Patent Publication Number: US-9422937-B2

Title: Vacuum pump

Description:
The present invention relates to a vacuum pump having at least one molecular pump stage, in particular a Holweck stage, and having at least one side channel pump stage arranged downstream of the molecular pump stage. 
     Vacuum pumps which have an additional side channel pump stage downstream of a molecular pump stage are known in principle. The side channel pump serves to improve the pumping behavior of the vacuum pump, in particular in the working ranges of the vacuum pump in which particularly high roughing pressures, high inlet pressures or high gas loads occur, and to reduce the power consumption of the vacuum pump in these working ranges. The side channel pump stage implements a pumping principle which is optimized for use with higher gas pressures and in particular also allows an energy-efficient pump operation in the laminar flow region, that is in the pressure range disposed above the molecular flow region. The achievable exit pressure and the achievable intake performance of the vacuum pump are therefore increased by the side channel pump stage arranged downstream of the molecular pump stage and the power consumption of the vacuum pump is simultaneously kept low. 
     Different construction solutions have been proposed for the integration of a side channel pump stage and of a molecular pump stage in a common vacuum pump. A vacuum pump is, for example, known from EP 1 668 255 A1 in which a pump stage which is similar to a side channel pump stage is arranged, including its rotor elements and its stator, within a Holweck sleeve of a molecular pump stage. The Holweck sleeve and the rotor elements of the inwardly disposed pump stage are in this respect arranged on a common rotor hub, with the rotor elements of the inwardly disposed pump stage being arranged radially inwardly offset with respect to the Holweck sleeve. 
     The achievable pump power of the inwardly disposed pump stage is restricted in this embodiment due to the radially inwardly disposed arrangement of the rotor elements and due to the correspondingly relatively small radius of rotation, whereby the achievable exit pressure and the intake performance of the pump are reduced and their power consumption are increased. The inwardly disposed rotor elements and the corresponding stator of the inwardly disposed pump stage extending into the interior of the Holweck sleeve furthermore take up valuable construction space which is not available for other pump components, whereby the dimensions of the pump are increased. In addition, the rotor elements of the inwardly disposed pump stage and the associated stator are nested with the Holweck sleeve and the associated Holweck stator and are only accessible from the outside with difficulty due to their arrangement within the Holweck sleeve, whereby the manufacturing and assembly effort required for the manufacture of the pump is increased and the implementation of a cooling device, for example, for the effective cooling of the corresponding components is made more difficult in the operation of the vacuum pump. 
     It is the object of the invention to provide a vacuum pump which has an increased exit pressure and an increased intake power, which can be operated under any desired operating conditions with a low energy consumption and which can simultaneously be implemented in a small construction space and with a small manufacturing and assembly effort. 
     This object is satisfied by a vacuum pump having the features of claim  1  and by a vacuum pump having the features of claim  10 . 
     The vacuum pump in accordance with claim  1  forms a first subject of the invention and includes at least one molecular pump stage, in particular a Holweck stage, which includes a rotor member which forms the pump-active surface of the molecular pump stage. The vacuum pump furthermore includes at least one side channel pump stage which is arranged downstream of the molecular pump stage and which includes a plurality of rotor elements. The rotor elements of the side channel pump stage are supported by the rotor member of the molecular pump stage. 
     It has been recognized in accordance with the invention that a minimal space requirement is achieved with an ideal performance of the side channel pump stage when the rotor member of the molecular pump stage is simultaneously used as a support for the rotor elements of the side channel pump stage. The rotor elements consequently do not have to be arranged at a radial spacing from the rotor member of the molecular pump stage so that the construction space present inside the rotor member of the molecular pump stage is available for other components of the vacuum pump, for example for a drive of the vacuum pump. The rotor elements are furthermore located at a relatively large radial spacing from the axis of rotation of the vacuum pumps which can approximately correspond to the radius of the rotor member so that a side channel pump stage having a large radius of rotation and a correspondingly high pump performance is provided. A powerful and energy-saving operation of the pump is thus also ensured at high exit pressures and/or roughing pressures and high inlet pressures. 
     The accessibility of the rotor elements is improved due to their arrangement at the rotor member, whereby the complexity of the pump design is reduced and e.g. also the installation of a cooling apparatus for the side channel pump stage is facilitated. 
     Advantageous embodiments of the vacuum pump are also described in the description, in the dependent claims and in the Figures. 
     The vacuum pump can include a support of the rotor member as described in the following or a support part of the rotor member at which the rotor elements are arranged and by which the rotor elements are supported. The support or the support part can also be considered as part of the side channel pump stage instead of the rotor member. The support or the support part is, in accordance with an embodiment, not arranged at an axial end of a Holweck rotor to which the support or the support part is connected. The Holweck rotor can include the rotor member and can additionally include a hub of the vacuum pump supporting the rotor member. The support or the support part can be arranged at a region of the Holweck rotor spaced apart from an or each axial end of the Holweck rotor instead of at an axial end of the Holweck rotor. 
     The rotor elements are preferably arranged outside a region surrounded by the rotor member formed, for example, as a Holweck sleeve. A particularly good accessibility and a particularly low complexity of the pump structure can thereby be achieved with a simultaneously large radius of rotation of the side channel pump stage. The rotor elements can be arranged fully or partly outside the region which is entirely surrounded by the pump-active surface of the rotor motor or by the rotor member. 
     The rotor member can be supported by a rotor hub. In this embodiment, the rotor elements of the side channel pump stage are therefore supported by the rotor member which is in turn supported by the rotor hub. The rotor hub is preferably flat and in particular of disk shape and preferably extends substantially in a radial plane with respect to the axis of rotation of the rotor. The rotor member preferably projects from the rotor hub in an axial direction. The rotor hub is in turn preferably connected to a rotor shaft. The rotor hub and the rotor member can in principle be formed as different parts connected to one another or can be connected to one another in one part. 
     The rotor elements are preferably arranged an end, in particular a free end, of the rotor member. The in particular free end of the rotor member can be formed, for example, by an axial end, and preferably by an end of the rotor member remote from the rotor hub, for example by an axial end of the rotor member remote from the rotor hub. The rotor elements, which are preferably designed as rotor vanes, can project from the rotor member in the axial direction or in a direction which has at least one direction component in parallel to the axis of rotation of the vacuum pump and is preferably in parallel to the axis of rotation of the vacuum pump. The rotor elements can also have an orientation inclined radially inwardly or radially outwardly by up to 45°, for example, with respect to the axis of rotation of the vacuum pump and can project from the rotor member in this direction. The stator of the side channel pump stage can be arranged in the region of the free end of the rotor member or in an oppositely disposed static region of the vacuum pump. A particular favorable structure results from this since in particular no nesting of the rotor member with the stator of the side channel pump stage is required so that a particularly simply assemblable and compact construction shape of the vacuum pump is achieved. 
     The rotor elements can extend in the axial direction beyond the pump-active surface of the rotor member and preferably beyond the rotor member as a whole. This permits a particularly favorable arrangement of the stator and of the stator channels of the side channel pump stage in a construction respect in a static region of the pump disposed opposite the rotor elements in the axial direction, without a complex nesting of rotor elements and stator elements of the different pump stages being necessary. The accessibility of the side channel pump stage is furthermore increased. The stator channel or side channel in which the rotor elements revolve can have an open design e.g. in the axial direction, e.g. to allow the reception of rotor elements projecting in the axial direction. 
     The rotor elements which are formed as rotor vanes, for example, are preferably arranged directly at the rotor member and are supported by it. The rotor member can include a support which is preferably arranged at an in particular free axial end of the rotor member and at which the rotor elements are arranged. The support is preferably of ring-shaped design and preferably includes a support surface which extends in ring shape about the axis of rotation of the vacuum pump and at which the rotor elements are arranged. The support surface can, for example, be formed as planar and can face in the axial direction of the vacuum pump or it can have a substantially frustoconical jacket shape and have a surface normal which is radially inwardly or radially outwardly inclined with respect to the axis of rotation of the vacuum pump, e.g. by up to 45°. 
     The free end of the rotor member can be formed wholly or partly by the support of the rotor member. The support surface of the support can be formed, for example, by an axial end face of the rotor member. The design is suitable, for example, for an embodiment as described above in which the rotor elements project in the axial direction and stator channels which are oppositely disposed in the axial direction e.g. are associated with the rotor elements. 
     The support for the rotor elements can form a step or overhang of the rotor member projecting in the radial direction. In particular when a radial outer surface of the rotor member forms the pump-active surface of the rotor member such as can, for example, be the case with a Holweck sleeve as the rotor member, the support can form a step or an overhang projecting inwardly in the radial direction. In principle, the support can, however, also project outwardly in the radial direction and form such a step or overhang. The rotor member can be designed substantially in L shape viewed in the longitudinal direction, with the short limb of the L shape being able to be formed by the step or overhang of the rotor member. A shape of the support suitable for the support of the rotor element can be provided by such a step or overhang without the rotor member having to be made thickened over its total length so that the space requirement of the rotor member is kept small. In principle, the support can also be formed by a region of the rotor member which is aligned with an adjacent region of the rotor member in the axial direction, that is without any real radial step or overhang. In this case, the rotor elements can be arranged directly at the axial end face of a rotor member, with the rotor member having an at least approximately unchanging inner cross-section and/or outer cross-section over its total longitudinal extent. 
     The rotor member is preferably substantially designed as a sleeve and in particular forms a Holweck sleeve or a Holweck cylinder. The rotor member can in this respect extend in sleeve shape about the axis of rotation of the vacuum pump and can be formed substantially rotationally symmetrical to the axis of rotation, with a longitudinal axis of the sleeve preferably substantially coinciding with the axis of rotation of the vacuum pump. The sleeve-like rotor member can be arranged at one of its axial ends at a rotor hub as described above or can be supported by it or fastened to it, whereas the rotor elements of the side channel pump stage are arranged at the other axial end. 
     In accordance with an advantageous embodiment, the rotor member includes a base which is in particular substantially formed as a sleeve and which preferably has a form closed in ring shape about the axis of rotation and preferably substantially rotationally symmetrical. The base preferably extends from a rotor hub supporting the rotor member up to a support of the rotor member such as described above and at which the rotor elements are arranged. The pump-active surface of the molecular pump stage is preferably formed at least partly or substantially completely by the base. 
     The support of the rotor member can be formed substantially as a sleeve which preferably has a form closed in ring shape about the axis of rotation and preferably has a substantially rotationally symmetrical form. 
     At least one of the components of base and support is preferably connected directly in one part or in multiple parts to the rotor hub and is supported by it. The respective other component can be supported by the component directly connected to the rotor hub, in particular without itself being connected directly to the rotor hub and being supported by it. In principle, both components, i.e. both the base and the support, can also be connected directly in one part or in multiple parts to the rotor hub and can be supported by it. The base and the support are preferably mutually connected in one part or in multiple parts, preferably independently of the rotor hub. For example, the base and the support can contact one another in an overlapping manner in the radial direction and can be connected to one another in the overlap region. The base and the support can equally be spaced apart from one another in the radial direction and can be connected to one another or held at one another independently of the rotor hub. 
     The rotor member can in principle have a multipart design, with e.g. a base such as is described above which is supported by a rotor hub and a support such as is described above at which the rotor elements are arranged each forming a respective part of the rotor member, i.e. the rotor member can in particular include a base part or component forming the base and a support part or component forming the support which are preferably connected to one another, with the support part being able to be carried by the base part. Corresponding to the preferably sleeve-shaped design of the base and of the support, the base part can be formed by a base sleeve and the support part can be formed by a support sleeve. In principle, the rotor member can, however, also be made as a single part or at least include a base and a support which are formed in one part with one another. 
     The connection between the base part and the support part can, for example, include a clamp connection which can in particular be established by a shrinking procedure. A screw connection and/or a bond connection can equally be provided between the base part and the support part. The base part and the support part can mutually overlap in the region of their connection in the radial direction. The support part can, for example, have a sleeve-like connection section whose outer diameter at least approximately corresponds to the inner diameter of the preferably sleeve-like base part, with the outer surface of the connection section of the support part and the inner surface of the base part contacting one another areally. The rotor elements can in this respect be arranged at a support section of the support part adjoining the connection section of the support part, preferably in the axial direction, with the support section being able to protrude radially inwardly or outwardly with respect to the connection section. 
     One or more rotor elements can be formed as separate parts and can be connected in multiple parts to a support and in particular to a support part as described above. 
     The base part and the support part of the rotor member can in principle be formed from different or identical materials. The base part can, for example, comprise or consist of a material containing carbon or a metallic material, for example a carbon fiber reinforced composite (CRP) material. The support part can likewise comprise or consist of a material containing carbon, for example a carbon fiber reinforced composite (CRP) material and/or a metallic material such as aluminum. For example, the support part can be a ring-shaped component which is made as metallic and is provided with a reinforcement of fiber-reinforced material. The support part can, for example, be a CRP-reinforced metal sleeve. 
     In principle, the rotor member can also be formed in one part and can comprise or consist of a carbon fiber reinforced composite (CRP) material or a metallic material. The rotor member or a base part of the rotor member and a rotor hub supporting the rotor member can likewise be designed as parts connected to one another or in one part to one another. It is preferred if the base part of the rotor member is formed as an independent part and preferably as a sleeve in the shape of a cylinder jacket which comprises CRP material, for example. 
     The rotor member, the base and/or the support or the base part and/or the support part are each preferably formed, as described above, substantially in sleeve shape or as a sleeve. The respective component is in this respect preferably formed substantially in the shape of a cylinder jacket at least in a longitudinal section, with the longitudinal axis of the cylinder jacket preferably substantially coinciding with the axis of rotation of the pump. 
     The rotor member preferably has at least one longitudinal section in which the rotor member is bounded by a radially inner surface substantially in the shape of a cylinder jacket and/or by a radial outer surface substantially in the shape of a cylinder jacket, with the cylinder respectively defined by the inner surface or outer surface preferably being made substantially straight and being oriented at least approximately in parallel to the axis of rotation of the pump. 
     The rotor member can, for example, have a longitudinal section such as described above having a radially outer surface which is at least approximately the shape of a cylinder jacket and which extends e.g. over at least 50% or 75% and preferably at least approximately over the total axial length of the rotor member. 
     The radial outer surface of the rotor member in the shape of a cylinder jacket can, for example, be formed by the radial outer surface of a base or of a base part of the rotor member, with the base part being formed e.g. as a rotating Holweck sleeve and having the shape over a part of its axial length, and preferably at least approximately over its total axial length, of a straight cylinder jacket oriented in the axial direction and preferably having a constant wall thickness. The radial outer surface of the rotor member can in this respect form at least a part of the pump-active surface of the molecular pump stage. The pump-active surface is in this respect preferably formed as a smooth surface and can e.g. be disposed opposite the radial inner side of a stator sleeve at which a Holweck thread can be arranged. In principle, however, the pump-active surface of the Holweck sleeve can also have a Holweck thread, with then the oppositely disposed surface of the stator sleeve preferably being made smooth. The rotor member can have a unchanging, preferably rotationally symmetrical outer cross-section over substantially its whole length. 
     The radial inner surface of the rotor member can also have the shape of a straight cylinder jacket oriented in the direction of rotation of the axis in at least a longitudinal section of the rotor member, with the radial inner surface and the radial outer surface of the rotor member preferably forming a cylinder jacket with a substantially constant wall thickness in this longitudinal section. The radial inner surface can in this respect be formed in this longitudinal section by the radial inner surface of a base or of a base part of the rotor member as described above. This longitudinal section can, for example, cover at least 40% or 75% and in particular at least approximately the total axial length of the rotor member. 
     The radial extent of the rotor member can be kept as small as possible by the above-described embodiment so that a compact construction shape of the vacuum pump is achieved. The preferably cylindrical free space defined by the radial inner surface in the interior of the rotor member is, for example, suitable for accommodating a drive of the vacuum pump. 
     The rotor member can also have a first and a second longitudinal section in which the radial inner surface of the rotor member respectively has the shape of a straight cylinder jacket oriented in the direction of the axis of rotation and which together preferably cover at least 40% or 75% and in particular at least approximately the whole axial length of the rotor member. The radial inner surface can, for example, be formed by a base or by a base part of the rotor member in the first longitudinal section of the rotor member, whereas it is formed by the radial inner surface of a support or of a support part of the rotor member in the second longitudinal section. 
     The diameter of the cylinder jacket respectively defined by the radial inner surface can in this respect be different for the first and second longitudinal sections. Accordingly, the wall thickness of a cylinder jacket respectively defined by the radial inner surface and the radial outer surface of the rotor member can also be different in the first and second longitudinal sections. The support or the support part can in this respect define a smaller inner diameter of the rotor member in the second longitudinal section than the base or the base part of the rotor member in the first longitudinal section. The transition between the first and second longitudinal sections of the rotor member can in this respect include a radial projection or overhang of the rotor member as described above formed by the support or the support part. 
     In the second longitudinal section in which the radial inner surface of the rotor member is preferably formed by the support or the support part, the support or the support part is preferably arranged within the base or the base part so that the support or the support part and the base or the base part overlap in the radial direction. The support part can, for example, be formed by a support sleeve having a sleeve-like connection section such as described above and which is inserted into the base part and is preferably connected to the base part at an axial end of the base part. 
     As described above, the molecular pump stage is preferably formed as a Holweck stage, with the rotor member forming a Holweck sleeve and with a corresponding stator sleeve preferably being associated with the Holweck sleeve. The Holweck stage includes a Holweck thread having at least one, and preferably a plurality of spiral or helical grooves extending in the direction of the axis of rotation and open in the radial direction and includes a substantially smooth surface arranged opposite the Holweck thread, moving with respect to the Holweck thread and defining a narrow gap with the Holweck thread. The grooves each form a flow channel of the Holweck stage. The Holweck thread can in principle be arranged either at the rotor member of the Holweck stage or at a stator or at a stator sleeve of the Holweck stage. It is preferred if the Holweck thread is arranged at the stator sleeve and if the rotor member forms a substantially smooth pump-active surface rotating with respect to the stator sleeve, in particular in the form of a radial outer surface of the rotor member in the shape of a cylinder jacket. 
     In accordance with an advantageous embodiment, the molecular pump stage includes an upstream first section and a downstream second section leading to the side channel pump stage, with a smaller number of flow channels being formed in the second section than in the first section. The flow channels of the second section can in this respect form one or more supply channels which lead into the side channel pump stage. The first and second sections preferably follow one another in the axial direction. The number of supply channels can correspond, for example, to the number of gas inlets of the side channel pump stage. The supply channels serve for the bundling of the gas conveyed through the first section of the molecular pump stage, with a collection channel being able to be formed between the first and second sections, which preferably revolves about the axis of rotation in the peripheral direction and which connects the flow channels of the first section to one another. The flow channels of the first and/or second sections are preferably part of a Holweck thread of a Holweck stage and are preferably arranged at the static part of the molecular pump stage such as at a stator sleeve of the Holweck stage. 
     The vacuum pump can include a plurality of Holweck stages which are connected behind one another in the flow direction and which are flowed through by the gas, preferably one after the other. The Holweck stages can in this respect be arranged within one another in the radial direction and can be nested with one another, whereby an ideal utilization of space is ensured. The gas can flow over the plurality of Holweck stages from radially inwardly to radially outwardly or from radially outwardly to radially inwardly. The rotor member at which the rotor elements of the side channel pump stage are supported in this respect preferably form a Holweck stage which is arranged downstream of one or more further Holweck stages. A further rotor member can be associated with the further Holweck stages and is preferably formed as a Holweck stage substantially in the shape of a cylinder jacket. In this respect, both the radial outer surface and the radial inner surface of the further rotor member can form a pump-active surface of a respective Holweck stage. In the rotor member supporting the rotor elements, in contrast in particular only the radially outer surface can form a pump-active surface of the Holweck stage. 
     The rotor elements of the side channel pump stage can be formed in a manner known per se as vanes or rotor vanes which are preferably arranged in a plant extending perpendicular to the axis of rotation along a circular ring revolving about the axis of rotation, with the vane surfaces of the rotor elements preferably facing at least partly in the revolving direction. The vane surfaces can in this respect have a shape slightly inclined against the revolving direction toward the rear in the axial direction and/or in the radial direction. The vanes can be part of a wheel of vanes in accordance with the side channel principle which includes the side channel pump stage. The side channel pump stage preferably further includes at least one stator channel or side channel in which the rotor elements revolve and which is preferably arranged in ring shape about the axis of rotation in accordance with the ring-shaped arrangement of the rotor elements. The side channel preferably has a cross-section enlarged with respect to the rotor elements over at least a part of its length in a manner known per se. The side channel preferably has the enlarged cross-section over approximately its whole length, with a scraping region with a scraper preferably being provided at an end associated with the outlet of the side channel in which the channel is narrowed to a cross-section which substantially corresponds to the outline of the rotor elements so that the rotor elements can just pass through the narrowed region and the scraper scrapes off the gas conveyed through the side channel and introduces the gas flow into the gas outlet of the side channel pump stage. A gas inlet of the side channel pump stage can be arranged at the other end of the scraper and is preferably connected to a supply passage of the molecular pump stage as described above. The side channel can also comprise a plurality of part channels each having an inlet, an outlet and a scraping region therebetween, with preferably a supply channel of the molecular pump being associated with each part channel and being connected to its inlet. 
     In accordance with an embodiment, beside the above-described side channel pump stage, a further second side channel pump stage is provided whose design can correspond to the above-described side channel pump stage. The second side channel pump stage is preferably arranged directly downstream of the above-described side channel pump stage, with the two side channel pump stages preferably being arranged nested in one another in the radial direction. The rotor elements of the second side channel pump stage are in this respect preferably likewise supported by the rotor member of the molecular pump stage and in particular by a support of the rotor member supporting the rotor elements of the above-described side channel pump stage. The rotor elements of the second side channel pump stage can in this respect be arranged with the rotor elements of the above-described side channel pump stage substantially in a common plane extending perpendicular to the axis of rotation. The rotor elements of the second side channel pump stage can be arranged along a circular ring revolving about the axis of rotation, said ring being concentric to the axis of rotation and to the circular ring formed by the above-described side channel pump stage and having a smaller or larger radius than this ring. The outlet of the one side channel pump stage is in this respect connected by a flow channel to an inlet of the other side channel pump stage. 
     In accordance with an advantageous embodiment, a balancing plane is provided which is arranged in the region of a support of the rotor member supporting the rotor elements. The balancing plane can have a plurality of devices arranged distributed over the periphery of the support for attaching balancing masses. Such a device can, for example, include an opening such as a balancing bore, for example a threaded bore and/or a blind bore with a preferably metric thread, which can be formed, for example of the type M2 or M3. The openings or balancing bores are preferably arranged in a support surface of the support at which the rotor elements are arranged, and indeed preferably in the regions of the support surface arranged between the rotor elements. A respective balancing weight can be screwed into one or more balancing bores and is preferably arranged at least approximately completely countersunk in the balancing bore and terminates flush e.g. with the support surface of the support. Any imbalance which may be caused by the support for the rotor elements can be eliminated by such a balancing plane and the running properties of the pump can be improved. 
     A second subject of the invention is formed by a vacuum pump having a Holweck pump section which includes a Holweck rotor and having a roughing pressure stage which follows in the gas flow and which includes a rotor component, with the rotor component being connected to the Holweck rotor and being arranged at an axial end of the Holweck rotor. 
     The embodiment is advantageous according to which the Holweck rotor is connected to a shaft at a second axial end. This enhances the cost advantage and reduces the construction volume of the vacuum pump since the drive motor can be arranged within the inner space of the Holweck pump section and/or of the roughing pressure stage. 
     In accordance with an embodiment, the roughing pressure stage has a ring-shaped component or rotor component which includes a pump structure and is connected to a sleeve of the Holweck rotor. 
     A particularly simple embodiment provides a ring-shaped component of the roughing pressure stage which is provided at the axial end of a sleeve of the Holweck rotor. The exit pressure of the pump in the region above 10 Hectopascal is improved by the roughing pressure stage. The embodiment of the roughing pressure stage in accordance with the side channel principle is particularly effective and inexpensive. The roughing pressure stage can include a ring of vanes in accordance with the side channel principle. The roughing pressure stage can have a multistage design. 
     The roughing pressure stage can include a ring-shaped component which is designed in one piece with a hub of the Holweck rotor. 
     The ring-shaped component can be of a metallic design and be reinforced by a reinforcement of fiber-reinforced material. 
     The Holweck pump section can include a plurality of pump stages. 
     A dynamic seal can be arranged between the Holweck pump and the roughing pressure stage. The Holweck pump section can include a passage at the stator side through which gas enters into the roughing pressure stage and a part of the stator associated with the channel can form a sealing stator of the dynamic seal. 
     An additional advantage can be achieved if a component of the roughing pressure stage is provided with a balancing means, for example a balancing bore. The smooth running increases to that clearances can be reduced. In turn, this increases the performance capability of the pump stages so that the cost-related performance capability increases. 
     An additional intermediate inlet through which gas can be sucked into the roughing pressure stage allows the simplification of pump systems having a plurality of vacuum pumps, for example. A further molecular pump can be connected to this intermediate inlet and a second chamber is, for example, evacuated by it. The roughing pressure stage then acts as a pump stage for the vacuum pump and the molecular pump. 
     The invention also comprises all the technically realizable embodiments of a pump which result starting from a pump such as described herein in accordance with the first subject of the invention by additional implementation of any desired features or feature combinations of a pump in accordance with the second subject of the invention and vice versa. 
     A third subject of the invention is a vacuum pump having the features of claim  10 . 
     The vacuum pump includes a molecular pump stage, in particular a Holweck stage, and at least one side channel pump stage which is arranged downstream of the molecular pump stage and which includes a plurality of rotor elements, with the side channel pump stage being arranged between a pump inlet and the molecular pump stage. 
     The order in which the side channel pump stage and the molecular pump stage follow one another in the axial direction starting from the pump inlet is consequently swapped over with respect to the order in which the pump stages are flowed through by the gas since the side channel pump stage is arranged downstream in the gas flow direction and at the inlet side of the molecular pump stage in a geometrical respect. Within the framework of the inlet-side arrangement of the side channel pump stage, its rotor elements can be arranged outside a rotor member of the molecular pump stage, for example of a Holweck sleeve or of a Holweck cylinder, and the diameter of the side channel pump stage can accordingly be selected to be relatively large and in particular at least approximately equally as large or even larger than the diameter of the rotor member of the molecular pump stage. A particularly powerful vacuum pump is provided in this manner. 
     In addition, no additional space requirements at the side of the molecular pump stage remote from the inlet is provided due to the arrangement of the side channel pump stage at the inlet side. This has the advantage that the accessibility of the molecular pump stage in this region remote from the inlet is not restricted by the side channel pump stage so that it is easily possible, for example, to install the stator elements of the molecular pump stage, in particular one or more stator sleeves of a Holweck stage, at a rear wall of the housing of the vacuum pump remote from the inlet. A particularly simple construction form is thereby achieved which results in a particularly small axial length of the vacuum pump. An excessive additional axial space requirement for the side channel pump stage is in this respect just as equally avoided as a complicated nesting of rotor elements and/or stator elements of the molecular pump stage and of the side channel pump stage. In addition, further components of the pump such as a drive can be arranged in the freely accessible interior of the molecular pump stage without increasing the complexity of the pump structure. 
     In accordance with an embodiment, a gas flow path from the pump inlet leads past the pump-active structure of the side channel pump stage into the molecular pump stage. Such a bypass path can, for example, lead radially inwardly and/or radially outwardly past the pump-active structure into the molecular pump stage. The pump-active structure of the side channel pump stage which the gas is led past can in principle have a design such as was described above with respect to the vacuum pump in accordance with claim  1  and can in particular have rotor elements formed as rotor vanes and at least one side channel at the stator side. 
     In accordance with an advantageous embodiment, the gas flow path provided for bypassing the side channel pump stage leads through one or more openings of a rotor hub, in particular of disk shape, supporting the rotor elements of the side channel pump stage. The openings can in this respect be formed by apertures extending though the rotor hub in the axial direction. The rotor hub of the side channel pump stage in this embodiment forms a gas inlet into the molecular pump stage. 
     A gas flow path such as described above and extending through the rotor hub of the side channel pump stage can expediently be radially inwardly led past the pump-active structure of the side-channel pump stage. It is equally possible that a gas flow path leads radially outwardly past the side channel pump stage into the molecular pump stage. Such a gas flow path can include, for example, a channel arranged in the stator or in the housing of the vacuum pump and leading past the pump-active structure. 
     The molecular pump stage preferably effects a reversal of the gas flow direction so that the gas flow can enter into the side channel pump stage arranged at the inlet side of the molecular pump without any complex bypassing after running through the molecular pump stage. Such a reversal of direction can be effected in a simple manner in that the molecular pump stage includes a plurality of Holweck stages, with an identical number of Holweck stages being provided pumping in the axial direction away from the gas inlet and in the axial direction toward the gas inlet. 
     In accordance with an embodiment, a gas flow path leading from the molecular pump stage into the side channel pump stage extends through one or more openings of a rotor hub, in particular of disk shape, supporting a rotor member of the molecular pump stage. The gas can thereby move through the rotor hub into the side channel pump stage arranged at the inlet side after any reversal of direction effected by the molecular pump stage so that the rotor hub supporting the rotor member forms a gas inlet for the side channel pump stage. In principle, the gas flow can, however, also enter into the side channel pump stage at the inlet side laterally past the rotor hub. In an embodiment which will be explained in the following, the rotor elements of the side channel pump stage are located with the rotor member of the molecular pump stage at the same hub, in which case the gas flow from the molecular pump stage can enter from the molecular pump stage into the side channel pump stage from the molecular pump stage directly and without a complete crossing or bypassing of the rotor hub. 
     As described above with reference to specific examples, in the vacuum pump in accordance with the invention, a rotor hub supporting the rotor elements of the side channel pump stage and/or supporting a rotor element of the molecular pump stage can be formed as a gas inlet which leads either into the molecular pump stage or from the molecular pump stage into the side channel pump stage. The respective rotor hub can for this purpose preferably have one or more apertures which extend through the rotor hub in the axial direction and form flow channels for the gas. The respective rotor hub can in principle be formed by a rotor hub as described above with respect to the vacuum pump in accordance with claim  1 , said rotor hub preferably being of disk shape and being oriented in the radial direction. 
     In accordance with an advantageous embodiment, the rotor elements of the side channel pump stage are arranged in the region of a radial outer side of a, preferably disk-shaped, rotor hub. The rotor elements can in this respect project from a margin of the rotor hub. The rotor elements preferably project in the radial direction from the margin or in a direction which has at least one radial component and is preferably at least approximately parallel to the radial direction. A particularly large radial spacing of the rotor elements from the axis of rotation and thus a large radius of rotation and a correspondingly high performance of the side channel pump stage can thereby be achieved. In addition, in this embodiment, the side channels at the stator side can be formed as channels open in the radial direction and/or can be arranged in the region of a radial outer wall of the vacuum pump, whereby an extremely compact construction shape of the vacuum pump is made possible which in particular manages without complex nestings of rotor elements and stator elements. 
     In accordance with an advantageous embodiment, the rotor member of the molecular pump stage and the rotor elements of the side channel pump stage are supported by a common, preferably disk-shaped, rotor hub. The rotor elements can in this respect project from a margin of the rotor hub, whereas one or more rotor members of the molecular pump stage preferably extend in the axial direction starting from a flat side of the rotor hub. A particularly compact construction shape is thereby achieved since separate rotor hubs for the side channel pump stage and the molecular pump stage can be dispensed with. In addition, the gas can enter directly from the molecular pump stage into the side channel pump stage without crossing the rotor hub or completely bypassing it in so doing, whereby the complexity of the pump structure is reduced and the pump efficiency is increased since a high leak-tightness of the gas flow path is achieved overall. 
     The molecular pump stage is preferably a Holweck stage which can in principle be designed as described above with respect to the vacuum pump in accordance with claim  1 . The Holweck stage preferably includes at least one rotor member, which forms a pump-active surface of the Holweck stage and is preferably designed as a Holweck sleeve, and a stator sleeve corresponding with the rotor members. The vacuum pump can also have a plurality of molecular pump stages or Holweck stages such as described above with respect to the vacuum pump in accordance with claim  1  and which are connected behind one another in the gas flow direction, which are preferably arranged in one another in the radial direction and nested with one another and via which a gas flow path leads e.g. from radially inwardly to radially outwardly or from radially outwardly to radially inwardly. 
     If the gas flow path leads via the molecular pump stages from radially inwardly to radially outwardly, a gas inlet for the molecular pump stages preferably includes one or more apertures of a rotor hub at which one or more rotor members of the molecular pump stages are arranged. In this manner, the gas can be supplied to the molecular pump stages at a radially inwardly disposed position. If the gas flow path leads via the molecular pump stages from radially outwardly to radially inwardly, the gas of the molecular pump stage can in contrast be supplied via a gas flow path bypassing the side channel pump stage radially outwardly. The gas inlet into the side channel pump stage can then include one or more apertures of a rotor hub supporting one or more rotor members of the molecular pump stage to supply the gas from the radially inwardly disposed end of the molecular pump stage of the side channel pump stage. 
     In accordance with an advantageous embodiment, at least one further pump stage is provided which is arranged upstream of the molecular pump stage. It can in this respect in particular be a turbomolecular pump stage. The side channel pump stage is in this respect preferably arranged between the further pump stage and the molecular pump stage. The further pump stage, the side channel pump stage and the molecular pump stage can accordingly be arranged behind one another and follow one another in this order starting from the pump inlet along the axial direction of the vacuum pump. The gas flow path of the vacuum pump preferably leads from the pump inlet into the further pump stage, e.g. turbomolecular pump stage, and from there past the side channel pump stage into the molecular pump stage and from there into the side channel pump stage. 
     The molecular pump stage and the further pump stage can be arranged at different sides of a rotor hub supporting a rotor member of the molecular pump stage. 
     A further pump stage, in particular a turbomolecular pump stage, as described above, can also be provided in a vacuum pump as described above with respect to claim  1 . A turbomolecular pump stage can generally have one or more rotor disks and stator disks in a manner known per se which extend in a radial plane, are arranged behind one another in the axial direction, are nested with one another and have gas channels extending obliquely to the axial direction. An upstream end of the further pump stage can in this respect be arranged directly in the region of a pump inlet whose diameter can, for example, at least approximately correspond to the diameter of a rotor disk of the turbomolecular pump stage. 
     The pump inlet is in principle preferably surrounded by a flange which can extend in ring shape around the axis of rotation of the vacuum pump. A vacuum pump in accordance with the invention furthermore preferably has a pump outlet which can be surrounded, for example, by a small flange. The pump outlet is preferably connected to a gas outlet of the side channel pump stage and is arranged, viewed in the direction of the axis of rotation, preferably at least approximately at the level of the side channel pump stage. 
     In addition to the pump inlet arranged upstream of the pump stage and the pump outlet arranged downstream of the pump stages, a pump in accordance with the invention can include one or more taps or intermediate inlets which can be arranged at a point along the gas flow path between the pump inlet and the pump outlet and leading from a pump inlet to a pump outlet and can form an opening into the gas flow path at the respective point. For example, a tap or an intermediate inlet can be provided, for example, arranged downstream of the turbomolecular pump stage and upstream of the molecular pump stag or a tap or an intermediate inlet arranged downstream of the molecular pump stage and upstream of the side channel pump and through which gas can be sucked into the side channel pump stage. 
    
    
     
       The invention will be described in the following by way of example with reference to advantageous embodiments and to the enclosed Figures. There are shown: 
         FIG. 1  a schematic representation of a vacuum pump in accordance with an embodiment of the invention in an axial section; 
         FIG. 2  a flattened representation of an inner stator sleeve of the vacuum pump shown in  FIG. 1 ; 
         FIG. 3  a vacuum pump in accordance with a further embodiment of the invention in an axial section; 
         FIG. 4  the support sleeve with the rotor elements of the vacuum pump shown in  FIG. 3  in a perspective representation; 
         FIG. 5  the rotor member of the vacuum pump shown in  FIG. 3  including the support sleeve and the rotor elements shown in  FIG. 4  in an axial section; 
         FIG. 6  a vacuum pump in accordance with a further embodiment of the invention in an axial section; and 
         FIG. 7  a vacuum pump in accordance with a further embodiment of the invention in an axial section. 
     
    
    
       FIG. 1  shows a schematic representation of a vacuum pump in accordance with an embodiment of the invention in an axial section. Parts of the vacuum pump are not shown in  FIG. 1  for better clarity. 
     The vacuum pump includes a turbomolecular pump stage  10 , a plurality of molecular pump stages  12 ,  14 ,  16  and a side channel pump stage  18  which follow one another in the gas flow or in the flow direction of the gas. 
     The vacuum pump includes a rotor shaft  22  which is rotatingly drivable about an axis of rotation  20  and at which rotating elements of the pump stages  10  to  16  explained individually in the following are arranged. The rotating elements and the associated stator elements of the pump stages  10  to  16  shown only in part in  FIG. 1  are formed substantially rotationally symmetrically to the axis of rotation  20 . For reasons of better clarity, only the respective left component of the corresponding elements are shown in  FIG. 1  and the part in mirror symmetry with the axis of rotation  20  is not shown. The same applies to the flange  26  which defines a pump inlet  24 , which is only shown schematically in  FIG. 1 , which surrounds the inlet region and which can likewise be formed substantially rotationally symmetrically to the axis of rotation  20 . 
     The turbomolecular pump stage  10  arranged in the region of the pump inlet  24  includes a plurality of rotor disks  28  arranged at the rotor shaft  22 , with in  FIG. 1  only one rotor disk  28  being shown and a plurality of stator disks, not shown in  FIG. 1 , corresponding to the rotor disks  28 . Furthermore a disk-shaped rotor hub  30  is attached to the shaft  22  and extends in a radial plane; an outer rotor member  32  associated with the molecular pump stages  12  and  14  and an inner rotor member  34  associated with the molecular pump stage  16  are arranged at said rotor hub and are supported by the hub  30 . The molecular pump stages  12 ,  14 ,  16  are designed as Holweck stages. The rotor member  34  is in this respect arranged within the rotor member  32  and the rotor members  32 ,  34  are nested in one another. 
     The outer rotor member  32  is formed by a Holweck sleeve which has the form of a straight cylinder jacket oriented in the direction of the axis of rotation  20  and having a substantially constant wall thickness and with a straight radial outer surface  36  in the shape of a cylinder jacket and a straight radial inner surface  38  in the shape of a cylinder jacket. The outer surface  36  and the inner surface  38  each form the pump-active surface of one of the pump stages  12  and  14  and act in a pump-active manner with corresponding rotationally symmetrical Holweck stator sleeves  40 ,  42  in the shape of a cylinder jacket. The outer surface  36  of the rotor member  32  cooperates with an outer Holweck stator sleeve  40  which forms a narrow Holweck gap  39  with the rotor member  32  and at which a Holweck thread  41  is provided. The Holweck thread  41  has grooves which extend spirally in the direction of the axis of rotation  20  and which form flow channels for the gas. Such a Holweck thread  43  is also arranged at the outer side of the inner Holweck stator sleeve  42  and cooperates with the radial inner surface  38  of the outer rotor members  32  in a pump-active manner with which it forms a Holweck gap  39 . 
     The radial outer surface  36  and inner surface  38  of the rotor member  32  are each formed as smooth surfaces and effect the pump effect of the respective pump stage together with the Holweck threads  41  or  43  of the stator sleeves  40 ,  42  arranged respectively opposite. In principle it would also be possible to provide the Holweck thread of one or both Holweck stages  12 ,  14  at the rotor member  32  and to form the corresponding surfaces of the stator sleeves  40 ,  42  as smooth. The same applies accordingly to the Holweck stage  16 , i.e. its Holweck thread  57  can be arranged, as explained in the following, at the stator sleeve  42  or at the rotor member  34 . 
     The inner rotor member  34  has a base part  44  attached to the rotor hub  30  and a support part  46  which is connected at the free axial end of the base part  44  to the base part  44  and at which the rotor elements  48  of the side channel pump stage  18  are arranged. The base part  44  has, corresponding to the outer rotor member  32 , the shape of a straight cylinder jacket oriented in parallel to the axis of rotation  20  and having a constant wall thickness and having a radial outer surface  50  and a radial inner surface  52  respectively having the shape of a straight cylinder jacket. The radial outer surface  50  of the rotor member  34  in this respect forms the pump-active surface of the rotor member  34  and cooperates with the radial inner surface  55  of the Holweck stator sleeve  42 . The inner surface  55  of the Holweck stator sleeve  42  has a Holweck thread  57  which will be explained more exactly in the following with respect to  FIG. 2  and has flow channels through which the gas flows in the direction of the side channel pump stage  18  during operation of the pump. The support part  45  is likewise made in sleeve shape and substantially has the shape of a straight cylinder jacket oriented in parallel to the axis of rotation  20  and having a straight radial outer surface  54  and radial inner surface  56  in the shape of a cylinder jacket. The support part  46  is in this respect inserted into the base part  44  so that the radial outer surface  54  of the support part  46  areally contacts the radial inner surface  52  of the base part  44 . The base part  44  and the support part  46  can be held at one another, for example, by a clamping effect present in the region of their mutual contact and caused, for example, by a shrinking process. 
     The support part  46  forms, as shown in  FIG. 1 , a step or overhang of the rotor member  34  projecting radially inwardly with respect to the base part  44 . The radial inner surface of the rotor member  34  comprising the base part  44  and the support part  46  overall is thus formed by two longitudinal sections which follow one another in the direction of the rotor axis  20  and which each on their own have the shape of a straight cylinder jacket in parallel with the axis of rotation  20  and having an unchanging diameter. The radial inner surface of the rotor member  34  in a first longitudinal section is in this respect formed by the radial inner surface  52  of the base part  44  and defines a larger cylinder diameter and the radial inner surface of the rotor member  34  in a second longitudinal section is formed by the radial inner surface  56  of the support part  46  and defines a smaller cylinder diameter. The radial inner surface of the rotor member  34  bounds a free space  58  in which, for example, a drive unit of the vacuum pump not shown in  FIG. 1  can be arranged. 
     The radial inner surface  56  of the support part  46  forms a dynamic seal or a dynamic sealing gap having an oppositely disposed static pump component as shown e.g. in  FIG. 3 . This seal or this sealing gap can contain any desired type of seal, for example a pumping seal which is in particular similar to a Holweck stage and/or which has a conveying direction directed out of the space  58  sealed by the seal. 
     The support part  46  has a support surface  60  facing in the axial direction at which the rotor elements  48  are arranged and from which the rotor elements  48  project in the axial direction. The rotor elements  48  are in this respect formed by vanes each having a vane surface facing in the direction of revolution and are arranged behind one another in a plane oriented perpendicular to the axis of rotation  20  along a ring revolving in circular form about the axis of rotation  20 . 
     The side channel pump stage  18  furthermore includes a side channel stator  62  in which a side channel  46  is formed which is open in the axial direction in the present embodiment, which has a ring-shaped extent which corresponds to the ring-shaped arrangement of the rotor element  48  and in which the rotor elements  48  revolve. The side channel  64  is enlarged with respect to the rotor elements  48  over the large part of its longitudinal extent as is shown in  FIG. 1 . In the operation of the vacuum pump, the gas can be driven by the rotor vanes  48  in the longitudinal direction of the ring-shaped side channel  64  and simultaneously rotatingly about the longitudinal axis of the side channel  64  so that a spiral flow extent results with a plurality of spiral revolutions along a revolution in the side channel  64 , whereby a high pressure difference is ensured between the inlet and the outlet of the side channel pump stage  18 . The pumping principle of the side channel pump stage  18  also ensures a high and efficient pump effect in the high pressure range and in particular in the laminar flow range. 
     In the region of an outlet of the side channel pump stage  18 , a so-called scraper of the side channel stator  62  is provided which effects a narrowing of the side channel  64  such that the cross-section of the side channel  64  in the narrowed region corresponds at least approximately to the cross-section of the rotor elements  48  and is only minimally expanded with respect thereto. The gas conveyed through the rotor elements  48  is thereby scraped off by the scraper and is urged into the outlet of the side channel pump stage  18 . The outlet of the side channel pump stage  18  can be connected to a pump outlet of the vacuum pump which can, for example, comprise or include a small flange. 
       FIG. 2  shows the radial inner surface  55  of the inner Holweck stator sleeve  42  in a flattened view or a view projected into one plane. The Holweck stator sleeve  42  has a Holweck thread  57  which could in principle, however, also be arranged at the radial outer surface  50  of the rotor member  34  made smooth in the present embodiment. In this embodiment, the radial inner surface  55  of the Holweck stator sleeve  42  could be made substantially smooth. 
     The Holweck thread  57  includes two sections  66  and  68  following one another in the axial direction. A plurality of threaded projections  70  oriented toward the axis of rotation  20  and having thread channels  72  arranged therebetween which form flow channels (Holweck grooves) for the gas are formed in the section  66 . The thread channels  72  open into a deepened collection region  74  which runs around the axis of rotation  20  in the peripheral direction and in which the gas conveyed through the thread channels  72  is collected. The collection region  74  opens into a supply channel  76  of the section  68  which is bounded by two areal elevated projections  78  and which leads to an inlet of the side channel pump stage  18 . The gas conveyed substantially uniformly over the total periphery in the upper section  66  can in this manner be bundled in the supply channel  76  and directly supplied to an inlet of the side channel pump stage  18 , whereby the pump efficiency in the side channel pump stage  18  is optimized. The above-described projections  70  and  78  can also be seen in the representation of  FIG. 1 , with the sectional plane of the representation of  FIG. 1  corresponding to the dashed line  80  in  FIG. 2 . 
     In the Holweck thread  57  shown in  FIG. 2 , the section  68  or the channel  76  has a larger axial extent than the collection region  74 . The section  68  or the channel  76  can, however, also have a smaller axial extent than the collection region  74  and/or than the section  66 . In accordance with an embodiment, the elevated projections  78  of the region  68  have a larger construction height in the radial direction than the projections  70  of the section  66 . A particular good sealing effect can thereby be achieved in the region of these projections  78  which bound the channel  76  by a particularly small clearance between the Holweck stator  42  and the rotor member  34  and gas losses at the transition between the Holweck stage  16  and the side channel pump stage  18  are minimized. 
     As shown in  FIG. 1 , a Holweck gap  39  is formed between the projections  70 ,  78  and the radial outer surface  50  of the rotor member  54  and, like the Holweck gap  39  of the pump stage  12  and  14  is shown exaggeratedly large in relation and is in reality selected so small that a high sealing effect is achieved between the projections  70 ,  78  and the oppositely disposed smooth surfaces of the rotor members  32 ,  34 . The gas flows in this respect almost completely through the channels which are defined by the grooves of the Holweck threads  41 ,  43 ,  57 . 
     The rough extent of the gas flow through the vacuum pump shown in  FIG. 1  in the sectional plane of  FIG. 1  is illustrated by a dashed arrow  84 . As shown in  FIG. 1 , the gas first runs through the turbomolecular pump stage  10  after its entry through the pump inlet  24  and thereupon through the Holweck stages  12 ,  14  and  16 , in this order, before the gas enters into the side channel pump stage  18  and is conveyed after passing through the side channel pump stage  18  to the pump outlet not shown in  FIG. 1 . An ideal pump effect and high pump efficiency of the vacuum pump is achieved by the cooperation of the pump stages  10  to  18  in all operating conditions and in particular also at high exit pressures and gas loads, with the vacuum pump simultaneously being able to be realized in a very small construction space. 
       FIG. 3  shows a vacuum pump in accordance with a further embodiment of the invention in an axial section which substantially corresponds to the vacuum pump shown in  FIGS. 1 and 2 . In this respect, additional components of the vacuum pump can be recognized in  FIG. 3  which are not shown in  FIG. 1  such as a plurality of rotor disks  28  and a stator disk  86  of the turbomolecular pump stage  10  arranged therebetween. Furthermore, a drive  88  of the vacuum pump is shown which is arranged within the rotor member  34  as well as a contactless seal  90  formed between the drive  8  and the rotor hub  30  and a rotary bearing  92  of the vacuum pump. 
     A pump housing  94  is equally shown which is connected to a gas outlet  95  of the side channel pump stage  18  as well as a tap  96  which is arranged upstream of the Holweck stage  12  and downstream of the turbomolecular stage  10  and via which gas can flow from outside the vacuum pump directly into the Holweck stage  12 . 
     The projections (webs) of the Holweck threads  41 ,  43 ,  57  are shown in  FIG. 3  so that its spiral shape is visible, just as the sense of rotation of the Holweck threads  41 ,  43 ,  57  alternating from Holweck stage  12 ,  14 ,  16  to Holweck stage  12 ,  14 ,  16  which corresponds to the alternating axial conveying direction from top to bottom or from bottom to top in  FIG. 3 . In the embodiment of  FIG. 3 , the number of Holweck channels of the Holweck threads  41 ,  43 ,  57  in the gas flow direction increases from Holweck stage to Holweck stage and the axial extent of the Holweck channels becomes correspondingly smaller. The pump behavior of the Holweck stages  12 ,  14   16  is thereby optimized. The Holweck thread  57  of the innermost Holweck stage  16  is formed homogeneous with Holweck channels extending over the total axial length of the Holweck stator sleeve  42  in the embodiment shown in  FIG. 3 , unlike the shape shown in  FIG. 2 . In principle, the Holweck thread  57  could, however, also be designed in the embodiment shown in  FIG. 3  as is shown in  FIG. 2  for the pump of  FIG. 1 . 
     The pump shown in  FIG. 3  includes a support part  46  explained in more detail in the following with respect to  FIG. 4  and a support sleeve which has a support surface  60  which is inclined by approximately 45° with respect to the axis of rotation  20 , which has a frustoconical jacket shape, at which the vane-like rotor elements  48  are arranged and from which the rotor elements  48  project substantially perpendicular, i.e. at an angle of likewise approximately 45° to the axis of rotation. A scraper  98  of the side channel pump stage  18  is shown at the left hand side in  FIG. 3  and serves for scraping off the gas driven in the side channel  64  and for its conveying to the pump outlet  94 . 
     The rough gas flow extent from the pump inlet  24  to the pump outlet  94  is also illustrated in  FIG. 3  by a dashed arrow  84  in the sectional plane of  FIG. 3 . 
       FIG. 4  and  FIG. 5  each show further details of the support sleeve  46 , with  FIG. 4  showing a perspective representation of the support sleeve  46  with the rotor elements  48  enlarged with respect to  FIG. 3  and  FIG. 5  showing the support sleeve  46  in the axial section in the state installed at the base part  44 . 
     The sleeve-shaped support part  46  includes a connection section  100  in the shape of a cylinder jacket whose radial outer surface  54  in the assembled state contacts the radial inner surface  52  of the base part  44  and is connected to the base part  44 . The support sleeve  46  furthermore includes a connection section  100  at which the rotor elements  48  are arranged and which projects outwardly in the radial direction with respect to the connection section  100  so that the connection section  100  and the support section  102  form a substantially L-shaped cross-section shown in  FIG. 5 . The support section  102  in this respect is aligned in the assembled state with the radial outer surface  50  of the base part  44  as is the radially outwardly disposed outer edges of the rotor elements  48 . 
     As shown in  FIG. 4 , the rotor elements  48  are formed as vanes which have a shape slightly inclined toward the rear against the direction of rotation in the axial direction and in the radial direction. A shape of the vanes  48  inclined to the front is also conceivable, but not shown. The support sleeve  46  preferably comprises a metallic material which contains e.g. aluminum or consists thereof, whereas the base part  44  formed as a Holweck sleeve can comprise a CRP material, for example. 
     As shown in  FIG. 4 , the support surface  60  of the support section  102  has a plurality of balancing bores  104  arranged distributed over the periphery of the support part  46  and having threads into which corresponding balancing weights can be screwed, and indeed preferably such that the screwed-in balancing weights are arranged completely countersunk in the balancing bores  104  and in particular terminate substantially flush with the support surface  60 . The balancing bores  104  form a balancing plane of the vacuum pump oriented perpendicular to the axis of rotation  20 . 
       FIG. 6  shows a vacuum pump in accordance with a further embodiment in the axial section. The vacuum pump includes a turbomolecular stage  10 , which has a plurality of rotor disk  28 , as well as two molecular pump stages  12 ,  14  formed as Holweck stages and a side channel pump stage  18  which follow one another in this order in the flow direction. The side channel pump stage  18  is arranged between the molecular pump stages  12 ,  14  and the pump inlet  24 . The pump inlet  24 , the side channel pump stage  18  and the molecular pump stages  12 ,  14  thus follow one another in this order in the direction of the axis of rotation  20  and the side channel pump stage  18  is arranged closer to the pump inlet  24  than the Holweck stages  12 ,  14  although it is connected after the Holweck stages  12 ,  14  with respect to the gas flow. 
     The rough gas flow extent through the pump in the sectional plane of  FIG. 6  is illustrated in  FIG. 6  by an arrow  84 . The gas first enters via the pump inlet  24  into the turbomolecular stage  10  which is flowed through by the gas substantially axially, that is in parallel to the axis of rotation  20 . A gas flow channel  106  shown schematically in  FIG. 6  and arranged in the static part of the vacuum pump leads radially outwardly past the pump-active structure of the side channel pump stage  18  formed by the rotor elements  48 ′ and the side channel  64 ′ so that the gas moves past the side channel pump stage  18  into the Holweck stage  12 . The Holweck stages  12  and  14  substantially correspond to the Holweck stages  12  and  14  explained above with respect to  FIG. 1 . The Holweck stages  12  and  14  include a common rotor member  32  which is arranged at a disk-shaped and substantially radially oriented rotor hub  30 ′ and is formed as a straight Holweck sleeve oriented in the axial direction and having the shape of a cylinder jacket. The rotor member  32  accordingly has a radial outer surface  36  and a radial inner surface  38  which each have the shape of a straight, axial cylinder jacket and each form the pump-active surface of one of the Holweck stages  12 ,  14 . These pump-active surfaces  36 ,  38  in this respect cooperate with Holweck stator sleeves  40 ,  42  (cf.  FIG. 1 ) as shown in  FIG. 1  and not shown separately in  FIG. 6 . The Holweck stator sleeves each have a Holweck thread with helical or spiral Holweck channels through which the gas is driven in a pumping manner at their cylindrical inner or outer sides facing the respective pump-active surface  36 ,  38  of the rotor member 
     The gas first moves from the gas flow channel  106  into the Holweck stage  12  and flows downwardly through the Holweck stage  12  in the axial direction away from the pump inlet  24  and thereupon into the Holweck stage  14  in which it is conveyed upwardly in the axial direction in the direction toward the pump inlet  24 . The two Holweck stages  12 ,  14  thus effect a reversal of direction of the flow direction of the gas and simultaneously a conveying of the gas from radially outwardly to radially inwardly. The rotor hub  30 ′ has an axial aperture  108  at the end of the Holweck stage  14  facing the rotor hub  30 ′, said aperture serving as a gas outlet of the Holweck stage  14  and as a gas inlet of the side channel pump stage  18  and via which the gas enters into a flow channel  110  of the side channel stator  62 ′ leading into the side channel  64 ′. Only the left hand part of the side channel stator  62 ′ is shown in  FIG. 6  which is preferably formed rotationally symmetrically to the axis of rotation  20 . A gap  112  which extends in the radial direction is formed between the rotor hub  30  and the side channel stator  62 ′ and has a small axial extent to achieve a sealing effect between the rotor hub  30  and the side channel stator  62 ′ and to ensure that the gas moves at least approximately completely from the aperture  108  into the flow channel  110 . The rotor hub  30 ′ preferably includes a plurality of apertures  108  distributed over its periphery as shown in  FIG. 6 . Equally, the side channel stator  62 ′ can have a plurality of corresponding flow channels  110 . The Holweck thread of the Holweck stage  14  can in principle be formed homogeneous with webs and Holweck channels extending over the whole axial length. The Holweck thread can also be designed, as shown in  FIG. 2 , to achieve a direct introduction of the gas into the inlet of the side channel pump. The Holweck thread not shown separately in  FIG. 6  can in this respect be located at the Holweck stator, likewise not shown, or at the radial inner surface of the rotor member  32 . 
     The pump-active structure of the side channel pump stage  18  is formed in principle as explained above with respect to  FIG. 1 . The side channel pump stage  18  includes vane-like rotor elements  48 ′ which are arranged on a rotor hub  114  which is spaced apart from the rotor hub  30 ′ of the Holweck stages  12 ,  14  in the axial direction. The rotor hub  114  is formed in disk form and extends in the radial direction. The rotor elements  48 ′ project in the radial direction from the margin of the rotor hub  114  and into the side channel  64 ′ open in the radial direction. A large diameter of the side channel pump stage  18  and a correspondingly good pumping effect is thereby achieved with a simultaneously compact structure of the pump. The pump shown in  FIG. 6  can have a pump outlet at the axial level of the side channel pump stage  18  which is connected to an outlet of the side channel pump stage  18  and is surrounded, for example, by a small flange. In addition to the Holweck stages  12 ,  14 , the pump shown in  FIG. 6  could have still further Holweck stages connected in series with the Holweck stage  12 ,  14  and preferably arranged in one another in the radial direction. 
     The installation of the Holweck stator sleeves not shown in  FIG. 6  is in this respect possible in a particularly simple manner since the axial end of the Holweck stages  12 ,  14  remote from the rotor hub  30 ′ and shown at the bottom in  FIG. 6  is freely accessible and the access is in particular not blocked by the side channel pump stage  18  so that a particularly simple and compact structure of the vacuum pump is achieved. 
       FIG. 7  shows a vacuum pump in accordance with a further embodiment of the invention in an axial section which substantially corresponds to the vacuum pump shown in  FIG. 6 . 
     The pump shown in  FIG. 7  includes, in addition to the side channel pump stage  18 , a plurality of molecular pump stages  12 ,  14 ,  116 ,  118  which are formed as Holweck stages and which include two rotor members  32  having the shape of a cylinder jacket and corresponding Holweck stator sleeves not shown in  FIG. 7 . The Holweck stages  12 ,  14 ,  116 ,  118  are in this respect each formed as described above with respect to  FIG. 6 . The side channel pump stage  18  is also arranged between the pump inlet  24  and the molecular pump stages  12 ,  14 ,  116 ,  118  formed as Holweck stages in the vacuum pump shown in  FIG. 7 . 
     The rotor elements  48  of the side channel pump stage  18  and the rotor members  32  of the Holweck stages  12 ,  14 ,  116 ,  118  are arranged on a  30  common rotor hub  30 ″, with the rotor elements  48 ″ projecting from the margin of the rotor hub  30 ″ in the radial direction and beyond the radial extent of the rotor hub  30 ″. The rotor elements  48  in this respect extend into the side channel  64  open in the radial direction and carry out a revolving movement about the axis of rotation  20  in it. 
     As indicated by the gas flow arrow  84  in  FIG. 7 , the gas enters via the pump inlet  24  into the turbomolecular stage  10  in operation of the pump and is there conveyed in the axial direction to the rotor hub  30 . The rotor hub  30  has one or more axial apertures  120  which provide a gas flow path from the turbomolecular stage  10  radially inwardly past the pump-active structure of the side channel pump stage  16  into the Holweck stage  12  and represent a gas inlet for the Holweck stage  12 . As described above with respect to the Holweck stages  12 ,  14  of the pump shown in  FIG. 6 , the gas is conveyed through the Holweck stages  12 ,  14 ,  116 ,  118  in the axial direction respectively twice from top to bottom and from bottom to top so that overall a reversal of direction of the gas flow direction is effected. In contrast to the embodiment shown in  FIG. 6 , the Holweck stages  12 ,  14 ,  116 ,  118  are, however, flowed through in the order from radially inwardly to radially outwardly so that a gas flow direction from radially inwardly to radially outwardly results. The gas enters at the end of the radially most outwardly disposed Holweck stage  118  facing the pump inlet  24  directly into the side channel pump stage  18  via a flow channel  122  of the side channel stator  62 ″ which is arranged disposed opposite the margin of the rotor hub  30 ″ in the radial direction. After passing through the side channel pump stage  18 , the gas can move to a pump outlet which is preferably arranged at the axial level of the side channel pump stage  18 . 
     Due to the arrangement of the Holweck sleeves  32  and of the rotor elements  48  of the side channel pump stage  18  on a common rotor hub  30 ″, in the embodiment shown in  FIG. 7 , a construction shape is achieved which is extremely compact in the axial direction. However, a rotor hub  114  (see  FIG. 6 ) separate from the rotor hub  40  could also be provided for the side channel pump stage  18 . It could then optionally have apertures through which the gas can be conveyed radially inwardly past the pump-active structure of the side channel pump stage. In principle, the side channel pump stage  18  could also be radially outwardly flowed around, for example through a bypass channel  106  arranged in the housing of the vacuum pump ( FIG. 6 ). 
     The end of the Holweck stages  12 ,  14 ,  116 ,  118  remote from the pump inlet  24  are also freely accessible in the pump shown in  FIG. 7 . The associated stator sleeves which are not shown in  FIG. 7  can thus easily be arranged at an outer wall of the vacuum pump which is disposed opposite the free axial end of the rotor members  32 . 
     REFERENCE NUMERAL LIST 
     
         
           10  turbomolecular pump stage 
           12 ,  14 ,  16  molecular pump stage 
           18  side channel pump stage 
           20  axis of rotation 
           22  rotor shaft 
           24  pump inlet 
           26  flange 
           28  rotor disk 
           30  rotor hub 
           32 ,  34  rotor member 
           36  radial outer surface 
           38  radial inner surface 
           39  Holweck gap 
           40 ,  42  Holweck stator sleeve 
           41 ,  43  Holweck thread 
           44  base part 
           46  support part, support sleeve 
           48  rotor elements 
           50 ,  54  radial outer surface 
           52 ,  55 ,  56  radial inner surface 
           57  Holweck thread 
           58  free space 
           60  support surface 
           62  side channel stator 
           64  side channel, stator channel 
           66 ,  68  section 
           70  threaded projection 
           72  thread channel 
           74  collection region 
           76  supply channel 
           78  projection 
           80  intersection line 
           84  arrow 
           86  stator disk 
           88  drive 
           90  seal 
           92  rotary bearing 
           94  pump outlet 
           95  gas outlet 
           96  tap 
           98  scraper 
           100  connection section 
           102  support section 
           104  balancing bore 
           106  gas flow path 
           108  aperture 
           110  flow channel 
           112  gap 
           114  rotor hub 
           116 ,  118 ,  16  molecular pump stage 
           120  aperture 
           122  flow channel