the upper rotor disk 16, and the second rotor section, here the lower rotor disk 16. Again, in other words, the stator section is arranged closer to one of the adjacent rotor sections, namely closer to the upper rotor disk 16, than to the respective other rotor section, viewed in the axial direction, that is, along the rotor shaft 14.

A pumping direction P describes a desired direction of movement of the gas molecules to be conveyed during a pumping process. The intermediate space immediately following the upper rotor disk 16 in the pumping direction P, which is assigned to the first axial distance A1, is smaller than the second intermediate space in the pumping direction, which immediately follows the stator disk 22 and the second axial distance A2 is assigned. It may be desirable to make the first axial distance A1 as small as possible in order to further improve the pumping capacity of the turbo molecular pump.

The mode of operation of the invention will now be based on Fig. 2 and a simplified physical model can be illustrated in more detail.

In Fig. 2 rotor blades 18 and stator blades 24 are shown in simplified form, namely as a simplified developed view in the radial direction, ie in the direction of the rotor shaft 14 shown here only as a dashed line is arranged in front of a stator disk including the stator blades 24, also not shown in detail.

The rotor blades 18 move in at high speed during pumping Fig. 2 to the right (direction of rotation) while the stator blades 24 are fixed, ie not moving. The rotor blades 18 and the stator blades 24 are arranged obliquely at a respective angle of attack of 45 °, the stator blades 24 being oriented obliquely opposite to the rotor blades 18. The angle of attack is measured here in each case starting from a plane running perpendicular to the rotor shaft 14.

A molecule to be conveyed, which gets into the axial area of the rotor blades 18, is to a certain extent captured by the obliquely downwardly directed surface of a rotor blade 18 moving rapidly to the right, the molecule being adsorbed on the surface. The molecule then desorbs from the surface, moving away from the rotor blade. The molecule adopts a preferred direction which is perpendicular to the surface from which the molecule was previously desorbed. In Fig. 2 the stator blades 24 are also aligned perpendicular to the obliquely downwardly directed surfaces of the rotor blades 18, so that a molecule which moves in the preferred direction can pass parallel to the stator blades 24 and thus almost unhindered through the axially following stator disk 22, with only the - relatively small - thickness of the stator blades 24 opposing this movement.

However, the further the distance that the molecule has already covered after desorption from the rotor blade 18 when entering the axial area of the following stator disk 22, the more likely its direction of movement will deviate from the preferred direction mentioned above. This is due, for example, to impacts with the housing wall, the rotor shaft or other molecules and can also be referred to as "blurring". According to the invention, it was recognized that the passage probability for a respective molecule to be conveyed increases if the stator disk is arranged as close as possible to the rotor disk and, as a result, there is a high probability that the molecule does not already have a direction of movement deviating from the preferred direction when it reaches the stator disk. In contrast, the axial distance between the stator disk and the rotor disk following in the pumping direction has less of an influence on the pumping power. This is because here the molecule to be conveyed can be actively captured by the rotor disk, essentially regardless of its direction of movement, and thus transported further. The pumping performance of the turbo molecular pump is therefore improved by the invention, in particular in the molecular working range.

List of reference symbols

14th

Rotor shaft

16

Rotor disk

18th

Rotor blade

22nd

Stator disc

24

Stator blade

P.

Pumping direction

Claims (9)

1. A vacuum pump, in particular a turbomolecular pump, comprising

   at least one rotor which has a rotor shaft (14) and a plurality of rotor sections (16) which are arranged at the rotor shaft (14), which are axially spaced apart along the rotor shaft (14) and which each comprise a plurality of rotor blades (18) arranged distributed in the peripheral direction; and

   at least one stator which is associated with the rotor and which has a plurality of stator sections (22) which each have a plurality of stator blades (24) arranged distributed in the peripheral direction,

   wherein a respective stator section (22) is arranged in the axial direction between a first and a second rotor section (16) and is in each case arranged adjacent to these two rotor sections (16),

   wherein a first axial spacing (A1) is provided between the first rotor section (16) and a respective stator section (22) and a second axial spacing (A2) is provided between the respective stator section (22) and the second rotor section (16),

   wherein the second axial spacing (A2) is different from the first axial spacing (A1),

   wherein the first rotor section (16) is arranged before a respective stator section (22) in the pump direction (P) and the second rotor section (16) is arranged after the respective stator section (22) in the pump direction (P), wherein the first axial spacing (A1) is smaller than the second axial spacing (A2), characterized in that the first axial spacing (A1) amounts to less than 0.7 times the second axial spacing (A2);

   and in that the two different spacings (A1, A2) of a respective stator section (22) from the two adjacent rotor sections (16) are defined by corresponding spacer rings between the individual stator sections (22).
2. A vacuum pump in accordance with claim 1,
   characterized in that
   the first axial spacing (A1) is smaller than half the second axial spacing (A2).
3. A vacuum pump in accordance with claim 1 or claim 2,
   characterized in that
   the rotor shaft (14) is supported at the inlet side by a lubrication-free bearing, in particular a magnetic bearing.
4. A vacuum pump in accordance with any one of the preceding claims,
   characterized in that
   the rotor shaft (14) is supported at the outlet side by a lubricated bearing, in particular a roller element bearing.
5. A vacuum pump in accordance with any one of the preceding claims,
   characterized in that
   at least one rotor section (16) is formed in one piece with the rotor shaft (14).
6. A vacuum pump in accordance with any one of the preceding claims,
   characterized in that
   at least one stator section (22) is designed as a stator disk produced from sheet metal.
7. A vacuum pump in accordance with claim 6,
   characterized in that
   the stator disk is stamped from sheet metal.
8. A vacuum pump in accordance with any one of the preceding claims,
   characterized in that
   the rotor blades (18) and the stator blades (24) are each inclined with respect to a plane extending at least substantially perpendicular to an axis of rotation (R), with the rotor blades (18) having a blade angle and the stator blades (24) having a blade angle and the sum of the blade angle of the stator blades (24) and the blade angle of the rotor blades (18) amounting to at least substantially 90°.
9. A vacuum pump in accordance with claim 8,
   characterized in that
   the blade angle of the rotor blades (18) amounts to at least substantially 45°.

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