Molecular vacuum pump with improved pumping speed and method of operating a molecular vacuum pump to achieve improved pumping speed - Patents.com

Abstract

To provide a molecular vacuum pump having a housing for housing a pump mechanism driven by a rotor shaft for pumping a process gas from a pump inlet to a pump outlet, where the pump mitigates the problem of a reflux and improves the exhaust speed.SOLUTION: The pumping mechanism comprises N pumping stages connected in series with each other to take a pumping effect between the pump inlet and the pump outlet, where the pumping stage closest to the pump inlet is a first pumping stage and the pumping stage closest to the pump outlet is an Nth pumping stage. A housing (119) has a carrier gas connection (225), and the carrier gas connection (225) opens into the pump mechanism upstream of a pump stage M.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a molecular vacuum pump, particularly a turbomolecular vacuum pump, also referred to herein simply as a pump, that is specially configured to achieve improved pumping speed, and to a method of operating a molecular vacuum pump to achieve improved pumping speed. [Background technology]

[0002] Molecular vacuum pumps operate in the high vacuum range and ultra-high vacuum range, with the pressure in the high vacuum range being 10 -3 hPa to 10 -7 The ultra-high vacuum range is between 10 -7 lower than hPa.

[0003] In this case, in a molecular vacuum pump, such as a turbomolecular pump, 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. In this case, the backflow tendency is greater the higher the pump assist pressure, i.e. the pressure at the pump outlet of the vacuum pump. Correspondingly, the pumping speed of the turbomolecular pump is lower in the range of high assist pressures due to the described backflow tendency than the pumping speed of the turbomolecular pump when the assist pressure is relatively low.

[0004] The described backflow problem occurs in particular with process gases to be pumped that have a relatively low molar mass. This is due to the fact that heavier process gases can be pumped better than lighter process gases. Thus, with a relatively light process gas, such as hydrogen or helium, the pressure difference between the pump inlet and the pump outlet is smaller or the pressure ratio is smaller than with a heavier process gas, given the same auxiliary pressure and other similar environmental conditions, so that with a process gas having a lower molar mass the backflow problem is greater than with a process gas having a higher molar mass. Summary of the Invention [Problem to be solved by the invention]

[0005] The problem underlying the present invention is therefore to reduce the described backflow problems and thus improve the pumping speed in molecular vacuum pumps, such as for example turbomolecular vacuum pumps. [Means for solving the problem]

[0006] According to a first aspect of the present invention, the problem is solved by , minutes By means of the molecular vacuum pump, in particular, the housing of the pump has a carrier gas connection, through which gas can be introduced into the pump mechanism during operation of the molecular vacuum pump, with the carrier gas connection according to the invention opening into the pump mechanism upstream of the pump stage M, where

number

[0007] In this case, the pump stage located closest to the pump inlet is referred to as the first pump stage and the pump stage located closest to the pump exhaust is referred to as the Nth pump stage, with the individual pump stages being numbered with consecutive integers from the first pump stage to the Nth pump stage toward the pump exhaust.

[0008] If a ceiling function using Gaussian symbols is used to define the location of the carrier gas connection, the ceiling function is expressed as follows for a real number x:

number

[0009] During operation of the turbomolecular pump, a gas different from the process gas, hereinafter also referred to as carrier gas, is introduced into the pump mechanism of the turbomolecular pump through a carrier gas connection, so that the backflow of the process gas from the pump outlet to the pump inlet is reduced, since the process gas molecules are entrained or dragged by the carrier gas molecules towards the pump outlet, hence the term "carrier gas". In this case, the process gas molecules are entrained by the carrier gas molecules towards the pump outlet, since the carrier gas molecules transfer their momentum to the process gas molecules. In this case, the momentum transfer from the carrier gas to the process gas is greater, the greater the molecular weight of the carrier gas. In any case, however, a gas having a molar mass greater than the process gas should be used as the carrier gas, so that, for example, nitrogen and / or argon can be used as the carrier gas when helium or hydrogen is used as the process gas.

[0010] By preventing the tendency of the process gas to flow back, the pressure at the pump inlet is reduced for the same auxiliary pressure, which means that the pumping speed of the pump is increased. The effective pumping speed of the high vacuum side of the turbomolecular pump is therefore increased by introducing a carrier gas into the pump mechanism, since the tendency of the process gas to flow back is prevented by the introduction of the carrier gas into the pump mechanism. In this case, this effect is more pronounced the closer the carrier gas connection is located to the pump inlet, since in this case more time is provided for the carrier gas molecules to transfer their momentum to the process gas molecules. And on the other hand, the carrier gas connection should not be placed too close to the pump inlet, since in this case the carrier gas may flow back towards the pump inlet due to the vacuum present at the pump inlet. Accordingly, the carrier gas connection should always be placed downstream of the first pump stage, preferably downstream of the second pump stage, regardless of the number of pump stages, so that the backflow of the carrier gas towards the pump inlet is prevented.

[0011] In the case of molecular vacuum pumps with four or more pumping stages, in particular turbomolecular vacuum pumps, the relationship between M and N preferably satisfies:

number

[0012] Particularly advantageously, for molecular vacuum pumps, in particular turbomolecular pumps, having six or more pump stages, the relationship between M and N is

number

[0013] According to a further aspect of the invention, the same problem underlying the invention is further achieved in a method for operating a molecular vacuum pump, in particular a turbomolecular vacuum pump, as defined in claim 1. 1 In particular, this is achieved by introducing a predetermined amount of carrier gas into the pump mechanism while process gas is being pumped from the pump inlet to the pump outlet of the pump, and thus during normal operating conditions of the pump when the electric motor of the pump is energized.

[0014] When normal pump operation is mentioned here, this may be an operating state during which the molecular vacuum pump is operated continuously at at least 75% of its maximum permissible power or at least 75% of its maximum permissible rotation speed. In this case, it can be assumed that the carrier gas is preferably continuously introduced into the pump mechanism for at least 50% of this period, i.e. during this period the molecular vacuum pump is operated continuously at at least 75% of its maximum permissible power or at least 75% of its maximum permissible rotation speed.

[0015] Preferably, the carrier gas can be continuously introduced into the pump mechanism for at least 60% of the period, in particular for at least 70% of the period, particularly preferably for at least 80% of the period.

[0016] Unlike when venting a turbomolecular vacuum pump through a vent inlet, carrier gas is not only introduced to the pump mechanism temporarily for a relatively short period of time, but rather, in accordance with the present invention, carrier gas is introduced to the pump mechanism for the majority of the time that process gas is pumped using the pump, thereby reducing the tendency of process gas to backflow in order to improve the pumping speed of the pump.

[0017] In this case, it can in particular be envisaged that the carrier gas is continuously introduced during pumping of the process gas to the pump mechanism over a period of at least 1 hour, in particular over a period of at least 10 hours, preferably over a period of more than 24 hours.

[0018] In order to optimize the momentum transfer from the carrier gas molecules to the process gas molecules, depending on the aforementioned configuration, it may prove advantageous to use as the carrier gas a gas having a larger molar mass than the process gas. Accordingly, in particular when the process gas is a relatively light gas, such as hydrogen or helium, it may prove particularly advantageous to use, for example, nitrogen and / or argon as the carrier gas.

[0019] The more carrier gas is introduced, the more the tendency of the process gas to flow back is reduced, but the power consumption of the pump increases as the amount of carrier gas increases. On the other hand, if the amount of carrier gas is too small, the desired effect of reducing the tendency of the process gas to flow back is not achieved. Therefore, tests were carried out to determine the optimal ratio between the amount of process gas and the amount of carrier gas. The tests showed that it is advantageous for the amount of carrier gas introduced into the pump mechanism (measured in standard cubic centimeters per minute (sccm)) to the amount of pumped process gas, also measured in standard cubic centimeters per minute, to be in a ratio of 1:X, where 5≦X≦15, in particular 7≦X≦13, preferably 9≦X≦11, and particularly preferably X is approximately 10 or equal to 10.

[0020] The invention will now be described on the basis of exemplary advantageous embodiments with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0021] [Figure 1] 1 shows a perspective view of a known turbomolecular pump; [Diagram 2] FIG. 2 shows a bottom view of the turbomolecular pump of FIG. [Diagram 3] 3 shows a cross-sectional view of a turbomolecular pump taken along the section line AA shown in FIG. 2. [Figure 4] 3 shows a cross-sectional view of the turbomolecular pump taken along the section line BB shown in FIG. 2. [Diagram 5] 3 shows a cross-sectional view of a turbomolecular pump taken along section line CC shown in FIG. 2. [Figure 6] 1 shows a cross-sectional view of a turbomolecular pump according to the invention; [Figure 7] 1 shows a diagram for explaining the carrier gas effect according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The turbomolecular pump 111 shown in Fig. 1 has a pump inlet 115 surrounded by an inlet flange 113 to which a recipient, not shown, may be connected in a manner known per se. Gas coming from the recipient can be sucked in through the pump inlet 115 and pumped through the pump to a pump outlet 117 to which an auxiliary vacuum pump, for example a rotary vane pump, may be connected.

[0023] The inlet flange 113 forms the upper end of a housing 119 of the vacuum pump 111 in the orientation of the vacuum pump according to Fig. 1. The housing 119 has a lower part 121, on which an electronics housing 123 is arranged laterally. In the electronics housing 123, electrical and / or electronic components of the vacuum pump 111 are accommodated, for example for operating an electric motor 125 (see also Fig. 3) arranged in the vacuum pump. The electronics housing 123 is provided with a number of connections 127 for accessories. Furthermore, a data interface 129 (for example according to the RS485 standard) and a current supply connection 131 are arranged in the electronics housing 123.

[0024] There are also turbomolecular pumps that do not have this type of attached electronics housing, but are connected to external drive electronics.

[0025] A ventilation inlet 133, in particular in the form of a ventilation valve, is provided in the housing 119 of the turbomolecular pump 111. Via the ventilation inlet 133, the vacuum pump 111 can be vented. In the region of the lower part 121, a sealing gas connection 135 (also called purge gas connection) is also arranged. Via the sealing gas connection 135, a purge gas can be fed into a motor chamber 137 in order to protect the electric motor 125 (see, for example, FIG. 3) against the gas pumped by the pump. In the motor chamber 137, the vacuum pump 111 accommodates the electric motor 125. In the lower part 121, two coolant connections 139 are also arranged. In this case, one coolant connection is provided as an inlet for the coolant and the other coolant connection is provided as an exhaust. A coolant can be introduced into the vacuum pump for cooling purposes. The further turbomolecular vacuum pump present (not shown) is operated exclusively air-cooled.

[0026] The underside 141 of the vacuum pump can be used as a base, so that the vacuum pump 111 can be operated vertically with respect to the underside 141. Moreover, the vacuum pump 111 can be fixed to the recipient via the inlet flange 113 and thus operated in a suspended state, so to speak. Furthermore, the vacuum pump 111 can be configured so that it can be operated even when oriented in a different direction than shown in FIG. 1. Vacuum pump configurations are also feasible in which the underside 141 can be arranged not only downwards, but also sideways or upwards. In this case, in principle, any angle is conceivable.

[0027] In particular, other turbomolecular vacuum pumps (not shown) that are present and are larger than the pump shown cannot be operated in a vertical position.

[0028] Various screws 143 are further arranged on the underside 141 shown in Fig. 2. By means of these screws 143, components of the vacuum pump, not specified in detail here, are fixed to one another. For example, a bearing cover 145 is fixed to the underside 141.

[0029] Fastening holes 147 are furthermore arranged in the underside 141. Via the fastening holes 147, the pump 111 can be fixed, for example, to a mounting surface. This is not possible with other existing turbomolecular vacuum pumps (not shown), in particular those larger than the pump shown.

[0030] 2 to 5 show a coolant line 148. In the coolant line 148 a coolant can be circulated which is introduced and discharged via the coolant connection 139.

[0031] As shown in the cross-sectional views of Figures 3 to 5, the vacuum pump has multiple process gas pumping stages for pumping process gas acting on a pump inlet 115 to a pump exhaust 117.

[0032] A rotor 149 is disposed within the housing 119. The rotor 149 has a rotor shaft 153 that is rotatable about a rotation axis 151.

[0033] The turbomolecular pump 111 has a number of turbomolecular pump stages connected in series to provide a pumping action. The turbomolecular pump stages have a number of radially extending rotor blades 155 fixed to the rotor shaft 153 and a number of stator vanes 157 arranged between the rotor blades 155 and fixed within the housing 119. In this case, each of the rotor blades 155 and the adjacent stator vanes 157 forms one turbomolecular pump stage. The stator vanes 157 are held at a desired axial distance from each other by spacer rings 159.

[0034] The vacuum pump further comprises Holweck pump stages arranged radially inside and outside one another and connected in series to provide a pumping action. There are alternative turbomolecular vacuum pumps (not shown) that do not comprise Holweck pump stages.

[0035] The rotor of the Holweck pump stage comprises a rotor hub 161 arranged on the rotor shaft 153 and two Holweck rotor sleeves 163, 165 with cylindrical flanks fixed to and supported by the rotor hub 161. The Holweck rotor sleeves 163, 165 are oriented coaxially with respect to the axis of rotation 151 and engage one another radially. Two Holweck stator sleeves 167, 169 with cylindrical flanks are further provided. The Holweck stator sleeves 167, 169 are likewise oriented coaxially with respect to the axis of rotation 151 and engage one another radially.

[0036] The pumping surfaces of the Holweck pump stages are formed by the lateral surfaces, i.e. by the radially inner and / or outer surfaces of the Holweck rotor sleeves 163, 165 and the Holweck stator sleeves 167, 169. The radially inner surface of the outer Holweck stator sleeve 167 faces the radially outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171, and together with this outer surface forms the first Holweck pump stage following the turbomolecular pump. The radially inner surface of the outer Holweck rotor sleeve 163 faces the radially outer surface of the inner Holweck stator sleeve 169, forming a radial Holweck gap 173, and together with this outer surface forms the second Holweck pump stage. The radially inner surface of the inner Holweck stator sleeve 169 opposes the radially outer surface of the inner Holweck rotor sleeve 165 forming a radial Holweck gap 175 and together with this outer surface forms the third Holweck pump stage.

[0037] The lower end of the Holweck rotor sleeve 163 may be provided with a radially extending channel, through which the radially outer Holweck gap 171 is connected to the central Holweck gap 173. The upper end of the inner Holweck stator sleeve 169 may be provided with a further radially extending channel, through which the central Holweck gap 173 is connected to the radially inner Holweck gap 175. In this way, the multiple mutually interlocking Holweck pump stages are connected in series with each other. The lower end of the radially inner Holweck rotor sleeve 165 may be further provided with a connecting channel 179 leading to the exhaust port 117.

[0038] The pumping surfaces of the Holweck stator sleeves 167, 169 each have a number of Holweck grooves extending in the axial direction and spiraling around the rotation axis 151, while the opposing sides of the Holweck rotor sleeves 163, 165 are smoothly formed and pump the gas for the operation of the vacuum pump 111 forward in the Holweck grooves.

[0039] For the rotatable support of the rotor shaft 153, a rolling bearing 181 is provided in the area of ​​the pump outlet 117 and a permanent magnetic bearing 183 is provided in the area of ​​the pump inlet 115.

[0040] In the region of the rolling bearing 181, the rotor shaft 153 is provided with a conical splash nut 185. The splash nut 185 has an outside diameter that increases towards the rolling bearing 181. The splash nut 185 is in sliding contact with at least one scraping member of the working medium reservoir. In other existing turbomolecular vacuum pumps (not shown), instead of a splash nut, a splash screw may be provided. Since various configurations are thereby possible, the term "splash tip" is also used in the above context.

[0041] The working medium reservoir comprises a number of absorbent discs 187 stacked one above the other, which are impregnated with a working medium for the rolling bearings 181, for example a lubricant.

[0042] During operation of the vacuum pump 111, the working medium is transferred by capillary action from the working medium reservoir via the scraping element to the rotating splash nut 185 and is then forced by centrifugal force along the splash nut 185 towards the increasing outer diameter of the splash nut 185 towards the rolling bearing 181, where it fulfills, for example, a lubrication function. The rolling bearing 181 and the working medium reservoir are enclosed in the vacuum pump by a trough-like insert 189 and a bearing cover 145.

[0043] The permanent magnetic bearing 183 has a rotor-side bearing half 191 and a stator-side bearing half 193. Each of these has a ring stack, which consists of several rings 195, 197 of permanent magnets stacked axially one above the other. The ring magnets 195, 197 face each other forming a radial bearing gap 199, with the rotor-side ring magnet 195 arranged radially outward and the stator-side ring magnet 197 arranged radially inward. The magnetic field present in the bearing gap 199 induces a magnetic repulsion between the ring magnets 195, 197. This repulsion provides a radial support for the rotor shaft 153. The rotor-side ring magnet 195 is supported by a support part 201 of the rotor shaft 153. The support part 201 surrounds the ring magnet 195 radially outward. The stator-side ring magnet 197 is supported by a support part 203 on the stator side. The support part 203 extends through the ring magnet 197 and is suspended on radial struts 205 of the housing 119. Parallel to the axis of rotation 151, the ring magnet 195 on the rotor side is fixed by a cover element 207 connected to the support part 203. The ring magnet 197 on the stator side is fixed in one direction parallel to the axis of rotation 151 by a fixing ring 209 connected to the support part 203 and a fixing ring 211 connected to the support part 203. Between the fixing ring 211 and the ring magnet 197, a disc spring 213 may further be provided.

[0044] An emergency or safety bearing 215 is provided in the magnetic bearing. During normal operation of the vacuum pump, the emergency or safety bearing 215 runs free without contact and only engages if the rotor 149 is displaced too far radially relative to the stator, thus forming a radial stop for the rotor 149, so that a collision between the rotor-side and stator-side structures is prevented. The safety bearing 215 is configured as a non-lubricated rolling bearing and forms a radial gap together with the rotor 149 and / or the stator. The gap ensures that the safety bearing 215 is not engaged during normal pump operation. The safety bearing 215 engages during radial displacement, which is dimensioned to be sufficiently large so that the safety bearing 215 is not engaged during normal operation of the vacuum pump and at the same time is sufficiently small so that a collision between the rotor-side and stator-side structures is prevented in all circumstances.

[0045] The vacuum pump 111 has an electric motor 125 which drives a rotor 149 in rotation. The armature of the electric motor 125 is formed by the rotor 149. A rotor shaft 153 of the rotor 149 extends through a motor stator 217. A permanent magnet assembly may be arranged radially outwardly or embedded in the part of the rotor shaft 153 which extends through the motor stator 217. An intermediate chamber 219 is arranged between the motor stator 217 and the part of the rotor 149 which extends through the motor stator 217. The intermediate chamber 219 has a radial motor gap. Through the motor gap, the motor stator 217 and the permanent magnet assembly may magnetically interact to transmit a driving torque.

[0046] The motor stator 217 is fixed in the housing in a motor chamber 137 provided for the electric motor 125. Via a seal gas connection 135, a seal gas (also called purge gas, which can be, for example, air or nitrogen) can reach the motor chamber 137. Via the seal gas, the electric motor 125 can be protected against process gases, for example against corrosive parts of the process gas. The motor chamber 137 can be evacuated via the pump outlet 117, i.e. a vacuum pressure acts in the motor chamber 137, which is realized at least approximately by an auxiliary vacuum pump connected to the pump outlet 117.

[0047] A so-called labyrinth seal 223, known per se, may furthermore be provided between the rotor hub 161 and the wall 221 which defines the motor chamber 137. This in particular achieves better sealing of the motor chamber 217 with respect to the radially outer Holweck pump stages.

[0048] Hereinafter, the turbomolecular pump 111 according to the present invention will be described with reference to Fig. 6. The turbomolecular pump 111 according to the present invention shown in Fig. 6 is constructed almost identically to the turbomolecular pump 111 constructed with reference to Figs. 1 to 5 above. Therefore, for the basic structure of the turbomolecular pump 111 according to the present invention shown in Fig. 6, reference can be made to the above description of the turbomolecular pump 111 shown in Figs. 1 to 5. However, compared to the turbomolecular pump 111 previously described with reference to Figs. 1 to 5, the turbomolecular pump 111 according to the present invention shown in Fig. 6 additionally has a carrier gas connection 225. The position and function of the carrier gas connection 225 will be described in more detail below.

[0049] As mentioned above, the above-mentioned turbomolecular pump 111 has a ventilation inlet 133 opening into a Holweck pump stage of the pump 111. Moreover, the ventilation inlet 133 may also be provided in the region of the serially connected turbomolecular pump stages, in which case the ventilation inlet 133 is usually located in the downstream region of the pump mechanism formed by the serially connected turbomolecular pump stages. In a turbomolecular pump having, for example, ten turbomolecular pump stages, the ventilation inlet 133 may be located, for example, in the region of the seventh pump stage. Via such a ventilation inlet 133, for example, air can be ventilated to the pump 111 after the pump 111 has stopped operating or after the power supply to the electric motor 125 has been interrupted.

[0050] According to the invention, it is envisaged that the turbomolecular vacuum pump 111 has, in addition to or instead of the vent inlet 133, a carrier gas connection, which is only diagrammatically identified in FIG. 6 by the reference "225". In this case, the carrier gas connection 225 is a housing opening through which the carrier gas can be introduced into the pump mechanism formed by the turbomolecular pump stage. In this case, the housing opening 227 of the carrier gas connection 225 can be closed, for example, by a screw closure, not shown here, which can be removed if necessary, so that a supply line can be connected to the carrier gas connection 225 and carrier gas can be supplied to the carrier gas connection 225 via the supply line. Alternatively to this, 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 infinitely variable, so that the amount of carrier gas supplied to the carrier gas connection 225 can be infinitely adjusted, in particular controlled.

[0051] In this case, according to the invention, the carrier gas connection 225 opens upstream of the turbomolecular pump stage M into the pump mechanism formed by the N turbomolecular pump stages, in which case:

number

[0052] Basically, however, it has proven to be advantageous to provide the carrier gas connection 225 near the upstream end of the turbomolecular pumping mechanism, in particular in the upstream third of the pumping mechanism formed by a number of turbomolecular pumping stages, which can be seen, for example, in accordance with the relationship

number

number

[0053] Unlike the vent inlet 133, the carrier gas is not introduced into the pump mechanism via the carrier gas connection 225 until after the pump has been shut off, but rather, according to the invention, it is envisaged that the carrier gas is introduced into the pump mechanism via the carrier gas connection 225 from the pump inlet 115 to the pump outlet 117 during operation of the turbomolecular pump 111 and thus during pumping of the process gas. In other words, the carrier gas is introduced into the pump mechanism while the electric motor 125 is energized.

[0054] Thus, the carrier gas is introduced into the pump mechanism during normal pumping operation of the turbomolecular pump 111 via the carrier gas connection 225. In this case, this normal pumping operation may be defined as a period during which the turbomolecular vacuum pump 111 is continuously operated at at least 75% of its maximum permissible power and / or at least 75% of its maximum permissible rotation speed. In this case, in particular, the carrier gas is introduced into the pump mechanism through the carrier gas connection 225 for at least 50% of the time of the period thus defined. In this case, for example, it can be envisaged that the carrier gas is continuously introduced into the pump mechanism during pumping of the process gas for a period of at least 1 hour, in particular for a period of 10 hours, preferably for a period of more than 24 hours.

[0055] In this case, the carrier gas introduced via the carrier gas connection 225 entrains or carries the process gas being pumped from the pump inlet 115 to the pump exhaust 117, in particular preventing the process gas from flowing back from the pump exhaust 117 to the pump inlet 115. The pressure at the pump inlet is thus reduced in the desired manner, and therefore the pumping speed of the pump is increased in the desired manner.

[0056] The turbomolecular vacuum pump 111 described herein with reference to Figure 6 includes a Holweck pump stage downstream of the turbomolecular pump stage in the manner previously described. However, the Holweck pump stage is optional just like the vent inlet 133 and is not required to obtain the carrier gas effect according to the invention. In short, the turbomolecular vacuum pump 111 according to the invention may include a Holweck pump stage but does not have to.

[0057] Below, with reference to Fig. 7, test results observed on a turbomolecular pump without Holweck pump stages are presented. Here, the turbomolecular pump has 10 turbomolecular pump stages (N=10). In the diagram of Fig. 7, the pressure at the pump inlet 115 is plotted on the Y axis and the auxiliary pressure at the pump outlet 117 is plotted on the X axis. In this case, the turbomolecular pump used during the tests has a vent inlet in the region of the seventh turbomolecular pump stage and a carrier gas connection in the region of the fourth turbomolecular pump stage.

[0058] In this case, the top line of the diagram shows the operating state of the pump in which no gas was introduced into the pump mechanism either through the vent inlet or through the carrier gas connection. In contrast, the middle line of the diagram relates to an operating state in which nitrogen was introduced into the pump mechanism during operation of the pump via the vent inlet in the region of the seventh turbomolecular pump stage. In contrast, the bottom line of the diagram relates to an operating state of the pump in which nitrogen was introduced into the pump mechanism via the carrier gas connection in the region of the fourth turbomolecular pump stage. In this case, the pump was operated such that 1000 sccm of hydrogen gas was pumped as process gas from the pump inlet 115 to the pump outlet 117 during all three operating states.

[0059] As can be seen from the middle line of the diagram, the introduction of nitrogen gas already through the vent inlet causes a drop in pressure at the pump inlet relative to an operating condition where no carrier gas is introduced into the pump mechanism according to the top line of the diagram.

[0060] Thus, if already by introducing nitrogen through the vent inlet the pumping speed is improved, and as can be seen from the bottom line of the diagram, the pump inlet pressure is even further reduced if nitrogen as carrier gas is introduced into the pump mechanism not through the vent inlet in the region of the seventh turbomolecular pump stage, but through the carrier gas connection in the region of the fourth turbomolecular pump stage.

[0061] In the above test results, the pump was continuously operated at 1000sccmH 2 The pump was operated to pump 100 sccm of nitrogen through the vent inlet or seal gas connection 225. Thus, in summary, tests have shown that a ratio of about 10:1 (standard cubic centimeters per minute of process gas:standard cubic centimeters per minute of carrier gas) reliably reduces the backflow problem described above, and therefore increases the pumping speed, without excessively taxing the power consumption of the pump. This application relates to the invention described in the claims, but also includes the following as other aspects. 1. A molecular vacuum pump (111), a housing (119) containing a pump mechanism driven by a rotor shaft (153) for pumping process gas from a pump inlet (115) to a pump outlet (117); The pump mechanism has a plurality of pump stages N connected in series between a pump inlet (115) and a pump exhaust (117) to produce a pumping effect, the pump stage closest to the pump inlet (115) being a first pump stage and the stage closest to the pump exhaust (117) being an Nth pump stage; The housing (119) has a carrier gas connection (225) which opens into the pump mechanism upstream of the pump stage M, where:

number

number

number

[0062] 111 Turbomolecular pump 113 Intake flange 115 Pump Inlet 117 Pump exhaust port 119 Housing 121 Lower part 123 Electronics Housing 125 Electric Motor 127 Accessory connection 129 Data Interface 131 Current supply connection 133 Ventilation Intake 135 Seal gas connection 137 Motor Room 139 Coolant Connection 141 Bottom surface 143 Screw 145 Bearing cover 147 Fixed hole 148 Coolant Line 149 Rotor 151 Rotation axis 153 rotor shaft 155 Moving blade 157 Stator blade 159 Spacer ring 161 rotor hub 163 Holbeck Rotor Sleeve 165 Holbeck Rotor Sleeve 167 Holbeck Sterling Sleeve 169 Holbeck Sterling Sleeve 171 Holbeck Gap 173 Holbeck Gap 175 Holbeck Gap 179 Connection Channels 181 Rolling bearings 183 Permanent magnet type magnetic bearing 185 Splash Nut 187 Disc 189 Insert 191 Rotor side bearing half 193 Stator side bearing half 195 Ring Magnet 197 Ring Magnet 199 Bearing clearance 201 Support part 203 Support part 205 Radial Struts 207 Cover Elements 209 Support Ring 211 Fixing ring 213 Disc spring 215 Emergency or safety bearings 217 Motor Stator 219 Intermediate Room 221 Wall 223 Labyrinth Seal 225 Carrier gas connection 227 Housing opening

Claims

1. A method for operating a molecular vacuum pump (111), comprising the steps of: The molecular vacuum pump (111) comprises a housing (119) containing a pumping mechanism driven by a rotor shaft (153) using an electric motor to pump a process gas from a pump inlet (115) to a pump outlet (117); The pump mechanism has a plurality of pump stages N connected in series to each other and exerting a pumping effect between a pump inlet (115) and a pump outlet (117), the pump stage located closest to the pump inlet (115) being the first pump stage, and the stage located closest to the pump outlet (117) being the Nth pump stage; The housing (119) has a carrier gas connection (225) which opens into the pump mechanism upstream of the pump stage M, where: [0010] holds, or When N≧4 [0025] holds, or When N≧6 [0030] holds true, The method includes introducing a quantity of carrier gas into a pump mechanism while pumping a process gas from a pump inlet (115) to a pump outlet (117), wherein: the ratio of the amount of carrier gas introduced into the pumping mechanism, measured in standard cubic centimeters per minute (sccm), to the amount of process gas pumped, measured in standard cubic centimeters per minute (sccm), is 1:X, where 5≦X≦15, 7≦X≦13, or 9≦X≦11, or is equal to 10; A method comprising:

2. 10. The method of claim 1, further comprising introducing a carrier gas into the pump mechanism while the electric motor is energized.

3. 3. The method according to claim 1 or 2, wherein the method is carried out using a turbomolecular vacuum pump (111), the turbomolecular vacuum pump having a number N of turbomolecular pump stages connected in series with each other in a pumping effect, each turbomolecular pump stage having rotor blades (155) attached to a rotor shaft (153) and fixed stator vanes (157).

4. 3. The method according to claim 1, wherein a gas having a molar mass greater than the process gas is used as carrier gas, and wherein nitrogen and / or argon are used as carrier gas.

5. 3. The method of claim 1 or 2, wherein the carrier gas is introduced continuously during pumping of the process gas for a period of at least 1 hour, for a period of at least 10 hours, or for a period of more than 24 hours.

6. 3. The method according to claim 1 or 2, wherein the carrier gas is continuously introduced for at least 50% of the time during which the molecular vacuum pump (111) is continuously operated at at least 75% of the maximum allowable power or at least 75% of the maximum allowable rotation speed.

Images