Vacuum pump

Abstract

The present invention relates to a vacuum pump, in particular a turbomolecular pump, with an inlet, an outlet, and a pumping system comprising at least one Holweck pumping stage, including a Holweck thread formed by Holweck grooves in a Holweck stator, which, together with a Holweck rotor rotating about an axis of rotation during operation of the vacuum pump, generates a pumping action. The Holweck stator has a first pump-active stator section and a second pump-active stator section, which are arranged coaxially. The Holweck stator has a gas outlet of the Holweck pumping stage, which is arranged axially between the first pump-active stator section and the second pump-active stator section and which is in fluid communication with the outlet of the vacuum pump.

Description

[0001] The invention relates to a vacuum pump, in particular a turbomolecular pump.

[0002] Vacuum pumps are used in a wide variety of fields to provide a suitable vacuum for the respective application, for example a fine vacuum (pressure range of about 1 to 10 -3< mbar), a high vacuum (HV, pressure range of about 10 -3< to 10 -8< mbar) or an ultra-high vacuum (UHV, pressure range of about 10 -8< to 10 -11< mbar).

[0003] However, not all components or areas of the pumps may come into contact with the gas being pumped, for example, if it is comparatively aggressive. This could lead to corrosion or other adverse effects. Components requiring protection include, for example, the pump's drive motor and / or bearing assemblies that support a rotor driven by the drive motor, which carries pump-active structures, and / or electronic components.

[0004] In many cases, a barrier gas (also called a protective gas or purge gas) is used, which is introduced at a slight overpressure (i.e., a pressure higher than the pressure at the pump outlet) into the area of ​​the components to be protected, so that they are surrounded by the non-damaging barrier gas (e.g., an inert gas). For example, the barrier gas is introduced into an engine compartment housing the drive motor to displace the gas being pumped.

[0005] However, there are applications where the use of barrier gas is undesirable or even prohibited.

[0006] It is therefore an object of the present invention to create a vacuum pump in which reliable protection of sensitive components or areas of the pump is ensured even in these application cases.

[0007] This problem is solved using a vacuum pump with the features of claim 1.

[0008] The vacuum pump according to the invention – particularly for HV and UHV applications – comprises an inlet, an outlet, and a pumping system with at least one Holweck pumping stage. The Holweck pumping stage in turn comprises a Holweck thread formed by Holweck grooves in a Holweck stator, which, together with a Holweck rotor rotating about a rotational axis during operation of the vacuum pump, generates a pumping action.

[0009] The vacuum pump can be a turbomolecular pump in which the pumping system has one or more turbopump stages, each formed by at least one rotor disk and one stator disk. The rotor disk can be supported by a rotor that is also rotationally fixed to the Holweck rotor.

[0010] The Holweck stator has a first pump-active stator section and a second pump-active stator section arranged coaxially. It has a gas outlet of the Holweck pump stage, which is arranged axially between the first pump-active stator section and the second pump-active stator section and is in fluid communication with the outlet of the vacuum pump.

[0011] In principle, it is conceivable that the Holweck pump stage has an additional gas outlet located at the downstream end of the pump stage. Preferably, however, the gas outlet between the stator sections is the only gas outlet of the Holweck pump stage.

[0012] Further embodiments of the invention are specified in the claims, the description and the accompanying drawings.

[0013] According to one embodiment, the Holweck thread has different properties in the region of the first pump-active stator section and in the region of the second pump-active stator section. In particular, the Holweck thread in the region of the second pump-active stator section is designed such that the pumping action generated is directed opposite to that generated by the Holweck thread in the region of the first pump-active stator section. Specifically, the two stator sections are designed such that they both pump gas in the direction of the gas outlet of the Holweck pump stage located between them.

[0014] The second stator section then acts as a barrier stage, preventing the gas being pumped from entering the second stator section or even beyond it in an axial direction, thus preventing it from reaching unwanted areas. Furthermore, the pumping action of the second stator section allows gas that has accumulated in these areas – for whatever reason – to be pumped out.

[0015] The Holweck grooves in the area of ​​the first pump-active stator section can have an inclination opposite to that of the Holweck grooves in the area of ​​the second pump-active stator section.

[0016] According to a further embodiment, the axial extent of the first pump-active stator section is greater than that of the second pump-active stator section. In particular, the axial extent of the second pump-active stator section is less than 80%, preferably less than 70%, and most preferably less than 60% of the axial extent of the first pump-active stator section. The longer the second pump-active stator section (blocking stage), the better its blocking effect. The longer the first pump-active stator section, the better the pump compression. In many applications, an axial extent of the second pump-active stator section in the range of 20% to 80% of the axial extent of the first pump-active stator section has proven to be a good balance between these two competing effects.

[0017] In particular, the gas outlet comprises a collecting groove that is closed in the circumferential direction and is in fluid communication with the Holweck grooves of the first and second pump-active stator sections. The axial extent of the collecting groove (width of the collecting groove) can be smaller than the axial extent of the first pump-active stator section; in particular, it is less than 80%, preferably less than 70%, and most preferably less than 50% of the axial extent of the first pump-active stator section.

[0018] The axial extent of the collecting groove can be in a range corresponding to 75% to 125% of the axial extent of the second pump-active stator section. It is also conceivable that the axial extent of the collecting groove is less than 80%, preferably less than 70%, and particularly preferably less than 50% of the axial extent of the second pump-active stator section.

[0019] Generally speaking, the width of the collecting groove can be optimized for the specific application. Pump designs are conceivable where the collecting groove has a width less than 20% of the axial extent of the first and / or the second pump-active stator section.

[0020] According to a structurally simple embodiment, the collecting groove is in fluid communication with at least one outlet channel, which extends axially in a stator component on which the Holweck stator is arranged or formed. Such a channel can be created by a simple bore. In particular, the collecting groove is deep enough to intersect the outlet channel.

[0021] The collecting groove can be incorporated into the stator component by machining.

[0022] The end of the outlet channel facing the interior of the pump can be closed with a closing element to prevent a flow-related short circuit. While not strictly necessary, it is preferred that the closing element seal the outlet channel gas-tight. The closing element can, for example, be a plug. Alternatively, the end of the channel can be permanently sealed. If the channel is a blind hole, a closing element can be omitted with a suitable design.

[0023] The stator component can be connected to a base or lower part of the vacuum pump. In particular, it is formed integrally with the base or lower part.

[0024] The stator component can accommodate a motor stator of a drive motor for the pump system.

[0025] According to one embodiment, the Holweck stator is formed in one piece; preferably, it is also formed in one piece with the stator component.

[0026] For example, the Holweck stator is manufactured from a cylindrical component or a cylindrical section of a larger component, into which the Holweck grooves of the two stator sections and the collecting groove are milled. However, it is also conceivable that the two stator sections are formed on separate sleeves supported by a base component, on which the aforementioned outlet channel can be provided.

[0027] The pumping system may include at least two Holweck pump stages arranged radially inside one another. In particular, the number of Holweck pump stages is even. For example, the pumping system has four Holweck pump stages nested within each other.

[0028] Preferably, only the radially innermost Holweck pump stage has the gas outlet. That is, the radially outer Holweck pump stages do not have an outlet located in the pumping-active area of ​​the respective Holweck stator.

[0029] With an even number of conventional Holweck stages, the problem often arises that gas accumulates in the area of ​​the gas outlet of the Holweck stage assembly, which is difficult to completely remove. The inventive design of the innermost Holweck stage efficiently solves this problem in a simple manner. The slight loss in pumping power is more than compensated for by the advantages described.

[0030] The accompanying drawings illustrate the structure of a known turbomolecular pump and examples of its implementation according to the aspects explained above. They show: Fig. 1 a perspective view of a turbomolecular pump, Fig. 2 a view of the underside of the turbomolecular pump of Fig. 1 , Fig. 3 a cross-section of the turbomolecular pump along the in Fig. 2 Section line AA shown, Fig. 4 a cross-sectional view of the turbomolecular pump along the in Fig. 2 Section line BB, Fig. 5 shows a cross-sectional view of the turbomolecular pump along the line shown in Fig. 2 The section line CC shown, Fig. 6 a simplified cross-section through an embodiment of a vacuum pump according to the invention and Fig. 7 a perspective view of an embodiment of a stator component.

[0031] The in Fig. 1The turbomolecular pump 111 shown 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.

[0032] 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. 3The 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.

[0033] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0034] 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. 3The 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.

[0035] 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.

[0036] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in a standing position.

[0037] 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 to one another. For example, a bearing cover 145 is attached to the underside 141.

[0038] 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.

[0039] In the Figures 2 to 5 A coolant line 148 is shown, in which the coolant introduced and removed via the coolant connections 139 can circulate.

[0040] Like the sectional views of the Figures 3 to 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.

[0041] A rotor 149 is arranged in the housing 119, which has a rotor shaft 153 rotatable about a rotation axis 151.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 repulsion forces between the ring magnets 195, 197, which result in the radial support of the rotor shaft 153. The rotor-side ring magnets 195 are supported by a carrier 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 in one direction, parallel to the axis of rotation 151, 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] Fig. 6 Figure 1 shows a cross-section through a schematic representation of a vacuum pump 11 with several turbopump stages 10, of which only the lowest is shown. The gas pumped by the pump stages 10 enters a first Holweck stage 12 of a Holweck pump stage arrangement 14. The Holweck stage 12 comprises a Holweck stator 16 and a cylindrical Holweck sleeve 18, which is also part of a second Holweck stage 20 with a Holweck stator 22. The Holweck stage 20 is thus arranged radially within the Holweck stage 12.

[0058] The Holweck stator 22 is formed on a stator component 24, which also has an outlet channel 26 that is in direct or indirect fluid connection with an outlet of the pump 11, to which a backing pump is usually connected.

[0059] The Holweck sleeve 18 is supported by a hub 28, which is rotationally fixed to a rotor 30 that also carries rotor disks 32 of the turbopump stages 10. When the pump 11 is operating, the rotor 30 is driven into rotation by a motor. Its motor stator 34 is arranged in a central recess 24A of the stator component 24, forming a motor compartment. The motor compartment can be enclosed by additional walls and – as already mentioned above with reference to the Figs. 1 to 5 described - sealed by a labyrinth seal against the radially outside Holweck pump stages 12, 20.

[0060] In conventional pumps, the second Holweck pump stage 20 would deliver the pumped gas into an outlet chamber 36, from which it is then discharged through the outlet channel 26. This can be disadvantageous, especially in Holweck pump stage arrangements with an even number of Holweck pump stages, because the outlet chamber 36 is then located relatively far inside the pump 11, approximately at the same axial height as the inlet of the Holweck pump stage arrangement. This can lead to gas accumulation, which is particularly problematic if no barrier gas can be used to protect the engine compartment from the pumped gas.

[0061] Therefore, a gas outlet 38 is provided in the pumping area of ​​the Holweck pump stage 20, which is in fluid communication with the outlet channel 26. It divides the Holweck stator 22 into a first stator section 22A and a second stator section 22B.

[0062] To reliably prevent gas from entering the outlet chamber 36, the Holweck grooves of the stator section 22B are designed such that, when the pump 11 is operating, gas is conveyed from the outlet chamber 36 to the gas outlet 38, thereby evacuating the outlet chamber 36. The stator section 22B also acts as a barrier against the gas pumped in the opposite direction by the stator section 22A. The gas conveying path indicated by the dashed arrows is then established.

[0063] The outlet channel 26 can be a through axial bore that is very easy to insert into the stator component 24. To optimize the gas flow path, its end facing the outlet chamber 36 is closed with a plug (not shown). Alternatively, the channel 26 can also be a blind bore inserted into the stator component 24 from below.

[0064] Fig. 7Figure 1 shows a pump lower section 40 with a base 42 having a plurality of connections and a stator section 24 carrying a Holweck stator 22 of the innermost Holweck pump stage of a four-stage Holweck pump stage arrangement. In the illustrated embodiment, the stator section 24 and the base 42 are formed in one piece, for example by machining. However, it is understood that it can also be designed in multiple parts. The stator section 24 itself can also be in multiple parts. For example, the stator sections 22A, 22B can be sleeves mounted on a cylindrical support.

[0065] The stator component 24 has two parallel, axial outlet channels 26. The gas outlet 38, arranged axially between the stator sections 22A and 22B, is designed as a collecting groove onto which the Holweck grooves 44A and 44B of the stator sections 22A and 22B converge. The collecting groove 38 is deep enough to intersect the channels 26, thereby establishing a fluid connection between them. This connection allows the gas to be discharged from the Holweck pump stage assembly without entering the outlet chamber 36. To prevent a flow-related short circuit, the Fig. 7 The open ends of the outlet channels 26 in the fully assembled state of the pump are each closed with a plug (or similar).

[0066] The geometry of slots 44A and 44B is designed differently to produce the opposite pumping effect. They may be optimized for the properties of the gas being pumped.

[0067] Stator section 22B acts as a barrier stage to prevent gas pumped by stator section 22A from entering the outlet chamber 36. Since stator section 22B also generates a pumping action, the concept described above can also be used with pumps operating with a barrier gas. In this case, stator section 22B assists in the discharge of the barrier gas introduced into the motor chamber.

[0068] In the illustrated embodiment, the axial extent of the stator section 22B and the collecting groove 38 is approximately the same. Both have a smaller axial extent than the stator section 22A. The respective axial extent of the aforementioned components can be optimized for the specific application. Reference symbol list

[0069] 10 Turbo pump stage 12, 20 Holweck pump stage 14 Holweck pump stage assembly 16, 22 Holweck stator 18 Holweck sleeve 24 Stator component 24a Recess 26 Outlet channel 28 Hub 28 Rotor 32 Rotor disk 34 Motor stator 36 Outlet chamber 38 Gas outlet, collecting groove 40 Pump base 42 Base 111, 11 Turbomolecular pump 113 Inlet flange 115 Pump inlet 117 Pump outlet 119 Housing 121 Base 123 Electronics housing 125 Electric motor 127 Accessory connection 129 Data interface 131 Power supply connection 133 Flood inlet 135 Barrier gas connection 137 Motor compartment 139 Coolant connection 141 Underside 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 half193 Stator-side bearing half 195 Ring magnet 197 Ring magnet 199 Bearing gap 201 Carrier section 203 Carrier section 205 Radial strut 207 Cover element 209 Support ring 211 Mounting ring 213 Disc spring 215 Emergency or catch bearing 217 Motor stator 219 Gap 221 Wall 223 Labyrinth seal

Claims

1. Vacuum pump, in particular turbomolecular pump, with - an inlet, - an outlet and - a pumping system with at least one Holweck pumping stage (20), comprising a Holweck thread formed by Holweck grooves (44A, 44B) in a Holweck stator (22), which together with a Holweck rotor (18) rotating about an axis of rotation when the vacuum pump is operated generates a pumping action, wherein the Holweck stator (22) has a first pump-active stator section (22A) and a second pump-active stator section (22B) which are arranged coaxially, and wherein the Holweck stator (22) has a gas outlet (38) of the Holweck pumping stage (20) which is arranged in the axial direction between the first pump-active stator section (22A) and the second pump-active stator section (22B) and which is in fluid communication with the outlet of the vacuum pump.

2. Vacuum pump according to claim 1, wherein the Holweck thread has different properties in the area of ​​the first pump-active stator section (22A) and in the area of ​​the second pump-active stator section (22B).

3. Vacuum pump according to claim 2, wherein the Holweck thread in the area of ​​the second pump-active stator section (22B) is designed such that the pumping action generated is directed opposite to that generated by the Holweck thread in the area of ​​the first pump-active stator section (22A).

4. Vacuum pump according to claim 2 or 3, wherein the Holweck slots (44A) in the region of the first pump-active stator section (22A) have an inclination opposite to the Holweck slots (44B) in the region of the second pump-active stator section (22B).

5. Vacuum pump according to at least one of the preceding claims, wherein the axial extent of the first pump-active stator section (22A) is greater than that of the second pump-active stator section (22B), in particular wherein the axial extent of the second pump-active stator section (22B) is less than 80%, preferably less than 70%, particularly preferably less than 60% of the axial extent of the first pump-active stator section (22A).

6. Vacuum pump according to at least one of the preceding claims, wherein the gas outlet comprises a collecting groove (38) which is closed in the circumferential direction and which is in fluid communication with the Holweck grooves (44A, 44B) of the first and the second pump-active stator section (22A and 22B, respectively).

7. Vacuum pump according to claim 6, wherein an axial extent of the collecting groove (38) is smaller than the axial extent of the first pump-active stator section (22A), in particular less than 80%, preferably less than 70%, particularly preferably less than 50% of the axial extent of the first pump-active stator section (22A).

8. Vacuum pump according to claim 6 or 7, wherein an axial extent of the collecting groove (38) is in a range corresponding to 75% to 125% of the axial extent of the second pump-active stator section (22B), or wherein an axial extent of the collecting groove (38) is less than 80%, preferably less than 70%, particularly preferably less than 50% of the axial extent of the second pump-active stator section.

9. Vacuum pump according to at least one of the preceding claims 6 to 8, wherein the collecting groove (38) is in fluid communication with at least one outlet channel (26) which extends in an axial direction in a stator component (24) on which the Holweck stator (22) is arranged or formed.

10. Vacuum pump according to claim 9, wherein an end of the outlet channel (26) facing the interior of the pump is closed with a closing element, in particular gas-tight.

11. Vacuum pump according to claim 9 or 10, wherein the stator component (24) accommodates a motor stator (34) of a drive motor of the pump system.

12. Vacuum pump according to at least one of the preceding claims, wherein the Holweck stator (22) is formed in one piece and / or wherein the stator component (24) is connected to a base (42) of the vacuum pump, in particular formed in one piece with the base (42).

13. Vacuum pump according to at least one of the preceding claims, wherein the pumping system comprises at least two Holweck pumping stages (12, 20) arranged radially inside one another.

14. Vacuum pump according to claim 13, wherein the number of Holweck pump stages (12, 20) is even.

15. Vacuum pump according to claim 13 or 14, wherein only the radially innermost Holweck pump stage (20) has the gas outlet (38).

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