LUBRICATION OF GEARS IN TWIN-SHAFT PUMPS

Abstract

A twin-shaft pump comprising: two shafts configured to rotate in synchronisation, each of the shafts comprising a gear mounted thereon, the gears each comprising gear wheels, the gear wheels being configured to intermesh to provide the synchronised rotation; an oil reservoir comprising a porous material, the reservoir being configured when supplied with oil to retain the oil within the porous material; and at least one wick extending from the oil reservoir towards a first of the two shafts and operable to supply oil by capillary action from the porous material along the wick to lubricate the gears.

Claims

1. A twin-shaft pump comprising: two shafts configured to rotate in synchronisation, each of said shafts comprising a gear mounted thereon, said gears each comprising gear wheels, said gear wheels being configured to intermesh to provide said synchronised rotation; an oil reservoir comprising a porous material, said oil reservoir being configured when supplied with oil to retain said oil within said porous material; and at least one wick extending from said oil reservoir towards a first of said two shafts and operable to supply oil by capillary action from said porous material along said wick to lubricate said gears.

2. The twin-shaft pump according to claim 1, wherein said at least one wick extends to contact a surface of at least one of: said first shaft and said gear mounted on said first shaft.

3. The twin-shaft pump according to claim 1, wherein said at least one wick extends to contact a tapered surface having a diameter that increases towards said gear wheel of said gear mounted on said first shaft, rotation of said first shaft causing said tapered surface to rotate and exerting a centrifugal force on oil contacting said tapered surface and causing said oil to migrate from said at least one wick along said increasing diameter surface towards said gear wheel.

4. The twin-shaft pump according to claim 1, wherein said gears mounted on said two shafts are offset with respect to each other.

5. The twin-shaft pump according to claim 1, wherein said gear mounted on a second of said two shafts is arranged to extend in an axial direction beyond said gear on said first shaft in a direction towards said wick extending towards said first shaft.

6. The twin-shaft pump according to claim 1, wherein said wick is arranged to extend towards a portion of said first shaft on a side of said gear wheel remote from a pumping chamber of said pump.

7. The twin-shaft pump according to claim 1, wherein said wick is arranged to extend towards a portion of said first shaft on a same side of said gear wheel as a pumping chamber of said pump.

8. The twin-shaft pump according to claim 6 when dependent on any one of claims 1 to 3, said pump comprising a further wick, said further wick extending towards said first shaft on a same side of said gear wheel as said pumping chamber.

9. The twin-shaft pump according to claim 8, said gear wheel mounted on said second shaft being thicker than said gear wheel mounted on said first shaft and extending beyond said gear wheel mounted on said first shaft on both sides of said gear wheel.

10. The twin-shaft pump according to claim 1, said pump comprising a further wick extending from said oil reservoir towards said second of said two shafts, said wick and said a further wick being configured to supply oil to said gears mounted on said respective shafts.

11. The twin-shaft pump according to claim 10, wherein one of said wick and said further wick is arranged to extend towards a portion of one of said shafts on a same side of said gear wheel as said pumping chamber and the other of said wick and said further wick is arranged to extend towards a portion of the other shaft on a side of said gear wheel remote from said pumping chamber.

12. The twin-shaft pump according claim 8, said pump comprising two further wicks extending from said oil reservoir towards said second of said two shafts, said two further wicks extending towards said second shaft on either side of said gear wheel.

13. The twin-shaft pump according to claim 1, said pump comprising two further wicks, respective ones of said further wicks extending towards each of said shafts and operable to supply oil by capillary action from said porous material along said wicks to lubricate bearings in which said shafts are mounted.

14. The twin-shaft pump according to claim 13, said pump comprising a tapered surface on each of shafts, said tapered surface having a diameter that increases towards said bearings, said two further wicks extending to contact said tapered surfaces.

15. The twin-shaft pump according to claim 1, wherein in operation said shafts are substantially horizontal and said oil reservoir is mounted below said first shaft and an opening in said reservoir through which said wick extends is in an upper surface of said reservoir.

16. The twin-shaft pump according to claim 1, wherein said twin-shaft pump comprises a vacuum pump.

17. The twin-shaft pump according to claim 16, wherein said vacuum pump comprises a screw pump.

18. The twin-shaft pump according to claim 16, wherein said vacuum pump comprises a multi-stage roots pump.

19. The twin-shaft pump according to claim 1, wherein said pump comprises a compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0038] FIG. 1 illustrates a twin-shaft pump according to an embodiment;

[0039] FIG. 2 illustrates the shafts, gear wheels and oil reservoir of an embodiment; and

[0040] FIG. 3 illustrates the shafts, gear wheels and oil reservoir of a further embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0041] Before discussing the embodiments in any more detail, first an overview will be provided.

[0042] Twin shaft pumps and in particular, vacuum pumps such as screw pumps and multi stage roots pumps require the shafts to be synchronised. Where the pumps are for example, high vacuum pumps that are sensitive to oil contamination and operate at high speeds, then alternatives to timing gears have been used to avoid the need to lubricate these gear wheels.

[0043] In this regard, gears require oil lubrication if they are to operate for more than a few hours at high speed. Grease lubrication of gears is only suitable for low speed or short run times. Dry running gears also have a very limited operational life and are not suitable for such applications.

[0044] This problem has been addressed in a low cost, simple and yet effective manner in embodiments of the invention. The solution involves the use of timing gears moubted on the shafts lubricated by oil supplied to the gears from a porous material within a reservoir via a wick.

[0045] Embodiments use a felt reservoir to hold oil within the felt, the oil then being fed to the gears via a wick system. This provides sufficient lubrication for the gears to operate at high speed and avoids the need for any free oil in a gearbox.

[0046] In this way, oil is provided to the gears while avoiding free oil within the pump by using a wick to feed oil from a felt reservoir onto a tapered portion of the shaft. The oil migrates up the taper due to centrifugal force. A gear is located at the end of the taper section and the oil migrates onto this gear and then spreads to the perimeter where it lubricates the teeth.

[0047] Provision of oil in this way allows the pump to be shipped and perhaps even operated at any angle without issues of oil draining out of the gearbox into the pump mechanism.

[0048] FIG. 1 schematically shows a pump according to an embodiment, where twin shafts 10, 20 rotate driving interlocking rotors (not shown) within pumping chamber 70.

[0049] The two shafts 10, 20 extend beyond pumping chamber 70 on either side and are rotationally mounted by bearings 80. Timing gears 60 are mounted towards one end of both first shaft 10 and second shaft 20 and interlock via teeth 63 on the two gear wheels 62. This interlocking forces the shafts to rotate in synchronisation with each other and allows only one of the shafts to be directly driven, the other rotating in response to rotation of the driven shaft.

[0050] Lubrication of gears 60 is provided by oil from oil reservoir 30 which contains a porous material (not shown) such as felt. This oil is wicked from the reservoir 30 by wick 40 which extends from the oil reservoir 30 to a tapered conical surface 50 mounted on the first shaft 10. This tapered surface might be a part of the gear 60, such as the gear hub, or it may be a separate component mounted on shaft 10, or it may be machined into the shaft.

[0051] The oil is pulled by capillary action along wick 40 onto surface 50. The spinning of surface 50, when the pump is operational, pulls oil by centrifugal force along the increasing diameter of cone 50 to gear wheel 62. The oil migrates to the outer surface of this gear wheel and lubricates the interlocking teeth. Some of the oil is flung from the outer surface of the gear wheel 62 and due to the overlap of gear wheel 62 mounted on the second shaft 20 at an offset to gear wheel 62 on the first shaft 10, some of this oil is directed onto the overlapping surface and serves to help lubricate the gear wheel 62 on the second shaft 20. Any oil not caught by the gear wheel 62 on the second shaft 20 drains back into the reservoir. In this way both gear wheels are effectively lubricated by a single wick.

[0052] In this embodiment the gear wheels are at the high vacuum or inlet end of the vacuum pump where the pressure is generally sub-atmospheric. This reduces the effect of windage or air drag from disturbing the wick and the oil migration. In other embodiments, the gear wheels may be mounted on the atmospheric or exhaust end and this may also be effective depending on operational conditions.

[0053] In the embodiment of FIG. 1 first shaft 10, is shown as mounted below second shaft 20, this is purely for ease of illustration and in general the two shafts will be mounted side by side. The two shafts are mounted above an oil reservoir 30 such that oil flung from the gear wheels on either shaft will drain back into the oil reservoir. The shafts can be arranged in a different manner, they may for example be mounted as schematically shown that is one on top of the other or in a vertical orientation. In each case the oil reservoir 30 will be located beneath the shafts such that the wick 40 extends out of an upper surface of the reservoir 30 as is shown.

[0054] FIG. 2 shows an embodiment similar to that of FIG. 1 but with an additional wick 40 which extends towards the second shaft 20. In this embodiment each of the two wicks contacts a tapered surface which in this embodiment is the tapered hub 64 of the gears 60. This additional wick 40 means that the gear wheel 62 mounted on the second shaft 20 receives oil via a wick from the reservoir and not just from the gear wheel 62 mounted on the first shaft. This may improve lubrication. By supplying oil to the opposite side of the gear wheel, the offset mounting of the two gear wheels provides an overlap on the wick side for each gear wheel not directly lubricated by a wick on this side. Thus, oil flung from the lubricated side of each gear wheel will be directed towards the overlapping surface of the other gear wheel. In this embodiment as for FIG. 1 the shafts are mounted side by side although they are shown as one on top of the other for ease of illustration.

[0055] In other embodiments not shown, the two gear wheels may be aligned. In such an embodiment, one of the gear wheels may be lubricated by a wick or they may both be lubricated independently using wicks extending to tapered surfaces on both shafts. In some cases, oil will be supplied to either side of the gear wheels and both gear wheels will be lubricated from both sides.

[0056] FIG. 3 schematically shows a further embodiment, where the gear wheel 62 on the first shaft 10 is narrower than the gear wheel 62 on the second shaft 20, such that the gear wheel on the second shaft extends beyond the gear wheel 62 on the first shaft 10 on both sides. In this embodiment, two wicks 40 extend to tapered surfaces 50 on either side of the gear wheel 62 on the first shaft 10. Oil is thereby supplied to either side of the gear wheel 62 on the first shaft 10 and in operation rotation of this gear wheel causes oil to migrate to the outer surface and some of the oil to be flung from the outer surface and be received by the overlapping surfaces of gear wheel 62 on the second shaft 20, such that this thicker gear wheel is lubricated from oil supplied to the thinner gear wheel.

[0057] In summary, embodiments use an oil felt reservoir to lubricate the gears of a twin shaft vacuum pump, such as a screw pump or multi stage roots pump. The bearings may be grease lubricated, although in some embodiments these too are lubricated using the oil felt reservoir system. The advantage of this system is that there is no free oil in the pump that could drain into the pump mechanism if the pump is turned upside down say in transit.

[0058] 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.

REFERENCE SIGNS

[0059] 10 first shaft

[0060] 20 second shaft

[0061] 30 oil reservoir

[0062] 40 wick

[0063] 50 cone shaft extension

[0064] 60 gear

[0065] 62 gear wheel

[0066] 63 gear teeth

[0067] 64 gear hub

[0068] 70 pump chamber

[0069] 80 bearings