SCROLL PUMP

Abstract

A scroll vacuum pump has an axially extending drive shaft with an eccentric shaft portion, such that rotation of the drive shaft imparts an orbiting motion to an orbiting scroll relative to a fixed scroll. An axial adjustment mechanism has a plurality of adjustment members angularly spaced around the drive shaft and extending through the pump housing towards the orbiting scroll, the plurality of adjustment members each being configured to provide an independently adjustable axial position of the orbiting scroll. A plurality of sealing means isolate the plurality of adjustment members from a pump chamber, the plurality of sealing means extending around each of the plurality of adjustment members and comprising at least one flexible portion such that one end of the sealing means may orbit relative to a fixed other end of the sealing means.

Claims

1. A scroll vacuum pump comprising: an orbiting scroll; a fixed scroll; a pump housing enclosing a pump chamber of said scroll vacuum pump; an axially extending drive shaft having an eccentric shaft portion, said orbiting scroll being mounted on said eccentric shaft portion such that rotation of said drive shaft imparts an orbiting motion to said orbiting scroll relative to said fixed scroll; an axial adjustment mechanism for adjusting an axial position of said orbiting scroll and thereby a distance between said fixed scroll and said orbiting scroll, said axial adjustment mechanism comprising a plurality of adjustment members angularly spaced around said drive shaft and extending through said pump housing towards said orbiting scroll, said plurality of adjustment members each being configured to provide an independently adjustable axial position of said orbiting scroll; and a plurality of sealing means for isolating said plurality of adjustment members from said pump chamber, said plurality of sealing means extending around each of said plurality of adjustment members and comprising at least one flexible portion such that one end of said sealing means may orbit relative to a fixed other end of said sealing means.

2. The scroll vacuum pump according to claim 1, wherein said plurality of sealing means each comprises bellows, wherein said bellows are optionally formed of at least one of a metal and a polymer.

3. The scroll vacuum pump according to claim 1, wherein said plurality of sealing means are each attached at one end to said pump housing and at an other end to at least one surface orbiting with said orbiting scroll.

4. The scroll vacuum pump according to claim 1, wherein said axial adjustment mechanism comprises an axial thrust bearing arrangement, said axial thrust bearing arrangement comprising: a plurality of ball bearings mounted between said orbiting scroll and at least one thrust surface; and said plurality of adjustment members, said plurality of adjustment members each being configured to independently adjust an axial position of said at least one thrust surface, wherein said at least one thrust surface is optionally mounted on an end of said plurality of adjustment members.

5. The scroll vacuum pump according to claim 4, wherein said at least one thrust surface is mounted such that a radially central point of said at least one thrust surface is between 30% and 80% of a radius of said orbiting scroll.

6. The scroll vacuum pump according to claim 4, wherein said at least one thrust surface comprises a ring-shaped surface facing said orbiting scroll and extending around a central axis of said orbiting scroll.

7. The scroll vacuum pump according to claim 4, wherein said plurality of sealing means are each attached at one end to said pump housing and at another end to at least one surface orbiting with said orbiting scroll, said scroll vacuum pump further comprising at least one receptacle mounted on said orbiting scroll, said at least one receptacle enclosing said ball bearings and comprising said at least one surface, said plurality of adjustment members each extending through a corresponding aperture in said at least one surface, said other end of said plurality of sealing members sealing to said at least one surface around said plurality of apertures.

8. The scroll vacuum pump according to claim 7, wherein said at least one thrust surface comprises a ring-shaped surface facing said orbiting scroll and extending around a central axis of said orbiting scroll and wherein said receptacle has a ring form and is configured and mounted to enclose said ring-shaped thrust surface, said at least one surface comprising a single ring surface and comprising a plurality of apertures at locations corresponding to said plurality of adjustment members.

9. The scroll vacuum pump according to claim 4, wherein said axial thrust bearing arrangement comprises a plurality of thrust surfaces corresponding to said plurality of adjustment members, wherein said plurality of thrust surfaces are optionally substantially circular surfaces.

10. The scroll vacuum pump according to claim 9, wherein said axial thrust bearing arrangement comprises a plurality of modules corresponding to said plurality of adjustment members, said plurality of modules each comprising a plurality of ball bearings mounted within a restraint, said restraint being configured to hold said ball bearings within said module while allowing each of said ball bearings to describe a circular path corresponding to the orbiting motion of the orbiting scroll, wherein said restraint optionally comprises at least one cage comprising a plurality of circular recesses for holding said plurality of ball bearings, said circular recesses having a larger diameter than said ball bearings such that said ball bearings can describe said circular path.

11. The scroll vacuum pump according to claim 9, said scroll vacuum pump comprising a plurality of said receptacles corresponding to said plurality of adjustment members, each of said plurality of receptacles comprising said at least one surface and an aperture in said at least one surface.

12. The scroll vacuum pump according to claim 1, wherein said plurality of adjustment members comprises three adjustment members.

13. The scroll vacuum pump according to claim 1, said fixed scroll comprising a central aperture through which said drive shaft extends.

14. A scroll pump comprising: an orbiting scroll; a fixed scroll; a pump housing enclosing a pump chamber; an axially extending drive shaft having an eccentric shaft portion, said orbiting scroll being mounted on said eccentric shaft portion such that rotation of said drive shaft imparts an orbiting motion to said orbiting scroll relative to said fixed scroll; an axial thrust bearing arrangement comprising: a plurality of ball bearings modules each comprising a plurality of ball bearings, said plurality of ball bearing modules being mounted between said orbiting scroll and a plurality of thrust surfaces; and an adjustment mechanism for adjusting an axial position of said plurality of thrust surfaces and thereby a distance between said fixed scroll and said orbiting scroll, said adjustment mechanism comprising: a plurality of adjustment members angularly spaced around said drive shaft and each being configured for independent adjustment of an axial position of a corresponding one of said plurality of thrust surfaces.

15. The scroll pump according to claim 14, wherein said plurality of thrust surfaces are substantially circular and are each mounted on a corresponding end of said plurality of adjustment members.

16. The scroll pump according to claim 14, wherein said plurality of ball bearings within each of said modules are mounted within a restraint, said restraint being configured to hold said ball bearings within said module while allowing each of said ball bearings to describe a circular path corresponding to the orbiting motion of the orbiting scroll.

17. The scroll vacuum pump according to claim 16, wherein said restraint comprises at least one cage comprising a plurality of circular recesses for holding said plurality of ball bearings, said circular recesses having a larger diameter than said ball bearings such that said ball bearings can describe said circular path, wherein said restraint optionally comprises two cages, a thickness of each of said two cages being between 60 and 99.9% of a radius of said ball bearings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0070] FIG. 1 shows a scroll pump according to one embodiment;

[0071] FIG. 2 shows an end view of the sealing and adjustment members of an embodiment;

[0072] FIG. 3 shows a bearing module according to an embodiment; and

[0073] FIG. 4 shows a side view of the bearing module of FIG. 3.

DETAILED DESCRIPTION

[0074] Before discussing the embodiments in any more detail, first an overview will be provided.

[0075] Embodiments provide a scroll pump, in some cases a scroll vacuum pump with a precision controlled axial thrust bearing to set tip clearance and thereby dispense with the need for tip seals. The thrust bearing is in the inlet vacuum space and there may be mini bellow seals around each axial thrust bearing arrangement to isolate the lubricant from the inlet vacuum space.

[0076] Embodiments provide a set of three metal or polymer bellows to seal the axial thrust bearing and its adjustment system, from the inlet space of the vacuum pump.

[0077] In embodiments, the thrust bearing is mounted on the back of the orbiting scroll. A sealed cover or receptacle is arranged over this bearing. The places at which the adjustment members or screws pass through the cover and connect to the bearing are then sealed with a bellows which allows the cover to move in an orbiting motion with the scroll, while the part of the bearing held by the adjustment screws remains stationary.

[0078] In embodiments there are three adjustment screws and three bellows. The axial thrust bearing can be split into three separate thrust bearings, each individually sealed, or can be a single ring with three adjustment members or screws.

[0079] Using three bellows instead of a single large diameter bellows means that the bellows length can be shorter which makes the pump shorter and more importantly, less susceptible to differential thermal expansion of the parts and therefore maintains improved precision control of the thrust bearing and the scroll-to-scroll axial clearance.

[0080] Where the thrust bearings are individual modules, the individual non-orbiting thrust plates that are mounted on the adjustment members may be supported on a central adjusting pin allow pivoting, and making them self-levelling thereby ensuring good ball contact and potentially better life.

[0081] This arrangement provides a reduced orbiting mass, reducing pump vibration. Furthermore, sealing the bearing covers is potentially easier with this modular arrangement and the bearing parts and the covers are smaller, which reduces costs.

[0082] FIG. 1 shows a scroll pump 10 according to one embodiment. Scroll pump 10 comprises an orbiting scroll 30 mounted on an eccentric cam portion 44 of a rotatable drive shaft 42. The drive shaft 42 is driven by a motor 60 and during use rotation of the drive shaft 42 imparts an orbiting motion to the orbiting scroll 30 relative to a fixed scroll 32. The orbiting motion pumps fluid along a fluid flow path between a pump inlet located near the edge of the scrolls towards a pump outlet near the centre.

[0083] In this arrangement, the fixed scroll 32 comprises an opening through which the drive shaft 42 extends. The motor 60 driving the drive shaft is located on the fixed scroll side of the pump. An inlet vacuum region is located towards the right hand side of the figure away from the motor and bearings. A lower vacuum, or atmospheric, region is located towards the outlet side of the pump towards the motor.

[0084] The drive shaft 42 is sealed from the inlet vacuum space defined by pump housing 40 by cover 50. As the drive shaft 42, drive motor 60 and associated bearings for mounting the drive shaft 42 are located on the exhaust side of the scroll pump, contamination from any lubricants associated with these parts are to some extent isolated from the fluid being pumped simply by the direction of flow of that fluid.

[0085] However, in this embodiment there are axial thrust bearings 15, which themselves contain lubricant within the inlet vacuum region. These provide control of the axial position of the orbiting scroll and thus, of the gap between the scrolls. If contamination by lubricant is to be inhibited these axial thrust bearings 15 should themselves be isolated to some degree from this inlet vacuum region.

[0086] The axial thrust bearings 15 comprise axial adjustment members 12 which extend out through a wall of pump housing 40 allowing access to the adjustment members such that their axial length and thus, the clearances between the scrolls can be adjusted. These axial adjustment members 12 abut against a thrust surface 16 which in this embodiment has a ring shape extending around a central axis of the orbiting scroll 30. The thrust surface 16 is pushed by the adjustment member against the ball bearings 14 of the axial thrust bearing 15 which in turn push against orbiting scroll 30. Thus, by adjusting the lengths of adjustment members 12 the clearance distance between the scroll plates can be controlled.

[0087] In this embodiment there are three adjustment members 12 that can each be independently adjusted allowing not only the clearance distance to be altered but also any swash or lean associated with the orbiting scroll to be reduced. The ball bearings 14 are held in position by retaining rings 18 which extend on either side of ball bearings 14. The ball bearings follow a circular path as the orbiting scroll orbits. There is a further thrust surface mounted on the plate of the orbiting scroll that the ball bearings abut against. In this way, any wear on the orbiting scroll plate by the ball bearings movement is reduced.

[0088] In order to inhibit any leakage of lubricant from the axial thrust bearing into the chamber defined by pump housing 40 and fixed scroll 32 the axial thrust bearing 15 and adjustment members 12 are enclosed within sealing means 20, 22. These sealing means comprise a ring like receptacle or cover 20 having apertures corresponding to the multiple adjustment members 12. These receptacles are fixedly mounted on the back of the orbiting scroll plate. The sealing means further comprises bellows 22 configured to extend from the receptacles 20 and to seal to the receptacle surface around the apertures. The bellows 22 extend from the surface of the receptacle to the end wall of pump housing 40 enclosing the adjustment members 12. The bellows seal to the inner surface of the end wall 40 around an aperture that the adjustment members pass through. In this way, the sealing means 20, 22 seal to surfaces in a fixed way, the relative movement between the orbiting scroll and the end wall of the pump housing being absorbed by the flexibility of the walls of the bellows 22.

[0089] Although, in this embodiment the flexible portion of the sealing means comprises bellows 22, in other embodiments other flexible arrangements may be used to provide the flexible portion of the sealing means. An advantage of the bellows arrangement is that it inhibits rotational movement of the orbiting scroll.

[0090] By providing individual sealing means to surround each of the individual adjustment members of the axial thrust bearing arrangement, the diameter of the sealing means and also the length, which is related to diameter, can be significantly smaller than were the whole axial thrust bearing arrangement to be enclosed in a single sealing means. This allows for a smaller pump to be produced and thereby reduces thermal differentials within the pump allowing for greater precision in the axial control of the scroll positions.

[0091] FIG. 2 shows an end view of the scroll pump of FIG. 1 without the housing 40. In this embodiment, there is a single axial thrust bearing having a ring type shape and a corresponding ring shaped receptacle 20. There are three adjustment members 12 extending through apertures in the surface of the receptacle 20 that faces away from the orbiting scroll. Each of the adjustment members 12 are enclosed by sealing means 22 in the form of bellows which seal to the surface of receptacle 20 around the apertures through which the adjustment members 12 extend and extend up to the housing 40 of the pump (not shown) and seal to this housing. In this way, the adjustment members 12 and the thrust bearings within receptacle 20 are isolated from the vacuum inlet space within pump housing. Sealing members 22 are flexible and this allows the portion contacting receptacle 20 to perform an orbital motion with this receptacle, while the other end of the sealing means 22 is attached to the housing 40 and does not move. In some embodiments, the orbiting motion results in the ball bearings following a circular path of a diameter of between 1 and 9 mm, while the diameter of each of the bellows is between 30 and 150 mm, and the length is between 30 and 160 mm.

[0092] FIG. 3 shows a bearing module 80 of an alternative embodiment where rather than having a single ring-shaped axial thrust bearing, there are a plurality of individual axial thrust bearings corresponding to the plurality of adjustment members. Each adjustment member has a thrust surface on an end face which contacts the ball bearings 14 within individual bearing modules 80, which ball bearings in turn contact a thrust surface on the orbiting scroll.

[0093] In this embodiment there are seven ball bearings 14, although there may be a different number, for example six if there is no central ball bearing, located within a cage 70. The cage 70 has recesses 72 within which the balls can move. The recesses 72 are configured to be large enough to accommodate the balls describing the circular path that allows them to follow the orbiting motion of the scroll.

[0094] FIG. 4 shows a side view of the bearing module 80 along with the thrust plate 82 mounted on the adjustment member. This thrust plate 82 is supported on a central pin (not shown) which allows pivoting of this plate making the thrust plate 82 self-levelling and ensuring good ball contact and potentially a longer life for the bearing. There is a further thrust plate 84 connected to the orbiting scroll and configured to orbit with the scroll. The bearing module 80 comprises two cages 70, one mounted to thrust plate 82 on the adjustment member and the other to thrust plate 84 on the orbiting scroll. Between the two cages 70 are ball bearings 14. The cages 70 are configured such that they have a thickness that is less than the radius of the balls such that the balls 14 contact the thrust plate. The thicknesses may only be slightly less, in some embodiments they are between 70 and 99.9% of the radius of the balls 14. For example, the ball bearings may have a diameter of 8 mm, a radius of 4 mm and the cage may have a thickness of 3.99 mm, giving a cage to radius ratio of 99.75%.

[0095] Providing individual bearing modules 80 rather than a ring bearing allows the thrust plates to be smaller and thus, the orbiting mass to be lower which reduces the pump mass and vibrations. It also potentially allows sealing of the bearing covers to be easier. Furthermore, all of the bearing parts, the covers and the thrust surfaces will be smaller which reduces costs.

[0096] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0097] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0098] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.