Vacuum pump and method of operating a vacuum pump

Abstract

The present invention relates to a vacuum pump having a gas inlet, a gas outlet, a housing enclosing a pump chamber for a gas to be pumped from the inlet to the outlet in a pumping direction, and at least one intermediate gas inlet opening into the pump chamber between the gas inlet and the gas outlet, as viewed in the pumping direction. The pump further comprises a rotor carrying pump-active components of at least one turbomolecular pump stage, and a drive unit for driving the rotor to rotate, said drive unit being arranged in a drive chamber enclosed by the housing. A cooling gas inlet is provided through which a cooling gas can be introduced into the housing such that it can flow from the cooling gas inlet via the drive chamber to the gas outlet, in particular wherein the cooling gas inlet opens into the drive chamber.

Description

[0001] The invention relates to a vacuum pump with multiple inlets. Such pumps are generally known and are also referred to as split-flow vacuum pumps. The terms "SplitFlow" and "SPLIT-FLOW" are registered trademarks of Pfeiffer Vacuum GmbH. Other names for such a vacuum pump include multi-inlet vacuum pump and multi-inlet vacuum pump.

[0002] Split-flow vacuum pumps are used primarily for pumping multiple chambers (recipients) at different pressures, especially those arranged in series. Split-flow vacuum pumps typically comprise two to six inlets spaced along a pump axis. Split-flow vacuum pumps usually comprise a stack, i.e., a series arrangement, of pumping stages connected one behind the other within a pump chamber. The pumping stages are supported by a rotor, which is driven to rotate during pump operation.

[0003] In a typical application, the highest pumping speed and the lowest pressure range are available at the first inlet, i.e., the one upstream of all other inlets. The downstream inlets, according to their sequence, are located in higher pressure ranges and deliver lower pumping speeds. However, split-flow vacuum pumps are also known, in which the highest pumping speed or the highest pumping speed is available at an inlet located between two other inlets. The specific design of a particular split-flow pump depends particularly on the specific application.

[0004] In various applications, it has been shown that the rotor temperature of split-flow vacuum pumps increases significantly, especially when there is a high gas load. If the ambient temperature is comparatively high, e.g., due to waste heat from the application, the problem is exacerbated.

[0005] In the context of the present disclosure, the term "gas load" refers to a gas flow rate, i.e. a molecular amount of gas per unit of time under standard conditions (specified in sccm = "Standard Cubic Centimeters per Minute").

[0006] Since the rotor typically rotates very quickly during pump operation, all mechanical components involved must be manufactured with great precision and coordinated with each other. Only small tolerances are acceptable. Therefore, excessive heat buildup of the rotor is problematic due to thermal expansion effects alone. Ultimately, rotor heat buildup often limits the pump's effective performance.

[0007] It is therefore an object of the present invention to provide a vacuum pump of the type mentioned at the outset which addresses the problem described.

[0008] This object is achieved by a pump having the features of claim 1.

[0009] According to the invention, such a pump is provided with a gas inlet, a gas outlet, a housing enclosing a pump chamber for a gas to be pumped from the inlet to the outlet in a pumping direction, and at least one intermediate gas inlet opening into the pump chamber between the gas inlet and the gas outlet, as viewed in the pumping direction. It further comprises a rotor carrying pump-active components of at least one turbomolecular pump stage and a drive unit for driving the rotor in a rotary motion, which drive unit is arranged in a drive chamber enclosed by the housing. A cooling gas inlet is provided, through which a cooling gas can be introduced into the housing such that it can flow from the cooling gas inlet via the drive chamber to the gas outlet, in particular wherein the cooling gas inlet opens—directly or indirectly—into the drive chamber.

[0010] The pump according to the invention is therefore a split-flow vacuum pump, a pump type that is used in particular in mass spectroscopy, where comparatively high gas loads often occur at the intermediate gas inlet.

[0011] The inventors recognized that introducing an additional gas load (namely the cooling gas) contributes to effective cooling of the rotor, which ultimately increases the pump's performance. This measure is counterintuitive given prevailing theory, as it would further increase the total gas load to be pumped by the pump, thus resulting in increased power consumption and, consequently, an increase in rotor temperature.

[0012] According to the invention, the cooling gas is guided through the drive chamber to ensure efficient heat transport.

[0013] It can be provided that the cooling gas flows from the drive chamber to the gas outlet via the pump chamber. The flow path of the cooling gas can be configured such that it flows into the pump chamber behind the last pump-active component in the pumping direction in order to minimize the flow path of the cooling gas in the pump chamber.

[0014] Further embodiments of the present invention are set forth in the claims, the description and the accompanying drawings.

[0015] According to one embodiment, at least two, in particular at least three intermediate gas inlets are provided.

[0016] At least one further pumping stage may be provided, which is designed as a Holweck stage. In particular, the intermediate gas inlet opens into the Holweck stage.

[0017] According to a further embodiment, the drive chamber is separated from the pump chamber by a drive housing. The drive housing can be formed, for example, by a portion of a base or lower part, which is part of the housing of the vacuum pump, and a cover-shaped element.

[0018] To ensure a seal between the drive chamber and the pump chamber, a labyrinth seal can be provided, acting between the drive housing and the rotor. The seal can be formed by at least one groove associated with the drive housing or the rotor, and at least one web engaging therein, which is associated with the rotor or the drive housing. Such a groove / web pairing can also be referred to as a "turn." Preferably, the seal comprises at least two turns, in particular three to five turns. In special cases, more than five turns can also be provided.

[0019] In principle, a temperature sensor can be provided with which a temperature is measured on a static component of the pump, for example, on an outer bearing ring of a rotor bearing, which allows conclusions to be drawn about the rotor temperature (indirect measurement). However, a temperature measuring device is preferably provided with which the temperature of the rotor can be determined, in particular wherein the temperature measuring device comprises an infrared sensor. Direct measurement of the rotor temperature is more accurate and allows the operation of the vacuum pump to be controlled even more effectively based on the measured data.

[0020] The temperature measuring device can be arranged on a surface of the drive housing facing the pump chamber. In particular, the surface extends transversely, preferably perpendicularly, to a rotational axis of the rotor. If the temperature measuring device is an infrared sensor, with the aforementioned orientation of the surface in the axial direction, it can "look" at a component of the rotor and determine the temperature prevailing there. This component can, for example, be a Holweck hub that supports pump-active sleeves.

[0021] Even greater flexibility is achieved if the cooling gas inlet is designed such that a cooling gas mass flow can be variably adjusted, e.g., by means of a manually adjustable screw. This can also be achieved by means of a controllable valve. A control device can be provided with which the controllable valve can be controlled. In particular, the control device is designed and configured such that the controllable valve can be controlled as a function of the rotor temperature.

[0022] The turbomolecular pump stage may comprise at least two rotor / stator pairs, wherein the rotors and / or stators of the two pairs are configured differently in order to provide the desired performance characteristics. In particular, the last rotor of the turbomolecular pump stage has a different configuration than the other rotors of the stage.

[0023] The present invention further relates to a method for operating a turbomolecular pump, in particular a pump according to one of the embodiments described above, having at least one gas inlet, having a gas outlet, and having a housing enclosing a pump chamber for a gas to be pumped from the inlet to the outlet in a pumping direction. The turbomolecular pump further comprises a rotor carrying pump-active components of at least one turbomolecular pump stage, and a drive unit for driving the rotor to rotate, which drive unit is arranged in a drive chamber enclosed by the housing. A cooling gas inlet is provided through which a cooling gas is introduced into the housing such that it can flow from the cooling gas inlet via the drive chamber and the pump chamber to the gas outlet, in particular wherein the cooling gas inlet opens directly or indirectly into the drive chamber.

[0024] According to the invention, the introduced cooling gas load amounts to at least 1%, preferably 2% to 6%, of the total gas load entering the turbomolecular pump through the inlet or - if more than one inlet is provided - through the inlets (total gas load). It has been shown that only at a cooling gas load of more than 1%, preferably more than 2%, of the total gas load is a sufficiently effective cooling performance achieved, which allows, for example, more drive power to be released and the pump's pumping power to be increased. In many applications, at a cooling gas load of more than 6% of the total gas load, no significantly improved cooling performance can be observed and / or the additional gas load due to the cooling gas has a detrimental effect. However, for some applications, higher cooling gas loads of up to 10%, 20%, or even 30% of the total gas load are conceivable.

[0025] In a turbomolecular pump in which a Holweck stage and an intermediate gas inlet opening into it are provided downstream of the turbomolecular pump stage in the pumping direction, the cooling gas load introduced can be at least 1%, preferably 1% to 8%, of the gas load entering the turbomolecular pump through the intermediate gas inlet.

[0026] According to one embodiment, the drive chamber is separated from the pump chamber by a drive housing. This can be a wall that divides the interior of the pump into the two chambers. The interior of the pump can have additional chambers in addition to the drive chamber and the pump chamber.

[0027] A labyrinth seal can be provided, acting between the drive housing and the rotor. The seal is formed by at least one groove and at least one web engaging in this groove. A groove-web pair forms a seal flight. With three or fewer webs and / or grooves (flights), the cooling gas load can be selected so that it amounts to at least 2% of the total gas load. According to the invention, it was recognized that the greater the sealing effect of the labyrinth seal, the lower the cooling gas load required for the desired cooling effect.

[0028] Even more efficient, demand-based operation of the turbomolecular pump can be achieved if the cooling gas load is controlled as a function of the temperature of a component of the turbomolecular pump, in particular as a function of the rotor temperature. The rotor temperature can be determined directly, for example, using an infrared sensor. However, it is also possible to determine the rotor temperature based on the temperature of another component of the pump (indirect measurement). The measured temperature can be used—additionally or alternatively—to control the pump's performance.

[0029] The invention is described below by way of example with reference to the drawings. 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. 2shown 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. 2 Fig. 6 shows a known vacuum pumping system with a split-flow vacuum pump, which can be designed according to the invention, and with a device to be evacuated, and Fig. 7 schematically shows part of an embodiment of a split-flow vacuum pump. Fig. 8 shows another embodiment of a split-flow vacuum pump.

[0030] 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.

[0031] The inlet flange 113 forms when the vacuum pump is aligned 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.

[0032] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0033] 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.

[0034] 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 way than in Fig. 1 As shown. Embodiments of the vacuum pump can also be realized in which the underside 141 is arranged facing sideways or upwards rather than downwards. In principle, any angle is possible.

[0035] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in an upright position.

[0036] On the underside 141, which is 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.

[0037] Mounting holes 147 are also arranged on the underside 141, via 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.

[0038] 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.

[0039] 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.

[0040] A rotor 149 is arranged in the housing 119 and has a rotor shaft 153 rotatable about a rotation axis 151.

[0041] The turbomolecular pump 111 comprises several turbomolecular pumping 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 pumping stage. The stator disks 157 are held at a desired axial distance from one another by spacer rings 159.

[0042] 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.

[0043] 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 rotation 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 rotation axis 151 and nested within one another in the radial direction.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 roller 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, and at the same time small enough so that collision of the rotor-side structures with the stator-side structures is prevented under all circumstances.

[0053] 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.

[0054] The motor stator 217 is fixed in the housing within the motor compartment 137 provided for the electric motor 125. A seal gas, also referred to as purge gas, which can be, for example, air or nitrogen, can enter the motor compartment 137 via the seal gas connection 135. The seal 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 the vacuum pressure generated by the backing pump connected to the pump outlet 117.

[0055] 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.

[0056] The turbomolecular vacuum pump described above, which is known from the prior art, is not a split-flow vacuum pump. However, the design and operation of this turbomolecular vacuum pump also apply in principle to the vacuum pump according to the invention.

[0057] Fig. 6 shows a vacuum system with a split-flow vacuum pump 10 and a device 12 to be evacuated by means of this vacuum pump 10.

[0058] In this exemplary embodiment, the device 12 comprises three vacuum chambers 14 arranged one behind the other, wherein gas entering the lowest chamber 14 can reach the respective subsequent chamber 14, as indicated by the arrows. Each chamber has a gas outlet 16, which leads to an inlet 11, 11a, or 33, also referred to as a port, of the vacuum pump 10. The inlet 33 of the vacuum pump 10, corresponding to the gas outlet 16 of the lowest chamber 14, is a further inlet within the meaning of the invention, which—as described in more detail elsewhere—leads to a Holweck region of the vacuum pump 10.

[0059] The split-flow vacuum pump 10, which is shown here only schematically, has a housing 15 and, within the housing 15 in a pump chamber 17, a rotor shaft 18 which rotates during operation and thus sets rotating components of the individual pump stages attached to it in rotation about a rotation axis A which is defined by the rotor shaft 18.

[0060] In the example shown here, these pump stages are turbomolecular pump stages 47, which are followed in a pumping direction P in the pump chamber 17 by a Holweck region with two Holweck pump stages 19, 21.

[0061] From this Holweck area 19, 21 is in Fig. 6 only schematically a Holweck rotor 31 is shown, which comprises a Holweck sleeve 32 and a Holweck hub 30, via which the Holweck sleeve 32 is attached to the rotor shaft 18. This Holweck rotor 31 belongs to both Holweck pump stages 19, 21, as described below in connection with Fig. 7 is explained in more detail.

[0062] Gas to be pumped thus enters the pump chamber 17 of the split-flow vacuum pump 10 from the device 12 to be evacuated via its outlets 16 of the individual chambers 14 at different points via the inlets 11, 33 and is pumped by means of the individual pump stages 47, 19, 21 mentioned in the pumping direction P to an outlet 13, via which the gas leaves the vacuum pump 10. The basic structure and its functionality explained above are generally known and can - as also mentioned in the introductory section - be varied in many ways, in particular with regard to the number and arrangement of the chambers 14 to be evacuated of the device 12 to be evacuated, as well as with regard to the number, arrangement, and design of the individual pump stages of the split-flow vacuum pump 10.

[0063] The Fig. 7 The schematically shown area of a split-flow vacuum pump 10 would be Fig. 6shown vacuum pump 10 are located approximately (apart from the position of a pump base) at the location shown in Fig. 6 indicated by a dashed square V, i.e. to the left of the Fig. 7 not shown rotation axis A at the lower end of the Holweck sleeve 32 of the Holweck rotor 31 pointing towards the outlet 13.

[0064] In Fig. 7 The housing 15, a lower part 51, an outer Holweck stator 23, an inner Holweck stator 25 and the Holweck sleeve 32 of the Holweck rotor 31 are partially shown.

[0065] The Holweck stators 23, 25 are each provided with a Holweck thread on their pump-active side facing the Holweck sleeve 32. In Fig. 7For each Holweck stator 23, 25, a Holweck groove 55 is shown, which is delimited by a web 53. These are conical Holweck stators 23, 25, in which the groove base diameter varies, whereby the height of the webs 53 also varies and the web tip diameter and thus the radial distance of the webs 53 from the Holweck sleeve 32 is constant in the axial direction.

[0066] Thus, the Holweck sleeve 32 and the radially outer Holweck stator 23 form a radially outer Holweck pumping region 27 and the Holweck sleeve 32 and the radially inner Holweck stator 25 form a radially inner Holweck pumping region 29.

[0067] The two Holweck pumping areas 27, 29 merge into one another in a transition area 43. Relative to the pumping direction P indicated by an arrow, the height of the webs 53 decreases in the pumping direction P in both Holweck pumping areas 27, 29, whereby in the radially outer Holweck pumping stage 19, the groove base diameter decreases in the pumping direction P, whereas in the radially inner Holweck pumping stage 21, the groove base diameter increases in the pumping direction P.

[0068] It is known in the art to provide a tap into the Holweck region 27, 29 at the transition region 43 via an inlet of the split-flow vacuum pump. According to the invention, however, the tap is positioned downstream relative to the pumping direction P and thus relative to the direction of flow of the gas to be pumped, with the tap being made laterally into the inner Holweck stator 23.

[0069] According to the invention, an inlet channel 35 extends from a further inlet 33 of the vacuum pump to an opening 37 in the radially inner Holweck pumping region 29, wherein the opening 37 is formed in the groove 55 of the radially inner Holweck stator 25.

[0070] In the embodiment shown here, the inlet channel 35 consists of an inlet section 49 which initially runs in the radial direction and which, like the further inlet 33, is also formed in the pump base 51. The inlet section 49 extends in an axial direction - relative to the rotation axis A (not shown here) (cf. Fig. 6 ) - extending section in the lower part 51, which is immediately adjoined by an axial channel section 39 formed in the radially inner Holweck stator 25. This axial channel section 39 merges into a radial channel section 41 of the inner Holweck stator 25, which leads to the mouth 37.

[0071] The inlet channel 35 extending from the further inlet 33 to the orifice 37 thus has an inlet section 49 formed in the lower part 51, which begins at the further inlet 33, and an orifice section formed in the radially inner Holweck stator 25 and formed by the two mentioned channel sections 39, 41, which ends at the orifice 37.

[0072] Since the radially inner Holweck stator 25 has a comparatively large wall thickness—measured in the radial direction—the axial channel section 39 and the radial channel section 41 can be provided with a comparatively large diameter, thereby achieving relatively high conductance values. The two channel sections 39, 41 can be manufactured by drilling or milling.

[0073] Depending on the respective requirements, a different axial position can also be selected for the orifice 37. The length of the axial channel section 39 can then be varied accordingly. The radial bore or radial milling 41 can, in principle, be made at any desired axial position in order to reach the bore forming the axial channel section 39, extending from the base side 45 of the radially inner Holweck stator 25 facing the lower part 51.

[0074] Furthermore, several channels can also open into the radially inner Holweck pumping area 29, ie several openings 37 can be provided which differ in terms of their axial position and / or their circumferential position - in each case relative to the rotation axis A (cf. Fig. 6 ) - differ from each other.

[0075] In principle, it is additionally or alternatively possible to provide one or more taps in the radially outer Holweck pumping area 27, ie to form one or more orifices in the radially outer Holweck stator 23 and to connect these via a channel having a suitable course to the further inlet 33 or to another inlet for gas to be pumped.

[0076] In other embodiments, the inlet channel can be formed in another component separate from the outer Holweck stator, in particular in an intermediate component, which is also referred to as an intermediate piece. A gas guide for tapping via the further inlet 33 therefore does not have to be provided, as in the exemplary embodiment of the Fig. 7 through the pump base 51, but can also be done in other ways. As mentioned elsewhere, the gas can be guided through a section of the pump that is integrally formed with the Holweck stator.

[0077] Fig. 8 shows a section of a cross-section of a split-flow vacuum pump 10a, which comprises at least one turbomolecular pump stage 20a (only the lower part shown) and a Holweck stage 20b. The stages 20a, 20b can be constructed in a basically known manner, including the Fig. 3 , 4 , 5 and 7 shown.

[0078] The split-flow vacuum pump 10a has an intermediate gas inlet (not shown) that opens into the Holweck stage 20b. The intermediate gas inlet can be designed as Fig. 6 and 7 shown. However, in connection with the present invention, its design is not important. Additionally or alternatively, at least one further intermediate gas inlet can be provided between two turbomolecular pump stages 20a (cf. inlet 11a, Fig. 6 The number, arrangement and / or design of the intermediate gas inlets can be freely selected according to requirements.

[0079] The split-flow vacuum pump 10a may have a housing (not shown in detail) similar to that of the pump 111 described above. The housing has a pump chamber 17 in which the pump stages 20a, 20b are arranged. Furthermore, a drive or motor chamber 137a is provided, which is formed separately from the pump chamber 17. The motor chamber 137a is defined by a portion of a base or lower part 121a and a cover 221a. It accommodates a motor 125a, which serves to drive a rotor 149a with a rotor shaft 153a.

[0080] A rotor hub 161a is arranged on the rotor shaft 153a, which supports Holweck rotor sleeves of the Holweck stage 20b. To separate the motor chamber 137a from the pump chamber 17, a labyrinth seal 223a is provided between the hub 161a and the cover 221a. Its sealing effect is based on the extension of the flow path through the gap to be sealed, thereby significantly increasing the flow resistance for a gas flowing through the gap. The seal comprises grooves (formed here, for example, on the hub 161a) and webs engaging therein (formed here, for example, on the cover 221a). Each groove / web pairing forms a flight 223b. The higher the number of threads 223a (here 5 as an example, the number can be selected as required), the greater the sealing effect of the seal 223a - assuming otherwise the same dimensions / design of the grooves and webs.

[0081] In order to cool the rotor 149a, which heats up during operation of the pump 10a, a cooling gas (symbolized by the arrows KG) is introduced into the motor compartment 137a. For this purpose, a separate inlet or an already existing inlet or fluid channel can be used. The inlet can, for example, comprise a channel that runs transversely, in particular perpendicularly, to the axis of rotation A. However, it is also possible to first guide the cooling gas through a space or area that accommodates components of a bearing of the rotor 149a before it reaches the motor compartment 137a. Such a bearing space can be part of the drive compartment or merge into it. For example, a bearing cover that closes off the bearing compartment from the outside space (comparable to the cover 145 in the Fig. 3 ) have a cooling gas seal.

[0082] The inlet used to introduce the cooling gas is preferably designed such that the amount of cooling gas introduced can be selectively selected. For example, a manually operable screw or similar device is provided for this purpose, which is inserted into a cooling gas channel connecting the engine compartment 137a with the outside. However, it is also possible to provide a controllable valve that can be controlled as needed by a control device (not shown), which is, for example, part of a control unit of the pump 10a or integrated therein, in order to regulate the cooling gas load as needed.

[0083] The introduced cooling gas fills the motor compartment 137a and also enters the gap formed by the labyrinth seal 223a. According to the invention, it was recognized that the cooling gas in the gap contributes significantly to the transfer of heat from the hub 161a to the cover 221a. The cooling gas thus functions as a heat conductor between the components 161a, 221a. To fulfill this function efficiently, a certain amount of gas is required in the gap. In principle, heat conduction increases with an increasing amount of gas in the gap. It was recognized that with a cooling gas load of more than 1% of the total gas load, a condition arises in which heat conduction is significantly improved. While a higher relative cooling gas load ensures improved heat conduction on the one hand, it also increases the friction acting between the components 161a, 221a on the other.The total gas load is the sum of all gas flows flowing into the pump 10a through the (main) inlet and the intermediate gas inlet(s).

[0084] An optimal setting of the relative cooling gas load, i.e., the ratio of cooling gas load to total gas load (greater than 1% according to the invention), for the specific application requires a balance between the advantages of improved heat conduction and the disadvantages of increased friction. Extensive studies have shown that a relative cooling gas load in the range of 2% to 6% is particularly effective in most cases.

[0085] When feeding a gas at an intermediate gas inlet in the area of a Holweck stage (intermediate gas load), a relative cooling gas load related to the intermediate gas load in the range of 1% to 8% has proven to be advantageous as an additional condition.

[0086] However, for certain applications, relative cooling gas loads (relative to the total gas load) of up to 30% are also conceivable.

[0087] The design of the labyrinth seal 223a is also a relevant factor for heat conduction efficiency. It has been recognized that with increasing number of turns of the labyrinth seal 223a, a lower relative cooling gas load is required. For example, in some applications, with a number of turns of five, a relative cooling gas load of just over 1% is sufficient, while with a number of turns of three or fewer—under otherwise comparable conditions—a minimum cooling gas load of at least 2% is required.

[0088] The cooling gas flowing through the labyrinth seal 223a passes behind the last pump-active component of the Holweck stage 20b, so that the flow path of the cooling gas to the pump outlet is minimal.

[0089] The heat dissipated via the cooling gas from the hub 161a to the cover 221a is transferred from the cover 221a to the base part 121a. Since the components 221a and the base part 121a are generally metallic, heat dissipation is very effective. This is improved if the cover 221a and a wall section 121b of the base part 121a connected to it, which also defines the motor compartment 137a, have comparatively thick walls (e.g., > 2 mm or even > 4 mm). A good thermal coupling of the cover 221a with the wall section 221b also contributes to improved heat dissipation.

[0090] The cover 221a carries an infrared temperature sensor 57 on its side facing the Holweck hub 161a, which runs perpendicular to the rotor shaft 153a. This sensor "looks" in the axial direction and measures the infrared radiation emitted by the hub 161a, which is a measure of the temperature of the rotor 149a. The temperature determined by the sensor 57 can be used to control the pump 10a. For example, the power of the pump 10a can be limited if the temperature of the rotor 149a exceeds a certain threshold. The same applies to the reverse case: If the temperature falls below a certain threshold, the pump power can be increased if necessary.

[0091] The cooling of the rotor 149a can be achieved by introducing the cooling gas. It is particularly advantageous if the introduction of the cooling gas itself is controlled based on the measured rotor temperature. Thus, when cooling requirements increase, more cooling gas can be introduced into the motor compartment 137a, for example, by opening a controllable valve in a cooling gas supply channel slightly wider. Conversely, the supply of cooling gas can be reduced if it is detected that the temperature of the rotor 149a is below a critical temperature in order to reduce friction in the area of the labyrinth seal 223a.

[0092] In other words, a control of the pump 10a can adjust the heat transfer provided by the cooling gas from the rotor 149a to the lower part 121a and thus ultimately the cooling capacity as needed based on the measured rotor temperature.

[0093] In this context, it should be pointed out again that the inventive concept is based on the finding that efficient cooling of the rotor 149a is not achieved by heat dissipation through the cooling gas, but rather by a targeted increase in heat conduction in the area of the labyrinth seal 223a.

[0094] Due to the spatial proximity of the section of the hub 161a whose temperature is measured (for better heat radiation, this section can be roughened and / or blackened) and the labyrinth seal 223a enabling the heat transfer between the rotor 149a and the cover 221a, the effect of the cooling gas can be observed in a timely manner.

[0095] In principle, this concept can also be implemented with an indirect measurement of the rotor temperature (e.g. in the area of the rotor bearing). List of reference symbols

[0096] 111Turbomolecular pump 113Inlet flange 115Pump inlet 117Pump outlet 119Housing 121, 121aLower section 121bWall section 123Electronics housing 125, 125aElectric motor 127Accessory connection 129Data interface 131Power supply connection 133Venting inlet 135Purge gas connection 137, 137aMotor compartment 139Coolant connection 141Underside 143Screw 145Bearing cover 147Mounting hole 148Coolant line 149, 149aRotor 151Rotation axis 153, 153aRotor shaft 155Rotor disc 157Stator disc 159Spacer ring 161, 161a Rotor hub 163 Holweck rotor sleeve 165 Holweck rotor sleeve 167 Holweck stator sleeve 169 Holweck stator sleeve 171 Holweck gap 173 Holweck gap 175 Holweck gap 179 Connecting channel 181 Rolling bearing 183 Permanent magnet bearing 185 Injection nut 187 Washer 189 Insert 191 Rotor-side bearing half 193 Stator-side bearing half 195 Ring magnet 197 Ring magnet 199 Bearing gap 201 Support section 203 Support section 205 Radial strut 207 Cover element 209 Support ring 211 Fastening ring 213 Disc spring 215 Emergency orSafety bearing 217Motor stator 219Gap 221, 221aWall, cover 223, 223aLabyrinth seal 223bGear . 10, 10a Vacuum pump 11 Inlet 12 Device to be evacuated 13 Outlet 14 Vacuum chamber 15 Housing 16 Gas outlet 17 Pump chamber 18 Rotor shaft 19 Outer Holweck pumping stage 21 Inner Holweck pumping stage 20a, 47 Turbomolecular pumping stage 20b Holweck stage 23 Outer Holweck stator 25 Inner Holweck stator 27 Outer Holweck pumping area 29 Inner Holweck pumping area 30 Holweck hub 31 Holweck rotor 32 Holweck sleeve 11a, 33 Further inlet, intermediate gas inlet 35 Inlet channel 37 Orifice 39 Axial channel section 41 Radial channel section 43 Transition area 45 Base side 49 Inlet section 51 Component 53Bridge 55Groove 57Infrared temperature sensor PPumping direction ARotation axis KGCooling gas

Claims

1. Vacuum pump, with - a gas inlet (11), - a gas outlet (13), - a housing (15) which encloses a pump chamber (17) for a gas to be pumped from the inlet (11) to the outlet (13) in a pumping direction (P), and - at least one intermediate gas inlet (11a, 33) which, viewed in the pumping direction (P), opens into the pump chamber (17) between the gas inlet (11) and the gas outlet (13), further comprising a rotor (149a) which carries pump-active components of at least one turbomolecular pump stage (20a), and a drive unit (125a) for driving the rotor (149a) to a rotary movement, which is arranged in a drive chamber (137a) enclosed by the housing (15), wherein a cooling gas inlet is provided, through which a cooling gas can be introduced into the housing (15) in such a way that it flows from the cooling gas inlet via the Drive chamber (137a) can flow to the gas outlet (13), in particular wherein the cooling gas inlet opens into the drive chamber (137a).

2. Vacuum pump according to claim 1, wherein at least two, in particular at least three intermediate gas inlets (11a, 33) are provided.

3. Vacuum pump according to claim 1 or 2, wherein at least one further pumping stage is provided, which is designed as a Holweck stage (20b).

4. Vacuum pump according to claim 3, wherein the intermediate gas inlet (33) opens into the Holweck stage (20b).

5. Vacuum pump according to one of the preceding claims, wherein the drive chamber (137a) is separated from the pump chamber (17) by a drive housing (221a, 121b).

6. Vacuum pump according to claim 5, wherein a labyrinth seal (223a) is provided which acts between the drive housing (221a, 121b) and the rotor (149a).

7. Vacuum pump according to one of the preceding claims, wherein a temperature measuring device (57) is provided with which the temperature of the rotor (149a) can be determined, in particular wherein the temperature measuring device (57) comprises an infrared sensor.

8. Vacuum pump according to claim 7, wherein the temperature measuring device (57) is arranged on a surface of the drive housing (221a, 121b) facing the pump chamber (17), in particular wherein the surface extends transversely, preferably perpendicularly to a rotational axis (A) of the rotor (149a).

9. Vacuum pump according to one of the preceding claims, wherein the cooling gas inlet is designed such that a cooling gas mass flow is variably adjustable, in particular by means of a controllable valve.

10. Vacuum pump according to claim 9, wherein a control device is provided with which the controllable valve can be controlled, in particular wherein the control device is designed and arranged such that the controllable valve can be controlled as a function of a temperature of the rotor (149).

11. Vacuum pump according to one of the preceding claims, wherein the turbomolecular pumping stage (20a) has at least two rotor / stator pairs, wherein the rotors and / or the stators of the two pairs are designed differently.

12. A method for operating a turbomolecular pump, in particular a vacuum pump according to one of the preceding claims, with - at least one gas inlet (11), - a gas outlet (13) and - a housing (15) enclosing a pump chamber (17) for a gas to be pumped from the inlet (11) to the outlet (13) in a pumping direction (P), further comprising a rotor (149a) carrying pump-active components of at least one turbomolecular pump stage (20a), and a drive unit (125a) for driving the rotor (149a) to rotate, which is arranged in a drive chamber (137a) enclosed by the housing (15), wherein a cooling gas inlet is provided, through which a cooling gas is introduced into the housing (15) in such a way that it can flow from the cooling gas inlet via the drive chamber (137a) and the pump chamber (17) to the gas outlet (13), in particular wherein the cooling gas inlet is in the drive chamber (137a), and wherein the introduced cooling gas load is at least 1%, preferably 2% to 6%,of the total gas load entering the turbomolecular pump (20a) through the inlet (11) or - if more than one inlet is provided - through the inlets (11, 11a, 33).

13. The method according to claim 12, wherein a Holweck stage (20b) and an intermediate gas inlet (11a, 33) opening into it are provided downstream of the turbomolecular pump stage (20a) in the pumping direction (P), and wherein the cooling gas load introduced is at least 1%, preferably more than 1% and up to 8%, of the gas load entering the turbomolecular pump through the intermediate gas inlet (11a, 33).

14. The method according to claim 12 or 13, wherein the drive chamber (137a) is separated from the pump chamber (17) by a drive housing (221a, 121b) and wherein a labyrinth seal (223a) is provided which acts between the drive housing (221a, 121b) and the rotor (149a) and which is formed by at least one groove and at least one web engaging therein, wherein the cooling gas load is at least 2% of the total gas load when there are 3 or fewer webs and / or grooves.

15. The method according to claim 12, 13 or 14, wherein the introduced cooling gas load is controlled as a function of a temperature of a component of the turbomolecular pump, in particular as a function of a temperature of the rotor (149a).

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