Vacuum pump with lubricated drive mechanism

Abstract

A vacuum pump comprising a pumping mechanism 20 and a lubricated drive mechanism 10; the drive mechanism has a housing, a lubricant thrower 16 for distributing lubricant around the drive mechanism, an

Description

FIELD OF THE INVENTION The field of the invention relates to vacuum pumps with lubricated drive 5 mechanism. BACKGROUND The drive mechanisms of vacuum pumps generally require lubrication, and the pressure difference between the pumping mechanism of the vacuum pump and 10 the drive mechanism may encourage the flow of lubricants from the drive mechanism into the pumping mechanism. Although some vacuum pumps may tolerate lubricant within the pumping space, for others, such as dry pump, such lubricant is not desirable and leads to unacceptable contamination of the vacuum space. 15 A particular problem may arise with lubricant throwers that distribute the lubricants around the drive mechanism. These can cause foaming of the lubricant, particularly during pump down mode, which foam tends to fill the housing of the drive mechanism making the leakage of lubricant through any 20 leakage paths more likely. It would be desirable to be able to reduce the leakage of lubricant from a drive mechanism to a pumping mechanism in a vacuum pump. 25 SUMMARY An aspect provides vacuum pump comprising: a pumping mechanism; a lubricated drive mechanism, said drive mechanism comprising: a housing; a lubricant thrower for distributing lubricant around said drive mechanism; and at least one partitioning means for partitioning said drive mechanism into at least 30 two regions, said lubricant thrower being located within a lubricant thrower region and at least one inlet to a leakage path between said drive mechanism and said pumping mechanism being located in at least one other region; wherein said at least one partitioning means is configured such that a flow path is provided between said lubricant thrower region and said at least one other region, said flow path being configured to allow a flow of at least one of gas or liquid lubricant and to impede a flow of foam. 5 It was recognised that lubricant throwers within drive mechanisms, such as gear boxes of vacuum pumps, may cause the lubricant to foam which foam can spread throughout the drive mechanism housing and where there are leakage flow paths between the drive mechanism and the pumping mechanism such foam 10 will tend to be sucked along these leakage flow paths due to the pressure differential and can cause contamination of the vacuum space within the pumping mechanism. The inventors have sought to address this by partitioning the drive mechanism into at least two regions, the region comprising the lubricant thrower where the foaming is triggered and at least one other region, the at least one 15 other region comprising an inlet to one of the leakage flow paths. In this way, the foam can be contained within the drive mechanism housing in a region remote from the leakage flow path(s), thereby providing some protection from lubricant leakage between the drive mechanism and the pumping mechanism. 20 In some embodiments, said at least one partitioning means comprises a wall between a region of said drive mechanism closest to said pumping mechanism and said lubricant thrower region, said flow path being formed by a gap between said housing and said wall. 25 One straightforward way of partitioning the drive mechanism is to provide a wall. A gap between the wall and the housing provides the flow path, the gap being sized such that it is smaller than the size of bubbles within the foam so that the bubbles are impeded from passing through this gap. 30 In some embodiments, the region of the drive mechanism closest to the pumping mechanism comprises the leakage path through the dynamic seals of the vacuum pump and around the circumference of the shaft. ln some embodiments, this region comprises liquid lubricant and the flow path is configured to allow the flow of liquid lubricant and impede the flow of foam or bubbles. 5 In some embodiments, said gap comprises a width of less than 0.5mm. Although, the size of the gap will depend upon the size of the generated bubbles, a size of 0.5mm will generally be sufficient to impede bubbles that are formed in io lubricating oil. In some embodiments, said wall and said drive mechanism housing are configured to provide a contorted or labyrinth type flow path between said regions. 15 In other embodiments, said wall and said drive mechanism housing provide a straight flow path between said regions. A straight flow path between the regions is easier to machine and may allow the 20 flow of liquid and impede the flow of foam. In some embodiments, where the bubbles are small, then a contorted flow path might provide better protection from the travel of foam. In some embodiments, said at least one partitioning means comprises a 25 rotatably mounted partitioning means arranged to separate a region comprising an inlet to a pressure equalisation channel linking said drive mechanism to said pumping mechanism of said vacuum pump and said lubricant thrower region, an outer surface of said partitioning means providing a surface delimiting said flow path from said lubricant thrower region to said region with said flow equalisation 30 channel, said outer surface comprising an increasing diameter such that liquid lubricant flowing along said flow path is pumped along said outer surface by centrifugal force. It may be desirable for the pressure equalisation channel within the drive mechanism to be protected from both the foam and the liquid lubricant and a partitioning means that is configured to spin and has a flow path at least a partial 5 circular configuration with an increasing diameter will allow the flow of liquid to be pushed by centrifugal force along this increasing diameter, and when it reaches the end of the partitioning means the liquid will drop from the surface and not enter the region where the pressure equalisation channel is located. 10 Although the rotatably mounted partitioning means may have a number of forms provided that its diameter increases towards the region having the pressure equalisation channel, in some embodiments it comprises a frustoconical wall mounted to a shaft. Such a shape is easy to manufacture and provides an effective increase in centrifugal force. 15 In some embodiments, said drive mechanism housing comprises an end wall facing a largest diameter end surface of said rotatably mounted partitioning means, said at least one partitioning means further comprising at least one protrusion extending from said end wall around said rotatably mounted 20 partitioning means said at least one protrusion providing a labyrinth type flow path for impeding the flow of foam from said gear wheel region to said region comprising said pressure equalisation channel inlet. The rotatable partitioning means with an increasing diameter is an effective 25 means for inhibiting the flow of liquid but is less effective at inhibiting the flow of foam. A protrusion extending around the rotatably mounted partitioning means and providing a labyrinthine path provides an additional impediment to the flow of foam and also may act as a drip surface for any liquid being expelled from the end of the rotating partitioning means. 30 In some embodiments, said region comprising said inlet to said pressure equalisation channel comprises a spinning lubricant separator, said spinning lubricant separator comprises a porous disc configured to condense lubricant vapour. It is desirable to impede lubricant vapour from entering the pumping mechanism 5 and a spinning lubricant separator within the region comprising the pressure equalisation channel may provide this function. In some embodiments, said porous disc is formed of a material with a high thermal conductivity, preferably a metal, more preferably aluminium or brass. 10 A porous disc with high thermal conductivity may provide an effective surface for the condensation of the vapour. A metal such as aluminium or brass may be particularly effective. The disc may be a porous metal disc and / or a sintered metal disc. Such a disc will capture aerosols and the centrifugal force will help 15 expel them where they will land on the rotatably mounted frustoconical partitioning means and be pumped by the increasing diameter along this path and out of the region via the protrusions which form a drip path. In some embodiments, said pressure equalisation channel runs along a shaft of 20 said drive mechanism and said inlet to said pressure equalisation channel is offset from a centre of said shaft such that said inlet is at substantially a same radial distance from said centre of said shaft as an outlet of said pressure equalisation channel. 25 The pressure equalisation channel may run along the shaft from the driving mechanism into the pumping mechanism. The shaft in the pumping mechanism may have an increased diameter and thus the outlet from such a channel may generally be at an increased offset from the centre of the shaft. This increase in offset between the inlet and outlet leads to fluid being pumped from the inlet to 30 the outlet by centrifugal force. Embodiments address this by providing the inlet at substantially the same radial offset as the outlet and thereby eliminating or at least reducing the centrifugal force. In this regard, substantially the same is taken to be within 10%, preferably within 5% of the distance. In some embodiments, a portion of said shaft within said drive mechanism 5 comprises an increased diameter, said inlet to said pressure equalisation channel being within said increased diameter portion. In order to match the increased diameter of the pumping mechanism shaft, the portion of the shaft comprising the inlet to the pumping equalisation channel may io also be given an increased diameter to provide the same offset. In some embodiments, a portion of said pressure equalisation channel contains a filter for filtering liquid from a flow of fluid flowing through said channel. 15 A filter may be provided within the pressure equalisation channel to remove any remaining lubricant vapour from the fluid flow. Where an effective lubricant separator is used this may not be necessary. The mist filter may also reduce the speed of flow along the channel which can reduce the transmission of any pressure shock that happens when the inlet to the vacuum pump opens. 20 In some embodiments, said filter comprises a mist filter formed of felt material. In some embodiments, said drive mechanism comprises two of said partitioning means such that said drive mechanism comprises said lubricant thrower region 25 and two other regions, one adjacent to said pumping mechanism and one comprising said pressure equalisation channel inlet. Although, the drive mechanism may be divided into two regions, in some embodiments it may be divided into further regions, in some cases three regions. 30 This may be required where there are additional leakage paths, perhaps two leakage paths, one going through the dynamic seals and being adjacent to the pumping mechanism and the other being along the pressure equalisation channel and being at the other end of the drive mechanism. Where there are two potential leakage paths on either side of the lubricant thrower then there may be two partitioning means required to separate the lubricant thrower region from each of these leakage paths. It should be noted that the leakage path through 5 the dynamic seal may be in a region of liquid lubricant and thus, the flow path between this region and the lubricant thrower region may seek to impede foam from the lubricant thrower region flowing in this direction but allow liquid lubricant to pass. The partitioning means between the pressure equalisation channel and the lubricant thrower means may seek to impede both liquid and foam and thus, 10 this partitioning means may comprises a labyrinth type path as well as a spinning partitioning means to inhibit both the liquid and the foam flow. Although, the drive mechanism may comprise any lubricated mechanism where there is a lubricant thrower, in some embodiments said drive mechanism 15 comprises a gear box and said region comprising said lubricant thrower comprises gear wheels. A gear box within a vacuum pump may be a particular source of lubricant foam and thus, it may be particularly advantageous to provide partitioning means within 20 this gear box to protect the leakage paths from the foam generating lubricant thrower region. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be 25 combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that 30 function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 shows a cross section through a drive mechanism and pumping 5 mechanism and leakage paths between the two; Figure 2 schematically shows a vacuum pump according to an embodiment; Figure 3 schematically shows the pressure equalisation path within a shaft of a vacuum pump according to an embodiment; and Figure 4 schematically shows a cross section through a gear box of a vacuum io pump according to an embodiment. DESCRIPTION OF THE EMBODIMENTS Before discussing the embodiments in any more detail, first an overview will be provided. 15 Lubricated drive mechanisms within a vacuum pump that comprise lubricant throwers may become filled with lubricant foam during operation. Leakage paths between the drive mechanism and pumping mechanism may be susceptible to such foam and contamination of the pumping mechanism may occur. 20 Embodiments seek to create lubricant foam free or low concentration zones within the drive mechanism such as a gear box in regions where there are inlets to leakage paths between the drive mechanism and pumping mechanism. The zones may be created either by a separation wall and / or by introducing a combination of centrifugal separator and static labyrinth. 25 During operation the gear box during pump down mode of the vacuum pump may become filled with oil foam due to rotating parts, such as an oil thrower, moving through liquid oil. Consequently, during pressure equalising between the gear box and pumping mechanism the oil foam may enter the pumping mechanism 30 and pollute the mechanism and at the same time the oil content in the gear box is decreasing. Embodiments seek to prevent or at least impede the oil foam from entering those areas where the pressure equalising takes place. Figure 1 shows a drive mechanism 10 and pumping mechanism 20 of a vacuum pump. The drive mechanism is lubricated and has a lubricant thrower 16 mounted on shaft 22. There are potential leakage paths from the lubricated drive 5 mechanism into the pumping mechanism one around the shaft through the dynamic seals and the other through the pressure equalisation channel 37 that runs through the shaft 22. It is desirable to inhibit the flow of lubricant from the drive mechanism to the pumping mechanism along these paths and embodiments seek to address this. io Figure 2 schematically shows a vacuum pump 5 according to an embodiment. Vacuum pump 5 comprises a motor 30, a pumping mechanism 20 and a gearbox 10. The gearbox is a lubricated gearbox and comprises a lubricant thrower 16 for distributing the lubricant around the gear box. This lubricant thrower 16 can 15 cause the lubricant to foam, particularly during pump down, and this foam fills the housing 11 of the gearbox 10 and may travel through the leakage paths 36 and 37 between the gearbox 10 and pumping mechanism 20. In order to mitigate this problem, gearbox 10 comprises partitioning means 18 and 19a and 19b to partition the gearbox into different regions. In effect there is a central region 32 20 that comprises the lubricant thrower 16 and which during operation, particularly pump down, will fill with lubricant foam. There is a further region 31 adjacent to the pumping mechanism 32 which is lubricated and has a leakage path 36 into the pumping mechanism. This leakage path is susceptible to the travel of foam and thus, it is desirable to impede foam from entering region 31. There is 25 another region 33 which encompasses an inlet to the pressure equalisation channel 37 that travels along shaft 22 and connects this region with the pumping mechanism 20. Again it is good if foam is kept out of this region. To address the problem of foam entering the regions 31, 33 that have inlets to 30 leakage paths embodiments provide a partitioning means 18 in the form of a wall that separates the region 31 adjacent to the pumping mechanism with leakage path 36 from the central region 32 that has the lubricant thrower 16 and the gear wheels 17. This partitioning means has a narrow path 34 that allows liquid lubricant to flow between the two regions but has a width that is generally less than the diameter of a bubble of the foam and thus impedes the passage of foam through this flow path and into region 31. In this way region 31 is kept 5 substantially free from foam. Region 33 which has the inlet to pressure equalisation channel 37 should be kept substantially clear of both foam and liquid lubricant and it is partitioned from the central region 32 using partitioning means 19a and 19b. Partitioning means 19a io comprise a protrusion extending from the end wall of housing 11 and surrounding a frustoconical member 19b mounted on shaft 22. There is a flow path 35 that provides a labyrinthine type flow path and has as one surface the outer surface of the frustoconical rotating member. The labyrinthine nature of the path impedes the passage of foam and the spinning of the outer wall of the frustoconical 15 member 35 has an increase in diameter that provides a pumping effect sending any liquid in the flow path along the surface of the frusto-concial member 35 to the larger end where it drips off and falls onto the partitioning means 19a from where it flows back into region 32. In this way, both the foam and liquid are impeded from entering region 33. Region 33 additionally has a spinning disc 14 20 that acts as a lubricant separator and may be formed of a porous material with a high thermal conductivity such as sintered aluminium. This disc acts to condense lubricant vapour within the gas in region 33 prior to it entering the pressure equalisation channel. In this way pumping mechanism within region 22 is kept substantially free from lubricant. 25 Figure 3 schematically shows the pressure equalisation channel 37 passing along shaft 22. The inlet 39A to the channel that is within the gear box 10, is offset from the centre of the shaft and configured to substantially radially align with the outlet 39B to this channel. In this way there is substantially no 30 centrifugal force between the inlet and outlet which force might pump fluid along the channel. In this embodiment there is a mist filter 38 within the pressure equalisation channel 37 to remove lubricant vapour from any gas flowing along the channel. Figure 4 shows a cross section of a drive mechanism of a vacuum pump 5 according to an embodiment. Drive mechanism 10 comprises a lubricant thrower 16 mounted on shaft 22. Shaft 22 has a pressure equalisation channel 37 that flows through the centre of the shaft towards the pumping mechanism. The drive mechanism 10 is contained within housing 11 and is partitioned into regions by partitioning wall 18 which has a wall that runs substantially perpendicular to the io shaft across the cross section of the housing 11 and has a curved section running parallel to the shaft 22 close to the wall of the housing 11 leaving a narrow gap 34 which forms a flow path that allows lubricant to flow between the different regions but impedes the flow of foam that may be generated by lubricant thrower 16. 15 There are further partitioning means 19a and 19b which protect the region with the inlet to the pressure equalisation channel 37 from the region housing the lubricant thrower 16. These partitioning means 19a, 19b comprise a projection from the end wall of housing 11 that extends around a rotatable frustoconical 20 member 19b. The protrusion 19a forms one side of a labyrinthine path 35 between the region housing the lubricant thrower and the region with the inlet to the pressure equalisation channel 37. The other part of a surface forming this flow channel is the outer surface of the rotatable frustoconical member 19b. The labyrinth type nature of the path 35 impedes the passage of foam along the path, 25 while the rotatable frustoconical member 35 pumps liquid along the outer surface towards the end with increased diameter, which liquid when it reaches the end drops off onto the protrusion 19a which forms a drip surface back into the central region. In this way the region with the inlet to the pressure equalisation channel is protected from both lubricant foam and lubricant liquid. 30 Within the region with the inlet to the pressure equalisation channel 37 there is also a lubricant separator 14 mounted on shaft 22. This lubricant separator spins with the shaft and is formed of a porous metal allowing lubricant vapour within the gas entering this region to condense. The lubricant vapour when condensed forms a liquid which is expelled from the spinning separator 14 and lands on the inner surface of the spinning partitioning member 19b. The increasing diameter 5 of this frustoconical member pumps the liquid along to the end where it drips off onto partitioning means 19a and back into the region with the lubricant thrower. In this way, the pressure equalisation channel is protected from both lubricant liquid, lubricant vapour and lubricant foam. io 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 15 equivalents. REFERENCE SIGNS 5 vacuum pump 10 drive mechanism or gear box 11 housing 5 14 lubricant separator 16 lubricant thrower 17 gear wheels 18 partitioning wall 19A partitioning protrusion io 19B partitioning frustoconical spinning member 20 pumping mechanism 22 shaft 30 motor 31 region adjacent to pumping mechanism 15 32 central region with lubricant thrower 33 region with pressure equalisation channel 34 flow path between region 31 and 32 35 flow path between region 32 and 33 36 leakage path around the shaft 20 37 pressure equalisation channel 38 mist filter 39A inlet to pressure equalisation channel 39B outlet to pressure equalisation channel

Claims

1. A vacuum pump comprising: a pumping mechanism;5 a lubricated drive mechanism, said drive mechanism comprising:a housing;a lubricant thrower for distributing lubricant around said drive mechanism; andat least one partitioning means for partitioning said driveio mechanism into at least two regions, said lubricant thrower being locatedwithin a lubricant thrower region and at least one inlet to a leakage path between said drive mechanism and said pumping mechanism being located in at least one other region; whereinsaid at least one partitioning means is configured such that a flow15 path is provided between said lubricant thrower region and said at leastone other region, said flow path being configured to allow a flow of at least one of gas or liquid lubricant and to impede a flow of foam.

2. A vacuum pump according to claim 1, wherein said at least one20 partitioning means comprises a wall between a region of said drive mechanism closest to said pumping mechanism and said lubricant thrower region, said flow path being formed by a gap between said housing and said wall.

3. A vacuum pump according to claim 2, wherein said gap comprises a width 25 of less than 0.5mm.

4. A vacuum pump according to any one of claims 2 or 3, wherein said wall and said drive mechanism housing are configured to provide a contorted or labyrinth type flow path between said regions.

305. A vacuum pump according to any preceding claim, wherein said at least one partitioning means comprises a rotatably mounted partitioning meansarranged to separate a region comprising an inlet to a pressure equalisation channel linking said drive mechanism to said pumping mechanism of said vacuum pump and said lubricant thrower region, an outer surface of said partitioning means providing a surface delimiting said flow path from said5 lubricant thrower region to said region with said flow equalisation channel, said outer surface comprising an increasing diameter such that liquid lubricant flowing along said flow path is pumped along said outer surface by centrifugal force.

6. A vacuum pump, according to claim 5, wherein said rotatably mounted io portioning means comprises a frustoconical wall mounted to a shaft of saidvacuum pump.

7. A vacuum pump, according to claim 5 or 6, wherein said drive mechanism housing comprises an end wall facing a largest diameter end surface of said15 rotatably mounted partitioning means, said at least one partitioning means further comprising at least one protrusion extending from said end wall around said rotatably mounted partitioning means said at least one protrusion providing a labyrinth type flow path for impeding the flow of foam from said gear wheel region to said region comprising said pressure equalisation channel inlet.

208. A vacuum pump according to any one of claims 5 to 7, wherein said region comprising said inlet to said pressure equalisation channel comprises a spinning lubricant separator, said spinning lubricant separator comprises a porous disc configured to condense lubricant vapour.

259. A vacuum pump according to claim 8, wherein said porous disc is formed of a material with a high thermal conductivity, preferably a metal, more preferably one of aluminium or brass.30 10. A vacuum pump according to any one of claims 5 to 9, wherein saidpressure equalisation channel runs along a shaft of said drive mechanism and said inlet to said pressure equalisation channel is offset from a centre of saidshaft such that said inlet is at substantially a same radial distance to said centre of said shaft as an outlet of said pressure equalisation channel.

11. A vacuum pump according to claim 10, wherein a portion of said shaft 5 within said drive mechanism comprises an increased diameter, said inlet to said pressure equalisation channel being within said increased diameter portion.

12. A vacuum pump according to any one of claims 5 to 11, wherein a portion of said pressure equalisation channel contains a filter for filtering liquid from a io flow of fluid flowing through said channel.

13. A vacuum pump according to claim 12, wherein said filter comprises a felt material.15 14. A vacuum pump according to any preceding claim, wherein said drivemechanism comprises two of said partitioning means such that said drive mechanism comprises said lubricant thrower region and two other regions one adjacent to said pumping mechanism and one comprising said pressure equalisation channel inlet.2015. A vacuum pump according to claim 14, wherein said drive mechanism comprises a gear box and said region comprising said lubricant thrower comprises gear wheels.

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