Vacuum pump with reduced seal requirements

Abstract

The vacuum pump (10) includes a substantially sealed housing (40), a core pump assembly disposed within the housing (40), and an inert purge gas inlet (70) fluidly connected to the housing (40) for supplying an inert purge gas to the interior of the housing (40) surrounding the core pump assembly, such that an inert positive pressure is applied to the core pump assembly, reducing leakage of process gas from the core pump assembly, and enabling the elimination or reduction of seals within the core pump assembly, particularly expensive and process sensitive elastomeric seals.

Description

[Technical field]

[0001] The present invention relates to a vacuum pump in which seals between the stator halves or between the stator halves and their end plates can be eliminated. [Background technology]

[0002] Vacuum pumps are typically used as components of vacuum systems to evacuate working gases from the system. These pumps may be used, for example, to evacuate manufacturing equipment used in the manufacture of semiconductors. Rather than performing the compression from vacuum to atmospheric pressure in a single stage using a single pump, it is common in such applications to provide a multi-stage vacuum pump, with each stage performing a portion of the compression range required to transition from vacuum to atmospheric pressure. Additionally, in many vacuum pump applications, the working or process gas must be kept above a minimum temperature to prevent the gas from condensing into a liquid or solid, which would adversely affect the operation of the pump.

[0003] Multi-stage vacuum pumps may generally have a clamshell structure, which requires the use of two stator shell halves and two end plates on either side of the stator halves to enclose the pump area. Traditionally, longitudinal and annular seals are used between the two stator halves and between the stator halves and the two end plates, respectively, to prevent leakage between the pump and the surrounding environment. Generally, elastomeric seals are used for this purpose, but it is difficult to achieve an effective sealing system to seal these mating surfaces. WO 2018 / 138487 and WO 2018 / 138489 present solutions for sealing the stator shell using elastomeric seals. However, there are applications where elastomeric seals are undesirable. For example, elastomeric seals are prone to degradation and may lose their sealing properties at certain operating temperatures and in certain corrosive process gas environments. They may also be subject to outgassing under certain conditions and may have unacceptable gas permeability. Additionally, the use of elastomeric seals with the necessary sealing performance for a particular application can add cost and complexity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 138487 [Patent Document 2] International Publication No. 2018 / 138489 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, to overcome these limitations, a vacuum pump with a clamshell construction that can maintain a seal in such applications and avoid or reduce the need for elastomeric seals is desired. [Means for solving the problem]

[0006] According to one aspect of the present invention, a vacuum pump is provided that includes a substantially sealed housing, a core pump assembly that includes two stator halves disposed within the housing and joined to define a plurality of pump chambers therein, and an inert purge gas inlet fluidly connected to the housing for supplying an inert purge gas to an interior of the housing surrounding the core pump assembly.

[0007] It has been found that by providing a sealed enclosure around the core pump assembly and supplying an inert purge gas thereto via an inlet, an inert positive pressure can be applied to the core pump assembly, reducing leakage of process gas from the core pump assembly and eliminating or reducing internal seals. This makes the core pump assembly more suitable for use in higher temperature or more corrosive operating environments where such seals may be subject to degradation or may not be suitable. It also reduces costs and eliminates outgassing / permeation issues associated with such seals. This is particularly true of elastomeric seals traditionally used to seal between the stator halves and the end plates.

[0008] Optionally, the vacuum pump further comprises a thermal spacer disposed between the core pump assembly and the housing and thermally isolating the core pump assembly from the housing.

[0009] The thermal spacer allows the core pump assembly to be thermally isolated from other pump components (e.g., the exterior of the housing) so that the core pump assembly can be maintained at an appropriately high operating temperature (e.g., to prevent condensation of process gases therein) without negatively heating other pump components that are better suited to operating at lower temperatures.

[0010] In one example, the thermal spacer is disposed between the core pump assembly and the housing and is in contact with both the core pump assembly and the housing. In this manner, the thermal spacer is used to minimize heat transfer from the core pump assembly to the housing. In one example, the housing includes a radial wall and the thermal spacer is disposed between the radial wall and the core pump assembly.

[0011] Optionally, the thermal spacer comprises a ceramic material.

[0012] Ceramic materials generally have low thermal conductivity, so that thermal conduction between the core pump assembly and the housing can be minimized. Any suitable ceramic material can be used, such as alumina (Al2O3), zirconia (ZrO2), magnesia (MgO), etc. In alternative embodiments, any other suitable thermally insulating material can be used as the thermal spacer.

[0013] Optionally, the plurality of pump chambers include an inlet pump chamber configured to receive process gas from a vacuum system; the two stator halves extend between a first axial end face on a high vacuum, inlet side of the pump and an opposing second axial end face on a low vacuum, outlet side of the pump, each of the two stator halves defining a radial inner surface and joined together along the radial inner surface; and at least one stator half includes a purge gas leakage flow passage fluidly connecting the first axial end face to a pump chamber downstream of the inlet pump chamber.

[0014] The purge gas leakage path allows inert purge gas that may leak into the high vacuum, inlet stage (e.g., the first axial end) of the core pump assembly to instead be supplied to the low vacuum stage, allowing leakage of purge gas to be properly removed through the pump while reducing the impact on the high vacuum efficiency and capacity of the pump.

[0015] In one example, the purge gas leakage passages are provided in the lower stator half, but in other examples they can be provided in the upper stator half instead, or in both the upper and lower stator halves.

[0016] It should be understood that the multiple pump chambers are pump chambers where the pump's compression work is applied to the process gas, and thus define multiple pump stages. Thus, the inlet pump chamber corresponds to the inlet stage of the pump. The purge gas leakage path can communicate with pump chambers other than the inlet pump chamber. The inlet pump chamber is the pump chamber with the largest volume, so downstream pump chambers have smaller volumes.

[0017] Optionally, at least one stator half includes a plurality of purge gas leakage passages fluidly connecting the first axial end face to different pumping chambers downstream of the inlet pumping chamber.

[0018] Optionally, the multiple purge gas leakage passages are radially spaced apart, with a radially outer one of the purge gas leakage passages fluidly connected to a pump chamber having a smaller volume than the pump chamber to which a radially inner one of the purge gas leakage passages is fluidly connected.

[0019] In this manner, a first one of the plurality of purge gas leakage paths, located radially outward of a second one of the plurality of purge gas leakage paths, fluidly connects to a pump chamber having a smaller volume than the pump chamber to which the second one of the plurality of purge gas leakage paths fluidly connects. In a further embodiment, a third one of the plurality of purge gas leakage paths is located radially inward of a second one of the plurality of purge gas leakage paths, fluidly connects to a pump chamber having a larger volume than the pump chamber to which the second one of the plurality of purge gas leakage paths fluidly connects. Any suitable number of purge gas leakage paths may be used, for example, up to one for each pump chamber except the inlet pump chamber.

[0020] Multiple purge gas leakage passages connected to pumping chambers of increasing volume allow leakage gas to be collected over a range of decreasing pressures, thereby allowing purge gas to be collected in stages as it leaks into the core pump assembly, increasing leakage collection rates, thereby further reducing the impact of the inert purge gas on the high vacuum efficiency and capacity of the pump.

[0021] Optionally, the purge gas leakage passage extends axially from the first axial end face and is substantially Z-shaped in cross section.

[0022] In this manner, the purge gas leakage path(s) can include a first axially extending section extending from the first axial end face, a first bend (e.g., a 90 degree bend) into the radially extending section, and a second bend (e.g., a 90 degree bend) into the second axially extending section that fluidly connects to the downstream pump chamber. This substantially Z-shape can help prevent leakage backwards through the purge gas leakage path(s).

[0023] Optionally, the purge gas leakage passage further includes a portion of the purge gas leakage passage extending across the first axial end face.

[0024] In this way, the purge gas leakage passage extends across the axial end face and also along the radially inner surface of the stator half(s). This allows the purge gas leakage passage to collect more purge gas leakage across the interface defined by the first axial end face (e.g., between the stator half and the end piece). In this way, a larger amount of purge gas leakage can be removed, further improving the high vacuum efficiency.

[0025] In examples in which multiple gas leakage flow paths are provided, each of the gas leakage flow paths can include a respective portion extending across the first axial end face and can be nested radially spaced apart across the axial end face according to the radial spacing between the multiple flow paths.

[0026] Optionally, a portion of the purge gas leakage passage that extends across the first axial end face fluidly connects opposing radial sides of the radially inner surface.

[0027] In this manner, the portion of the gas leakage flow path surrounds the portion of the stator half(s) and collects much of the purge gas that leaks to the interface defined by the first axial end surface and transports it to the pump chamber for removal.

[0028] The portion of the gas leakage passage on the first axial end surface can have any other suitable shape for connecting the opposing radial sides of the radially inner surface. In one example, the portion is substantially U-shaped in cross section. In another example, the portion is substantially semicircular.

[0029] Optionally, the portion of the purge gas leakage flow path on the first axial end surface comprises a groove defined in the first axial end surface.

[0030] By providing a groove in the first axial end face, a purge gas leakage passage can be opened in the interface between the stator half and the end piece, from where the purge gas can be collected and removed. Providing a groove in the first axial end face can be a particularly simple way of implementing a part of the gas leakage passage therein. For example, this can be achieved by simply machining (e.g. milling) a part of the first axial end face.

[0031] Optionally, the purge gas leakage flow path comprises a pair of grooves defined in the radially inner surface on opposing radial sides of the radially inner surface.

[0032] In this manner, a pair of grooves are spaced substantially the same radial distance from the longitudinal axis L of the pump 20 on opposing sides of the stator half (s), and both open at the first axial end face and fluidly connect to the same downstream pump chamber.

[0033] The grooves on the radially inner surface open the purge gas leakage flow paths to the interface between the stator halves, allowing collection and removal of purge gas that may leak through the interface to the core pump assembly. In this way, a larger amount of purge gas can be removed, further improving the high vacuum efficiency. Moreover, providing grooves on the radially inner surface of the stator halves is a particularly simple way of implementing gas leakage flow paths. For example, this can be achieved by simply machining (e.g., milling) parts of the radially inner surface.

[0034] Optionally, the core pump assembly further comprises end pieces joined to the first and second opposing axial end faces.

[0035] In this manner, the axial end faces contact the stator halves and help seal the core pump assembly.

[0036] Optionally, the core pump assembly does not include an elastomeric seal.

[0037] Various features of the disclosed pump configuration allow for the complete elimination of elastomeric seals from the core pump assembly, including longitudinal seals between the radially inner faces of the stator halves (i.e., seals that extend axially along the mating surfaces between the stator halves), annular seals in the end pieces that abut the first and second axial end faces of the stator halves, and T-junction seals that join the longitudinal seals and the annular seals.

[0038] In some instances, longitudinal seals, annular seals, and T-junction seals may be provided in the core pump assembly to help protect against purge gas leakage, depending on circumstances, however, the sealing effect is of less concern and may be non-elastomeric, resulting in lower implementation costs.

[0039] Optionally, the vacuum pump further comprises a motor, a gear cover, and an end cover, each of the motor, the gear cover, and the end cover disposed outside the housing.

[0040] By locating the motor, gear cover and end covers outside of the housing, they can be maintained at a cooler operating temperature than the core pump assembly, thereby improving the life and operating characteristics of these components.

[0041] Optionally, the vacuum pump further comprises a pair of head plates for supporting a rotor assembly of the pump, the pair of head plates being spaced apart from the core pump assembly.

[0042] The head plate is known to include bearings and / or seals that support the rotor assembly (e.g., rotor shaft) during pump operation. By spacing the head plate away from the core pump assembly, the head plate can be maintained at a cooler operating temperature than the core pump assembly. This can improve the life and operating characteristics of the head plate and its contents, such as by better maintaining the lubrication of the bearings and the integrity of the seals therein. In one example, the head plate is axially spaced from the core pump assembly.

[0043] In a further example, the head plate is separated from the core pump assembly by a thermal spacer. In such an example, the head plate may be in contact with the thermal spacer, which helps keep the head plate cool by minimizing heat transfer from the core pump assembly.

[0044] In yet another example, the head plate forms the walls of the housing, for example to which the top and bottom covers of the housing are attached. This can simplify the design of the pump and keep the housing more compact. In other examples, the head plate can instead be located outside the housing, or instead inside the housing. In such examples, the housing is formed with walls and covers separate from the head plate, or is formed using other pump components (e.g., gear covers and end covers) and covers. By placing the head plate outside the housing, its temperature can be further reduced.

[0045] Various embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0046] [Figure 1a] 1 illustrates an exemplary pump assembly according to one embodiment of the present disclosure. [Figure 1b] 1 illustrates another exemplary pump assembly according to an embodiment of the present disclosure. [Diagram 2] 1 shows an exemplary cross-section of a stator of a core pump assembly according to one embodiment of the present disclosure taken along line XX in FIG. 1a. [Diagram 3] 1 illustrates another exemplary stator according to an embodiment of the present disclosure. [Figure 4] 1A shows another exemplary cross-section of a stator of a core pump assembly according to an embodiment of the present disclosure taken along line YY of FIG. 1a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Referring to Figures 1a and 1b, a multi-stage vacuum pump 10 comprises a first stator component 12 and a second stator component 14 between which a rotor assembly (not shown) is mounted.

[0048] The two stator components 12, 14 are secured together to form pumping chambers 80a-g therein (shown in Figures 2 and 3 below). As such, the two stator components 12, 14 are known as stator halves 12, 14 (i.e., stator "clamshell" halves 12, 14) and are joined together along a joining surface 13 defined by radially inner surfaces 13a, 13b of the stator halves 12, 14.

[0049] The pump 10 defines a central longitudinal axis L along which the stator halves 12, 14 extend, and a perpendicular radial direction R. An interface 13 is disposed along the longitudinal axis L.

[0050] The rotor assembly may be any suitable type of rotor assembly, and in the illustrated embodiment will generally include two counter-rotating shafts with a rotor attached to each shaft (not shown). The rotors interact within chambers 80a-g to pump working / processing gases through the pump from an inlet of high vacuum chamber 80a to an outlet of low vacuum chamber 80g. The rotor assembly may be any suitable type of rotor assembly, and may form, for example, a claw-type vacuum pump, a roots-type vacuum, or a combination thereof. Such rotor assemblies are commonly known and are not the focus of this disclosure, and will not be described in further detail.

[0051] End pieces 50, 52 are attached to the opposite axial ends of the two stator components 12, 14 to complete the core pump assembly. It should thus be understood that the core pump assembly is that portion of the vacuum pump 10 where compression and pumping of process gas between the chambers 80a-g occurs.

[0052] It should be noted that while conventional vacuum pumps include longitudinal seals between the two stator components 12, 14 and annular seals between the stator components 12, 14 and the end pieces 50, 52, these are not required in the vacuum pump 10 of the present invention.

[0053] The core pump assembly (defined by the two stator components 12, 14 and the two end plates 50, 52) is disposed within a sealed housing 40, which in the illustrated embodiment is defined by a housing cover 16 and a head plate 18. The two head plates 18 are disposed on either axial side of the core pump assembly and provide bearings and seals for the shaft of the rotor assembly (not shown). The two housing covers 16 are disposed on either radial side of the core pump assembly (i.e. above and below the core pump assembly) and extend axially between the two head plates 18 to form the housing 40. A seal 42 is provided between the housing covers 16 and the head plates 18 to ensure that the housing 40 is substantially sealed. In other words, the housing 40 is sealed in a substantially gas-tight manner such that a pressure differential can be maintained between the interior of the housing 40 and the surrounding atmosphere when the pump 10 is operating. The arrangement of the housing cover 16 and seal 42 may be such that the housing 40 is sealed from the environment while allowing for differential thermal expansion between the head plate 18 and the housing cover 16, such as a piston seal arrangement as shown in Figure 1a and / or a face seal arrangement as shown in Figure 1b. Unlike the core pump assembly, the seal 42 may be comprised of an elastomeric seal or some other suitable type of seal (e.g., non-elastomeric).

[0054] Outside the housing 40, the vacuum pump 10 further comprises a motor 20, an end cover 30 through which the shaft of the rotor assembly extends, and a gear cover 22 disposed axially between the motor 20 and the head plate 18 (closest to the end piece 50) and housing a gear (not shown) for the rotor assembly. The motor 20, the gear cover 22, and the end cover 30 each comprise seals 24, 26, 32 that maintain a seal between these components and help to further seal the housing 40 from the environment. In an alternative embodiment, the housing cover 16 can extend axially between some elements of the pump 10, for example, the gear cover 22 and the end cover 30, such that the housing 40 contains these components therein. In such an example, instead of using the head plate 18, an additional plate would be disposed axially outside these components and disposed in sealing engagement with the cover 16. In a further alternative embodiment, the housing 40 can surround all of the components of the pump 10.

[0055] During operation of the vacuum pump 10, the required operating temperature for the core pump assembly is typically 200-400°C (e.g., to prevent condensation of process gases therein), while the suitable temperatures for the bearings, gearing, motor and elastomeric seals are typically less than 150°C. To help maintain the proper temperatures of each component during operation, thermal spacers 60 are provided between the end pieces 50, 52 and the respective head plates 18. In this manner, the thermal spacers 60 can be used to reduce the transfer of heat from the core pump assembly to the head plates 18 and other pump components with lower operating temperatures. Thus, the thermal spacers 60 can comprise any material having a suitably low thermal conductivity, such as a ceramic material, and can have a relatively small cross-sectional area to further minimize the transfer of heat between the end pieces 50, 52 and the head plates 18. The shaft of the rotor assembly can also be provided with a thermal break to help prevent heat from being transferred through the shaft to the exterior of the core pump assembly.

[0056] The vacuum pump 10 further includes an inert purge gas inlet 70 fluidly connected to the housing 40. In the illustrated embodiment, the inert purge gas inlet 70 penetrates the upper housing cover 16. The inert gas inlet 70 allows an inert gas, such as nitrogen, to be supplied to and filled within the interior of the housing 40. The inert gas would be supplied to the inlet 70 via an inert purge gas line (not shown). The temperature of the purge gas can be selected to any temperature suitable for the application. For example, the purge gas can be heated to help the core pump assembly reach and maintain a suitable operating temperature (e.g., to prevent condensation of process gases).

[0057] It is important that the purge gas be inert so as to prevent adverse or undesirable effects on the pump 10 and the process gas therein. Although nitrogen is illustrated, other suitable inert gases, such as argon, may be used.

[0058] It should be understood that the inert purge gas inlet 70 is separate and distinct from a process gas inlet (not shown) that is fluidly connected to transport process gas to the core pump assembly (i.e., to the inlet (high vacuum) stage 80a). Such a process gas inlet would also extend through the housing 40, but would be fluidly connected to a pump inlet (not shown) defined between the stator components 12, 14, and would not be fluidly connected to the interior space of the housing 40, which may be filled with purge gas, as is the case for the inert purge gas inlet 70.

[0059] The inert purge gas enters the housing 40 through an inlet 70 and is then removed through an exhaust port 72. The exhaust port 72 is a duct or pipe that passes through the housing 40 and, in the embodiment shown, is fluidly connected to the exhaust port of the core pump assembly, in other words, connected to the outlet of the low vacuum (i.e., outlet) stage 80g and is not fluidly open to the interior of the housing 40.

[0060] In this embodiment, an inert purge gas removal passage 90 is defined through the stator component 14 (see FIGS. 2 and 3) and is in fluid communication with the inlet of the low vacuum stage 80g. In this manner, the purge gas within the housing 40 is removed by being supplied via the passage 90 to the inlet of the low vacuum stage 80g, where it travels through the low vacuum stage 80g and is transferred to the exhaust port 72 along with the process gas also passing through the low vacuum stage 80g. In alternative embodiments, the purge gas can be supplied to an outlet rather than an inlet of the low vacuum stage 80g, or directly to the exhaust port 72. In other embodiments, any other suitable arrangement (e.g., pipes and / or passages) can be used to accomplish removal of the purge gas from the housing 40 via the exhaust port 72.

[0061] Pressure and / or temperature sensors may be incorporated into pump 10 to monitor the pressure and / or temperature of the purge gas within enclosure 40. The sensors may be in communication with a purge gas flow controller (e.g., a flow control valve disposed at inlet 70 and / or passage 90) to maintain a desired pressure and / or temperature within enclosure 40 by controlling the flow of inert purge gas into and / or out of enclosure 40. Any suitable pressure and / or temperature sensors may be used, and any suitable flow controller may be used, such as a flow control valve or a pressure control valve (pressure regulator).

[0062] It will be appreciated that by providing a seal around the core pump assembly with the housing 40 and supplying and maintaining a desired amount of inert gas therein (e.g., via the inlet 70 and exhaust 72), a positive pressure differential can be maintained around the core pump assembly. This helps minimize leakage of process gas from the core pump assembly, even though the core pump assembly does not include seals, and also helps prevent ingress of atmospheric gases from the environment into the housing 40. It will also be appreciated that this seal configuration is more resistant to changes in operating temperatures and corrosive process gases than applications that use seals, and can eliminate potential outgassing, permeability, and cost issues associated with using multiple elastomeric seals in the core pump assembly.

[0063] Additionally, the housing 40 in combination with the thermal spacer 60 can allow for separation of different components having different operating temperature limits. For example, the shaft bearings and seals of the head plate 18 can be maintained at a lower operating temperature than the operating temperature of the core pump assembly. This can improve the life and operating characteristics of the different pump components.

[0064] Referring now to Figure 2, there is shown a cross section of the core pump assembly of Figure 1a taken along line XX. The cross section shows the radially inner surface 13b of the second stator component 14, where the pump chambers 80a-g are visible. The following embodiments will be described in relation to the second stator component 14, but it should be understood that the same can (but is not necessarily) be applied to the first stator component 12, which will have a corresponding radially inner surface 13a (not shown).

[0065] The stator components 12, 14 are joined across a joining surface 13 defined by their respective radially inner surfaces 13a, 13b to form the core pump assembly. Each stator component 12, 14 thus comprises one half of a respective pump chamber 80a-g such that when joined together to form the core pump assembly, pump chambers 80a-g are formed. As mentioned above, in the illustrated embodiment, the inert purge gas is removed from the housing 40 using a passage 90 that fluidly connects to an inlet of the outlet (or rough vacuum) chamber 80g.

[0066] As can be seen in FIG. 2, the pump chambers 80a-g are successively smaller in size in the axial direction, with the largest volume inlet (or high vacuum) pump chamber 80a closest to the motor 20 and the smallest volume outlet (or low vacuum) pump chamber 80g closest to the end cover 30. The inlet pump chamber 80a is configured to receive process gas from the vacuum system via a process gas inlet, and the outlet pump chamber 80g is configured to exhaust process gas from the core pump assembly via an outlet (discussed above). The gradual decrease in volume from pump chamber 80a to pump chamber 80g corresponds to an equivalent gradual increase in pressure from the desired operating pressure of the vacuum to atmospheric pressure. By using multiple pump chambers, and therefore multiple compression stages, pump efficiency is improved and higher vacuum pressures can be maintained.

[0067] Also as shown, the stator components 12, 14 extend axially between opposing axial end faces 15a, 15b to which end pieces 50, 52 are joined. As such, the end pieces 50, 52 can be said to provide joint interfaces with the stator components 12, 14 along end faces 15a, 15b, respectively. Further, with respect to their position relative to the pumping chambers 80a-80g, the first axial end face 15a is at the high vacuum, inlet side of the pump 10 and the opposite second axial end face 15b is at the low vacuum, outlet side of the pump 10.

[0068] Because there are no seals between the first and second stator components 12, 14, and between the stator components 12, 14 and the end pieces 50, 52, the inert purge gas from the housing 40 can leak into the core pump assembly. If measures are not taken to prevent this, the leaking purge gas 110 can enter the pump chambers 80a-g and be compressed with the process gas therein, increasing the required compression work and thereby reducing the efficiency of the pump 10.

[0069] To combat this effect, in this embodiment, the stator component 14 further includes purge gas leakage paths 100a and 100b that extend from a first axial end 15a that interfaces with the end piece 50 on the high vacuum, inlet side of the pump 10 to the third and fifth pump chambers 80c, 80e, respectively. Although two purge gas leakage paths 100a, 100b are shown in this embodiment, embodiments are envisioned that include between 1 and n-1 purge leakage paths, where n is the number of pump stages 80. Additionally, although paths 100a, 100b are shown connected to the third and fifth pump chambers 80c, 80e, path 100 may be connected to any of the pump chambers 80, except for the inlet (high vacuum) pump stage 80a.

[0070] The purge gas leakage paths 100a, 100b serve to capture purge gas 110 that leaks into the core pump assembly. Since paths 100a, 100b are connected to pumping chambers 80c, 80e, respectively, leakage gas 110 that enters paths 100a, 100b is pumped by pumping stages 80c, 80e together with the process gas. For example, leakage gas 110 closer to the high vacuum inlet end, i.e., end piece 50, of pump 10 will first come into contact with path 100b. Path 100b is connected to pumping chamber 80e, which is pressurized, for example, at about 100 mbar. Thus, leakage gas 110 is pumped into pumping chamber 80e until the pressure in path 100b is also at 100 mbar. The leakage gas 110, now at 100 mbar pressure, is allowed to continue flowing radially inwards. In doing so, it will come into contact with path 100a. Flow path 100a is connected to pump chamber 80c, which is pressurized at a lower pressure, for example around 10 mbar. Similar to flow path 100b, this means that the flow of leakage gas 110 is reduced to a pressure of 10 mbar. Thus, assuming that the leakage gas 110 was initially at atmospheric pressure (~1 bar), the leakage volume has been reduced to 1 / 100 of its original pressure. By reducing the pressure of the leakage gas 110 in this way, this ensures that when the leakage gas 110 comes into contact with the lowest pressure pump stages 80a, 80b, the extra work required by these stages 80a, 80b to compress the leakage gas 110 is significantly reduced.

[0071] It should be understood that in the illustrated configuration, due to the relative gas pressures present, the radially inner flow passage 100 must be connected to a pump chamber 80 of a larger volume than the radially outer flow passage 100 in order for the radially inner flow passage 100 to provide any benefit.

[0072] Each of the illustrated flow paths 100a, 100b resembles a substantially Z-shape in cross section, such that it includes two bends 102, 104. These bends 102, 104 may aid in preventing leakage out of the core pump assembly using the flow paths 100a, 100b. However, the flow paths 100a, 100b may have any suitable shape for capturing and transporting the leaking gas 110 to the required pumping chamber 80.

[0073] Additionally, flow paths 100a, 100b are shown as connecting axially into pump chamber 80. In this embodiment, this is because the inter-stage ports of each pump stage 80 are between the two parallel shafts of the rotor assembly and are not accessible. However, in embodiments in which the inlet of a pump stage 80 is not between the two shafts, it is contemplated that flow paths 100a, 100b may be connected to the inlet of that pump stage (i.e., the inlet that carries process gas to the pump stage for compression).

[0074] The illustrated passages 100a, 100b are provided as a pair of grooves in opposing radial sides of the radially inner surface 13b of the stator component 14. The grooves may be machined (e.g., milled) into the radially inner surface 13b of the stator component 14. However, the passages 100a, 100b may take any other suitable form and be made in any other suitable manner for capturing and transporting the leaking gas 110 to the required pumping chamber 80. For example, they may be cast or drilled into the stator component 14.

[0075] 3, the vacuum pump 10 can combine the flow passage 100 with conventional sealing methods such as a longitudinal seal 120 and / or annular seal 130. The longitudinal seal 120 can extend from the high vacuum end piece 50 to the low vacuum end piece 52, radially outward of the flow passage 100, in a groove in the stator components 12, 14. The longitudinal seal 120 and its groove can be discontinuous to prevent fluidly connecting both ends of the core pump assembly. The annular seal 130 is disposed between the end pieces 50, 52 and the stator components 12, 14, and has a diameter that is radially outward of the flow passage 100. The purpose of these optional seals is to reduce the amount of leakage gas 110 that reaches the radially outer flow passage 100b, thus reducing the work required by the pump stage 80e to which the flow passage 100b is connected, further improving the efficiency of the pump 10. However, the seal system 120, 130 of the core pump assembly of this embodiment does not need to be as precise or robust as a conventional seal system since any leakage through the seals 120, 130 into the core pump assembly is reduced by the flow path 100 as described above. This means that precise alignment between the two stator components 12, 14, and between the stator components 12, 14 and the end pieces 50, 52 is not required. Furthermore, this means that the seals 120, 130 can be constructed of either elastomeric or non-elastomeric seals, in contrast to conventional seal systems where elastomeric seals are a requirement.

[0076] 4, there is shown a cross section of the core pump assembly of FIG. 1a taken along line YY looking towards the first axial end faces 15a of the two stator components 12, 14. It can be seen that the purge gas leakage flow paths 100a, 100b further comprise portions 101a, 101b that extend across the first axial end faces 15a of the stator components 12, 14. This allows for additional purge gas leakage to be collected at the interface defined by the first axial end faces 15a (i.e., the interface between the stator components 12, 14 and the end piece 50).

[0077] In the illustrated embodiment, the portions 101a, 101b are used to fluidly connect the opposing radial sides of the radial inner surfaces 13a, 13b, and are therefore fluidly connected to the portions of the flow passages 100a, 100b of the radial inner surfaces 13a, 13b. In this manner, the portions 101a, 101b surround a portion of the stator components 12, 14 at the first axial end surface 15a, and collect purge gas leaking to the first axial end surface 15a and transfer it to the portions of the flow passages 100a, 100b at the radial inner surfaces 13a, 13b. This allows the purge gas leakage flow passages 100a, 100b to collect more of the leakage gas 110 that may leak to the interface between the stator components 12, 14 and the end pieces 50, since the portions 101a, 101b surrounding the first axial end surface 15a extend substantially 360 degrees at the interface with the end plate 50.

[0078] In this manner, more leakage gas 110 can be prevented from entering the lowest pressure pump stage 80a, 80b, thereby further improving the high vacuum efficiency of the pump 10.

[0079] 4 are substantially U-shaped, but may have any other suitable shape, such as a semicircular shape, for connecting opposing radial sides of the radially inner surfaces 13a, 13b. As shown, the portions 101a, 101b have different radii and are radially spaced apart and nested across the first axial end face 15a.

[0080] The illustrated portions 101a, 101b are provided as grooves connecting opposing radial sides of the first axial end faces 15a of the stator components 12, 14. The grooves may be machined (e.g., milled) into the first axial end faces 15a of the stator components 12, 14. However, they may take any other suitable form for capturing and transporting leakage gas 110 across the first axial end faces 15a.

[0081] Although the present invention has been described in the context of clamshell-type stator structures (e.g., Roots-type and claw-type pumps) having pump chambers defined therein, it is envisioned that the present disclosure is applicable to other pumps in which a seal-free design is desirable. For example, a screw pump may incorporate flow paths similar to those described herein, but the flow paths may be connected at different locations along the length of the screw. In the context of a screw pump, the different screw length locations are considered to correspond to the different pump chambers 80a-80g discussed in this disclosure. The following list of reference numerals used in accompanying Figures 1 through 4 is provided for ease of reference. [Explanation of symbols]

[0082] 10 Vacuum Pump 12 First stator component 13 Stator component interface 13a, 13b radially inner surface of stator component 14 Second stator component 15a, 15b Axial end faces of stator components 16 Case cover 18 Head Plate 20 Motor 22 Gear cover 24 Motor seal 26 Gear cover seal 30 End cover 32 End cover seal 40 Case 42 Housing seal 50 First end piece 52 Second End Piece 60 Thermal Spacer 70 Inert purge gas inlet 72 Exhaust port 80a-g Pump room 90 Inert gas removal passage 100a, 100b Purge gas leakage flow path 101a, 101b Purge gas leakage flow path 102a, 102b: Bends of the first flow path 104a, 104b: Bends of the second flow path 110 Purge gas leak 120 Longitudinal Seal 130 Annular seal LL Longitudinal axis RR radial axis

Claims

1. 1. A vacuum pump comprising: a substantially sealed enclosure; a core pump assembly disposed within the housing and including two stator halves joined to define a plurality of pump chambers therein; an inert purge gas inlet fluidly connected to the housing surrounding the core pump assembly for supplying an inert purge gas to an interior of the housing; A vacuum pump comprising:

2. 2. The vacuum pump of claim 1, further comprising a thermal spacer disposed between said core pump assembly and said housing for thermally isolating said core pump assembly from said housing.

3. The vacuum pump of claim 2 , wherein the thermal spacer comprises a ceramic material.

4. the plurality of pumping chambers includes an inlet pumping chamber configured to receive a process gas from a vacuum system; the two stator halves extend between a first axial end face on a high vacuum, inlet side of the vacuum pump and an opposing second axial end face on a low vacuum, outlet side of the vacuum pump, each of the two stator halves defining a radial inner surface and joined together along the radial inner surfaces; at least one stator half includes a purge gas leakage passage fluidly connecting the first axial end face to a pumping chamber downstream of the inlet pumping chamber.

4. A vacuum pump according to claim 1, 2 or 3.

5. 5. The vacuum pump of claim 4, wherein the at least one stator half includes a plurality of purge gas leakage passages fluidly connecting the first axial end face to different pumping chambers downstream of the inlet pumping chamber.

6. 6. The vacuum pump according to claim 5, wherein the plurality of purge gas leakage passages are arranged at intervals in a radial direction, and a radially outer one of the purge gas leakage passages is fluidly connected to a pump chamber having a smaller volume than a pump chamber to which a radially inner one of the purge gas leakage passages is fluidly connected.

7. 7. A vacuum pump as claimed in claim 4, 5 or 6, wherein the purge gas leakage passage extends axially from the first axial end face and is substantially Z-shaped in cross section.

8. 8. A vacuum pump according to claim 4, wherein the purge gas leakage passage further comprises a portion of the purge gas leakage passage extending across the first axial end face.

9. 9. The vacuum pump of claim 8, wherein the portion of the purge gas leakage passage that extends across the first axial end face fluidly connects opposing radial sides of a radially inner surface.

10. 10. A vacuum pump as claimed in claim 8 or 9, wherein the portion of the purge gas leakage flow path on the first axial end face comprises a groove defined in the first axial end face.

11. 11. A vacuum pump as claimed in any one of claims 4 to 10, wherein the purge gas leakage flow path comprises a pair of grooves defined in the radially inner surface on opposing radial sides of the radially inner surface.

12. 12. A vacuum pump according to claim 4, wherein the core pump assembly further comprises end pieces joined to the first and second opposing axial end faces.

13. 12. A vacuum pump according to any one of claims 4 to 11, wherein the core pump assembly does not include an elastomeric seal.

14. A motor; Gear cover, End covers and Further equipped with 14. A vacuum pump according to claim 1, wherein each of the motor, the gear cover and the end cover is disposed outside the housing.

15. a pair of head plates for supporting a rotor assembly of the vacuum pump; 15. A vacuum pump according to any preceding claim, wherein the pair of head plates are spaced apart from the core pump assembly.

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