TW202106979A - Molecular drag stage - Google Patents

Abstract

A molecular drag stage (14), preferably for a turbomolecular pump (10), with a housing (16) comprising an inlet (28) and an outlet (30), a rotor shaft (18) rotatably supported within the housing (16), a electric motor (22) wherein the motor (22) is built by a motor stator (58) surrounding the rotor shaft (18) in order to rotate the rotor shaft (18). Thereby, a small gap (60) is defined between the outer side (62) of the rotor shaft (18) and the inner side (64) of the motor stator (58). The outer side (62) of the rotor shaft (18) or the inner side (64) of the motor stator (58) comprises a thread (66) or a threaded groove in order to convey a gaseous medium from the inlet (28) to the outlet (30).

Description

Molecular drag phase

The present invention relates to a molecular drag phase that is preferably used in a turbomolecular pump. The present invention further relates to a turbomolecular pump with such a molecular drag stage.

The known turbomolecular vacuum pump includes a casing forming an inlet and an outlet. A motor is arranged in the housing to rotate a rotor shaft. The turbomolecular vacuum pump includes a turbomolecular stage in which the vessel interacts with the stator so that a gaseous medium is transported from the inlet to the outlet. The turbomolecular phase is followed by a molecular drag phase, such as a Holweck phase. The known molecular drag phase includes a rotating cylinder near a stator with a narrow gap therebetween, where the stator or cylinder has a threaded groove or a thread.

In order to improve the efficiency of the molecular drag stage, several stages are nested together to keep the size of the shell small. Thereby, in the subsequent molecular drag phase, the gaseous medium is pumped in the opposite direction. An even-numbered stage complicates the design by leaving the gas in the pump mechanism, requiring additional channels or drilling to facilitate the movement of the gas to the exhaust port. Therefore, usually only an odd number of molecular drag phases are feasible, so that the last molecular drag phase ends toward the outlet of the vacuum pump, thereby limiting the freedom of design of the vacuum pump.

However, the known concept includes an even-numbered molecular drag phase in which a gaseous medium flows through a gap between a motor stator and a rotor shaft toward the outlet. However, this configuration causes heat accumulation in one of the motors and causes friction loss, making this configuration inefficient.

One object of the present invention is to provide a molecular drag stage and a turbomolecular pump, which are more efficient and provide a high degree of freedom in design.

This technical problem is solved by a molecular drag phase according to technical solution 1 and a turbomolecular pump according to technical solution 11.

A molecular drag stage according to the present invention includes a shell having an inlet and an outlet. A rotor shaft is rotatably supported in the housing. The molecular drag stage further includes an electric motor within the housing, wherein the motor is constructed by a motor stator surrounding the rotor shaft to rotate the rotor shaft. Thereby, a small gap is defined between the outer side of the rotor shaft and the inner side of the motor stator, so that the rotor shaft and the motor stator have no contact and the rotor shaft can rotate in the motor stator. Thereby, the outer side of the rotor shaft or the inner side of the motor stator includes a screw thread or a screw groove to convey a gaseous medium from the inlet to the outlet. Therefore, one of the outer side of the rotor shaft or the inner side of the motor stator includes a thread or a thread groove, and the opposite surface is smooth. Therefore, the motor itself in the molecular drag phase is adapted to effectively transport the gaseous medium toward the outlet. The motor itself can be used as an effective element for conveying the gaseous medium to prevent heat accumulation in one of the motors and improve the efficiency of the molecular drag phase. Therefore, the innermost side of the motor stator and the outer side of the rotor shaft together construct an additional molecular drag stage. In this way, molecules of the gaseous medium are transported by a molecular drag process.

Preferably, at least one further pumping stage constructed as a molecular drag stage is implemented, wherein the pumping stage includes a rotor element connected to the rotor shaft to interact with a non-rotating pump stator element, In order to transport the gaseous medium from the inlet to the outlet. Thereby, the rotor element can be constructed as a cylindrical element surrounded by the pump stator element or surrounding the pump stator element. Thereby, the rotor element or the pump stator element includes a thread or thread groove to construct a molecular drag stage. In order for one of the rotor elements to rotate without contact, a small gap is defined between the rotor element and the pump stator to transport a gaseous medium from the inlet to the outlet.

Preferably, at least two and preferably four further pumping stages are implemented, wherein more preferably, adjacent pumping stages share a common rotor element and transport the gaseous medium in opposite directions. Therefore, the outer surface of the rotor element can belong to a first pumping stage, and the inner surface of the same rotor element can belong to the adjacent pumping stage to achieve a compact design of the molecular drag stage.

Preferably, the gap between the outer side of the rotor shaft and the inner side of the motor stator defines an inlet through which the gaseous medium enters the gap and an outlet through which the gaseous medium leaves the gap, wherein the The inlet is in fluid communication with an outlet of the last pumping stage and the outlet of the gap is preferably in direct fluid communication with the outlet. Therefore, in the molecular drag phase, the gaseous medium first flows to one or more pumping phases constructed by the respective rotor elements and pump stator elements, and after that, the gaseous medium passes through the electric motor formed by the The gap is conveyed toward the outlet. Therefore, since the effective gap of the electric motor is used to transport the gaseous medium through the outlet, an even number of pumping stages can be implemented without disadvantages.

Preferably, at the entrance of the gap, a pressure is lower than 30 mbar and more preferably lower than 10 ^-2 mbar. At the outlet of the gap, preferably, a pressure is equal to or lower than the ambient pressure. More preferably, the pressure at the outlet is between 100 mbar and 0.02 mbar.

Preferably, the main flow of the gaseous medium is guided through the gap. Therefore, the gap of the electric motor is not used as a bypass or the like.

Preferably, no purge gas is delivered through the gap.

Preferably, the outlet of the last pumping stage is connected with the outlet only through the gap. Therefore, the gas leaving the last pumping stage can only reach the outlet when flowing through the effective gap of the electric motor.

Preferably, the pump stages are constructed as Holweck stages.

Preferably, the motor stator is constructed as a laminated stator core including a plurality of chip elements. Thereby, the plurality of chip elements are arranged in the motor stator, or in other words, the motor stator surrounds the plurality of chip elements connected to the rotor shaft. In particular, the chip elements of the motor stator are made of steel.

Preferably, the directly adjacent chip elements of the motor stator differ from each other in at least one structural feature (such as a protrusion or indentation from one chip element shifted from one chip element to the next one) at their inner sides, Wherein along the length of the gap, the thread or thread groove is formed by the sum of the individual displacement features. Therefore, the thread or thread groove of the gap is constructed in a stepwise manner by the angular displacement of the structural feature of the directly adjacent sheet-like element. Thereby, it is easy to manufacture the effective gap of the electric motor. Since the motor stator of the electric motor usually includes chip elements in any manner, these chip elements can be used to construct the thread or thread groove to form the effective gap of the electric motor.

Furthermore, the present invention relates to a vacuum pump including a molecular drag stage as described above. Preferably, the molecular pump system includes a turbomolecular pump in a turbomolecular pump stage. The turbomolecular pumping stage includes pulse tubes connected to the rotor shaft, and the pulse tubes interact with the stator pulse tubes to transport a gaseous medium from the inlet to the outlet. Thereby, preferably, the turbo molecular pumping stage is arranged upstream of the molecular dragging stage according to the general flow of the gaseous medium in the vacuum pump. Preferably, the vacuum pump can generate a vacuum ^{ranging from 10 -2} mbar to 10 ^-12 mbar.

The vacuum pump 10 of FIG. 1 is constructed as a turbomolecular vacuum pump including a turbomolecular pump stage 12 and a molecular drag stage 14. The vacuum pump 10 includes a housing 16 in which a rotor shaft 18 is rotatably supported by, for example, a ball bearing 20. The rotor shaft 18 is rotated by an electric motor 22.

In the turbomolecular pumping stage 12, the rotor shaft 18 is connected to the rotor element constructed as a vessel 24 and interacts with the stator vessel 26 so that a gaseous medium is transported from an inlet 28 to an outlet 30. The gaseous medium is transported through the turbo molecular pump stage 12 and enters the molecular drag stage 14. In the molecular drag phase 14, a first cylinder 34 and a second cylinder 36 are used to connect the rotor shaft 18 to a rotor element 32. Furthermore, a threaded first stator 38 is implemented, wherein the thread of the first stator 38 faces the outer surface of the first cylinder 34, so that the gaseous medium passes through the first pump stage 40 from one of the inlets 42 of the molecular drag stage 14 The pump reaches a first turning point 44. The inner surface of the first cylinder 34 faces a second threaded pump stator 46 to form a second pumping stage 48 that pumps the gaseous medium from the first turning point 44 to a second turning point 50. From the second turning point 50, the gaseous medium passes through a third pump stage 52 and a fourth pump stage 54 via the pump, which have the same or similar construction as the first pump stage 40 or the second pump stage 48. Therefore, the gas reaches one of the final turning points 56 located in the vacuum pump 10.

The electric motor 22 includes a motor stator 58 in which a gap 60 is defined between the motor stator 58 and the outer surface 62 of the rotor shaft 18. Thereby, the inner surface 64 of the motor stator 58 includes a thread 66, thereby effectively pumping the gaseous medium from the last turning point 56 of the entrance forming the gap 60 toward the exit 30. Therefore, the gaseous medium entering the molecular drag stage 14 through the inlet 42 can only reach the outlet 30 through the gap 60. Thereby, the gaseous medium is effectively pumped in the gap 60 by the thread 66 to improve the efficiency of the molecular drag stage 14 and avoid friction loss and heat generation in the electric motor 22. Alternatively, the outer surface 62 of the rotor shaft 18 may include a thread or a thread groove. In this case, the inner surface 64 of the motor stator 58 may be constructed as a flat surface.

The motor stator 58 is constructed of a plurality of chip elements 68 preferably made of steel. Thereby, the sheet element 68 may include a structural feature 70, which may be constructed as a protrusion or indentation. Figure 2 shows the structural feature 70 as a protrusion. Thereby, the structural feature 70 is displaced from one sheet element 68 to the next or adjacent one by a smaller angle, thereby forming the thread 66 from the structural feature 70 in a stepwise manner. Of course, one sheet element 68 may include more than one structural feature 70. Therefore, the thread or the thread groove in the movable gap 60 of the electric motor 22 is easy to manufacture, so that the manufacturing cost of the motor stator 58 of the electric motor 22 can be reduced.

10: Vacuum pump 12: Turbomolecular pumping stage 14: molecular drag phase 16: shell 18: Rotor shaft 20: Ball bearing 22: electric motor 24: Vessel 26: stator vessel 28: entrance 30: Exit 32: Rotor element 34: The first cylinder 36: second cylinder 38: first stator 40: The first pump stage 42: entrance 44: The first turning point 46: The second thread pump stator 48: The second pump stage 50: second turning point 52: The third pump stage 54: The fourth pump stage 56: Last turning point 58: Motor stator 60: Clearance 62: outer surface 64: inner surface 66: Thread 68: chip components 70: Structural Features

In the following, the present invention will be described in relation to a specific embodiment with reference to the drawings.

Figure 1 shows a schematic diagram of a vacuum pump according to the present invention, and

Figure 2 shows a detailed view of the motor stator according to the present invention.

10: Vacuum pump

12: Turbomolecular pumping stage

14: molecular drag phase

16: shell

18: Rotor shaft

20: Ball bearing

22: electric motor

24: Vessel

26: stator vessel

28: entrance

30: Exit

32: Rotor element

34: The first cylinder

36: second cylinder

38: first stator

40: The first pump stage

42: entrance

44: The first turning point

46: The second thread pump stator

48: The second pump stage

50: second turning point

52: The third pump stage

54: The fourth pump stage

56: Last turning point

58: Motor stator

60: Clearance

62: outer surface

64: inner surface

66: Thread

Claims (11)

A molecular drag stage (14) preferably used in a turbomolecular pump (10), which has: A housing (16), which includes an inlet (28) and an outlet (30), A rotor shaft (18), which is rotatably supported in the housing (16), An electric motor (22), wherein the motor (22) is constructed by a motor stator (58) surrounding the rotor shaft (18) to rotate the rotor shaft (18), A small gap (60) is defined between the outer side (62) of the rotor shaft (18) and the inner side (64) of the motor stator (58), Wherein the outer side (62) of the rotor shaft (18) or the inner side (64) of the motor stator (58) includes a thread (66) or a thread groove to convey a gaseous medium from the inlet (28) To this exit (30). For example, the molecular drag stage of claim 1, which has at least one further pumping stage (40), wherein the pumping stage (40) includes a rotor element (34), the rotor element (34) is connected to the rotor shaft ( 18) to interact with a non-rotating pump stator element (38) to transport the gaseous medium from the inlet (28) to the outlet (30). For example, the molecular drag stage of claim 2, which has at least two and preferably four further pump stages (40, 48, 52, 54), wherein more preferably, adjacent pump stages share a common rotor element ( 34, 36) and convey the gaseous medium in the opposite direction. Such as the molecular drag phase of claim 2 or 3, wherein the gap (60) defines an inlet through which the gaseous medium enters the gap (60) and an outlet through which the gaseous medium leaves the gap (60), wherein the The inlet is in fluid communication with an outlet (56) of the last pumping stage (54) and the outlet is preferably in direct fluid communication with the outlet (30). Such as the molecular drag phase of any one of claims 1 to 3, wherein the main flow of the gaseous medium is guided through the gap (60). Such as the molecular drag phase of any one of claims 1 to 3, wherein no purge gas is transported through the gap (60). Such as the molecular drag phase of claim 2 or 3, wherein the outlet (56) of the last pump phase (54) is connected with the outlet (30) only through the gap (60). Such as the molecular drag phase of claim 2 or 3, wherein the pump phases (40, 48, 52, 54) are constructed as Holweck phases. Such as the molecular drag phase of any one of claims 1 to 3, wherein the motor stator (58) is constructed as a laminated stator core including a plurality of sheet elements (68), wherein the sheet elements (68) are more Jia is made of steel. Such as the molecular drag phase of claim 9, in which the directly adjacent sheet-like elements (68) are different from each other at their inner sides, so that at least one feature (70) is shifted from one sheet-like element (68) to the next sheet-like element , Wherein along the length of the gap (60), the thread (66) is formed by the sum of the individual displacement features (70). A vacuum pump (10), specifically a turbomolecular vacuum pump, includes a molecular drag stage (14) as in any one of claims 1 to 10.

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