CN110925303A

CN110925303A - Combined bearing

Info

Publication number: CN110925303A
Application number: CN201911339981.1A
Authority: CN
Inventors: 靳普; 刘慕华
Original assignee: Zhiyue Tengfeng Technology Group Co Ltd
Current assignee: Liu Muhua
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2020-03-27
Also published as: WO2021129427A1

Abstract

The invention discloses a combined bearing, which comprises a radial parallel bearing and a thrust bearing, wherein the parallel bearing comprises a rotating shaft bearing and a stator bearing; the rotating shaft bearing is a contact bearing, and the stator bearing is a non-contact bearing; the stator bearing is sleeved on the rotating shaft bearing, and a gap is reserved between the inner wall of the stator bearing and the outer wall of the rotating shaft bearing; the thrust bearing comprises a foil, an elastomer and a thrust bearing housing; the thrust bearing shell is a disc-shaped shell with a central through hole, at least one end face of the thrust bearing shell is fixed with a foil through an elastic body, and the side wall of the thrust bearing shell is provided with a thrust bearing air inlet. The invention can solve the technical problems that the existing contact bearing has high dependence on lubricant and the friction between the existing non-contact bearing and a rotating shaft rotating at high speed is overlarge.

Description

Combined bearing

Technical Field

The invention relates to the technical field of bearings, in particular to a combined bearing.

Background

Theoretically, the thicker the shaft diameter of the rotating shaft is, the larger load can be borne, and the larger critical rotating speed can be borne, but the DN value of the bearing matched with the rotating shaft is increased, the lubricating oil with higher performance is needed, and otherwise, the faults of bearing abrasion, shaft clamping and the like can be caused. DN is a reference value of selected rolling bearing lubricating oil, wherein D is the diameter of the bearing, and N is the relative rotating speed of the inner ring and the outer ring of the bearing. Bearings with high DN values have high requirements for grease or oil adhesion, operating life, and operating temperature, which are generally expensive.

For non-contact bearings, such as radial air bearings, the support function is achieved by means of compressed air between the shaft and the inner ring of the bearing, and generally, a rubber ring is installed between the outer diameter of the bearing and a bearing seat, and the bearing is fixed by means of friction between the rubber ring and the outer diameter of the bearing to prevent circumferential rotation. However, in the practical operation of the air bearing, when the rotating speed of the rotating shaft reaches more than about 10 thousands of revolutions, air friction exists between the compressed air film and the rotating shaft, the friction also increases along with the increase of the rotating speed of the rotating shaft, and the torque generated by the friction force makes the rotation of the air bearing along with the rotating shaft more obvious and frequent. And with the further improvement of the rotating speed of the rotating shaft or the increase of the shaft diameter of the rotating shaft, the friction force between the air film and the inner diameter of the radial air bearing is further increased, the rotating speed of the radial air bearing relative to the bearing seat is increased, and the rubber ring can be easily abraded and damaged.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a combined bearing, which can solve the technical problems that the existing contact bearing has high dependence on a lubricant and the friction between the existing non-contact bearing and a rotating shaft rotating at a high speed is overlarge.

The definition of the parallel bearing to which the invention relates is: the parallel bearing comprises at least two bearings with different diameters, wherein the bearings are sequentially nested from outside to inside or from inside to outside, the axes of the bearings in the parallel bearing are parallel to each other when the parallel bearing works, and the bearings are completely or partially nested.

In order to achieve the above object, the present invention adopts the following technical solutions.

A combined bearing comprises a radial parallel bearing and a thrust bearing,

the parallel bearing comprises a rotating shaft bearing and a stator bearing; the rotating shaft bearing is a contact bearing, and the stator bearing is a non-contact bearing; the stator bearing is sleeved on the rotating shaft bearing, and a gap is reserved between the inner wall of the stator bearing and the outer wall of the rotating shaft bearing;

the thrust bearing comprises a foil, an elastomer and a thrust bearing housing; the thrust bearing shell is a disc-shaped shell with a central through hole, at least one end face of the thrust bearing shell is fixed with a foil through an elastic body, and the side wall of the thrust bearing shell is provided with a thrust bearing air inlet.

The rotating shaft bearing is sleeved on the rotating shaft and is tightly matched with the rotating shaft, and the rotating shaft is driven to rotate by the driving device; the stator bearing is fixed on the stator; the rotating shaft is provided with a thrust disc which is integrally formed or fixed with the rotating shaft; the thrust bearing shell is covered outside the thrust disc and sleeved on the rotating shaft, and a gap is reserved between the foil and the thrust disc; the thrust bearing housing is fixed to the stator.

The driving device is a motor.

The rotating shaft bearing is a ball bearing, and the stator bearing is an air bearing.

The air bearing is in an annular cylinder shape, at least one annular groove is formed in the outer wall of the air bearing in parallel to the end face, a damper is nested in the annular groove and is an annular rubber ring, and the top of the rubber ring protrudes out of the outer wall of the air bearing.

The air bearing is characterized in that a plurality of lugs are axially and uniformly arranged on the annular end face of the air bearing, one end of each lug arranged on the air bearing is provided with an anti-rotation end cover, the anti-rotation end cover corresponds to the lug which is provided with an anti-rotation hole, and the lug is embedded into the anti-rotation hole and is fixed on the end face of the stator through screws.

Prevent rotating and set up the cross hole on the end cover, including four anti-rotation holes of mutually perpendicular intercommunication, the lug correspondence sets up to four, each the lug imbeds respectively that each prevents rotating downtheholely, adjacent two prevent setting up the screw hole between the rotation hole, the stator terminal surface sets up screw hole one, screw hole and screw hole align with the back with screw fastening.

The rotating shaft bearing is a pair of angular contact ball bearings which are oppositely arranged, and a preload spring is arranged between the outer rings of the two angular contact ball bearings; and two ends of the preloading spring are respectively fixed at the end parts of the outer rings of the two angular contact ball bearings.

The parallel bearing further comprises at least one middle bearing, the middle bearing is a contact bearing, the middle bearing is sleeved between the rotating shaft bearing and the stator bearing, and a gap is reserved between the stator bearing and the middle bearing.

The intermediate bearing is a ball bearing.

And the surface of the shaft section of the rotating shaft sleeved in the rotating shaft bearing is coated with a tetrafluoroethylene anti-abrasion coating.

The rotating shaft bearing is a ball bearing, a roller bearing, a ceramic bearing or a tetrafluoroethylene bearing.

The ball bearing, the roller bearing, the ceramic bearing or the tetrafluoroethylene bearing are single-row, double-row or multi-row.

The ball bearing, the roller bearing, the ceramic bearing or the tetrafluoroethylene bearing is single-layer, double-layer or multi-layer.

The stator bearing is an air bearing, an oil film floating ring bearing or an inclined tile bearing.

The invention has the beneficial effects that:

(1) the combined bearing has low cost, can support the bearing in the radial direction and can limit the displacement of the rotating shaft in the axial direction; the surface of the thrust foil bearing is flexible, and has the advantages of high bearing capacity, low friction power consumption, high stability, allowable bearing gap loss, vibration impact resistance and the like; the radial parallel bearings are low in cost, the relative rotating speed of each stage of bearing is reduced, the bearing is not limited by a theoretical DN value, and the dependence on lubricating oil is low.

(2) In the prior art, an air film exists between a rotating shaft and an air bearing, and the friction force is further increased along with the further increase of the rotating speed of the rotating shaft or the increase of the shaft diameter of the rotating shaft.

(3) The rotating speeds of a plurality of combined bearings on the same rotating shaft can be adjusted in a self-adaptive mode, manual setting or adjusting of the rotating speeds is not needed, and the effect of synchronous rotation can be achieved.

(4) The rotor not only can be used for low rotating speed, but also is suitable for high rotating speed working conditions, and can be used for rotors with rotating speeds of tens of thousands to hundreds of thousands of revolutions.

Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.

Drawings

Fig. 1 is a schematic view of a parallel bearing structure according to a first embodiment of the present invention.

Fig. 2 is a schematic view of a parallel bearing structure according to a second embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a parallel bearing according to a third embodiment of the present invention.

Fig. 4 is a schematic structural view of a parallel bearing according to a fourth embodiment of the present invention.

Fig. 5 is a schematic view of the parallel bearing arrangement of the present invention at both ends of a shaft.

Fig. 6 is a schematic view of a fixing mode of the parallel bearing of the invention.

Figure 7 is a side view of the parallel bearing with lugs of the present invention.

FIG. 8 is a schematic structural view of an anti-rotation end cap of the present invention.

FIG. 9 is a side view of the air bearing with bumps of the present invention.

FIG. 10 is a graph of air bearing friction torque versus time for the present invention.

FIG. 11 is a graph of ball bearing friction torque versus time in accordance with the present invention.

The reference numbers: 1-rotating shaft bearing, 2-stator bearing, 21-rubber ring, 22-lug, 4-stator, 41-screw hole I, 5-anti-rotation end cover, 51-anti-rotation hole, 52-screw hole, 6-intermediate bearing, 100-rotating shaft, 210-thrust disc, 800-thrust bearing, 801-foil, 802-elastomer and 803-thrust bearing shell.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention.

The present invention provides a parallel bearing for being mounted to a rotating shaft 100 to support the rotating shaft 100 in a radial direction.

A combination bearing, see fig. 1-4, includes a radial parallel bearing and a thrust bearing 800,

the parallel bearing comprises a rotating shaft bearing 1 and a stator bearing 2; the rotating shaft bearing 1 is a contact bearing; the stator bearing 2 is a non-contact bearing, the stator bearing 2 is sleeved on the rotating shaft bearing 1, and a gap is reserved between the inner wall of the stator bearing 2 and the outer wall of the rotating shaft bearing 1.

The thrust bearing 800 comprises a foil 801, an elastomer 802 and a thrust bearing housing 803; the thrust bearing housing 803 is a disk-shaped housing with a central through hole, at least one end surface of the interior of the housing is fixed with a foil 801 through an elastic body 802, and the side wall of the housing is provided with a thrust bearing air inlet.

The rotating shaft bearing 1 is sleeved on the rotating shaft 100 and is tightly matched with the rotating shaft 100, and the rotating shaft 100 is driven to rotate by a driving device; the stator bearing 2 is fixed on the stator 4; the rotating shaft 100 is provided with a thrust disc 210 which is integrally formed or fixed with the rotating shaft; the thrust bearing housing 803 covers the thrust disc 210 and is sleeved on the rotating shaft 100, and a gap is reserved between the foil 801 and the thrust disc 210; the thrust bearing housing 803 is fixed to the stator 4.

In the invention, the parallel bearing has the following four embodiments:

example one

The rotating shaft bearing 1 is a ball bearing, and the stator bearing 2 is an air bearing.

Referring to fig. 1, the parallel bearing in this embodiment includes a shaft bearing 1 and a stator bearing 2. The rotating shaft bearing 1 is sleeved on the rotating shaft 100, and the stator bearing 2 is sleeved outside the rotating shaft bearing 1 and keeps a certain gap with the outer wall of the rotating shaft bearing 1.

The air bearing is in an annular cylinder shape, at least one annular groove is formed in the outer wall of the air bearing in parallel to the end face, a damper is nested in the annular groove and is an annular rubber ring 21, and the top of the rubber ring 21 protrudes out of the outer wall of the air bearing.

Referring to fig. 6, 7, 8, and 9, a plurality of protrusions 22 are axially and uniformly arranged on the annular end surface of the air bearing, an anti-rotation end cover 5 is arranged at one end of the air bearing where the protrusion 22 is arranged, an anti-rotation hole 51 is arranged on the anti-rotation end cover 5 corresponding to the protrusion 22, the protrusion 22 is embedded into the anti-rotation hole 51, and the anti-rotation end cover 5 is fixed on the end surface of the stator 4 through a screw.

Further, set up the cross hole on the anti-rotation end cover 5, including four anti-rotation holes 51 of mutually perpendicular intercommunication, lug 22 corresponds to set up to four, and in each lug 22 imbed each anti-rotation hole 51 respectively, set up screw hole 52 between two adjacent anti-rotation holes 51, the stator 4 terminal surface sets up screw hole one 41, and screw hole 52 aligns with screw hole one 41 with the screw fastening.

Example two

Referring to fig. 2, the parallel bearing further includes at least one intermediate bearing 6, the intermediate bearing 6 is a contact bearing, the intermediate bearing 6 is sleeved between the rotating shaft bearing 1 and the stator bearing 2, and a gap is left between the stator bearing 2 and the intermediate bearing 6.

The intermediate bearing 6 is a ball bearing.

Specifically, the parallel bearing includes a shaft bearing 1, a stator bearing 2, and an intermediate bearing 6.

In the present embodiment, on the basis of the first embodiment, one intermediate bearing 6 is sleeved on the rotating shaft bearing 1 (or a plurality of intermediate bearings 6 are sequentially sleeved outside and each intermediate bearing 6 is coaxial), and the stator bearing 2 is sleeved outside the outermost intermediate bearing 6 and keeps a certain gap with the outer wall of the outermost intermediate bearing 6.

EXAMPLE III

Further, the ball bearing, the roller bearing, the ceramic bearing or the tetrafluoroethylene bearing is a single layer, a double layer or a multilayer. The ball bearing or the roller bearing of the shaft bearing 1 according to the first and second embodiments of the present invention may be an integral multi-layer bearing, and the ball layer or the roller layer may be provided in multiple layers, as shown in fig. 3. The multilayer ball bearing or roller bearing comprises an inner ring, an intermediate ring and an outer ring which are nested with each other, wherein balls or rollers are respectively embedded between the inner ring and the intermediate ring and between the intermediate ring and the outer ring.

Example four

When the rotating shaft bearing 1 of the present invention is an angular contact ball bearing, since the inner ring of the bearing is fixed on the rotating shaft 100, relative displacement occurs between the outer ring, the retainer and the balls, which is commonly referred to as that the balls in the bearing are too loose, and appropriate treatment measures are required.

Referring to fig. 4, the rotating shaft bearing 1 is a pair of angular contact ball bearings which are arranged oppositely, and a preload spring is arranged between outer rings of the two angular contact ball bearings; and two ends of the preloading spring are respectively fixed at the end parts of the outer rings of the two angular contact ball bearings.

The preload force of the spring is adjusted to enable the balls and the retainer to be close to or far away from each other, namely the friction force in the bearing can be increased or reduced, so that the purpose of being suitable for the friction force under the required working condition is achieved.

Further, the surface of the shaft section of the rotating shaft 100 sleeved in the rotating shaft bearing is coated with a tetrafluoroethylene anti-wear coating.

Further, the stator bearing 2 is fixed on the stator 4 by one of key connection, pin connection and bolt connection.

Further, the rotating shaft bearing 1 is a ball bearing, a roller bearing, a ceramic bearing or a tetrafluoroethylene bearing.

Further, the stator bearing 2 is an air bearing, an oil film floating ring bearing or a tilt pad bearing.

Further, the ball bearing, the roller bearing, the ceramic bearing or the tetrafluoroethylene bearing is single-row, double-row or multi-row.

The starting process of the parallel bearing of the invention is as follows:

when the rotating shaft 100 is started, the rotating shaft bearing 1 of the outer sleeve of the rotating shaft 100 is contacted with the bottom of the stator bearing 2, the inner ring of the rotating shaft bearing 1 is driven to rotate along with the rotation of the rotating shaft 100, meanwhile, the stator bearing 2 and the outer ring of the rotating shaft bearing 1 are gradually separated under the action of an air film or an oil film, the rotating shaft bearing 1 eccentrically rotates in the stator bearing 2, and when the rotating shaft 100 stably runs at a high speed, the rotating shaft 100 and the rotating shaft bearing 1 are coaxial and eccentrically rotate around a circumference in the stator bearing 2. Meanwhile, the outer ring of the rotating shaft bearing 1 rotates.

Further, referring to fig. 1, the present invention employs a ball bearing as a shaft bearing 1 and an air bearing as a stator bearing 2. The following is a description of the working principle:

when the shaft diameter is constant, for the conventional ball bearing, when the rotating shaft 100 rotates, the rotation speed of the inner ring of the ball bearing is V2, and the rotation speed of the outer ring is V0, and since the outer ring is fixed on the stator 4 and V0 is approximately 0, the relative rotation speed n of the outer ring of the ball bearing is V2-V0.

After the parallel bearing is adopted, when the rotating shaft 100 rotates, the rotating speed of the inner ring of the ball bearing is set to be V2, the rotating speed of the outer ring is set to be V1, the rotating speed of the air bearing is set to be V0, the air bearing is fixed on the stator 4, the V0 is approximately 0, the speed difference a of the outer ring of the ball bearing relative to the inner ring is V2-V1, the speed difference b of the outer ring relative to the air bearing is V1-V0, and a and b are both smaller than n. Therefore, the relative rotating speed of the inner ring and the outer ring of the rolling bearing is reduced, namely under the same condition, the actual DN value is reduced, and the requirement can be met by selecting common lubricating grease.

By analogy, no matter how many ball bearings are sequentially sleeved on the rotating shaft bearing 1 in parallel, the actual DN value is not enabled to be overlarge, and the shaft diameter D and the bearing rotating speed N are decoupled. Therefore, the parallel bearing is suitable for working conditions of large shaft diameter and high rotating speed. The damping and the rigidity of the parallel bearing are not lower than those of a single bearing, and specifically, the damping of the parallel bearing is air bearing damping plus the damping of each bearing rubber ring; the parallel bearing stiffness is equal to the air bearing stiffness.

In a specific application, the parallel bearings of the present invention may be arranged on the rotating shaft 100 in pairs, referring to fig. 5, when the rotating shaft 100 rotates, the inner ring of the rotating shaft bearing 1 is driven to rotate, and the outer ring of the rotating shaft bearing 1 or the outer ring of the outermost intermediate bearing 6 rotates under the action of the air bearing or the oil film floating ring bearing. And the rotating speeds of a plurality of parallel bearings on the same rotating shaft can be adaptively adjusted according to stress, so that the effect of synchronous rotation is achieved.

Taking the case that the rotating shaft bearing 1 is a ball bearing and the stator bearing 2 is an air bearing, the parallel bearing of the invention has the working process that:

(1) starting a starting device of the rotating shaft 100 to enable the rotating shaft 100 to rotate to an initial preset speed; the inner ring of the ball bearing is driven by the rotating shaft 100 and rotates synchronously with the rotating shaft 100;

(2) after the rotating speed of the rotating shaft 100 is accelerated to the working rotating speed, the outer ring of the ball bearing starts to rotate under the action of the balls, the air between the outer ring of the ball bearing and the inner wall of the air bearing is whirled, when the outer ring of the ball bearing rotates to a certain speed, the air film is gradually stabilized, and the ball bearing is separated from the inner ring of the air bearing.

The working principle of the friction torque and time relationship diagram will be further explained below. See fig. 10, 11:

(1) in the time period from 0 to t1, namely the rotating shaft 100 is just started, the inner ring of the ball bearing rotates and the outer ring does not rotate, the linear velocity of the outer ring of the ball bearing is 0, and the friction torque of the outer ring of the ball bearing is increased due to the influence of the rotation of the balls; the air bearing is now unstressed so that the friction torque is 0 and the air bearing is in contact with the ball bearing outer race prior to time t 1.

(2) In the time period from t1 to t2, namely before the rotating shaft 100 gradually rotates to the stable operation, the friction torque of the outer ring of the ball is increased due to the influence of the rotation of the ball, and the outer ring of the ball gradually rotates but does not take off; the friction torque between the air bearing and the ball bearing is gradually increased until a critical point;

(3) at the time of t2, the friction torque between the air bearing and the ball bearing reaches a critical point, the friction torque borne by the air bearing and the ball bearing both reach a critical value, the outer ring of the ball bearing and the air bearing start to rotate relatively and are separated gradually, the air film between the outer ring of the ball bearing and the inner wall of the air bearing is gradually stabilized, and the friction torque of the ball bearing slowly increases along with the increase of the rotating speed after a small amount of reduction; meanwhile, the air bearing takes off, the friction torque of the air bearing is also instantaneously reduced, and then the friction torque is slowly increased along with the rising of the rotating speed.

The thrust bearing 800 of the present invention includes a foil 801, an elastomer 802, and a thrust bearing housing 803; the thrust bearing housing 803 covers the thrust disc 300 and is sleeved on the rotating shaft 200.

Foil 801 is fixed to both inner end surfaces (see fig. 1) or/and one inner end surface (see fig. 3) of thrust bearing housing 803 through elastic body 802, and elastic body 802 is bonded to foil 801 and thrust bearing housing 803.

The foil 801 is annular, the outer diameter of the foil 801 is larger than that of the thrust disc 300, a gap is reserved between the foil 801 and the end face of the thrust disc 210, a thrust bearing air inlet is formed in the thrust bearing shell 803, and during air inlet, air flows into the gap between the foil 801 and the thrust disc 210 to form an air film, so that displacement of the rotating shaft 100 is limited in the axial direction.

The combined bearing can be used for a rotor system.

The combined bearing can be used for a motor.

The application of the combination bearing of the present invention is not limited to the application described in the present invention, and those skilled in the art can easily conceive of applying the combination bearing to any high-speed rotation. The embodiments described in the present specification are only examples for understanding the present invention, and do not limit the application of the present invention.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims

1. A combined bearing is characterized by comprising a radial parallel bearing and a thrust bearing,

2. The combination bearing of claim 1, wherein the shaft bearing is disposed on the shaft and is tightly fitted to the shaft, and the shaft is driven by the driving device to rotate; the stator bearing is fixed on the stator; the rotating shaft is provided with a thrust disc which is integrally formed or fixed with the rotating shaft; the thrust bearing shell is covered outside the thrust disc and sleeved on the rotating shaft, and a gap is reserved between the foil and the thrust disc; the thrust bearing housing is fixed to the stator.

3. A combination bearing according to claim 2, wherein the drive means is an electric motor.

4. A parallel bearing according to claim 1 wherein the shaft bearing is a ball bearing and the stator bearing is an air bearing.

5. The parallel bearing of claim 4, wherein the air bearing is in the shape of an annular cylinder, the outer wall of the air bearing is provided with at least one annular groove parallel to the end face, the damper is nested in the annular groove and is an annular rubber ring, and the top of the rubber ring protrudes out of the outer wall of the air bearing.

6. A parallel bearing according to claim 5, wherein a plurality of protrusions are axially and uniformly arranged on the annular end face of the air bearing, an anti-rotation end cap is arranged at one end of the air bearing where the protrusions are arranged, anti-rotation holes are arranged on the anti-rotation end cap corresponding to the protrusions, the protrusions are embedded into the anti-rotation holes, and the anti-rotation end cap is fixed on the end face of the stator through screws.

7. A parallel bearing according to claim 6, wherein the rotation preventing end cap is provided with a cross-shaped hole comprising four rotation preventing holes vertically communicated with each other, the number of the protrusions is four, each protrusion is embedded into each rotation preventing hole, a screw hole is arranged between two adjacent rotation preventing holes, the end surface of the stator is provided with a first screw hole, and the first screw hole is aligned with the first screw hole and then fastened by a screw.

8. The combination bearing of claim 1, wherein the shaft bearing is a pair of angular contact ball bearings disposed opposite to each other, and a preload spring is disposed between outer races of the two angular contact ball bearings; and two ends of the preloading spring are respectively fixed at the end parts of the outer rings of the two angular contact ball bearings.

9. The combination bearing of claim 1, wherein the parallel bearing further comprises at least one intermediate bearing, the intermediate bearing is a contact bearing, the intermediate bearing is sleeved between the rotating shaft bearing and the stator bearing, and a gap is left between the stator bearing and the intermediate bearing.

10. A combination bearing according to claim 9, wherein the intermediate bearing is a ball bearing.

11. The combination bearing of claim 1, wherein the surface of the shaft section of the shaft sleeve disposed in the shaft bearing is coated with a tetrafluoroethylene wear-resistant coating.

12. A combination bearing according to claim 1, wherein the shaft bearing is a ball bearing, a roller bearing, a ceramic bearing or a tetrafluoroethylene bearing.

13. A combination bearing according to claim 12, wherein the ball, roller, ceramic or tetrafluoroethylene bearings are single, double or multiple row.

14. A combination bearing according to claim 12, wherein the ball bearing, roller bearing, ceramic bearing or tetrafluoroethylene bearing is single-layered, double-layered or multi-layered.

15. A combination bearing according to claim 1, wherein the stator bearing is an air bearing, an oil film floating ring bearing or a tilt-pad bearing.