Turbomolecular vacuum pump

Abstract

To improve a turbo-molecular pump such that, in relation to a radial gas inlet, backflow effects within a Holweck pump unit are minimized, and the highest possible pumping speed is provided for the radial gas inlet.SOLUTION: In addition to an axial gas inlet 33 into a Holweck pump region 27 on the radially outer side, radial gas inlets 35, 35' into the Holweck pump unit 13 are provided. The radial gas inlets open into a transition region 31 or, upstream of the transition region, into the radially outer Holweck pump region. An outlet region 27a and an inlet region 29a respectively have free cross sections defined by Holweck channels 23 in a cross-sectional plane extending perpendicular to a rotational axis 15, at which the pumping action ends or begins. The free cross section of the inlet region is larger than the free cross section of the outlet region by a factor f greater than 1.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a turbomolecular vacuum pump, comprising at least one turbomolecular pump unit and at least one Holweck pump unit arranged downstream of the turbomolecular pump unit in a pumping direction, the Holweck pump units having at least two successive Holweck stages arranged concentrically inside and outside of each other with respect to a common axis of rotation, the Holweck stages each having a Holweck stator with a Holweck thread, the Holweck thread having a Holweck web protruding from a channel bottom and a Holweck channel defined by a wall of the Holweck web, and the common Holweck pump units , a turbomolecular pump facing a Holweck rotor which rotates around a rotation axis during operation, which, together with one Holweck stator, defines a radially outer Holweck pumping region and, together with the other Holweck stator, defines a radially inner Holweck pumping region, in a transition region at the free end of the Holweck rotor, the outlet region of the radially outer Holweck pumping region transitions into the inlet region of the radially inner Holweck pumping region, in which, in addition to the axial gas inlet into the radially outer Holweck pumping region, a radial gas inlet into the Holweck pump unit is provided.

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

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

[0004] Turbomolecular vacuum pumps of this type are known in principle, for example from EP-A 3845764, EP-A 2933497 and EP-A 3657021. Vacuum systems and leak detection systems of the aforementioned type are also known in principle.

[0005] Vacuum pumps are used in various technical fields. Depending on the requirements, vacuum pumps have one or more pump units. Holweck pump units belong to the category of molecular vacuum pumps and generate a molecular flow by rotating a Holweck rotor relative to a respective Holweck stator. Holweck pump units have one or more Holweck stages, which may pump in series or in parallel with each other. Holweck pump units are typically used in turbomolecular vacuum pumps and are followed in the pumping direction by one or more turbomolecular pump stages that form the turbomolecular pump unit.

[0006] The Holweck stage includes a Holweck rotor and a Holweck stator, where the Holweck rotor is attached to the pump rotor, for example, by a disk-shaped Holweck hub, and the rotor is rotated by the pump's drive motor during pump operation. The Holweck rotor, also called a Holweck sleeve, typically has a hollow cylindrical shape. The Holweck pump unit may include multiple Holweck sleeves, which are concentrically attached to the Holweck hub. The Holweck stator has a single-start or multi-start Holweck thread. Gas molecules to be pumped are pumped along the thread from an inlet to an outlet by rotating the Holweck rotor relative to the Holweck stator. The thread has a circumferential Holweck channel (also called a Holweck groove) defined by the wall of the Holweck web, and gas molecules are pumped in the Holweck channel when the Holweck rotor rotates relative to the Holweck stator. To minimize backflow losses, the width of the radial gap (Holbeck gap) between the top surface, also referred to as the tip, of the Holbeck web and the Holbeck sleeve is kept relatively small compared to the web height.

[0007] So-called "folded" Holweck pump units are known in which several Holweck stages are arranged concentrically one inside the other (also referred to as "engaged" Holweck stages), so that the gas flows of immediately successive radial Holweck stages are opposite to each other. Two successive Holweck stages, i.e., the (radially) outer Holweck stage and the (radially) inner Holweck stage, may have a common Holweck stator with a Holweck thread on both sides, hereinafter also referred to as a "double" Holweck stator, which is located between two concentric Holweck rotors.

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

[0009] For many applications of turbomolecular vacuum pumps, for example in so-called split-flow or leak detection applications, it is necessary to provide at least one radial gas inlet, also referred to as an interstage port, into the Holweck pumping unit. It can be disadvantageous for such a radial gas inlet to be located relatively close to the turbomolecular pumping unit, axially relative to the axis of rotation, and in particular, undesirable backflow effects can occur. Therefore, attempts are made to position the radial gas inlet to the Holweck pumping unit in or near the transition region, or in any case closer to the transition region than the turbomolecular pumping unit. Furthermore, it is desirable to provide as high a pumping speed as possible for such an interstage port.

[0010] Pumping speed means the volumetric flow rate of the respective pumped gas pumped through a particular cross section per unit time. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent Application Publication No. 3845764 [Patent Document 2] European Patent Application Publication No. 2933497 [Patent Document 3] European Patent Application Publication No. 3657021 Summary of the Invention [Problem to be solved by the invention]

[0012] In view of this background, the object of the present invention is to improve a turbomolecular pump of the type mentioned at the beginning so that, in connection with a radial gas inlet, backflow effects in the Holweck pump unit are minimized and the highest possible pumping speed is provided for the radial gas inlet. [Means for solving the problem]

[0013] This problem is solved by the features of claim 1. Thus, according to the invention, it is provided that the radial gas inlet opens into the transition region or into a radially outer Holweck pumping region upstream of the transition region, in particular into the downstream half or the downstream ⅓, ¼, ⅕ or ⅙ of the radially outer Holweck pumping region, the outlet region and the inlet region having a free cross-section defined by the Holweck channels in a cross-sectional plane extending perpendicular to the axis of rotation, where the pumping action ends or begins, respectively, and the free cross-section of the inlet region is greater by a factor f>1 than the free cross-section of the outlet region.

[0014] The free cross section on the inlet or outlet side is hereinafter also referred to as the openness.

[0015] The Holbeck stators are preferably each multi-stranded, i.e. each has a plurality of, for example four, six or eight, Holbeck channels extending parallel to one another, the Holbeck channels being separated from one another in pairs by one of the Holbeck webs.

[0016] Tests of known Holweck pumping units have shown that the pumping speed decreases continuously in the pumping direction, i.e., from the inlet to the radially outer Holweck pump stage to the outlet from the radially inner Holweck pump stage, with a relatively strong reduction in pumping speed occurring in the transition region between the radially outer Holweck pumping region and the radially inner Holweck pumping region, depending on the particular situation. Furthermore, in many Holweck pumping units, the pumping speed in the inlet region of the radially inner Holweck pumping region is essentially lower than the pumping speed in the outlet region of the radially outer Holweck pumping region. In other words, in the transition region, also known as the turning point, an undesirable reduction in pumping speed occurs in many arrangements.

[0017] It has been determined that the increase in the inlet openness relative to the outlet openness according to the invention significantly increases the pumping speed in the inlet region of the radially inner Holweck pumping region, while at the same time minimizing backflow, and also provides a significantly increased pumping speed for the radial gas inlet, even when the radial gas inlet opens into the radially outer Holweck pumping region upstream of the transition region. In a practical turbomolecular vacuum pump, for example, the free cross section of the gas inlet in the inlet region of the radially inner Holweck pumping region is 142 mm 2 from 388mm 2 and as a result the pumping speed was found to increase from 2.69 l / s to 6.70 l / s (where l / s = liters per second) without changing the other geometric relationships of the Holweck pump unit.

[0018] The invention thereby allows a significant increase in the performance of the Holweck pumping unit and thus of the turbomolecular vacuum pump equipped with such a Holweck pumping unit, which is in fact highly advantageous in particular for split flow and leak detection applications requiring one or more radial gas inlets.

[0019] Advantageous developments of the invention are set forth in the dependent claims, the following description and the drawings.

[0020] According to some embodiments, it may be contemplated that 1 < f < 3, preferably 1 < f < 2, and suitably 1.2 < f < 1.5 are applied. An increase in the exhaust velocity that is advantageous for practice can already be obtained when the coefficient f is less than 1.5, where it has been recognized that a coefficient F of less than 2 or less than 3 is advantageous and only a relatively small radial structural space is required.

[0021] The degree of opening on the inlet side may be varied in various ways.

[0022] In many embodiments, it may be contemplated that in each cross-sectional plane, the height of the Holbeck web in the inlet region is greater than the height of the Holbeck web in the outlet region.

[0023] According to some embodiments, it may be contemplated that in each cross-sectional plane, the width of the Holbeck web measured in the circumferential direction in the inlet region is greater than the width in the outlet region.

[0024] According to some embodiments, it may be contemplated that the number of Holbeck webs in the radially inner Holbeck pump region is smaller than the number of Holbeck webs in the radially outer Holbeck pump region.

[0025] The foregoing means may be arbitrarily combined with each other.

[0026] The Holbeck stator that defines the radially inner Holbeck pump region may be a Holbeck stator having Holbeck threads on both sides, and the Holbeck stator further defines a further Holbeck pump region with a further Holbeck rotor radially more inwardly.

[0027] In this case, the Holbeck stator having Holbeck threads on both sides has a wall thickness measured in the radial direction, and in the inlet region, it can be assumed that the wall thickness is less than the height of the Holbeck web in the radially inner Holbeck pump region.

[0028] In many embodiments, it may be envisaged that the radially outer Holweck pumping region and / or the radially inner Holweck pumping region are each formed conically such that the height of the Holweck web continuously decreases in the pumping direction.

[0029] In this case, it can be provided that the cone angle defined by the channel bottom of the radially outer Holweck pumping region and the cone angle defined by the channel bottom of the radially inner Holweck pumping region are at least substantially the same as or different from each other, in which case, in particular, the cone angle of the radially outer Holweck pumping region can be larger or smaller than the cone angle of the radially inner Holweck pumping region.

[0030] Alternatively, the radially outer Holweck pumping region and / or the radially inner Holweck pumping region may each be cylindrically shaped.

[0031] According to some embodiments, it may be provided that at least one pumping portion of the radially outer Holweck stator, which defines the radially outer Holweck pumping region by the Holweck rotor, is constructed as a single unit. In this case, it may be provided that the radial gas inlet opens into the radially outer Holweck pumping region upstream of the transition region and extends through the single pumping portion of the radially outer Holweck stator. The single unit construction facilitates the manufacture and assembly of the Holweck pump unit. The relatively large inlet opening of the radially inner Holweck pumping region is also advantageous for the radial gas inlet located upstream of the transition region in terms of pumping speed and minimizing backflow, i.e., a two-part radially outer Holweck stator is not required to provide a relatively large opening downstream of the radial gas inlet opening.

[0032] In many embodiments, it can be envisaged that the radial gas inlets to the Holweck pump unit extend through the pump housing above the lower part or intermediate part of the vacuum pump, where at least part of the transition region is located. This is particularly advantageous, for example in the case of a split-flow vacuum pump, if there are one or more further radial gas inlets upstream, since in this case the outside of the pump housing can be used as a common sealing surface for the radial gas inlets.

[0033] According to some of the following embodiments, at least one further radial gas inlet is arranged upstream of the radial gas inlet into the Holweck pump unit, and in particular it can be provided that the further radial gas inlet opens into the Holweck pump unit or into the turbomolecular pump unit.

[0034] As mentioned above, at least some of the plurality of radial gas inlets extend through the outside of the pump housing, which may advantageously be used as a common sealing surface.

[0035] In the vacuum system according to the invention, one of the radial intakes is a radial gas inlet opening into the transition region or into a radially outer Holweck pump region upstream of the transition region.

[0036] In the leak detection system according to the invention, the radial gas inlet for the test gas is a radial gas inlet that opens into the transition region or into a radially outer Holweck pump region upstream of the transition region.

[0037] The invention will now be described, by way of example only, with reference to the drawings, in which: [Brief explanation of the drawings]

[0038] [Figure 1] 1 shows a perspective view of a turbomolecular vacuum pump according to the prior art; [Figure 2] 2 shows the underside of the turbomolecular vacuum pump of FIG. 1. [Figure 3] 3 shows a cross section of the turbomolecular vacuum pump along the section line AA shown in FIG. 2. [Figure 4] 3 shows a cross section of the turbomolecular vacuum pump along the section line BB shown in FIG. 2. [Figure 5] 3 shows a cross section of the turbomolecular vacuum pump along the section line CC shown in FIG. 2. [Figure 6] 1 shows a schematic diagram of a turbomolecular vacuum pump according to the prior art; [Figure 7] 1 shows a partial cross section parallel to the axis of rotation of a portion of a turbomolecular vacuum pump according to the prior art; [Figure 8] 1 shows a partial cross section parallel to the axis of rotation of a portion of a turbomolecular vacuum pump according to an embodiment of the present invention; [Figure 9] 1 shows a partial cross section perpendicular to the axis of rotation of a Holweck pump unit of a turbomolecular vacuum pump according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0039] The turbomolecular pump 111 (hereinafter also referred to as turbomolecular pump or vacuum pump for short) shown in Fig. 1 has a pump inlet 115 surrounded by an inlet flange 113. In a manner known per se, a recipient (not shown) may be connected to the pump inlet 115. Gas coming from the recipient can be sucked from the recipient via the pump inlet 115 and pumped through the pump to a pump outlet 117. An auxiliary vacuum pump, for example a rotary vane pump, may be connected to the pump outlet 117.

[0040] The inlet flange 113 forms the upper end of a housing 119 of the vacuum pump 111 in the orientation of the vacuum pump according to Figure 1. The housing 119 has a lower part 121. Arranged laterally on the lower part 121 is an electronics housing 123. The electronics housing 123 accommodates electrical and / or electronic components of the vacuum pump 111, for example for operating an electric motor 125 (see also Figure 3) arranged in the vacuum pump. The electronics housing 123 is provided with a number of connections 127 for accessories.

[0041] Furthermore, a data interface 129 (for example according to the RS485 standard) and a current supply connection 131 are arranged in the electronics housing 123 .

[0042] There are also turbomolecular pumps that do not have this type of attached electronics housing, but are connected to external drive electronics.

[0043] The housing 119 of the turbomolecular pump 111 is provided with a ventilation inlet 133, in particular in the form of a ventilation valve, via which the vacuum pump 111 may be vented. A seal gas connection 135 (also referred to as a purge gas connection) is also arranged in the region of the lower part 121. Via the seal gas connection 135, a purge gas can be fed into a motor chamber 137 to protect the electric motor 125 (see, for example, FIG. 3) against the gas being pumped by the pump. In the motor chamber 137, the electric motor 125 of the vacuum pump 111 is accommodated. Two coolant connections 139 are also arranged in the lower part 121. One coolant connection serves as an intake for the coolant, and the other as an exhaust. Coolant can be introduced into the vacuum pump for cooling purposes. A further turbomolecular vacuum pump (not shown) is operated exclusively air-cooled.

[0044] The underside 141 of the vacuum pump can be used as a base, so that the vacuum pump 111 can be operated in a vertical position relative to the underside 141. Moreover, the vacuum pump 111 can be fixed to the recipient via the inlet flange 113 and thus operated in a suspended state, so to speak. Furthermore, the vacuum pump 111 can be configured so that it can be operated even when oriented in a different direction than that shown in FIG. 1. Vacuum pump configurations are also possible in which the underside 141 can be arranged not only facing downwards, but also facing sideways or upwards. In this case, any angle is conceivable in principle.

[0045] In particular, other turbomolecular vacuum pumps (not shown) that exist, which are larger than the pump shown, cannot be operated in a vertical position.

[0046] 2 further comprises various screws 143. These screws 143 secure components of the vacuum pump, not specifically identified here, to one another. For example, a bearing cover 145 is secured to the lower surface 141.

[0047] Further fastening holes 147 are arranged in the underside 141. Via the fastening holes 147, the pump 111 can be fixed, for example, to a mounting surface. This is not possible with other existing turbomolecular vacuum pumps (not shown), in particular those larger than the pump shown.

[0048] 2 to 5 show a coolant line 148 in which a coolant can be circulated, the coolant being introduced and withdrawn via the coolant connection 139.

[0049] As shown in the cross-sectional views of Figures 3-5, the vacuum pump has multiple process gas pumping stages for pumping process gas acting on a pump inlet 115 to a pump outlet 117.

[0050] A rotor 149 is disposed within the housing 119. The rotor 149 has a rotor shaft 153 that is rotatable about a rotation axis 151.

[0051] The turbomolecular pump 111 has multiple turbomolecular pump stages connected in series to provide a pumping action. Each turbomolecular pump stage has multiple radially extending rotor blades 155 fixed to the rotor shaft 153 and multiple stator vanes 157 arranged between the rotor blades 155 and fixed within the housing 119. In this case, each rotor blade 155 and its adjacent stator vane 157 form one turbomolecular pump stage. The stator vanes 157 are held at a desired axial distance from each other by spacer rings 159.

[0052] The vacuum pump further comprises Holweck pump stages arranged radially inside and outside one another and connected in series to provide a pumping action. There are alternative turbomolecular vacuum pumps (not shown) that do not have Holweck pump stages.

[0053] The rotor of the Holweck pump stage includes a rotor hub 161 disposed on the rotor shaft 153 and two cylindrically sided Holweck rotor sleeves 163, 165 fixed to and supported by the rotor hub 161. The Holweck rotor sleeves 163, 165 are oriented coaxially with respect to the rotation axis 151 and engage radially with one another. Two cylindrically sided Holweck stator sleeves 167, 169 are also provided. The Holweck stator sleeves 167, 169 are likewise oriented coaxially with respect to the rotation axis 151 and engage radially with one another.

[0054] The pumping surfaces of the Holweck pump stages are formed by the side surfaces, i.e., the radially inner and / or outer surfaces of the Holweck rotor sleeves 163, 165 and the Holweck stator sleeves 167, 169. The radially inner surface of the outer Holweck stator sleeve 167 faces the radially outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together with this outer surface forms the first Holweck pump stage following the turbomolecular pump. The radially inner surface of the outer Holweck rotor sleeve 163 faces the radially outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together with this outer surface forms the second Holweck pump stage. The radially inner surface of the inner Holweck stator sleeve 169 opposes the radially outer surface of the inner Holweck rotor sleeve 165, forming a radial Holweck gap 175, and together with this outer surface forms the third Holweck pump stage.

[0055] A radially extending channel may be provided at the lower end of the Holweck rotor sleeve 163. The radially outer Holweck gap 171 is connected to the central Holweck gap 173 via the channel. A further radially extending channel may be provided at the upper end of the inner Holweck stator sleeve 169. The central Holweck gap 173 is connected to the radially inner Holweck gap 175 via the channel. This allows multiple Holweck pump stages that engage with each other in series. A connecting channel 179 that leads to the exhaust port 117 may be provided at the lower end of the radially inner Holweck rotor sleeve 165.

[0056] The pumping surfaces of the Holweck stator sleeves 167, 169 each have a plurality of Holweck grooves that extend axially and spirally around the rotation axis 151. On the other hand, the opposing sides of the Holweck rotor sleeves 163, 165 are smoothly formed and pump gas for operating the vacuum pump 111 forward in the Holweck grooves.

[0057] For the rotatable support of the rotor shaft 153, a rolling bearing 181 is provided in the region of the pump outlet 117 and a permanent magnetic bearing 183 is provided in the region of the pump inlet 115.

[0058] In the region of the rolling bearing 181, the rotor shaft 153 is provided with a conical splash nut 185. The splash nut 185 has an outer diameter that increases towards the rolling bearing 181. The splash nut 185 is in sliding contact with at least one scraping element of the working medium reservoir. In other existing turbomolecular vacuum pumps (not shown), a splash screw may be provided instead of a splash nut. This allows for various configurations to be realised, so that the term "splash tip" is also used in this context.

[0059] The working medium reservoir comprises a number of absorbent discs 187 stacked one above the other, which are impregnated with a working medium, e.g., a lubricant, for the rolling bearings 181.

[0060] During operation of the vacuum pump 111, the working medium is transferred by capillary action from the working medium reservoir via the scraping element to the rotating splash nut 185 and is then forced by centrifugal force along the splash nut 185 towards the increasing outer diameter of the splash nut 185 towards the rolling bearing 181, where it performs, for example, a lubrication function. The rolling bearing 181 and the working medium reservoir are enclosed in the vacuum pump by a trough-like insert 189 and a bearing cover 145.

[0061] The permanent magnet magnetic bearing 183 has a rotor-side bearing half 191 and a stator-side bearing half 193. Each half has a ring stack, which consists of multiple rings 195, 197 of permanent magnets stacked axially one above the other. The ring magnets 195, 197 face each other, forming a radial bearing gap 199, with the rotor-side ring magnet 195 positioned radially outward and the stator-side ring magnet 197 positioned radially inward. The magnetic field present in the bearing gap 199 generates a magnetic repulsion force between the ring magnets 195, 197. This repulsion force provides radial support for the rotor shaft 153. The rotor-side ring magnet 195 is supported by a support portion 201 of the rotor shaft 153. The support portion 201 surrounds the ring magnet 195 radially outward. The stator-side ring magnet 197 is supported by a support portion 203 of the stator shaft 153. The support part 203 extends through the ring magnet 197 and is suspended on radial struts 205 of the housing 119. The rotor-side ring magnet 195 is fixed parallel to the rotation axis 151 by a cover element 207 connected to the support part 203. The stator-side ring magnet 197 is fixed in one direction parallel to the rotation axis 151 by a fixing ring 209 connected to the support part 203 and a fixing ring 211 connected to the support part 203. A disc spring 213 may further be provided between the fixing ring 211 and the ring magnet 197.

[0062] An emergency or safety bearing 215 is provided within the magnetic bearing. During normal operation of the vacuum pump, the emergency or safety bearing 215 runs free and only engages if the rotor 149 is displaced excessively radially relative to the stator, thereby forming a radial stop for the rotor 149 so that collisions between rotor-side and stator-side structures are prevented. The safety bearing 215 is configured as a non-lubricated rolling bearing and forms a radial gap with the rotor 149 and / or the stator. This gap prevents the safety bearing 215 from engaging during normal pump operation. The radial displacement that the safety bearing 215 engages is dimensioned to be sufficiently large so that the safety bearing 215 does not engage during normal operation of the vacuum pump, and at the same time is sufficiently small so that collisions between rotor-side and stator-side structures are prevented under all circumstances.

[0063] The vacuum pump 111 includes an electric motor 125 that rotates a rotor 149. The rotor 149 forms an armature of the electric motor 125. A rotor shaft 153 of the rotor 149 extends through a motor stator 217. A permanent magnet assembly may be disposed radially outward or embedded in the portion of the rotor shaft 153 that extends through the motor stator 217. An intermediate chamber 219 is disposed between the motor stator 217 and the portion of the rotor 149 that extends through the motor stator 217, and the intermediate chamber 219 has a radial motor gap. Through the motor gap, the motor stator 217 and the permanent magnet assembly may magnetically interact to transmit a driving torque.

[0064] The motor stator 217 is fixed in the housing in a motor chamber 137 provided for the electric motor 125. A seal gas connection 135 allows a seal gas (also called purge gas, which may be, for example, air or nitrogen) to reach the motor chamber 137. The seal gas protects the electric motor 125 against process gases, for example corrosive parts of the process gas. The motor chamber 137 may be evacuated via the pump outlet 117, i.e., a vacuum pressure is applied to the motor chamber 137 at least approximately, which is achieved by an auxiliary vacuum pump connected to the pump outlet 117.

[0065] A so-called labyrinth seal 223, known per se, may further be provided between the rotor hub 161 and the wall 221 that defines the motor chamber 137. This achieves better sealing of the motor chamber 217, in particular with respect to the radially outer Holweck pump stages.

[0066] FIG. 6 shows a schematic representation of some components of a turbomolecular vacuum pump according to the prior art, which may be further configured as described above in relation to FIGS. 1 to 5.

[0067] Figure 6 shows a turbomolecular pump unit 11 and a Holweck pump unit 13. Both pump units 11, 13 have a common rotor 12 which rotates about a rotation axis 15 during pumping operation. The drive motor for rotor 12 is not shown in Figure 6.

[0068] The turbomolecular pump unit 11 has a plurality of rotor blades 11a. The rotor blades 11a are connected to the rotor 12 so as not to rotate relative to the rotor blades 11a. Not shown in the figure are stator blades of the turbomolecular pump unit 11 that interact with the rotor blades 11a in a known manner to provide a pumping action.

[0069] The Holweck pump unit 13 is shown with a Holweck hub 26 connected to the rotor 12 so as not to rotate relative to the rotor 12, a Holweck rotor 25 also called a Holweck sleeve connected to the Holweck hub 26 so as not to rotate relative to the rotor 12, a radially outer Holweck stator 17a and a radially inner Holweck stator 17b.

[0070] Thus, in the illustrated embodiment, the Holweck pump unit 13 has two successive Holweck stages in the pumping direction, positioned concentrically inside and outside the rotation axis 15. Each Holweck stage has a respective Holweck stator 17a, 17b having a multi-start Holweck thread with a Holweck web 21 protruding from a channel bottom 19 and a Holweck channel 23 defined by the walls of the Holweck web 21, which thread faces each side of a Holweck rotor 25.

[0071] Thus, in a manner known per se, the Holweck rotor 25 together with the radially outer Holweck stator 17a forms a radially outer Holweck pumping region 27 and together with the radially inner Holweck stator 17b forms a radially inner Holweck pumping region 29.

[0072] The flow path of the gas to be pumped is indicated by arrows in Fig. 6. The gas to be pumped first flows via an axial pump inlet (not shown) in the pump housing (not shown) into the turbomolecular pump unit 11, through the turbomolecular pump unit 11 towards the axial gas inlet 33 into the radially outer Holweck pumping region 27, through the radially outer Holweck pumping region 27 towards the outlet region 27a of the radially outer Holweck pumping region 27 into the transition region 31 at the free end of the Holweck rotor 25, into the inlet region 29a of the radially inner Holweck pumping region 29, through the inlet region 29a and subsequently towards the outlet of the turbomolecular vacuum pump via a flow path (not shown).

[0073] The outlet region 27a of the radially outer Holweck pumping region 27 lies in a cross-sectional plane perpendicular to the rotation axis 15 at an axial position with respect to the rotation axis 15 where the pumping action of the radially outer Holweck pumping region 27 ends, i.e. where the Holweck channels 23 terminate. Correspondingly, the pumping action of the radially inner Holweck pumping region 29 begins at its inlet region 29a, and therefore in a cross-sectional plane extending perpendicular to the rotation axis 15, where the Holweck channels 23 begin.

[0074] The cross-sectional plane in which the outlet region 27a is located and thus the radially outer Holweck pumping region 27 ends may coincide with the cross-sectional plane in which the inlet region 29a is located and thus the pumping action of the radially inner Holweck pumping region 29 begins. Moreover, depending on the specific configuration and arrangement of both Holweck pump stages, these two cross-sectional planes may be located axially apart from each other.

[0075] In the respective cross-sectional planes, the outlet region 27a and the inlet region 29a have respective free cross sections defined by the Holweck channels 23. Each free cross section will hereinafter also be referred to as an openness for simplicity's sake. That is to say, the radially outer Holweck pumping region 27 has, with its outlet region 27a, a certain openness on the outlet side that is determined by the geometry of its Holweck channels 23. Correspondingly, the radially inner Holweck pumping region 29 has, with its inlet region 29a, a certain openness on the inlet side that is determined by the geometry of its Holweck channels 23.

[0076] 6, it can be seen that the opening on the inlet side is significantly smaller than the opening on the outlet side, since the height of the Holweck stages 21 in the radially inner Holweck pumping region 29 is smaller than the height of the Holweck stages 21 in the radially outer Holweck pumping region 27. For simplicity's sake, it is assumed that the width of the Holweck stages 21 and the number of Holweck channels 23, which are also variables specifying the degrees of freedom, are not different.

[0077] Furthermore, as can be seen from FIG. 6 , the radially outer Holweck pump region 27 is conically shaped, such that the height of the Holweck web 21 decreases in the pumping direction. The radially outer Holweck pump stage is therefore a conical pump stage. In this case, the conicity or the respective cone angle measured relative to the rotation axis 15 is determined by the channel bottom 19. Such conical Holweck pump stages are generally known. The radially inner Holweck stage here is cylindrically shaped. It is also generally known that both the radially outer and the radially inner Holweck pump stages each have a common Holweck rotor 25 that is conically shaped, as in the example of FIG. 6 .

[0078] While FIG. 6 shows a turbomolecular vacuum pump only diagrammatically, FIG. 7 shows a specific example according to the prior art.

[0079] Unlike Figure 6, here a pump housing 41 is additionally shown. Furthermore, Figure 7 shows the lower part 39 of the vacuum pump, in which the radially inner Holweck stator 17b is supported at its lower end. It can be seen that the Holweck rotor 25 extends with its free end into the lower part 39, so that the transition region 31 between the outlet region of the radially outer pump region 27 and the inlet region of the radially inner Holweck pump region 29 is located in the lower part 39.

[0080] In the example of Fig. 7, the radially inner Holweck stator 17b is a Holweck stator provided with Holweck stator threads on both sides, which together with a further radially inner Holweck stator 25 define a further Holweck pumping region 43. The Holweck pumping regions 29, 43 defined by the radially inner Holweck stator 17b are each cylindrical, while the radially outer Holweck region 27 is conically shaped, as in the example of Fig. 6.

[0081] As can be seen from Figure 7, when the width of the Holweck web and the number of Holweck channels are the same, due to the different heights of the Holweck web 21, the degree of opening on the inlet side of the radially inner Holweck pumping region 29 is again smaller than the degree of opening on the outlet side of the radially outer Holweck pumping region 27.

[0082] As will be explained below on the basis of an embodiment according to the invention in FIG. 8, the Holweck pump unit 13 of the turbomolecular vacuum pump according to the invention differs from the prior art, as explained above on the basis of FIGS. 6 and 7, in that the inlet area 29a of the radially inner Holweck pump area 29 has a greater degree of opening than the outlet area 27a of the radially outer Holweck pump area 27.

[0083] As mentioned at the beginning, this results in increased pumping speed and reduced backflow effects in the transition region and also at the radial gas inlet (interstage port) to the Holweck pump unit 13.

[0084] The axial height of the radial gas inlets with respect to the rotation axis, which is not shown here, can actually vary. Two different possibilities are illustrated in FIG. 8. Arrow 35 indicates a gas inlet opening into the transition region 31 between the outlet region 27a and the inlet region 29a. Alternatively, the radial gas inlet may open somewhat further upstream into the radially outer Holweck pumping region 27, as indicated by arrow 35' in FIG. 8. A radial gas inlet 35' located somewhat upstream of such a transition region 31 may be provided, for example, when the transition region 31 is located in the lower pump section 39, as illustrated in FIG. 7. Even with such a radial gas inlet 35', the increased pumping speed resulting from the relatively greater openness of the inlet region 29a of the radially inner Holweck pumping region 29 is advantageous.

[0085] As further shown in Figure 8, the two Holweck pumping regions 27, 29 are conically shaped, i.e. the height of the Holweck web 21 respectively decreases in the pumping direction. Thus, in the embodiment of Figure 8 as well, the gas to be pumped comes from the turbo vacuum pump 11, for example corresponding to the example of Figure 7, and enters the radially outer Holweck pumping region 27 via the axial gas inlet 33 and then via the transition region 31 to the radially inner Holweck pumping region 29 and from there to the gas outlet of the vacuum pump or to one or more further Holweck pumping regions. Thus, also in the turbomolecular vacuum pump according to the invention, the radially inner Holweck stator 17b of the Holweck pumping unit 13 can be a "double-sided" Holweck stator, which is provided with Holweck threads on both sides, i.e. radially outer and radially inner, which interact in a pumping manner with respective Holweck sleeves 25 mounted on a common Holweck hub 26.

[0086] As already mentioned elsewhere, the conicity of each of the Holweck pumping regions 27, 29 relative to the axis of rotation is measured. The cone angles βa and βi of the radially outer Holweck pumping region 27 or the radially inner Holweck pumping region 29 are plotted in Figure 8 using dashed auxiliary lines. The cone angles βa and βi may be the same or different.

[0087] Figure 9 clearly shows the geometry of the inlet region 29a of the radially inner Holweck pumping region 29, specifically in the cross-sectional plane extending perpendicular to the axis of rotation 15 where the Holweck channel 23 defined by the Holweck web 21 begins, i.e., where the pumping action of the radially inner Holweck pumping region 29 begins.

[0088] 9 also shows a Holweck rotor 25. The Holweck rotor 25 interacts with a Holweck thread of the radially inner Holweck stator 17b, which has a Holweck web 21. The Holweck thread on the cylindrical wall 17c of the Holweck stator 17b is multi-started and has eight Holweck channels 23 that pump in parallel, each pair separated by the Holweck web 21. The Holweck rotor 25 and the stator wall 17c may start from a different cross-sectional plane than the Holweck web 21. Nevertheless, the pumping action of the radially inner Holweck pumping region 29 begins where the Holweck channels 23 start, and the Holweck channels 23 are commonly defined by the channel bottom 19, i.e., the outer surface of the stator wall 17c, and the Holweck web 21, and require the radially inner surface of the Holweck rotor 25 for pumping.

[0089] Thus, a geometric situation can be envisaged in the inlet region 29a of the Holweck pump unit 13 according to the invention, for example in Fig. 8, as shown schematically in Fig. 9. The radially outer Holweck stator 17a is not shown in Fig. 9. However, the geometric situation also corresponds to the outer Holweck stator 17a, where the Holweck thread of the radially outer Holweck stator 17a interacts with the radially outer surface of the Holweck rotor 25, and, as mentioned elsewhere, the pumping action of the radially outer Holweck pump region may end in a cross-sectional plane different from the cross-sectional plane in which the pumping action of the radially inner Holweck stator 27a begins.

[0090] In a known manner, the tip of the Holweck web 21 is slightly spaced from the inner surface of the Holweck rotor 25 facing the Holweck web 21. The actual size ratio is not shown to scale in Figure 9. When viewed in the illustrated cross section, the tip of the Holweck web 21 lies on a circle, indicated by a dashed line in Figure 9, which, as mentioned above, is centered on the axis of rotation 15 and which has a smaller radius than the inner surface of the Holweck rotor 25.

[0091] As mentioned above, the Holweck channels 23 perform the pumping action. The size of the free cross-section providing pumping in the inlet region 29a, i.e., in the cross-sectional plane shown in FIG. 9, is therefore determined by the number of Holweck channels 23 and their free cross-section, which in turn is determined by the width B and height H (i.e., the distance between the web tip and the channel bottom 19) of the defining Holweck webs 21, measured in the circumferential direction. The relatively narrow annular region between the tip of the Holweck webs 21 and the inner surface of the Holweck rotor 25 does not count toward the free cross-section in the inlet region 29a and, in that sense, does not contribute to the openness of the inlet side of the radially inner Holweck pumping region 29. The same applies to the openness of the outlet side of the radially outer Holweck pumping region 27, not shown in FIG. 9.

[0092] Thus, variations in both the inlet-side and outlet-side openness can be achieved by varying the width B, height H, or number of the Holweck webs 21. These measures may also be combined in any way. For example, if the number of Holweck webs 21 and thus Holweck channels 23 is constant, the openness can be varied by varying the height H and width B of the Holweck webs. The height H can be varied by having a cylindrical region of the Holweck stator 17b, i.e., the wall 17c of the Holweck stator 17b (from which the Holweck webs 21 project radially outward), have a smaller wall thickness, thereby bringing the channel bottom 19 closer to the rotation axis 15, when the radial distance between the tips of the Holweck webs 21 and the inner surface of the Holweck rotor 25 is constant. Additionally or alternatively, the height H of the Holweck webs 21 can be varied by varying the radial distance between the web tips and the inner surface of the Holweck rotor 25, if this is possible without impairing the basic functionality of the Holweck pump stage, i.e., the pumping action. [Explanation of symbols]

[0093] 11 Turbomolecular pump unit 11a Moving blade 12 rotors 13 Holbeck Pump Unit 15 Rotation axis 17a Radially outer Holweck stator 17b Radially inner Holweck stator 17c Radially inner Holweck stator wall 19 Channel Bottom 21 Holbeck Webb 23 Holbeck Channel 25 Holbeck Rotor 26 Holbeck Hub 27 Radially outer Holweck pump region 27a Exit area 29 Radially inner Holweck pump region 29a Entrance area 31 Transition Zone 33 Axial gas inlet 35, 35' Radial gas inlet 39 Lower or intermediate part 41 Pump housing 43 Further Holbeck Pump Area H Holbeck web height B Holbeck web width βa Cone angle of the radially outer Holweck pump region βi Cone angle of the radially inner Holweck pump region 111 Turbomolecular pump 113 Intake flange 115 Pump intake 117 Pump exhaust port 119 Housing 121 Lower part 123 Electronics Housing 125 electric motor 127 Accessory Connection 129 Data Interface 131 Current supply connection 133 Ventilation intake 135 Seal gas connection 137 Motor Room 139 Coolant Connection 141 Bottom surface 143 Screw 145 Bearing cover 147 Fixed hole 148 Coolant line 149 Rotor 151 Rotation axis 153 rotor shaft 155 Moving blade 157 Stator blade 159 Spacer ring 161 rotor hub 163 Holbeck Rotor Sleeve 165 Holbeck Rotor Sleeve 167 Holbeck Sterling Sleeve 169 Holbeck Sterling Sleeve 171 Holbeck Gap 173 Holbeck Gap 175 Holbeck Gap 179 Connection Channels 181 Rolling bearings 183 Permanent magnet type magnetic bearing 185 Splash Nut 187 discs 189 Insert 191 Rotor side bearing half 193 Stator side bearing half 195 Ring Magnet 197 Ring Magnet 199 Bearing clearance 201 Support part 203 Support part 205 Radial Struts 207 Cover Elements 209 Support Ring 211 Fixing ring 213 Disc spring 215 Emergency bearings or safety bearings 217 Motor Stator 219 Intermediate Room 221 Wall section 223 Labyrinth Seal

Claims

1. 1. A turbomolecular vacuum pump, comprising: at least one turbomolecular pump unit (11) and at least one Holweck pump unit (13) arranged downstream of said turbomolecular pump unit (11) in the pumping direction, said Holweck pump unit (13) having at least two Holweck stages arranged concentrically inside and outside each other with respect to a common rotation axis (15) and successive in the pumping direction, Each Holweck stage has a Holweck stator (17a, 17b) with a Holweck thread portion, the Holweck thread portion having a Holweck web (21) protruding from a channel bottom (19) and a Holweck channel (23) defined by the wall of the Holweck web (21), facing a common Holweck rotor (25) of the Holweck pump unit (13) that rotates about a rotation axis (15) during operation, the Holweck rotor (25) defining, together with one Holweck stator (17a), a radially outer Holweck pump area (27) and, together with the other Holweck stator (17b), a radially inner Holweck pump area (29); 1. A turbomolecular vacuum pump, in which an outlet area (27a) of a radially outer Holweck pumping area (27) transitions into an inlet area (29a) of a radially inner Holweck pumping area (29) in a transition area (31) at the free end of the Holweck rotor (25), In addition to the axial gas inlet (33) into the radially outer Holweck pumping region (27), a radial gas inlet (35, 35') into the Holweck pumping unit (13) is provided, which opens into the transition region (31) or into the radially outer Holweck pumping region (27) upstream of the transition region (31), in particular into the downstream half or into the downstream one-third, one-quarter, one-fifth or one-sixth of the radially outer Holweck pumping region (27), 1. A vacuum pump comprising: an outlet region (27a) and an inlet region (29a) each having a free cross-section defined by said Holweck channels (23) in a cross-sectional plane extending perpendicular to the axis of rotation (15), in which the pumping action ends and begins, respectively, and wherein the free cross-section of the inlet region (29a) is greater by a factor f>1 than the free cross-section of the outlet region (25a).

2. 2. Vacuum pump according to claim 1, wherein 1<f<3, preferably 1<f<2, suitably 1.2<f<1.5 applies.

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

4. 4. A vacuum pump according to claim 1, wherein in each cross-sectional plane, the width (B) of the Holweck web (21) in the inlet region (29a) is greater than the width in the outlet region (27a), measured in the circumferential direction.

5. 5. A vacuum pump according to claim 1, wherein the number of Holweck webs (21) in a radially inner Holweck pumping region (29) is smaller than the number of Holweck webs (21) in a radially outer Holweck pumping region (27).

6. 6. A vacuum pump according to any one of claims 1 to 5, wherein the Holweck stator (17b) defining a radially inner Holweck pumping region (29) is a Holweck stator provided with Holweck threads on both sides, and the Holweck stator defines a further Holweck pumping region (43) further radially inward together with a further Holweck rotor (25).

7. 7. A vacuum pump according to claim 6, wherein the Holweck stator (17b), provided with Holweck threads on both sides, has a wall thickness measured radially, and in the inlet region (29a) of the radially inner Holweck pump region (29), the wall thickness is less than the height of the Holweck web (21).

8. 8. A vacuum pump according to claim 1, wherein the radially outer Holweck pumping region (27) and / or the radially inner Holweck pumping region (29) are each formed conically such that the height of the Holweck web (21) decreases continuously in the pumping direction.

9. 9. A vacuum pump according to claim 8, wherein the cone angle (βa) defined by the channel bottom (19) of the radially outer Holweck pumping region (27) and the cone angle (βi) defined by the channel bottom (19) of the radially inner Holweck pumping region (29) are at least substantially identical or different from each other, in particular the cone angle (βa) of the radially outer Holweck pumping region (27) is larger or smaller than the cone angle (βi) of the radially inner Holweck pumping region (29).

10. 10. A vacuum pump according to claim 1, wherein at least one pumping section of the radially outer Holweck stator (17a), which together with the Holweck rotor (25) defines a radially outer Holweck pumping region (27), is of one-piece construction, in particular a radial gas inlet (35) opening into the radially outer Holweck pumping region (27) upstream of the transition region (31) and extending through the one-piece pumping section of the radially outer Holweck stator (17a).

11. 11. A vacuum pump according to any one of claims 1 to 10, wherein a radial gas inlet (35) extends through the pump housing (41) above a lower or intermediate part (39) of the vacuum pump, where at least a part of the transition area (31) is located.

12. 12. A vacuum pump according to claim 1, wherein at least one further radial gas inlet is arranged upstream of the radial gas inlet (35) into the Holweck pump unit (13), in particular the further radial gas inlet opens into the Holweck pump unit (13) or the turbomolecular pump unit (11).

13. In vacuum systems, 13. A vacuum system comprising: a vacuum pump according to any one of claims 1 to 12; and a recipient to be evacuated, the vacuum pump being configured as a split-flow vacuum pump, the vacuum pump having one or more radial inlets, the inlets being connected during operation to respective openings in the recipient, one of the radial inlets being a radial gas inlet (35) opening into a transition region (31) or into a Holweck pump region (27) radially outward of and upstream of the transition region (31).

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

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