Dry vacuum pump with pressurized bearing and seal

Abstract

A dry vacuum pump, comprising a pump housing, which forms a plurality of suction chambers, wherein rotor elements are arranged in the suction chambers, in order to convey a pump medium from a high-vacuum-side inlet to an outlet. At least one rotor element is arranged in each suction chamber. The rotor elements are connected to a rotor shaft. The rotor shaft is supported by bearings, wherein a high-vacuum-side bearing is arranged in a cut-out. A sealing device is arranged between the high-vacuum-side bearing and at least one suction chamber adjacent to the high-vacuum-side bearing. The cut-out is connected, by means of a first channel, to a region of the dry vacuum pump in which there is a higher pressure than in at least one suction chamber adjacent to the high-vacuum-side bearing.

Claims

1. A dry vacuum pump, comprising: a pump housing defining a plurality of suction chambers, rotor elements arranged in the plurality of suction chambers for conveying a pump medium from a high vacuum-side inlet to an outlet, wherein at least one rotor element of the rotor elements is arranged in each of the plurality of suction chambers, a rotor shaft connected with the rotor elements, and bearings supporting the rotor shaft, wherein the bearings comprise a high vacuum-side bearing arranged in a recess, wherein a seal is arranged between the high vacuum-side bearing and one suction chamber of the plurality of suction chambers is adjacent the high vacuum-side bearing, and wherein a first duct connects the recess with a region of the dry vacuum pump in which a higher pressure prevails than in the one suction chamber adjacent the high vacuum-side bearing.

2. The dry vacuum pump of claim 1, wherein the high vacuum-side bearing is a grease-lubricated bearing.

3. The dry vacuum pump of claim 1, wherein oil is present neither in the recess, nor in the seal.

4. The dry vacuum pump of claim 1, wherein the seal comprises at least one lip seal.

5. The dry vacuum pump of claim 4, wherein the at least one lip seal is a PTFE lip seal.

6. The dry vacuum pump of claim 1, wherein the seal comprises at least two lip seals, and an intermediate chamber between the at least two lip seals is connected, via a second duct, with a second region of the dry vacuum pump in which a pressure prevails that is higher than the pressure in the one suction chamber adjacent the high vacuum-side bearing and lower than the pressure in the recess.

7. The dry vacuum pump of claim 6, wherein two suction chambers are connected by a connecting duct for a fluid communication of the plurality of suction chambers, and that the first duct and/or the second duct are respectively connected with one connecting duct.

8. The dry vacuum pump of claim 6, wherein the first and/or the second duct are directly connected with a respective suction chamber.

9. The dry vacuum pump of claim 1, wherein, in the one suction chamber adjacent the high vacuum-side bearing, a pressure less than 0.01 mbar prevails.

10. The dry vacuum pump of claim 1, wherein a pressure prevailing in the recess is lower than an ambient pressure of other regions of the dry vacuum pump.

11. The dry vacuum pump of claim 1, wherein a pressure prevailing in the recess is higher than 100 mbar.

12. The dry vacuum pump of claim 11, wherein two of the plurality of suction chambers are separated by a partition wall and the connecting duct is arranged in the partition wall.

13. The dry vacuum pump of claim 11, wherein the pressure prevailing in the recess is higher than 400 mbar.

14. The dry vacuum pump of claim 1, wherein a pressure difference between the one suction chamber adjacent the high vacuum-side bearing and the recess is less than 300 mbar.

15. The dry vacuum pump of claim 14, wherein the pressure difference between the one suction chamber adjacent the high vacuum-side bearing and the recess is less than 200 mbar.

16. The dry vacuum pump of claim 1, wherein the first duct has two points of connection with the recess, wherein a respective one of the points of connection is arranged on a respective side of the high vacuum-side bearing, so that no pressure difference exists between the sides of the high vacuum-side bearing.

17. The dry vacuum pump of claim 1, wherein the high vacuum-side bearing is arranged in an end region of the rotor shaft.

18. The dry vacuum pump of claim 1, wherein the plurality of suction chambers comprise a first suction chamber, an intermediate suction chamber, and a last suction chamber, wherein the first suction chamber is the one suction chamber arranged immediately adjacent the high vacuum-side bearing, wherein the high vacuum-side inlet is connected with the intermediate suction chamber, wherein the outlet is connected with the last suction chamber, and wherein the pump medium is conveyed from the intermediate suction chamber to the first suction chamber and the pump medium is conveyed from the first suction chamber to the last suction chamber.

19. The dry vacuum pump of claim 1, further comprising a separation plane of the pump housing extends in the longitudinal direction of the rotor shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the Figures:

(2) FIG. 1 is a schematic illustration of a dry vacuum pump according to the disclosure, cut along a separating plane of the pump housing,

(3) FIG. 2 is a detail of the high vacuum-side bearing and the sealing device of the dry vacuum pump shown in FIG. 1, and

(4) FIG. 3 an alternative embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) The dry vacuum pump of the present disclosure comprises a plurality of pump stage arranged in axial succession. A plurality of suction chambers 12 is provided in one pump housing 10. First rotor elements 14 and second rotor elements 16 are arranged in the suction chambers 12. The first rotor elements 14 are connected to a first rotor shaft 18, and the second rotor elements 16 are connected to a second rotor shaft 20. First rotor elements 14 and second rotor elements 16 cooperate in such a manner that a pump medium is conveyed from the inlet 22 to the outlet 24. For this purpose, the individual pump stages are connected via connecting ducts 26 arranged in the partitioning walls 28 that separate the suction chambers 12 from each other.

(6) The rotor shafts 18 and 20 are rotatably supported by vacuum-side bearings 30, as well as by high vacuum-side bearings 32. In the embodiment illustrated, the high vacuum-side bearing 32 is arranged in the end region of the respective shaft 18, 20.

(7) A first suction chamber 34 is immediately adjacent to the high vacuum-side bearing 32. The inlet is connected to the first suction chamber 34 so that a low pressure prevails in the first suction chamber 34. A sealing device 36 is arranged between the high vacuum-side bearing 32 and the first suction chamber 34, which sealing device is illustrated in detail in FIG. 2. The sealing device 36 comprises a first lip seal 38, as well as a second lip seal 40. These are separated from each other by a spacer 43. Both the first lip seal 38 and the second lip seal 40 are in contact with the rotor shaft 18.

(8) The high vacuum-side bearing 32 is arranged in a recess 42. A first duct 44 is connected to the recess 42. The first duct 44 has two points of connection 48 connected to the recess 42 on one side of the high vacuum-side bearing 32, respectively. It is thereby ensured that no pressure difference prevails across the high vacuum-side bearing, which would have to be compensated by the bearing. This would lead to increased wear or a compromised performance of the bearing. The first duct 44 is connected to a connecting duct 26. In the embodiment illustrated in FIG. 1, the first duct 44 is connected to the connecting duct between the last suction chamber 50 and the penultimate suction chamber 52. At this site, a relatively high pressure of preferably up to 500 mbar already prevails. However, due to the last pump stage arranged in the last suction chamber 50, this pressure is always lower than the ambient pressure around the vacuum pump. It is ensured via the first duct 44 that the same pressure prevails in the recess 42 as in the connecting duct between the last suction chamber 50 and the penultimate suction chamber 52. If the pressure in this region is e.g. 500 mbar, the high vacuum-side bearing is also arranged in a pressure of 500 mbar. Thus, it is possible to use a variety of further lubricants for the high vacuum-side bearing 32. Specifically, the high vacuum-side bearing 32 can therefore be a grease-lubricated bearing.

(9) In the embodiment illustrated, a pressure difference of about 500 mbar exists between the first suction chamber 34 and the recess 42. Usually, this great pressure difference cannot be sealed in a sufficient manner by a dry seal, in particular because of the high rotational speed of the rotor shaft 18. For this reason, the sealing device 36 comprises the first lip seal 38 and the second lip seal 40, between which an intermediate chamber 54 is formed. Here, the intermediate chamber 54 is connected to a region of the vacuum pump via a second duct 56, in which region a higher pressure prevails than in the first suction chamber 34, yet a lower pressure than in the recess 42 in which the high vacuum-side bearing 32 is arranged. For this purpose, it is possible e.g. to connect the second duct 56 to a connecting duct 26 situated, seen in the flow direction, upstream of the connecting duct 26 which the first duct 44 is connected to. By providing the second duct 56, it can be ensured that only a pressure difference is applied across a single lip seal 38, 40 for which the lip seal is actually designed. Thus, strong wear or a burning of the lip seal 38, 40 is prevented.

(10) FIG. 1 shows the dry vacuum pump in section, where the sectional plane coincides with the separation plane of the pump housing 10. The Figure shows the lower pump housing half which has a contact surface 58 by which the lower half of the pump housing 10 is joined to an upper half of the pump housing 10. Here, the first duct 44 and the second duct 56 are formed as grooves in the contact surface 58. By assembling the first pump housing part to the second pump housing part, the groove formed is closed so that the first duct 44 and the second duct 56 are formed.

(11) Of course, further lip seals may be provided in the sealing device 36. The intermediate chambers formed thereby may be connected to further ducts so that a step-wise equalization of the pressure between the first suction chamber 34 and the recess 42 is effected.

(12) Another embodiment is illustrated in FIG. 3, in which like elements are identified by like reference numerals.

(13) In the dry vacuum pump illustrated in FIG. 3, an inlet 60 is connected to an intermediate suction chamber 62. Thus, the lowest pressure prevails in the intermediate suction chamber 62. From the intermediate pump chamber 62, the pump medium s conveyed by the rotor elements 14 into a first suction chamber 34 via connecting ducts 26. Here, a higher pressure already prevails in the first suction duct 34 than in the intermediate suction chamber 62. The pressure difference between the recess 42 in which the high vacuum-side bearing 32 is arranged and the first suction chamber 34 is thus reduced so that the structure of the sealing device 36 can be simplified. Via a connecting duct (not illustrated), the pump medium flows from the first suction chamber, via further suction chambers possibly provided, into a last suction chamber 50 and from there to the outlet 24.

(14) Owing to the arrangement of the pump stages, it is possible to reduce the requirements to the sealing device 36 in a simple manner, so that a higher pressure is achieved in the recess 42. It is thus possible to use a grease-lubricated bearing as the high vacuum-side bearing 32.

(15) In neither of the two embodiments it is required to actively cool the lip seals. Nor is it required to provide oil in the region of the sealing device 36 so as to achieve a suitable sealing effect of the lip seals 38, 40.

(16) If the dry vacuum pump is a double-shaft pump. Sealing devices 36 are provided in particular at both high vacuum-side bearings 32. Preferably, the sealing devices 36 are of identical design in this case.