Turbomolecular vacuum pump with optimized barrier gas supply

Abstract

The present invention relates to a turbomolecular vacuum pump comprising a housing with a pump inlet and a pump outlet, a first pumping mechanism with at least one turbomolecular pumping stage in the housing, a second pumping mechanism located downstream of the first pumping mechanism with at least one Holweck pumping stage in the housing, and a rotor comprising a rotor shaft for both the first and second pumping mechanisms, and an electric motor for driving the rotor shaft. The electric motor is arranged within the second pumping mechanism in a motor compartment, which is surrounded by a cylindrical partition and bounded on the side facing the first pumping mechanism by a radially extending partition that surrounds the rotor, forming an annular gap.The rotor shaft extends from the first pumping mechanism, through the second pumping mechanism and the motor compartment, to an end supported in the housing by a roller bearing. The housing has at least one purge gas connection for introducing a purge gas to protect the electric motor. A flow channel is formed in the cylindrical partition, which is connected to the purge gas connection on one side and, via a flow path, to the annular space on the other.

Description

[0001] The present invention relates to a turbomolecular vacuum pump with optimized seal gas supply. In particular, the invention relates to a turbomolecular vacuum pump with a Holweck pumping stage, within which the electric motor of the turbomolecular vacuum pump, also referred to here simply as a turbomolecular pump or "pump," is located. A seal gas inlet opens into the Holweck pumping stage, through which a seal gas can be introduced to protect the motor and the adjacent bearing area from corrosive components that may be part of the process gas to be pumped. Such components do not necessarily have to have a corrosive effect; rather, they can also be particles or dust that can contaminate the operating fluid or clog gaps. Furthermore, other components can also simply contaminate the operating fluid.

[0002] Since the barrier gas is usually introduced into the pump system near a mostly oil-lubricated rolling bearing, it can happen, especially when large quantities of barrier gas are introduced into the pump system, that the barrier gas absorbs and entrains oil vapors, which can diffuse from the bearing area. The barrier gas, enriched with oil in this way, can then spread through the pump system and reach an instrument connected to the pump inlet, where it can cause erroneous measurements and / or damage. Likewise, the barrier gas spreading through the pump system can reach the forevacuum region near the pump outlet, which is in fluid communication with the outlet of the Holweck pump stage, where the oil particles contained in the barrier gas can precipitate as an oil film, which can cause irritation to the pump user.

[0003] The invention is therefore based on the object of providing a turbomolecular vacuum pump with a Holweck pumping stage and a sealing gas inlet in which the probability that the sealing gas absorbs oil particles from the bearing area is minimized.

[0004] This object is achieved with a turbomolecular vacuum pump having the features of claim 1.

[0005] In particular, the object is achieved in that at least one inflow channel is formed in the cylindrical partition wall, which is part of an engine cover and separates the engine compartment from the forevacuum area at the outlet of the most downstream Holweck pump stage. This inflow channel is oriented substantially axially with respect to the rotor axis, and is fluidly connected at one end to the barrier gas connection and at the other end, via a flow path that may be complex, to the annular space located at forevacuum level, which surrounds the cylindrical partition wall of the engine cover in question. The at least one inflow channel is oriented substantially axially and thus extends inside the cylindrical partition wall.In other words, the end of the inflow channel that is in fluid communication with the barrier gas connection is located in a different radially extending plane in the axial direction than the other end of the inflow channel. The radial planes in which the two ends of the inflow channel are located are therefore spaced apart from each other in the axial direction.

[0006] The barrier gas is therefore not introduced in a radial direction directly into the motor compartment, where, due to the fact that the motor compartment directly adjoins the bearing area of ​​the pump rotor, the probability of oil being absorbed by the barrier gas from the bearing area is high; rather, due to the fact that the inflow channel in question is formed in or within the axially extending cylindrical partition wall, the barrier gas is initially guided through the inflow channel in an axial direction away from the bearing area and towards the electric motor or towards the first pumping mechanism, thereby minimizing the probability of oil being absorbed from the bearing area.If the barrier gas is directed into the engine compartment after flowing through the inflow channel near the radially extending partition of the engine cover, it can then spread through the engine / rotor gap toward the bearing area, where it then acts as a type of buffer or barrier for the barrier gas subsequently flowing through the inflow channel. Instead, the barrier gas then flows through the annular gap between the rotor and the radially extending partition of the engine cover into the annular space surrounding the cylindrical partition, which is at the pre-vacuum level. This barrier gas, which flows in, contains little or no oil vapor due to the fact that it does not come into contact with the bearing area due to the buffer effect of the barrier gas initially flowing into the engine compartment.

[0007] According to the invention, it is thus ensured, to a certain extent, that the barrier gas spreading in the pump system cannot come into contact with the bearing area. Rather, the barrier gas is initially directed axially away from the bearing area through the essentially axially extending inflow channel, thereby minimizing the likelihood of oil vapors being absorbed by the barrier gas. As a result, larger quantities of barrier gas can be admitted.

[0008] Since the purge gas connection can also be used for flooding during pump shutdown, larger quantities of flooding gas can be used, which shortens the time required to shut down the pump.

[0009] Preferred embodiments of the invention will now be discussed below. Further embodiments may arise from the dependent claims, the description of the figures, and the drawings.

[0010] Thus, according to one embodiment, the sealing gas connection can be formed in a lower housing section of the turbomolecular vacuum pump housing, wherein this lower housing section accommodates the rolling bearing or the bearing mount containing the rolling bearing. The cylindrical partition wall, which together with the radially extending partition wall forms the motor cover, extends from a radial plane in which the rolling bearing is located, in the axial direction to an upper housing section connected to the lower housing section, in which the first pumping mechanism is located and which, together with the lower housing section, forms a receiving space for the second pumping mechanism, including the electric motor.

[0011] According to a further embodiment, it can be provided that the at least one sealing gas connection, which can be provided on the lower housing part, is in fluid communication with the inflow channel via a radially extending sealing gas channel, which is also formed in the lower housing part. Thus, starting from the sealing gas connection, there is a direct flow path to the inflow channel, which is formed in the axially extending cylindrical partition wall of the engine cover, so that the sealing gas cannot even enter the engine compartment, which is circumferentially delimited by the cylindrical partition wall.

[0012] According to yet another embodiment, it can be provided that the turbomolecular vacuum pump, and in particular the housing lower part, has at least two sealing gas connections, one of which is provided at a radially outer end of the sealing gas channel, whereas the other sealing gas connection is in fluid communication with the sealing gas channel via a sealing gas bore that opens into the sealing gas channel at a point located radially inside the radially outer end of the sealing gas channel. For example, the other sealing gas connection can be provided on an underside of the housing lower part and connected to the sealing gas channel by an axially extending sealing gas bore. In confined spaces, sealing gas can thus be supplied to the pump in the radial or axial direction, as required, by means of a corresponding sealing gas supply line.

[0013] To ensure the most even distribution of the sealing gas within the pump system, a further embodiment can provide for the inflow channel to open downstream into a circumferential annular channel formed circumferentially in the cylindrical partition wall and which, in turn, is fluidly connected to the annular space, possibly via the engine compartment, via a flow path that may be complex. The sealing gas can thus spread and distribute in the circumferential direction through the annular channel, from where it enters the engine compartment and / or the annular space surrounding the cylindrical partition wall.

[0014] In order to be able to form the annular channel in the cylindrical partition wall, it can be provided according to a further embodiment that the cylindrical partition wall is composed of two axially aligned cylindrical wall sections, wherein the annular channel is formed at the connection point at which the two cylindrical wall sections are connected to one another. Specifically, it can be the case that a first of the two cylindrical wall sections extends from the lower housing part in the direction of the first pump mechanism to a free end at which the first cylindrical wall section is connected to the second of the two cylindrical wall sections, which from there also extends in the direction of the first pump mechanism to an end at which the radially extending partition wall is connected to the second cylindrical wall section.Thus, for example, an annular circumferential recess can be formed at the free end of the first cylindrical wall section and / or at the adjoining end of the second cylindrical wall section, which then forms the annular channel when the two cylindrical wall sections are connected to one another.

[0015] According to a preferred embodiment, it can be provided that the first cylindrical wall section has a circumferential first annular projection at its free end, which has a smaller thickness than the first cylindrical wall section. Correspondingly, the end of the second cylindrical wall section, which is connected to the free end of the first cylindrical wall section, can have a circumferential second annular projection that surrounds the first annular projection and has a smaller thickness than the second cylindrical wall section. In this case, the annular channel between the two annular projections can be created by a chamfer or rounding that is formed circumferentially along the inner edge of the free end of the second annular projection.

[0016] To allow the sealing gas to flow from the annular channel into the engine compartment, a further embodiment may provide for the engine compartment to be fluidly connected to the annular channel via at least one distribution channel defined by the cylindrical partition wall. Preferably, several such connecting channels are provided, which are spaced apart from one another in the circumferential direction of the annular channel, preferably evenly spaced, in order to ensure the most even possible supply of sealing gas to the engine compartment.

[0017] To ensure that as much of the same amount of sealing gas as possible can flow into the engine compartment through each of the distribution channels in question, a further embodiment may provide for the distribution channels to have at least partially different flow cross-sections and / or for the flow cross-section of the annular channel to increase with increasing distance from the inflow channel in the circumferential direction. In particular, it may be provided that those distribution channels that are further away from the inflow channel in the circumferential direction than distribution channels located closer to the inflow channel have a larger flow cross-section than the distribution channels located closer to the inflow channel.Since the sealing gas seeks the path of least resistance, it can be ensured that the sealing gas entering the annular channel via the inflow channel does not immediately escape again through the distribution channels located in the immediate vicinity of the inflow channel, but can also reach the distribution channels further away from the inflow channel, thus ultimately ensuring an even distribution of the sealing gas through all distribution channels.

[0018] According to yet another embodiment, it can be provided that a section of the respective distribution channel is formed by an axially extending recess in the first and / or second cylindrical wall section, preferably by a respective axially extending recess in the first and / or second annular projection. For example, the second cylindrical wall section can be penetrated by a slot extending in the axial direction, so that the sealing gas can escape from the annular channel through this slot to flow toward the radially extending partition wall of the engine cover.

[0019] According to yet another embodiment, the electric motor in the engine compartment has a motor stator that rests on the inside of the cylindrical partition wall only along a central circumferential region. On the side of the central circumferential region facing the first pump mechanism, however, the motor stator is spaced from the cylindrical partition wall by a circumferential annular space. Since the motor stator thus does not rest on the inside of the cylindrical partition wall in the region of the annular space in question, the at least one previously described distribution channel can open into the engine compartment in this region.Sealing gas, which enters the annular space between the motor stator and the cylindrical partition wall through the aforementioned distribution channels, can thus spread further axially from there within the motor compartment to reach a gap serving as an expansion volume, by which the motor stator is spaced from the radially extending partition wall on its side facing the first pump mechanism. Since the annular gap between the radially extending partition wall and the pump rotor directly adjoins the expansion volume in question, the annular gap can thus be sealed by the sealing gas, thereby preventing corrosive components from the process gas from entering the interior of the motor compartment in the desired manner.

[0020] According to the previously described flow path, the sealing gas thus passes from the annular channel via the motor compartment to the annular gap, from where it can reach the outlet of the Holweck pump stage via the annular space surrounding the cylindrical partition wall, which is at the pre-vacuum level. Additionally or alternatively, according to a further embodiment, the annular channel can be directly fluidically connected to the annular space radially outside the cylindrical partition wall via at least one distribution channel extending radially through the cylindrical partition wall. Preferably, several such distribution channels can be provided, which are spaced apart from one another, preferably evenly, in the circumferential direction of the annular channel.In this embodiment, too, it can be provided that the distribution channels have at least partially different flow cross-sections from one another and / or that the flow cross-section of the annular channel increases with increasing distance from the inflow channel in order to achieve the most uniform distribution of the barrier gas possible.

[0021] In order to prevent backflow of process gas, which is conveyed from the Holweck pump stage to the pump outlet, into the engine compartment via the annular space surrounding the cylindrical partition, it can be provided according to yet another embodiment that the cylindrical partition is surrounded on the outer circumference by a barrier geometry, such as a circumferential annular flange. Preferably, the barrier geometry is located closer in the axial direction to the radially extending partition of the engine cover than the distribution channels penetrating the cylindrical partition. This ensures that process gas escaping from the Holweck pump stage cannot even reach the barrier geometry, whereby the annular space surrounding the cylindrical partition is also effectively protected from corrosive components of the process gas.Additionally or alternatively, the barrier geometry can also be designed as a pump-active structure in the manner of a Holweck thread section, which reduces the probability of process gas flowing into the annular space surrounding the cylindrical partition wall.

[0022] The invention is described below by way of example using advantageous embodiments with reference to the accompanying figures. They show, schematically: Fig. 1a perspective view of a turbomolecular pump, Fig. 2a view of the underside of the turbomolecular pump of Fig. 1 , Fig. 3 a cross-section of the turbomolecular pump along the Fig. 2 shown section line AA, Fig. 4 a cross-sectional view of the turbomolecular pump along the Fig. 2 shown section line BB, Fig. 5 a cross-sectional view of the turbomolecular pump along the Fig. 2 shown section line CC, Fig. 6one of the Fig. 3corresponding cross-section of a turbomolecular vacuum pump designed according to the invention, Fig. 7 the detail "X" of the Fig. 6 in the top view according to section MM, Fig. 8 the detail "Y" of the Fig. 6 in plan view according to section MM, Fig. 9that in the Fig. 6 marked detail "X" in enlarged view, Fig. 10 the sealing gas flow path of the turbomolecular vacuum pump according to Fig. 6 , Fig. 11 and 12 the sealing gas flow path according to two further embodiments of a turbomolecular vacuum pump.

[0023] The Fig. 1The turbomolecular pump 111 shown comprises a pump inlet 115 surrounded by an inlet flange 113, to which a recipient (not shown) can be connected in a manner known per se. The gas from the recipient can be sucked out of the recipient via the pump inlet 115 and conveyed through the pump to a pump outlet 117, to which a backing pump, such as a rotary vane pump, can be connected.

[0024] The inlet flange 113 forms the vacuum pump alignment according to Fig. 1 the upper end of the housing 119 of the vacuum pump 111. The housing 119 comprises a lower part 121, on which an electronics housing 123 is arranged laterally. Electrical and / or electronic components of the vacuum pump 111 are housed in the electronics housing 123, e.g., for operating an electric motor 125 arranged in the vacuum pump (see also Fig. 3). Several connectors 127 for accessories are provided on the electronics housing 123. In addition, a data interface 129, e.g., according to the RS485 standard, and a power supply connector 131 are arranged on the electronics housing 123.

[0025] There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

[0026] On the housing 119 of the turbomolecular pump 111, a flooding inlet 133, in particular in the form of a flooding valve, is provided, via which the vacuum pump 111 can be flooded. In the area of ​​the lower part 121, a sealing gas connection 135, which is also referred to as a purge gas connection, is also arranged, via which purge gas is supplied to protect the electric motor 125 (see e.g. Fig. 3) can be admitted into the motor compartment 137, in which the electric motor 125 is housed in the vacuum pump 111, before the gas delivered by the pump. Furthermore, two coolant connections 139 are arranged in the lower part 121, one of which serves as an inlet and the other as an outlet for coolant, which can be fed into the vacuum pump for cooling purposes. Other existing turbomolecular vacuum pumps (not shown) are operated exclusively with air cooling.

[0027] The lower side 141 of the vacuum pump can serve as a base, so that the vacuum pump 111 can be operated standing on the underside 141. However, the vacuum pump 111 can also be attached to a recipient via the inlet flange 113 and thus operated in a suspended position. Furthermore, the vacuum pump 111 can be designed so that it can also be operated when oriented in a different manner than in Fig. 1 As shown. Embodiments of the vacuum pump can also be realized in which the underside 141 is arranged facing either sideways or upwards, rather than downwards. In principle, any angle is possible.

[0028] Other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here, cannot be operated in an upright position.

[0029] 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 together. For example, a bearing cover 145 is attached to the underside 141.

[0030] Mounting holes 147 are also arranged on the underside 141, through which the pump 111 can be attached, for example, to a support surface. This is not possible with other existing turbomolecular vacuum pumps (not shown), which are particularly larger than the pump shown here.

[0031] In the Figures 2 to 5 a coolant line 148 is shown in which the coolant introduced and discharged via the coolant connections 139 can circulate.

[0032] As the sectional views of the Figures 3 to 5 show, the vacuum pump comprises several process gas pumping stages for conveying the process gas present at the pump inlet 115 to the pump outlet 117.

[0033] A rotor 149 is arranged in the housing 119 and has a rotor shaft 153 rotatable about a rotation axis 151.

[0034] The turbomolecular pump 111 comprises several turbomolecular pump stages connected in series for pumping purposes, with several radial rotor disks 155 attached to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and secured in the housing 119. A rotor disk 155 and an adjacent stator disk 157 each form a turbomolecular pump stage. The stator disks 157 are held at a desired axial distance from one another by spacer rings 159.

[0035] The vacuum pump also includes Holweck pump stages arranged radially one inside the other and connected in series for pumping efficiency. Other turbomolecular vacuum pumps (not shown) exist that do not have Holweck pump stages.

[0036] The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical-shell-shaped Holweck rotor sleeves 163, 165 attached to and supported by the rotor hub 161, which are oriented coaxially to the rotational axis 151 and nested within one another in the radial direction. Furthermore, two cylindrical-shell-shaped Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the rotational axis 151 and nested within one another in the radial direction.

[0037] The pumping surfaces of the Holweck pump stages are formed by the lateral surfaces, i.e., the radial inner and / or outer surfaces, of the Holweck rotor sleeves 163, 165 and the Holweck stator sleeves 167, 169. The radial inner surface of the outer Holweck stator sleeve 167 lies opposite the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together with the latter forms the first Holweck pump stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 lies opposite the radial outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together with the latter forms a second Holweck pump stage. The radial inner surface of the inner Holweck stator sleeve 169 lies opposite the radial outer surface of the inner Holweck rotor sleeve 165, forming a radial Holweck gap 175 and together forming the third Holweck pumping stage.

[0038] At the lower end of the Holweck rotor sleeve 163, a radially extending channel can be provided, via which the radially outer Holweck gap 171 is connected to the central Holweck gap 173. Furthermore, at the upper end of the inner Holweck stator sleeve 169, a radially extending channel can be provided, via which the central Holweck gap 173 is connected to the radially inner Holweck gap 175. This connects the nested Holweck pump stages in series. A connecting channel 179 to the outlet 117 can also be provided at the lower end of the radially inner Holweck rotor sleeve 165.

[0039] The above-mentioned pump-active surfaces of the Holweck stator sleeves 167, 169 each have a plurality of Holweck grooves extending spirally around the rotation axis 151 in the axial direction, while the opposite lateral surfaces of the Holweck rotor sleeves 163, 165 are smooth and propel the gas in the Holweck grooves for operating the vacuum pump 111.

[0040] 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.

[0041] In the area of ​​the rolling bearing 181, a conical spray nut 185 with an outer diameter increasing toward the rolling bearing 181 is provided on the rotor shaft 153. The spray nut 185 is in sliding contact with at least one wiper of a fluid reservoir. In other existing turbomolecular vacuum pumps (not shown), a spray screw can be provided instead of a spray nut. Since different designs are thus possible, the term "spray tip" is also used in this context.

[0042] The operating fluid storage comprises several stacked absorbent discs 187, which are impregnated with an operating fluid for the rolling bearing 181, e.g. with a lubricant.

[0043] During operation of the vacuum pump 111, the operating fluid is transferred by capillary action from the operating fluid reservoir via the wiper to the rotating injection nut 185. As a result of centrifugal force, it is conveyed along the injection nut 185 in the direction of the increasing outer diameter of the injection nut 185 to the rolling bearing 181, where it fulfills a lubricating function, for example. The rolling bearing 181 and the operating fluid reservoir are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

[0044] The permanent magnet bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each comprising a ring stack of several permanent magnetic rings 195, 197 stacked one on top of the other in the axial direction. The ring magnets 195, 197 lie opposite one another, forming a radial bearing gap 199, with the rotor-side ring magnets 195 being arranged radially on the outside and the stator-side ring magnets 197 being arranged radially on the inside. The magnetic field present in the bearing gap 199 creates magnetic repulsion forces between the ring magnets 195, 197, which effect a radial bearing of the rotor shaft 153. The rotor-side ring magnets 195 are carried by a support section 201 of the rotor shaft 153, which surrounds the ring magnets 195 on the radial outside.The stator-side ring magnets 197 are supported by a stator-side support section 203, which extends through the ring magnets 197 and is suspended from radial struts 205 of the housing 119. The rotor-side ring magnets 195 are secured parallel to the rotation axis 151 by a cover element 207 coupled to the support section 201. The stator-side ring magnets 197 are secured parallel to the rotation axis 151 in one direction by a fastening ring 209 connected to the support section 203 and a fastening ring 211 connected to the support section 203. A disc spring 213 can also be provided between the fastening ring 211 and the ring magnets 197.

[0045] Within the magnetic bearing, an emergency or backup bearing 215 is provided, which runs idle without contact during normal operation of the vacuum pump 111 and only engages upon excessive radial deflection of the rotor 149 relative to the stator, forming a radial stop for the rotor 149 to prevent collision of the rotor-side structures with the stator-side structures. The backup bearing 215 is designed as an unlubricated rolling bearing and forms a radial gap with the rotor 149 and / or the stator, causing the backup bearing 215 to be disengaged during normal pumping operation. The radial deflection at which the backup bearing 215 engages is large enough so that the backup bearing 215 does not engage during normal operation of the vacuum pump, yet small enough so that collision of the rotor-side structures with the stator-side structures is prevented under all circumstances.

[0046] The vacuum pump 111 comprises the electric motor 125 for rotating the rotor 149. The armature of the electric motor 125 is formed by the rotor 149, whose rotor shaft 153 extends through the motor stator 217. A permanent magnet arrangement can be arranged radially on the outside or embedded in the portion of the rotor shaft 153 extending through the motor stator 217. Between the motor stator 217 and the portion of the rotor 149 extending through the motor stator 217, an intermediate space 219 is arranged, which comprises a radial motor gap, via which the motor stator 217 and the permanent magnet arrangement can magnetically influence each other to transmit the drive torque.

[0047] The motor stator 217 is secured in the housing within the motor compartment 137 provided for the electric motor 125. A seal gas, also referred to as purge gas, which may be air or nitrogen, for example, can enter the motor compartment 137 via the seal gas connection 135. The seal gas can be used to protect the electric motor 125 from process gas, e.g., from corrosive components of the process gas. The motor compartment 137 can also be evacuated via the pump outlet 117, i.e., the vacuum pressure in the motor compartment 137 is at least approximately equal to the vacuum pressure created by the backing pump connected to the pump outlet 117.

[0048] A so-called labyrinth seal 223, known per se, can also be provided between the rotor hub 161 and a wall 221 delimiting the motor chamber 137, in particular to achieve better sealing of the motor chamber 217 with respect to the Holweck pump stages located radially outside. In the previously described turbomolecular vacuum pump 111, the seal gas passes directly into the motor chamber 137 via the seal gas connection 135 in the manner already described. The motor chamber 137 is fluidically largely separated from the forevacuum area at the outlet of the Holweck pump stage by the wall 221, also referred to below as the motor cover, and in particular by the labyrinth seal 223. However, since the bearing area and in particular the oil-lubricated rolling bearing 181 is located in the engine compartment 137, the barrier gas flowing into the engine compartment 137 can undesirably absorb oil vapors that diffuse from the rolling bearing 181 into the engine compartment 137.The sealing gas enriched with oil in this way can then flow through the gap 219 and through the labyrinth seal 223, from where it can reach the connecting channel 179 at the outlet of the Holweck pump stage, where it can deposit in an undesirable manner as an oil film.

[0049] In order to counteract this problem, it is necessary to use the following, with reference to the Fig. 6In the turbomolecular vacuum pump 300 described above, which is designed as a so-called split-flow pump, it is provided that the sealing gas channel 302, which extends radially inward from the sealing gas connection 304 in the housing lower part 306, does not open directly into the motor compartment 320, but rather that the sealing gas channel 302 continues into an adjoining inflow channel 312, which is formed in the motor cover and in particular in its cylindrical partition wall 314. The sealing gas flowing in through the sealing gas channel 302 is thus initially guided away from the bearing area in which the rolling bearing 318 is located, in the axial direction, in order to subsequently reach the annular space 320 surrounding the cylindrical partition wall 314 via a flow path that will be described in more detail later. Although the pump in the figure is a split-flow pump, the sealing gas concept according to the invention can of course also be used in a conventional turbomolecular pump according to Figs. 1 to 5be realized.

[0050] Before we take a closer look at the structural design of the Fig. 6 Before discussing the turbomolecular vacuum pump 300 shown in Figure 1, it should be noted that the structural design of this pump 300 largely corresponds to the design of the pump 300 shown in Figure 1 with reference to Fig. 1 to 5 described pump, which is why only the differences essential to the invention will be discussed below.

[0051] As already mentioned above, the turbomolecular vacuum pump 300 according to the invention provides that the barrier gas channel 302, which extends radially inward from the barrier gas connection 304 in the housing lower part 306, continues into an axially extending inflow channel 312 formed within the cylindrical partition wall 314 of the motor cover. In addition to the radial barrier gas connection 304, the pump 300 has an axially aligned barrier gas connection 305, which is fluidly connected to the barrier gas channel 302 via a barrier gas bore 307, so that barrier gas can be supplied to the inflow channel 312 via the radial barrier gas connection 304 and / or the axial barrier gas connection 305, as required.

[0052] In the embodiment shown here, the cylindrical partition 314, which circumferentially surrounds the motor compartment 310, is composed of a first cylindrical wall section 322 and a second cylindrical wall section 324. The first cylindrical wall section 322 extends from the housing base 308 in the direction of the first pumping mechanism, which is formed by the rotor and stator disks of the turbomolecular pumping mechanism. The free end of this first cylindrical wall section 322 is connected, in the manner described in more detail below, to the second cylindrical wall section 324, which extends from the free end of the first cylindrical wall section 322 in the direction of the first pumping mechanism to an end at which the radially extending partition 316 is connected to the second cylindrical wall section 324.

[0053] Again Fig. 6 in connection with the Fig. 9can be removed, the first cylindrical wall section 322 has at its free end a circumferential first annular projection 326 extending therefrom, wherein the thickness of this first annular projection 326 is less than that of the first cylindrical wall section 322. In a corresponding manner, the end of the second cylindrical wall section 324 connected to the free end of the first cylindrical wall section 322 also has a circumferential second annular projection 328, the thickness of which is less than that of the second cylindrical wall section 324. The second annular projection 328 surrounds the first annular projection 326 and can be screwed or pressed thereto, for example. As can be seen in particular from the detailed illustration of the Fig. 9can be seen, the inner edge of the free end of the second annular projection 328 is rounded, so that by this rounding 330, which can alternatively also be designed as a simple chamfer, a circumferential annular channel 332 is formed between the two annular projections 326, 328, into which the inflow channel 312 opens from below, see also the top view detail of the Fig. 7 .

[0054] As the top view detail of the Fig. 7can further be removed, the first annular projection 326 has a recess in the form of a slot 334 extending in the axial direction, wherein this recess can continue as a groove on the inside of the second cylindrical wall section 324. Sealing gas that reaches the annular channel 332 via the inflow channel 312 can thus spread in the axial direction through the distribution channel 336 designed as a slot 334 and the groove (not shown) continuing therefrom on the inside of the second cylindrical wall section 324, in order to reach the upper region of the engine compartment 310 from there.

[0055] As the top view detail of the Fig. 8can be removed, a further distribution channel 336 branches off from the annular channel 332 in the axial direction, which is located on the side of the annular channel 332 opposite the distribution channel 336 formed by the slot 334. Specifically, this distribution channel 336 is formed by an axially extending slot 338 in the lower annular projection 326 and by a recess 340 in the second annular projection 328, which, like the slot 338, extends in the axial direction. The distribution channel 336 formed by this slot 338 and by the recess 340 has a larger flow cross-section than the distribution channel 336 formed by the slot 334, which ensures that approximately the same amount of sealing gas can reach the engine compartment 310 through both distribution channels 336.For the sake of clarity, it should be noted at this point that the flow cross-section formed by the slot 338 and the recess 340 can continue in the axial direction into the second cylindrical wall section 324 in order to allow the sealing gas to flow into the engine compartment 310.

[0056] Although in the embodiment described here only two distribution channels 336 branch off from the annular channel 332 in the axial direction, three or more distribution channels 336 can also branch off from the annular channel 332, as shown in the Fig. 8are indicated by dashed lines as semicircular recesses in the two annular projections 326, 328, wherein these additional distribution channels 336 should preferably be evenly spaced from one another in the circumferential direction. Preferably, the flow cross-section of the respective distribution channels 336 should be larger the further they are circumferentially removed from the inflow channel 312, in order to ensure a uniform supply of sealing gas to the engine compartment 310.

[0057] Additionally or alternatively, the flow cross-section of the annular channel 332 may increase with increasing distance from the inflow channel 312, since this can also ensure that substantially the same amount of barrier gas can flow into the engine compartment 310 through the distribution channels 336 further away from the inflow channel 312 as through the distribution channels 336 located closer to the inflow channel 312.

[0058] The fact that the barrier gas can flow unhindered through the previously described distribution channels 336 into the motor compartment 310 is due to the fact that the motor stator 342 only rests on the inside of the cylindrical partition 314 along a central circumferential region 344. In contrast, the motor stator 342 is spaced from the cylindrical partition 314 on both sides of this central region 344 by an annular space 346, so that on the side of the central circumferential region 344 facing the first pump mechanism, the barrier gas can flow unhindered from the distribution channels 336 into the annular space 346, from where it can expand further in the direction of the annular gap 348, through which the rotor 356 is separated from the radially extending partition 316. Specifically, the sealing gas expands in the area serving as expansion volume 350, which is formed by the distance between the motor stator 342 and the radially extending partition wall 316.

[0059] Sealing gas, which reaches the annular gap 348 on the previously described flow path, thus reliably seals it, wherein due to the fact that the sealing gas does not come into contact with oil vapors from the rolling bearing 380 on its way to the annular gap 348, it can be prevented that the sealing gas entrains oil particles from the rolling bearing 318 on its further path to the annular space 320 surrounding the cylindrical partition wall 314, which could otherwise undesirably precipitate as an oil film in the forevacuum area at the outlet of the Holweck pump stage.

[0060] According to the schematic representation of the Fig. 10A portion of the initially introduced barrier gas flows through the motor / rotor gap 353 into the lower region of the motor compartment 310 and thus into the vicinity of the bearing area or the rolling bearing 318; however, this barrier gas volume initially flowing through the motor / rotor gap represents a buffer for barrier gas flowing into the expansion volume 350, so that with continuous barrier gas application during pumping operation, no further barrier gas can flow into the lower region of the motor compartment 310. Thus, the lower region of the motor compartment 310 is not flowed through by barrier gas during pumping operation, which can prevent the barrier gas from entraining oil particles from the rolling bearing 318 on its way to the annular gap 348, which could otherwise subsequently precipitate as an oil film in the forevacuum area.

[0061] In contrast to the previously described embodiment, whose sealing gas flow path is shown schematically in the Fig. 10and in which the sealing gas first passes through the inflow channel 312 into the upper section of the engine compartment 310, from there through the annular gap 348 into the annular space 320 outside the cylindrical partition wall 314, it is in the cases described with reference to the Fig. 11 and 12 In the embodiments shown very schematically, it is provided that the sealing gas passes into the annular space 320, which surrounds the cylindrical partition wall 314, bypassing the engine compartment 310: Thus, in the embodiment of the Fig. 11 the inflow channel 312 in turn into an annular channel 332 in the cylindrical partition wall 314, wherein this annular channel 223 is in fluid communication with the annular space 320 outside the cylindrical partition wall 314 via a plurality of distribution channels 336 which extend radially through the cylindrical partition wall 314.

[0062] Alternatively, it is possible to use the Fig. 12In the embodiment shown, it is provided that the barrier gas channel 302 initially merges into an annular channel 332 in the lower housing part 306, from where a plurality of inflow channels 312 extend upwards in the cylindrical partition wall 314, wherein these inflow channels 312 are in fluid communication with the annular space 320 outside the cylindrical partition wall 314 via radial bores. In addition, it is provided in this embodiment that the cylindrical partition wall 314 is surrounded on the outer circumference by a barrier geometry 354, such as an annular flange here, which prevents backflow of process gas via the annular space 320 into the motor compartment 310. Additionally or alternatively, the barrier geometry can also be designed as a pump-active structure in the manner of a Holweck threaded section, which reduces the probability of process gas flowing into the annular space surrounding the cylindrical partition wall. List of reference symbols

[0063] 111Turbomolecular pump 113Inlet flange 115Pump inlet 117Pump outlet 119Housing 121Lower section 123Electronics housing 125Electric motor 127Accessory connection 129Data interface 131Power supply connection 133Flood inlet 135Seal gas connection 137Motor compartment 139Coolant connection 141Underside 143Screw 145Bearing cover 147Mounting hole 148Coolant line 149Rotor 151Rotation axis 153Rotor shaft 155Rotor disc 157Stator disc 159Spacer ring 161Rotor hub 163Holweck rotor sleeve 165Holweck rotor sleeve 167Holweck stator sleeve 169Holweck stator sleeve 171Holweck gap 173Holweck gap 175Holweck gap 179Connecting channel 181Rolling bearing 183Permanent magnet bearing 185Injection nut 187Disc 189Insert 191Rotor-side bearing half 193Stator-side bearing half 195Ring magnet 197Ring magnet 199Bearing gap 201Support section 203Support section 205Radial strut 207Cover element 209Support ring 211Fastening ring 213Disc spring 215Emergency orSafety bearing 217 Motor stator 219 Intermediate space 221 Wall 223 Labyrinth seal 300 Turbomolecular pump 302 Sealing gas channel 304 Radial sealing gas connection 305 Axial sealing gas connection 306 Lower housing section 307 Sealing gas bore 308 Upper housing section 310 Motor compartment 312 Inflow channel 314 Cylindrical partition wall 316 Radially extending partition wall 318 Rolling bearing 320 Annular space 322 First cylindrical wall section 324 Second cylindrical wall section 326 First annular projection 328 Second annular projection 330 Rounding 332 Annular channel 334 Slot 336 Distribution channel 338 Slot 340 Recess 342 Motor stator 344 Middle area 346 Annular space 348Annular gap 350Expansion volume 353Motor / rotor gap 354Blocking geometry 356Rotor 358Rotor shaft.

Claims

1. Turbomolecular vacuum pump (300) comprising: - a housing (306, 308) with a pump inlet (115) and a pump outlet (117); - a first pumping mechanism with at least one turbomolecular pumping stage in the housing (306, 308); - a second pumping mechanism located downstream of the first pumping mechanism with at least one Holweck pumping stage in the housing (306, 308), wherein the first and second pumping mechanisms are designed to jointly convey a process gas from the pump inlet (115) to the pump outlet (117); - a rotor (360) comprising a rotor shaft (358) for both the first pumping mechanism and the second pumping mechanism; and - an electric motor (125) for driving the rotor shaft (358);wherein the electric motor (125) is arranged in a motor chamber (310) located radially inside the second pumping mechanism, which motor chamber is surrounded on the circumferential side by a cylindrical partition (314) and is delimited on the side facing the first pumping mechanism by a radially extending partition (316) which surrounds the rotor (360) to form an annular gap (348), via which the motor chamber (310) is fluidly connected to an annular chamber (320) surrounding the cylindrical partition (314) and leading to the pump outlet; wherein the rotor shaft (358) extends from the first pumping mechanism through the second pumping mechanism and through the motor chamber (310) to an end which is mounted in the housing (306, 308) by means of a rolling bearing (318); wherein the housing (306, 308) has at least one barrier gas connection (304, 305) for introducing a barrier gas to protect the electric motor (125);and wherein an inflow channel (312) is formed in the cylindrical partition wall (314), which is in fluid communication on the one hand with the barrier gas connection (304, 305) and on the other hand via a flow path with the annular space (320); 2. Turbomolecular vacuum pump (300) according to claim 1, wherein the barrier gas connection (304, 305) is formed in a lower housing part (306) of the housing (306, 308), which receives the rolling bearing (318) and from which the cylindrical partition wall (314) extends in the axial direction to a housing upper part (308) connected to the lower housing part (306), in which the first pumping mechanism is located and which, together with the lower housing part (306), forms a receiving space in which the second pumping mechanism is located.

3. Turbomolecular vacuum pump (300) according to claim 1 or 2, wherein the at least one barrier gas connection (304, 305) is in fluid communication with the inflow channel (312) via a barrier gas channel (302) extending in the radial direction.

4. Turbomolecular vacuum pump (300) according to claim 3, wherein the turbomolecular vacuum pump (300) has two barrier gas connections (304, 305), one of which is provided at a radially outer end of the barrier gas channel (302), whereas the other barrier gas connection (305) is in fluid communication with the barrier gas channel (302) via a barrier gas bore (307) which opens into the barrier gas channel (302) at a point which is located radially inside the radially outer end of the barrier gas channel (302).

5. Turbomolecular vacuum pump (300) according to one of the preceding claims, wherein the inflow channel (312) opens downstream into a circumferential annular channel (332) which is formed circumferentially in the cylindrical partition wall (314) and which in turn is at least indirectly in fluid communication with the annular space (320).

6. Turbomolecular vacuum pump (300) according to claim 5, wherein the cylindrical partition wall (314) has a first cylindrical wall section (322) which extends from the housing lower part (306) in the direction of the first pumping mechanism to a free end, and a second cylindrical wall section (324) which is connected to the free end of the first cylindrical wall section (322) and which extends from there in the direction of the first pumping mechanism to an end at which the radially extending partition wall (316) is connected to the second cylindrical wall section (324), wherein the annular channel (332) is formed by the two cylindrical wall sections (322, 324) at the junction of the latter.

7. Turbomolecular vacuum pump (300) according to claim 6, wherein the first cylindrical wall section (322) has at its free end a circumferential first annular projection (326) which has a smaller thickness than the first cylindrical wall section (322), and wherein the end of the second cylindrical wall section (324) connected to the free end has a circumferential second annular projection (328) which surrounds the first annular projection (326) and has a smaller thickness than the second cylindrical wall section (324), wherein an annular channel (332) is created between the two annular projections by a chamfer or rounding (330) which is formed circumferentially along the inner edge of the free end of the second annular projection (328).

8. Turbomolecular vacuum pump (300) according to at least one of claims 5 to 7, wherein the motor chamber (310) is in fluid communication with the annular channel (332) via at least one distribution channel (336) defined by the cylindrical partition wall (314), wherein preferably a plurality of such distribution channels are provided, which are spaced apart from one another in the circumferential direction of the annular channel (332), preferably evenly.

9. Turbomolecular vacuum pump (300) according to claim 8, wherein the distribution channels have at least partially different flow cross-sections from one another and / or wherein the flow cross-section of the annular channel (332) increases with increasing distance from the inflow channel (312).

10. Turbomolecular vacuum pump (300) according to claim 8 or 9, wherein a portion of the respective distribution channel (336) is formed by an axially extending recess (334, 338, 340) in the first and / or in the second cylindrical wall portion (324), preferably by a respective axially extending recess (334, 338, 340) in the first and / or in the second annular projection (328).

11. Turbomolecular vacuum pump (300) according to at least one of claims 8 to 10, wherein the electric motor (125) in the motor compartment (310) has a motor stator (342) which bears against the cylindrical partition wall (314) on the inside only along a central circumferential region, wherein the at least one distribution channel (336) opens into an annular space (346) through which the motor stator (342) is spaced from the cylindrical partition wall (314) on the side of the central circumferential region (344) facing the first pump mechanism.

12. Turbomolecular vacuum pump (300) according to claim 11, wherein the motor stator (342) is spaced from the radially extending partition wall (316) on its side facing the first pumping mechanism by a distance serving as an expansion volume (350) for the barrier gas.

13. Turbomolecular vacuum pump (300) according to at least one of claims 5 to 12, wherein the annular channel (332) is in fluid communication with the annular space (320) radially outside the cylindrical partition wall (314) via at least one distribution channel (336) which extends in the radial direction through the cylindrical partition wall (314), wherein preferably a plurality of such distribution channels are provided which are spaced apart from one another, preferably evenly, in the circumferential direction of the annular channel (332).

14. Turbomolecular vacuum pump (300) according to claim 13, wherein the distribution channels have at least partially different flow cross-sections from one another and / or wherein the flow cross-section of the annular channel (332) increases with increasing distance from the inflow channel (312).

15. Turbomolecular vacuum pump (300) according to one of the preceding claims, wherein the cylindrical partition wall (314) is surrounded on the outer circumference by a blocking geometry (354) which prevents a backflow of process gas via the annular space (320) into the motor space (310).

Images