EP4108931B1 - Method for operating a molecular vacuum pump to achieve improved suction capacity - Google Patents

Description

The present invention relates to a method according to the preamble of claim 1 for operating a molecular vacuum pump to achieve an improved suction capacity, such as the type essentially consisting of EP 0 974 756 A2 known. Furthermore, EP 3 438 460 A1 , JP H03 233193 A , US 5 092 740 A and EN 25 07 430 A1 pointed out.

Molecular vacuum pumps operate in the high and ultra-high vacuum range, with the pressure in the high vacuum range being between 10 ^-3 and 10 ^-7 hPa and in the ultra-high vacuum range being less than and 10 ^-7 hPa.

In molecular vacuum pumps, such as turbomolecular pumps, the process gas to be pumped from the pump inlet to the pump outlet tends to flow back from the pump outlet to the pump inlet due to the fact that the pressure at the pump inlet is lower than the pressure at the pump outlet. This tendency for backflow is greater the higher the pump pre-pressure, i.e. the pressure at the pump outlet of the vacuum pump. Accordingly, due to the tendency for backflow described, the pumping speed of a turbomolecular pump is lower in the range of high pre-pressures than the pumping speed of the turbomolecular pump at lower pre-pressures.

The described backflow problem occurs particularly when pumping process gases that have a relatively low molar mass. This is due to the fact that heavier process gases are easier to pumped than lighter process gases. With relatively light process gases such as hydrogen or helium, a smaller pressure difference between the pump inlet and the pump outlet or a smaller pressure ratio is therefore achieved at the same pre-pressure and other boundary conditions than with heavier process gases, which means that the backflow problem is greater with process gases with a lower molar mass than with process gases with a higher molar mass.

The invention is therefore based on the object of reducing the described backflow problem in molecular vacuum pumps such as turbomolecular vacuum pumps and thus ensuring an improved suction capacity.

According to the present invention, the object underlying the same is achieved with a method for operating a molecular vacuum pump, in particular a turbomolecular vacuum pump, according to claim 1.

The tendency of the process gas to flow back can be reduced the more the more carrier gas is introduced; however, the power consumption of the pump increases as the amount of carrier gas increases. Too small carrier gas quantities, on the other hand, do not have the desired effect in terms of reducing the tendency of the process gas to flow back. Tests were therefore carried out to determine the optimum ratio between the amount of process gas and the amount of carrier gas. These tests have shown that it is advantageous if the amount of carrier gas introduced into the pump mechanism, which is measured in standard cubic centimeters per minute (sccm), is related to the amount of process gas conveyed - also measured in standard cubic centimeters per minute - as 1 : X, where: 5 ≤ X ≤ 15, in particular 7 ≤ X ≤ 13, preferably 9 ≤ X ≤ 11 and particularly preferably X is substantially equal to or equal to 10.

If normal pump operation is mentioned here, this can be an operating state during which the molecular vacuum pump is continuously operated with at least 75% of its maximum permissible power or at least 75% of its maximum permissible speed. Preferably, it can be provided that the carrier gas is continuously introduced into the pump mechanism during at least 50% of this time window, i.e. during the time window during which the molecular vacuum pump is continuously operated with at least 75% of its maximum permissible power or at least 75% of its maximum permissible speed.

Preferably, the carrier gas can be continuously introduced into the pumping mechanism during at least 60% of the time of this time window, in particular during at least 70% of the time of this time window and particularly preferably during at least 80% of the time of this time window.

Unlike when flooding a turbomolecular vacuum pump via a flood inlet, the entraining gas is not only introduced into the pump mechanism temporarily for a relatively short period of time; rather, according to the invention, the entraining gas is introduced into the pump mechanism for the majority of the time during which process gas is conveyed by means of the pump, in order to reduce the tendency of the process gas to flow back in favor of improving the pumping capacity of the pump.

In particular, it can be provided that the carrier gas is continuously introduced into the pump mechanism over a period of at least one hour during the conveyance of process gas, in particular over a period of at least 10 hours and preferably over a period of more than 24 hours.

In order to optimize the momentum transfer from the carrier gas molecules to the process gas molecules, it may prove advantageous, as stated above, to use a gas as the carrier gas that has a larger molar mass than the process gas. Accordingly, it may prove particularly advantageous to use nitrogen and/or argon, for example, as the carrier gas, particularly when the process gas is a relatively light gas, such as hydrogen or helium.

.The housing of the pump has a carrier gas connection through which a gas can be introduced into the pump mechanism during operation of the molecular vacuum pump, wherein it is provided that this carrier gas connection opens into the pump mechanism upstream of a pump stage M, wherein $\mathrm{M}=\lceil \left(\mathrm{N}+1\right)/2\rceil$

.

The pump stage closest to the pump inlet is referred to as the first pump stage and the pump stage closest to the pump outlet is referred to as the Nth pump stage, whereby the individual pump stages are numbered consecutively with whole numbers from the first to the Nth in the direction of the pump outlet.

. Weißt also beispielsweise eine Turbomolekularpumpe zehn Turbomolekularpumpstufen auf (N = 10), so ist M = 6, was bedeutet, dass sich der Schleppgasanschluss stromaufwärts der sechsten Turbomolekularpumpstufe befindet. Bei einer Turbomolekularpumpe mit beispielsweise acht Turbomolekularpumpstufen (N = 8) gilt hingegen beispielsweise M = 5, was bedeutet, dass sich der Schleppgasanschluss stromaufwärts der fünften Turbomolekularpumpstufe befindet. Die Nomenklatur ist dabei wie bereits erwähnt so gewählt, dass die am nächsten am Pumpeneinlass befindliche Turbomolekularpumpstufe die erste und die am nächsten am Pumpenauslass befindliche Turbomolekularpumpstufe die N-te Pumpstufe ist, wobei die einzelnen Turbomolekularpumpstufen von der ersten bis zur N-ten in Richtung des Pumpenauslasses fortlaufend mit ganzen Zahlen durchnummeriert sind.If the rounding function using upper Gaussian brackets is used to define the position of the towing gas connection, this rounding function is defined such that for a real number x: $\mathrm{x}=\min \left\{\mathrm{K}\in \mathbb{Z}|\mathrm{K}\ge \mathrm{x}\right\}$

. For example, if you know a turbomolecular pump ten turbomolecular pump stages (N = 10), then M = 6, which means that the carrier gas connection is upstream of the sixth turbomolecular pump stage. In the case of a turbomolecular pump with, for example, eight turbomolecular pump stages (N = 8), however, M = 5, which means that the carrier gas connection is upstream of the fifth turbomolecular pump stage. As already mentioned, the nomenclature is chosen so that the turbomolecular pump stage closest to the pump inlet is the first and the turbomolecular pump stage closest to the pump outlet is the Nth pump stage, with the individual turbomolecular pump stages being numbered consecutively with whole numbers from the first to the Nth in the direction of the pump outlet.

By introducing a gas other than the process gas into the pump mechanism of the turbomolecular pump through the carrier gas connection during operation, which is also referred to below as carrier gas, the tendency of the process gas to flow back from the pump outlet to the pump inlet is reduced, since the molecules of the process gas are entrained or dragged along by the molecules of the carrier gas in the direction of the pump outlet, hence the term "carrier gas". The molecules of the carrier gas transfer their momentum to the molecules of the process gas, so that the process gas molecules are dragged along by the carrier gas molecules in the direction of the pump outlet. The greater the molecular weight of the carrier gas, the greater the momentum transfer from the carrier gas to the process gas. In any case, however, a gas with a higher molar mass than the process gas should be used as the carrier gas, which is why, for example, in the case of helium or hydrogen as the process gas, nitrogen and/or argon can be used as the carrier gas.

By preventing the tendency of the process gas to flow back, the pressure at the pump inlet is reduced at the same pre-pressure, which results in an increase of the pumping speed. The effective high-vacuum side pumping speed of the turbomolecular pump is thus increased by introducing a carrier gas into the pump mechanism, since introducing a carrier gas into the pump mechanism reduces the tendency of the process gas to flow back. This effect is more noticeable the closer the carrier gas connection is to the pump inlet, since in this case more time is available during which the carrier gas molecules can transfer their momentum to the process gas molecules. On the other hand, however, the carrier gas connection should not be located too close to the pump inlet, since in this case there is a risk that the carrier gas will flow back towards the pump inlet due to the vacuum at the pump inlet. Accordingly, regardless of the number of pump stages, the carrier gas connection should always be located downstream of the first, preferably downstream of the second, pump stage in order to prevent the carrier gas from flowing back towards the pump inlet.

. Bei einer Turbomolekularvakuumpumpe mit beispielsweise sechs Pumpstufen (N = 6) befindet sich also der Schleppgaseinlass vorzugsweise stromaufwärts der dritten Pumpstufe, bei einer Turbomolekularvakuumpumpe mit acht Pumpstufen (N = 8) stromaufwärts der vierten Pumpstufe und bei einer Turbomolekularpumpe mit insgesamt zehn Pumpstufen (N = 10) stromaufwärts der fünften Pumpstufe. In jedem Falle sollte jedoch der Schleppgasanschluss stromabwärts der ersten Pumpstufe, vorzugsweise stromabwärts der zweiten Pumpstufe gelegen sein, um so einem Rückströmen des Schleppgases in Richtung des Pumpeneinlasses zuvorzukommen.In the case of a molecular vacuum pump, in particular a turbomolecular vacuum pump, with four or more pumping stages, the relationship between M and N is preferably $\mathrm{N}=\lceil \mathrm{N}/2\rceil$

. In a turbomolecular vacuum pump with, for example, six pumping stages (N = 6), the entraining gas inlet is preferably located upstream of the third pumping stage, in a turbomolecular vacuum pump with eight pumping stages (N = 8) upstream of the fourth pumping stage, and in a turbomolecular pump with a total of ten pumping stages (N = 10) upstream of the fifth pumping stage. In any case, however, the entraining gas connection should be located downstream of the first pumping stage, preferably downstream of the second pumping stage, in order to prevent the entraining gas from flowing back towards the pump inlet.

. Bei einer Turbomolekularpumpe mit sechs Pumpstufen (N = 6) befindet sich also der Schleppgaseinlass vorzugsweise stromaufwärts der zweiten Pumpstufe, bei einer Turbomolekularpumpe mit acht Pumpstufen (N = 8) stromaufwärts der dritten Pumpstufe und bei einer Turbomolekularvakuumpumpe mit zehn Pumpstufen (N = 10) stromaufwärts der vierten Pumpstufe. In jedem Falle sollte jedoch auch hier der Schleppgasanschluss stromabwärts der ersten Pumpstufe, vorzugsweise stromabwärts der zweiten Pumpstufe gelegen sein, um einem Rückströmen des Schleppgases in Richtung des Pumpeneinlasses zuvorzukommen.It has proven particularly advantageous for molecular vacuum pumps, especially turbomolecular pumps, with six or more pumping stages to choose the relationship between M and N such that: $\mathrm{M}=\lceil \mathrm{N}/2\rceil -1$

In a turbomolecular pump with six pumping stages (N = 6), the entraining gas inlet is preferably located upstream of the second pumping stage, in a turbomolecular pump with eight pumping stages (N = 8) upstream of the third pumping stage, and in a turbomolecular vacuum pump with ten pumping stages (N = 10) upstream of the fourth pumping stage. In any case, however, the entraining gas connection should be located downstream of the first pumping stage, preferably downstream of the second pumping stage, in order to prevent the entraining gas from flowing back towards the pump inlet.

Fig. 1

eine perspektivische Ansicht einer Turbomolekularpumpe,

Fig. 2

eine Ansicht der Unterseite der Turbomolekularpumpe von Fig. 1,

Fig. 3

einen Querschnitt der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie A-A,

Fig. 4

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie B-B,

Fig. 5

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie C-C,

Fig. 6

eine Querschnittsansicht einer Turbomolekularpumpe, und

Fig. 7

ein Diagramm zur Erläuterung des erfindungsgemäßen Schleppgaseffekts.

The invention is described below by way of example using advantageous embodiments with reference to the attached figures. They show, each schematically:

Fig.1

a perspective view of a turbomolecular pump,

Fig.2

a view of the bottom of the turbomolecular pump from 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 cutting line BB,

Fig.5

a cross-sectional view of the turbomolecular pump along the Fig.2 shown section line CC,

Fig.6

a cross-sectional view of a turbomolecular pump, and

Fig.7

a diagram to explain the entraining gas effect according to the invention.

In the Fig.1 The 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.

The inlet flange 113 forms the vacuum pump in the 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 on the side. 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 connections 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 connection 131 are arranged on the electronics housing 123.

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

A flood inlet 133, in particular in the form of a flood valve, is provided on the housing 119 of the turbomolecular pump 111, 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 can be fed to protect the electric motor 125 (see e.g. Fig.3 ) can be let 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. In the lower part 121, two coolant connections 139 are also arranged, one of the coolant connections being provided as an inlet and the other coolant connection as an outlet for coolant that can be fed into the vacuum pump for cooling purposes. Other existing turbomolecular vacuum pumps (not shown) are operated exclusively with air cooling.

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. The vacuum pump 111 can also be attached to a recipient via the inlet flange 113 and thus operated in a hanging position. In addition, the vacuum pump 111 can be designed in such a way that it can also be put into operation when it is aligned in a different way than in Fig.1 is shown. It is also possible to realize embodiments of the vacuum pump in which the underside 141 is not arranged facing downwards, but to the side or facing upwards. In principle, any angle is possible.

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

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

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

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.

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.

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

The turbomolecular pump 111 comprises several turbomolecular pump stages connected in series with a pumping effect, with several radial rotor disks 155 attached to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and fixed in the housing 119. 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.

The vacuum pump also includes Holweck pump stages arranged radially one inside the other and connected in series to pump effectively. There are other turbomolecular vacuum pumps (not shown) that do not have Holweck pumping stages.

The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylinder-jacket-shaped Holweck rotor sleeves 163, 165 which are fastened to and supported by the rotor hub 161 and which are oriented coaxially to the rotation axis 151 and nested in one another in the radial direction. Furthermore, two cylinder-jacket-shaped Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the rotation axis 151 and are nested in one another in the radial direction.

The pump-active surfaces of the Holweck pump stages are formed by the lateral surfaces, i.e. by 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 is opposite the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together with this forms the first Holweck pump stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 is opposite the radial outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together with this 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.

A radially extending channel can be provided at the lower end of the Holweck rotor sleeve 163, via which the radially outer Holweck gap 171 is connected to the central Holweck gap 173. In addition, a radially extending channel can be provided at the upper end of the inner Holweck stator sleeve 169, via which the central Holweck gap 173 is connected to the radially inner Holweck gap 175. As a result, the nested Holweck pump stages are connected in series with one another. At the lower end of the radially inner Holweck rotor sleeve 165, a connecting channel 179 to the outlet 117 can also be provided.

The above-mentioned pump-active surfaces of the Holweck stator sleeves 167, 169 each have a plurality of Holweck grooves running 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.

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.

In the area of the roller bearing 181, a conical spray nut 185 with an outer diameter that increases towards the roller bearing 181 is provided on the rotor shaft 153. The spray nut 185 is in sliding contact with at least one scraper 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.

The operating fluid storage comprises several absorbent disks 187 stacked on top of each other, which are impregnated with an operating fluid for the rolling bearing 181, e.g. with a lubricant.

During operation of the vacuum pump 111, the operating fluid is transferred by capillary action from the operating fluid reservoir via the scraper to the rotating spray nut 185 and, as a result of the centrifugal force, is pressed along the spray nut 185 into The fluid is pumped in the direction of the increasing outer diameter of the injection nut 185 to the roller bearing 181, where it fulfills a lubricating function, for example. The roller bearing 181 and the operating fluid reservoir are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

The permanent magnet bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each of which comprises a ring stack of several permanent magnet rings 195, 197 stacked on top of one another in the axial direction. The ring magnets 195, 197 lie opposite one another to form 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 causes magnetic repulsion forces between the ring magnets 195, 197, which cause the rotor shaft 153 to be radially supported. 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 fixed parallel to the rotation axis 151 by a cover element 207 coupled to the support section 201. The stator-side ring magnets 197 are fixed 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.

An emergency or safety bearing 215 is provided within the magnetic bearing, which runs empty without contact during normal operation of the vacuum pump 111 and only comes into contact with the rotor 149 when there is an excessive radial deflection relative to the stator. engages to form a radial stop for the rotor 149 so that a collision of the rotor-side structures with the stator-side structures is prevented. The safety bearing 215 is designed as an unlubricated roller bearing and forms a radial gap with the rotor 149 and/or the stator, which causes the safety bearing 215 to be disengaged during normal pumping operation. The radial deflection at which the safety bearing 215 engages is large enough so that the safety bearing 215 does not engage during normal operation of the vacuum pump, and at the same time small enough so that a collision of the rotor-side structures with the stator-side structures is prevented under all circumstances.

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 on the section of the rotor shaft 153 extending through the motor stator 217. Between the motor stator 217 and the section of the rotor 149 extending through the motor stator 217 there is an intermediate space 219 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.

The motor stator 217 is fixed in the housing within the motor compartment 137 provided for the electric motor 125. A sealing gas, which is also referred to as purge gas and which can be air or nitrogen, for example, can enter the motor compartment 137 via the sealing gas connection 135. The electric motor 125 can be protected from process gas, e.g. from corrosive components of the process gas, via the sealing gas. The motor compartment 137 can also be evacuated via the pump outlet 117, ie in the motor compartment 137, the vacuum pressure prevails at least approximately as that produced by the forevacuum pump connected to the pump outlet 117.

Furthermore, a so-called labyrinth seal 223, which is known per se, can be provided between the rotor hub 161 and a wall 221 delimiting the motor compartment 137, in particular in order to achieve a better sealing of the motor compartment 217 with respect to the Holweck pump stages located radially outside.

In the following, with reference to the Fig.6 another turbomolecular pump 111 is described. The turbomolecular pump 111 according to Fig.6 is largely identical to the one previously mentioned with reference to the Figs. 1 to 5 designed turbomolecular pump 111, which is why the basic structure of the turbomolecular pump 111 according to Fig.6 to the above description of the turbomolecular pump 111 according to the Figs. 1 to 5 Compared to the previous one with reference to the Figs. 1 to 5 However, the turbomolecular pump 111 described in Fig.6 additionally has a towing gas connection 225, the position and function of which will be discussed in more detail below.

As already mentioned, the previously described turbomolecular pump 111 has a flood inlet 133 which opens into the Holweck pump stage of the pump 111. However, a flood inlet 133 can also be provided in the area of the series-connected turbomolecular pump stages, in which case the flood inlet 133 is usually located in the downstream area of the pump mechanism which is formed by the series-connected turbomolecular pump stages. In a turbomolecular pump with, for example, ten turbomolecular pump stages, the flood inlet 133 can be located, for example, in the area of the seventh pump stage. The pump 111 can be flooded with air, for example, via such a flood inlet 133 after the pump 111 was taken out of service or the power supply to the electric motor 125 was interrupted.

The turbomolecular vacuum pump 111 has, in addition to or instead of the flood inlet 133, a carrier gas connection which is connected to the Fig.6 is identified purely schematically with the reference symbol "225". The carrier gas connection 225 is a housing opening through which a carrier gas can be introduced into the pump mechanism formed by the turbomolecular pump stages. The housing opening 227 of the carrier gas connection 225 can be closed, for example, with a screw cap (not shown here), which can be removed if necessary in order to be able to connect a supply line to the carrier gas connection 225, via which a carrier gas can be supplied to the carrier gas connection 225. Alternatively, a flow control valve (not shown here) can be connected to the housing opening 227 of the carrier gas connection 225, the flow cross-section of which can be continuously changed in order to be able to continuously adjust and in particular regulate the amount of carrier gas supplied to the carrier gas connection 225.

. Die Nomenklatur ist dabei so gewählt, dass die am nächsten am Pumpeinlass 115 befindliche Turbomolekularpumpstufe als die erste und die am nächsten am Pumpenauslass 117 befindliche Turbomolekularpumpstufe als die N-te Pumpstufe bezeichnet wird, wobei die einzelnen Turbomolekularpumpstufen von der ersten bis zur N-ten in Richtung des Pumpenauslasses 117 fortlaufend mit ganzen Zahlen durchnummeriert sind. Im Falle von beispielsweise zehn Turbomolekularpumpstufen mündet somit der Schleppgasanschluss stromaufwärts der sechsten Turbomolekularpumpstufe in den von den Turbomolekularpumpstufen gebildeten Pumpmechanismus. Weist die Turbomolekularpumpe hingegen beispielsweise acht Turbomolekularpumpstufen auf, so mündet der Schleppgasanschluss 225 stromaufwärts der fünften Turbomolekularpumpstufe in den von den Turbomolekularpumpstufen gebildeten Pumpmechanismus.According to the invention, the carrier gas connection 225 opens upstream of a turbomolecular pump stage M into the pump mechanism formed by the N turbomolecular pump stages, where: $\mathrm{M}=\lceil \left(\mathrm{N}+1\right)/2\rceil$

. The nomenclature is chosen such that the turbomolecular pump stage closest to the pump inlet 115 is referred to as the first and the turbomolecular pump stage closest to the pump outlet 117 is referred to as the Nth pump stage, with the individual turbomolecular pump stages from the first to the Nth being numbered consecutively with whole numbers in the direction of the pump outlet 117. In the case of, for example, ten turbomolecular pump stages, the carrier gas connection thus opens upstream of the sixth turbomolecular pump stage into the pump mechanism formed by the turbomolecular pump stages. If the turbomolecular pump has However, if, for example, the pumping system has eight turbomolecular pump stages, the carrier gas connection 225 opens upstream of the fifth turbomolecular pump stage into the pump mechanism formed by the turbomolecular pump stages.

ausdrücken lässt, wobei N die Anzahl der Turbomolekularpumpstufen und M die Nummer der Pumpstufe ist, stromaufwärts derer der Schleppgasanschluss 225 in den Pumpmechanismus münden sollte. Vorzugsweise gilt dabei für die Beziehung $\mathrm{M}=\lceil \mathrm{N}/2\rceil -1$

, wobei jedoch der Schleppgasanschluss 225 in jedem Falle stromabwärts der ersten Turbomolekularpumpstufe, vorzugsweise stromabwärts der zweiten Turbomolekularpumpstufe vorgesehen werden sollte, um ein Rückströmen des Schleppgases in Richtung des Pumpeneinlasses 115 zu verhindern.In principle, however, it proves to be advantageous to provide the carrier gas connection 225 near the upstream end of the turbomolecular pumping mechanism and in particular in the upstream third of the pumping mechanism formed by the turbomolecular pumping stages, which is expressed, for example, by the relationship $\mathrm{M}=\lceil \mathrm{N}/2\rceil$

where N is the number of turbomolecular pump stages and M is the number of the pump stage upstream of which the carrier gas connection 225 should flow into the pump mechanism. Preferably, the relationship $\mathrm{M}=\lceil \mathrm{N}/2\rceil -1$

, however, the carrier gas connection 225 should in any case be provided downstream of the first turbomolecular pump stage, preferably downstream of the second turbomolecular pump stage, in order to prevent a backflow of the carrier gas in the direction of the pump inlet 115.

In contrast to the flood inlet 133, a carrier gas is not introduced into the pump mechanism via the carrier gas connection 225 only after the pump has been switched off; rather, the invention provides that carrier gas is introduced into the pump mechanism via the carrier gas connection 225 during operation of the turbomolecular pump 111 and thus during the conveyance of process gas from the pump inlet 115 to the pump outlet 117. In other words, the carrier gas is introduced into the pump mechanism while the electric motor 125 is energized.

The carrier gas is thus introduced into the pump mechanism via the carrier gas connection 225 during the normal pumping operation of the turbomolecular pump 111. This normal pumping operation can be defined as a time window during which the turbomolecular vacuum pump 111 is continuously operated at at least 75% of its maximum permissible power and/or at at least 75% of its maximum permissible speed. In particular, it can be provided that the carrier gas is introduced into the pump mechanism through the carrier gas connection 225 during at least 50% of the time of the time window defined in this way. For example, it can be provided that the carrier gas is continuously introduced into the pump mechanism over a period of at least one hour during the conveyance of process gas, in particular over a period of 10 hours and preferably over a period of more than 24 hours.

The carrier gas introduced via the carrier gas connection 225 entrains or drags the process gas conveyed from the pump inlet 115 to the pump outlet 117 and in particular prevents process gas from flowing back from the pump outlet 117 to the pump inlet 115. The pressure at the pump inlet thus drops in the desired manner, so that the pumping capacity increases in the desired manner.

Although the text here with reference to the Fig.6 The turbomolecular vacuum pump 111 described has a Holweck pumping stage downstream of the turbomolecular pumping stages in the manner described above. However, like the flood inlet 133, this is optional and is not required to achieve the entraining gas effect according to the invention. The turbomolecular vacuum pump 111 according to the invention can therefore have a Holweck pumping stage, but does not have to.

In the following, with reference to the Fig.7 The test results are presented which were observed for a turbomolecular pump without a Holweck pumping stage, where the turbomolecular pump had ten turbomolecular pumping stages (N = 10). In the diagram of the Fig.7 is the pressure at the inlet 115 of the pump on the Y-axis above the pressure at the pump outlet 117 on the X-axis The turbomolecular pump used in the test had a flood inlet in the area of the seventh turbomolecular pump stage and a carrier gas connection in the area of the fourth turbomolecular pump stage.

The top diagram line shows an operating state of the pump in which no gases were introduced into the pump mechanism via the flood inlet or the carrier gas connection. The middle diagram line, on the other hand, refers to an operating state during which nitrogen was introduced into the pump mechanism via the flood inlet in the area of the seventh turbomolecular pump stage while the pump was operating. The bottom diagram line, on the other hand, refers to an operating state of the pump in which nitrogen was introduced into the pump mechanism via the carrier gas connection in the area of the fourth turbomolecular pump stage. The pump was operated during all three operating states in such a way that 1,000 sccm of hydrogen gas were pumped as process gas from the pump inlet 115 to the pump outlet 117.

As can be seen from the middle line of the diagram, the introduction of nitrogen gas through the flood inlet already results in a reduction in the pressure at the pump inlet compared to the operating condition in which no carrier gas is introduced into the pump mechanism according to the top line of the diagram.

Although the pump's suction capacity is improved by introducing nitrogen via the flood inlet, as can be seen from the bottom line of the diagram, the pump inlet pressure drops even further if nitrogen is introduced into the pump mechanism as a carrier gas not via the flood inlet in the area of the seventh turbomolecular pump stage, but via the carrier gas connection in the area of the fourth turbomolecular pump.

In the test results explained above, the pump was operated in such a way that it continuously delivers 1,000 sccm of H ₂ , with 100 sccm of nitrogen being introduced into the pump mechanism via the flood inlet or the seal gas connection 225. Tests have shown that at a ratio of around 10:1 (standard cubic centimetres of process gas per minute: standard cubic centimetres of carrier gas per minute), the previously described backflow problem can be reliably reduced and the pump's suction capacity can thus be increased without this being at the expense of the pump's power consumption. According to the invention, the ratio of the amount of entraining gas introduced into the pump mechanism measured in standard cubic centimeters per minute (sccm) to the amount of process gas conveyed measured in standard cubic centimeters per minute (sccm) is 1:X, where 5 ≤ X ≤ 15, where the ratio of the amount of entraining gas introduced into the pump mechanism to the amount of process gas conveyed is constant during the conveying of process gas.

List of reference symbols

111

Turbomolecular pump

113

Inlet flange

115

Pump inlet

117

Pump outlet

119

Housing

121

Bottom part

123

Electronic housing

125

Electric motor

127

Accessory connection

129

Data interface

131

Power supply connection

133

Flood inlet

135

Sealing gas connection

137

Engine compartment

139

Coolant connection

141

bottom

143

screw

145

Bearing cap

147

Mounting hole

148

Coolant line

149

rotor

151

Rotation axis

153

Rotor shaft

155

Rotor disc

157

Stator disc

159

Spacer ring

161

Rotor hub

163

Holweck rotor sleeve

165

Holweck rotor sleeve

167

Holweck stator sleeve

169

Holweck stator sleeve

171

Holweck gap

173

Holweck gap

175

Holweck gap

179

Connecting channel

181

roller bearing

183

Permanent magnet bearings

185

Injection nut

187

disc

189

Mission

191

rotor-side bearing half

193

stator side bearing half

195

Ring magnet

197

Ring magnet

199

Bearing gap

201

Carrier section

203

Carrier section

205

radial strut

207

Cover element

209

Support ring

211

Mounting ring

213

Disc spring

215

Emergency or rescue camp

217

Motor stator

219

Space

221

Wall

223

Labyrinth seal

225

Towing gas connection

227

Housing opening

Claims (10)

1. A method of operating a molecular vacuum pump (111) comprising a housing (119) for receiving a pump mechanism, which is driven by a rotor shaft (153) by means of an electric motor, for conveying a process gas from a pump inlet (115) to a pump outlet (117), wherein the pump mechanism comprises a plurality of N pump stages connected to one another in series in a pump-active manner between the pump inlet (115) and the pump outlet (117), wherein the pump stage closest to the pump inlet (115) is the first pump stage and the pump stage closest to the pump outlet (117) is the Nth pump stage, wherein the housing (119) has a carrier gas connection (225) which opens into the pump mechanism upstream of a pump stage M, where $\mathrm{M}=\lceil \left(\mathrm{N}+1\right)/2\rceil$

   

   applies;

   wherein a quantity of a carrier gas is introduced into the pump mechanism through the carrier gas connection (225) during the conveying of process gas from the pump inlet (115) to the pump outlet (117),

   characterized in that

   the quantity of the carrier gas introduced into the pump mechanism, measured in standard cubic centimeters per minute (sccm), relates to the quantity of the conveyed process gas, measured in standard cubic centimeters per minute (sccm), as 1 : X, where 5 ≤ X ≤ 15 applies, wherein the ratio of the quantity of the carrier gas introduced into the pump mechanism to the quantity of the conveyed process gas is constant during the conveying of process gas.
2. A method according to claim 1,
   wherein the carrier gas is introduced into the pump mechanism while the electric motor is energized.
3. A method according to claim 1 and/or 2,
   wherein the quantity of the carrier gas introduced into the pump mechanism, measured in standard cubic centimeters per minute (sccm), relates to the quantity of the conveyed process gas, measured in standard cubic centimeters per minute (sccm), as 1 : X, where 9 ≤ X ≤ 11 applies, and in particular X is substantially equal to 10 or equal to 10.
4. A method according to any one of the claims 1 to 3, wherein the method is carried out using a molecular vacuum pump (111) which has a housing (119) for receiving a pump mechanism, which is driven by a rotor shaft (153), for conveying a process gas from a pump inlet (115) to a pump outlet (117), wherein the pump mechanism comprises a plurality of N pump stages connected to one another in series in a pump-active manner between the pump inlet (115) and the pump outlet (117), wherein the pump stage closest to the pump inlet (115) is the first pump stage and the pump stage closest to the pump outlet (117) is the Nth pump stage, wherein the housing (119) has a carrier gas connection (225) which opens into the pump mechanism upstream of a pump stage M, wherein $\mathrm{M}=\lceil \left(\mathrm{N}+1\right)/2\rceil$

   

   applies, and wherein the carrier gas is introduced into the pump mechanism through the carrier gas connection (225).
5. A method according to claim 4,
   wherein $\mathrm{M}=\lceil \mathrm{N}/2\rceil$

   

   applies, where N ≥ 4 further applies.
6. A method according to claim 4,
   wherein $\mathrm{M}=\lceil \mathrm{N}/2\rceil -1$

   

   applies, where it further applies: N ≥ 6.
7. A method according to any one of the claims 4 to 6,
   wherein the molecular vacuum pump (111) is a turbomolecular vacuum pump (111) which comprises a plurality of N turbomolecular pump stages which are connected to one another in series in a pump-active manner and each of which comprise a rotor disk (155) fastened to the rotor shaft (153) and a stationary stator disk (157).
8. A method according to any one of the claims 1 to 7, wherein a gas which has a greater molar mass than the process gas is used as the carrier gas, wherein it is in particular provided that nitrogen and/or argon is used as the carrier gas.
9. A method according to any one of the claims 1 to 8, wherein the carrier gas is continuously introduced over a period of at least one hour during the conveying of process gas, in particular over a period of at least 10 hours, preferably over a period of more than 24 hours.
10. A method according to any one of the claims 1 to 9, wherein the carrier gas is continuously introduced during at least 50% of the time of a time window during which the molecular vacuum pump (111) is continuously operated with at least 75% of its maximum permissible power or with at least 75% of its maximum permissible rotational speed.

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