EP2594803A1 - Friction vacuum pump - Google Patents

Abstract

The pump has a rotor (2) rotatably supported by a rolling bearing (4), and comprising a case (10) that is fastened at a hub (8). A stator (20) is concentrically arranged to the case under formation of a gap (30) with a gap width (100), where the gap width is decreased to the rolling bearing. A permanent magnet bearing is attached to an end (12) of the case for supporting the rotor, where another end (14) of the case is arranged at height of the rolling bearing. A turbo-molecular pumping structure is provided between the hub and the permanent magnet bearing.

Description

The invention relates to a vacuum pump according to the preamble of the first claim.

The turbomolecular pumps, which have been successful on the market for decades in many different industrial applications, for example in gas analysis and semiconductor manufacturing, are partly designed as so-called compound pumps. This term clarifies that in addition to the turbomolecular pumping section, a molecular pumping stage is provided on the rotor of the pump.

A successful design of such molecular pumping stages is the Holweck pumping stage named after its inventor. A generally smooth sleeve rotates in a stator arranged inside or outside the sleeve, which usually has a plurality of helical grooves on the side facing the sleeve. There is a gap between the stator and the sleeve, which is usually less than a millimeter wide, often only fractions of a millimeter, for example a few tenths of a millimeter.

Decisive for the dimensioning of the gap are geometric data, for example manufacturing tolerances, the influence of the centrifugal forces on the core diameter and the thermal expansion during operation. These influences lead to a wide gap, which limits the quality of the vacuum data, for example the compression.

It is therefore an object to present a Holweckpumpstufe with improved vacuum data.

This object is achieved by a vacuum pump with the features of claim 1. The dependent claims 2 to 13 indicate advantageous developments of the invention.

The gap width of the gap between sleeve and stator varies, wherein the gap width of the gap preferably changes in the axial direction of the vacuum pump and assumes different values at different axial heights. The non-constant gap width can be adjusted in a simple manner to the expected in the region of the respective axial height maximum radial deflection of the rotor, whereby the pump efficiency is increased.

The sleeve may have a first end and a free second end remote from the hub.

According to a preferred embodiment, the rotor of the vacuum pump is rotatably supported by a rolling bearing and decreases the gap width in the direction of the rolling bearing. Due to its low clearance, a narrow gap is achieved, which significantly improves the vacuum data. For example, with light gases such as helium, the compression can be improved by a good decade.

In addition to the rolling bearing, a permanent magnet bearing can be used to support the rotor. In this case, the claimed gap design is particularly advantageous, since permanent magnet bearings have a large game and thus require large gaps. The gap is then preferably narrow in the direction of the permanent magnet bearing and in the direction of the rolling bearing or has a gap width increasing in the direction of the permanent bearing. However, in the prior art, the gap would be sized after the clearance of the permanent magnet bearing. By applying the features of claims 1 to 13 is of this deviated from decades used procedure and achieved at least in sections, a gap that takes no account of the game in the permanent magnet bearing. When storing the rotor with permanent magnet bearings and bearings therefore a particularly advantageous performance increase.

The sleeve and the stator are preferably part of a Holweckpumpstufe or form a Holweckpumpstufe. The sleeve may be carried by the hub. The sleeve is preferably concentric and in particular rotationally symmetrical to the axis of rotation of the vacuum pump and preferably has the shape of a coaxial with the axis of rotation cylinder jacket.

In principle, within the scope of the invention, a configuration is also conceivable in which the gap width does not decrease in the direction of the roller bearing but, for example, increases steadily or stepwise in the direction of the rolling bearing.

According to one embodiment, the vacuum pump comprises two sleeves arranged one behind the other in the axial direction, which in particular together form a common Holweckpumpstufe or may be part of a common Holweckpumpstufe. The two sleeves can together form at least part of a particular cylinder jacket-shaped and / or smooth surface of the rotor, which defines the gap together with a stator. The hub, to which at least one of the sleeves is attached, may be in the axial direction between the sleeves and the sleeves may extend in opposite axial directions with respect to the hub. The two sleeves can in principle be arranged on the same hub or carried by the same hub. The sleeves may also be carried by different hubs, with the two hubs spaced apart axially and / or with one of the two hubs interposed between the other hub and a permanent magnet bearing of the vacuum pump.

A sleeve of the vacuum pump may also be connected to the hub or carried by the hub in a region spaced from its axial ends or in an area located between its axial ends, the sleeve extending in opposite axial directions from the hub.

The vacuum pump may include a stator concentrically disposed within the sleeve and a stator concentrically disposed outside the sleeve, each stator forming a gap with the sleeve and having the two gaps preferably parallel to one another, ie, converged at their downstream ends. The gap formed by the inner stator can be accessible via one or more openings of the hub for the gas to be delivered, which each form a gas inlet for the gap. The two columns can each be part of a Holweckstufe. The gap width of the gap formed by the outer stator and / or the gap width of the gap formed by the inner stator can, in particular in the axial direction, vary and in particular decrease towards the rolling bearing. According to an advantageous embodiment, the gap width of the gap formed by the inner stator varies more strongly and in particular increases more towards the rolling bearing than the gap width of the gap formed by the outer stator. Alternatively or additionally, the minimum gap width of the gap formed by the inner stator may be less than the minimum gap width of the gap formed by the outer stator. This makes it possible to compensate for a different pumping behavior of the two pumping stages, which is due to the different radial distances of the two gaps from the axis of rotation and the different relative speeds produced thereby, whereby an improved pumping behavior is achieved, in particular in the parallel operation of the pumping stages. The gap width of one of the gaps, in particular of the gap formed by the outer stator, can in principle also be constant.

Advantageously, a gap width which decreases towards the roller bearing also has an effect on a parallel-pumping arrangement of the outer and inner surfaces of a sleeve or a plurality of sleeves. In this case, the gap width decrease allows a very accurate tuning of the compressions of the different parallel pumping column, for example, the influence of different relative velocities between stationary and stationary components can be compensated for the compression.

According to an advantageous embodiment, the gap width increases or decreases linearly or stepwise. The gap width can in principle vary over part of the gap length or the entire gap length. The gap width can e.g. vary in a first section and be constant in a second section. Likewise, the gap width in different sections vary differently and, for example, in a first section steadily and in particular linearly and in a second section gradually increase or decrease. The gap width can increase or decrease over its entire length in the same axial direction, but it can also increase in a first portion in the axial direction and decrease in another portion in the same axial direction. The various sections are preferably formed by different axial lengths of the gap. A variation of the gap width in the axial direction which is present over a part of the axial length or the entire axial length of the sleeve can be present over the entire circumference of the sleeve, which is not mandatory.

The gap may be formed at least over a part of its axial length and in particular over substantially its entire axial length substantially conical or truncated cone-shaped.

With reference to an embodiment and its developments, the invention will be explained in more detail and the representation of its benefits to be deepened.

Fig. 1:

Schematische Schnittdarstellung von Rotor und Stator einer Holweckstufe mit zwei Wälzlagern;

Fig. 2:

Schematische Schnittdarstellung von Rotor und Stator einer Holweckstufe, gelagert mit einem Wälzlager und einem Permanentmagnetlager;

Fig. 3:

Schematische Schnittdarstellung von Hülse und Stator der Holweckstufe;

Fig. 4:

Schematische Schnittdarstellung eines Rotors mit turbomolekularen Pumpelementen und mehreren Hülsen sowie Stator;

Fig. 5:

Schematische Schnittdarstellung eines Rotors mit parallel wirkenden Hülsen.

Show it:

Fig. 1:

Schematic sectional view of rotor and stator of a Holweck stage with two rolling bearings;

Fig. 2:

Schematic sectional view of rotor and stator of a Holweckstufe, mounted with a rolling bearing and a permanent magnet bearing;

3:

Schematic sectional view of sleeve and stator of Holweckstufe;

4:

Schematic sectional view of a rotor with turbomolecular pumping elements and multiple sleeves and stator;

Fig. 5:

Schematic sectional view of a rotor with parallel acting sleeves.

In Fig. 1 are shown in a schematic representation of the rotor 2 and the stator 20 of a vacuum pump. The rotor 2 has a hub 8, which carries a sleeve 10.

The rotor 2 is rotatably supported by a rolling bearing 4, which is located at a distance 102 to the hub 8. For further support of the rotor 2, a second rolling bearing 6 may be provided.

Concentric with the sleeve 10, a stator 20 is provided, which surrounds the sleeve 10 to form a gap 30. The stator 20 has on its radially inner surface helical grooves 24 or similar pump structures suitable for achieving a pumping effect. Between the grooves remain webs 22 stand. The gap 30 has a width 100 which determines between the sleeve 10 facing surface of the webs 22 and the surface of the sleeve 10 becomes. In addition or as an alternative to stator-side pump structures, the sleeve 10 may also have pump structures suitable for achieving a pumping effect, the gap width 100 of the gap 30 also referring in this case to the surface of the webs of the pump structures.

The rotor 2 is rotated by a drive, wherein the drive stator side, a motor coil 42 and the rotor side, a drive magnet 44 may include. The speed is such that in the gap 30 between the sleeve 10 and the stator 20, a molecular pumping effect is effected. As a result, gas is pumped in the direction 104, which is oriented towards the rolling bearing 4.

The sleeve has a first end 12 to which it may be attached to the hub 8. This may be an adhesive connection, which advantageously facilitates the choice of material pairing of hub 8 and sleeve 10. A second end 14 is remote from the hub 8 and free. Depending on the length of the sleeve 10, this second end 14 may be arranged between the hub 8 and rolling bearing 4. Alternatively, the rolling bearing 4 between hub 8 and second end 14 may be located.

By the rotation, the sleeve 10 expands. Therefore, it is advantageous to make sleeve 10 and disc 8 of different materials, the sleeve 10, for example made of a carbon fiber reinforced plastic (CFRP), the hub 8 made of aluminum. Here, it is observed that the hub 8 expands more strongly under the influence of centrifugal force and temperature than the sleeve 10. When using a second rolling bearing 6, the expansion of the hub 8 is the determining factor. It is now proposed not to define the gap 30 after this expansion but to make it so that the gap width 100 decreases to the rolling bearing 4 back. This conical gap 30 causes the vacuum data to become better in the pumping direction. Especially for light gases For example, the compression improved by a good decade. Due to the small clearance of the rolling bearing 4, the gap width 100 may be the lowest there.

In an advantageous development, the second end 14 is arranged at an axial height in a range between 0.8 times and 1.2 times the distance 102 between the hub 8 and rolling bearing 4. The advantage of improving the vacuum data is hereby pronounced, because in this range of axial height, the deflection of the sleeve 10 is low and it can be very narrow column 30 are selected.

In a next advantageous development, the second end 14 is therefore at the height of the rolling bearing 4, since then highest working pressure within the gap 30 and smallest gap width 100 coincide.

The Fig. 2 shows a development in which instead of the second rolling bearing 6, a permanent magnet bearing 40 is provided to support the rotor 2. The advantage of such a bearing 40 is the high vacuum capability and freedom from wear. However, even with the use of state-of-the-art magnetic materials, permanent magnet bearings 40 have a lower rigidity in the radial direction than a rolling bearing 4, 6, even if modern magnetic materials are used. This means, depending on the operating conditions, for example installation position, a greater radial deflection of the rotor 2 on the permanent magnet bearing 40, but also Therefore, the gap width 100 of the gap 30 between the stator 20 and the sleeve 10 was determined according to the prior art knowledge over its entire length after the deflection of the hub 8. Depending on the sleeve material was still the centrifugal expansion of the sleeve 10 added. It is now proposed that the gap width 100 decreases towards the rolling bearing 4. As a result, the vacuum data are due to the pumping effect increased in the pumping direction 104 due to the decreasing dimensions improved. This is achieved, in particular, if, according to an embodiment of the idea, the permanent magnet bearing 40 is assigned to the first end 12 of the sleeve 10, ie is spaced apart in particular in the axial direction from the sleeve 10 and is less far away from the first end 12 of the sleeve 10 than from the latter second end 14.

Advantageously, a further development, according to which the sleeve 10 is made of a carbon fiber reinforced plastic (CFRP), whereby the rolling bearing 4 towards, in particular at the height of the rolling bearing 4, a very small gap 30 is achieved.

Additional design features that can be combined with the features already mentioned, are based on Fig. 3 be clarified. Shown are rotor 2 and stator 20 and in the right part of the figure, the course of the gap width 100 over the gap length.

The first end 12 of the sleeve 10 may be connected to the hub 8, for example, by an adhesive, clamping or shrinking connection. Alternatively, the sleeve 10 may be pulled out beyond the hub 8 in the axial direction as shown in FIG Fig. 3 is shown by dashed lines. The hub 8 is arranged between the dotted illustrated first end 12 'of the hub 8 beyond the extended sleeve 10 and the second end 14 of the sleeve 10. The stator 20 may then be extended accordingly, also shown dotted. It is also conceivable to simplify the production, to separate the stator 20 along a Statorteilungslinie 110 and perform several pieces.

Instead of a continuous linear change of the gap width over the gap length 108, the change in the gap width may also extend in sections. The division into a first and a second section 90 and 92 is shown by way of example. According to the first exemplary curve 94, the gap width first decreases linearly and then changes continuously into a constant part. According to a second exemplary profile 96, the reduction of the gap width occurs stepwise, the gap width decreases in jumps from the second end 14 to the first end 12.

The training after Fig. 4 shows a supported by a roller bearing 4 and a permanent magnet bearing 40 rotor 2. Between the hub 8 and the permanent magnet bearing a turbomolecular pumping structure 50 is provided which can surround components of the permanent magnet bearing 40.

The hub 8 carries a first sleeve 10 and in addition to this, a second sleeve 16 which is fixed to the hub 8 or integral with her and arranged on one of the first sleeve 10 from facing side of the hub. A stator 20 concentrically surrounds the first and second sleeves 16 to form a gap. This over the lengths of both sleeves 10, 16 extending gap is designed according to the aspects already shown. In particular, the gap width decreases over the gap length 108 in the direction of the rolling bearing 4. This arrangement allows the use of a metal as material for the second sleeve 16, since the gap then has the largest gap width in the region of the largest centrifugal force expansion.

The hub 8 may be divided along a hub pitch line 112 in the direction of the rotor longitudinal axis to form a second hub 8b which may be spaced from the first.

Other sleeves may be provided to form a molecular pumping section, for example a third sleeve 18 concentrically disposed within the first sleeve 10.

According to the training, which in Fig. 5 is shown in schematic section, it is proposed to provide the hub 8 fixed to the rotor 2 with at least one opening 60 and an intermediate stator 62 concentric with the first sleeve 10 and to arrange radially within this. The intermediate stator 62 forms with the first sleeve 10 a pump-active inner gap 64. The first sleeve 10 also interacts with a concentrically surrounding the first sleeve 10 stator 20 to form the gap 30 pumping together. By this arrangement creates a parallel pumping stage or two parallel pumping stages, in which or in which along the outside and along the inside of the first sleeve 10 gas is promoted. In molecular pumping, the pumping action depends on the relative speeds of the moving components to the stationary components. Therefore, it is not easy to create an effectively parallel pumping arrangement. It is now proposed that the gap width 100 of the gap 30 and the gap width 106 of the gap 64 to the rolling bearing 4 decreases towards. By selecting the gap width change, this decrease allows a fine adjustment of the compression achieved by the respective gap 30, 64, that is to say the pressure ratio between the beginning of the gap and the end of the gap. This fine tuning results in a very effective parallel pumping Holweck stage with better performance data than in the prior art.

In addition to the first sleeve 10, a third sleeve 18 may be disposed concentric with the first and radially within the intermediate stator 62. This creates another pumping channel. Other pods, also according to Fig. 4 , can be combined.

Claims (13)

A vacuum pump comprising a rotor (2) having at least one hub (8) and at least one sleeve (10) attached to the hub, and at least one stator (20) forming a gap (30, 64) with a gap width (100, 106) is arranged concentrically to the sleeve (10), characterized in that the gap width (100, 106) varies. Vacuum pump according to claim 1, characterized in that the rotor (2) by a rolling bearing (4) is rotatably supported and the gap width (100, 106) to the rolling bearing (4) decreases towards. Vacuum pump according to claim 1 or 2, characterized in that a permanent magnet bearing (40) for supporting the rotor (2) is provided. Vacuum pump according to claim 3, characterized in that the permanent magnet bearing (40) is associated with a first end (12, 12 ') of the sleeve (10). Vacuum pump according to one of claims 2 to 4, characterized in that a free, the hub (8) remote from the second end (14) of the sleeve (10) at the height of the rolling bearing (4) is arranged. Vacuum pump according to one of claims 2 to 5, characterized in that a free, the hub (8) facing away from the second end (14) of the sleeve (10) at an axial height in a range between 0.8 times and 1.2 times a distance (102) between the hub (8) and roller bearings (4) is arranged. Vacuum pump according to one of claims 3 to 6, characterized in that a turbomolecular pumping structure (50) is provided between the hub (8) and the permanent magnetic bearing (40). Vacuum pump according to one of claims 1 to 7, characterized in that a first end (12, 12 ') of the sleeve (10) is fixed to the hub (8). Vacuum pump according to one of claims 1 to 8, characterized in that a second sleeve (16) attached to the hub (8) and on a side facing away from the first sleeve (10) side of the hub (8) is arranged. Vacuum pump according to claim 9, characterized in that the second sleeve (16) is fixed to a second hub (8b) which is arranged between the hub (8) and a permanent magnet bearing (40) of the vacuum pump. Vacuum pump according to one of the preceding claims, characterized in that the sleeve (10) is connected by means of an adhesive connection with the hub (8). Vacuum pump according to one of the preceding claims, characterized in that the hub (8) has at least one opening (60) which allows gas to enter between the sleeve (10) and an intermediate stator (62) arranged concentrically within the sleeve (10) with the sleeve (10) forms a pump-active inner gap (64), the gap width (106) varies and in particular decreases to a rolling bearing (4) of the vacuum pump out. Vacuum pump according to one of the preceding claims, characterized in that the gap width (100, 106) increases or decreases linearly or stepwise.

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