EP3657021B1 - Vacuum pump - Google Patents

Description

The present invention relates to a vacuum pump, in particular a turbo-molecular vacuum pump, with an inlet, an outlet, and at least two Holweck stages which are concentric with respect to a common axis of rotation and which follow one another in the pumping direction between the inlet and the outlet according to the preamble of claim 1.

Vacuum pumps are used in various fields of technology. Depending on the requirements, the vacuum pumps have one or more pump stages. A Holweck pump stage (also referred to here simply as a Holweck stage) belongs to the genus of molecular vacuum pumps and generates a molecular flow through the rotation of the Holweck rotor relative to the Holweck stator. A vacuum pump can comprise one or more Holweck stages, with several Holweck stages being able to pump both in series and in parallel with one another. Holweck stages are typically used in turbo-molecular vacuum pumps and follow one or more turbo-molecular pump stages.

A Holweck stage comprises a Holweck rotor and a Holweck stator, the Holweck rotor having a rotor shaft on which one or more Holweck sleeves (hereinafter also referred to as rotor sleeves) are concentrically attached by means of a disk-shaped Holweck hub, for example. The Holweck stator is provided with a single or multiple Holweck thread. The gas molecules to be conveyed are conveyed by the rotating movement of the Holweck rotor relative to the Holweck stator along the threads from an inlet to an outlet. A thread comprises a circumferential Holweck channel, which is delimited by the walls of a web and in which the gas molecules are conveyed when the rotor sleeve rotates relative to the stator. About backflow losses To minimize the width of the radial gap (Holweck gap) between the top of the web and the rotor sleeve must be kept small.

So-called "folded" Holweck arrangements are known in which several Holweck stages are arranged concentrically one inside the other, so that the pumping directions of Holweck stages which follow one another radially are opposite to one another. Two consecutive Holweck stages, a (radially) outer Holweck stage and a (radially) inner Holweck stage, can comprise a common Holweck stator, which is provided on both sides with a Holweck thread, hereinafter also referred to as "double-sided" and which is located between two rotor sleeves.

Furthermore, it is basically known to provide so-called “conical” Holweck steps, in which the Holweck stator is designed in such a way that the web height decreases in the pumping direction. This is achieved with the web top sides lying at a constant diameter over the axial length of the Holweck stator in that the so-called groove base diameter increases in the pumping direction. It has been shown that such conical Holweck steps have improved pumping properties.

In the context of the present disclosure, the web height at a certain point in the axial direction should be understood to mean half the difference between the nominal diameter of the Holweck thread and its groove base diameter at this point. Consequently, the ridge height is equal to the thread depth at the relevant point.

Vacuum pumps with the features of the preamble of claim 1 are from EP 0 260 733 A1 and from JP H11 210674 A known.

It is an object of the present invention to optimize the pumping properties of a vacuum pump of the type mentioned at the outset without adversely affecting other properties of the vacuum pump such as in particular the mechanical stability, in particular the stability of the Holweck stages.

This object is achieved by a vacuum pump with the features of claim 1.

According to the invention it is provided that the Holweck steps each comprise a Holweck thread and a Holweck sleeve rotating about the axis of rotation, and that in the Holweck steps the web height of the Holweck thread decreases in the pumping direction.

The invention is based on the general idea of not leaving the web height constant in at least two successive Holweck stages. For example, at least two Holweck steps each having their own Holweck stator or a common Holweck stator can follow one another, each of which is conical.

It has been shown, surprisingly, that this measure brings improved pumping properties without leading to an unacceptable impairment of the stability of the Holweck arrangement.

As a result of the invention, the pumping capacity of a Holweck arrangement can consequently be improved with sufficient mechanical stability.

If the vacuum pump does not have a further pump stage upstream of the Holweck arrangement, the inlet of the Holweck arrangement is the actual inlet of the vacuum pump. Otherwise, if, for example, according to a preferred embodiment, a turbo-molecular pump stage (also in the following simply turbo stage) is connected upstream, then the inlet of the Holweck arrangement is downstream of the outlet of the turbo stage. Independently of this, one or more further Holweck steps can be connected upstream and / or downstream of the concentric Holweck steps.

In a possible embodiment of the invention, three or more concentrically arranged Holweck steps can be provided, each with a web height decreasing in the pumping direction. Two consecutive Holweck stages can have a common Holweck stator. Such a special embodiment will be discussed in more detail below.

The Holweck stages can connect to a turbo stage.

According to the invention, it is provided that two consecutive Holweck stages comprise a common Holweck stator provided on both sides with a Holweck thread and a Holweck sleeve rotating around the axis of rotation, the web height of the Holweck thread in each case on the outside of the Holweck stator and on the inside of the Holweck stator Pumping direction decreases.

It has been shown, surprisingly, that this measure on the one hand brings improved pumping properties and on the other hand does not lead to an unacceptable impairment of the stability of the common Holweck stator even if the width of the annular space delimited by the two rotor sleeves remains unchanged.

In a preferred embodiment, a turbo stage is followed by three concentrically arranged Holweck stages, each with a web height decreasing in the pumping direction, the last two Holweck stages in the pumping direction having the common Holweck stator. Between the outer Holweck step this In both Holweck stages and the first Holweck stage in the pumping direction, the vacuum pump can have an intermediate inlet which is assigned directly to the inlet of the outer Holweck stage. Such an arrangement can be used in particular in so-called split-flow vacuum pumps, which are basically known to the person skilled in the art and do not need to be explained in more detail here.

In general, for the sake of completeness, it should be mentioned that the size of the Holweck gap can change slightly during operation of the pump due to the centrifugal force acting on the rotating rotor sleeve. The extent of the change can depend on the axial position, i. a constant width of the Holweck gap in the axial direction when the rotor sleeve is stationary can vary in the axial direction during operation.

Further embodiments of the invention are also specified in the dependent claims, the following description and the figures.

According to one embodiment, the outside of the Holweck stator has an outer groove base diameter which increases in the pumping direction.

According to a further embodiment, the inside of the Holweck stator has an inner groove base diameter which decreases in the pumping direction.

The outer groove base diameter preferably increases in the pumping direction and the inner groove base diameter decreases in the pumping direction.

In this way, decreasing web heights of the Holweck threads in the pumping direction can be achieved in conjunction with cylindrical Holweck sleeves.

In this context, the groove base diameter is to be understood as the diameter of the Holweck stator at the respective axial point (hereinafter also "local"), based on the base of the respective Holweck channel. In other words, the groove base diameter is the locally smallest diameter on the outside of the Holweck stator and the locally largest diameter on the inside of the Holweck stator.

According to one development, the inlet-side groove base diameter on the outside of the Holweck stator is smaller than the inlet-side groove base diameter on the inside of the Holweck stator.

In other words, the groove bottom of the outer Holweck step is closer to the axis of rotation at its inlet than the groove bottom of the inner Holweck step on the inlet side. With such a shape of the Holweck stator, a particularly high pump output can be achieved. In particular, comparatively large web heights can thereby be achieved on the inlet side.

According to the invention, an (outer) taper angle defined by the groove base of the outer Holweck thread and an (inner) taper angle defined by the groove base of the inner Holweck thread are different from one another. The outer angle of conicity is preferably greater than the inner angle of conicity.

The following specific values and ratios relate to a Holweck stator with an axial length of 50mm, but can also be within the specified value ranges for a different axial length. A preferred value for the size of the Holweck gap is 0.3 mm.

The outer angle of conicity can be between 5 and 15 °, preferably between 8 ° and 10 °, and in particular around 9.1 °.

The inner angle of conicity can be between 1 ° and 5 °, preferably between 2 ° and 4 ° and in particular around 3.1 °.

According to a further embodiment, on the outer Holweck thread on the inlet side, the ratio of double the web height to the groove base diameter is greater than 0.1, preferably greater than 0.15, and in particular approximately 0.19.

Furthermore, it can be provided that on the inner Holweck thread on the inlet side the ratio of double the web height to the groove base diameter is greater than 0.4, preferably greater than 0.6, and in particular approximately 0.8.

Relatively large web heights on the inlet side can ensure sufficient stability of the Holweck stator with a relatively small wall thickness of the Holweck stator at the same time.

The (local) wall thickness of the Holweck stator is half of the difference between the outer groove base diameter and the inner groove base diameter at the relevant axial point.

According to a development, the ratio of the inlet-side web height to the outlet-side web height on the outer Holweck thread is less than 0.1, preferably less than 0.25, and in particular approximately 0.23.

Furthermore, it can be provided that the ratio of the web height on the inlet side to the web height on the outlet side is less than 0.5, preferably less than 0.4 and in particular about 0.36 on the inner Holweck thread.

It has been shown that the above-mentioned embodiments, taken individually and also in any combination, lead to particularly good pump performance of the Holweck arrangement without impairing the stability of the double-sided Holweck stator.

According to an embodiment which does not belong to the invention, the Holweck stator has a constant wall thickness along its axial extension.

With a constant wall thickness, the outer angle of conicity is equal to the inner angle of conicity.

According to a further embodiment, the Holweck stator has an increasing wall thickness along its axial extent, in particular in the pumping direction of the outer Holweck stage, the wall thickness preferably increasing steadily.

The increasing wall thickness is accompanied by different conicity angles of the two Holweck steps. Different requirements can be placed on the two Holweck stages. For this purpose, different Holweck threads can be formed outside and inside. The fact that the wall thickness increases in the pumping direction of the outer Holweck step means that the taper angle of the outer Holweck thread is greater than the taper angle of the inner Holweck thread.

In a further development, the wall thickness of the Holweck stator is minimal in the area of the maximum web height.

It was recognized that the web height can contribute to the stability of the Holweck stator, so that comparatively small wall thicknesses can be present in the area of relatively large web heights.

The minimum wall thickness of the Holweck stator is preferably less than 2 mm, preferably less than 1.5 mm and particularly preferably about 1 mm. According to one embodiment, the Holweck stator is made of aluminum. According to a further embodiment, the Holweck stator is manufactured integrally, in particular milled from one piece.

Fig. 1

eine perspektivische Ansicht einer nicht erfindungsgemäßen Turbomolekularpumpe,

Fig. 2

eine Ansicht der Unterseite der Turbomolekularpumpe von Fig. 1,

Fig. 3

einen Querschnitt der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie A-A,

Fig. 4

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie B-B,

Fig. 5

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie C-C,

Fig. 6

schematisch einen Längsschnitt durch eine Holweckanordung mit drei Holweckstufen und einem doppelseitigen Holweckstator,

Fig. 7

eine Detailansicht von Fig. 6,

Fig. 8

in einem Längsschnitt eine Ausführungsform eines erfindungsgemäßen Holweckstators.

The invention is described below by way of example with reference to the accompanying figures. Show it:

Fig. 1

a perspective view of a turbo molecular pump not according to the invention,

Fig. 2

a view of the bottom of the turbo molecular pump of Fig. 1 ,

Fig. 3

a cross section of the turbo molecular pump along the in Fig. 2 shown section line AA,

Fig. 4

a cross-sectional view of the turbo molecular pump along the line in FIG Fig. 2 shown section line BB,

Fig. 5

a cross-sectional view of the turbo molecular pump along the line in FIG Fig. 2 shown section line CC,

Fig. 6

schematically a longitudinal section through a Holweck arrangement with three Holweck steps and a double-sided Holweck stator,

Fig. 7

a detailed view of Fig. 6 ,

Fig. 8

in a longitudinal section an embodiment of a Holweck stator according to the invention.

In the Fig. 1 The turbo-molecular pump 111 shown comprises a pump inlet 115 which is surrounded by an inlet flange 113 and 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.

In the orientation of the vacuum pump, the inlet flange 113 forms according to FIG 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 accommodated in the electronics housing 123, for example for operating an electric motor 125 arranged in the vacuum pump. A plurality of connections 127 for accessories are provided on the electronics housing 123. In addition, a data interface 129, for example in accordance with the RS485 standard, and a power supply connection 131 are arranged on the electronics housing 123.

A flood inlet 133, in particular in the form of a flood valve, is provided on the housing 119 of the turbo molecular pump 111, via which the vacuum pump 111 can be flooded. In the area of the lower part 121 there is also a sealing gas connection 135, which is also referred to as a purge gas connection, via which purge gas to protect the electric motor 125 from the gas conveyed by the pump into the engine compartment 137, in which the electric motor 125 is in the vacuum pump 111 is housed, can be brought. Two coolant connections 139 are also arranged in the lower part 121, one of the coolant connections being provided as an inlet and the other coolant connection being provided as an outlet for coolant which can be passed into the vacuum pump for cooling purposes.

The lower side 141 of the vacuum pump can serve as a standing surface, so that the vacuum pump 111 can be operated standing on the lower side 141. The vacuum pump 111 can, however, also be attached to a recipient via the inlet flange 113 and can thus be operated in a suspended manner, as it were. In addition, the vacuum pump 111 can be designed in such a way that it can also be put into operation when it is oriented in a different way than in FIG Fig. 1 is shown. Embodiments of the vacuum pump can also be implemented in which the underside 141 cannot be arranged facing downwards, but facing to the side or facing upwards.

At the bottom 141, which in Fig. 2 is shown, various screws 143 are also arranged, by means of which components of the vacuum pump not specified here are attached to one another. For example, a bearing cap 145 is attached to the underside 141.

Fastening bores 147 are also arranged on the underside 141, via which the pump 111 can be fastened to a support surface, for example.

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.

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

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

The turbo-molecular pump 111 comprises several turbo-molecular pump stages connected in series with one another with 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. A rotor disk 155 and an adjacent stator disk 157 each form a turbomolecular one Pumping stage. The stator disks 157 are held at a desired axial distance from one another by spacer rings 159.

The vacuum pump also comprises Holweck pump stages which are arranged one inside the other in the radial direction and are connected in series with one another for effective pumping. The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylinder-shell-shaped Holweck rotor sleeves 163, 165 which are attached to the rotor hub 161 and carried by the latter, which are oriented coaxially to the axis of rotation 151 and nested in one another in the radial direction. Furthermore, two cylinder jacket-shaped Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the axis of rotation 151 and, viewed in the radial direction, are nested inside one another.

The active pumping surfaces of the Holweck pump stages are formed by the jacket surfaces, that is to say by 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 with this forms the first Holweck pumping stage following the turbo molecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 is opposite the radial outer surface of the inner Holweck stator sleeve 169 with the formation of a radial Holweck gap 173 and forms with this a second Holweck pump stage. The radial inner surface of the inner Holweck stator sleeve 169 lies with the radial outer surface of the inner Holweck rotor sleeve 165 with the formation of a radial Holweck gap 175 opposite and with this forms the inner Holweck pump stage.

At the lower end of the Holweck rotor sleeve 163, a radially running channel can be provided, via which the radially outer Holweck gap 171 is connected to the central Holweck gap 173. In addition, a radially running channel can be provided at the upper end of the inner Holweck stator sleeve 169, via which the middle Holweck gap 173 is connected to the radially inner Holweck gap 175. As a result, the nested Holweck pump stages are connected in series with one another. At the lower end of the radially inner Holweck rotor sleeve 165, a connection channel 179 to the outlet 117 can also be provided.

The aforementioned pump-active surfaces of the Holweck stator sleeves 163, 165 each have a plurality of Holweck grooves running helically around the axis of rotation 151 in the axial direction, while the opposite lateral surfaces of the Holweck rotor sleeves 163, 165 are smooth and the gas for operating the Drive vacuum pump 111 in the Holweck grooves.

For the rotatable mounting of the rotor shaft 153, a roller bearing 181 is provided in the area of the pump outlet 117 and a permanent magnetic bearing 183 in the area of the pump inlet 115.

In the area of the roller bearing 181, a conical injection molded nut 185 is provided on the rotor shaft 153 with an outer diameter that increases towards the roller bearing 181. The injection-molded nut 185 is in sliding contact with at least one stripper of an operating medium store. The operating medium reservoir comprises several absorbent disks 187 stacked on top of one another, which are impregnated with an operating medium for the roller bearing 181, for example with a lubricant.

During operation of the vacuum pump 111, the operating medium is transferred by capillary action from the operating medium reservoir via the stripper to the rotating injection nut 185 and, as a result of the centrifugal force, is conveyed along the injection nut 185 in the direction of the increasing outer diameter of the injection nut 92 to the roller bearing 181, where it is e.g. fulfills a lubricating function. The roller bearing 181 and the operating medium store are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

The permanent magnetic bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each of which comprises a ring stack of several permanent magnetic rings 195, 197 stacked on top of one another in the axial direction. The ring magnets 195, 197 are opposite one another with the formation of a radial bearing gap 199, 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 causes magnetic repulsive forces between the ring magnets 195, 197, which cause the rotor shaft 153 to be supported radially. The rotor-side ring magnets 195 are carried by a carrier section 201 of the rotor shaft 153 which surrounds the ring magnets 195 radially on the outside. The stator-side ring magnets 197 are carried 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 ring magnets 195 on the rotor side are fixed parallel to the axis of rotation 151 by a cover element 207 coupled to the carrier section 203. The stator-side ring magnets 197 are fixed parallel to the axis of rotation 151 in one direction by a fastening ring 209 connected to the carrier section 203 and a fastening ring 211 connected to the carrier section 203. A plate spring 213 can also be provided between the fastening ring 211 and the ring magnet 197.

An emergency or retainer bearing 215 is provided inside the magnetic bearing, which runs empty during normal operation of the vacuum pump 111 without contact and only comes into engagement with an excessive radial deflection of the rotor 149 relative to the stator to create a radial stop for the rotor 149 to form, since a collision of the rotor-side structures with the stator-side structures is prevented. The backup bearing 215 is designed as an unlubricated roller bearing and forms a radial gap with the rotor 149 and / or the stator, which has the effect that the backup bearing 215 is disengaged during normal pumping operation. The radial deflection at which the backup bearing 215 engages is dimensioned large enough that the backup bearing 215 does not come into engagement during normal operation of the vacuum pump, and at the same time small enough so that a collision of the rotor-side structures with the stator-side structures under all circumstances is prevented.

The vacuum pump 111 comprises the electric motor 125 for rotatingly driving the rotor 149. The armature of the electric motor 125 is formed by the rotor 149, the rotor shaft 153 of which 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. Between the motor stator 217 and the section of the rotor 149 extending through the motor stator 217 there is an intermediate space 219 which comprises a radial motor gap, via which the motor stator 217 and the permanent magnet arrangement for transmitting the drive torque can magnetically influence each other.

The motor stator 217 is fixed in the housing within the motor compartment 137 provided for the electric motor 125. A sealing gas, which is also referred to as a flushing gas and which can be air or nitrogen, for example, can enter the engine compartment 137 via the sealing gas connection 135. The electric motor 125 can advance process gas, for example, via the sealing gas corrosive parts of the process gas are protected. The engine compartment 137 can also be evacuated via the pump outlet 117, ie the vacuum pressure produced by the backing pump connected to the pump outlet 117 prevails in the engine compartment 137 at least approximately.

A so-called labyrinth seal 223, known per se, can also be provided between the rotor hub 161 and a wall 221 delimiting the engine compartment 137, in particular in order to achieve a better sealing of the motor compartment 217 from the Holweck pump stages located radially outside.

A Holweck arrangement according to the invention, as described below with reference to the Figures 6 to 8 is described, can in particular in a vacuum pump according to the Figs. 1 to 5 can be used.

The Fig. 6 and 7th show only the Holweck arrangement of a vacuum pump 11, for example a turbomolecular pump, with three Holweck stages, each also referred to simply as a pump stage below. The vacuum pump comprises a rotor shaft 15 which is rotatably mounted about an axis of rotation 13. A rotor hub 17, which carries two cylindrical rotor sleeves 19, is arranged on the rotor shaft 15.

Furthermore, two Holweck stators 21, 23 are provided. The inner Holweck stator 21, positioned between the two rotor sleeves 19, is designed on both sides in the manner according to the invention, ie provided with Holweck threads 37, 39 on both sides ( Fig. 7 ). The outer Holweck stator 23, which can be formed, for example, by the pump housing, is arranged radially outside the outer rotor sleeve 19. The outer Holweck stator 23 and the outer rotor sleeve 19 form a first Holweck stage 25. The outer rotor sleeve 19 also forms with the inner Holweck stator 21, more precisely with its outside, a second pump stage 27, which is also referred to here as the outer pump or Holweck stage. The inner rotor sleeve 19 and the inside of the Holweck stator 21 form a third pumping stage 29, which is also referred to here as the inner pumping or Holweck stage. Arrows indicate the pumping direction and thus the conveying direction of the gas molecules conveyed in the Holweck stages 25, 27, 29.

The pumping direction runs from an inlet 33 of the Holweck arrangement 25, 27, 29 to an outlet 35 of the pump stage 25, 27, 29. As mentioned in the introductory part, the vacuum pump can have an intermediate inlet, not shown, which is directly assigned to the inlet of the outer Holweck stage . This intermediate inlet can, for example, be a "split flow" inlet from which gas molecules to be conveyed - as in FIG Fig. 6 indicated by a dashed line - can flow to the inlet of the outer Holweck step 27.

The Holweck stator 21 according to the invention is based on Fig. 7 described in more detail.

Fig. 7 is a detailed view of the Fig. 6 . A section along the axis of rotation 13 through one half of the Holweck arrangement is shown.

The pumping direction illustrated by arrows runs at the outer Holweck step 27 from its inlet to its outlet. The outlet of the outer Holweck step 27 is consequently located on the outside of the Holweck stator 21. The inlet of the inner Holweck step 29 is connected to its outlet. The inlet is accordingly located on the inside of the Holweck stator 21. The pumping direction runs from this inlet to the outlet of the inner Holweck stage 29.

The Holweck stator 21 has an outer thread 37 and an inner thread 39. The webs 41 of the threads 37, 39 each have a web height 43 that decreases in the pumping direction, i.e. the thread depth decreases, the web top lying on a circular cylinder around the axis of rotation 13 both outside and inside, around a constant Holweck gap 47 with the respective rotor sleeve 19 to form. This is achieved by a conical shape of the Holweck stator 21 both on the inside and on the outside, the angle of conicity being greater on the outside than on the inside.

As already mentioned at the beginning, the size of the Holweck gap 47 can change slightly during operation of the pump due to the effective centrifugal force.

The taper angles are in Fig. 6 and 7th Exaggerated only for illustration purposes and are in specific embodiments (cf. also Fig. 8 ) preferably not more than 10 °.

Because of the differently large conicity angles, the wall thickness of the Holweck stator 21 is not constant. Here the wall thickness of the Holweck stator 21 increases in the pumping direction of the outer pumping stage 27. In other words, the wall thickness at the inlet of the outer pump stage 27 and thus at the outlet of the inner pump stage 29 is minimal and smaller than at the outlet of the outer pump stage 27 and thus at the inlet of the inner pump stage 29.

Fig. 8 shows a possible specific embodiment of a Holweck stator 21 in a longitudinal section along the axis of rotation 13. The Holweck stator 21 has an inside with an inner Holweck thread and an outside with an outer Holweck thread. Arrows again illustrate the pumping direction of the respective pumping stage.

The geometry of the Holweck stator 21 according to Fig. 8 corresponds qualitatively to that of the in Fig. 7 Holweck stator 21 schematically, not shown to scale. The wall thickness of Holweck stator 21 consequently increases again in the pumping direction of the outer pumping stage and in pumping direction of the inner pumping stage, while the height of each with its top on a circular cylinder around the axis of rotation 13 lying webs 41 both in the pumping direction of the outer pump stage 27 and in the pumping direction of the inner pump stage 29 decreases.

The conicity of the two pump stages is each defined by the groove base 53, 55, ie by the respective groove base 53, 55 - as in FIG Fig. 8 shown - a cone set with a conicity angle _, the conicity angle α _a relates to the outer groove base 53 and the conicity angle α _i to the inner groove base 55. The angle of conicity α _a is greater than the angle of conicity α _i . This results in the changing wall thickness. If the two conicity angles α _a , α _{i were the} same, the wall thickness would be constant. Such a Holweck stator 21 would also be conical on both sides in the manner according to the invention.

The outer groove base diameter at the inlet of the outer pump stage is in Fig. 8 with NGDAE, the outer groove base diameter at the outlet of the outer pump stage with NGDAA, the inner groove base diameter at the inlet of the inner pump stage with NGDIE and the inner groove base diameter at the outlet of the inner pump stage with NGDIA. The axial positions of the inlets and outlets are defined here by the respective axial end of the Holweck stator. In the illustrated embodiment, NGDAE is slightly smaller than NGDIE. However, embodiments with NGDAE> NGDIE or with NGDAE = NGDIE are also possible.

List of reference symbols

11

Vacuum pump

13

Axis of rotation

15th

Rotor shaft

17th

Holweck hub

19th

Holweck sleeve

21st

double-sided Holweck stator

23

outer Holweck stator

25th

first Holweck stage

27

second, outer Holweck stage

29

third, inner Holweck stage

33

inlet

35

Outlet

37

external Holweck thread

39

inner Holweck thread

41

web

43

Web height

47

Holweck gap

53

outer groove base

55

inner groove base

111

Turbo molecular pump

113

Inlet flange

115

Pump inlet

117

Pump outlet

119

casing

121

Lower part

123

Electronics housing

125

Electric motor

127

Accessory connection

129

Data interface

131

Power supply connection

133

Flood inlet

135

Sealing gas connection

137

Engine compartment

139

Coolant connection

141

bottom

143

screw

145

Bearing cap

147

Mounting hole

148

Coolant line

149

rotor

151

Axis of rotation

153

Rotor shaft

155

Rotor disk

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

Connection channel

181

roller bearing

183

Permanent magnet bearings

185

Injection nut

187

disc

189

commitment

191

rotor-side bearing half

193

stator-side bearing half

195

Ring magnet

197

Ring magnet

199

Bearing gap

201

Beam section

203

Beam section

205

radial strut

207

Cover element

209

Support ring

211

Fastening ring

213

Disc spring

215

Emergency or fishing camp

217

Motor stator

219

Space

221

Wall

223

Labyrinth seal

α _i

internal taper angle

α _a

external taper angle

NGDAE

outer groove base diameter at the inlet

NGDAA

outer groove base diameter at the outlet

NGDIE

inner groove base diameter at the inlet

NGDIA

inner groove base diameter at the outlet

Claims (12)

1. A vacuum pump (11), in particular a turbomolecular pump, comprising an inlet (33);
   an outlet (35); and
   at least two Holweck stages (25, 27, 29) which are concentric with respect to a common axis of rotation (13), which follow one another in the pump direction between the inlet (33) and the outlet (35), which each comprise a Holweck thread (37, 39) and a Holweck sleeve (19) rotating about the axis of rotation (13) and in which the web height (43) of the Holweck thread (37, 39) decreases in the pump direction in each case,
   wherein two Holweck stages (27, 29) following one another comprise a common Holweck stator (21) provided with a Holweck thread (37, 39) at both sides, and wherein the web height (43) of the Holweck thread (37, 39) decreases in the pump direction in each case both at the outer side of the Holweck stator (21) and at the inner side of the Holweck stator (21), characterized in that
   a conicity angle (α_a) defined by the groove base (53) of the outer Holweck thread (37) and a conicity angle (α_i) defined by the groove base (55) of the inner Holweck thread (39) are different from one another.
2. A vacuum pump (11) in accordance with claim 1,
   wherein the outer side of the common Holweck stator (21) has an outer groove base diameter which increases in the pump direction.
3. A vacuum pump (11) in accordance with claim 1 or claim 2,
   wherein the inner side of the common Holweck stator (21) has an inner groove base diameter which decreases in the pump direction.
4. A vacuum pump (11) in accordance with any one of preceding claims,
   wherein the outer groove base diameter increases in the pump direction and the inner groove base diameter decreases in the pump direction.
5. A vacuum pump (11) in accordance with any one of preceding claims,
   wherein the inlet-side groove base diameter (NGDAE) at the outer side of the Holweck stator (21) is smaller than the inlet-side groove base diameter (NGDIE) at the inner side of the Holweck stator (21).
6. A vacuum pump (11) in accordance with any one of preceding claims,
   wherein a conicity angle (α_a) defined by the groove base (53) of the outer Holweck thread (37) is between 5° and 15°, preferably between 8° and 10°, and in particular amounts to approximately 9.1°; and/or
   wherein a conicity angle (α_i) defined by the groove base (55) of the inner Holweck thread (39) is between 1° and 5°, preferably between 2° and 4°, and in particular amounts to approximately 3.1°.
7. A vacuum pump (11) in accordance with any one of preceding claims,
   wherein the ratio of double the web height (43) to the groove base diameter at the outer Holweck thread (37) at the inlet side is greater than 0.10, preferably greater than 0.15, and in particular amounts to approximately 0.19; and/or wherein the ratio of double the web height (43) to the groove base diameter at the inner Holweck thread (39) at the inlet side is greater than 0.4, preferably greater than 0.6, and in particular amounts to approximately 0.8.
8. A vacuum pump (11) in accordance with any one of preceding claims, wherein the ratio of the inlet-side web height (43) to the outlet-side web height (43) at the outer Holweck thread (37) is less than 0.3, preferably less than 0.25, and in particular amounts to approximately 0.23; and/or wherein the ratio of the inlet-side web height (43) to the outlet-side web height (43) at the inner Holweck thread (39) is less than 0.5, preferably less than 0.4, and in particular amounts to approximately 0.36.
9. A vacuum pump (11) in accordance with any one of preceding claims,
   wherein the Holweck stator (21) has an increasing wall thickness (45) along its axial extent, in particular in the pump direction of the outer Holweck stage (27), with the wall thickness (45) preferably increasing continuously.
10. A vacuum pump (11) in accordance with claim 9,
    wherein the wall thickness (45) of the Holweck stator (21) is minimal in the region of the maximum web height (43) of the outer Holweck stage (27).
11. A vacuum pump (11) in accordance with claim 9 or claim 10,
    wherein the minimum wall thickness (45) of the Holweck stator (21) amounts to less than 2mm, preferably to less than 1.5mm, and in particular preferably to approximately 1mm.
12. A vacuum pump (11) in accordance with any one of preceding claims,
    wherein the Holweck stator (21) is produced from aluminum; and/or wherein the Holweck stator (21) is integrally produced, in particular milled from one piece.

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