Turbomolecular vacuum pump

Abstract

The invention relates to a turbomolecular vacuum pump with at least one turbomolecular pump unit and at least one Holweck pump unit arranged downstream of the turbomolecular pump unit in the pumping direction, the Holweck pump unit having at least two Holweck stages arranged concentrically within one another with respect to a common axis of rotation and following one another in the pumping direction, wherein the Holweck stages each comprise a Holweck stator with a Holweck thread, which has Holweck webs projecting from a channel base and Holweck channels bounded by the walls of the Holweck webs and faces a common Holweck rotor of the Holweck pump unit, which rotates about the axis of rotation during operation and which, with one Holweck stator, defines a radially outer Holweck pumping area and, with the other Holweck stator, a radially inner Holweck pumping area.wherein in a transition region at the free end of the Holweck rotor an outlet region of the radially outer Holweck pumping region transitions into an inlet region of the radially inner Holweck pumping region, wherein in addition to an axial gas inlet into the radially outer Holweck pumping region a radial gas inlet into the Holweck pumping unit is provided, which opens either into the transition region or upstream of the transition region into the radially outer Holweck pumping region, and wherein the outlet region and the inlet region each have a free cross-sectional area defined by the Holweck channels in a cross-sectional plane perpendicular to the axis of rotation, in which the pumping action ends or begins, and the free cross-sectional area of ​​the inlet region is larger by a factor f > 1 than the free cross-sectional area of ​​the outlet region.

Description

[0001] The invention relates to a turbomolecular vacuum pump with at least one turbomolecular pump unit and at least one Holweck pump unit arranged downstream of the turbomolecular pump unit in the pumping direction, the Holweck pump unit having at least two Holweck stages arranged concentrically within one another with respect to a common axis of rotation and following one another in the pumping direction, wherein the Holweck stages each comprise a Holweck stator with a Holweck thread, which has Holweck webs projecting from a channel base and Holweck channels bounded by the walls of the Holweck webs and faces a common Holweck rotor of the Holweck pump unit, which rotates about the axis of rotation during operation and which, with one Holweck stator, defines a radially outer Holweck pumping area and, with the other Holweck stator, a radially inner Holweck pumping area.wherein in a transition area at the free end of the Holweck rotor an outlet area of ​​the radially outer Holweck pump area transitions into an inlet area of ​​the radially inner Holweck pump area, and wherein in addition to an axial gas inlet into the radially outer Holweck pump area a radial gas inlet into the Holweck pump unit is provided.

[0002] The invention further relates to a vacuum system with a turbomolecular vacuum pump as disclosed herein and with a recipient to be evacuated, wherein the turbomolecular vacuum pump is designed as a split-flow vacuum pump having one or more radial suction inlets which are each connected to an opening of the recipient during operation.

[0003] The invention further relates to a leak detection system with a turbomolecular vacuum pump as disclosed herein, which can be connected to a test object to be evacuated, and with a detector, in particular a mass spectrometer, for detecting a test gas, wherein the turbomolecular vacuum pump is connected to the detector via an axial or radial gas inlet and a radial gas inlet for the test gas is provided downstream of the gas inlet into the Holweck pump unit.

[0004] Such turbomolecular vacuum pumps are generally known, for example from EP 3 845 764 A2, EP 2 933 497 A2 and EP 3 657 021 A1. Vacuum systems and leak detection systems of the aforementioned type are also generally known.

[0005] Vacuum pumps are used in various fields of engineering. Depending on the requirements, vacuum pumps have one or more pumping units. A Holweck pump unit belongs to the class of molecular vacuum pumps and generates a molecular flow through the rotation of the Holweck rotor relative to the respective Holweck stator. A Holweck pump unit can comprise one or more Holweck stages, with multiple Holweck stages able to pump both serially and in parallel. Holweck pump units are typically used in turbomolecular vacuum pumps and are arranged downstream of one or more turbomolecular pump stages that form a turbomolecular pump unit, in the pumping direction.

[0006] A Holweck stage comprises a Holweck rotor and a Holweck stator. The Holweck rotor is attached to a pump rotor by means of, for example, a disc-shaped Holweck hub. During pumping operation, the pump rotor is set in motion by a drive motor. The Holweck rotor, also referred to as a Holweck sleeve, typically has a hollow cylindrical shape. A Holweck pump unit can have several Holweck sleeves mounted concentrically on the Holweck hub. The Holweck stator is equipped with a single- or multi-start Holweck thread. The gas molecules to be pumped are conveyed from an inlet to an outlet by the rotating motion of the Holweck rotor relative to the Holweck stator along the threads. A thread comprises a circumferential Holweck channel (also referred to as a Holweck groove) bounded by walls of Holweck webs, in which the gas molecules are conveyed as the Holweck rotor rotates relative to the Holweck stator.To minimize backflow losses, the width of the radial gap (Holweck gap) between the top of the Holweck web, also called the tip, and the Holweck sleeve is kept relatively small compared to the web height.

[0007] So-called "folded" Holweck pump units are also known, in which several Holweck stages are arranged concentrically within one another (also referred to as "nested" Holweck stages), such that the gas flows of radially consecutive Holweck stages are opposite to each other. Two successive Holweck stages, namely a (radially) outer Holweck stage and a (radially) inner Holweck stage, can comprise a common Holweck stator, which is provided with a Holweck thread on both sides and is hereinafter also referred to as a "double-sided" Holweck stator, and which is located between two concentric Holweck rotors.

[0008] Furthermore, it is generally known to provide so-called "conical" Holweck stages, in which the Holweck stator is designed such that the web height decreases continuously in the pumping direction. The web height is the radial distance between the web tip and the channel bottom at any given axial point.

[0009] For many applications of turbomolecular vacuum pumps, such as split-flow or leak detection applications, it is necessary to provide at least one radial gas inlet—also known as an interstage port—into the Holweck pump unit. An axial position of such a radial gas inlet relatively close to the turbomolecular pump unit, relative to the axis of rotation, can be disadvantageous, particularly due to adverse backflow effects. Therefore, it is desirable to position the radial gas inlet in the Holweck pump unit at or near the transition zone, and in any case, closer to the transition zone than to the turbomolecular pump unit. Furthermore, it is desirable for such an interstage port to have the highest possible pumping speed.

[0010] The term suction capacity refers to the volume flow rate of a given gas that is conveyed through a specific cross-sectional area per unit of time.

[0011] The aforementioned EP 2 933 497 A2 discloses a vacuum pump with the features of the preamble of claim 1. The aforementioned EP 3 657 021 A1 also discloses a vacuum pump with a radial gas inlet into the Holweck pump unit.

[0012] Against this background, the object of the invention is to improve a turbomolecular vacuum pump of the type mentioned above in such a way that backflow effects in the Holweck pump unit are minimized in connection with a radial gas inlet and that the highest possible pumping speed is available for the radial gas inlet.

[0013] This problem is solved by the features of claim 1. According to the invention, it is accordingly provided that the radial gas inlet opens either into the transition region or upstream of the transition region into the radially outer Holweck pumping region, in particular into the downstream half or into the downstream third, quarter, fifth or sixth of the radially outer Holweck pumping region, and that the outlet region and the inlet region each have a free cross-sectional area defined by the Holweck channels in a cross-sectional plane perpendicular to the axis of rotation, in which the pumping action ends or begins, and that the free cross-sectional area of ​​the inlet region is larger by a factor f > 1 than the free cross-sectional area of ​​the outlet region.

[0014] The free cross-sectional area on the inlet or outlet side is also referred to as openness in the following.

[0015] The Holweck stators are preferably designed with multiple threads, i.e., they each have a plurality, e.g., 4, 6 or 8, of parallel Holweck channels, which are separated from each other in pairs by one of the Holweck webs.

[0016] Investigations of known Holweck pump units have shown that the pumping speed decreases continuously in the pumping direction, i.e., from the inlet to the radially outer Holweck pump stage to the outlet of the radially inner Holweck pump stage. Depending on the specific conditions, a comparatively sharp decrease in pumping speed is observed in the transition region between the radially outer and radially inner Holweck pump sections. Furthermore, in many Holweck pump units, the pumping speed at the inlet of the radially inner Holweck pump section is generally lower than at the outlet of the radially outer Holweck pump section. In other words, a considerable reduction in pumping speed occurs at the transition region—also referred to as the reversal point—in some configurations.

[0017] It was found that the increase in inlet-side openness according to the invention, compared to the outlet-side openness, considerably increases the pumping speed at the inlet of the radially inner Holweck pump section. Furthermore, while simultaneously minimizing backflow, a significantly higher pumping speed is also available for the radial gas inlet, even when the radial gas inlet opens upstream of the transition zone into the radially outer Holweck pump section. For example, in a real turbomolecular vacuum pump, it was found that increasing the free cross-sectional area at the inlet of the radially inner Holweck pump section from 142 mm² to 388 mm² resulted in an increase in the pumping speed from 2.69 l / s to 6.70 l / s (where l / s = liters per second), with all other geometric conditions of the Holweck pump unit remaining unchanged.

[0018] The invention thus enables a considerable increase in the performance of Holweck pump units and therefore of turbomolecular vacuum pumps equipped with such Holweck pump units, which is of great advantage in practice, especially for split-flow applications and leak detection applications that require one or more radial gas inlets.

[0019] Advantageous further developments of the invention are also specified in the dependent claims, the following description and in the figures.

[0020] According to some embodiments, it can be provided that: 1 < f < 3, preferably 1 < f < 2, preferably 1.2 < f < 1.5. It has been found that practically advantageous increases in suction speed can already be achieved when the factor f is less than 1.5, with a factor F of less than 2 or less than 3 having the advantage that comparatively little radial installation space is required.

[0021] The openness on the inlet side can be varied in different ways.

[0022] In some embodiments, it may be provided that in the respective cross-sectional plane the height of the Holweck webs in the inlet area is greater than the height of the Holweck webs in the outlet area.

[0023] According to some embodiments, it can be provided that in the respective cross-sectional plane the circumferentially measured width of the hollow webs in the inlet area is greater than in the outlet area.

[0024] According to some embodiments, it can be provided that the number of Holweck webs in the radially inner Holweck pump area is smaller than the number of Holweck webs in the radially outer Holweck pump area.

[0025] The aforementioned measures can also be combined in any way desired.

[0026] The Holweck stator that limits the radially inner Holweck pumping area can be a Holweck stator provided with a Holweck thread on both sides, which limits another Holweck pumping area radially further inwards with another Holweck rotor.

[0027] It can be provided that the Holweck stator, which is provided with the Holweck thread on both sides, has a wall thickness measured in the radial direction, wherein in the inlet area the wall thickness is smaller than the height of the Holweck webs of the radially inner Holweck pumping area.

[0028] In some embodiments, it may be provided that the radially outer Holweck pumping area and / or the radially inner Holweck pumping area are each conically designed such that the height of the Holweck webs decreases continuously in the pumping direction.

[0029] It may be provided that a conicity angle defined by the channel base of the radially outer Holweck pumping area and a conicity angle defined by the channel base of the radially inner Holweck pumping area are at least substantially the same or different from each other. In particular, the conicity angle of the radially outer Holweck pumping area may be larger or smaller than the conicity angle of the radially inner Holweck pumping area.

[0030] Alternatively, the radially outer Holweck pump area and / or the radially inner Holweck pump area can each be cylindrical.

[0031] According to some embodiments, at least one pump-effective section of the radially outer Holweck stator, which together with the Holweck rotor defines the radially outer Holweck pumping area, can be formed in one piece. The radial gas inlet can open upstream of the transition zone into the radially outer Holweck pumping area and extend through the one-piece pump-effective section of the radially outer Holweck stator. The one-piece design simplifies the manufacture and assembly of the Holweck pumping unit. The greater inlet-side openness of the radially inner Holweck pumping area is also advantageous for a radial gas inlet located upstream of the transition zone with regard to pumping speed and backflow minimization; that is, a two-part radially outer Holweck stator is not required to provide greater openness downstream of the radial gas inlet opening.

[0032] In some embodiments, the radial gas inlet to the Holweck pump unit may extend through a pump housing above a lower or intermediate section of the vacuum pump, in which the transition area is at least partially located. This is particularly advantageous if, for example, one or more additional radial gas inlets are present upstream of a split-flow vacuum pump, as the outside of the pump housing can then serve as a common sealing surface for the radial gas inlets.

[0033] According to some embodiments, at least one further radial gas inlet may be arranged upstream of the radial gas inlet into the Holweck pump unit, in particular wherein the further radial gas inlet opens into the Holweck pump unit or into the turbomolecular pump unit. As mentioned above, an outer surface of a pump housing, through which at least some of the multiple radial gas inlets extend, can advantageously be used as a common sealing surface.

[0034] In the vacuum system according to the invention, one of the radial suction inlets is the radial gas inlet opening into the transition region or upstream of the transition region into the radially outer Holweck pump region.

[0035] In the leak detection system according to the invention, the radial gas inlet for the test gas is the radial gas inlet opening into the transition area or upstream of the transition area into the radially outer Holweck pump area.

[0036] The invention is described below by way of example with reference to the drawing. The drawing shows: Fig. 1 a perspective view of a turbomolecular vacuum pump according to the prior art, Fig. 2 a view of the underside of the turbomolecular vacuum pump of Fig. 1 , Fig. 3 a cross-section of the turbomolecular vacuum pump along the in Fig. 2 Section line AA shown, Fig. 4 a cross-sectional view of the turbomolecular vacuum pump along the in Fig. 2 Section line BB, Fig. 5 shows a cross-sectional view of the turbomolecular vacuum pump along the line shown in Fig. 2 The section line CC shown, Fig. 6 a schematic view of a turbomolecular vacuum pump according to the prior art, Fig. 7 partially a cross-section parallel to the axis of rotation through a part of a turbomolecular vacuum pump according to the prior art, Fig. 8 partially a cross-section parallel to the axis of rotation through a part of a turbomolecular vacuum pump according to an embodiment of the invention, and Fig. 9 partially a cross-section perpendicular to the axis of rotation through a Holweck pump unit of a turbomolecular vacuum pump according to the invention.

[0037] The in Fig. 1 The turbomolecular vacuum pump 111 shown (hereinafter also referred to as turbomolecular pump or vacuum pump) comprises a pump inlet 115 surrounded by an inlet flange 113, to which a receiver (not shown) can be connected in a manner known per se. The gas from the receiver can be drawn out of the receiver 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.

[0038] The inlet flange 113 forms a Fig. 1 The upper end of the housing 119 of the vacuum pump 111. The housing 119 comprises a lower part 121, to which an electronics housing 123 is attached laterally. The electronics housing 123 contains electrical and / or electronic components of the vacuum pump 111, e.g., for operating an electric motor 125 located in the vacuum pump (see also Fig. 3 The electronics housing 123 has several connections 127 for accessories. In addition, a data interface 129, e.g. according to the RS485 standard, and a power supply connection 131 are located on the electronics housing 123.

[0039] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0040] The housing 119 of the turbomolecular pump 111 has a flood inlet 133, in particular in the form of a flood valve, through which the vacuum pump 111 can be flooded. In the area of ​​the lower part 121, a purge gas connection 135, also referred to as a purge gas connection, is also arranged, through which purge gas can be supplied to protect the electric motor 125 (see e.g. Fig. 3 The gas pumped by the pump can be introduced into the motor compartment 137, in which the electric motor 125 is housed in the vacuum pump 111. Two coolant connections 139 are also arranged in the lower part 121, one of which serves as an inlet and the other as an outlet for coolant that can be directed into the vacuum pump for cooling purposes. Other existing turbomolecular vacuum pumps (not shown) are operated exclusively with air cooling.

[0041] The lower side 141 of the vacuum pump can serve as a base, allowing the vacuum pump 111 to be operated standing upright on its underside 141. Alternatively, the vacuum pump 111 can be attached to a receiver via the inlet flange 113 and thus operated in a suspended position. Furthermore, the vacuum pump 111 can be designed to operate even when oriented differently than described. Fig. 1 As shown. It is also possible to implement embodiments of the vacuum pump in which the underside 141 can be arranged facing sideways or upwards instead of downwards. In principle, any angle is possible.

[0042] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in a standing position.

[0043] On the underside 141, which is in Fig. 2 As shown, various screws 143 are arranged, by means of which components of the vacuum pump, not further specified here, are fastened to one another. For example, a bearing cover 145 is attached to the underside 141.

[0044] Mounting holes 147 are also arranged on the underside 141, via which the pump 111 can be attached to a support surface, for example. This is not possible with other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here.

[0045] In the Fig. 2 bis 5 A coolant line 148 is shown, in which the coolant introduced and removed via the coolant connections 139 can circulate.

[0046] Like the sectional views of the Figuren 3 bis 5 As shown, 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.

[0047] A rotor 149 is arranged in the housing 119, which has a rotor shaft 153 rotatable about a rotation axis 151.

[0048] The turbomolecular pump 111 comprises several turbomolecular pump stages connected in series to provide pumping action. These stages have several radial rotor disks 155 attached to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and fixed in the housing 119. Each rotor disk 155 and an adjacent stator disk 157 form a turbomolecular pump stage. The stator disks 157 are held at a desired axial distance from each other by spacer rings 159.

[0049] The vacuum pump also includes Holweck pump stages arranged radially within one another and connected in series to effectively pump the pump. Other turbomolecular vacuum pumps exist (not shown) that do not have Holweck pump stages.

[0050] The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical Holweck rotor sleeves 163, 165 attached to and supported by the rotor hub 161, which are oriented coaxially to the axis of rotation 151 and nested one inside the other in the radial direction. Furthermore, two cylindrical Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the axis of rotation 151 and nested one inside the other in the radial direction.

[0051] The pump-active surfaces of the Holweck pump stages are formed by the outer 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 faces the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together they form the first Holweck pump stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 faces the radial outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together they form 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 they form the third Holweck pumping stage.

[0052] At the lower end of the Holweck rotor sleeve 163, a radially extending channel can be provided, through which the radially outer Holweck slot 171 is connected to the central Holweck slot 173. Furthermore, a radially extending channel can be provided at the upper end of the inner Holweck stator sleeve 169, through which the central Holweck slot 173 is connected to the radially inner Holweck slot 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.

[0053] The aforementioned pump-active surfaces of the Holweck stator sleeves 167, 169 each have several Holweck grooves spiraling around the axis of rotation 151 in the axial direction, while the opposite outer surfaces of the Holweck rotor sleeves 163, 165 are smooth and drive the gas forward in the Holweck grooves for the operation of the vacuum pump 111.

[0054] 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.

[0055] In the area of ​​the rolling bearing 181, a conical injection nut 185 with an outer diameter increasing towards the rolling bearing 181 is provided on the rotor shaft 153. The injection nut 185 is in sliding contact with at least one wiper of a fluid reservoir. In other existing turbomolecular vacuum pumps (not shown), an injection screw may be provided instead of an injection nut. Since different designs are thus possible, the term "injection tip" is also used in this context.

[0056] The operating fluid reservoir comprises several stacked absorbent discs 187, which are impregnated with an operating fluid for the rolling bearing 181, e.g. with a lubricant.

[0057] During operation of the vacuum pump 111, the operating fluid is transferred by capillary action from the fluid reservoir via the wiper to the rotating injection nut 185 and, as a result of centrifugal force, is conveyed along the injection nut 185 in the direction of the increasing outer diameter of the injection nut 185 towards the rolling bearing 181, where it performs, for example, a lubricating function. The rolling bearing 181 and the fluid reservoir are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

[0058] The permanent magnet bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each containing a ring stack of several axially stacked permanent magnet rings 195, 197. The ring magnets 195, 197 face each other, forming a radial bearing gap 199, with the rotor-side ring magnets 195 arranged radially outside and the stator-side ring magnets 197 radially inside. The magnetic field present in the bearing gap 199 induces magnetic repulsive forces between the ring magnets 195, 197, which cause the rotor shaft 153 to be radially supported. The rotor-side ring magnets 195 are supported by a support section 201 of the rotor shaft 153, which radially surrounds the ring magnets 195 on the 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. Parallel to the axis of rotation 151, the rotor-side ring magnets 195 are fixed by a cover element 207 coupled to the support section 201. The stator-side ring magnets 197 are fixed parallel to the axis of rotation 151 in one direction by a retaining ring 209 connected to the support section 203 and a retaining ring 211 also connected to the support section 203. A disc spring 213 may also be provided between the retaining ring 211 and the ring magnets 197.

[0059] Within the magnetic bearing, an emergency or catch bearing 215 is provided, which runs freely without contact during normal operation of the vacuum pump 111 and only engages when there is excessive radial deflection of the rotor 149 relative to the stator, in order to form a radial stop for the rotor 149 and thus prevent a collision between the rotor-side and stator-side structures. The catch bearing 215 is designed as an unlubricated rolling bearing and forms a radial gap with the rotor 149 and / or the stator, which causes the catch bearing 215 to be disengaged during normal pump operation. The radial deflection at which the catch bearing 215 engages is dimensioned to be large enough so that the catch bearing 215 does not engage during normal operation of the vacuum pump, and simultaneously small enough to prevent a collision between the rotor-side and stator-side structures under all circumstances.

[0060] 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 section of the rotor shaft 153 extending through the motor stator 217. A space 219 is arranged between the motor stator 217 and the section of the rotor 149 extending through the motor stator 217. This space comprises a radial motor gap through which the motor stator 217 and the permanent magnet arrangement can magnetically influence each other to transmit the drive torque.

[0061] The motor stator 217 is fixed in the housing within the motor compartment 137 provided for the electric motor 125. A purge gas, also known as a sealing gas, which can be, for example, air or nitrogen, can enter the motor compartment 137 via the purge gas connection 135. This purge gas protects 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, meaning that the vacuum pressure in the motor compartment 137 is at least approximately equal to that produced by the backing pump connected to the pump outlet 117.

[0062] Between the rotor hub 161 and a wall 221 bounding the engine compartment 137, a so-called labyrinth seal 223, which is known per se, can also be provided, in particular to achieve a better seal of the engine compartment 217 against the radially outside Holweck pump stages.

[0063] Fig. 6 schematically shows some components of a turbomolecular vacuum pump according to the prior art, wherein the turbomolecular vacuum pump can also be designed as described above in connection with the Fig. 1 bis 5 has been described.

[0064] In Fig. 6 Shown are a turbomolecular pump unit 11 and a Holweck pump unit 13. Both pump units 11 and 13 have a common rotor 12, which rotates around a rotational axis 15 during pump operation. The drive motor for the rotor 12 is in Fig. 6 not shown.

[0065] The turbomolecular pump unit 11 comprises a plurality of rotor disks 11a which are rotationally fixed to the rotor 12. The stator disks, which interact with the rotor disks 11a in a known manner to provide pumping action, are not shown in the turbomolecular pump unit 11.

[0066] The Holweck pump unit 13 includes the Holweck hub 26, which is non-rotatably connected to the rotor 12, the Holweck rotor 25, which is also referred to as the Holweck sleeve and is non-rotatably connected to the Holweck hub 26, as well as a radially outer Holweck stator 17a and a radially inner Holweck stator 17b.

[0067] In the embodiment shown here, the Holweck pump unit 13 comprises two Holweck stages arranged concentrically within one another with respect to the axis of rotation 15 and successively in the pumping direction. Each Holweck stage comprises the respective Holweck stator 17a, 17b, which includes a multi-start Holweck thread with Holweck webs 21 projecting from a channel base 19 and Holweck channels 23 bounded by the walls of the Holweck webs 21. This Holweck thread faces the respective side of the Holweck rotor 25.

[0068] In a generally known manner, the Holweck rotor 25 thus forms a radially outer Holweck pumping area 27 with the radially outer Holweck stator 17a and a radially inner Holweck pumping area 29 with the radially inner Holweck stator 17b.

[0069] The flow path of a gas to be pumped is in Fig. 6 as indicated by the arrows. The gas to be pumped initially flows through an axial pump inlet (not shown) in the pump housing (also not shown) into the turbomolecular pump unit 11, through this unit to an axial gas inlet 33 in the radially outer Holweck pump section 27, through this section to an outlet section 27a of the radially outer Holweck pump section 27, into a transition section 31 at the free end of the Holweck rotor 25, into an inlet section 29a of the radially inner Holweck pump section 29, through this section, and then via a flow path (not shown) to an outlet of the turbomolecular vacuum pump.

[0070] The outlet region 27a of the radially outer Holweck pump region 27 is located in a cross-sectional plane perpendicular to the axis of rotation 15 in an axial position relative to the axis of rotation 15, at which point the pumping action of the radially outer Holweck pump region 27 ends, i.e., where the Holweck channels 23 end. Correspondingly, the pumping action of the radially inner Holweck pump region 29 begins at its inlet region 29a and thus in a cross-sectional plane perpendicular to the axis of rotation 15, in which the Holweck channels 23 begin.

[0071] The cross-sectional plane in which the outlet region 27a lies, and in which the pumping action of the radially outer Holweck pump region 27 thus ends, and the cross-sectional plane in which the inlet region 29a lies, and in which the pumping action of the radially inner Holweck pump region 29 consequently begins, can coincide. Depending on the specific design and arrangement of the two Holweck pump stages, these two cross-sectional planes can also be spaced apart from each other in the axial direction.

[0072] In their respective cross-sectional planes, the outlet region 27a and the inlet region 29a each possess a free cross-sectional area defined by the Holweck channels 23. For the sake of simplicity, the respective free cross-sectional area will hereinafter also be referred to as the openness; that is, the radially outer Holweck pump region 27 has a specific outlet-side openness at its outlet region 27a, defined by the geometry of its Holweck channels 23. Similarly, the radially inner Holweck pump region 29 has an inlet-side openness at its inlet region 29a, defined by the geometry of its Holweck channels 23.

[0073] It can be seen that in the Fig. 6 In the schematically represented example of the prior art, the inlet-side openness is significantly smaller than the outlet-side openness, since the height of the Holweck webs 21 of the radially inner Holweck pumping area 29 is smaller than the height of the Holweck webs 21 of the radially outer Holweck pumping area 27. For the sake of simplicity, it is assumed here that there are no differences in the width of the Holweck webs 21 and the number of Holweck channels 23 - parameters that also determine the openness.

[0074] Furthermore, in Fig. 6 It can be seen that the radially outer Holweck pump section 27 is conically shaped such that the height of the Holweck webs 21 decreases in the pumping direction. The radially outer Holweck pump stage is therefore a conical pump stage. The conicity, or a respective conicity angle measured with respect to the axis of rotation 15, is defined by the channel base 19. Such conical Holweck pump stages are generally known. The radially inner Holweck stage here is cylindrical. It is also generally known to have both a radially outer Holweck pump stage and a radially inner Holweck pump stage, which—as in the example of the Fig. 6 - have a common Holweck rotor 25, each to be conically shaped.

[0075] While Fig. 6 The fact that a turbomolecular vacuum pump is only shown schematically illustrates Fig. 7 a concrete example from the state of the art.

[0076] Unlike in Fig. 6 A pump housing 41 is also shown here. Furthermore, it shows Fig. 7 A lower part 39 of the vacuum pump, on which the radially inner Holweck stator 17b is supported at its lower end. It can be seen that the transition region 31 between the outlet region of the radially outer pumping region 27 and the inlet region of the radially inner Holweck pumping region 29 is located within the lower part 39, since the Holweck rotor 25 extends with its free end into the lower part 39.

[0077] In the example of the Fig. 7 The radially inner Holweck stator 17b is a Holweck stator provided with a Holweck thread on both sides. This double-sided Holweck stator 17b, together with another radially inner Holweck rotor 25, delimits a further Holweck pumping area 43. While the Holweck pumping areas 29 and 43 delimited by the radially inner Holweck stator 17b are each cylindrical, the radially outer Holweck pumping area 27 – as also in the example of the Fig. 6 - conically shaped.

[0078] In Fig. 7 It can be seen that - with the same width of the Holweck webs and the same number of Holweck channels - the inlet-side openness of the radially inner Holweck pump area 29 is again smaller than the outlet-side openness of the radially outer Holweck pump area 27 due to the different height of the Holweck webs 21.

[0079] As shown below with reference to the embodiment according to the invention, Fig. 8 As described, the Holweck pump unit 13 of a turbomolecular vacuum pump according to the invention differs from the prior art, as exemplified above by reference to the Fig. 6 and 7 has been described by the fact that the inlet area 29a of the radially inner Holweck pump area 29 has a greater openness than the outlet area 27a of the radially outer Holweck pump area 27.

[0080] As explained in the introduction, this results in a higher pumping speed at the transition area and also for a radial gas inlet (interstage port) into the Holweck pump unit 13, as well as a reduction of backflow effects.

[0081] The axial height of the radial gas inlet – relative to the rotation axis not shown here – can vary in practice. Two different possibilities are illustrated in Fig. 8 shown. Arrow 35 indicates a radial gas inlet that opens into the transition region 31 between outlet region 27a and inlet region 29a. Alternatively, a radial gas inlet can open slightly further upstream into the radially outer Holweck pump region 27, as shown in Fig. 8 as represented by arrow 35'. Such a radial gas inlet 35' located somewhat upstream of the transition region 31 can, for example, be present if – as in the example of the Fig. 7 shown - the transition area 31 is located within a pump lower section 39. Even with such a radial gas inlet 35', the higher pumping speed generated by the greater openness at the inlet area 29a of the radially inner Holweck pump section 29 has an advantageous effect.

[0082] How Fig. 8 Furthermore, both Holweck pump sections 27, 29 are conically shaped, i.e., the height of the Holweck webs 21 decreases in the pumping direction. Consequently, the gas to be pumped also emerges in the exemplary embodiment of the Fig. 8 - coming from the turbomolecular pump unit 11 - enters the radially outer Holweck pumping area 27 via an axial gas inlet 33 and then passes through the transition area 31 into the radially inner Holweck pumping area 29 and from there either to a gas outlet of the vacuum pump or into one or more further Holweck pumping areas, for example according to the example of the Fig. 7 . Thus, in a turbomolecular vacuum pump according to the invention, the radially inner Holweck stator 17b of the Holweck pump unit 13 can also be a "double-sided" Holweck stator, which is provided on both sides, i.e. radially outside and radially inside, with a Holweck thread that interacts effectively with a respective Holweck sleeve 25 attached to the common Holweck hub 26.

[0083] As mentioned elsewhere, the respective conicity of the Holweck pump section 27, 29 with respect to the axis of rotation is measured. The conicity angles βa and βi of the radially outer Holweck pump section 27 and the radially inner Holweck pump section 29, respectively, are given in Fig. 8 The diagram is drawn using dashed guidelines. The conicity angles βa and βi can be equal or different.

[0084] Fig. 9 The geometry at the inlet area 29a of the radially inner Holweck pumping area 29 is illustrated in the cross-sectional plane perpendicular to the axis of rotation 15 in which the Holweck channels 23 bounded by the Holweck webs 21 begin, i.e. in the cross-sectional plane in which the pumping action of the radially inner Holweck pumping area 29 begins.

[0085] In Fig. 9 Also shown is the Holweck rotor 25, which interacts with the Holweck thread of the radially inner Holweck stator 17b, encompassing the Holweck webs 21. The Holweck thread on the cylindrical wall 17c of the Holweck stator 17b is multi-start and here comprises eight parallel pumping Holweck channels 23, each separated from the others in pairs by a Holweck web 21. The Holweck rotor 25 and stator wall 17c can begin in a different cross-sectional plane than the Holweck webs 21. The pumping action of the radially inner Holweck pumping area 29 nevertheless begins where the Holweck channels 23 begin, which are jointly bounded by the channel base 19, i.e., by the outside of the stator wall 17c, and by the Holweck webs 21, and for whose pumping effectiveness the radial inner side of the Holweck rotor 25 is required.

[0086] Just like in Fig. 9 schematically represented, one can imagine the geometric situation at the inlet area 29a in a Holweck pump unit 13 according to the invention - e.g. according to Fig. 8 - introduce. In Fig. 9 The radially outer Holweck stator 17a is not shown. However, the geometric situation is corresponding for the outer Holweck stator 17a, whereby the Holweck thread of the radially outer Holweck stator 17a interacts with the radial outer surface of the Holweck rotor 25 and – as mentioned elsewhere – the pumping action of the radially outer Holweck pumping area can end in a cross-sectional plane that differs from the cross-sectional plane in which the pumping action of the radially inner Holweck pumping area 27a begins.

[0087] As is known, the tips of the Holweck ribs 21 are slightly spaced away from the inner side of the Holweck rotor 25 facing the direction of travel. The actual dimensions are shown in Fig. 9 The points of the Holweck webs 21 lie in the cross-sectional view shown on a circle around the axis of rotation 15, which is in Fig. 9 represented by a dashed line and which - as mentioned - has a smaller radius than the inside of the Holweck rotor 25.

[0088] The Holweck channels 23 are effective for pumping, as mentioned. The size of the effective free cross-sectional area at the inlet area 29a, i.e., in the area shown in Fig. 9 The cross-sectional area shown is thus determined by the number of Holweck channels 23 and by their free cross-sectional areas, the latter being determined by the circumferentially measured width B and the height H – i.e., by the distance between the rib tip and the channel base 19 – of the respective bounding Holweck ribs 21. The comparatively narrow ring area between the tips of the Holweck ribs 21 and the inner side of the Holweck rotor 25 is not included in the free cross-sectional area at the inlet area 29a and therefore does not contribute to the inlet-side openness of the radially inner Holweck pump area 29. The same applies to the outlet-side openness of the Holweck rotor 25. Fig. 9 radial outer Holweck pump area 27, not shown.

[0089] A variation in both the inlet-side and outlet-side openness can therefore be achieved, for example, by changing the width B, the height H, or the number of hollow webs 21. These measures can also be combined as desired. For example, with a constant number of hollow webs 21 and thus hollow channels 23, the openness can be changed by altering the height H and the width B of the hollow webs. The height H can be changed, with a constant radial distance between the tips of the hollow webs 21 and the inside of the hollow rotor 25, by reducing the wall thickness of the cylindrical section of the hollow stator 17b, i.e., its wall 17c, from which the hollow webs 21 project radially outwards, thereby bringing the channel base 19 closer to the axis of rotation 15.Alternatively or additionally, the height H of the Holweck ribs 21 can also be changed by changing the radial distance between the rib tips and the inside of the Holweck rotor 25, insofar as this is possible without impairing the basic functionality, i.e. pumping efficiency, of the Holweck pump stage. Bezugszeichenliste

[0090] 11 Turbomolecular pump unit 11a Rotor disk 12 Rotor 13 Holweck pump unit 15 Rotation axis 17a Radial outer Holweck stator 17b Radial inner Holweck stator 17c Wall of radial inner Holweck stator 19 Channel base 21 Holweck web 23 Holweck channel 25 Holweck rotor 26 Holweck hub 27 Radial outer Holweck pumping area 27a Outlet area 29 Radial inner Holweck pumping area 29a Inlet area 31 Transition area 33 Axial gas inlet 35, 35' Radial gas inlet 39 Lower part or intermediate part 41 Pump housing 43 Further Holweck pumping area HH Height of the Holweck bridges B Width of the Holweck bridges βa Taper angle of the radially outer Holweck pumping area βi Taper angle of the radially inner Holweck pumping area 111 Turbomolecular pump 113 Inlet flange 115 Pump inlet 117 Pump outlet 119 Housing 121 Bottom section 123 Electronics housing 125 Electric motor 127 Accessory connection 129 Data interface 131 Power supply connection 133 Flood inlet 135 Sealing gas connection 137 Motor compartment 139 Coolant connection 141 Bottom side 143 Screw 145 Bearing cover 147 Mounting hole 148 Coolant line 149 Rotor 151 Rotation shaft 153 Rotor shaft 155 Rotor disc 157 Stator disc 159 Spacer ring 161 Rotor hub 163 Holweck rotor sleeve 165 Holweck rotor sleeve 167 Holweck stator sleeve 169 Holweck stator sleeve 171 Holweck gap 173 Holweck gap 175 Holweck gap 179 Connecting channel 181 Rolling bearing 183 Permanent magnet bearing 185 Injection nut 187 Washer 189 Insert 191 Rotor-side bearing half 193 Stator-side bearing half 195 Ring magnet 197 Ring magnet 199 Bearing gap 201 Support section 203 Support section 205 Radial strut 207 Cover element 209 Support ring 211 Mounting ring 213 Disc spring 215 Emergency orFanglager 217Motorstator 219Zwischenraum 221Wandung 223Labyrinthdichtung.

Claims

1. A turbomolecular vacuum pump comprising at least one turbomolecular pump unit (11) and at least one Holweck pump unit (13) which is arranged downstream of the turbomolecular pump unit (11) in the pumping direction and which has at least two Holweck stages which are disposed concentrically in one another with respect to a common axis of rotation (15) and which follow one another in the pumping direction, wherein the Holweck stages each comprise a Holweck stator (17a, 17b) having a Holweck thread which has Holweck webs (21) projecting from a channel base (19) and Holweck channels (23) bounded by the walls of the Holweck webs (21) and which faces a common Holweck rotor (25) of the Holweck pump unit (13), said common Holweck rotor (25) rotating about the axis of rotation (15) during operation and bounding a radially outer Holweck pump region (27) with the one Holweck stator (17a) and bounding a radially inner Holweck pump region (29) with the other Holweck stator (17b), wherein, in a transition region (31) at the free end of the Holweck rotor (25), an outlet region (27a) of the radially outer Holweck pump region (27) merges into an inlet region (29a) of the radially inner Holweck pump region (29), wherein, in addition to an axial gas inlet (33) into the radially outer Holweck pump region (27), a radial gas inlet (35, 35') into the Holweck pump unit (13) is provided and either opens into the transition region (31) or upstream of the transition region (31) into the radially outer Holweck pump region (27), in particular into the half disposed downstream or into the third, quarter, fifth or sixth of the radially outer Holweck pump region (27) that is disposed downstream, characterized in that the outlet region (27a) and the inlet region (29a) each have a free cross-sectional area, which is defined by the Holweck channels (23), in a cross-sectional plane, which extends perpendicular to the axis of rotation (15) and in which the pumping effect ends or starts, and the free cross-sectional area of the inlet region (29a) is larger by a factor f > 1 than the free cross-sectional area of the outlet region (27a).

2. A vacuum pump according to claim 1, wherein it applies: 1 < f < 3, preferably 1 < f < 2, preferably 1.2 < f < 1.5.

3. A vacuum pump according to claim 1 or 2, wherein, in the respective cross-sectional plane, the height of the Holweck webs (21) in the inlet region (29a) is greater than the height (H) of the Holweck webs (21) in the outlet region (27a).

4. A vacuum pump according to any one of the preceding claims, wherein, in the respective cross-sectional plane, the width (B) of the Holweck webs (21) measured in the peripheral direction is greater in the inlet region (29a) than in the outlet region (27a).

5. A vacuum pump according to any one of the preceding claims, wherein the number of Holweck webs (21) in the radially inner Holweck pump region (29) is smaller than the number of Holweck webs (21) in the radially outer Holweck pump region (29).

6. A vacuum pump according to any one of the preceding claims, wherein the Holweck stator (17b) bounding the radially inner Holweck pump region (29) is a Holweck stator which is provided with a Holweck thread at both sides and which bounds a further Holweck pump region (43) radially further inwardly with a further Holweck rotor (25).

7. A vacuum pump according to claim 6, wherein the Holweck stator (17b) which is provided with the Holweck thread at both sides has a wall thickness measured in the radial direction, and wherein, in the inlet region (29a), the wall thickness is smaller than the height of the Holweck webs (21) of the radially inner Holweck pump region (29).

8. A vacuum pump according to any one of the preceding claims, wherein the radially outer Holweck pump region (27) and / or the radially inner Holweck pump region (29) is / are each conically shaped such that the height of the Holweck webs (21) decreases continuously in the pumping direction.

9. A vacuum pump according to claim 8, wherein a conicity angle (βa) defined by the channel base (19) of the radially outer Holweck pump region (27) and a conicity angle (βi) defined by the channel base (19) of the radially inner Holweck pump region (29) are at least substantially the same or different from one another, in particular wherein the conicity angle (βa) of the radially outer Holweck pump region (27) is greater or smaller than the conicity angle (βi) of the radially inner Holweck pump region (29).

10. A vacuum pump according to any one of the preceding claims, wherein at least one pump-active section of the radially outer Holweck stator (17a), said pump-active section bounding the radially outer Holweck pump region (27) with the Holweck rotor (25), is formed in one part, in particular wherein the radial gas inlet (35) opens upstream of the transition region (31) into the radially outer Holweck pump region (27) and extends through the single-piece pump-active section of the radially outer Holweck stator (17a).

11. A vacuum pump according to any one of the preceding claims, wherein the radial gas inlet (35) extends above a lower part or an intermediate component (39) of the vacuum pump, in which lower part or intermediate component the transition region (31) is at least partly located, through a pump housing (41).

12. A vacuum pump according to any one of the preceding claims, wherein at least one further radial gas inlet is arranged upstream of the radial gas inlet (35) into the Holweck pump unit (13), in particular wherein the further radial gas inlet opens into the Holweck pump unit (13) or into the turbomolecular pump unit (11).

13. A vacuum system comprising a vacuum pump according to any one of the preceding claims and a recipient to be evacuated, wherein the vacuum pump is configured as a split-flow vacuum pump which has one or more radial suction inlets, which are each in communication with an opening of the recipient during operation, and wherein one of the radial suction inlets is the radial gas inlet (35) opening into the transition region (31) or upstream of the transition region (31) into the radially outer Holweck pump region (27).

14. A leak detection system comprising a vacuum pump according to any one of the claims 1 to 12, which can be connected to a test object to be evacuated, and a detector, in particular a mass spectrometer, for detecting a test gas, and wherein the vacuum pump is connected to the detector via an axial or a radial gas inlet and, downstream of the gas inlet, a radial gas inlet for the test gas into the Holweck pump unit (13) is provided, wherein the radial gas inlet for the test gas is the radial gas inlet (35) opening into the transition region (31) or upstream of the transition region (31) into the radially outer Holweck pump region (27).

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