EP2532895B1 - Vacuum pump with pump rotor bearings on a single side - Google Patents

Description

The invention relates to a vacuum pump, preferably with a pumping speed of less than 50 m ³ / h, with a screw pump unit with two helical, intermeshing rotors in a suitably shaped pump chamber of a screw pump stator having a suction side with an inlet and a pressure side with an outlet , and with a two-shaft synchronous drive with two magnetized, non-contacting cylinders which are mounted on the rotor bearing rotor shafts and synchronize them in opposite directions due to their mutual magnetic interaction, and one or more, the two magnetized cylinder surrounding windings of a motor stator, the magnetic fields traveling through suitable current supply generate such that the two magnetized cylinders and thus the rotor shafts rotate in opposite directions synchronously, the bearing of the two rotor shafts being provided only on the drive, in particular therefore no bearing the remote from the drive side of the pump chamber is present.

Thus, the invention thus relates to a vacuum pump with a screw pump unit running oil-free and non-contact in the pump chamber. Such a vacuum pump is regularly provided for a final vacuum range 10 ² Pa to 10 ^-2 Pa (fine vacuum).

Numerous processes in research and industry require a vacuum in the range of 10 ² Pa to 10 ^-2 Pa, which often also condensing and / or aggressive vapors or gases must be promoted. To generate a negative pressure in this area, liquid-sealed or lubricated vacuum pumps such as oil-sealed rotary vane pumps are often used. The use of such pumps, in which the pumped medium comes into contact with oil or other liquids, has numerous disadvantages. Thus, the pumped media can contaminate or react with the lubricant, which reduces the lubricity and sealing effect. Backflow of gaseous components or decomposition products of the lubricant in the process plant can interfere with the processes there sensitive.

For this reason, the development of so-called "dry" vacuum pumps, ie pumps in which the pumped media does not come into contact with a liquid, has long been the subject of much work.

At higher pressures, ie in the range 10 ⁵ Pa to 10 ² Pa, membrane vacuum pumps are very advantageous because the pumping chamber is hermetically separated from the drive range by the gas-tight clamped membrane. Due to the limited compression ratio and the normally operated only by the gas flow valves, however, pressures below 50 Pa are difficult to achieve.

In addition to fine vacuum pumps such as piston pumps, scroll pumps, claw pumps and Roots pumps also screw vacuum pumps are known.

In screw vacuum pumps (short: screw pumps), two helical rotors mesh with each other without contact in a suitably shaped pump chamber of a screw pump stator, so that their counter rotation rotates gas from an inlet to an outlet.

An advantage of screw pumps is a high possible compression, as screw pumps can be built intrinsically multi-stage, because each thread acts as a stage. Screw pumps thus offer the possibility of achieving a good final vacuum with only one pair of rotors.

With screw pumps a so-called flying bearing of the rotor pair is possible. In a flying storage, storage takes place only from one side of the rotor pair. The screw pump stator itself has no bearing of the rotor pair. This allows easy disassembly of the screw pump stator, e.g. for maintenance and cleaning purposes.

The EP 0 811 766 B1 shows a vacuum pump with two screw pump units and in between the drive of the rotor shafts, which serve for both screw pump units as a carrier of the helical, intermeshing rotors. Both pairs of rotors are each mounted on the fly.

Disadvantages of a flying bearing of the rotors are a higher structural complexity and higher requirements in terms of stability and accuracy of the individual components. For applications with condensing or corrosive media, however, outweigh the benefits of a horizontal bearing of the rotors.

Previously known screw pumps with overhung rotors usually have a pumping speed of over 100 m ³ / h and are therefore significantly larger than for laboratory applications. In such pumps, the storage is sometimes in housed the rotors. For compact screw pumps with a pumping speed of well below 50 m ³ / h, this can hardly be used because the rotors are too small for that. Compact screw pumps therefore require other technological approaches.

Other known types of screw pump with floating rotors provide conventional gear transmissions with bearings outside the rotors and the pumping chamber. Sometimes there is still a seal between these bearings and the pump chamber with abrasive seals, e.g. Shaft seals, or with gap seals, often with labyrinth and external purge gas supply.

Abrasive seals are disadvantageous because they wear. Gap seals with labyrinth and external purge gas supply are complex, require a lot of space and require an external purge gas supply. For the typical use of conventional, large-scale screw pumps, for example in production plants, this is not a significant problem. Even with this aspect, however, different requirements arise for compact screw pumps with a pumping speed below 50 m ³ / h.

The drive of the rotors in two-shaft pumps (such as Roots, claw and screw pumps), for example, by two synchronously running motors or by a means for driving and synchronizing the rotors from a single drive shaft such as a transmission. Mechanical transmissions are large, noisy, expensive and heavy, and require sealing the gear lubricant out and to the pump chamber. Conventional known drives with two motors, which are synchronized electronically, are expensive due to the necessary precise angle measurement and control electronics and are worthwhile, at best, for very large screw pumps.

A vacuum pump with a screw pump unit and such a two-shaft synchronous drive shows the DE 195 22 560 A1 from which the present invention starts. In this vacuum pump, the rotor shafts are provided with cooperating gears, which cause the synchronization of the rotor shafts or in addition to an electronic synchronization enable emergency synchronization. Each rotor shaft is connected to a rotor of a drive motor whose stator is arranged in a motor housing.

The gears of the known vacuum pump can also serve as pulser discs, which are scanned by sensors. These sensors are connected to a control device which monitors the respective rotational position of the rotors relative to a desired value and corrects them via the drive. It is a synchronization of the rotors by electronic means.

Alternatively to the drive from the DE 195 22 560 A1 known vacuum pump, a transmission may also be designed as a so-called magnetic transmission. Here, the synchronization of the two rotor shafts takes place by contactless passing cylinders, disks or the like .. By appropriate magnetization or applied magnets, the associated cylinders are kept in synchronization. Since the cylinders do not touch, a magnetic gearbox runs quietly, free of wear and lubricant. The disadvantage is that between the cylinders high magnetic attraction forces must act.

If one surrounds such a magnetic transmission with suitably arranged coils for generating migrating magnetic fields and energizes them suitably and, if appropriate, according to the position of the magnetized cylinders, a synchronous two-shaft drive analogous to a brushless DC drive or synchronous motor is obtained. The magnetized cylinders of the gearbox serve as motor rotors ( JP-A-04-178143 ).

The from the EP 0 811 766 B1 known vacuum pump applies a magnetic synchronous drive of the type described above for driving the screw pump units. In this vacuum pump with two screw pump units and the seated synchronous two-shaft drive located in the pump chambers on the drive side edges of the rotors sealing rings, which are held stationary on the drive and engage in grooves in the rotors. They form gap seals or abrasive seals as well as at the passage points of the rotor shafts.

A similar construction of a vacuum pump results from the WO 2004/031585 A1 ).

Basically, a synchronous two-shaft drive with magnetized cylinders on the rotor shafts carrying rotor is very compact and therefore very suitable for vacuum pumps with low flow rate of less than 50 m ³ / h. It is disadvantageous if the drive and the bearings are in the area touched by the conveyed gas are located. Such a construction is disadvantageous for many applications, as gases with a certain dust or vapor content or even corrosive gases and vapors often have to be conveyed. Even if the vapors are not corrosive per se, they can in condensed form, for example, damage the bearings by washing out the bearing greases or causing rusting of the bearings. Even pumping out containers filled with ambient air may cause the humidity in the vacuum pump to cause further consequential damage.

For corrosive media, arrangements as disclosed above can not be used. Also, for applications in which the conveyed media contain particles, such arrangements are not suitable.

Therefore, it is provided according to claim 1, the pressure side of the screw pump - at the atmospheric pressure prevails - to put on the drive side, and to keep the storage / drive range to atmospheric pressure, so that on the drive side no sliding seals - apart from lubricant seals within the bearing - are required and a good cooling of the two-shaft synchronous motor is possible. Since, however, due to the flying bearing of the rotors and on the gas inlet side no rotary joints and thus no sliding seals are required, it is possible to design the entire pump for virtually non-contact operation of the rotors. Such a pump contains no wearing parts per se. It can be practically called maintenance-free.

A similar construction again shows that from the DE 195 22 560 A1 known vacuum pump, in which all the storage and the drive of the rotors relevant organs are arranged on the pressure side. However, in each case a bearing of the two rotors is arranged in a bearing body within the respective rotor in this vacuum pump.

The advantageous for the easy disassembly of Schraubenpumpenstators flying mounting of the rotors requires that the storage takes place on the drive side and that outside the rotors, there - as explained above - this in compact pumps, especially those with a pumping capacity less than 50 m ³ / h too small for storage inside the rotors. An important parameter for the size of a vacuum pump with a screw pump unit is the lateral spacing of the rotor shafts. In the focus here are compact Pumps this is preferably between 20 mm and 100 mm. The further dimensions of such a vacuum pump then result structurally from this basic distance measure.

A compact construction of the type described above places considerable demands on the precision of the bearing and on the orientation of the rotors. The dimensions of the total pump are correspondingly small, so that the allowable gaps between the rotors and the housing are extremely narrow. They are typically only in the range 0.02 mm to 0.07 mm. Accordingly, the rotors have to be guided extremely precisely, the screw pump stator must be aligned correctly relative to the rotors, and the angular orientation of the rotors relative to one another must be exactly adjustable.

In a compact vacuum pump of the type in question, the thermal expansion of the individual parts of the vacuum pump is critical. The compression heat and the waste heat of the drive makes the individual components of the vacuum pump very hot. This places high demands on the dimensional accuracy of the parts and in particular on the bearing of the rotor shafts. Here one may have to work with particularly complex production methods in order to be able to meet the requirements with such compact vacuum pumps.

Some relief is provided by the use of purge gas supplies (as described above). This is helpful on the drive side not only for protecting the drive and storage area of the pump from pumped media, but also for cooling the gas and screws in the area of the pressure end of the screw. In this area a large part of the compression heat is released. By the gas delivery device permanently cool purge gas is conveyed past this area, so that hot gas is discharged and the area is cooled.

The teaching of the present invention is based on the problem arising from the DE 195 22 560 A1 Known vacuum pump with a screw pump unit in such a way and further develop that it can be made compact and precise guidance of the rotors or rotor shafts allows, but they can be manufactured and assembled despite the resulting high demands on the manufacturing accuracy of the components with conventional manufacturing methods.

The aforementioned problem is solved in a vacuum pump with the features of claim 1. This is preferably a vacuum pump with a pumping speed of less than 50 m ³ / h.

For the design of a compact vacuum pump, for example, for use in laboratory applications, where it depends on compact design, flexible use and universal chemical and / or high condensate compatibility, according to the invention results in the optimal design a screw pump with flying rotors, with synchronization and drive the two waves by a magnetic gearbox with integrated synchronous drive in the form of coils that directly drive the magnetized cylinders of the magnetic transmission by means of suitable current supply.

To realize a largely backlash-free and exact mounting of the screw rotors, the screw pump according to the invention has a bearing of the two rotor shafts, for example in radial or thrust ball bearings. The rotor shafts each have a so-called fixed bearing in which an outer ring fixedly mounted in the housing and an inner ring fixed to the rotor shaft, and a so-called floating bearing, in which an outer ring and / or inner ring is mounted axially displaceable to the housing or to the rotor shaft. Such an arrangement is advantageous to provide i.a. to compensate for the different thermal expansions of rotor shafts and housing parts.

In the screw pump according to the invention, the two fixed bearings are arranged closer to the pump chamber, so that the rotor shafts are guided here with the least possible play. The two movable bearings are housed according to the invention on the side facing away from the pumping chamber side of the pump, wherein the floating bearings have an axial bias by means of resilient elements in order to achieve a backlash-free operation. Preferably, the spring force acts parallel and in the same direction as the gas force on the rotors at final vacuum, so that under varying suction - and thus changing gas forces on the rotors - the rotors can not be moved axially within the bearing clearance.

This arrangement ensures an exact and play-free guidance of the rotor shafts, a compensation of the thermal expansion of the rotor shafts and housing parts, a cheap and easy installation and the ability to disassemble the drive-side mounting without much effort, for example, for a repair.

According to a preferred embodiment of the teaching of the invention described here, the magnetized cylinders of the drive are arranged on the rotor shafts in each case between rotor shaft bearings spaced apart from one another.

According to a further preferred teaching, the vacuum pump is constructed so that between the drive and the pump chamber, a one-piece or multi-part housing bearing shield is provided, which receives a respective bearing of the two rotor shafts. Preferably, the respective fixed bearing. The bearings of the rotor shafts in this housing bearing shield are preferably arranged on the side facing away from the pump chamber of the housing bearing shield. Furthermore, one finds on the drive side, a one-piece or multi-part motor bearing plate, each receiving a further bearing of the two rotor shafts, preferably the respective floating bearing with the biasing arrangement described above by means of resilient elements. Between the two is the Schraubenpumpenstator, so the component of the pump housing, which forms the suction chamber. The cylinders of the two-shaft synchronous drive are advantageously arranged between the bearings of the two rotor shafts, so that the occurring magnetic forces can be transmitted with a short path into the bearings.

It has already been pointed out above that the construction of the vacuum pump according to the invention makes it possible to dispense with grinding seals as far as possible or completely. In particular, it is not necessary to provide sliding seals between the rotor shaft bearings in the central housing bearing shield and the pump chamber, since atmospheric pressure prevails here anyway.

According to a preferred variant, the housing bearing shield has means for exact alignment of the screw pump stator on one side and a motor bearing shield on the other side. The position of the motor bearing plate to the housing bearing shield determines the orientation of the two rotors, since in these elements, the bearing of the rotor shafts takes place. These must run exactly parallel to each other and centrally in the screw pump stator. The screw pump stator must therefore be aligned exactly centric and parallel to the alignment of the housing bearing shield and the motor end shield.

In order to ensure an exact alignment of screw pump stator to motor bearing plate, the housing bearing shield is preferably designed so that at least a part of this alignment determining mechanical means at the same time serves for the exact positioning of the screw pump stator and the motor end shield.

For example, at least a portion of these mechanical elements are designed so that their formation - for example by machining the housing bearing shield - from one side, i. can be done without rotation of the housing bearing shield during the formation of these mechanical elements.

This can be done, for example, by aligning the screw pump stator and motor end shield relative to the housing bearing shield by means of pins, wherein the crucial elements in the housing bearing shield - the bores for the pins - are continuous and can thus be introduced from one side into the housing bearing shield. Thus, the housing bearing shield does not have to be turned over during the machining of these mechanical elements, which has a very positive effect on the precision of these mechanical elements. As a result, a complex special processing can be omitted.

Another possibility for such mechanical elements that position both screw pump stator and motor end shield would be a centering on the housing bearing shield, but other embodiments are conceivable.

In a further exemplary variant, at least part of this mechanical means is in line with the receiving bores for the rotor shaft bearings. In the preferred embodiment of these mechanical elements in the form of a pinning thus the holes for the pins are arranged in a line with the two shaft bearing bores, so that the machining device must be moved from one hole to the next in one direction only. The precision is further improved and the demands on the processing machine are reduced. At the same time, the travel paths of the processing machine are minimized in this arrangement.

Such an arrangement also implies that the corresponding elements, such as pin bores, in the counterparts of the housing bearing shield, that is the engine bearing shield and the screw pump stator, are in line with the bearing bores in the engine bearing shield or with the main axis of the pump chamber, with corresponding advantages the production of these components.

Furthermore, it is expedient that, since both rotor shafts each have two axially spaced-apart bearings, the axial spacing of these rotor shaft bearings is 0.3 times to 2 times, preferably 0.05 times to 1.5 times, the free length the rotor waves in the pump chamber is.

The previously described conditions create a prerequisite for an exact bearing of the rotor shafts in a compact construction of the vacuum pumps.

It has already been pointed out above that the lateral spacing of the axes of rotation of the rotor shafts is a measure of the compact construction of the vacuum pump according to the invention. According to a preferred teaching, it is provided that the vacuum pump according to the invention is a very compact screw pump unit Has. For this purpose, it is provided that the lateral spacing of the axes of rotation of the rotor shafts is 20 mm to 100 mm, preferably 25 mm to 60 mm.

The upper limit of the lateral distances of the rotor shafts is assigned to the upper limit of the pumping speed for the vacuum pumps according to the invention. A typical value for an exemplary vacuum pump according to the invention has a lateral spacing of the axes of rotation of the rotor shafts of about 40 mm at a pumping speed of about 10 m ³ / h.

According to a further preferred teaching of the invention, the vacuum pump on the drive side even further simplify and optimize their dimensional stability, that you a motor stator comprehensive motor housing together with the housing bearing plate cup-shaped executes one piece and attaches only the engine mount plate separately. As a further preferred alternative, the motor bearing plate together with the motor stator comprehensive motor housing together pot-shaped run in one piece and then connect this cup-shaped unit with the housing bearing plate, in particular spigot (see the above explanations of a preferred variant of the vacuum pump according to the invention).

Fig. 1

ein erstes bevorzugtes Ausführungsbeispiel einer erfindungsgemäßen Vakuumpumpe im Schnitt,

Fig. 2a

in perspektivischer Ansicht die Vakuumpumpe aus Fig. 1, das Motorgehäuse abgenommen, in einer Ausführung mit einer einteiligen Magnethalterung auf jeder Rotorwelle,

Fig. 2b

einen Schnitt durch die Vakuumpumpe gemäß Fig. 1 entlang der dortigen Schnittlinie II - II,

Fig. 3a

in perspektivischer Ansicht die Vakuumpumpe aus Fig. 1 von der Antriebsseite her,

Fig. 3b

in perspektivischer Ansicht die Vakuumpumpe aus Fig. 1 von der Seite des Schöpfraums her,

Fig. 4

in einer Stirnansicht die Vakuumpumpe aus Fig. 1 und 3, Ansicht von der Antriebsseite her bei abgenommenem Motorgehäuse.

In the following, the invention will now be explained in more detail with reference to a drawing showing merely exemplary embodiments. In the drawing shows

Fig. 1

a first preferred embodiment of a vacuum pump according to the invention in section,

Fig. 2a

in a perspective view of the vacuum pump Fig. 1 , the motor housing removed, in a version with a one-piece magnet holder on each rotor shaft,

Fig. 2b

a section through the vacuum pump according to Fig. 1 along the section line II - II,

Fig. 3a

in a perspective view of the vacuum pump Fig. 1 from the drive side,

Fig. 3b

in a perspective view of the vacuum pump Fig. 1 from the side of the scoop,

Fig. 4

in an end view of the vacuum pump Fig. 1 and 3 , View from the drive side with the motor housing removed.

The figures described below show schematically and by way of example possible embodiments and details of the vacuum pump according to the invention.

Fig. 1 This consists essentially of a screw pump unit 2, a drive part 3 and an intermediate housing bearing plate 4. The screw pump unit 2 here has two mutually engaged helical rotors 5, 5 ', in this case in one piece represented with the rotor shafts 6, 6 '. The rotors 5, 5 'run without contact in a screw pump stator 7 with an essentially 8-shaped pump chamber 7 "and cooling ribs 36. In the example shown here, the pump chamber 7" is closed off by a cover 8 having an inlet 9. Due to the counter-synchronous rotation of the two rotors 5, 5 ', gas is conveyed from the inlet 9 to an outlet 10 (not shown here) on the drive side of the rotors 5, 5'.

The drive part 3 has non-contact magnetized cylinders 11, 11 '. A motor stator 12 surrounds the magnetized cylinders 11, 11 'in an essentially 8-shaped manner. The existing of a permanent magnet material with suitable properties cylinder 11, 11 'are suitably magnetized, so that their magnetic interaction causes the synchronization of the two rotor shafts 6, 6' in the form of a magnetic transmission. The winding contained in the motor stator 12 (not shown separately) can be energized by a suitable controller (not shown), so that the magnetized cylinder 11, 11 '- and thus the rotor shafts 6, 6' and the rotors 5, 5 '- in offset in opposite synchronous rotation.

The rotor shafts 6, 6 'have no bearings in the region of the pump chamber 7 ", but rather a first bearing pair 13, 13' is accommodated in the housing bearing shield 4. These bearings 13, 13 'are seated in bearing bores 14, 14' ie outer rings of the bearings 13, 13 'are fixed in the bearing bores 14, 14', and inner rings are fixedly mounted on the rotor shafts 6, 6 'A second bearing pair 15, 15' is mounted in bearing bores 16, 16 ', which are in a motor bearing plate 17 shown in one piece here are arranged.

In the example illustrated here, the axial distance between the bearings 13, 15 or 13 ', 15' assigned to a rotor shaft 6 or 6 'is similar to the free rotor wavelength (protruding into the pump chamber 7 from the bearings 13, 13'). ,

The second bearing 15, 15 'are designed as a floating bearing. In the case shown here sit respective outer rings of the bearings 15, 15 'axially displaceable but with little play in the bearing bores 16, 16', wherein springs 18, 18 ', the bearings 15, 15' suitably bias, so that the storage and thus the Rotor shafts 6, 6 'run free of play. The springs 18, 18 'press the bearings 15, 15' and thus the rotor shafts 6, 6 'with the rotors 5, 5' in the direction of the inlet 9. At negative pressure at the inlet 9 - ie the usual operating state - the gas force acts on the Rotors 5, 5 'due to the pressure difference from the inlet 9 to the outlet 10 in the same direction as the spring force.

In the preferred embodiment shown here, the bearings 13, 13 'are provided on the side facing away from the pump chamber 7 "side of the housing bearing plate 4, and between these bearings 13, 13' and the pump chamber 7" no sliding seals are present.

Preferably, the housing bearing plate 4 on one side means 19 for the exact positioning of Schraubenpumpenstators 7 and on the other side means 20 for the exact positioning of the motor bearing plate 17, wherein at least a portion of these means 19, 20 simultaneously serves for exact positioning for both main components. In this example, these means in the form of pins 19, 19 'and 20, 20', which sit in exactly mounted holes 21, 21 'executed.

The illustrated and preferred embodiment shows in Fig. 1 in that here the drive 3 has a motor housing 17 'comprising the motor stator 12, which in this case is designed in one piece with the motor bearing plate 17 in the form of a cup. This results in a particularly precise positioning of the motor bearing plate 17. In addition to the precisely machined contact surfaces for screw pump stator 7 and motor bearing plate 17 on the housing bearing plate 4, the pinnacles 19, 20, 21 ensure the exact alignment of the motor bearing plate 17 - and thus on the bearing of the rotor shafts 6, 6 '. Also the rotors 5, 5 '- to the screw pump stator 7. By way of example, the holes 21, 21' are arranged continuously and thus introduced from one side into the housing bearing plate 4. In addition, these holes 21, 21 'are in line with the bearing bores 14, 14 'executed (in the direction of view parallel to the rotor shafts, see also Fig. 2 and 4 ), so that in the manufacture of the housing bearing plate 4, the machining device for attaching this crucial for the alignment of the rotor shafts 6, 6 'of the screw pump stator 7 and the motor bearing plate 17 elements must be moved only in one dimension.

Due to the inventive design of the housing bearing plate 4 and the associated parts, the vacuum pump can be very compact, with few parts and comparatively easy to manufacture and assemble.

In Fig. 1 Also shown are gas delivery devices 22, 22 ', which are mounted on the rotor shafts 6, 6' and by their rotation suck gas from feeds 23 for purge gas and blow in the direction of the pump chamber 7. Thus, conveyed medium should be kept away from the storage / drive area In addition, the purge gas stream constantly supplies cool gas to the hot region at the pressure-side end of the rotors 5, 5 ', and the gas which is particularly heated by the compression is permanently exchanged and the pump chamber 7 "is cooled from the inside. The distribution of the scavenging air around the rotor shafts 6, 6 'takes place through cavities 24, 24' around each rotor shaft 6, 6 ', the cross section of the openings from these cavities 24, 24' to the scoop space 7 "being greater than or equal to the cross section the openings to the bearings 13, 13 '.

By way of example, markings (not explicitly shown) are provided on the end faces of the rotors 5, 5 ', which allow the exact alignment of the rotors 5, 5' during pump assembly without manual alignment.

In the embodiment shown here, the holders of the magnetized cylinders 11, 11 'each consist of a first soft-magnetic, substantially cylindrical portion 26, 26', on which the magnetized cylinders 11, 11 'are fixed, for example by gluing. These outer parts 26, 26 'sit snugly, but in itself easily rotatable, on inner, substantially cylindrical parts 27, 27', which for example by means of fits 28, 28 'to the rotor shaft 6, 6' are exactly guided. The power transmission from the inner parts 27, 27 'of the brackets for the magnetized cylinders 11, 11' on the rotor shafts 6, 6 'takes place in the illustrated and preferred embodiment by means of at least one tolerance ring 29, 29', each in a suitable groove the associated rotor shaft 6, 6 'is arranged. Through the tolerance ring 29, 29 'results in a press fit of the inner parts 27, 27' on the rotor shaft 6, 6 'and thus a rotationally fixed connection.

For assembly, the two rotors 5, 5 'aligned with their rotor shafts 6, 6' exactly matching each other, fixed and mounted in the housing bearing plate 4. This can be done by means of a suitable device, for example with the aid of markings on the rotors 5, 5 ', which indicate the exact alignment of the screw threads. For mounting the cylinders 11, 11 ', the preassembled units of the outer parts 26, 26' with the cylinders 11, 11 'and the inner parts 27, 27' are mounted on the rotor shafts 6, 6 '. The outer parts 26, 26 'can still easily be rotated on the inner parts 27, 27' at this time, so that the magnetized cylinders 11, 11 'can align relative to each other (north to south pole). In this position, the cylinders 11, 11 'with their own brackets, namely the outer parts 26, 26', for example by screwing on the inner parts 27, 27 ', fixed.

In Fig. 1 one sees only one fixing screw 30, 30 'of the screw connections on the two rotor shafts 6, 6'. More details can be seen in Fig. 4 , the Stim view from the drive side with removed motor housing 17, 17 'and motor end plate 17. The fixing screws 30, 30' are provided with disc-shaped plates 31, 31 '(washers) for power distribution.

Fig. 2b shows a cut in Fig. 1 identified with II-II. It can be seen here the structure of the brackets for the magnetized cylinders 11, 11 'very well. Inside are the rotor shafts 6, 6 '. On these are the there permanently arranged inner cylindrical parts 27, 27 'of the holder. Coaxially arranged thereon are the outer parts 26, 26 ', which then in turn support the magnetized cylinders 11, 11'.

In an alternative manner, which is not shown here, one can limit the relative adjustability to one of the two brackets. In such a case, one will first mount the magnetized cylinder with a one-piece fixed support on its rotor shaft.

Subsequently, the second magnetized cylinder can then be aligned and fixed relative to the first magnetized cylinder by means of its adjustable holder.

Fig. 2a shows a further embodiment, compared to the in Fig. 1 and Fig. 2b illustrated embodiment with respect to the holder of the magnetized cylinder 11, 11 'is modified. Here you can not see adjustable, one-piece brackets 32, 32 'of the magnetized cylinder 11, 11', which are provided for the purpose of correct assembly already from the outset with marks 33, 33 'in the form of transverse notches. Thus, you can here the cylinder 11, 11 'directly and without further adjustment in their correct orientation on the rotor shafts 6, 6' mount. The advantage of such a construction lies in the smaller number of individual components of the brackets. However, the assembly only with alignment of the notches 33, 33 'is somewhat more difficult.

In the Fig. 2a Given representation of the screw pump 1, in which the motor housing 17 'is removed with the motor bearing plate 17, can also still the pin holes 21, 21' for the positioning means 20, 20 'recognize. It can be seen well that the holes 21, 21 'are in line with the bearing bores 14, 14' for the bearings 13, 13 'of the rotor shafts 6, 6' in the housing bearing plate 4.

Fig. 3a and 3b show schematic exterior views of the vacuum pump 1 according to the invention with the main external components housing bearing shield 4, engine mounting plate 17 and motor housing 17 'and screw pump stator 7, once from the drive side ( Fig. 3a ) and once from the pump chamber side ( Fig. 3b , Ribs 36 partially cut off) ago. One recognizes in Fig. 3a Incidentally stud bolts 17 ", with which the cup-shaped motor housing 17 'integral with the motor bearing plate 17 is fastened to the housing bearing shield 4.

In the example shown, the motor bearing housing 17 'integrally shown here motor bearing plate 17 openings 34 for a cooling air inlet and openings 35 for a cooling air outlet. By a suitable cooling air flow, generated for example by a fan (not shown), which is axially parallel in the extension of the rotor shafts 6, 6 'on the motor bearing plate 17 and blows on the engine mounting plate 17, air flows through the openings 34 in the motor housing 17' and there cools the magnetized cylinder 11, 11 'on the rotor shafts 6, 6' and the motor stator 12, wherein the cooling air can also flow through the gap between the magnetized cylinders 11, 11 'and the motor stator 12. In addition, air flows outside the motor stator 12 in the gap to the motor housing 17 'over. The heated cooling air exits at the openings 35 again.

In the example shown here also has the housing bearing plate 4 to the motor bearing plate 17 matching openings 35 so that the cooling air can flow through there. By the cooling air thus the drive 3 and the housing bearing plate 4 are effectively cooled. Conveniently, the cooling air flow is dimensioned so that a part thereof passes outside on the engine mount plate 17, on the housing bearing shield 4 and on the screw pump stator 7 and thus also cools these components. Possibly. Means are provided to direct the flow of cooling air along the pump.

The openings 34 in the engine mount plate 17 at the same time allow access to the brackets of the cylinder 11, 11 'and their fasteners 30, 30', if present.

It can be provided that the screw pump stator 7 is designed as an extruded profile made of an aluminum alloy and that the extruder profile forming the screw pump stator 7 has longitudinal grooves and / or external means 36 for improved heat transfer to the ambient air, for example. In the case of the means 36 for improved heat transfer to the ambient air, which are referred to here, cooling fins 36 extending in the longitudinal direction of the screw pump stator 7 are concerned in the illustrated exemplary embodiment.

In the illustrated embodiment, it is preferably a vacuum pump with a capacity of about 10 m ³ / h. In this it is provided that the lateral distance of the axes of rotation of the rotor shafts 6, 6 'is about 40 mm.

Typically, for vacuum pumps with a capacity of less than 50 m ³ / h, the lateral spacing of the axes of rotation of the rotor shafts 6, 6 'is at most 100 mm. Values below 20 mm for this lateral distance are difficult to realize.

Overall, the vacuum pump according to the invention is very compact. It is particularly suitable for laboratory applications. <B> LIST OF REFERENCES </ b> 1 screw pump 31, 31 ' plate 2 Screw pump unit 32, 32 ' one-piece bracket 3 driving part 33, 33 ' score 4 Housing bearing plate 34 Cooling air inlet / opening 5, 5 ' Rotor (helical, counter-rotating) 35 Cooling air outlet / opening 6, 6 ' rotor shaft 36 Longitudinal rib = cooling fins 7 Stator = pump stator 7 " suction chamber 8th End cover 9 inlet 10 outlet 11, 11 ' magnetized cylinder 12 motor stator 13, 13 ' 1st bearing of 6, 6 ' 14, 14 ' 1st bearing bore 15, 15 ' 2nd bearing of 6, 6 ' 16, 16 ' 2nd bearing bore 17 Motor bearing shield 17 ' motor housing 17 " studs 18, 18 ' feather 19, 19 ' Positioning means = pins 20, 20 ' Positioning means = pins 21, 21 ' pin hole 22, 22 ' Gas extraction device 23 Feed for purge gas 24, 24 ' cavity 26, 26 ' cylindrical part, outside 27, 27 ' cylindrical part, inside 28, 28 ' fit 29, 29 ' tolerance ring 30, 30 ' fixing screw

Claims (8)

1. Vacuum pump, preferably with a suction capacity of below 50 m³/h, with a screw-pump assembly (2) having two screw-like mutually engaged rotors (5; 5') in a suction chamber (7") of a screw-pump stator (7) which has a suction side with an inlet (9) and a delivery side with an outlet (10), and with a two-shaft synchronous drive (3) with two cylinders (11, 11') which are fastened to rotor shafts (6, 6') carrying the rotors (5, 5') and synchronizable in opposition by the two cylinders (11, 11'), and with one or more windings of a motor stator (12) which surround the two cylinders (11, 11'), the mounting of the two rotor shafts (6, 6') being provided only on the drive (3), that is to say there is no mounting on that side of the suction chamber (7") which is remote from the drive (3), and the delivery side of the screw-pump assembly (2) lying on that side of the suction chamber (7") which faces the drive (3), and the mounting of the rotor shafts (6, 6') and the drive (3) being under atmospheric pressure, characterized in that the two cylinders (11, 11') are magnetized and do not touch one another, in that the rotor shafts (6, 6') are synchronizable in opposition as a result of a mutual magnetic interaction of the two cylinders (11, 11'), in that, by current being applied to the windings of the motor stator (12), travelling magnetic fields can be generated and the two cylinders (11, 11') and consequently the rotor shafts (6, 6') can thereby be rotated synchronously in opposition, in that the two rotor shafts (6, 6') have in each case a fixed bearing (13, 13'), in which an outer ring is fixedly mounted in a housing and an inner ring is fixedly mounted on the rotor shaft (6, 6'), and in each case a loose bearing (15, 15'), in which an outer ring and/or an inner ring are/is mounted axially displaceably in relation to the housing and in relation to the rotor shaft (6, 6') respectively, in that the fixed bearings (13, 13') are arranged nearer to the suction chamber (7'') than the loose bearings (15, 15'), in that the loose bearings (15, 15') have axial prestress by means of resilient elements (18, 18'), and in that the resilient elements (18, 18') are arranged such that the spring force acts parallel to and in the same direction as the gas force upon the rotors (5, 5') under final vacuum.
2. Vacuum pump according to Claim 1, characterized in that the magnetized cylinders (11, 11') are arranged on the rotor shafts (6, 6') in each case between the fixed bearings (13, 13') and loose bearings (15, 15') spaced axially apart from one another.
3. Vacuum pump according to one of the preceding claims, characterized in that a one-part or multipart housing bearing plate (4) is provided between the drive (3) and the suction chamber (7'') and receives the fixed bearings (13, 13') of the two rotor shafts (6, 6'), in that a one-part or multipart motor bearing plate (17) is provided on the drive side and receives the loose bearings (15, 15') of the two rotor shafts (6, 6'), and in that, preferably, the fixed bearings (13, 13') of the rotor shafts (6, 6') in the housing bearing plate (4) are arranged on that side of the housing bearing plate (4) which faces away from the suction chamber (7'').
4. Vacuum pump according to one of the preceding claims, characterized in that a one-part or multi-part housing bearing plate (4) is arranged between the drive (3) and the suction chamber (7'') and a one-part or multi-part motor bearing plate (17) is arranged on the drive side, in that means (19) for positioning the screw-pump stator (7) and means (20) for positioning the motor bearing plate (17) are provided on the housing bearing plate (4), and in that the housing bearing plate (4) is designed such that at least some of these means (19, 20) serve at the same time for positioning the screw-pump stator (7) and the motor bearing plate (17).
5. Vacuum pump according to Claim 4, characterized in that at least some of the means (19, 20) for simultaneously positioning the screw-pump stator (7) and motor bearing plate (17) consist of pins (19, 20) which engage into bores (21), the bores (21) preferably being arranged in the housing bearing plate (4) and preferably, further, being formed as through-bores.
6. Vacuum pump according to one of the preceding claims, characterized in that the axial spacing between the fixed bearings (13, 13') and the loose bearings (15, 15') amounts to 0.3 times to twice, preferably 0.5 times to 1.5 times, the free length of the rotor shafts (6, 6') in the suction chamber (7'').
7. Vacuum pump according to one of the preceding claims, characterized in that the lateral spacing of the axes of rotation of the rotor shafts (6, 6') amounts to 20 mm to 100 mm, preferably 25 mm to 60 mm.
8. Vacuum pump according to one of the preceding claims, characterized in that the drive (3) has a motor housing (17') surrounding the motor stator (12), and in that the motor housing (17') is formed, pot-shaped, in one piece together with the housing bearing plate (4) or, preferably, with the motor bearing plate (17).

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