The present invention relates to a bearing assembly in particular for a vacuum pump. Further the present invention relates to a vacuum pump, in particular a turbomolecular pump, comprising such a bearing assembly and a method for replacing an emergency bearing of such a vacuum pump.

Common vacuum pumps and in particular turbomolecular pumps comprise a housing having an inlet and an outlet. A rotor assembly comprising a rotor shaft is disposed in the housing and supported by two bearings. The rotor assembly comprises at least one rotor element interacting with at least one stator element being connected to the housing. The rotor assembly is rotated by an electromotor in order to convey a gaseous medium from the inlet to the outlet. In the case of a turbomolecular pump the rotor assembly comprises a plurality of vanes interacting with respective vanes of the stator.

Therein the bearing supporting the rotor assembly can be built as roller bearings and/or magnetic bearing such as a permanent magnetic bearing.

In hybrid turbomolecular vacuum pumps a magnetic bearing is used at the high vacuum end of the rotor assembly. Magnetic bearings are quite 'soft' compared to traditional mechanical bearings; hence large movement can occur if the turbomolecular pump is knocked. To protect the magnetic bearing from contacting and damaging itself, a mechanical backup bearing or emergency bearing is also used to limit radial excursion of the rotor during a knock or shock of some sort to the customer system. Therein, to ensure the emergency bearing does not contaminate the vacuum system, hydro-carbon lubrication is not used to protect the rolling elements of the bearing. Material coatings help reduce contact friction, but overtime and with repeated engagement the bearing will wear and require replacement. However, if the backup bearing or emergency bearing must be replaced, in common vacuum pumps the complete rotor assembly must be disassembled from the vacuum pump thereby separating the components of the magnetic bearing to gain access to the emergency bearing and being able to replace the emergency bearing. This maintenance requires time and can only be carried out by professional personnel often requiring special tools. Therein, vacuum pumps and in particular fast rotating molecular pumps contain main close running surfaces and intricate parts which need to be carefully handled during disassembly and when the pump is rebuilt. To maintain reliable operation and a robust product, disassembly within the field is not desirable.

Thus, it is an object of the present invention to provide a bearing assembly including an emergency bearing which can be easily replaced.

The problem of the prior art is solved by a bearing assembly according to claim 1, a vacuum pump according to claim 10 and a method for replacing an emergency bearing according to claim 12.

The bearing assembly according to the present invention, which is in particular a bearing assembly for a vacuum pump, supporting the rotor assembly having a magnetic bearing including a rotated magnetic element and static magnetic element arranged next to each other in mutual repulsion, wherein the rotated magnetic element radially surrounds the static magnetic element. In particular, the rotated magnetic element comprises a plurality of magnetic rings stacked in axial direction in order to create a magnetic repulsion between corresponding magnetic rings of the static magnetic element to support the rotor assembly during normal operation of the vacuum pump. Therein, the static magnetic element is connected to a bearing support, wherein the bearing support can be connected to a housing of the vacuum pump. The bearing support comprises a recess and an opening to receive an extension of the rotor assembly extending through the opening into the recess. Therein, the extension is connected to a rotor shaft of the rotor assembly.

In accordance with the present invention an emergency bearing is arranged in the recess and configured to surround the extension of the rotor shaft. Thus, by the configuration of the bearing assembly the emergency bearing can be easily replaced due to access via the recess without disassembly of the rotor assembly from the vacuum pump. Since the emergency bearing is accessible via the recess, simplified replacement of the emergency bearing is feasible.

Preferably, the magnetic bearing and the emergency bearing are arranged next to each other. Thus, clearance control between the emergency bearing and shaft on the one hand and the magnetic bearing rings on the other hand is simplified.

Preferably, the magnetic bearing is arranged radially next to the emergency bearing, i.e. the magnetic bearing surrounds the emergency bearing. Since magnetic bearing and emergency bearing are on a similar axial plane clearance control is simplified and the effect on clearance of rotor distortion, thermal growth, rotodynamic effects of the impeller etc. are reduced.

Preferably, the recess is open in a direction opposite to the rotor shaft. Thus, the recess is accessible even if the rotor shaft is assembled, i.e. the extension of the rotor shaft is extending through the opening of the bearing support, thereby providing access to the emergency bearing even if the bearing assembly is mounted to the vacuum pump.

Preferably, the inner diameter of the emergency bearing is larger than the outer diameter of the extension. Thus, under normal operation no contact between the extension and the emergency bearing occurs. Only under knock or shock to the vacuum pump and in particular to the rotor assembly, the extension comes in contact with emergency bearing and maintains support of the rotor assembly. Preferably, the radial distance between the emergency bearing and the extension of the rotor shaft is smaller than the radial distance between the static magnetic element and the rotated magnetic element. Thereby it is assured that no contact occurs between the static magnetic element and the rotated magnetic element which would otherwise damage or destroy the elements of the magnetic bearing.

Preferably, the opening comprises an annular contact surface surrounding the extension of the rotor shaft and extending in an axial direction. The annular contact surface might support the rotor shaft in case of failure even of the emergency bearing. Therein, by the annual contact surface radial movement of the rotor shaft is limited even in case of failure of the emergency bearing.

Preferably, the contact surface is arranged axially before the emergency bearing in the direction towards the vacuum side of the rotor shaft.

Preferably, the inner diameter of the contact surface is larger than the inner diameter of the emergency bearing. Thus, the contact surface comes into contact with the extension of the rotor shaft only in case of failure of the emergency bearing. Thus, under normal condition if a knock or shock occurs to the vacuum pump or the rotor assembly, the rotor shaft comes into contact with the emergency bearing. Only if the emergency bearing fails to withstand this shock or knock, the rotor shaft, i.e. the extension of the rotor shaft, comes into contact with the contact surface to limit radial movement of the rotor assembly maintaining support of the rotor assembly.

Preferably, the contact surface and/or at least a section of the rotor shaft corresponding to the contact surface, i.e. the section of the rotor shaft coming into contact with the contact surface is coated with an anti-friction coating, such as molydenum disulphide, teflon or the like. Preferably, the radial distance between the contact surface and the extension of the rotor shaft is smaller than the radial distance between the static magnetic element and the rotated magnetic element. Thus, even if the extension of the rotor shaft comes into contact with the contact surface, damage of the magnetic bearing is avoided. In particular, the radial distance between the contact surface and the extension of the rotor shaft is smaller than the minimum clearance between the rotor assembly and the stator of the vacuum pump in order to also avoid contact between the rotor elements and the stator elements in the vacuum pump which would otherwise result in damage or destroying of these elements.

Preferably, fixing means are employed to fix the emergency bearing in the recess. Therein the fixing means are configured to be removable via the recess. The fixing means might be built as snap-fit ring, fixing the emergency bearing in the recess, a threaded element or as clamping ring wherein for the clamping ring a radial recess might be arranged in order to receive the clamping ring partially and avoid axial movement of the clamping ring and consequently of the emergency bearing. Other fixing means are also possible as long as they provide fixture of the emergency bearing in the recess and avoidance of at least axial movement and/or vibration of the emergency bearing within the recess during operation.

Preferably, the bearing assembly comprises a sensor for detecting a contact between the rotor shaft and the emergency bearing, wherein the sensor is connected to a control unit and the control unit is configured to generate a signal if the number of contacts exceeds a predetermined threshold. Thus, if the number of contacts between the emergency bearing and the extension of the rotor shaft exceeds the predetermined threshold, maintenance of the emergency bearing is signalled by the signal generated from the control unit. The signal can be any kind of signal such as optical signal, acoustical signal or electronical signal read out by the customer or manufacturer of the vacuum pump being able to indicate the necessity of maintenance of the emergency bearing. In particular, the control unit is part or integral part of the controller of the vacuum pump itself. Thus, no additional unit or component is necessary. In particular, the sensor can be built as acceleration sensor measuring the shock during touch of the extension of the rotor shaft with the emergency bearing. However other sensors which are able to detect a contact between the rotor shaft and the emergency bearing are also possible.

Another aspect the present invention relates to a vacuum pump and in particular to a turbomolecular pump comprising a housing having an inlet and an outlet. A rotor assembly is disposed in the housing having a rotor shaft and at least one pump element connected to the rotor shaft. The rotor assembly is rotated by an electromotor and upon rotation conveys a gaseous medium from the inlet to the outlet. Therefore, the rotor assembly is rotatably supported by two bearing assemblies, wherein at least one and preferably two bearing assemblies are built according to the bearing assembly as described above. The rotated magnetic element of the bearing assembly may be connected to the rotor assembly. Therein, an extension of the rotor shaft is extending through the opening of the bearing support into the recess. The extension of the rotor shaft can be built as a separate part fixed to the rotor shaft or can be integrally build with the rotor shaft. In particular, the extension is arranged at one end of the rotor shaft and in particular at the vacuum-sided end of the rotor shaft. Thereby the extension of the rotor shaft can be inserted through the opening into the recess of the bearing assembly.

Preferably, the recess of the bearing assembly and in particular the emergency bearing of the bearing assembly is accessible from the outside of the vacuum pump in particular without disassembly of the rotor assembly from the vacuum pump. In particular, the emergency bearing is accessible via the inlet of the vacuum pump. Preferably, no covers or oil cartridge (as for the lower bearing or bearing on the exhaust side) need to be removed to reach the emergency bearing and or the fixing means. Thus, direct access to the emergency bearing is feasible.

In addition, the present invention relates to a method for replacing an emergency bearing of a vacuum pump as described above. The method includes the steps of: disassembly of the vacuum pump form a vacuum apparatus; replacing the emergency bearing through the recess without disassembly of the rotor assembly; and attaching the vacuum pump to the vacuum apparatus.

Preferably, no further steps are necessary in order to replace the emergency bearing and the method is exclusively limited to the steps mentioned above.

Thus, replacement of the emergency bearing even in the field with limited downtime of the vacuum pump is possible reducing costs and enabling the customer to replace the emergency bearing by himself.

In the following the present invention will be described in more detail with reference to the accompanying figures.

The figures show:

Figure 1 A vacuum pump according to the present invention,

Figure 2 A detailed view to the bearing assembly of the vacuum pump according to figure 1 and Figure 3 A schematic flow diagram to replace the emergency bearing of the vacuum pump according to figure 1.

Figure 1 shows a vacuum pump 10 according to the present invention comprising a housing 12 wherein a rotor assembly 14 is disposed in the housing. The rotor assembly 14 comprises a rotor shaft 32 and at least one pump element 16 build as vanes connected with the rotor shaft 32. The at least one pump element 16 interact with vanes of a stator element 18. The rotor assembly 14 is rotated by an electromotor 20 in order to convey a gaseous medium from the inlet 22 to the outlet 24. Therein, as shown in figure 1, the vacuum pump might also comprise a Holweck stage 26 including a rotated cylinder 28 and a threaded stator element 30 to support pumping of the vacuum pump 10 of the gaseous medium. However, the present invention is not limited to a specific configuration of the vacuum pump

The rotor shaft 32 is rotatably supported by two bearing assemblies, wherein a first bearing assembly may have a roller bearing 34 preferably arranged at an end of the rotor shaft 32 opposite to the inlet 22 of the vacuum pump 10. Therein, the roller bearing 34 can be build for example as ball bearing or the like. However, the present invention is not limited to this specific kind of the first bearing assembly and also the roller bearing 34 of the first bearing assembly can be built as magnetic bearing. However, the vacuum pump according to the present invention comprises at least one magnetic bearing. Further, the rotor shaft 32 is supported by a bearing assembly 36 according to the present invention and shown in detail in Figure 2.

The bearing assembly 36 according to the present invention as shown in Figure 2 is build as permanent magnetic bearing comprising a static magnetic element 38 comprising a plurality of magnetic rings 40 and connected to a bearing support 42. The bearing support 42 is connected to the housing 10 of the vacuum pump. Further, the magnetic bearing comprises a rotated magnetic element 44 comprising the same number of magnetic rings 46 surrounding the magnetic rings 40 of the static magnetic element 38 and being in mutual magnetic repulsion to each other in order to support the rotor shaft 32 of the rotor assembly 14. Therein, the bearing support 42 comprises a recess 48 and an opening 50. An extension 52 of the rotor shaft 32 is extends through the opening 50 into the recess 48. An emergency bearing 54 is arranged in the recess and surrounding the extension 52 of the rotor shaft 32. Therein, the extension 52 can be connected to the rotor shaft 32 or integrally build with the rotor shaft 32. The emergency bearing 54 is fixed in the recess by fixing means 56 build for example as clamping ring in order to limit axial movement of the emergency bearing. Thus, for replacement of the emergency bearing 54, the clamping ring 56 can be removed via the recess 48 from outside the vacuum pump 10 and afterwards the emergency bearing 54 can be replaced without disassembly of the rotor assembly 14 from the vacuum pump 10. In particular, no covers need to be removed to reach the emergency bearing 54. Thereby downtime of the vacuum pump is reduced and replacement of the emergency bearing can even be performed by the customer. However, a cover or plug can be used in order to close the recess 48 in order to achieve separation from the process chamber connected to the inlet of the vacuum pump and avoid contamination.

As shown in Fig. 2, the permanent magnetic bearing surrounds the emergency bearing 54 and the rotated magnetic element 44 and the static magnetic element 38 are arranged at the same axial plane as the emergency bearing 54. Thus, clearance control between the emergency bearing and shaft on the one hand and the static/rotated magnetic elements 38, 44 on the other hand is simplified. Since magnetic bearing and emergency bearing are on a similar axial plane clearance control is simplified and the effect on clearance of rotor distortion, thermal growth, rotodynamic effects of the impeller etc. are reduced.

Therein, the inner diameter of the emergency bearing 54 is larger than the outer diameter of the extension 52 of the rotor shaft 32. Thus, under normal operation of the vacuum pump, there is no contact between the emergency bearing 54 and the extension 52 of the rotor shaft 32. Only upon shock or knock onto the vacuum pump 10 or the rotor assembly 14, the extension 52 touches the emergency baring 54 thereby limiting radial movement of the rotor assembly 14. Preferably, the radial distance between the extension 52 and the emergency bearing 54 is smaller than the radial distance between the static magnetic element 38 and the rotated magnetic element 44, thus avoiding damage or destroying of the magnetic bearing. Preferably, the clearance between the extension 52 and the emergency bearing 54 is smaller than the minimum clearance between the rotor elements 16 and the stator elements 18 in order to avoid collision during rotation.

The opening 50 may comprise a contact surface 58 surrounding the extension 52 and extending in an axial direction. Therein the inner diameter of the contact surface 58 is larger than the outer diameter of the extensions 52. Thus, during normal operation of the vacuum pump, no contact between the contact surface 58 and the extension 52 occurs. In addition, the inner diameter of the contact surface 58 may be larger than the inner diameter of the emergency bearing. Thus, upon shock or knock to the vacuum pump 10 and/or the rotor assembly 14, the extension 52 first touches the emergency bearing 54. Only upon failure of the emergency bearing 54 the extension 52 comes into contact with the contact surface 58 and avoid collision between the magnetic elements of the magnetic bearing and/or the rotor elements of the rotor assembly with the stator elements 18.

Preferably, a sensor 60 is attached to the bearing assembly and in particular in proximity to the emergency bearing 54. The sensor 50 might be built as acceleration sensor and is connected to a control unit (not shown). Therein by the sensor 60 contact between the extension 52 and the emergency bearing 54 can be detected. Alternatively, the sensor 60 can be built as microphone detecting the characteristic noise when the extension 52 touches the emergency bearing 54. The emergency bearing 54 can withstand a certain number of contacts between the extension 52 and the emergency bearing 54 before failure. Thus, by detecting the number of contacts between those parts, replacement of the emergency bearing 54 can be facilitated early enough to avoid breakdown of the emergency bearing. Thus, by the control unit the number of contacts between the extension 52 and 54 is detected and upon exceeding a predetermined threshold a signal is generated indicating the necessity to replace the emergency bearing. Therein the generated signal might be an optical signal, an acoustical signal or an electronical signal by the manufacturer or customer of the vacuum pump.

Thus, by the configuration shown in Figures 1 and 2, replacement of the emergency bearing 54 is simplified. In particular the steps of replacing the emergency bearing 54 include the steps as depicted in Figure 3:

In step SOI, the vacuum pump is dissembled from the vacuum apparatus in order to gain access to the inlet side of the vacuum pump.

In step S02, the emergency bearing 54 is replaced through the recess 48 without disassembly of the rotor assembly 14. This may include losing the fixing means 56, disassembly of the emergency bearing 54, assembly of the new emergency bearing 54 through the recess 48 and refixing the fixing means 56 to fix the emergency bearing 54 in the recess 48.

In step S03, the vacuum pump is again attached to the vacuum apparatus.

In particular, no further steps are necessary in order to replace the emergency bearing 54 and thus maintenance of the emergency bearing 54 can be done by the customer himself thereby reducing downtime of the vacuum pump as well as costs.