Vacuum pump with one Holbeck pump stage with variable Holbeck geometry

Description

[0001] The present invention relates to a vacuum pump, also referred to here only as a pump, in particular a turbomolecular vacuum pump, according to the preamble of claim 1, as is essentially known from DE 2411 247 A1.

[0002] With regard to the further prior art, reference is made to the documents US 3 947 193 A and US 2023 / 096 958 A1.

[0003] Vacuum pumps are used in various fields of technology. Depending on the requirements, vacuum pumps can have one or more pumping stages. Holweck pumping stages generally belong to the class of molecular vacuum pumps and generate a molecular flow by rotating a Holweck rotor relative to a stationary Holweck stator. In principle, a vacuum pump can comprise one or more Holweck pumping stages, with several Holweck pumping stages being able to be operated both in series and in parallel. Holweck pumping stages are typically used in turbomolecular vacuum pumps, where they are arranged downstream of one or more turbomolecular pumping stages in the direction of flow.

[0004] A Holweck pump stage typically comprises a Holweck rotor and a Holweck stator. The Holweck rotor has a rotor shaft on which one or more Holweck rotor sleeves are concentrically arranged by means of a disc-shaped Holweck hub, for example. The Holweck stator sleeve is provided with a single or multiple-start Holweck thread. The gas molecules to be pumped are conveyed by the rotating movement of the Holweck rotor relative to the Holweck stator along the threads from an inlet to an outlet of the respective Holweck pump stage. A thread comprises a spiral-shaped Holweck channel in the form of a thread groove, delimited by the walls of a web, in which the gas molecules are conveyed when the rotor sleeve rotates relative to the stator sleeve.

[0005] Furthermore, so-called "folded" Holweck arrangements are known, in which several Holweck pump stages are arranged concentrically to one another and nested within one another, so that the pumping direction of radially immediately consecutive Holweck pump stages is opposite to one another. Two Holweck pump stages arranged in succession in the flow direction—a (radially) outer Holweck pump stage and a (radially) inner Holweck pump stage—can thus comprise a common Holweck stator, each provided with a Holweck thread on both sides and located radially between two rotor sleeves.

[0006] In principle, the Holweck geometry, and in particular the design of the Holweck thread, influences the parameters of the Holweck pump stage, such as its suction and / or compression capacity, as well as the power consumption of the pump motor. However, since the Holweck geometry typically does not change across the axial extent of a Holweck stator sleeve, these parameters can only be adjusted to a limited extent during pump design.

[0007] To provide more flexibility in pump design regarding the parameters of a Holweck pump stage, such as its suction and / or compression capacity and power consumption, the Holweck stator of a Holweck pump stage can be formed by several separate sleeve sections arranged axially one behind the other or directly adjacent to each other in the pumping direction. The individual sleeve sections can differ, for example, in the number of webs or the threads formed by the webs, which influences the parameters in question.

[0008] However, the axial extension of Holweck stator sleeves is limited downwards, for example, for manufacturing and assembly reasons. Since Holweck stator sleeves must not fall below a certain minimum axial extension, replacing one sleeve section with another with, for example, a larger number of webs and / or a different thread pitch can only change the parameters of a Holweck pump stage in relatively large increments.

[0009] The invention is therefore based on the object of developing a vacuum pump of the generic type in such a way that the parameters of the Holweck pumping stage can be changed in relatively small steps or in a finely dosed manner.

[0010] This object is achieved with a vacuum pump which is characterized by the features of claim 1 or those of claim 11.

[0011] The stator sleeve is formed in one piece according to claim 1, and the thread geometry of the Holweck thread varies across the axial extent of the stator sleeve. In particular, it is provided that, in a stator sleeve formed in one piece, at least one thread parameter of the Holweck thread from the group of thread parameters consisting of the number of lands, the thread pitch, the width of the thread grooves, the width of the lands, and the height of the lands above the groove base, varies across the axial extent of the stator sleeve.

[0012] The Holweck thread comprises a first threaded section which extends in the axial direction over a first height dimension of the stator sleeve, downstream of the first threaded section a second threaded section which extends in the axial direction over a second height dimension of the stator sleeve, and downstream of the second threaded section at least one third threaded section which extends in the axial direction over a third height dimension of the stator sleeve, wherein at least one threaded section of the three threaded sections differs from another threaded section of the three threaded sections by at least one thread parameter from the group of thread parameters. According to the invention, the number of lands in the first threaded section is greater than in the second threaded section. Furthermore, the number of lands in the first threaded section is the same as the number of lands in the third threaded section.In other words, it is intended that the number of thread grooves in the middle second thread section is lower than in the inlet and outlet side first and third thread sections.

[0013] For example, to ensure a higher compression capacity on the backing vacuum side or at the outlet of the Holweck pumping stage, and a lower compression capacity or a higher suction capacity on the high vacuum side or at the inlet of the Holweck pumping stage, the stator sleeve can have a threaded section at the outlet of the Holweck pumping stage with a relatively small axial extension, in which the number of lands or the number of thread grooves is greater than in a threaded section located upstream of it. Since the height dimension or the axial extension of the outlet-side threaded section can be made almost arbitrarily small due to the one-piece design of the stator sleeve, it is thus possible to change the compression capacity at the outlet of the Holweck pumping stage in relatively small steps.This applies in particular if not only the number of webs but also, for example, the thread pitch and / or the width of the thread grooves as well as the width of the webs change over the axial extent of the stator sleeve.

[0014] Furthermore, the characteristics of Holweck pump stages with a relatively small axial extension can also be modified, since a stator sleeve with a relatively small height dimension can also be designed in such a way that at least one thread parameter changes across the axial extension of the stator sleeve. However, for such stator sleeves with a relatively small axial extension, a multi-part design of the stator sleeve consisting of two separate sleeve sections arranged axially one behind the other is not possible, since a minimum axial extension of the sleeve sections cannot be exceeded for manufacturing and / or assembly reasons.

[0015] Preferred embodiments of the invention will now be discussed below. Further embodiments may also emerge from the dependent claims, the description of the figures, and the drawings themselves.

[0016] For example, according to an exemplary embodiment, it can be provided that the number of lands in the third threaded section is twice as large as in the second threaded section. Because the number of lands and thus the number of thread grooves is greater on the fore-vacuum side or in the outlet of the Holweck pumping stage than at the inlet of the Holweck pumping stage, a higher compression capacity can be achieved at the outlet of the Holweck pumping stage than at the inlet of the Holweck pumping stage. Likewise, because the number of lands in the third threaded section is greater than in the second threaded section, a greater suction capacity can be achieved on the high-vacuum side or at the inlet of the Holweck pumping stage than at the outlet of the Holweck pumping stage.

[0017] The suction capacity is defined as the volume flow, i.e., the volume that can be pumped per unit of time through the cross-sectional area of ​​a thread groove. The compression capacity is preferably related to the component length, i.e., it is based on the compression capacity per unit length. Compression capacity can be defined as the compression ratio that can be achieved by the respective thread section at its respective downstream end. In other words, compression capacity describes the pressure ratio between the inlet and outlet of a respective thread groove.

[0018] Contrary to the invention, the number of webs in the second threaded section can be greater than the number of webs in the first threaded section, which would mean that the number of webs increases gradually from the inlet of the Holweck pump stage towards the outlet thereof; contrary to the invention, the number of webs in the second threaded section can also be the same as the number of webs in the first threaded section, so that from this perspective, the stator sleeve has, so to speak, only two threaded sections with different numbers of webs.

[0019] According to a further embodiment, it can be provided that the width of the thread grooves in the third thread section is smaller than in the second thread section. In particular, it can be provided that the width of the thread grooves in the third thread section is less than half as large as in the second thread section. If, for example, the Holweck stator sleeve has a first set of spirally circumferential webs that extend from the inlet to the outlet of the Holweck pump stage, additional webs can be formed in the thread grooves formed thereby in the third thread section, by means of which the mutual distance between the webs of the first set of webs is reduced.

[0020] According to a further embodiment, it can be provided that the width of the thread grooves in the second thread section is the same as the width of the thread grooves in the first thread section.

[0021] As already mentioned above, contrary to the invention, it can be provided that the number of lands in the second threaded section is greater than in the first threaded section. With a constant land width, this means that the width of the thread grooves in the third threaded section is significantly smaller than in the first threaded section, whereby the compression capacity tends to increase towards the outlet of the Holweck pumping stage, whereas the suction capacity increases towards the inlet of the Holweck pumping stage. Although the groove base of all thread grooves can lie on a cylindrical outer surface, should it be desirable for the suction capacity to increase towards the outlet of the Holweck pumping stage, it can be provided according to a further embodiment that the groove base defines a basic envelope which is conical in at least one of the three threaded sections.In particular, it can be provided that the groove base defines a conicity angle which has a different value in at least one of the three thread sections than in another thread section.

[0022] For example, the taper angle in the first threaded section can be smaller than in the second threaded section and / or than in the third threaded section, which means that the base envelope tapers less sharply in the first threaded section toward the outlet of the Holweck pumping stage than in the second or third threaded section. This configuration can prove particularly advantageous if the Holweck pumping stage has an intermediate inlet at the downstream end of the first threaded section, since in this case, an increase in the suction capacity can be recorded at the intermediate inlet.

[0023] According to a further embodiment, the height dimension of the respective threaded section can be 15 to 50%, preferably 25 to 40%, and particularly preferably 30 to 35% of the total axial extension of the stator sleeve. Particularly when the height dimension of one of the threaded sections is only 30 to 35% of the axial extension of the stator sleeve—i.e., the threaded section in question has a relatively small axial extension—the parameters such as the suction capacity, the compression capacity, and / or the power consumption of the Holweck pump stage can be adjusted in relatively small steps.

[0024] In a single-stage Holweck pump, the stator sleeve typically surrounds the rotor sleeve. In this case, the Holweck thread is designed as an internal thread on the stator sleeve. If, however, the rotor sleeve surrounds the stator sleeve, the Holweck thread would be designed as an external thread on the stator sleeve.

[0025] According to a further embodiment, however, the vacuum pump can also comprise a "folded" Holweck arrangement, as described above. In this case, the Holweck rotor comprises an inner rotor sleeve and an outer rotor sleeve concentrically surrounding the inner rotor sleeve, whereas the Holweck stator comprises an outer stator sleeve concentrically surrounding the outer rotor sleeve and an inner stator sleeve concentrically surrounding the inner rotor sleeve. In this case, the Holweck thread is designed as an internal thread on the outer stator sleeve, an internal thread on the inner stator sleeve, and / or an external thread on the inner stator sleeve.

[0026] According to a further development of the subject matter of claim 11, it can additionally be provided that the groove base of the threaded portion of the ring defines a conical base envelope, wherein the base envelope tapers in the direction of the outlet of the Holweck pump stage.

[0027] The invention is described below with reference to the accompanying figures. They show: 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. 2shown section line CC, Fig. 6 a development of a conventional Holweck stator sleeve in a schematic representation; Fig. 7 a development of an embodiment of a Holweck stator sleeve not according to the invention in a schematic representation; Fig. 8 a development of a further embodiment of a Holweck stator sleeve not according to the invention in a schematic representation; Fig. 9 a development of yet another embodiment of a Holweck stator sleeve according to the invention in a schematic representation; Fig. 10 a schematic sectional representation through a folded Holweck pump stage with a Holweck stator sleeve designed according to the invention according to a further embodiment; and Fig. 11 a diagram to explain the suction capacity in the Holweck pump stage of the Fig. 10 ; and Fig. 12 a schematic sectional view through a folded Holweck pump stage according to yet another embodiment.

[0028] 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.

[0029] 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.

[0030] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0031] 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.

[0032] 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.

[0033] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in an upright position.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] A rotor 149 is arranged in the housing 119 and has a rotor shaft 153 rotatable about a rotation axis 151.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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. As a result of centrifugal force, it 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. 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The motor stator 217 is secured in the housing within the motor compartment 137 provided for the electric motor 125. A purge gas, also referred to as a purge gas, which may be air or nitrogen, for example, can enter the motor compartment 137 via the purge gas connection 135. The purge 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.

[0053] 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.

[0054] In the case of the above-mentioned Fig. 1 to 5 In the turbomolecular vacuum pump 111 described, the Holweck stator sleeves 167, 169 can have an internal or external Holweck thread 16, as shown schematically in the developed form in the Fig. 6 As can be seen from this illustration, the Holweck geometry is consistent over the entire axial extent of the Holweck stator sleeve 167, 169 between the inlet E and the outlet A of the Holweck pump stage, and in particular, the number of lands 12 forming the Holweck thread 16 is constant between the inlet E and the outlet A. The pitch of the thread, the width of the lands 12, the width of the thread grooves 14, and the height of the lands 12 are also constant over the axial extent of the stator sleeves 167, 169.

[0055] In the following, various embodiments of stator sleeves 10 are described which can be installed in the turbomolecular vacuum pump 111 instead of the stator sleeves 167, 169 shown, whereby, however, the other structure of the turbomolecular vacuum pump 111 as well as the basic structure of the Holweck pump stage with three nested pump stages can be retained.

[0056] How the processing of the Fig. 7can be removed, the stator sleeve 10 or the Holweck thread 16 formed by its thread webs 12 between inlet E and outlet A has three thread sections I, II, III, wherein the number of thread webs 12 in the downstream third thread section III is twice as large as in the second thread section II. In contrast, the number of webs 12 in the second thread section II is, contrary to the invention, the same size as the number of webs 12 in the first thread section I, so that in the embodiment of the Fig. 7 Basically there are only two thread sections with different Holweck geometries.

[0057] Because in the third thread section III the number of webs 12 is twice as large as in the first and second thread sections I, II and consequently the width of the thread grooves 14 in the third thread section III is significantly smaller than in the other two thread sections I, II, the compression capacity increases in the direction of the outlet A, whereas in the direction of the inlet E the suction capacity of the Holweck pump stage increases.

[0058] In the design of the Fig. 8In contrast, the stator sleeve 10 effectively has three threaded sections I, II, and III, each with a different Holweck geometry. In particular, contrary to the invention, the number of webs 12 in the central second threaded section II is greater than in the inlet-side first threaded section I and smaller than in the outlet-side third threaded section III, which results in the width of the thread grooves in the third threaded section III being significantly smaller than in the first threaded section I.

[0059] According to the embodiment of the Fig. 9According to the invention, the number of webs 12 in the middle threaded section II is smaller than both in the inlet-side first threaded section I and in the outlet-side third threaded section III. Contrary to the invention, the opposite situation may also exist depending on the characteristic value to be achieved, so that, for example, in the middle second threaded section II, the number of webs 12 may be greater than in the inlet-side first threaded section I and in the outlet-side third threaded section III.

[0060] Although the thread pitch changes in the previously mentioned with reference to the Fig. 7 to 9described embodiments between the inlet E and the outlet A; however, depending on the design of the respective Holweck pump stage, the thread pitch may also change over the axial extent of the stator sleeve 10, as may equally apply to the width of the thread grooves 14, the width of the webs 12 and / or the height of the webs 12 above the groove base 18 of the respective thread groove 14.

[0061] As best as the embodiment in Fig. 9 can be seen, the threaded sections I, II, III each have an axial extension between inlet E and outlet A, which amounts to approximately 30 to 35% of the axial extension of the stator sleeve 10. The axial extension of the respective threaded sections can thus be very small, particularly if the stator sleeve 10 as a whole already has a relatively small axial extension, whereby the parameters of the Holweck pump stage can be finely adjusted.

[0062] The Fig. 10 shows a further embodiment of a folded Holweck pump stage, in which the radially outer stator sleeve 10 is formed by two threaded sections I, II located between inlet E and outlet A. Here, both the groove base 18 of the first threaded section I and the groove base 18 of the second threaded section II, which is located downstream of the first threaded section I, form a conical base envelope, wherein in the embodiment shown here the conicity angle α in the first threaded section I is smaller than in the second threaded section II. Alternatively, however, the conicity angle α in the second threaded section II can also be smaller than in the first threaded section I.

[0063] Although the conicity angle α can be the same in both thread sections I and II, if the conicity angle α in the second thread section II is larger than in the first thread section I, as shown in the Fig. 10 As shown, this allows an increase in suction capacity of up to 20% at the transition from the first threaded section I to the second threaded section II, particularly when the inlet pressure or the pressure at the outlet A is relatively high and lies in the range between 1 and approximately 10 mbar, see the diagram of the Fig. 11 This can be particularly advantageous if the Holweck pump stage is designed according to the illustration of the Fig. 10in the transition area between the first and the second threaded section I, II has an intermediate inlet 20, since in this case the increased suction capacity at the intermediate inlet 20 can prevent the process gas sucked in from flowing back towards the inlet E of the Holweck pump stage.

[0064] When referring to the Fig. 12 In the embodiment described, it is ultimately provided that the third threaded section III, which is located at the outlet A of the Holweck pump stage, is formed by a separately manageable ring 22 with an internal thread formed thereon, wherein here too the basic envelope of the thread grooves 14 is conical and tapers in the direction of the outlet A.

[0065] To accommodate the ring 22, the stator sleeve 10 has a section 24 with a thread-free cylindrical outer surface 26 at its outlet-side end A, into which the ring 22 can be fitted, so that the two upstream threaded sections I, II together with the threaded section of the ring 22 form the Holweck thread 16 of the stator sleeve 10. The threaded section of the ring 22 can differ from the other two threaded sections I, II by at least one thread parameter, such as the thread pitch, the number of webs 12, the width of the thread groove 14, the width of the webs 12 and the height of the webs 12 above the groove base 18, in order to be able to finely adjust the characteristics of the Holweck pump stage.

[0066] Although the ring 22 is, in a sense, a separately handled stator sleeve, since the ring 22 is received by the section 24 with the thread-free cylindrical outer surface 26 of the stator sleeve 10, the ring 22 can be manufactured with a relatively small axial extension without this leading to a loss of stability, since the ring 22 is, in a sense, supported and stiffened by the section 24 with the thread-free cylindrical outer surface 26. List of reference symbols

[0067] EInlet AOutlet 10Stator sleeve 12Webs 14Thread grooves 16Holweck thread 18Groove base 20Intermediate inlet 22Ring 24Section 26Side surface I, II, IIIThread sections αConicity angle 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 orFanglager 217Motorstator 219Zwischenraum 221Wandung 223Labyrinthdichtung.

Claims

1. A vacuum pump (111), in particular a turbomolecular vacuum pump (111), comprising at least one Holweck pump stage having an inlet (E) and an outlet (A) in the pump direction downstream of the inlet (E), wherein the Holweck pump stage comprises a Holweck rotor having a rotor sleeve (163, 165) and a Holweck stator having a stator sleeve (10) which is arranged coaxially to the Holweck rotor while forming a Holweck gap (171, 173, 175), wherein the stator sleeve (10) has a Holweck thread (16) having a plurality of thread grooves (14) which are bounded by webs (12) formed at the stator sleeve (10) and by a groove base (18) formed by the stator sleeve (10); wherein the stator sleeve (10) is formed in one piece and at least one thread parameter of the Holweck thread (16) from the group of thread parameters, which consists of the number of webs (12), the thread pitch, the width of the thread grooves (14), the width of the webs (12) and the height of the webs (12) above the groove base (18), changes over the axial extent of the stator sleeve (10); wherein the Holweck thread (16) comprises a first threaded section (I) which extends in the axial direction over a first height dimension of the stator sleeve (10); downstream of the first threaded section (I), a second threaded section (II) which extends in the axial direction over a second height dimension of the stator sleeve (10); and, downstream of the second threaded section (III), at least a third threaded section (III) which extends in the axial direction over a third height dimension of the stator sleeve (10), wherein at least one threaded section of the three threaded sections (I, II, III) differs from another one of the three threaded sections (I, II, III) by at least one thread parameter from the group of thread parameters, characterized in that the number of webs (12) in the first threaded section (I) is greater than in the second threaded section (II), with the number of webs (12) in the first threaded section (I) being the same as the number of webs (12) in the third threaded section (III).

2. A vacuum pump according to claim 1, wherein the number of webs (12) in the third threaded section (III) is twice as large as in the second threaded section (II).

3. A vacuum pump according to claim 1 or 2, wherein the width of the thread grooves (14) in the third threaded section (III) is smaller than in the second threaded section (II), and / or wherein the width of the thread grooves (14) in the second threaded section (II) is the same as the width of the thread grooves (14) in the first threaded section (I).

4. A vacuum pump according to claim 1, wherein the width of the thread grooves (14) in the third threaded section (III) and in the first threaded section (I) is smaller than in the second threaded section (II), and / or wherein the width of the thread grooves (14) in the third threaded section (III) is the same as the width of the thread grooves (14) in the first threaded section (I).

5. A vacuum pump according to any one of the preceding claims, wherein the groove base (18) defines a base envelope which is conical in at least one of the three threaded sections (I, II, III).

6. A vacuum pump according to claim 5, wherein the groove base (18) defines a conicity angle (α) with respect to the axis of rotation (151) of the Holweck rotor, said conicity angle having a different value in at least one of the three threaded sections (I, II, III) than in another threaded section.

7. A vacuum pump according to claim 6, wherein the conicity angle (α) between the groove base (18) and the axis of rotation (151) of the Holweck rotor is smaller in the first threaded section (I) than in the second threaded section (II) and / or in the third threaded section (III).

8. A vacuum pump according to any one of the preceding claims, wherein the height dimension of the respective threaded section (I, II, III) is 15% to 50%, preferably 25% to 40%, and in particular preferably 30% to 35% of the axial extent of the stator sleeve (10).

9. A vacuum pump according to any one of the preceding claims, wherein the stator sleeve (10) surrounds the rotor sleeve (163, 165) and the Holweck thread (16) is configured as an internal thread at the stator sleeve (10); and / or wherein the rotor sleeve (163) surrounds the stator sleeve (10) and the Holweck thread (16) is configured as an external thread at the stator sleeve (10).

10. A vacuum pump according to any one of the preceding claims, wherein the Holweck rotor comprises an inner rotor sleeve (165) and an outer rotor sleeve (163) concentrically surrounding the inner rotor sleeve (165), and the Holweck stator comprises an outer stator sleeve (10) concentrically surrounding the outer rotor sleeve (163) and an inner stator sleeve (10) concentrically surrounding the inner rotor sleeve (165), wherein the Holweck thread (16) is configured as an internal thread at the outer stator sleeve (10), as an internal thread at the inner stator sleeve (10) and / or as an external thread at the inner stator sleeve (10).

11. A vacuum pump (111), in particular a turbomolecular vacuum pump (111), comprising at least one Holweck pump stage having an inlet (E) and an outlet (A) in the pump direction downstream of the inlet (E), wherein the Holweck pump stage comprises a Holweck rotor having a rotor sleeve (163, 165) and a Holweck stator having a stator sleeve (10) which is arranged coaxially to the Holweck rotor while forming a Holweck gap (171, 173, 175), wherein the stator sleeve (10) has a Holweck thread (16) having a plurality of thread grooves (14) which are bounded by webs (12) formed at the stator sleeve (10) and by a groove base (18) formed by the stator sleeve (10); wherein the stator sleeve (10) is formed in one piece and at least one thread parameter of the Holweck thread (16) from the group of thread parameters, which consists of the number of webs (12), the thread pitch, the width of the thread grooves (14), the width of the webs (12) and the height of the webs (12) above the groove base (18), changes over the axial extent of the stator sleeve (10); wherein the Holweck thread (16) comprises a first threaded section (I) which extends in the axial direction over a first height dimension of the stator sleeve (10) and, downstream of the first threaded section (I), a second threaded section (II), wherein the two threaded sections (I, II) differ from one another by at least one thread parameter from the group of thread parameters, characterized in that the number of webs (12) in the first threaded section (I) is greater than in the second threaded section (II), wherein the stator sleeve (10), downstream of the second threaded section (II), further forms a section (24) that has a thread-free cylindrical lateral surface (26) and that receives a ring (22) which can be handled separately and which has a threaded section that continues the Holweck thread (16), formed by the first and second threaded sections (I, II), of the stator sleeve (10) downstream of the second threaded section (II), wherein the threaded section of the ring (22) differs from the second threaded section (II) by at least one thread parameter from the group of thread parameters.

12. A vacuum pump according to claim 11, wherein the groove base (18) defines a conical base envelope.