Vacuum pump with optimised flow technology and temperature

Abstract

The present invention relates to a vacuum pump with at least one Holweck pumping stage, comprising a Holweck rotor and a Holweck stator. The Holweck rotor comprises a rotor shaft with a hub provided thereon, and at least two Holweck rotor sleeves provided on the hub, which concentrically surround the rotor shaft, wherein a radially inner Holweck rotor sleeve has a first diameter and a radially outer Holweck rotor sleeve has a second diameter. The Holweck stator comprises, between the two Holweck rotor sleeves, a Holweck stator sleeve concentric to them, which has a fixed end attached to a stationary housing section of the vacuum pump, a free end axially opposite the fixed end, an inner surface with an internal thread formed thereon, and an outer surface with an external thread formed thereon.The second diameter of the radially outer Holweck rotor sleeve is at least 30% larger than the first diameter of the radially inner Holweck rotor sleeve.

Description

[0001] The present invention relates to a vacuum pump, in particular a turbomolecular vacuum pump, with at least one Holweck pumping stage, wherein the vacuum pump and in particular its Holweck pumping stage is optimized in terms of flow and / or thermal aspects.

[0002] Vacuum pumps are used in many areas of industry and research. The basic design of such vacuum pumps is well known, which is why reference is made to EP 4 108 931 A1 for a purely exemplary description.

[0003] Although such turbomolecular vacuum pumps with an integrated Holweck pumping stage are technically sophisticated devices that fulfill their purpose, there is nevertheless a continuing need to optimize such turbomolecular vacuum pumps in terms of fluid dynamics and / or thermal aspects.

[0004] The invention is therefore based on the object of providing a vacuum pump and in particular a turbomolecular vacuum pump which meets the previously described need.

[0005] According to a first aspect of the present invention, this object is achieved with a vacuum pump, in particular with a turbomolecular vacuum pump, which is characterized by the features of claim 1 and in particular in that the diameter of the radially outer Holweck rotor sleeve or the second diameter is at least 30% and preferably at least 35% larger than the diameter of the radially inner Holweck rotor sleeve or the first diameter.

[0006] The radially outer Holweck rotor sleeve thus has a significantly larger diameter than the radially inner Holweck rotor sleeve. This allows the Holweck stator sleeve to be designed with a significantly greater core wall thickness than usual. The core wall thickness, which in the context of this application is also referred to simply as the wall thickness for the sake of simplicity, refers here to the pure wall thickness of the stator sleeve between the inner surface and the outer surface, where the internal and external threads are formed.

[0007] For example, it has been observed in conventional turbomolecular vacuum pumps and their Holweck pumping stage that the Holweck stator sleeve becomes up to around 25°C warmer during operation due to the gas flowing around or over the Holweck stator sleeve at its free end and the resulting gas friction at the free end of the Holweck stator sleeve than at its fixed end, which is attached to the lower housing section of the pump or the stationary housing section. Upon closer investigation, it was determined that this not insignificant and undesirable temperature gradient is due to the fact that, due to the usually relatively thin design of the Holweck stator sleeve, it has a relatively high thermal resistance in the axial direction. Due to this, the heat from the free end of the Holweck stator sleeve can only be transferred poorly by thermal conduction to the cooled stationary housing section or the cooled lower housing section.

[0008] In order to take this problem into account, the invention proposes for the first time to make the diameter of the radially outer Holweck rotor sleeve significantly larger than the diameter of the radially inner Holweck rotor sleeve in order to create more space between the two Holweck rotor sleeves for a correspondingly thicker Holweck stator sleeve, which then has a lower thermal resistance due to its greater wall thickness, which allows the heat to be better conducted from the free end of the Holweck stator sleeve towards the fixed end of the Holweck stator sleeve or to the stationary housing section.

[0009] According to a preferred embodiment, due to the significantly larger diameter of the outer Holweck rotor sleeve compared to the diameter of the inner Holweck rotor sleeve, it is possible according to the invention to form the Holweck stator sleeve with a core wall thickness that is greater than 5 mm, preferably greater than 6 mm, and particularly preferably greater than 7 mm, essentially over its entire axial extent between its fixed end and its free end. As already mentioned, this can reduce the thermal resistance of the Holweck stator sleeve, so that less heat accumulates at the free end of the Holweck stator sleeve; rather, due to the reduced thermal resistance, the heat can be dissipated largely unhindered towards the fixed end of the Holweck stator sleeve.

[0010] If it is stated here that the Holweck stator sleeve has a certain core wall thickness "essentially" over its entire axial extent, this means that an axial region of the Holweck stator sleeve located near the free end can be excluded from this, which is defined by the last two turns, preferably by the last turn of the internal or external thread, as will be explained in more detail below.

[0011] For further thermal optimization, according to a further embodiment, at least two concentric and axially extending annular webs are formed at the free end of the Holweck stator sleeve, and at least two concentric and axially extending annular webs are also formed on the hub of the Holweck rotor, which are nested with the annular webs located at the free end of the Holweck stator sleeve. Any accumulated heat that builds up in the rotor hub can thus be transferred via the nested annular webs to the Holweck stator sleeve, which, due to its reduced thermal resistance, can then dissipate this heat into the housing base or the stationary housing section.

[0012] Since the mutually nested annular webs form a certain flow resistance, which makes it difficult for the process gas to be pumped to flow around the free end of the Holweck stator sleeve without hindrance, it can be provided according to a further embodiment that the Holweck stator sleeve is penetrated in the radial direction near its free end by a plurality of gas flow bores that are evenly spaced from one another in the circumferential direction, so that the process gas to be pumped can flow through these bores between the radially outer and the radially inner Holweck gap.

[0013] According to a second aspect of the present invention, the underlying object is further achieved with a vacuum pump, in particular with a turbomolecular vacuum pump, which is characterized by the features of claim 6 and in particular in that the radially inner Holweck rotor sleeve has an axial extent that is 30% to 70%, preferably 40% to 60%, in particular 45% to 55%, of the axial extent of the outer Holweck rotor sleeve. This allows the vacuum pump, and in particular its Holweck pumping stage, to be equipped with a significantly more massive Holweck stator sleeve than is possible with conventional Holweck pumping stages, so that even in this embodiment, no accumulated heat can build up at the free end of the stator sleeve due to the relatively massive design of the stator sleeve.

[0014] Specifically, according to one embodiment, it can be provided that the Holweck stator sleeve has a base ring section attached to the stationary housing section and a cantilever ring section which extends from an end face of the base ring section facing the rotor hub in the axial direction to the free end of the Holweck stator sleeve in the annular space between the inner Holweck rotor sleeve and the outer Holweck rotor sleeve.

[0015] The cantilever ring section and the base ring section preferably have the same outer diameter, which allows the external thread of the Holweck stator sleeve to be formed on both the outer surface of the base ring section and the cantilever ring section. Likewise, the cantilever ring section can have a cylindrical inner surface with an internal thread formed thereon, in which case it can preferably be provided that the number of threads of the internal thread corresponds to the number of threads of the external thread.

[0016] The base ring section can thus be designed with a significantly greater wall thickness than the cantilever ring section, so that the base ring section extends radially inward from the external thread of the Holweck stator sleeve or its outer surface where the external thread is formed, extending beyond the inner Holweck rotor sleeve. Due to the relatively massive design of the base ring section, the thermal resistance of the Holweck stator sleeve is also reduced, so that the thermal energy that would otherwise accumulate at the free end of the Holweck stator sleeve can flow more or less unhindered toward the fixed end of the Holweck stator sleeve.

[0017] From a design perspective, the design of the Holweck stator sleeve with the relatively massive base ring section proves to be advantageous, since in this case the base ring section can support the motor stator of the electric motor driving the rotor shaft. In particular, it can be provided that the base ring section forms an annular inner surface that supports the motor stator.

[0018] To ensure that the process gas flowing through the Holweck pumping stage can continue to flow in the desired manner to the pump outlet after flowing around the free end of the cantilever ring section, a further embodiment can provide for the base ring section to be penetrated in the axial direction by a plurality of gas flow bores, preferably evenly spaced from one another in the circumferential direction. From a fluidic perspective, it can prove advantageous for the gas flow bores in question to also extend in the circumferential direction and / or in the radial direction. Likewise, from a fluidic perspective, it can also prove advantageous for the gas flow bores, viewed in the axial direction, to each have an elongated hole cross-section in order to reduce flow resistance.Furthermore, from a fluidic point of view, it may also prove advantageous to provide the gas flow holes in the same number as the threads of the internal thread of the cantilever section, so that the process gas flowing out of a respective thread can flow directly into a gas flow hole assigned to it.

[0019] According to yet another embodiment, which can be implemented both in a vacuum pump according to the first aspect and according to the second aspect of the present invention, it can be provided that at least two mutually concentric and axially extending annular grooves are formed in the stationary housing section, and in particular on the end face of the stationary housing section from which the Holweck stator sleeve extends towards its free end. These can, for example, be formed radially inside the Holweck stator sleeve and thus, to a certain extent, in the axial extension of the outer Holweck rotor sleeve in the end face of the stationary housing section. Additionally or alternatively, the annular grooves in question can also be formed in the axial continuation of the radially inner Holweck rotor sleeve in the end face of the stationary housing section.The annular grooves in question are located where the process gas is deflected around the free end of the respective Holweck rotor sleeve, and thus in an area where friction-related temperature peaks can occur due to the gas deflection. In this case, the annular grooves in question serve as cooling fins, cooling the process gas, thus preventing unwanted temperature peaks.

[0020] According to a third aspect of the present invention, the object underlying the same is further achieved with a vacuum pump, in particular with a turbomolecular vacuum pump, which is characterized by the features of claim 13. Specifically, it is provided that the second end faces, which form the thread webs of the external thread at the free end of the Holweck stator sleeve, have a defined offset in the circumferential direction relative to the first end faces, which form the thread webs of the internal thread of the Holweck stator sleeve at the free end thereof. d of a predetermined size, wherein this offset d is preferably determined as d = t / tan α, where t the radial core transformation thickness of the Holweck stator sleeve and α is the pitch angle of the external thread of the Holweck stator sleeve.

[0021] Because the internal and external threads or the end faces in question have a defined offset from one another in the circumferential direction, the gas flowing out of the external thread at the free end of the Holweck stator sleeve can flow into the corresponding threads of the internal thread without major flow losses, without friction-related flow losses occurring at the end face or at the free end of the Holweck stator sleeve, which would otherwise reduce the pump's suction capacity and result in increased power consumption of the pump.

[0022] Preferably, the number of first thread lands can be equal to the number of second thread lands, so that each thread groove of the external thread is assigned, so to speak, exactly one corresponding thread groove of the internal thread. A gas flowing out of a thread groove of the external thread can thus flow directly into a corresponding thread groove of the internal thread without causing undesirable gas turbulence when flowing around the free end of the Holweck stator sleeve.

[0023] In order to ensure particularly reliably that the process gas flows from a thread groove of the external thread into exactly one thread groove of the internal thread after flowing around the free end of the Holweck stator sleeve, a further embodiment can provide several evenly spaced flow contours in the circumferential direction at the free end of the Holweck stator sleeve, in the same number as the first and second thread lands. Each of these flow contours defines a defined thread flow path between a thread groove of the internal thread and a thread groove of the external thread, so that no undesirable gas turbulence occurs at the free end of the Holweck stator sleeve.

[0024] The flow contours in question can, for example, be guide vanes that extend between the end faces of the first threaded ridges and the end faces of the second threaded ridges. The guide vanes thus represent, in a sense, a continuation of the threaded ridges at the free end or end face of the Holweck stator sleeve.

[0025] In addition or alternatively to the circumferential offset d of the first and second end faces relative to one another, it can further be provided that the first end faces and / or the second end faces enclose an acute angle with a plane in which the free end of the Holweck stator sleeve lies, which angle is in particular between 10° and 40°, preferably between 20° and 30°. After flowing around the free end of the Holweck stator sleeve, the process gas therefore does not directly impact the first end face of the thread lands of the internal thread when flowing into the internal thread of the Holweck stator sleeve; rather, the process gas is slightly deflected by the slightly inclined first end faces before subsequently flowing into the thread grooves of the internal thread. Corresponding considerations apply to the case of a vacuum pump with a Holweck pumping stage, in which the process gas first flows through the internal thread and then the external thread of the Holweck stator sleeve.

[0026] In the vacuum pump of the third aspect of the present invention, in addition to or as an alternative to the design with end faces offset from one another in the circumferential direction and the acute-angled alignment of the end faces, it may be appropriate to design the Holweck stator sleeve such that it has a core wall thickness that decreases towards the free end of the Holweck stator. In principle, however, the Holweck stator sleeve has a substantially constant core wall thickness over its axial extent; the decrease in the core wall thickness, however, is limited only to a region defined by the first two turns of the internal thread and / or the external thread closest to the free end of the Holweck stator sleeve, preferably only by the first turn of the internal thread and / or the external thread.The core wall thickness therefore decreases towards the free end of the Holweck stator sleeve only in a very limited area, which is formed by a type of internal and / or external chamfer of the Holweck stator sleeve at its free end, whereby this chamfer can have a linear, convex, round or parabolic contour.

[0027] Due to this thickness reduction of the Holweck stator sleeve at its free end, the thread depth of the internal and / or external thread increases towards the free end of the Holweck stator sleeve and, at the same time, the thickness reduction at the free end of the stator sleeve creates an optimized flow geometry that enables flow around the free end of the Holweck stator sleeve with fewer losses.

[0028] According to a fourth aspect of the present invention, the object underlying the same is further achieved with a vacuum pump, in particular with a turbomolecular pump stage, which is characterized by the features of claim 20 and in particular in that a flow profile with a concave cross section is provided on the rotor hub of the Holweck rotor between the two Holweck rotor sleeves, which flow profile concentrically surrounds the rotor shaft.

[0029] The flow profile in question can be a separate part attached to the hub. This flow profile also ensures turbulence-free flow around the free end of the Holweck stator sleeve, which in turn has a positive effect on the pump's suction capacity and power consumption.

[0030] Further design options for the vacuum pump according to the four aspects explained above are discussed below. The design options explained below, also referred to as variations, relate in particular to a specific design of the Holweck pumping stage of the vacuum pump according to the four aspects explained above, and in particular to the design of the rotor hub of the Holweck pumping stage.

[0031] A variation 1 relates to a vacuum pump, in particular a turbomolecular pump, with at least one Holweck pumping stage, which comprises a rotor with a rotor shaft and a rotor hub connected to the rotor shaft, wherein the rotor hub: carries at least one Holweck rotor sleeve; radially within the at least one Holweck rotor sleeve, forms at least two mutually concentric annular lands which are configured to be nested with a plurality of stationary annular lands to form a labyrinth seal; has at least one balancing region in which material is removed from the rotor hub by means of laser ablation; and has a plurality of pump blades which are evenly spaced from one another along the outer circumference of the rotor hub.

[0032] Variation 2 relates to the vacuum pump according to Variation 1, wherein the rotor hub carries at least two mutually concentric Holweck rotor sleeves, wherein the at least two mutually concentric annular webs are provided radially inside the at least two Holweck rotor sleeves.

[0033] Variation 3 relates to the vacuum pump according to Variation 1 or 2, wherein the at least one balancing region is located on the outer circumference of the rotor hub between two adjacent pump blades.

[0034] Variation 4 relates to the vacuum pump according to one of variations 1 to 3, wherein the pump blades provided along the outer circumference of the rotor hub are spaced apart from one another in the circumferential direction without overlap, wherein the at least one balancing region is located in the non-overlapping region between two adjacent pump blades.

[0035] Variation 5 relates to the vacuum pump according to one of variations 2 to 4, wherein the at least one balancing region is located between the at least two Holweck rotor sleeves.

[0036] Variation 6 relates to the vacuum pump according to any one of variations 1 to 5, wherein the rotor hub forms an annular retaining web for each Holweck rotor sleeve, each of which carries a Holweck rotor sleeve, wherein at least one radially outermost retaining web has a radially outer exposed annular surface.

[0037] Variation 7 relates to the vacuum pump according to Variation 6, wherein the at least one balancing region is located on the radially outer exposed annular surface of the radially outermost retaining web.

[0038] Variation 8 relates to the vacuum pump according to one of variations 1 to 7, wherein the rotor hub forms at least one balancing ring concentric with the at least one Holweck rotor sleeve, on which the at least one balancing region is located.

[0039] Variation 9 relates to the vacuum pump according to Variation 8, wherein the balancing ring is located in the radial direction between two Holweck rotor sleeves, in particular on the side of the rotor hub opposite the Holweck rotor sleeves.

[0040] Variation 10 relates to the vacuum pump according to one of variations 1 to 9, wherein the vacuum pump further comprises at least one surface-treated section on the rotor hub and at least one sensor device with which a temperature of the at least one surface-treated section of the rotor hub can be determined in a contactless manner by measuring the heat radiation emitted by the section.

[0041] Variation 11 relates to the vacuum pump according to Variation 10, wherein the sensor device comprises an infrared sensor.

[0042] Variation 12 relates to the vacuum pump according to variation 10 or 11, wherein the section of the rotor hub is roughened or structured, in particular wherein the section of the rotor hub is roughened or structured such that it has an average roughness Ra of 5 to 25 µm and / or an average roughness depth Rz of 40 to 100 µm and / or that the section has surface structures in the range 15 to 50 µm.

[0043] Variation 13 relates to the vacuum pump according to any one of variations 10 to 12, wherein the surface-treated portion consists essentially of a material of the rotor hub in the region of the portion.

[0044] Variation 14 relates to the vacuum pump according to any one of variations 10 to 13, wherein the portion has a coating.

[0045] The invention is described below by way of example using advantageous embodiments with reference to the accompanying figures. They show, schematically: Fig. 1a perspective view of a turbomolecular pump, Fig. 2a view of the underside of the turbomolecular pump of Fig. 1 , Fig. 3 a cross-section of the turbomolecular pump along the Fig. 2 shown section line AA, Fig. 4 a cross-sectional view of the turbomolecular pump along the Fig. 2 shown section line BB, Fig. 5 a cross-sectional view of the turbomolecular pump along the Fig. 2 shown section line CC, Fig. 6 an enlarged section of the Fig. 4 to explain an inventive design of the Holweck pump stage, Fig. 7 an enlarged section of the Fig. 4to explain another embodiment of the Holweck pump stage according to the invention, Fig. 8 a plan view of the free end of a Holweck stator sleeve designed according to the invention with an offset provided in the circumferential direction between the internal thread and the external thread, Fig. 9 a schematic internal view of a developed version of a Holweck stator sleeve designed according to the invention, Fig. 10 an enlarged section of the Fig. 4 to explain an inventive design of the Holweck pump stage in the area of ​​the free end of the Holweck stator sleeve and the adjacent rotor hub, Fig. 11 an enlarged section of the Fig. 4 for explanation of the pump blades provided on the outer circumference of the rotor hub in a purely schematic representation, and Fig. 12 an enlarged section of the Fig. 4 with an exemplary arrangement of the surface-treated area or corresponding sensor devices.

[0046] The Fig. 1The turbomolecular pump 111 shown comprises a pump inlet 115 surrounded by an inlet flange 113, to which a recipient (not shown) can be connected in a manner known per se. The gas from the recipient can be sucked out of the recipient via the pump inlet 115 and conveyed through the pump to a pump outlet 117, to which a backing pump, such as a rotary vane pump, can be connected.

[0047] The inlet flange 113 forms the vacuum pump alignment according to Fig. 1 the upper end of the housing 119 of the vacuum pump 111. The housing 119 comprises a lower part 121, on which an electronics housing 123 is arranged laterally. Electrical and / or electronic components of the vacuum pump 111 are housed in the electronics housing 123, e.g., for operating an electric motor 125 arranged in the vacuum pump (see also Fig. 3). Several connectors 127 for accessories are provided on the electronics housing 123. In addition, a data interface 129, e.g., according to the RS485 standard, and a power supply connector 131 are arranged on the electronics housing 123.

[0048] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0049] On the housing 119 of the turbomolecular pump 111, a flooding inlet 133, in particular in the form of a flooding valve, is provided, via which the vacuum pump 111 can be flooded. In the area of ​​the lower part 121, a sealing gas connection 135, which is also referred to as a purge gas connection, is also arranged, via which purge gas is supplied to protect the electric motor 125 (see e.g. Fig. 3) can be admitted into the motor compartment 137, in which the electric motor 125 is housed in the vacuum pump 111, before the gas delivered by the pump. Furthermore, two coolant connections 139 are arranged in the lower part 121, one of which serves as an inlet and the other as an outlet for coolant, which can be fed into the vacuum pump for cooling purposes. Other existing turbomolecular vacuum pumps (not shown) are operated exclusively with air cooling.

[0050] The lower side 141 of the vacuum pump can serve as a base, so that the vacuum pump 111 can be operated standing on the underside 141. However, the vacuum pump 111 can also be attached to a recipient via the inlet flange 113 and thus operated in a suspended position. Furthermore, the vacuum pump 111 can be designed so that it can also be operated when oriented in a different manner than in Fig. 1 As shown. Embodiments of the vacuum pump can also be realized in which the underside 141 is arranged facing either sideways or upwards, rather than downwards. In principle, any angle is possible.

[0051] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in an upright position.

[0052] On the underside 141, which is in Fig. 2As shown, various screws 143 are arranged, by means of which components of the vacuum pump (not further specified here) are fastened together. For example, a bearing cover 145 is attached to the underside 141.

[0053] Mounting holes 147 are also arranged on the underside 141, through which the pump 111 can be attached, for example, to a support surface. This is not possible with other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here.

[0054] In the Figures 2 to 5 a coolant line 148 is shown in which the coolant introduced and discharged via the coolant connections 139 can circulate.

[0055] As the sectional views of the Figures 3 to 5 show, the vacuum pump comprises several process gas pumping stages for conveying the process gas present at the pump inlet 115 to the pump outlet 117.

[0056] A rotor 149 is arranged in the housing 119 and has a rotor shaft 153 rotatable about a rotation axis 151.

[0057] The turbomolecular pump 111 comprises several turbomolecular pump stages connected in series for pumping purposes, with several radial rotor disks 155 attached to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and secured in the housing 119. A rotor disk 155 and an adjacent stator disk 157 each form a turbomolecular pump stage. The stator disks 157 are held at a desired axial distance from one another by spacer rings 159.

[0058] The vacuum pump also includes Holweck pump stages arranged radially one inside the other and connected in series for pumping efficiency. Other turbomolecular vacuum pumps (not shown) exist that do not have Holweck pump stages.

[0059] The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical-shell-shaped Holweck rotor sleeves 163, 165 attached to and supported by the rotor hub 161, which are oriented coaxially to the rotational axis 151 and nested within one another in the radial direction. Furthermore, two cylindrical-shell-shaped Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the rotational axis 151 and nested within one another in the radial direction.

[0060] The pumping surfaces of the Holweck pump stages are formed by the lateral surfaces, i.e., the radial inner and / or outer surfaces, of the Holweck rotor sleeves 163, 165 and the Holweck stator sleeves 167, 169. The radial inner surface of the outer Holweck stator sleeve 167 lies opposite the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together with the latter forms the first Holweck pump stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 lies opposite the radial outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together with the latter forms a second Holweck pump stage. The radial inner surface of the inner Holweck stator sleeve 169 lies opposite the radial outer surface of the inner Holweck rotor sleeve 165, forming a radial Holweck gap 175 and together forming the third Holweck pumping stage.

[0061] At the lower end of the Holweck rotor sleeve 163, a radially extending channel can be provided, via which the radially outer Holweck gap 171 is connected to the central Holweck gap 173. Furthermore, at the upper end of the inner Holweck stator sleeve 169, a radially extending channel can be provided, via which the central Holweck gap 173 is connected to the radially inner Holweck gap 175. This connects the nested Holweck pump stages in series. A connecting channel 179 to the outlet 117 can also be provided at the lower end of the radially inner Holweck rotor sleeve 165.

[0062] The above-mentioned pump-active surfaces of the Holweck stator sleeves 167, 169 each have a plurality of Holweck grooves extending spirally around the rotation axis 151 in the axial direction, while the opposite lateral surfaces of the Holweck rotor sleeves 163, 165 are smooth and propel the gas in the Holweck grooves for operating the vacuum pump 111.

[0063] For the rotatable mounting of the rotor shaft 153, a rolling bearing 181 is provided in the area of ​​the pump outlet 117 and a permanent magnet bearing 183 is provided in the area of ​​the pump inlet 115.

[0064] In the area of ​​the rolling bearing 181, a conical spray nut 185 with an outer diameter increasing toward the rolling bearing 181 is provided on the rotor shaft 153. The spray nut 185 is in sliding contact with at least one wiper of a fluid reservoir. In other existing turbomolecular vacuum pumps (not shown), a spray screw can be provided instead of a spray nut. Since different designs are thus possible, the term "spray tip" is also used in this context.

[0065] The operating fluid storage comprises several stacked absorbent discs 187, which are impregnated with an operating fluid for the rolling bearing 181, e.g. with a lubricant.

[0066] During operation of the vacuum pump 111, the operating fluid is transferred by capillary action from the operating fluid reservoir via the wiper to the rotating injection nut 185 and, as a result of the centrifugal force, is conveyed along the injection nut 185 in the direction of the increasing outer diameter of the injection nut 185 to the rolling bearing 181, where it fulfills a lubricating function, for example.

[0067] The rolling bearing 181 and the operating fluid reservoir are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

[0068] The permanent magnet bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each comprising a ring stack of several permanent magnetic rings 195, 197 stacked one on top of the other in the axial direction. The ring magnets 195, 197 lie opposite one another, forming a radial bearing gap 199, with the rotor-side ring magnets 195 being arranged radially on the outside and the stator-side ring magnets 197 being arranged radially on the inside. The magnetic field present in the bearing gap 199 creates magnetic repulsion forces between the ring magnets 195, 197, which effect a radial bearing of the rotor shaft 153. The rotor-side ring magnets 195 are carried by a support section 201 of the rotor shaft 153, which surrounds the ring magnets 195 on the radial outside.The stator-side ring magnets 197 are supported by a stator-side support section 203, which extends through the ring magnets 197 and is suspended from radial struts 205 of the housing 119. The rotor-side ring magnets 195 are secured parallel to the rotation axis 151 by a cover element 207 coupled to the support section 201. The stator-side ring magnets 197 are secured parallel to the rotation axis 151 in one direction by a fastening ring 209 connected to the support section 203 and a fastening ring 211 connected to the support section 203. A disc spring 213 can also be provided between the fastening ring 211 and the ring magnets 197.

[0069] Within the magnetic bearing, an emergency or backup bearing 215 is provided, which runs idle without contact during normal operation of the vacuum pump 111 and only engages upon excessive radial deflection of the rotor 149 relative to the stator, forming a radial stop for the rotor 149 to prevent collision of the rotor-side structures with the stator-side structures. The backup bearing 215 is designed as an unlubricated rolling bearing and forms a radial gap with the rotor 149 and / or the stator, causing the backup bearing 215 to be disengaged during normal pumping operation. The radial deflection at which the backup bearing 215 engages is large enough so that the backup bearing 215 does not engage during normal operation of the vacuum pump, yet small enough so that collision of the rotor-side structures with the stator-side structures is prevented under all circumstances.

[0070] The vacuum pump 111 comprises the electric motor 125 for rotating the rotor 149. The armature of the electric motor 125 is formed by the rotor 149, whose rotor shaft 153 extends through the motor stator 217. A permanent magnet arrangement can be arranged radially on the outside or embedded in the portion of the rotor shaft 153 extending through the motor stator 217. Between the motor stator 217 and the portion of the rotor 149 extending through the motor stator 217, an intermediate space 219 is arranged, which comprises a radial motor gap, via which the motor stator 217 and the permanent magnet arrangement can magnetically influence each other to transmit the drive torque.

[0071] The motor stator 217 is secured in the housing within the motor compartment 137 provided for the electric motor 125. A seal gas, also referred to as purge gas, which may be air or nitrogen, for example, can enter the motor compartment 137 via the seal gas connection 135. The seal gas can be used to protect the electric motor 125 from process gas, e.g., from corrosive components of the process gas. The motor compartment 137 can also be evacuated via the pump outlet 117, i.e., the vacuum pressure in the motor compartment 137 is at least approximately equal to the vacuum pressure created by the backing pump connected to the pump outlet 117.

[0072] Furthermore, a so-called labyrinth seal 223, which is known per se, can be provided between the rotor hub 161 and a wall 221 delimiting the motor compartment 137, in particular in order to achieve a better sealing of the motor compartment 217 with respect to the Holweck pump stages located radially outside.

[0073] In the following, with reference to the Fig. 6 to 10 The various possible designs of the vacuum pump 111 according to the invention, and in particular its Holweck pumping stage according to the various aspects of the present invention, are discussed. At this point, it should be explicitly noted that the individual, different embodiments can of course also be combined with one another, provided that there are no technical reasons against such a combination.

[0074] The Fig. 6 shows an enlarged section of the Fig. 4 in particular to explain the first aspect of the present invention, according to which the outer rotor sleeve 163 has a significantly larger diameter than the inner rotor sleeve 165, which according to the invention makes it possible to provide a significantly thicker Holweck stator sleeve 169 between the two rotor sleeves 163, 165.

[0075] Specifically, the radially outer Holweck rotor sleeve 163 has a diameter that is at least 30%, preferably at least 35%, larger than the diameter of the radially inner Holweck rotor sleeve 165. This makes it possible, in accordance with the invention, to provide a Holweck stator sleeve 169 between the two rotor sleeves 163, 165, which has a significantly greater core wall thickness than is the case with conventional Holweck pump stages. In conventional Holweck pump stages, the stator sleeve is typically a relatively delicate component, the core wall thickness of which is not much larger than the wall thickness of the rotor sleeves, see, for example, the Fig. 3 and 4. This has the consequence that, due to the thermal resistance associated with the delicate design of the stator sleeves, heat accumulating at the free end of the Holweck stator sleeve cannot be dissipated, or can only be dissipated with difficulty, towards the pump base 121.

[0076] Since, according to the invention, the diameter of the radially outer rotor sleeve 163 is now selected to be significantly larger than the diameter of the radially inner rotor sleeve 165, a stator sleeve 169 with a significantly greater core wall thickness can now be used between the two rotor sleeves 163, 165, which is greater than 5 mm, preferably greater than 6 mm, and particularly preferably greater than 7 mm. The core wall thickness, which for the sake of simplicity is also referred to here simply as the wall thickness, is measured from the groove base 302 of the external thread 304 to the groove base 302 of the internal thread 308 and thus represents the thickness of the stator sleeve 169 less the height of the thread lands 306, 310 of the external thread 304 and the internal thread 308.Due to the significantly thicker design of the stator sleeve 169, it has a lower thermal resistance, so that hardly any heat accumulates at the free end 322 of the stator sleeve 169, since this can be continuously dissipated in the direction of the housing lower part or the stationary housing section 121.

[0077] In order to further optimise the heat balance of the Holweck pump stage, the design of the Fig. 6 At the free end 322 of the Holweck stator sleeve 169, a plurality of mutually concentric annular webs 324 are formed, which are nested with corresponding annular webs 326 extending axially from the rotor hub 161. The nested annular webs 324, 326 act, in a sense, as a type of heat exchanger, through which heat can be dissipated from the rotor hub 161 to the stator sleeve 169 and from there, in the manner explained above, to the stationary housing section 121.

[0078] In order for the process gas to be pumped to pass from the external thread 304 of the stator sleeve 169 into the internal thread 308 of the stator sleeve 169 despite the interlocking annular webs 324, 326, it is necessary in the embodiment of the Fig. 6 It is further provided that the stator sleeve 169 is penetrated in the radial direction near its free end 322 by a plurality of gas flow bores 328 through which the process gas can flow in the desired manner from the outer Holweck gap or from the external thread 304 into the inner Holweck gap or into the internal thread 308.

[0079] To further optimise the heat balance, the design of the Fig. 6 It is further provided that a plurality of mutually concentric annular grooves 330 are formed in the housing lower part 121. These are located in the embodiment of the Fig. 6in the lower part 121 radially outside the Holweck stator sleeve 169, whereby additionally or alternatively it can be provided that corresponding annular grooves are also located radially inside the Holweck stator sleeve 169 in the lower part 121 and thus in continuation of the inner rotor sleeve 165. These annular grooves 330 in the lower part 121 act as cooling fins, which cool the process gas flowing over them in the desired manner, so that friction-related heating of the stator sleeve 169 in the area of ​​the free end 322 thereof cannot even occur. For the sake of good order, it should be explicitly pointed out at this point that even in the case of the Fig. 7 described embodiment, corresponding annular grooves 330 can be provided in the lower housing part 121 of the pump 111.

[0080] In the following, with reference to the Fig. 7A further embodiment of the vacuum pump 111 and in particular its Holweck pumping stage is described, which is characterized in particular by the fact that the inner Holweck rotor sleeve 165 has a significantly shorter axial extent than the radially outer Holweck rotor sleeve 163. Specifically, the axial extent of the inner Holweck rotor sleeve 165 is only approximately 45% to 55% of the axial extent of the radially outer Holweck rotor sleeve 163. This makes it possible to design the Holweck stator sleeve 169 in the axial continuation of the inner rotor sleeve 165 to be more massive than is the case with conventional Holweck pumping stages, so that in this embodiment too, no accumulated heat can build up at the free end 322 of the stator sleeve 169 due to the relatively massive design of the stator sleeve 169.

[0081] Specifically, in the illustrated embodiment, the stator sleeve 169 is composed of a base ring portion 332, which is attached to the housing lower part 121, and a collar ring portion 434 extending axially from the base ring portion 332. Specifically, the collar ring portion 334 extends from the end face of the base ring portion 332 facing the rotor hub 161 and thus extends into the annular space between the shorter inner rotor sleeve 165 and the longer outer rotor sleeve 163. The external thread 304 of the stator sleeve 169 extends axially over the entire common outer surface 354 of the base ring portion 332 and the collar portion 334, whereas the internal thread 308 is provided only over the axial extent of the collar portion 334 on its inner side.

[0082] Since the base ring section 332 now extends in the radial direction beyond the inner shorter Holweck rotor sleeve 165, the motor stator 217 of the electric motor 125 driving the rotor shaft 153 can be attached directly to the annular inner surface 336 of the base ring section 332.

[0083] To ensure that the process gas can continue to flow to the pump outlet 117 after flowing through the internal thread 308, the base ring section 332 is penetrated in the axial direction by a plurality of gas flow bores 338, which are preferably present in the same number as the threads of the internal thread. As shown, these can be aligned obliquely to the rotation axis 151 and thus also extend partially in the radial direction. Likewise, the gas flow bores 338 can also extend at least partially in the circumferential direction, even if this is not shown in the illustration of the Fig. 7 is not recognizable.

[0084] Despite their designation as gas flow "bores," these do not have to be circular in cross-section and can instead have a slotted hole cross-section to reduce flow resistance.

[0085] The previously described temperature problem, which results in undesirably strong heating of the stator sleeve 169 in the region of its free end 322, is due, among other things, to the undesirable swirling of the process gas as it flows from the external thread 304 over the free end 322 into the internal thread 308. This is particularly the case because, in conventional Holweck pump stages, there is no specific assignment of the thread grooves of the external thread 304 to the thread grooves of the internal thread 308. In other words, this means that a gas flowing out of a thread groove of the external thread 304 is distributed between two or more thread grooves of the internal thread 304.

[0086] In order to counteract this problem, it is proposed for the first time according to the invention to align the external thread 304 and the internal thread 308 rotationally relative to one another in the circumferential direction in such a way that process gas flowing out of a thread groove of the external thread 304, after flowing around the free end 322, flows as far as possible only into a single thread groove of the internal thread 308. Specifically, it is provided for this purpose that the end faces 304, which form the thread webs 306 of the external thread 304 at the free end 322 of the Holweck stator sleeve 169, have an offset d in the circumferential direction compared to the end faces 344, which form the thread webs 310 of the internal thread 308 at the free end 322 of the stator sleeve 169, see the Fig. 8 . Specifically, the offset d can be determined as d = t / tan α , where t the radial core wall thickness of the stator sleeve 169 and αis the pitch angle of the external thread 304. Due to this relationship, process gas flowing out of a thread groove of the external thread 304 flows further at an angle over the free end 322 of the stator sleeve 169, in order to then flow into exactly one thread groove of the internal thread 308 on the inside of the stator sleeve 169, which of course requires that the number of thread lands 306 of the external thread 304 is the same as the number of thread lands 310 of the internal thread 308.

[0087] In order to facilitate the flow of the process gas into the thread grooves of the internal thread 308, it can be arranged as shown in the Fig. 9 It should be provided that the end faces 344 of the threaded webs 310 of the internal thread 308 form an acute angle with the plane in which the free end 322 of the Holweck stator sleeve 169 lies β which is preferably between 10 and 40°, particularly preferably between 20 and 30°.

[0088] To further facilitate the flow of the process gas into the grooves of the internal thread 308, it can additionally or alternatively be provided that the core wall thickness decreases towards the free end 322 of the Holweck stator sleeve 169, since this corresponds to an increase in the height of the threaded webs 306, 310 at the free end 322 of the stator sleeve 169. Thus, the inflow cross-section into the threaded grooves of the internal thread 308 is increased, which facilitates the flow of the process gas into the threaded grooves of the internal thread 308.

[0089] In particular, the Fig. 10As can be seen, the wall thickness can taper towards the free end 322 in the form of a chamfer 346, which is preferably formed only on the inside of the free end 322 of the stator sleeve 169. In the embodiment shown here, the chamfer 346 has a straight or linear contour; however, as shown, the chamfer 346 can also be provided on the outside and have a convex, round, or parabolic contour, as shown in dashed lines.

[0090] Again Fig. 10 As can also be seen, in the embodiment shown there, the chamfer 346 extends only over the first turn of the internal thread 308; however, as shown in dash-dotted lines, the chamfer 346 can also extend over an area defined by the two turns of the internal thread 308 closest to the free end 322.

[0091] In order to further optimize the flow around the free end 322 of the Holweck stator sleeve 169 and the inflow of the process gas into the grooves of the internal thread 308, it is possible in the embodiment of the Fig. 10 It is further provided that a flow profile 356 with a concave cross-section is provided on the rotor hub 161 of the Holweck rotor between the two Holweck rotor sleeves 163, 165, which concentrically surrounds the rotor shaft 153. The flow profile 356 is a part that can be handled separately from the hub 161 and is attached to the hub 161. This flow profile 356 also ensures a turbulence-free flow around the free end 322 of the Holweck stator sleeve 169, which in turn has a positive effect on the pump's suction capacity and its power consumption.

[0092] In order to ensure even more reliably that the process gas flows from a thread groove of the external thread 304 only into a thread groove of the internal thread 308, it can be guided according to the schematic representation of the Fig. 8 It may further be provided that the Holweck stator sleeve 169 has at its free end 322 a plurality of flow contours 348 evenly spaced from one another in the circumferential direction, wherein each flow contour 348 defines a defined flow path between a thread groove of the external thread 304 and a single thread groove of the internal thread 308, as indicated by the flow arrow SThe flow contours 348 can be guide vanes 350 formed on the free end 322 of the stator sleeve 169, each extending between an end face 340 of the external thread 304 and an end face 344 of the internal thread 308. Contrary to the illustrated embodiment, these can be curved, in particular concave or convex, in order to guide the process gas over the free end 322 of the stator sleeve 169 with as little turbulence as possible.

[0093] In the following, with reference to the Figs. 11 and 12 Further design options for the vacuum pump 111 and in particular its Holweck pumping stage according to the various aspects of the present invention will be discussed. At this point, it should be explicitly noted that the embodiments according to Figs. 11 and 12 also with the design options of the Fig. 6 to 10can be combined, provided that there are no technical reasons against such a combination.

[0094] The Fig. 11 shows an enlarged section of the Fig. 4 to explain the pump blades 230 provided on the outer circumference of the rotor hub 161. Specifically, the Fig. 11 The rotor shaft 153 of the rotor can be seen, which supports the rotor hub 161, to which the two concentric Holweck rotor sleeves 163, 165 are attached, which can preferably be made of a CFRP material. The Holweck stator sleeves 167, 169 are not shown here for the sake of clarity. Radially inside the two Holweck rotor sleeves 163, 165, several concentric annular webs 232 are formed on the rotor hub 161, which engage with several stationary annular webs (not shown here) to form the previously mentioned labyrinth seal 223.

[0095] According to the invention, the rotor hub 161 has a plurality of pump blades 230 along its outer circumference, which are evenly spaced from one another in the circumferential direction. Between these pump blades 230, material can be removed from the outer circumference of the rotor hub 161 in a balancing region 234 by means of laser ablation in order to compensate for any imbalances in the rotor. Preferably, the pump blades 230 can be spaced from one another in the circumferential direction without overlapping. This offers the possibility of locating the balancing region 234 in the non-overlapping region between two adjacent pump blades and thus performing the material removal precisely where the pump blades 230 do not overlap in the circumferential direction. Additionally or alternatively, the balancing region 234 can also be located between the two Holweck rotor sleeves 163, 165.

[0096] As already mentioned, the rotor hub 161 carries the two concentric Holweck rotor sleeves 163, 165. Specifically, the rotor hub 161 forms two annular retaining webs 236, 238, each of which carries a Holweck rotor sleeve 163, 165. As the Fig. 11 can be easily removed, the radially outermost holding web 236 has a radially outer exposed annular surface 242 on which the rotor or the rotor hub 161 can be balanced, as can be seen from the balancing area 234 shown.

[0097] At the one here in the Fig. 11 In the embodiment shown, it is further provided that the rotor hub 161 forms, on the side of the rotor hub 161 opposite the Holweck rotor sleeves 163, 165, a balancing ring 240 which is concentric with the Holweck rotor sleeves 163, 165 and on which a balancing area 234 is located.

[0098] Also the Fig. 12 shows an enlarged section of the Fig. 4. It includes, like the Fig. 11 the same area near the labyrinth seal 223. The rotor hub 161 has a Fig. 11 It has a recognizable surface section 225 that has undergone a surface treatment to locally increase the emissivity. In the present embodiment, it is arranged radially between the labyrinth seal 223 and the Holweck rotor sleeve 165.

[0099] The surface section 225 may have been treated with at least one of the methods described above and / or may have a coating. The coating—if provided—may itself have an emissivity-enhancing effect and / or protect a roughening or structuring of the section 225.

[0100] By measuring the thermal radiation emitted by section 225, conclusions can be drawn about the temperature of hub 161 and thus about the temperature of rotor 149. It is advantageous if the aforementioned components are coupled to one another with good thermal conductivity.

[0101] The thermal radiation was measured by a Fig. 12 visible infrared sensor 227, but also which is arranged on the cap-like wall 221. In the Fig. 11 There was no representation of the infrared sensor 227, although it is also present there.

[0102] Section 225 is a flat, annular surface area extending in a plane substantially perpendicular to a rotation axis 151 of rotor 149. As robot 149 rotates, sensor 227, statically mounted on wall 221, continuously receives a portion of the thermal radiation emitted by section 225, allowing continuous temperature measurement. In a thermal equilibrium state, the measured signal should exhibit only minimal fluctuations.

[0103] To increase measurement accuracy, a plurality of sensors 227 distributed in the circumferential direction may be provided. Alternatively or additionally, the section 225 may comprise separate subsections, which are evenly distributed in the circumferential direction in particular, in order to minimize the imbalance generated by them.

[0104] The section 225 is arranged downstream of the pumping stage formed by the rotor disks 155 and stator disks 157 in the pumping direction in order to minimize the effects of any outgassing that could occur due to the surface treatment. List of reference symbols

[0105] 111Turbomolecular pump 113Inlet flange 115Pump inlet 117Pump outlet 119Housing 121Lower section 123Electronics housing 125Electric motor 127Accessory connection 129Data interface 131Power supply connection 133Flood inlet 135Seal gas connection 137Motor compartment 139Coolant connection 141Underside 143Screw 145Bearing cover 147Mounting hole 148Coolant line 149Rotor 151Rotation axis 153Rotor shaft 155Rotor disc 157Stator disc 159Spacer ring 161Rotor hub 163Holweck rotor sleeve 165Holweck rotor sleeve 167Holweck stator sleeve 169Holweck stator sleeve 171Holweck gap 173Holweck gap 175Holweck gap 179Connecting channel 181Rolling bearing 183Permanent magnet bearing 185Injection nut 187Disc 189Insert 191Rotor-side bearing half 193Stator-side bearing half 195Ring magnet 197Ring magnet 199Bearing gap 201Support section 203Support section 205Radial strut 207Cover element 209Support ring 211Fastening ring 213Disc spring 215Emergency orSafety bearing 217Motor stator 219Gap 221Wall 223Labyrinth seal 225Surface-treated section 227Sensor 230Pump blades 232Ring webs 234Balancing area 236Retaining web 238Retaining web 240Balancing ring 242Ring surface . 302Groove root 304External thread 306Thread land of 304 308Internal thread 310Thread land of 308 322Free end of 169 324Ring lands 326Ring lands 328Gas flow bore 330Ring grooves 332Base ring section 334Cantilever ring section 336Annular inner surface of 332 338Gas flow bore 340End face of 304 344End face of 308 346Chamfer 348Flow contour 350Vane αThread pitch angle βEnd face angle SFlow arrow

Claims

1. A vacuum pump (111), in particular a turbomolecular vacuum pump (111), having at least one Holweck pumping stage comprising a Holweck rotor and a Holweck stator; wherein the Holweck rotor comprises a rotor shaft (153) with a hub (161) provided thereon and at least two Holweck rotor sleeves (163, 165) provided on the hub (161) which concentrically surround the rotor shaft (153), wherein a radially inner Holweck rotor sleeve (165) has a first diameter and a radially outer Holweck rotor sleeve (163) has a second diameter;and wherein the Holweck stator comprises, between the two Holweck rotor sleeves (163, 165), a Holweck stator sleeve (169) concentric with the latter, which has a fixed end (321) attached to a stationary housing section (121) of the vacuum pump (111), a free end (322) axially opposite the fixed end (321), and an inner surface (352) with an internal thread (308) formed thereon, and an outer surface (354) with an external thread (304) formed thereon; and wherein the second diameter of the radially outer Holweck rotor sleeve (163) is at least 30% larger than the first diameter of the radially inner Holweck rotor sleeve (165).

2. Vacuum pump (111) according to claim 1, wherein the second diameter of the radially outer Holweck rotor sleeve (163) is at least 35% larger than the first diameter of the radially inner Holweck rotor sleeve (165).

3. Vacuum pump (111) according to claim 1 or 2, wherein the Holweck stator sleeve (169) has a core wall thickness that is greater than 5 mm, preferably greater than 6 mm, and particularly preferably greater than 7 mm, substantially over its entire axial extent between the fixed end (321) and the free end (322).

4. Vacuum pump (111) according to one of the preceding claims, wherein at least two mutually concentric annular webs (324) are formed on the free end (322) of the Holweck stator sleeve (169) and at least two mutually concentric annular webs (326) are also formed on the hub (161), which are nested with the annular webs (324) of the free end (322) of the Holweck stator sleeve (169).

5. Vacuum pump (111) according to one of the preceding claims, wherein the Holweck stator sleeve (169) is penetrated at its free end (322) in the radial direction by a plurality of gas flow bores (328) which are uniformly spaced from one another in the circumferential direction.

6. Vacuum pump (111), in particular a turbomolecular vacuum pump (111), with at least one Holweck pumping stage comprising a Holweck rotor and a Holweck stator; wherein the Holweck rotor comprises a rotor shaft (153) with a hub (161) provided thereon and a radially outer Holweck rotor sleeve (163) extending axially from the hub (161) and a radially inner Holweck rotor sleeve (165) extending axially from the hub (161) and spaced from the radially outer Holweck rotor sleeve (163) by an annular space;wherein the Holweck stator comprises a Holweck stator sleeve (169) coaxially aligned with the two Holweck rotor sleeves (163, 165), which has a fixed end (321) attached to a stationary housing section (121) of the vacuum pump (111), a free end (322) axially opposite the fixed end (321), and a cylindrical outer surface (354) between the fixed end (321) and the free end (322) with an external thread (304) formed thereon; wherein the radially inner Holweck rotor sleeve (165) has an axial extent that is 30% to 70%, preferably 40% to 60%, in particular 45% to 55%, of the axial extent of the radially outer Holweck rotor sleeve (163); 7. Vacuum pump (111) according to claim 6, wherein the Holweck stator sleeve (169) has a base ring section (332) attached to the stationary housing section (121) and a cantilever ring section (334) which extends from an end face of the base ring section (332) facing the hub (161) in the axial direction to the free end (322) of the Holweck stator sleeve (169) in the annular space between the inner Holweck rotor sleeve (165) and the outer Holweck rotor sleeve (163).

8. Vacuum pump (111) according to claim 7, wherein the base ring portion (332) extends radially inwardly from the external thread (304) to over the inner Holweck rotor sleeve (165).

9. Vacuum pump (111) according to claim 7 or 8, wherein the cantilever ring portion (334) and the base ring portion (332) have the same outer diameter, wherein the external thread (304) of the Holweck stator sleeve (169) is formed on both the outer surface (354) of the base ring portion (332) and the cantilever ring portion (334).

10. Vacuum pump (111) according to one of claims 7 to 9, wherein the cantilever ring portion (334) has a cylindrical inner surface with an internal thread (308) formed thereon, wherein it is preferably provided that the number of threads of the internal thread (308) corresponds to the number of threads of the external thread (304).

11. Vacuum pump (111) according to one of claims 7 to 10, wherein the base ring portion (332) forms an annular inner surface (336) on which a motor stator (217) of an electric motor (125) driving the rotor shaft (153) is provided.

12. Vacuum pump (111) according to one of claims 7 to 11, wherein the base ring section (332) is penetrated in the axial direction by a plurality of gas flow bores (338), wherein it is preferably provided that: (i) the gas flow bores (338) also extend radially and / or in the circumferential direction; and / or (ii) the gas flow bores (338) each have an elongated hole cross-section when viewed in the axial direction of the Holweck stator sleeve (169); and / or (iii) the number of gas flow bores (338) corresponds to the number of threads of the internal thread (308) of the cantilever ring section (334).

13. Vacuum pump (111) according to one of the preceding claims, wherein at least two mutually concentric and axially extending annular grooves (330) are formed in the stationary housing section (121), wherein at least two mutually concentric annular grooves (330) are located radially outside the Holweck stator sleeve (169) and / or wherein at least two mutually concentric annular grooves (330) are located radially inside the Holweck stator sleeve (169).

14. Vacuum pump (111), in particular a turbomolecular vacuum pump (111), with at least one Holweck pump stage, which comprises a Holweck rotor and a Holweck stator with a Holweck stator sleeve (169) having a fixed end (321) attached to a stationary housing section (121) of the vacuum pump (111), a free end (322) axially opposite the fixed end (321), and an inner surface (352) with an internal thread (308) formed thereon, comprising a plurality of spirally encircling first thread ridges (310), and an outer surface (354) with an external thread (304) formed thereon, comprising a plurality of spirally encircling second thread ridges (306), wherein the first thread ridges (310) form first end faces (344) at the free end (322) of the Holweck stator sleeve (169), and the second thread ridges (306) form second end faces (340) at the free end (322) of the Holweck stator sleeve (169),wherein: (i) the second end faces (340) have an offset d of a predetermined size relative to the first end faces (344) in the circumferential direction, wherein , d > 0 applies; and / or (ii) the first end faces (344) and / or the second end faces (340) enclose an acute angle with a plane into which the free end (322) of the Holweck stator sleeve (169) lies, which angle is in particular between 10° and 40°, preferably between 20° and 30°; and / or (iii) the Holweck stator sleeve (169) has a wall thickness that decreases towards the free end (322) of the Holweck stator sleeve (169).

15. Vacuum pump (111) according to claim 14, wherein the offset d is: d = t / tan α , where t the radial wall thickness of the Holweck stator sleeve (169) and α is the pitch angle of the external thread (304).

16. Vacuum pump (111) according to claim 14 or 15, wherein the number of first threaded webs (310) is equal to the number of second threaded webs (306).

17. Vacuum pump (111) according to claim 16, wherein flow contours (348) are formed on the free end (322) of the Holweck stator sleeve (169) and are uniformly spaced from one another in the circumferential direction in the same number as the first and second threaded webs (306, 310), wherein each flow contour (348) defines a defined gas flow path between a thread groove of the internal thread (308) and a thread groove of the external thread (304).

18. Vacuum pump (111) according to claim 17, wherein the flow contours (348) comprise guide vanes (350) extending between the first end faces (344) of the first threaded webs (310) and the second end faces (340) of the second threaded webs (306), wherein the guide vanes (350) preferably have a concave or a convex curvature.

19. Vacuum pump (111) according to one of claims 14 to 18, wherein the wall thickness of the Holweck stator sleeve (169) decreases only over a region which is defined by the first two turns of the internal thread (308) and / or the external thread (304) closest to the free end (322) of the Holweck stator sleeve (169), preferably only by the first turn of the internal thread and / or the external thread (304).

20. Vacuum pump (111) according to claim 19, wherein the wall thickness decreases towards the free end (322) of the Holweck stator sleeve (169) due to an inside and / or outside chamfer (346) of the Holweck stator sleeve (169) at its free end (322), wherein it is preferably provided that the chamfer (346) has a linear, convex, round or parabolic contour.

21. A vacuum pump (111), in particular a turbomolecular vacuum pump (111), having at least one Holweck pumping stage comprising a Holweck rotor and a Holweck stator; wherein the Holweck rotor comprises a rotor shaft (153) with a hub (161) provided thereon and at least two Holweck rotor sleeves (163, 165) provided on the hub (161) and concentrically surrounding the rotor shaft (153);and wherein the Holweck stator comprises, between the two Holweck rotor sleeves (163, 165), a Holweck stator sleeve (169) which is concentric with the latter and which has a fixed end (321) attached to a stationary housing section (121) of the vacuum pump (111), a free end (322) axially opposite the fixed end (321), and an inner surface (352) with an internal thread (308) formed thereon and an outer surface (354) with an external thread (304) formed thereon, wherein a flow profile (356) which is concave in cross section and concentrically surrounds the rotor shaft (153) is provided on the hub (161) of the Holweck rotor between the two Holweck rotor sleeves (163, 165); 22. Vacuum pump (111) according to claim 21, wherein the airfoil (356) is a part that can be handled separately from the hub (161) and is attached to the hub (161).

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