Vacuum pump with optimized Holbeck pump stage to compensate for temperature-related performance losses

Description

[0001] The present invention relates to a vacuum pump, also referred to herein as a pump, in particular a turbomolecular pump, according to the preamble of claim 1, comprising at least one Holweck pump stage, which includes a Holweck rotor and a Holweck stator, wherein the Holweck rotor comprises a rotor shaft with a hub provided thereon and at least one Holweck rotor sleeve provided on the hub, which concentrically surrounds the rotor shaft, and wherein the Holweck stator comprises a Holweck stator sleeve arranged concentrically to the Holweck rotor sleeve, which has a fixed end attached to a stationary housing section of the vacuum pump, a free end opposite the fixed end in the axial direction, an inner surface with an internal thread formed thereon, and an outer surface with an external thread formed thereon.

[0002] Such a generic vacuum pump is essentially derived from US 2003 / 103 842 A1.

[0003] Vacuum pumps are used in various fields of engineering. Depending on the requirements, vacuum pumps have one or more pumping stages. Holweck pumping stages generally belong to the class of molecular vacuum pumps and generate a molecular flow by rotating a Holweck rotor relative to a stationary Holweck stator. This flow causes the vacuum pump to heat up during operation. A vacuum pump can, in principle, comprise one or more Holweck stages, which can be operated in series or in parallel. Holweck stages are typically used in turbomolecular vacuum pumps and are connected downstream of one or more turbomolecular pumping stages in the flow direction.

[0004] A Holweck stage comprises a Holweck rotor and a Holweck stator. The Holweck rotor has a rotor shaft to which one or more Holweck rotor sleeves are concentrically attached by means of, for example, a disc-shaped Holweck hub. The Holweck stator is equipped with a single- or multi-start Holweck thread. The gas molecules to be conveyed are transported by the rotating motion of the Holweck rotor relative to the Holweck stator along the threads from an inlet to an outlet of the respective Holweck pumping stage. A thread comprises a spirally circumferential Holweck channel bounded by the walls of a web, in which the gas molecules are conveyed when the rotor sleeve rotates relative to the stator sleeve. To minimize backflow losses, the width of the radial Holweck gap between the web or thread crests and the rotor sleeve should be kept as small as possible.

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

[0006] The Holweck stator comprises a fixed end attached to a stationary housing section of the vacuum pump, for example by a press fit; a free end located axially opposite the fixed end near the rotor hub; an inner surface with an internal thread; and an outer surface with an external thread. Due to the small cross-sectional area of ​​the Holweck stator, a comparatively high temperature difference within the stator is required to dissipate the input heat. This results in a temperature profile with the highest temperature at the free end.

[0007] The heating of the Holweck stator sleeve causes it to expand radially towards its free end, resulting in the Holweck gap deviating increasingly from its nominal width from the fixed end towards the free end. This, in turn, leads to an undesirable decrease in the pumping speed and thus the pumping capacity of the vacuum pump during operation.

[0008] The invention is therefore based on the objective of providing a solution to the problem described above, namely that the pumping capacity of a vacuum pump with a Holweck pump stage decreases due to temperature-induced deformations of the Holweck stator or the Holweck stator sleeve. In other words, the invention aims to ensure that the pumping speed of a vacuum pump, for which it is designed, is achieved even under operating conditions with elevated temperatures.

[0009] This problem is solved with a vacuum pump having the features of claim 1, in part by the fact that, in the cold state of the vacuum pump at room temperature, the internal thread at the free end of the Holweck stator sleeve has a smaller nominal internal diameter than at the free end of the Holweck stator sleeve, and that, correspondingly, the external thread in the cold state of the vacuum pump at room temperature also has a smaller nominal external diameter at the free end of the Holweck stator sleeve than at the fixed end of the Holweck stator sleeve.In particular, according to the invention, the nominal outer diameter of the external thread of the Holweck stator sleeve decreases in the cold state of the vacuum pump in such a way that, in the operating warm steady state of the vacuum pump, a radial Holweck gap forms between the Holweck rotor sleeve and the external thread, and in particular the thread crests of the external thread, which has a substantially constant width between the fixed end and the free end of the Holweck stator sleeve. Additionally or alternatively, according to the invention, the nominal inner diameter of the internal thread of the Holweck stator sleeve decreases in the cold state of the vacuum pump in such a way that, in the operating warm steady state, a radial Holweck gap forms between the Holweck rotor sleeve and the external thread, and in particular between the thread crests of the external thread, which has a substantially constant width between the fixed end and the free end of the Holweck stator sleeve.In the thermally steady state of the vacuum pump, a radial Holweck gap forms between the Holweck rotor sleeve and the internal thread, in particular the thread crests of the internal thread, which has a substantially constant width between the fixed end and the free end of the Holweck stator sleeve.

[0010] When the present invention refers to a "cold state" of the vacuum pump, this refers to the temperature of the vacuum pump when it is permanently switched off and operating at room temperature on the order of approximately 20°C. In other words, the vacuum pump, and in particular the Holweck stator sleeve, has a temperature on the order of approximately 20°C when cold. In contrast, when the present invention refers to a "warm steady state" or a "thermally steady state" of the vacuum pump, this refers to the temperature the vacuum pump reaches when it is continuously operated at its rated speed.

[0011] Due to the fact that the Holweck stator sleeve, in the manner according to the invention, has nominal inner and nominal outer diameters at its free end – measured between the web and thread crests of the internal and external threads, respectively – and thus the Holweck stator sleeve has smaller inner and outer circumferences at its free end than at its fixed end, the Holweck stator sleeve can expand radially at its free end during operation due to temperature changes until the inner and / or outer Holweck gap has the desired shape.

[0012] According to the invention, the Holweck stator sleeve thus has a shape in the cold state that deviates from the desired shape of the Holweck stator sleeve for achieving a desired Holweck gap. During operation, the Holweck stator sleeve can therefore deform due to temperature changes in such a way that the desired Holweck gap is established in the stationary, operating-temperature state of the vacuum pump.

[0013] Preferred embodiments of the invention will now be discussed. Further embodiments may be described in the dependent claims, the description of the figures, and the drawings themselves.

[0014] According to one embodiment, the hub is attached to the rotor shaft, and the Holweck rotor sleeve is attached to the hub. The hub and rotor shaft are thus separately handleable parts that are either detachably or permanently connected during assembly of the vacuum pump. Similarly, in this embodiment, the hub and the Holweck rotor sleeve are separately handleable parts that are only detachably or permanently connected during assembly of the vacuum pump.

[0015] Alternatively, in addition to the embodiment described above, it can be provided that the hub is integrally formed with the rotor shaft, whereas the Holweck rotor sleeve is attached to the hub, or that the Holweck rotor sleeve is integrally formed with the hub and the hub is attached to the rotor shaft.

[0016] Since the Holweck stator is designed as a double-sided Holweck stator with a Holweck stator sleeve featuring internal and external threads, the Holweck rotor consequently has an inner and an outer Holweck rotor sleeve, both of which concentrically surround the rotor shaft. The outer Holweck rotor sleeve concentrically surrounds the Holweck stator sleeve, and the Holweck stator sleeve concentrically surrounds the inner Holweck rotor sleeve. The inner Holweck rotor sleeve, together with the internal thread of the Holweck stator sleeve, thus forms an inner Holweck pumping stage, whereas the outer Holweck rotor sleeve, together with the external thread of the Holweck stator sleeve, forms an outer Holweck pumping stage. According to one aspect of the present invention, it can be provided that, in the cold state, the shape of the Holweck gap of both the inner and outer Holweck pumping stages deviates from the desired shape of the respective Holweck gap.However, due to the fact that the Holweck stator sleeve has smaller nominal inner and outer diameters at its free end than at its fixed end, it can expand radially at its free end during operation of the vacuum pump due to temperature changes, so that both the inner and outer Holweck pump stage have a Holweck gap in the thermally steady state that at least approximates the desired shape.

[0017] While the inner diameter of the internal thread of the Holweck stator sleeve can decrease stepwise towards its free end, a preferred embodiment provides that, in the cold state of the vacuum pump, the nominal inner diameter of the internal thread of the Holweck stator sleeve decreases continuously or steadily towards its free end. For example, the nominal inner diameter of the internal thread can decrease linearly or according to a concave curve as one approaches the free end of the Holweck stator sleeve.

[0018] Similarly, when the vacuum pump is cold, the nominal outside diameter of the external thread of the Holweck stator sleeve can decrease stepwise or continuously towards its free end. In the latter case, the nominal outside diameter can decrease linearly or according to a function with convex curvature as one approaches the free end of the Holweck stator sleeve. In any case, the nominal inside and outside diameters decrease progressively or monotonically towards the free end of the Holweck stator sleeve, meaning that the Holweck stator sleeve has its smallest nominal inside and outside diameters at its free end. This is due to the fact that the Holweck stator reaches its highest operating temperature at its free end, resulting in the greatest thermally induced expansion there.Accordingly, the Holweck stator sleeve has both the smallest nominal inner and the smallest nominal outer diameter at its free end, which in a sense compensates for the temperature-related deformation of the Holweck stator.

[0019] To ensure that a Holweck gap of constant size can establish itself in the thermally steady state, it proves advantageous if, when the vacuum pump is cold, both the nominal inner and outer diameters of the internal and external threads of the Holweck stator sleeve decrease steadily towards the free end of the sleeve, as previously described. This is because the temperature of the Holweck stator sleeve also increases steadily towards its free end during operation, reaching its highest temperature at the free end.The decrease in the nominal inner and outer diameters towards the free end of the Holweck stator sleeve thus follows, in a sense, the temperature profile of the Holweck stator sleeve towards its free end, whereby the temperature-related expansion of the Holweck stator sleeve can be specifically compensated for in such a way that the Holweck gap of both the inner and outer Holweck pump stage has an essentially constant size in the operating-temperature steady state.

[0020] According to yet another embodiment, it can be provided that the internal thread of the Holweck stator sleeve has a constant thread depth between its fixed end and its free end when the vacuum pump is cold, and that the inner surface of the Holweck stator sleeve, which forms the groove base of the internal thread, defines a core inner diameter of the internal thread that decreases towards the free end of the Holweck stator sleeve when the vacuum pump is cold.In addition or alternatively, according to a further embodiment, it can be provided that the external thread of the Holweck stator sleeve has a constant thread depth between its fixed end and its free end when the vacuum pump is cold, and that the outer surface of the Holweck stator sleeve, which forms the thread root of the external thread, defines a core outer diameter of the external thread that decreases towards the free end of the Holweck stator sleeve when the vacuum pump is cold.

[0021] In the case of constant thread depths of both the internal and external threads, and decreasing core inner and core outer diameters of the internal and external threads in the direction of the free end of the Holweck stator sleeve, a further embodiment may provide that the Holweck stator sleeve has a wall thickness that is constant between the fixed end and the free end of the Holweck stator sleeve, provided that, in the cold state of the vacuum pump, the core inner and core outer diameters of the internal and external threads decrease equally or at the same rate in the direction of the free end of the Holweck stator sleeve.

[0022] Contrary to the embodiment described above, it is not necessarily required that the core inner and core outer diameters of the internal and external threads decrease to the same extent towards the free end of the Holweck stator sleeve; rather, according to a further embodiment, the Holweck stator sleeve can have a wall thickness that decreases towards the free end of the Holweck stator sleeve, for example continuously or in steps, in which case either the core outer diameter decreases more than the core inner diameter towards the free end of the Holweck stator sleeve or the core outer diameter decreases more than the core inner diameter towards the free end of the Holweck stator sleeve.

[0023] As an alternative to the embodiments described above with a constant depth of internal and / or external thread, a further embodiment may provide that the inner surface of the Holweck stator sleeve defines a core inner diameter of the internal thread which is constant between the fixed end and the free end of the Holweck stator sleeve when the vacuum pump is cold, wherein in this case the internal thread has a thread depth that increases towards the free end of the Holweck stator sleeve, which means that the inner diameter of the internal thread decreases towards the free end of the Holweck stator sleeve in the desired manner.In addition or alternatively, according to a further embodiment, it can be provided that the outer surface of the Holweck stator sleeve defines a core outer diameter of the external thread which is constant in the cold state of the vacuum pump between the fixed end and the free end of the Holweck stator sleeve, wherein in this case the external thread has a thread depth that decreases in the direction of the free end of the Holweck stator sleeve, so that the outer diameter of the external thread decreases in the desired manner in the direction of the free end of the Holweck stator sleeve.

[0024] The invention is described below with reference to the accompanying figures. These show: Fig. 1 a perspective view of a turbomolecular pump not according to the invention, Fig. 2 a view of the underside of the turbomolecular pump of Fig. 1 , Fig. 3 a cross-section of the turbomolecular pump along the in Fig. 2Section line AA shown, Fig. 4 a cross-sectional view of the turbomolecular pump along the in Fig. 2 Section line BB, Fig. 5 shows a cross-sectional view of the turbomolecular pump along the line shown in Fig. 2Fig. 6 shows a section through a schematic Holweck pump stage with a Holweck stator sleeve designed according to the invention in the cold state at a room temperature of approximately 20°C; Fig. 7 shows a schematic section through another Holweck stator sleeve in the cold state at a room temperature of approximately 20°C, wherein the Holweck stator sleeve has cylindrical inner and outer surfaces; Fig. 8 shows a schematic section of yet another Holweck stator sleeve in the cold state at a room temperature of approximately 20°C, wherein the inner and outer surfaces of the Holweck stator sleeve taper in stages; Fig. 9 shows a schematic section of an embodiment of a Holweck rotor that can be used in the vacuum pump according to the invention; Fig.Fig. 10 a schematic sectional view of another embodiment of a Holweck rotor that can be used in the vacuum pump according to the invention, and Fig. 11 a schematic sectional view of a further embodiment of a Holweck rotor that can be used in the vacuum pump according to the invention.

[0025] The in Fig. 1 The turbomolecular pump 111 shown comprises a pump inlet 115 surrounded by an inlet flange 113, to which a receiver (not shown) can be connected in a manner known per se. The gas from the receiver can be drawn out of the receiver via the pump inlet 115 and conveyed through the pump to a pump outlet 117, to which a backing pump, such as a rotary vane pump, can be connected.

[0026] The inlet flange 113 forms a Fig. 1The upper end of the housing 119 of the vacuum pump 111. The housing 119 comprises a lower part 121, to which an electronics housing 123 is attached laterally. The electronics housing 123 contains electrical and / or electronic components of the vacuum pump 111, e.g., for operating an electric motor 125 located in the vacuum pump (see also Fig. 3 The electronics housing 123 has several connections 127 for accessories. In addition, a data interface 129, e.g. according to the RS485 standard, and a power supply connection 131 are located on the electronics housing 123.

[0027] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0028] The housing 119 of the turbomolecular pump 111 has a flood inlet 133, in particular in the form of a flood valve, through which the vacuum pump 111 can be flooded. In the area of ​​the lower part 121, a purge gas connection 135, also referred to as a purge gas connection, is also arranged, through which purge gas can be supplied to protect the electric motor 125 (see e.g. Fig. 3 The gas pumped by the pump can be introduced into the motor compartment 137, in which the electric motor 125 is housed in the vacuum pump 111. Two coolant connections 139 are also arranged in the lower part 121, one of which serves as an inlet and the other as an outlet for coolant that can be directed into the vacuum pump for cooling purposes. Other existing turbomolecular vacuum pumps (not shown) are operated exclusively with air cooling.

[0029] The lower side 141 of the vacuum pump can serve as a base, allowing the vacuum pump 111 to be operated standing upright on its underside 141. Alternatively, the vacuum pump 111 can be attached to a receiver via the inlet flange 113 and thus operated in a suspended position. Furthermore, the vacuum pump 111 can be designed to operate even when oriented differently than described. Fig. 1 As shown. It is also possible to implement embodiments of the vacuum pump in which the underside 141 can be arranged facing sideways or upwards instead of downwards. In principle, any angle is possible.

[0030] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in a standing position.

[0031] On the underside 141, which is in Fig. 2As shown, various screws 143 are arranged, by means of which components of the vacuum pump, not further specified here, are fastened to one another. For example, a bearing cover 145 is attached to the underside 141.

[0032] Mounting holes 147 are also arranged on the underside 141, via which the pump 111 can be attached to a support surface, for example. This is not possible with other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here.

[0033] In the Figures 2 to 5 A coolant line 148 is shown, in which the coolant introduced and removed via the coolant connections 139 can circulate.

[0034] Like the sectional views of the Figures 3 to 5 As shown, the vacuum pump comprises several process gas pumping stages for conveying the process gas present at the pump inlet 115 to the pump outlet 117.

[0035] A rotor 149 is arranged in the housing 119, which has a rotor shaft 153 rotatable about a rotation axis 151.

[0036] The turbomolecular pump 111 comprises several turbomolecular pump stages connected in series to provide pumping action. These stages have several radial rotor disks 155 attached to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and fixed in the housing 119. Each rotor disk 155 and an adjacent stator disk 157 form a turbomolecular pump stage. The stator disks 157 are held at a desired axial distance from each other by spacer rings 159.

[0037] The vacuum pump also includes Holweck pump stages arranged radially within one another and connected in series to effectively pump the pump. Other turbomolecular vacuum pumps exist (not shown) that do not have Holweck pump stages.

[0038] The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical Holweck rotor sleeves 163, 165 attached to and supported by the rotor hub 161, which are oriented coaxially to the axis of rotation 151 and nested one inside the other in the radial direction. Furthermore, two cylindrical Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the axis of rotation 151 and nested one inside the other in the radial direction.

[0039] The pump-active surfaces of the Holweck pump stages are formed by the outer surfaces, i.e., the radial inner and / or outer surfaces, of the Holweck rotor sleeves 163, 165 and the Holweck stator sleeves 167, 169. The radial inner surface of the outer Holweck stator sleeve 167 faces the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together they form the first Holweck pump stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 faces the radial outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together they form a second Holweck pump stage. The radial inner surface of the inner Holweck stator sleeve 169 lies opposite the radial outer surface of the inner Holweck rotor sleeve 165, forming a radial Holweck gap 175, and together they form the third Holweck pumping stage.

[0040] At the lower end of the Holweck rotor sleeve 163, a radially extending channel can be provided, through which the radially outer Holweck slot 171 is connected to the central Holweck slot 173. Furthermore, a radially extending channel can be provided at the upper end of the inner Holweck stator sleeve 169, through which the central Holweck slot 173 is connected to the radially inner Holweck slot 175. This connects the nested Holweck pump stages in series. A connecting channel 179 to the outlet 117 can also be provided at the lower end of the radially inner Holweck rotor sleeve 165.

[0041] The aforementioned pump-active surfaces of the Holweck stator sleeves 167, 169 each have several Holweck grooves spiraling around the axis of rotation 151 in the axial direction, while the opposite outer surfaces of the Holweck rotor sleeves 163, 165 are smooth and drive the gas forward in the Holweck grooves for the operation of the vacuum pump 111.

[0042] 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.

[0043] In the area of ​​the rolling bearing 181, a conical injection nut 185 with an outer diameter increasing towards the rolling bearing 181 is provided on the rotor shaft 153. The injection nut 185 is in sliding contact with at least one wiper of a fluid reservoir. In other existing turbomolecular vacuum pumps (not shown), an injection screw may be provided instead of an injection nut. Since different designs are thus possible, the term "injection tip" is also used in this context.

[0044] The operating fluid reservoir comprises several stacked absorbent discs 187, which are impregnated with an operating fluid for the rolling bearing 181, e.g. with a lubricant.

[0045] During operation of the vacuum pump 111, the operating fluid is transferred by capillary action from the fluid reservoir via the wiper to the rotating injection nut 185 and, as a result of centrifugal force, is conveyed along the injection nut 185 in the direction of the increasing outer diameter of the injection nut 185 towards the rolling bearing 181, where it performs, for example, a lubricating function. The rolling bearing 181 and the fluid reservoir are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

[0046] The permanent magnet bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each containing a ring stack of several axially stacked permanent magnet rings 195, 197. The ring magnets 195, 197 face each other, forming a radial bearing gap 199, with the rotor-side ring magnets 195 arranged radially outside and the stator-side ring magnets 197 radially inside. The magnetic field present in the bearing gap 199 induces magnetic repulsive forces between the ring magnets 195, 197, which result in the radial support of the rotor shaft 153. The rotor-side ring magnets 195 are supported by a support section 201 of the rotor shaft 153, which radially surrounds the ring magnets 195 on the outside.The stator-side ring magnets 197 are supported by a stator-side support section 203, which extends through the ring magnets 197 and is suspended from radial struts 205 of the housing 119. Parallel to the axis of rotation 151, the rotor-side ring magnets 195 are fixed by a cover element 207 coupled to the support section 201. The stator-side ring magnets 197 are fixed parallel to the axis of rotation 151 in one direction by a retaining ring 209 connected to the support section 203 and a retaining ring 211 also connected to the support section 203. A disc spring 213 may also be provided between the retaining ring 211 and the ring magnets 197.

[0047] Within the magnetic bearing, an emergency or catch bearing 215 is provided, which runs freely without contact during normal operation of the vacuum pump 111 and only engages when there is excessive radial deflection of the rotor 149 relative to the stator, in order to form a radial stop for the rotor 149 and thus prevent a collision between the rotor-side and stator-side structures. The catch bearing 215 is designed as an unlubricated rolling bearing and forms a radial gap with the rotor 149 and / or the stator, which causes the catch bearing 215 to be disengaged during normal pump operation. The radial deflection at which the catch bearing 215 engages is dimensioned to be large enough so that the catch bearing 215 does not engage during normal operation of the vacuum pump, and simultaneously small enough to prevent a collision between the rotor-side and stator-side structures under all circumstances.

[0048] The vacuum pump 111 comprises the electric motor 125 for rotating the rotor 149. The armature of the electric motor 125 is formed by the rotor 149, whose rotor shaft 153 extends through the motor stator 217. A permanent magnet arrangement can be arranged radially on the outside or embedded in the section of the rotor shaft 153 extending through the motor stator 217. A space 219 is arranged between the motor stator 217 and the section of the rotor 149 extending through the motor stator 217. This space comprises a radial motor gap through which the motor stator 217 and the permanent magnet arrangement can magnetically influence each other to transmit the drive torque.

[0049] The motor stator 217 is fixed in the housing within the motor compartment 137 provided for the electric motor 125. A purge gas, also known as a sealing gas, which can be, for example, air or nitrogen, can enter the motor compartment 137 via the purge gas connection 135. This purge gas protects the electric motor 125 from process gas, e.g., from corrosive components of the process gas. The motor compartment 137 can also be evacuated via the pump outlet 117, meaning that the vacuum pressure in the motor compartment 137 is at least approximately equal to that produced by the backing pump connected to the pump outlet 117.

[0050] Between the rotor hub 161 and a wall 221 bounding the engine compartment 137, a so-called labyrinth seal 223, which is known per se, can also be provided, in particular to achieve a better seal of the engine compartment 217 against the radially outside Holweck pump stages.

[0051] The following will now refer to the Figs. 6 to 8 Various embodiments of Holweck pump stages 10 designed according to the invention are described, which can be installed in the turbomolecular vacuum pump 111 instead of the previously described Holweck pump stage, whereby the other structure of the turbomolecular vacuum pump 111 as well as the basic structure of the Holweck pump stage with three nested pump stages, which are hereinafter also generically referred to as a single "Holweck pump stage".

[0052] Again Fig. 6 As can be seen from the diagram, the Holweck pump stage 10 shown there has essentially the same structure as the Holweck pump stage described in the diagram. Figs. 1 to 5The vacuum pump 111 described above is also included. In particular, the Holweck pump stage 10 also has a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical rotor sleeves 163, 165 attached to and supported by the rotor hub 161, which are oriented coaxially to the axis of rotation 151 and are nested one inside the other in the radial direction. Furthermore, two cylindrical Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the axis of rotation 151 and are nested one inside the other in the radial direction.

[0053] As explained above, the outer Holweck stator sleeve 167, together with the outer Holweck rotor sleeve 163, forms a first, or outer, Holweck pumping stage. The outer Holweck rotor sleeve 163, together with the inner Holweck stator sleeve 169, forms a second, or middle, Holweck pumping stage, and likewise, the inner Holweck stator sleeve 169, together with the inner Holweck rotor sleeve 165, forms a third, or inner, Holweck pumping stage. Therefore, the illustrated setup corresponds to the one described previously with reference to the Figs. 3 to 5 was described.

[0054] The Holweck stator sleeves 167, 169 also exhibit Fig. 6Several Holweck grooves spirally around the axis of rotation 151 in the axial direction. In the illustrated inner Holweck stator sleeve 169, these grooves are formed by webs 16 on both the inner surface 12 and the outer surface 14 of the stator sleeve 169, which spirally around the axis of rotation 151 and are only shown schematically here. The tips of the webs 16 thus form the respective nominal inner and outer diameters of the respective threads, whereas the inner and outer surfaces 12 and 14 correspond to the core inner and core outer diameters dki and dka of the respective threads 18 and 20, respectively. Since the respective Holweck gap refers to the distance between the tips of the webs 16 and the pump-effective surface of the rotor sleeves 163, 165, the envelope surrounding the web or thread tips is shown here, to which the reference numeral "26" is assigned.

[0055] Again Fig. 6 As can be further seen, in the illustrated Holweck pump stage 10, it is provided according to the invention that, in the cold state of the vacuum pump at approximately 20°C room temperature, the internal thread 18 at the free end 22 of the Holweck stator sleeve 169 has a smaller nominal inner diameter dni than at the fixed end 24 of the Holweck stator sleeve 169. Likewise, in the cold state, the external thread 20 at the free end 22 also has a smaller nominal outer diameter dna than at the fixed end 24 of the Holweck stator sleeve 169, where it is attached to a stationary housing section of the vacuum pump 111.

[0056] With reference to the Fig. 6In the illustrated embodiment, it is particularly provided that the inner and outer surfaces 12, 14 of the stator sleeve 169, on which the internal and external threads 18, 20 are formed, have a conical shape and taper continuously, especially towards the free end 22 of the Holweck stator sleeve 169. In contrast, the thread depth of the internal and external threads 18, 20, and the radial dimension of the webs 16, are constant between the fixed end 24 and the free end 22 of the stator sleeve 169. Likewise, in this embodiment, the Holweck stator sleeve 169 has a wall thickness that is constant between the fixed end 24 and the free end 22 of the Holweck stator sleeve 169.

[0057] Alternatively, the Holweck stator sleeve 169 may have a wall thickness that decreases towards the free end 22 of the Holweck stator sleeve 169, in which case it may also be provided that the thread height of the internal thread 18 increases towards the free end 22 and / or the thread height of the external thread 20 decreases towards the free end 22 in order to ensure that the internal and external threads at the free end 22 of the Holweck stator sleeve 169 have a smaller nominal internal and external diameter dni, dna than at the fixed end 24 of the Holweck stator sleeve 169.

[0058] Due to the tapered shape of the Holweck stator sleeve 169 and its outer casing 26, the Holweck stator sleeve 169 can expand radially due to temperature changes during operation of the vacuum pump 111, as shown in the Fig. 5as indicated by a dashed line. In the operating temperature steady state of the vacuum pump 111, an internal Holweck gap 175 can thus form between the inner Holweck rotor sleeve 165 and the double-sided Holweck stator sleeve 169, which has a substantially constant size or width between the fixed end 24 and the free end 22. Likewise, due to the shape of the Holweck stator sleeve 169 tapering towards the free end 22, an external Holweck gap 173 can form between the Holweck stator sleeve 169 and the outer rotor sleeve 163 in the operating temperature state of the vacuum pump 111, which has a substantially constant size or width between the fixed end 24 and the free end 22.

[0059] In contrast to the previous one referring to the Fig. 6 In the described embodiment, it is the case that in the embodiment of Fig. 7It is provided that the Holweck stator sleeve 169 does not taper conically on the inside and outside towards its free end 22; rather, in the embodiment of the Fig. 7 It is provided that the Holweck stator sleeve 169, and in particular its inner and outer surfaces 12, 14, have a substantially cylindrical shape. However, in order to ensure that the internal and external threads 18, 22 at the free end 22 of the stator sleeve 169 have a smaller nominal inner and outer diameter dni, respectively, than at the fixed end 24, it is provided in the embodiment of the Fig. 7 It is provided that the internal thread 18 has a thread depth that increases towards the free end 22 of the Holweck stator sleeve 169, whereas the external thread 20 has a thread depth that decreases towards the free end 22 of the Holweck stator sleeve 169. This allows, as with the previously mentioned [reference to the] Fig. 6In the described embodiment, it is ensured that the outer casing 26 of the Holweck stator sleeve 169 tapers both internally and externally towards the free end 22. The stator sleeve 169 can thus expand due to temperature changes during operation of the vacuum pump 111, so that, in the thermally steady state, internal and external Holweck gaps 173, 175 can form, which have a substantially constant size between the fixed end 24 and the free end 22 of the Holweck stator sleeve 169.

[0060] During the Fig. 8In the illustrated embodiment, the wall thickness of the Holweck stator sleeve 169 is constant, but it tapers in stages towards the free end 22 of the stator sleeve 169. To ensure that the outer casing 26 has nominal inner and outer diameters dni and dna, respectively, at the free end 22 when cold, which are smaller than the corresponding diameters at the fixed end 24, this embodiment provides that the thread depth of the internal thread 18 increases across each stage towards the free end 22 before decreasing abruptly at the transition to the next stage. Conversely, the thread depth of the external thread decreases in the region of each stage towards the free end 22 before increasing abruptly at the transition to the next stage, so that the nominal outer diameter dna decreases as desired towards the free end 22.

[0061] Although this will not be discussed in more detail here, the embodiments can be described in accordance with the Figs. 6, 7 and 8 can also be combined with each other, whereby it can additionally be provided that the wall thickness of the Holweck stator sleeve 169 is not constant, without deviating from the concept according to the invention, according to which the nominal inner and nominal outer diameters of the internal and external threads at the free end 22 of the stator sleeve 169 are smaller than at the fixed end 24 of the same, for which purpose the thread depth of the internal and external threads 18, 20 can vary in the axial direction of the stator sleeve 169 in order to ensure that the outer shell 26 tapers conically towards the free end 22 on both the inside and outside sides, regardless of the shape of the inner and outer surfaces 12, 14.

[0062] In the previously mentioned reference to the Figures 1 to 5In the described turbomolecular vacuum pump 111, the hub 161 and the rotor shaft 153 are separately handleable parts that are only detachably or permanently connected to each other during the assembly of the vacuum pump 111. Similarly, in this embodiment, the hub 161 and the Holweck rotor sleeves 163, 165 are also separately handleable parts that are only detachably or permanently connected to each other during the assembly of the vacuum pump. This design is particularly suitable for use in medium and large turbomolecular vacuum pumps.

[0063] Alternatively, according to the in the Fig. 9 In the schematically depicted embodiment, the hub 161 is integrally formed with the rotor shaft 153, and the Holweck rotor sleeves 163, 165 are also integrally formed with the hub 161. The Holweck rotor is therefore a single, one-piece component.

[0064] Alternatively, according to the in the Fig. 10 In the schematically illustrated embodiment, it is provided that only the two Holweck rotor sleeves 163, 165 are integrally formed with the hub 161, whereas the hub 161 and the rotor shaft 153 are separately handleable parts which are only detachably or indetachably connected to each other during the assembly of the vacuum pump.

[0065] Ultimately, according to the [document / section], it can [be] Fig. 11 In the schematically illustrated embodiment, it is provided that only the rotor shaft 153 is integrally formed with the hub 161, whereas the hub 161 and the Holweck rotor sleeves 163, 165 are separately handleable parts which are only detachably or permanently connected to each other during the assembly of the vacuum pump. This embodiment is particularly suitable for use in smaller turbomolecular vacuum pumps. Reference symbol list

[0066] 10 Holweck pump stage 12 Inner surface 14 Outer surface 16 Webs 18 Internal thread 20 External thread 22 Free end 24 Fixed end 26 Enveloping 111 Turbomolecular pump 113 Inlet flange 115 Pump inlet 117 Pump outlet 119 Housing 121 Bottom section 123 Electronics housing 125 Electric motor 127 Accessory connection 129 Data interface 131 Power supply connection 133 Flood inlet 135 Sealing gas connection 137 Motor compartment 139 Coolant connection 141 Bottom side 143 Screw 145 Bearing cover 147 Mounting hole 148 Coolant line 149 Rotor 151 Rotation shaft 153 Rotor shaft 155 Rotor disc 157 Stator disc 159 Spacer ring 161 Rotor hub 163 Holweck rotor sleeve 165 Holweck rotor sleeve 167 Holweck stator sleeve 169 Holweck stator sleeve 171 Holweck gap 173 Holweck gap 175 Holweck gap 179 Connecting channel 181 Rolling bearing 183 Permanent magnet bearing 185 Injection nut 187 Washer 189 Insert 191 Rotor-side bearing 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 Mounting ring 213 Disc spring 215 Emergency orFanglager 217Motorstator 219Zwischenraum 221Wandung 223Labyrinthdichtung . dniNenninnendurchmesser dnaNennaußendurchmesser dkiKerninnendurchmesser dkaKernaußendurchmesser

Claims

1. A vacuum pump (111), in particular a turbomolecular vacuum pump (111), comprising at least one Holweck pump stage (10) which comprises a Holweck rotor and a Holweck stator; wherein the Holweck rotor comprises a rotor shaft (153) with a hub (161) provided thereat as well as at least one Holweck rotor sleeve (163, 165) which is provided at the hub (161) and which concentrically surrounds the rotor shaft; and wherein the Holweck stator comprises a Holweck stator sleeve (169) which is arranged concentrically with respect to the Holweck rotor sleeve (163, 165) and which has a fixed end (24) attached to a stationary housing section of the vacuum pump (111), a free end (22) disposed opposite the fixed end (24) in the axial direction as well as an inner surface (12) with an internal thread (18) formed thereat and an outer surface (14) with an external thread (20) formed thereat; wherein, in the cold state of the vacuum pump (111), the internal thread (18) at the free end (22) of the Holweck stator sleeve (169) has a smaller nominal inner diameter (dni) than at the fixed end (24) of the Holweck stator sleeve (169), and wherein, in the cold state of the vacuum pump (111), the external thread (20) at the free end (22) of the Holweck stator sleeve (169) also has a smaller nominal outer diameter (dna) than at the fixed end (24) of the Holweck stator sleeve (169); characterized in that (i) the nominal inner diameter (dni) of the internal thread (18) of the Holweck stator sleeve (169) decreases toward the free end (22) of the Holweck stator sleeve (169) such that, in the steady-state operating temperature condition of the vacuum pump (111), a radial Holweck gap (175) is established between the Holweck rotor sleeve (165) and the internal thread (18) and has a substantially constant size, in particular a constant size, between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169); and / or (ii) the nominal outer diameter (dna) of the external thread (20) of the Holweck stator sleeve (169) decreases toward the free end (22) of the Holweck stator sleeve (169) such that, in the steady-state operating temperature condition of the vacuum pump (111), a radial Holweck gap (173) is established between the Holweck rotor sleeve (163) and the external thread (20) and has a substantially constant size, in particular a constant size, between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169).

2. A vacuum pump (111) according to claim 1, characterized in that the nominal inner diameter (dni) of the internal thread (18) of the Holweck stator sleeve (169) decreases continuously or in steps toward the free end (22) of the Holweck stator sleeve (169).

3. A vacuum pump (111) according to one of the preceding claims, characterized in that the internal thread (18) has a constant thread depth between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169) and the inner surface (12) of the Holweck stator sleeve (169) defines a core inner diameter (dki) of the internal thread (18) that decreases toward the free end (22) of the Holweck stator sleeve (169) in the cold state of the vacuum pump (111).

4. A vacuum pump (111) according to claim 1 or 2, characterized in that the inner surface (12) of the Holweck stator sleeve (169) defines a core inner diameter (dki) of the internal thread (18), which is constant between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169) in the cold state of the vacuum pump (111), and the internal thread (18) has a thread depth which increases toward the free end (22) of the Holweck stator sleeve (169).

5. A vacuum pump (111) according to any one of the preceding claims, characterized in that the nominal outer diameter (dna) of the external thread (18) of the Holweck stator sleeve (169) decreases continuously or in steps toward the free end (22) of the Holweck stator sleeve (169).

6. A vacuum pump (111) according to any one of the preceding claims, characterized in that the external thread (20) has a constant thread depth between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169) and the outer surface (14) of the Holweck stator sleeve (169) defines a core outer diameter (dka) of the external thread (20) that decreases toward the free end (22) of the Holweck stator sleeve (169) in the cold state of the vacuum pump (111).

7. A vacuum pump (111) according to any one of the claims 1 to 5, characterized in that the outer surface (14) of the Holweck stator sleeve (169) defines a core outer diameter (dka) of the external thread (20), which is constant between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169) in the cold state of the vacuum pump (111), and the external thread (20) has a thread depth which decreases toward the free end (22) of the Holweck stator sleeve (169).

8. A vacuum pump (111) according to any one of the preceding claims, characterized in that the Holweck stator sleeve (169) has a wall thickness which is constant between the fixed end (24) and the free end (22) of the Holweck stator sleeve (169); or in that the Holweck stator sleeve (169) has a wall thickness which decreases toward the free end (22) of the Holweck stator sleeve (169), and indeed either continuously or in steps.

9. A vacuum pump (111) according to any one of the preceding claims, characterized in that the Holweck rotor comprises an inner and an outer Holweck rotor sleeve (163) which concentrically surround the rotor shaft (153), wherein the outer Holweck rotor sleeve (163) concentrically surrounds the Holweck stator sleeve (169) and the Holweck stator sleeve concentrically surrounds the inner Holweck rotor sleeve (165).

10. A vacuum pump (111) according to any one of the preceding claims, characterized in that the hub (161) is fastened to the rotor shaft (153) and the Holweck rotor sleeve (163, 165) is fastened to the hub (161).

11. A vacuum pump (111) according to any one of the claims 1 to 9, characterized in that the hub (161) is formed integrally with the rotor shaft (153), whereas the Holweck rotor sleeve (163, 165) is fastened to the hub (161); or in that the Holweck rotor sleeve (163, 165) is formed integrally with the hub (161) and the hub (161) is fastened to the rotor shaft (153).