DRY-COMPRESSING VACUUM PUMP

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.

Claims

1. A dry-compressing vacuum pump comprising two rotor elements which are arranged in a suction chamber, two rotor shafts, each supporting a rotor element, two toothed belt wheels respectively arranged on one shaft end extending from the suction chamber, a drive means driving the rotor shafts, and a toothed belt connected with the drive means and the toothed belt wheels, wherein a circumferential backlash between the two rotor elements of more than 0.75 is provided.

2. The dry-compressing vacuum pump of claim 1, wherein the maximum volumetric efficiency of the vacuum pump at an operating point in particular between 1 and 10 mbar is at least 75%.

3. The dry-compressing vacuum pump of claim 1, wherein, for synchronizing rotor shafts rotating in opposite directions, the toothed belt is designed as a double-sided toothed belt.

4. The dry-compressing vacuum pump of claim 3, wherein the toothed belt extends between the two toothed belt wheels.

5. The dry-compressing vacuum pump of claim 1, wherein the tooth gap clearance of the two toothed belt wheels is larger than 0.15 mm.

6. The dry-compressing vacuum pump of claim 1, wherein the rotor shafts are supported by grease-lubricated bearings, one bearing being provided per rotor shaft in a housing wall through which the shaft ends are passed.

7. The dry-compressing vacuum pump of claim 1, wherein the vacuum pump compresses against atmosphere and generates a vacuum of at least 200 mbar absolute.

8. The dry-compressing vacuum pump of claim 1, furthere comprising a belt tensioning means provided on the housing wall.

Description

[0035] The invention will be explained hereinafter in detail with reference to a preferred embodiment and the accompanying drawings.

[0036] In the Figures:

[0037] FIG. 1 is a schematic longitudinal section through a screw-type vacuum pump,

[0038] FIG. 2 is a schematic illustration of the drive of the vacuum pump,

[0039] FIG. 3 is a schematic illustration of a combination of a toothed belt and a toothed belt disc with a tooth gap,

[0040] FIG. 4 is a schematic illustration of a combination of a toothed belt and a toothed belt disc without a tooth gap,

[0041] FIG. 5 is a schematic top plan view of a first preferred embodiment of a vacuum pump screw-type rotor,

[0042] FIG. 6 is a schematic top plan view of a second preferred embodiment of a vacuum pump screw-type rotor,

[0043] FIG. 7 is a schematic sectional view of displacer elements with an asymmetric profile, and

[0044] FIG. 8 is a schematic sectional view of displacer elements with an asymmetric profile.

[0045] FIG. 1 is a greatly simplified schematic illustration of a pump housing 10. A suction chamber is formed inside the pump housing 10, in which chamber two rotor elements 14 are arranged. In the embodiment illustrated the rotor elements 14 are screw-type rotors. The screw-type rotors 14 have helical compression elements that mesh with each other. The two screw-type rotors 14 are driven in opposite directions. In the embodiment illustrated the two screw-type rotors 14 have two pump stages 16, 18.

[0046] The two rotor elements are respectively arranged on a rotor shaft 22. On the suction side, the two rotor shafts 22 are supported in a housing cover 24 via bearing elements 26. On the opposite side, shaft ends 28 extend through a housing wall 30. The two rotor shafts 22 are supported in the housing wall 30 by grease-shaped bearings 32.

[0047] The dry-compressing vacuum pump convey a medium through an inlet 34 to an outlet 36.

[0048] For driving the two rotor elements 14, the two shaft ends 28 are each connected with a respective toothed belt wheel 38, wherein the two toothed belt wheels 38 do not mesh with each other. Synchronizing is effected via a toothed belt 40 (FIG. 2) not illustrated in FIG. 1. The toothed belt is designed as a double-sided toothed belt and, for synchronizing the two toothed belt wheels 38 or the two shaft ends 28 connected with the toothed belt wheels, is passed between these. Further, a drive means 42 is provided whose drive shaft 44 is connected with a toothed belt disc 46.

[0049] FIG. 3 schematically illustrates teeth of a toothed belt disc 38 or 46 in connection with a toothed belt 40. A tooth 48 of the toothed belt 40 is designed such that gap, illustrated in hatched lines, is formed opposite a tooth interstice 50 of two adjacent teeth 52 of the toothed belt wheel 38. Thereby, a certain play exists between the toothed belt 40 and the toothed belt wheel 38. The synchronizing of the two rotor shafts 22 may be somewhat compromised thereby, but the service life of the toothed belt 48 is extended.

[0050] As an alternative, a toothed belt may be provided, as schematically illustrated in FIG. 4. The same shows no distances between the tooth interstice 50 and the tooth 48 of the belt 40, which is referred to as a zero gap.

[0051] In the first preferred embodiment (FIG. 5) of the vacuum pump screw-type rotor, the rotor has two displacer elements 110, 112 forming the two pump stages 16, 18. A first, suction-side displacer element 110 has a large pitch of about 50-150 mm/rotation. The pitch is constant throughout the displacer element 110. The contour of the helical recess is constant as well. The second pressure-side displacer element 112 also has a constant pitch and a constant contour of the recess over its length. The pitch of the pressure-side displacer element 112 is preferably in the range of 10-30 mm/rotation. An annular cylindrical recess 114 is provided between the two displacer elements. The same serves to realize a tool run-out, due to the integral design of the screw-type rotor illustrated in FIG. 5.

[0052] Further, the integrally formed screw-type rotor has two bearing seats 116 and a shaft end 118. For example, a gear is connected with the shaft end 118 for driving.

[0053] In the second preferred embodiment illustrated in FIG. 6, the two displacer elements 110, 112 are manufactured separately and are then fixed on a rotor shaft 120, e.g. by pressing. This way of manufacturing may be somewhat more complex, but the cylindrical distance 114 between two adjacent displacer elements 110, 112 is not required as a tool run-out. The bearing seats 116 and the shaft ends 118 may be an integral part of the shaft 120. A continuous shaft 120 may also be made of another material different from that of the displacer elements 110, 112.

[0054] FIG. 7 illustrates a schematic sectional view of an asymmetric profile (e.g. a Quimby profile). The asymmetric profile illustrated is a so-called Quimby profile. The sectional view shows two screw-type rotors meshing with each other, their longitudinal direction being perpendicular to the drawing plane. The oppositely directed rotation of the rotors is indicated by the two arrows 115. With reference to a plane 117 perpendicular to the longitudinal axis of the displacer elements, the profiles of the flanks 119 and 121 are designed differently per rotor. The opposing flanks 119, 121 thus have to be manufactured independently. The manufacture which is therefore somewhat more complex and complicated, has the advantage, however, that no continuous blowhole exists and a short circuit exists merely between two adjacent chambers.

[0055] Such an asymmetric profile is preferably provided in the suction-side displacer element 110.

[0056] The schematic sectional view in FIG. 8 again shows a cross section through two displacer elements or two screw-type rotors which again rotate in opposite directions (arrows 115). With reference to the axis of symmetry 117, the flanks 123 of each displacer element are symmetrically designed. The preferred embodiment of a symmetrically designed contour illustrated in FIG. 8 is a cycloid profile.

[0057] A symmetric profile, as illustrated in FIG. 8, is preferably provided in the pressure-side displacer elements 112.

[0058] Further, it is possible that more than two displacer elements are provided. These may possibly also have different head diameters and corresponding base diameters. In this respect it is preferred that a displacer element with a larger head diameter is arranged at the inlet, i.e. at the suction side, so as to realize a higher suction capacity in this region and/or to increase the built-in volume ratio. Further, combinations of the above described embodiments are possible. For example, one or a plurality of displacer elements may be manufactured integrally with the shaft or an additional displacer element may be manufactured independently of the shaft and may then be mounted on the shaft.