GB2618812A

GB2618812A - Multi-stage vacuum pump with improved heat transmission

Info

Publication number: GB2618812A
Application number: GB2207238.3A
Authority: GB
Inventors: Turner Neil
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2022-05-18
Filing date: 2022-05-18
Publication date: 2023-11-22
Also published as: GB202207238D0

Abstract

A multi-stage vacuum pump comprises an inlet stage 100a, an outlet stage 100g and at least two intervening stages 100b-100f that have compression chambers of incrementally decreasing volume in flow series between the inlet stage and the outlet stage. A first of the intervening stages 100b defines a compression chamber of a second largest volume and a second of the intervening stages 100f defines a compression chamber of a second smallest volume. The inlet, outlet and intervening stages are positioned adjacent to each other in a non-sequential order such that the inlet stage has fewer than two other stages positioned between itself and the outlet stage. The arrangement of the stages enhances heat transfer between stages that generate more heat during pump operation and those that generate less heat to regulate the working gas temperatures across all stages. The inlet stage may be positioned adjacent to the outlet stage such that there are no intervening stages positioned between them. The outlet stage may be positioned between and closest to both the inlet stage and the first intervening stage. The first intervening stage may be positioned adjacent the inlet stage such that there are no other stages positioned between them.

Description

MULTI-STAGE VACUUM PUMP WITH IMPROVED HEAT TRANSMISSION

TECHNICAL FIELD

This disclosure relates to a multi-stage vacuum pump.

BACKGROUND

Vacuum systems commonly utilise pumps in order to evacuate Working' gases from the system. One type of vacuum pump used in such systems is a Roots vacuum pump.

A Roots vacuum pump generally includes two counter-rotating shafts with a rotor mounted on each shaft. The rotors include a series of lobes and recesses defined between the lobes. The rotors are mounted such that a lobe of the rotor on one shaft cooperates with a corresponding recess of the rotor on the other shaft. As the shafts and rotors rotate, gas is trapped and compressed between the cooperating lobes and the recesses. The repeated trapping and compression of gas between the rotors generates a pumping action that can be used to pump gas from an inlet on one side of the rotors to an outlet on the opposite side to evacuate working gases from a system.

It is common for Roots vacuum pumps to feature several stages of cooperating rotors; with each stage being axially spaced apart along the shafts and separated by a stator structure that defines a series of chambers that house the rotors of each stage. Each successive stage decreases in volume, such that the multiple stages progressively increase gas compression across the pump, and allow it to provide a higher degree of vacuum for the system in an efficient manner.

In many vacuum pump applications (e.g., semiconductor processing and manufacture), it is necessary to maintain the working gases passing through the pump stages at a minimum temperature that avoids the gases condensing into solids or liquids. Moreover, in some applications, it is also necessary to maintain the working gases below a maximum temperature in each stage to prevent the gases from decomposing or undergoing chemical reactions. Such decomposition and/or chemical reactions may form undesirable liquids and solids in the pump or have harmful effects (e.g., such as being corrosive).

As will be appreciated by the skilled person, as working gas passes through each stage, its pressure will change, and so the minimum and/or maximum temperatures that need to be maintained to avoid condensation and/or unwanted -2 -reaction will vary accordingly between stages. Moreover, each pump stage will generate differing amounts of heat depending on the compressive work being done by a particular stage for a particular vacuum pressure operating regime/amount of gas throughput. Therefore, maintaining the working gas in each stage within the appropriate temperature window can present a challenge for pump designers.

Although there are various known pump configurations that have been developed to help address this challenge, improvements are nonetheless desirable. Accordingly, there is a need to provide a multi-stage vacuum pump that enables improvements in the use and transmission of heat around the pump to maintain pump stages at appropriate temperatures during operation.

Although the present disclosure is exemplified with regards to a multi-stage Roots vacuum pump, it is to be appreciated that this disclosure and its benefits are applicable and extend to any other suitable type of multi-stage vacuum pump that includes a plurality of stages and needs to account for the different temperature conditions therein during operation. Such pumps may generally include a plurality of rotors interacting within a plurality of chambers in a stator, such as a claw type vacuum pump, and have four or more stages. In some such pumps, different types of rotors can be combined in the same pump, so the pump is of a mixture of types. For example, some stages in the pump may be of a Roots type and other stages in the pump may be of a claw type.

SUMMARY

From one aspect, the present disclosure provides a multi-stage vacuum pump. The pump comprises an inlet stage defining a compression chamber of a largest volume, an outlet stage defining a compression chamber of a smallest volume, and at least two intervening stages that have compression chambers of incrementally decreasing volume between that of the inlet stage and the outlet stage. A first of the intervening stages defines a compression chamber of a second largest volume and a second of the intervening stages defines a compression chamber of a second smallest volume. The inlet, outlet and intervening stages are positioned adjacent to each other in a non-sequential order, such that the inlet stage has fewer than two other stages positioned between itself and the outlet stage.

In this manner, the inlet stage can be said to be one of two stages closest to the outlet stage. In this context, 'closest' relates to the relative distance between -3 -the stages. In general, the stages are arranged adjacent to each other along an axis (e.g., a rotor central axis). Therefore, this distance will commonly be defined by the axial distance between stages parallel to this axis.

It will be understood, that although the inlet, outlet and intervening stages are positioned adjacent each other in a non-sequential order, they are nonetheless serially fluidly connected (e.g., via gas passages) in order of decreasing volume (i.e., in order to allow for normal compressive operation of the pump).

By placing the inlet stage out of normal sequential order and closer to the outlet stage in this manner, enhanced heat transfer between the outlet and inlet stages is permitted that can keep the working gases therein at the appropriate temperature during pump operation. This can prevent condensation and/or thermal decomposition/unwanted chemical reactions of the working gas. Moreover, this can be achieved without the need for additional heat transfer members or external devices.

In one embodiment, the inlet stage is positioned adjacent to the outlet stage such that there are no intervening stages positioned between them. In this manner, the inlet stage can be said to be directly adjacent to the outlet stage.

In this manner, the heating of working gas in the inlet stage due to heat transferred from the outlet stage can be sped up due to its closer proximity to the outlet stage.

In a further embodiment of either of the above, the outlet stage is positioned between and closest to both the inlet stage and the first intervening stage.

In this manner, the outlet stage is positioned directly adjacent to both the inlet and first intervening stage and separates them from each other.

This arrangement means both the inlet and first intervening stage are in close proximity to the outlet stage for improved heat transfer thereto. This can speed up heating of working gas in both the inlet and first intervening stage. Moreover, having the inlet and first intervening stage either side of the outlet stage can help act as a heatsink for the outlet stage.

In further embodiments of any of the above, the first intervening stage is positioned adjacent the inlet stage such that there are no other stages positioned between them.

In this manner, the inlet and first intervening stage are positioned directly adjacent to each other (i.e., paired together). Either one of the inlet or first intervening stage can be directly adjacent to the outlet stage in different examples -4 -of this embodiment. Again, this embodiment places both the inlet and first intervening stage in close proximity to the outlet stage which provides enhanced heat transfer thereto, and the paired inlet and first intervening stage can act as a heat sink for heat produced by the outlet stage.

In another embodiment, the first intervening stage is positioned between and closest to both the inlet stage and the outlet stage.

In this manner, the first intervening stage is positioned directly adjacent to both the inlet and outlet stage and separates them from each other.

As well as the heat transfer advantages discussed above, it is thought that by having the first intervening stage separating the inlet and outlet stage in this manner, the working gas pressure difference across the stages can be reduced (i.e., compared to the outlet and inlet stage being placed directly next to each other). This can help reduce (or make it easier to reduce) gas leakage between the stages.

In a further embodiment of any of the above, the second intervening stage is positioned adjacent the first intervening stage such that there are no other stages positioned between them.

In this manner, the second intervening stage is positioned directly adjacent the first intervening stage. This can help transfer heat generated in the second intervening stage to the first intervening stage.

In another embodiment, the second intervening stage is positioned adjacent the inlet stage such that there are no other stages positioned between them.

In this manner, the second intervening stage is positioned directly adjacent the inlet stage. This can help transfer heat generated in the second intervening stage to the inlet stage.

In a further embodiment of any of the above, a third of the intervening stages defines a compression chamber of a third largest volume, and the second intervening stage is positioned adjacent the third intervening stage such that there are no other stages positioned between them.

In this manner, the second intervening stage is positioned directly adjacent the third intervening stage. This can help transfer heat generated in the second intervening stage to the third intervening stage.

As discussed above, although the stages are positioned non-sequentially they are still serially fluidly connected in order of decreasing volume, such that in this example, working gas passes through the stages in the order: inlet stage > first -5 -intervening stage > third intervening stage (>further intervening stages, if present) > second intervening stage > outlet stage.

The various placements of intervening stages relative to each other provided within the scope of this disclosure can help enhance heat transfer between stages that typically generate more heat during pump operation to those that typically generate less heat. This can help keep working gases at suitable temperatures across all the stages of the pump, as well as help balance temperatures (i.e., reduce temperature gradients) across the pump.

Further embodiments can feature any suitable number of further intervening stages (e.g., fourth and/or fifth intervening stages) positioned adjacent to each other in various orders (e.g., either directly adjacent to each other or separated by one or more of the aforementioned intervening stages).

It will be appreciated that the total number of stages utilised in the vacuum pump will depend on the particular application and pumping requirements thereof.

In a further embodiment of any of the above, the multi-stage vacuum pump further comprises a stator assembly defining the compression chambers of each stage therein, a rotor assembly having rotors housed in respective ones of each of the compression chambers of each pump stage, and a plurality of gas passages serially fluidly connecting respective pairs of pump stages, wherein each connected pair of pump stages have compression chambers of incrementally decreasing volume.

In this manner, the gas passages enable serial fluid communication of working gas between the pump stages and can be of any suitable form.

In a further embodiment of the above, the plurality of gas passages are defined within the stator assembly.

In this manner, the gas passages are defined within the body of the stator assembly, which can keep the pump compact. The gas passages can be formed in the body of stator assembly in any suitable manner, such as by machining (e.g., drilling) or casting them into the stator assembly, or by additively manufacturing the stator assembly with them.

In an alternative embodiment, the gas passages are provided by pipes (or ducts) that connect to the stator assembly and extend externally therefrom. This may simplify the design of the stator assembly at the expense of compactness and increased assembly time. -6 -

In a further embodiment of any of the above, the rotor assembly includes a shaft rotatable about a central axis on which the rotors are mounted, the shaft having axially opposed ends each supported by a respective one of a first and second bearing. The rotor can be driven to rotate to operate the pump in any suitable manner, e.g., by a motor.

In a further embodiment of any of the above, at least one pump stage includes rotors of a Roots type and/or a claw type. In some examples, all the pump stages have rotors of a Roots and/or claw type. In other examples, the pump has a mixture of Roots and claw type stages.

Although certain advantages have been discussed in relation to certain features above, other advantages of certain features may become apparent to the skilled person following the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

One or more non-limiting embodiments according to the present disclosure will now be described, with reference to the accompanying figures in which: Figure 1 shows a cross-sectional view of a known multi-stage vacuum pump Figure 2 shows a schematic illustration of the pump stage arrangement for the pump of Figure 1; Figure 3 shows a schematic illustration of an example pump stage arrangement in a multi-stage vacuum pump in accordance with the present disclosure; Figure 4A shows a schematic illustration of another example pump stage arrangement in a multi-stage vacuum pump in accordance with the present

disclosure;

Figure 4B shows a schematic illustration of yet another example pump stage arrangement in a multi-stage vacuum pump in accordance with the present disclosure; Figure 40 shows a schematic illustration of yet another example pump stage arrangement in a multi-stage vacuum pump in accordance with the present disclosure; Figure 4D shows a schematic illustration of yet another example pump stage arrangement in a multi-stage vacuum pump in accordance with the present

disclosure. -7 -

DETAILED DESCRIPTION

With reference to Figure 1, a prior art multi-stage vacuum pump 100 is shown. An overview of the general structure and operation of the pump 100 will now be described.

The vacuum pump 100 includes a stator assembly 102 and a rotor assembly 110.

The rotor assembly 110 comprises a series of rotors 112a-112g that are mounted to a shaft 114 that extends axially along a central axis X-X. The rotors 112a-112g are spaced axially apart along the shaft 114 and protrude radially therefrom.

The rotors 112a-112g may be integrally formed with the shaft 114 (e.g., via casting) or may be formed and connected thereto separately (e.g., via welding). Moreover, although a single shaft 114 is shown, separate sections of shaft 114 may be provided and connected together instead. Such separate sections may include one or more rotors 112a-112g attached thereto.

Each rotor 112a-112g is housed within a respective chamber 104a-104g defined in the stator assembly 102. Each respective rotor 112a-112g and chamber 104a-104g combination defines a stage 100a-100g of the vacuum pump 100. In particular, an inlet stage 100a and an outlet stage 100g fluidly connected by a plurality of intervening stages 100b-100f.

Although only one rotor assembly 110 is shown in the sectional view of Fig. 1, it will be understood by the skilled person that a second cooperating rotor assembly is positioned adjacent the rotor assembly 110 within the stator assembly 102 and will interact therewith to provide the vacuum pump 100.

The depicted example is a Roots vacuum pump, and so the rotors 112a-112g will include a series of interacting lobes and recesses (not shown) as discussed above. Nonetheless, as discussed above, in other examples within the scope of this disclosure, the rotors 112a-112g and/or rotor assembly 110 may include different geometries (e.g., claw) depending on the type of multi-stage vacuum pump that is implemented.

The shaft 114 is supported for rotation by first and second bearings 120, 130. The first bearing 120 is disposed adjacent and axially outboard of the inlet 106 relative to central axis X-X. The second bearing 130 is disposed adjacent and axially outboard of the outlet 108 relative to central axis X-X. -8 -

In the depicted example, the bearings 120, 130 are ball bearings, and opposing axial ends 114a, 114b of the shaft 114 pass through respective apertures defined by an inner race of the bearings 120, 130, whilst an outer race of the bearings 120, 130 is connected to the stator assembly 102.

The chambers 104a-104g are arranged sequentially between an inlet 106 and an outlet 108. The inlet 106 and outlet 108 can be formed by openings or ports defined through the stator assembly 102 As is known, the chambers 104a-104g are in fluid communication with each other via passages (not shown) defined through the stator assembly 102. The passages may be defined in any suitable manner, such as by being drilled through the stator assembly 102, cast into the stator assembly 102 or provided by ducts or pipes extending between chambers 104a-104g. This provides a path for a gas flow G to pass from the inlet 106 (or high vacuum side of the pump 100) to the outlet 108 (or low vacuum side of the pump 100) via each stage 100a-100g of the vacuum pump 100.

As will be appreciated, this configuration provides a multi-stage vacuum pump 100 that can evacuate a system or space by ingesting gas at the inlet 106 and progressively compressing the gas through the pump stages 100a-100g (by rotating the shaft 114 and rotors 112a-112g within the chambers 104a-104g) before the gas is exhausted at the outlet 108. The rotor assembly 110 is rotated during operation by any suitable means, for example, the shaft 114 can be operatively connected to a motor (not shown).

The chambers 104a-104g progressively decrease in volume as gas is progressively compressed to a greater extent in each subsequent stage 100a-100g.

Accordingly, a larger volume chamber provides a so-called 'higher vacuum' stage than that of an adjacent chamber of smaller volume downstream thereof, which is thus a so-called 'lower vacuum' stage.

When the pump 100 is assembled, the rotor assembly 110 is positioned and secured within the stator assembly 102. In one example, a series of portions of the stator assembly 102 may be slid over the rotor assembly 110 and stacked on top of each other to surround the rotors 112a-112f, and then secured together. In another example, the stator assembly 102 may be defined by two stator clamshell halves that are positioned around the rotors 112a-112f and secured together.

Nonetheless, the pump 100 can be assembled in any other suitable manner. -9 -

Although a particular example of a multi-stage vacuum pump 100 is described above to aid understanding of the invention, it is to be understood that the teachings of the present disclosure can nevertheless apply to any other suitable configuration of multi-stage vacuum pump. Such pumps may have, for example, different bearing arrangements, stage counts and assembly methods. All such variations are envisaged within the scope of this disclosure.

Figure 2 shows a schematic representation of the arrangement of the stages 100a-100g of pump 100 and the gas passages defined between them.

As discussed briefly above, the stages 100a-100g are positioned next to each other in a sequential manner. In other words, the stages 100a-100g are positioned axially adjacent to each other in order of decreasing chamber volume. The stages 100a-100g can be numbered as first to seventh stages according to chamber volume. In other words, the first stage 100a is the inlet stage 100a having the highest chamber volume, the seventh stage 100g is the outlet stage 100g having the lowest chamber volume, and the second to sixth stages 100b-100f of decreasing chamber volume in between.

During pump operation, as gas is compressed in the stages 100a-100g, heat is generated. As discussed in more detail below, this heat can be distributed around the pump 100 to maintain the stages 100a-100g at particular temperatures to prevent unwanted condensation or decomposition of the working gas therein during operation.

The pump 100 is typically intended to maintain a system at a 'high' vacuum pressure in the order of 0.01 mbar, and compresses any gas to be exhausted to around atmospheric pressure (i.e., in the order of 1000 mbar or 1 bar). In other words, during normal 'high' vacuum operation of the pump 100, the pressure of gas sucked in the inlet 106 (high vacuum side) is around 0.01 mbar, whilst the pressure of gas being exhausted at the outlet 108 (low vacuum side) is around 1,000 mbar. Accordingly, there is a pressure factor difference across the pump 100 of in the order of about 105 (i.e., the gas pressure at the inlet 106 is about 100,000 times lower than the gas pressure at the outlet 108). In addition, the volume of the chambers 104a-104g across the pump 100 only differ by a factor of between 2-20 (i.e., the inlet stage chamber 104a is at most 20 times the volume of the outlet stage chamber 104g).

Owing to the high pressure difference between the high vacuum side and low vacuum side of the pump 100 in this operating mode, the lower volume, -10 -downstream stages (e.g., stages 100f-100g) do significantly more compressive work than the larger volume, upstream stages (e.g., stages 100a-100b). Accordingly, they generate significantly more heat (this difference being illustrated by the colour of shading across stages 100a-100g in Fig. 2).

The heat generated can advantageously keep the gas in these lower volume stages at a high enough temperature to avoid the gas condensing during pump operation. However, the higher volume stages may not heat up enough to do so. It is therefore necessary to provide additional heat to these stages during such operations to avoid gas condensation.

Moreover, although this normal 'high' vacuum level operation generates additional heat in the lower volume stages, the pump 100 can be used in several different operating regimes. For example, on start-up or during lower vacuum operation, the gas pressures at the inlet 106 are higher, and so the compressive work and heat generated in the larger volume stages (e.g., 100a-100b) may be greater than the smaller volume stages (e.g., 100f-100g) that remain relatively cool.

In such scenarios, it will therefore be necessary to transmit heat from the hotter, larger volume stages to the cooler, lower volume stages to avoid negative condensation effects.

As will be understood by the skilled person, one such example of this kind of mixed pump operation is in silicon wafer production and processing. For example, when depositing on a silicon wafer in a vacuum chamber, a relatively higher vacuum level is maintained and a relative low amount of working gas is put through the pump 100. However, once the wafer has been removed from the chamber, it can be necessary to clean the chamber. For the cleaning operation, a much higher amount of working gas is put through the pump 100, which will provide a much higher amount of compressive work through the larger volume stages.

In order to improve the speed of heat transfer between stages during pump operation (beyond what is available from the natural conduction of heat through the stator structure alone), it is known to provide pump 100 with heat transfer members.

The heat transfer members are attached to the pump 100 and extend along the stator assembly 102 between different stages to conduct heat from the hotter stages towards the cooler stages during operation. The heat transfer members have typically been implemented as blocks of conductive material (e.g., aluminium blocks), but could take other suitable forms (e.g., heat pipes).

Although these heat transfer members can be effective at transferring heat from hotter stages to warm cooler stages during pump operation, it has nevertheless been found that they have certain limitations. For example, there is a limit to the amount heat that can be transferred and where it can be directed, and they can add unwanted bulk and costs to the pump design.

In addition to heating cooler stages, depending on the working gas and application, the hotter stages may generate so much heat that they require cooling to keep the temperature of the working gas low enough to prevent thermal decomposition or reaction.

If this issue is known for a particular application, then it is known to provide the stages in question with additional cooling features. These additional cooling feature can include cooling fins extending from the stator assembly 102 and/or an external cooler directing cooling fluid onto the stator assembly 102. It would also be advantageous if such additional cooling features could be minimised or removed by providing improved heat transfer away from hotter stages during operation.

With reference to Figure 3, an example pump stage arrangement in a multi-stage vacuum pump 200 in accordance with the present disclosure is shown schematically.

It is to be understood that the structural and functional features of pump 100 discussed above under Figs 1 and 2 apply equally to pump 200, which only differs from pump 100 discussed above in that the stages 100a-100g have been rearranged and the gas passages defined between them have been reconfigured accordingly.

It has been found that appropriate repositioning of the stages 100a-100g (as will be discussed further below) removes the need for the heat transfer members discussed above and improves the heat transfer characteristics for pump 200. It may also reduce the need for active cooling of stages 100a-100g.

As shown in Fig. 3, the stages 100a-100g have been positionally rearranged such that they are no longer disposed sequentially in series of decreasing chamber volume. The black line arrows represent gas passages connecting the stages 100a-100g. Accordingly, although the stages 100a-100g have been rearranged non-sequentially in their positioning, the fluid flow still proceeds sequentially there through from inlet stage 100a to outlet stage 100g (i.e., from first stage 100a to seventh stage 100g).

-12 -The stator assembly 102 is generally made of a thermally conductive material (e.g., a metallic material, such as aluminium, cast iron or stainless steel). Therefore, the heat generated in one stage chamber will be conducted to the stage chambers adjacent thereto. By positioning stages that are known to generate more heat in a particular operating regime next (or relatively close) to stages that are known to generate less heat during that operating regime, the heat will more effectively be conducted away from the stages that generate more heat to those that generate less heat. In this manner, the stages that generate less heat for themselves can be heated to an appropriate temperature to avoid working gas condensation, without using additional external means or heat transfer members.

It has also been found that by rearranging the stages 100a-100g in this manner, lower heat generating stages can be grouped appropriately to provide effective heat sinks for the higher heat generating stages, such that enough heat can be transferred therefrom to keep them cool enough to avoid thermal decomposition or unwanted chemical reactions for working gases therein. This can eliminate or at least reduce the reliance on additional cooling features to achieve this.

As shown in Fig. 3, one example for pump 200 is to define the stage chambers 104a-104g in the stator assembly 102 such that the stages are non-sequentially positioned in the following order (from left to right): 9" stage 100e _ 4th stage 100d -6" stage 100f -3'd stage 100c -ls' stage 100a -2'd stage 1006 -7" stage 100g.

In this example, the pump 200 is configured to operate to maintain high vacuum levels/with a low through-put of working gas. Accordingly, the smallest volume stage 100g (i.e., the 7th or outlet stage 100g) that has the highest work of compression (and thus generates the most heat) at this operating condition is closest to (i.e., most adjacent) the two largest volume stages 100a, 100b (i.e., the 1st or inlet stage 100a and the 2nd stage 100b) that have the lowest work of compression (and thus generate the least heat) at this operating condition. This provides enhanced heat transfer to both stages 100a, 100b to prevent working gases from condensing therein, whilst also providing a sufficient enough heat sink to absorb enough heat to reduce the temperature of stage 100g sufficiently to avoid working gas undergoing thermal decomposition or unwanted chemical reactions.

Although the difference in relative heat generation is less pronounced in stages 100b-100f, by placing the 3rd largest volume stage 100c directly next to the -13 -second smallest volume stage in 61h stage 100f and placing the 41h largest volume stage 100d directly next to the third smallest volume stage in 5th stage 100e, these stages will also provide a balance of heat transfer between them to keep them in the appropriate temperature window.

Although this one example is shown in Fig. 3, it should be understood that many other examples are possible within the scope of this disclosure.

In one such other example, the position of the 1st and 2" stages 100a, 100b is switched around, such that 1st stage 100a is positioned directly next to 7th stage 100g (i.e., in-between stages 100b and 100g). In such an example, the positional order of stages (from left to right) would be: 5h stage 100e -4" stage 100d -61h stage 100f -3rd stage 100c -2I'd stage 1006 -lst stage 100a -71" stage 100g. It should be understood that although pump 200 is depicted with seven stages it is thought that the present disclosure can be usefully applied to a pump with any number of stages above three (i.e., at least four stages).

Examples of such multi-stage vacuum pumps 300, 400, 500, 600 are shown schematically in Figures 4A, 4B, 4C and 4D. The pumps 300, 400, 500, 600 generally include an inlet stage 100a defining a compression chamber of largest volume and an outlet stage 100d defining a compression chamber of smallest volume with at least two intervening stages 100b, 100c that have compression chambers of incrementally decreasing volume between that of the inlet stage 100a and the outlet stage 100d. For the avoidance of doubt, the compression chamber of stage 100b has a greater volume than that of stage 100c. In this manner, the intervening stage 100b has a compression chamber of the second largest volume and the intervening stage 100c has a compression chamber of the third largest (or second smallest) volume.

The stages 100a-100d are fluidly connected serially/sequentially in order of decreasing volume (as shown by the black arrow lines representing gas passages between the stages 100a-100d). However, the stages 100a-100d are not positioned in this serial/sequential order (i.e., from left to right in Figs 4A-4D). In other words, despite the stages 100a-100d being sequentially fluidly connected to each other they are non-sequentially positioned adjacent each other.

As shown in Figs 4A-4D, the inlet stage 100a is positioned such that it has fewer than two other stages 100b, 100c positioned between itself and the outlet stage 100d. In other words, the inlet stage 100a is positioned such that it is one of -14 -the two stages that are closest to (i.e., most adjacent) the outlet stage 100d and, at most, has only one intervening stage 100b positioned there between.

In this manner, the inlet stage 100a is either positioned directly adjacent the outlet stage 100d with no intervening stages there between as in Fig. 4A, 4C and 4D, or is positioned with only one intervening stage 100b there between as in Fig. 4B. It is thought that by having the inlet and outlet stages 100a, 100d positioned in this manner (i.e., within two adjacent stages of each other) the advantageous heat transfer characteristics between the two discussed above can be realised.

Moreover, it can also be preferable for the intervening stage positioned directly adjacent the inlet stage 100a to be the intervening stage 100b with a compression chamber of the second largest volume. As shown in Figs 4A and 4B, this can be accomplished by positioning stage 100b either in between the inlet stage 100a and the outlet stage 100d and directly adjacent thereto or directly next to the inlet stage 100a when the inlet stage 100a is directly next to the outlet stage 100d. Such configurations can advantageously help provide a larger heat sink to aid cooling of the outlet stage 100d.

Alternatively, as shown in Figs 4C, similar heat transfer and sink advantages can be achieved by the intervening stage 100b being instead placed outboard and directly next to the outlet stage 100d, with the inlet stage 100a inboard thereof.

In another advantageous example as shown in Fig. 4D, the inlet stage 100a can be placed outboard of the outlet stage 100d with the intervening stage 100b inboard thereof.

It is therefore also generally to be understood that the advantages of the present disclosure can be found without the outlet stage 100d needing to be an outermost stage (i.e., right-most in Figs 4A-4C) of the pump.

Although two intervening stages 100b, 100c are shown in Figs 4A-4D, within the scope of the disclosure any suitable number of intervening stages of two or more may be provided. For example, a suitable vacuum pump may include at least five stages, with three or more intervening stages in addition to the inlet and outlet stages.

As discussed above with reference to Fig. 3 and shown in Figs 4A and 4D, it is also advantageous for the intervening stages to be positionally interleaved with each other in such a way as to promote heat transfer between lower and higher compressive work intervening stages. This can be achieved generally by placing an intervening stage of lower volume between intervening stages of higher volume -15 -and vice versa. For example, when referring to Fig. 3, stage 100f is placed between and directly adjacent to the stages 100c, 100d. In the example shown in Figs 4A and 4D, the second largest volume stage 100b is positioned directly adjacent the second smallest volume stage 100c. Alternatively, intervening stages of lower compressive work (i.e., incrementally higher compression chamber volumes) can be suitably paired together and placed directly adjacent a higher compressive work intervening stage (i.e., of lower compression chamber volume) to act as heat sinks for the higher compressive work intervening stage and share in the heat transferred therefrom.

Although particular examples of inlet, outlet and intervening stage positions are shown in Figures 3 and 4A to 40, the teachings of the present disclosure will apply to a large number of examples having different specific stage positioning. All such examples falling within the scope of the claims are envisaged within the scope of this disclosure.

As can be seen when comparing Figs 3 and 4A-4D to Fig. 2, the pumps 200, 300, 400, 500, 600 require generally more complicated and longer gas passages (represented schematically as black arrows) to fluidly connect the pump stages than in pump 100. Nonetheless, these gas passages can still be provided by any suitable conventional means, such as by drilling passages or casting them into the stator assembly 102 or providing pipes of ducts that connect to the stator assembly 102 and extend externally from and around the stator assembly 102.

It is thought that the benefits of repositioning the pump stages in pumps 200, 300, 400, 500, 600 discussed above justifies the extra design and manufacture steps necessary to provide appropriate gas passages between the stages. In addition, the improvements to the amount and control of heat transfer provided across the pump improves its operating characteristics for a wide range of applications. This is again thought to outweigh the potential costs of redesigning the gas passages. Moreover, these improvements may also avoid the use of additional heat transfer members, which may help reduce additional costs and keeps the pump more compact. It may also eliminate or at least reduce the need for additional cooling features to be added to or used with the pump that would also add cost and bulk to pump designs.

LIST OF REFERENCE NUMERALS

-16 -A list of reference numerals used in the accompanying Figures 1 to 4D is provided for ease of reference: Multi-stage vacuum pump 100a-100f Pump stages 102 Stator assembly 104a-104f Chambers 106 Inlet 108 Outlet Rotor assembly 112a-112f Rotors 114 Shaft 114a,114b Opposing shaft ends First bearing Second bearing Pump 300 Pump 400 Pump 500 Pump 600 Pump G Gas flow path X-X Shaft central axis

Claims

-17 -CLAIMS1. A multi-stage vacuum pump comprising: an inlet stage defining a compression chamber of a largest volume; an outlet stage defining a compression chamber of a smallest volume; and at least two intervening stages that have compression chambers of incrementally decreasing volume between that of the inlet stage and the outlet stage; wherein a first of the intervening stages defines a compression chamber of a second largest volume and a second of the intervening stages defines a compression chamber of a second smallest volume; and wherein the inlet, outlet and intervening stages are positioned adjacent to each other in a non-sequential order such that the inlet stage has fewer than two other stages positioned between itself and the outlet stage.
2. The multi-stage vacuum pump of claim 1, wherein the inlet stage is positioned adjacent to the outlet stage such that there are no intervening stages positioned between them.
3. The multi-stage vacuum pump of claim 2, wherein the outlet stage is positioned between and closest to both the inlet stage and the first intervening stage.
4. The multi-stage vacuum pump of claim 1 or 2, wherein the first intervening stage is positioned adjacent the inlet stage such that there are no other stages positioned between them.
5. The multi-stage vacuum pump of claim 1, wherein the first intervening stage is positioned between and closest to both the inlet stage and the outlet stage.
6. The multi-stage vacuum pump of any of claims 1 to 4, wherein the second intervening stage is positioned adjacent the first intervening stage such that there are no other stages positioned between them.
-18 - 7. The multi-stage vacuum pump of any of claims 1 to 5, wherein the second intervening stage is positioned adjacent the inlet stage such that there are no other stages positioned between them.
8. The multi-stage vacuum pump of any preceding claim, wherein a third of the intervening stages defines a compression chamber of a third largest volume, and the second intervening stage is positioned adjacent the third intervening stage such that there are no other stages positioned between them.
9. The multi-stage vacuum pump of any preceding claim, further comprising: a stator assembly defining the compression chambers of each stage therein; a rotor assembly having rotors housed in respective ones of each of the compression chambers of each pump stage; and a plurality of gas passages fluidly connecting respective pairs of pump stages, wherein each connected pair of pump stages have compression chambers of incrementally decreasing volume.
10. The multi-stage vacuum pump of claim 9, wherein the plurality of gas passages are defined within the stator assembly.
11. The multi-stage vacuum pump of claim 9, wherein the plurality of gas passages are provided by pipes that connect to the stator assembly and extend externally therefrom.
12. The multi-stage vacuum pump of claim 9, 10 or 11, wherein the rotor assembly includes a shaft rotatable about a central axis on which the rotors are mounted.
13. The multi-stage vacuum pump of claim 12, wherein the shaft has axially opposed ends, and each of the ends is supported by a respective one of a first bearing and a second bearing.
14. The multi-stage vacuum pump of any of claims 9 to 13, wherein at least one pump stage includes rotors of a Roots type.-19 -
15. The multi-stage vacuum pump of any of claims 9 to 14, wherein at least one pump stage includes rotors of a claw type.