GB2590663A

GB2590663A - Vacuum pump

Info

Publication number: GB2590663A
Application number: GB1919161.8A
Authority: GB
Inventors: Horky David; Glyn Horler Richard; Chromek Lukas
Original assignee: Edwards sro
Current assignee: Edwards sro
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2021-07-07
Anticipated expiration: 2039-12-23
Also published as: GB201919161D0; GB2590663B; CN218509554U; WO2021130119A1

Abstract

A pump (10, fig 1) comprises an enclosure having a pumping chamber 20 which houses a pair of inter-engaging lobed rotors 60 (50, fig 1) each carried by respective bearings (57, 67, fig 1) located within bearing apertures within a head plate 40. A secondary (oil) chamber 30 is separated from the pumping chamber by the head plate. One of the rotors defines a conduit 70, 80 for fluid communication between the secondary chamber and a discharge aperture 90 in the pumping chamber. Fluid from within the secondary chamber is drawn into the pumping chamber. The discharge aperture is positioned offset from a sealing region (100, fig 5) between the lobed rotors. The sealing region is preferably defined by a converging surface(s) between said lobed rotors, which substantially fluidly isolates a higher-pressure region of said pumping chamber from a lower pressure region of said pumping chamber. The discharge aperture may extend between said lobed rotors and / or orientated parallel to an aligning axis extending between rotational centres of said lobed rotors. The discharge aperture may be defined by a groove (43, fig 4) extending along said head plate and / or by a recess in the head plate.

Description

VACUUM PUMP

FIELD OF THE INVENTION

The field of the invention relates to a vacuum pump.

BACKGROUND

Vacuum pumps such as twin shaft pumps are known. These pumps are typically employed as a component of a vacuum system to evacuate devices. Also, these pumps are used to evacuate fabrication equipment used in, for example, the io production of semiconductors. These twin shaft pumps operate on a cooperating rotor principle, where two rotors rotate in opposite directions and pumping chambers formed between the rotors and stator bore are moved between the gas inlet and gas outlet. In order to avoid back flow of gas between the inlet and outlet, the rotors are generally configured such that the pumping chamber is sealed from the inlet before it is opened to the outlet. To ensure synchronised rotation of the rotors, mechanical structures such as gears are generally housed outside of the pumping chamber.

Although such vacuum pumps provide advantages, they also have their own shortcomings. Accordingly, it is desired to provide an improved arrangement for vacuum pumps.

SUMMARY

According to a first aspect, there is provided a pump comprising: an enclosure having a pumping chamber which houses a pair of inter-engaging lobed rotors, each carried by respective bearings located within bearing apertures defined by a head plate; and a secondary chamber separated from the pumping chamber by the head plate, wherein the at least one of the rotors defines a conduit configured for fluid communication between the secondary chamber and a discharge aperture in the pumping chamber through which fluid from within the secondary chamber is drawn into the pumping chamber, the discharge aperture being -2 -positioned at a location which is offset from a sealing region between the lobed rotors.

The first aspect recognises that a problem with some pumps is that they have one or more secondary chambers separated from the pumping chamber within which gas resides. For example, at a low vacuum end, the gas in a motor housing will be at a pressure below, but close to atmospheric such as 900m bar. At a high vacuum end of the pump, the pressure will be closer to an inlet pressure of the pump, but not quite (somewhere inbetween the inlet pressure and io an exhaust pressure of a first stage). If the inlet pressure is at lmbar and the 1st stage exhaust pressure is 3m bar, then the gear cover will be -2-3mbar (closer to the higher pressure) and it will fluctuate up and down as gas moves in and out. When the pumping chamber operates then a fluid flow can occur from the secondary chamber into the pumping chamber, which can have undesirable consequences such as drawing contaminants into the pumping chamber. Accordingly, a pump is provided. The pump may comprise an enclosure or housing. The enclosure may have a pumping chamber within which at least a pair of rotors may be located. The rotors may operate together to cause pumping within the pumping chamber. The rotors may be carried on bearings. The bearings may be located within bearing apertures provided by a head plate.

Another or a secondary chamber may be separated or divided from the pumping chamber by the head plate. One of the rotors may define a conduit or tube which may provide for fluid communication between the secondary chamber and a discharge aperture or port in the pumping chamber. The discharge aperture in the pumping chamber may provide fluid drawn through the conduit and discharge aperture into the pumping chamber. The discharge aperture may be positioned or located at a location on the head plate which is offset or located away from a sealing region or area between the rotors. In this way, the fluid within the secondary chamber can be pumped from the secondary chamber into the pumping chamber via the conduit and discharge aperture to equalize the pressure between the secondary chamber and the pumping chamber, which helps prevent drawing in contaminants into the pumping chamber from the -3 -secondary chamber whilst also ensuring that the presence of the discharge aperture does not compromise the sealing integrity of the rotors by providing a bypass leakage route between a higher pressure side of the pumping chamber and a lower pressure side of the pumping chamber.

The sealing region may be defined wherein the sealing region is defined by at least one converging surface between the lobed rotors which substantially fluidly isolates a higher pressure region of the pumping chamber from a lower pressure region of the pumping chamber. Accordingly, the sealing region comprises the location where the radial outermost surfaces of the rotors are at a point of closest approach. That point of closest approach isolates or restricts fluid flow from the higher pressure region to the lower pressure region.

The discharge aperture may be positioned to avoid overlap with the sealing region. Accordingly, the discharge aperture may be positioned to avoid covering the sealing region.

The sealing region may intersect with an aligning axis extending between rotational centres of the lobed rotors. Accordingly, the sealing region may be located generally between the centres of the lobed rotors.

The sealing region may occupy an area extending a distance orthogonally from the aligning axis and the discharge aperture is positioned at a further distance orthogonally from the aligning axis than the sealing region. Accordingly, the sealing region may extend away from the aligning axis and the precise point of closest approach may reciprocate slightly about that aligning axis. The discharge aperture may be located further away than a maximum offset position of the point of closest approach.

The discharge aperture may extend between the lobed rotors. By extending between the lobed rotors, sufficient length of discharge aperture may be provided to ensure that fluid communication with the pumping chamber is maintained even -4 -when a lobe of the rotor is radially aligned with the elongate axis of the discharge aperture.

The discharge aperture may be orientated to be parallel to the aligning axis.

The discharge aperture may be defined by a groove extending along the head plate.

The groove may be defined by a recess in the head plate.

The discharge aperture may be positioned for fluid communication with one of an inlet side and an outlet side of the pumping chamber. Accordingly, the discharge aperture may discharge the fluid into either the inlet side or the outlet side. It may be preferable to locate the discharge aperture for discharge into the inlet side, where the pressure is lowest.

The inlet side may comprise a region where fluid to be compressed is received and the outlet side comprises a region where compressed fluid is output.

The discharge aperture may extend between the bearing apertures.

The discharge aperture may be in fluid communication with a plenum which at least partially extends around one of the apertures. Providing a plenum conveniently ensures that the discharge aperture can be in fluid communication with the conduit in all rotational positions of the rotor.

At least one of the lobed rotors may define at least one bore which is in fluid communication with the plenum.

The bore may extend between an inlet aperture defined by the at least one lobed rotor and located for fluid communication with the secondary chamber and an -5 -outlet aperture defined by the at least one lobed rotor and located for fluid communication with the plenum.

The bore may be non-linear.

The bore extend axially from the inlet aperture and bend radially to the outlet aperture defined by a circumferential surface of the at least one lobed rotor.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be 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 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 illustrates schematically a roots-type pump according to one embodiment; Figure 2 illustrates schematically a sectional view showing a portion of the rotor spindle; Figure 3 is an enlarged sectional view of the portion of the head plate in the vicinity of the spindle, where it emerges from the head plate into the pumping chamber; Figure 4 illustrates a recess formed in the surface of the head plate against which the axial end of the rotor faces; and Figure 5 illustrates the location of the recess in relation to the lobes of the rotors. -6 -

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide a pump which has a pressure equalizing structure which helps to equalize pressure within different parts of the pump.

Equalizing pressure can be important since otherwise the pressure differential can cause, for example, oil or other fluids to be transferred from one part of the pump to another, which may be undesirable. By providing a dedicated pressure equalization structure, such leakage and consequential flow of undesirable fluids can be avoided. The pressure equalization structure may also include a filter to help absorb and collect lubrication and contaminates and prevent them from being transmitted to the vacuum chamber. If the pressure equalization structure was not present then the flow may otherwise occur through other structures such as bearings which would make including a filter difficult. Accordingly, a conduit is provided which extends through the rotor spindle and which is in fluid communication with the chamber to be pressure equalized, together with an aperture in the pumping chamber. This provides a fluid flow path from the chamber to be pressure equalized to the pumping chamber. The rotors have a sealing location where the lobes of the two rotors come to their closest proximity, which effectively provides a seal between the uncompressed (inlet) side of the pumping chamber from the compressed (outlet) side of the pumping chamber. If the aperture within the pumping chamber bridges this sealing location then this compromises this sealing and provides a leakage path from the outlet back to the inlet, which reduces the performance of the pump. Accordingly, the aperture is located away from this sealing region to avoid bridging the seal.

Roots-Type Pump Figure 1 illustrates schematically a roots-type pump 10, according to one embodiment. Although a roots-type pump is shown, it will be appreciated that this technique can be applied to other twin shaft pumps such as screw pumps, claw pumps and the like. The pump 10 comprises a pumping chamber 20 separated from an oil chamber 30 by a head plate 40. The pumping chamber 20 houses a pair of lobed rotors 50, 60 supported on spindles 55, 65 supported by -7 -bearings 57, 67 located in the head plate 40 (a similar arrangement exists at the other end of the rotors 50, 60, but is omitted to improve clarity). Gears 59, 69 are attached to the spindles 55, 65 to provide for the required, synchronized counter-rotation of the rotors 50, 60. The oil chamber 30 contains oil which is used to lubricate the gears 59, 69.

As the pump 10 is operated, the pressure in the pumping chamber 20 reduces, which causes a pressure differential between the pumping chamber 20 and the oil chamber 30.

Rotor Spindle Figure 2 illustrates schematically a portion of the spindle 65. The spindle 65 has an axial blind bore 70 extending from an opening in the axial end of the spindle 65 within the oil chamber 30. A group of three bores 80 intersect with a blind end of the bore 70 and extend radially to a respective aperture 90 on the circumferential wall of the spindle 65. This provides a fluid path from the oil chamber 30 through the spindle 65 to the apertures 90.

Head plate Figure 3 is an enlarged view of the portion of the head plate 40 in the vicinity of the spindle 65, where it emerges from the head plate 40 into the pumping chamber 20. As can be seen, a very tight tolerance exists between the outer surface of the spindle 65 and the opening in the head plate 40. Furthermore, a very tight tolerance exists between an axial face 61 of the rotor 60 and an axial face 41 of the head plate 40 to minimize leakage from the outlet side back to the inlet side. Accordingly, the aperture through which the spindle 65 emerges has a chamfer 45 which defines a plenum 47 to allow gas to be received from the apertures 90.

As can be seen in Figure 4, a recess 43 is formed in the axial face 41 of the head plate 40 against which the axial face 61 of the rotor 60 faces. The recess 43 extends to the plenum 47 to provide for fluid communication from the plenum 47 -8 -into the recess 43. The recess 43 in this example extends in a direction parallel to the centres of the spindles 55, 65. However, it will be appreciated that this need not be the case and instead the recess 43 may be formed in any direction which does not bridge the sealing region formed by the lobes of the rotors 50, 60 and which extends beyond the rotational area of the lobes.

Figure 5 illustrates the location of the recess 43 in relation to the lobes 95, 96 of the rotors 50, 60. As can be seen, the recess 43 has a portion 43A which extends beyond the maximum rotational extent of the lobes 95, 96 to ensure that io fluid communication between the pumping chamber 20 and the oil chamber 30 is maintained for any rotational position of the lobes 95, 96. Furthermore, as can be seen, the location of the recess 43 is offset to avoid bridging or overlaying the sealing region 100 between the lobes 95, 96. In this example, the recess 43 is offset in a direction perpendicular to the direction parallel to the centres of the spindles 55, 65 and the width of the recess 43 is selected so as not to overlap the sealing region 100.

Accordingly, it can be seen that gas can be drawn from the oil chamber 30 into the pumping chamber 20 through a fluid path defined starting at the oil chamber 30, through the bore 70, through the bores 80, through the plenum 47, through the recess 43 and into the pumping chamber 20. This helps to ensure pressure equalization to prevent, for example, oil being drawn through the bearings 57, 67 whilst ensuring that the oil chamber can be constantly fluidly coupled with the pumping chamber 20 and ensuring that the seal between the inlet and outlet of the pumping chamber 20 is not compromised.

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

pump 10 pumping chamber 20 oil chamber 30 head plate 40 axial face 41,61 recess 43 portion 43A chamfer 45 plenum 47 rotors 50, 60 spindles 55, 65 bearings 57, 67 gears 59, 69 bore 70, 80 aperture 90 lobes 95, 96 sealing region 100 -9 -

Claims

-10 -CLAIMS1. A pump comprising: an enclosure having a pumping chamber which houses a pair of inter-engaging lobed rotors, each carried by respective bearings located within bearing apertures defined by a head plate; and a secondary chamber separated from the pumping chamber by said head plate, wherein said at least one of said rotors defines a conduit io configured for fluid communication between said secondary chamber and a discharge aperture in said pumping chamber through which fluid from within said secondary chamber is drawn into said pumping chamber, said discharge aperture being positioned at a location which is offset from a sealing region between said lobed rotors.
2. The pump of claim 1, wherein said sealing region is defined by at least one converging surface between said lobed rotors which substantially fluidly isolates a higher pressure region of said pumping chamber from a lower pressure region of said pumping chamber.
3. The pump of claim 1 or 2, wherein said discharge aperture is positioned to avoid overlap with said sealing region.
4. The pump of any preceding claim, wherein said discharge aperture 25 extends between said lobed rotors.
5. The pump of any preceding claim, wherein said discharge aperture is orientated to be parallel to an aligning axis extending between rotational centres of said lobed rotors.
6. The pump of any preceding claim, wherein said discharge aperture is defined by a groove extending along said head plate.
7. The pump of claim 6, wherein said groove is defined by a recess in said head plate.
8. The pump of any preceding claim, wherein said discharge aperture is positioned for fluid communication with one of an inlet side and an outlet side of said pumping chamber.
9. The pump of claim 8, wherein said inlet side comprises a region where io fluid to be compressed is received and said outlet side comprises a region where compressed fluid is output.
10. The pump of any preceding claim, wherein said discharge aperture extends between bearing apertures.
11. The pump of claim 10, wherein said discharge aperture is in fluid communication with a plenum which at least partially extends around one of said bearing apertures.
12. The pump of claim 11, wherein at least one of said lobed rotors defines at least one bore which is in fluid communication with said plenum.
13. The pump of claim 12, wherein said bore extends between an inlet aperture defined by said at least one lobed rotor and located for fluid communication with said secondary chamber and an outlet aperture defined by said at least one lobed rotor and located for fluid communication with said plenum.
14. The pump of claim 12 or 13, wherein said bore is non-linear.-12 -
15. The pump of any one of claims 13 to 14, wherein said bore extends axially from said inlet aperture and bends radially to said outlet aperture defined by a circumferential surface of said at least one lobed rotor.