EP3507496A1

EP3507496A1 - Dry-compressing vacuum pump

Info

Publication number: EP3507496A1
Application number: EP17751770.3A
Authority: EP
Inventors: Thomas Dreifert; Dirk Schiller; Wolfgang Giebmanns; Roland Müller
Original assignee: Leybold GmbH
Current assignee: Leybold GmbH
Priority date: 2016-08-30
Filing date: 2017-08-14
Publication date: 2019-07-10
Anticipated expiration: 2037-08-14
Also published as: CN109642574A; JP2019526738A; CA3034112A1; DE202016005208U1; CN109642574B; WO2018041620A1; EP3507496B1; KR20190043139A; US20190186493A1; BR112019002903A2

Abstract

A dry-compressing vacuum pump, in particular a screw pump, has two rotor elements (14) which are arranged in a pump chamber (12) and which are each carried by a rotor shaft (22). Two shaft ends of the rotor shafts (22) project through a side wall (28) of the pump housing (10). On the two shaft ends (28) there is arranged in each case one toothed belt pulley (38). Furthermore, a drive device and an electric motor for driving the rotor shaft (22) are provided. According to the invention, the rotor shafts (22) are driven by means of a toothed belt (40). To be able to use a toothed belt for drive purposes, a rotational flank clearance between the two rotor elements (14) of greater than ±0.75°, in particular greater than ±1°, is provided.

Description

Dry-compacting vacuum pump

The invention relates to a dry-running vacuum pump, in particular a screw pump.

Dry-compressing vacuum pumps, such as screw pumps, have two rotor elements arranged in a pump chamber. In screw pumps, the rotor elements are designed as helical displacement elements. Each rotor element is supported by a rotor shaft. The two rotor elements are arranged in a pump in the pump chamber formed by the pump chamber. The two rotor shafts protrude through a housing wall, which limits the suction space. Toothed wheels are connected to the two shaft ends. In screw pumps, the two gears mesh with each other. As a result, on the one hand synchronizing the two counter-rotating shafts, as well as on the other hand, driving the two shafts. By providing the meshing gears, only one of the two shafts needs to be driven. To achieve an efficient compaction process and a good degree of delivery, narrow gaps between the rotors are necessary, which necessitate a very exact synchronization. In this case, typically maximum synchronization errors or circumferential backlashes between the rotors of ± 0.25 ° are permissible. This can be the case with dry compressing vacuum pumps on the market by providing meshing gears be realized on the shaft ends. Due to the required precision and the low permissible tolerances, the costs are high.

Furthermore, it is necessary to provide oil lubrication when providing meshing gears for synchronization. This has the consequence that a complex and complicated seal in the housing wall, through which the shaft ends protrude, is required.

Also known is an electronic synchronization of the two rotor shafts. However, this is also complicated and expensive. To drive in the rotor shaft drive means usually electric motors are provided. These can be connected to increase the speed of the vacuum pump with a frequency converter. This is also a relatively expensive component. Optionally, intermediate gears are provided, which in turn must then be lubricated with oil.

Furthermore, it is known for example from DE 38 23 927 to synchronize two rotor shafts of a screw pump via a toothed belt. However, a corresponding product was not technically realized and offered on the market. In order to construct a screw drive driven with a belt drive, with which at least a vacuum of 200 mbar absolute pressure can be achieved when pumping against the atmosphere, correspondingly low synchronization errors between the helical rotor elements must be realized. This would only be possible with the use of toothed belts, if the toothed wheels or toothed belt pulleys, which are driven by the toothed belts, have a very tight tooth gap clearance. Depending on the profile, this is less than 0.1 mm or less than 0.2 mm according to ISO 13050. Alternatively, an enlarged effective diameter of typically 0.2 to 0.4 mm would have to be provided with toothed belt wheels. This results in a forced split error that degrades synchronization. The provision However, increased effective diameter considerably shortens the service life of the toothed belts used. This is not accepted in dry compressing vacuum pumps in the market.

The object of the invention is to provide a dry-compressing vacuum pump which is driven by a toothed belt and does not have the above disadvantages.

The object is achieved according to the invention by the features of claim 1.

The dry-compressing vacuum pump has a suction chamber formed by a pump housing. In the pump chamber two rotor elements are arranged, wherein it is in particular a screw pump in the vacuum pump. Each rotor element is supported by a rotor shaft. The two rotor shafts protrude through a housing wall delimiting the pump chamber so that one shaft end protrudes from the pump chamber per rotor shaft. On the two shaft ends a toothed belt wheel is arranged in each case. Since the drive of the two rotor shafts takes place via a toothed belt, the two toothed belt wheels do not mesh with one another. Furthermore, a drive device such as an electric motor is provided. Here, a pulley is arranged in particular on a drive shaft of the electric motor. The toothed belt is connected to the two toothed belt wheels and the drive device, in particular the pulley of the drive device. In order to be able to provide a toothed belt for driving the two rotor shafts, according to the invention a circumferential backlash between the two rotor elements of more than ± 0.75 °, in particular more than ± 1 °, is provided. Only due to the provision of such a large backlash is the use of timing belt possible.

In spite of the large backlash when compressed against atmospheric high vacuum of, in particular less than 200 mbar absolute pressure To be able to achieve special embodiments of the compression stages, ie, the displacers arranged on the rotor shaft are preferred, wherein the displacement elements can of course also be formed integrally with the rotor shaft.

Due to the large circumferential backlash permissible according to the invention, in particular in the case of the suction-side arranged compression elements, i. at the following on the pump inlet compression elements a comparatively high backflow.

In screw rotors with variable in the conveying direction slope of the profile engagement gap in the inlet area due to the existing here large pitch of the winding of the displacement elements is decisive for the maximum allowable synchronization error. Even comparatively small angular deviations lead to undesirable flank contacts in the suction-side displacement elements. To avoid this, a large backlash must be selected. In order to achieve a good degree of delivery of the pump despite the resulting large gap, it is preferable to increase the number of turns with a large pitch and a large profile gap in the inlet area. In particular, two to three turns are preferably provided in this area. Additionally or alternatively, the number of turns in the outlet region, i. be increased on the pressure side. This results in a lower pressure gradient in the inlet region and thus also a reduced backflow. In the outlet area, the turns have a lower slope. Preferably, in this case six to 10 turns are provided.

Furthermore, it is possible in an alternative preferred embodiment that the two screw rotors have a plurality of rotor or displacement elements or displacement stages. Preferably, at least two displacement elements or displacement stages are provided. Such a vacuum pump screw rotor preferably has at least two helical displacement elements arranged on a rotor shaft. The at least two displacement elements preferably have different pitches, wherein the pitch is constant per displacement element. For example, the vacuum pump screw rotor has two displacement elements, wherein a first suction-side displacement element has a larger constant pitch and a second pressure-side displacement element has a smaller constant pitch. The preferred provision of a plurality of displacement elements, each having a constant pitch, the production is considerably simplified.

Preferably, each displacement element has at least one helical recess which has the same contour over its entire length. The contours are preferably different per displacement element. The single displacement element thus preferably has a constant pitch and a constant contour. This simplifies the production considerably, so that the production costs can be greatly reduced.

To further improve the suction power, the contour of the suction-side displacement element, that is to say in particular of the first displacement element in the pumping direction, is asymmetrical. As a result of the asymmetrical design of the contour or of the profile, the flanks can be configured in such a way that the leakage surfaces, the so-called blow holes, in particular, completely disappear or at least have a small cross section. A particularly suitable asymmetric profile is the so-called "Quirn by profile". Although such a profile is relatively difficult to manufacture, it has the advantage that there is no continuous blow hole. A short circuit is only given between two adjacent chambers. Since it is an asymmetric profile with different profile flanks, At least two steps are required for the production, since the two flanks must be prepared in different steps due to their asymmetry.

The pressure-side displacement element, in particular the last displacement element in the pumping direction, is preferably provided with a symmetrical contour. The symmetrical contour has the particular advantage that the production is easier. In particular, both flanks can be produced with a symmetrical contour by a rotating end mill or by a rotating side milling cutter in one step. Such symmetrical profiles have only small blowholes, but these are continuous, ie. not just between two adjacent chambers. The size of the blow hole decreases as the slope decreases. In this respect, such symmetrical profiles can be provided in particular in the pressure-side displacement element, since in a preferred embodiment, this has a smaller pitch than the suction-side displacement element and preferably also as the displacement elements arranged between the suction-side and pressure-side displacement elements. Although the density of such symmetrical profiles is slightly lower, they have the advantage that the production is much easier. In particular, it is possible to produce the symmetrical profile in a single operation and preferably with a simple end mill or disc milling cutter. This reduces the costs considerably. A particularly suitable symmetrical profile is the so-called "cycloid profile".

The provision of at least two such displacement elements means that the corresponding screw vacuum pump can generate low inlet pressures with low power consumption. The thermal load is low. Arranging at least two such preferably configured displacement elements with constant pitch and constant contour in a vacuum pump leads to substantially same results as in a vacuum pump with a variable displacement displacement element. At high built volume ratios can be provided per rotor three or four Vedrängungselemente.

In order to reduce the achievable inlet pressure and / or to reduce the power consumption and / or the thermal load, in a particularly preferred embodiment, a pressure-side, that is in particular in the pumping last displacement element on a large number of turns on. Due to a high number of turns, a larger gap between the screw rotor and the housing can be accepted with consistent performance. The gap can have a cold gap width of 0.05-0.3 mm. A large number of outlet turns or number of turns in the pressure-side displacement element is inexpensive to produce, since this displacement element has a constant pitch and in particular a symmetrical contour. As a result, a simple and inexpensive production is possible, so that the provision of a larger number of turns is acceptable. Preferably, this pressure-side or last displacement element has more than 6, in particular more than 8 and particularly preferably more than 10 turns. The use of symmetrical profiles in a particularly preferred embodiment has the advantage that both flanks of the profile can be cut simultaneously with a milling cutter. In this case, the milling cutter is additionally supported by the respectively opposite flank, so that deformation or bending of the milling cutter during the milling process and thus caused inaccuracies are avoided.

To further reduce the manufacturing cost, it is particularly preferred to form the displacement elements and the rotor shaft in one piece.

In a further preferred embodiment, the change in pitch between adjacent displacement elements is discontinuous or erratic educated. Optionally, the two displacement elements are arranged in the longitudinal direction at a distance from each other, so that between two displacement elements, a circumferential cylindrical chamber is formed, which serves as a tool outlet. This is particularly advantageous in integrally formed rotors, since the helix producing tool can be brought out in this area in a simple manner. If the displacement elements are manufactured independently of each other and then mounted on a shaft, the provision of a tool outlet, in particular of such a ring-cylindrical region is not required.

In a preferred embodiment of the invention, no tool outlet is provided between two adjacent displacement elements on the pitch change. In the region of the pitch change, both flanks preferably have a defect or recess in order to be able to lead out the tool. Such a defect has no appreciable influence on the compression capacity of the pump, since it is a locally very limited defect or recess.

The vacuum pump screw rotor preferably has a plurality of displacement elements. These may each have the same or different diameters. It is preferred here that the pressure-side displacement element has a smaller diameter than the suction-side displacement element.

In the case of displacement elements which are produced independently of the rotor shaft, they are mounted on the shaft, for example by press fits. In this case, it is preferable to provide elements such as dowel pins for fixing the angular position of the displacement elements to one another.

In particular, in the one-piece design of the screw rotor but also in a multi-piece configuration, it is preferable to this Aluminum or aluminum alloy. It is particularly preferred to produce the rotor from aluminum or an aluminum alloy, in particular AISi9Mg or AISi 17Cu4Mg. The alloy preferably has a high silicon content of preferably more than 9%, in particular more than 15%, in order to reduce the expansion coefficient.

The aluminum used for the rotors has a low expansion coefficient in a further preferred development of the invention. It is preferred if the material has an expansion coefficient of less than 22 * 10 ^-6 / K, in particular of less than 20 * 10 ^-6 / K. In a further preferred embodiment, the surface of the displacement elements is coated, wherein in particular a coating against wear and / or corrosion is provided. In this case, it is preferable to provide an anodic coating or another suitable coating depending on the field of application.

The vacuum pump has at least two stages of compression.

Furthermore, it is preferred in the dry-compressing vacuum pump according to the invention that the vacuum pump has a maximum delivery of at least 75%, in particular at least 85%. The delivery rate is the quotient of the real maximum achieved volume flow and the theoretically possible volume flow in a lossless pump based on the pump chamber geometry and the operating speed. The maximum delivery rate is usually achieved in the range of 1 to 10 mbar.

The toothed belt used is preferably not only for driving but also for synchronizing the rotor shafts. The rotor shafts rotate counter-clockwise in screw pumps. The toothed belt is therefore formed in a preferred embodiment as a double-sided toothed belt. In plan view, therefore, the toothed belt preferably extends between the two connected to the shaft ends of the toothed belt wheels. In a preferred embodiment, with the rotor described above, backlashes of the two toothed belt wheels of more than 0.10 mm can be accepted. The gapping is defined here by the combination of the tooth shape of the toothed belt wheels used and the tooth shape and size of the teeth of the toothed belt. Due to the relatively large tooth gap clearance, the service life of the toothed belt is significantly increased.

To be able to achieve a further increase in the service life of the toothed belt, it is further preferred that the effective diameter is not increased and thus no forced pitch error arises.

The provision of a toothed belt for driving and synchronizing the two rotor shafts in particular has the advantage that no oil lubrication must be provided. This has the particular advantage that the sealing of the shaft ends relative to the pump chamber can be designed significantly cheaper. Furthermore, it is possible to provide grease-lubricated bearings. In particular, the two shafts are mounted in the housing wall through which the shaft ends are guided, wherein these bearings can be grease-lubricated bearings. The opposite shaft ends, which are arranged in the region of the inlet side, are preferably mounted on grease-lubricated bearings, but also oil-lubricated bearings can be used.

Furthermore, a belt tensioning device may be provided to keep the belt constantly tensioned. This is preferably an automatic clamping device, in which the voltage is generated for example by means of a spring or the like, or a fixed bias is applied during assembly. It is also possible to tension the belt by holding the drive motor in a displaceable manner. Another advantage of the drive according to the invention by means of a toothed belt is that it is possible in a simple manner to change the speed of the vacuum pump. For this purpose, only the connected to the drive device toothed belt pulley must be replaced. When replacing the timing belt pulley, the timing belt may need to be replaced.

The invention will be explained in more detail with reference to a preferred embodiment with reference to the accompanying drawings.

Show it :

1 is a schematic longitudinal section of a screw

Vacuum pump

2 is a schematic representation of the drive of the vacuum pump,

3 shows a schematic representation of a combination of toothed belt and toothed belt pulley with tooth space,

4 shows a schematic representation of a combination of toothed belt and toothed belt pulley without tooth gap,

Fig. 5 is a schematic plan view of a first preferred

Embodiment of a vacuum pump screw rotor,

Fig. 6 is a schematic plan view of a second preferred

Embodiment of a vacuum pump screw rotor,

Fig. 7 is a schematic sectional view of displacement elements with asymmetric profile, and Fig. 8 is a schematic sectional view of displacement elements with symmetrical profile.

In Fig. 1 is greatly simplified schematically a pump housing 10 is shown. Within the pump housing 10, a pump chamber is formed in which two rotor elements 14 are arranged. In the illustrated embodiment, the rotor elements 14 are screw rotors. The screw rotors 14 have helical compression elements that intermesh. The two screw rotors 14 are driven in opposite directions. The two screw rotors 14 have in the illustrated embodiment, two pumping stages 16, 18.

The two rotor elements are each arranged on a rotor shaft 22. The two rotor shafts 22 are mounted on the suction side in a housing cover 24 via bearing elements 26. On the opposite side, shaft ends 28 protrude through a housing wall 30. In the housing wall 30, the two rotor shafts 22 are mounted on grease-lubricated bearings 32.

The dry compacting vacuum pump delivers fluid through an inlet 34 to an outlet 36.

To drive the two rotor elements 14, the two shaft ends 28 are each connected to a toothed belt wheel 38, wherein the two toothed belt wheels 38 do not mesh with each other. The synchronization is effected by a toothed belt 40, not shown in FIG. 1 (FIG. 2). The toothed belt is designed as a double-sided toothed belt and for the synchronization of the two toothed belt wheels 38 and the two connected to the toothed belt wheels shaft ends 28 passed between them. Further, a drive device 42 is provided, the drive shaft 44 is connected to a toothed belt pulley 46. FIG. 3 schematically shows teeth of a toothed belt pulley 38 or 46 in conjunction with a toothed belt 40. A tooth 48 of a toothed belt 40 is designed in such a way that a gap hatched is formed in relation to a tooth space 50 between two adjacent teeth 52 of the toothed belt wheel 38. As a result, there is a certain amount of play between the toothed belt 40 and the toothed belt wheel 38. As a result, although the synchronization of the two rotor shafts 22 is somewhat deteriorated, but the life of the toothed belt 48 is increased.

Alternatively, a toothed belt, as shown schematically in Figure 4, may be provided. This has as a so-called zero gap no distances between the tooth space 50 and the tooth 48 of the belt 40.

In the first preferred embodiment (FIG. 5) of the vacuum pump screw rotor, the rotor has two displacement elements 110, 112, which form the two pump stages 16, 18. A first suction-side displacement element 110 has a large pitch of approximately 50-150 mm / revolution. The slope is constant over the entire displacement element 110. The contour of the helical recess is constant. The second pressure-side displacement element 112 again has a constant pitch over its length and a constant contour of the recess. The pitch of the pressure-side displacement element 112 is preferably in the range of 10 - 30 mm / revolution. Between the two displacement elements, a ring-cylindrical recess 114 is provided. This serves to realize a tool outlet due to the one-piece design of the screw rotor shown in FIG.

Furthermore, the integrally formed screw rotor has two bearing seats 116 and a shaft end 118. With the shaft end 118, for example, a gear is connected to the drive. In the second preferred embodiment shown in FIG. 6, the two displacement elements 110, 112 are made separately and then fixed on a rotor shaft 120, for example by pressing. Although this production is somewhat more complicated, the cylindrical distance 114 between two adjacent displacement elements 110, 112 is not required as a tool outlet. The bearing seats 116 and the shaft ends 118 may be integral with the shaft 120. A continuous shaft 120, be made of another, different from the displacement elements 110, 112 material.

Fig. 7 is a schematic sectional view of an asymmetrical profile (e.g., a Quimby profile). The illustrated asymmetrical profile is a so-called "Quimby profile". The sectional view shows two screw rotors that mesh with each other and whose longitudinal direction is perpendicular to the plane of the drawing. The opposite rotation of the rotors is indicated by the two arrows 115. Relative to a plane 117 running perpendicular to the longitudinal axis of the displacement elements, the profiles of the flanks 119 and 121 per rotor are configured differently. The opposing edges 119, 121 must therefore be made independently. However, therefore, although somewhat more complex and difficult production has the advantage that no continuous blow hole is present, but only between two adjacent chambers is a short circuit.

Such an asymmetrical profile is preferably provided in the suction-side displacement element 110.

The schematic sectional view in FIG. 8 again shows a cross section of two displacement elements or two screw rotors, which in turn rotate in opposite directions (arrows 115). Relative to the axis of symmetry 117, the flanks 123 are designed to be symmetrical per displacement element. At the in Fig. 8 illustrated preferred embodiment of a symmetrically designed contour is a cycloid profile.

A symmetrical profile, as shown in FIG. 8, is preferably provided at the pressure-side displacement elements 112.

Furthermore, it is possible that more than two displacement elements are provided. These may possibly also have different head diameters and corresponding foot diameters. In this case, it is preferred that a displacement element with a larger head diameter at the inlet, i. is arranged on the suction side in order to realize a greater pumping speed in this area and / or to increase the built-in volume ratio. Furthermore, combinations of the embodiments described above are possible. For example, one or more displacement elements may be made integral with the shaft or an additional displacement element independent of the shaft and then mounted on the shaft.

Claims

claims

1. A dry-compressing vacuum pump with two rotor elements (14) arranged in a pump chamber (12), two rotor shafts (22) each carrying a rotor element (14), two toothed belt wheels each arranged on a shaft end (28) protruding from the pump chamber (12). 38), a drive means (42) for driving the rotor shafts (22) and connected to the drive means (42) and the toothed belt wheels (38) toothed belt, characterized in that a Verdückfangenenspiel between the two rotor elements of more than ± 0.75 ° in particular more than ± 1 ° is provided.

2. Dry-compressing vacuum pump according to claim 1, characterized in that the maximum delivery rate of the vacuum pump at an operating point, in particular between 1 and 10 mbar is at least 75%, in particular at least 85%.

3. dry-compressing vacuum pump according to claim 1 or 2, characterized in that the toothed belt (40) for synchronizing counter-rotating rotor shafts (22) is designed as a double-sided toothed belt.

4. dry-compressing vacuum pump according to claim 3, characterized in that the toothed belt between the two toothed belt wheels (38).

5. Dry-compressing vacuum pump according to one of claims 1 to 4, characterized in that the tooth gap play of the two toothed belt wheels is greater than 0.15 mm, in particular greater than 0.2 mm.

6. Dry-compressing vacuum pump according to one of claims 1 to 5, characterized in that the rotor shafts (22) by grease-lubricated bearings (32) are mounted, preferably in a housing wall (30) through which the shaft ends (28) are guided per rotor shaft (22) a bearing (32) is arranged.

7. Dry-compressing vacuum pump according to one of claims 1 to 6, characterized in that the vacuum pump is compressed to atmosphere and generates a vacuum of at least 200 mbar absolute.

8. dry-compressing vacuum pump according to one of claims 1 to 7, characterized by a belt tensioning device, which is preferably arranged on the housing wall (32).