JPH05209620A - Touch-down bearing for magnetic bearing device - Google Patents

Abstract

PURPOSE:To prevent balls and spacers from being strongly press-contacted with each other in the case of advance or delay of the balls at the time of touch-down by holding clearances between the balls in a non-restricted state by means of the spacers loosely inserted between the balls. CONSTITUTION:A touch-down bearing 20 constituted of a pair of an upper and a lower angular ball bearing 22, 24 is disposed around a lower portion 11a of a rotary shaft 11 in a magnetic bearing device 9. Outer races 30, 32 of the ball bearings 22, 24 are press-fitted to the inner circumferential surface of a fitting hole 34 formed on a housing 8. The outer race 32 on a lower stage is supported at the lower surface thereof by a retaining ring 36 fixed to the housing 8. In the bearing 29, the same number of disk-like spacers 42 as that of the balls 38 are loosely inserted between balls 38, 38 of the ball bearings 22, 24. Both side surfaces of the spacer 42 are formed into recessed surfaces 44 each having a curvature radius (r) slightly larger than a radius of the ball 38. Consequently, the ball 38 abuts against the recessed surface 14 in the case of advance or delay.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a touchdown bearing which supports a rotary shaft when a magnetic bearing device such as a turbo molecular pump cannot be controlled.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional magnetic bearing device 9 such as a turbo molecular pump has touch-down bearings 12 at the upper and lower ends of a rotary shaft 11 which is vertically supported in a non-contact manner by a magnetic bearing 10. 13 is arranged, and when the magnetic bearing 10 becomes uncontrollable due to sudden disconnection or power failure, a pair of upper and lower touchdown bearings 12 and 13 support the rotating shaft 11,
It is configured to prevent damage to the magnetic bearing 10 and the rotating shaft 11. In particular, the lower touchdown bearing 12 is shown in FIG.
As shown in (a), two angular contact ball bearings 14, 15
As a frontal combination of, both radial load and axial load are received. Each of the angular ball bearings 14 and 15 is configured by incorporating a plurality of balls 3 held by a ring-shaped cage 4 between the inner ring 1 and the outer ring 2. Each ball 3 has a plurality of circular pocket holes 6 formed in the cage 4 at equal intervals in the circumferential direction as shown in FIG.
It is housed inside, and a pocket gap t is provided between the ball 3 and the inner peripheral surface of the pocket hole 6. Further, a clearance 16 is provided on the combined surface of each inner ring 1 by grinding so that an excessive preload is not applied to the bearing 12 due to thermal expansion of the inner ring 1 in the axial direction.

In the touchdown bearing 12 having the above structure, the inner ring 1 faces the rotary shaft 11, and the inner diameter surface and the upper end surface thereof become the touchdown surfaces 17 and 18. On the contrary, in FIG. 4, when the housing 8 side is rotated and the housing 8 is supported by the magnetic bearing 10 provided on the central rotating shaft 11, the outer ring 2 of the touchdown bearings 12 and 13 is a rotating member. It will face 8 and touch down on its outer diameter surface. Thus, the position of the touchdown surface changes depending on the bearing support structure.

[0004]

When the rotary shaft 11 comes into contact with the touchdown surfaces 17 and 18 of the inner ring, the inner ring 1 starts to rotate rapidly, and the ball 3 also rapidly starts to rotate and revolve. To do. At this time, there is a delay in the revolution between the ball 3 located in the non-load range and the ball 3 located in the load range.
There is advance, and due to this delay / advance, a large tensile force or compressive force acts on the cage 4. That is, the ball 3 and the cage 4 relatively move in the circumferential direction by the pocket clearance t, but in the conventional cage 4, the pocket hole 6 is circular and the circumferential clearance is set to be relatively small.
This is because the delay or advance of the revolution directly influences the degree of contact between the ball 3 and the pocket hole 6. The tensile / compressive force causes fatigue in the cage 4 and uneven wear on the surfaces of the pocket holes 6 and the balls 3. Therefore, the conventional touchdown bearings 12 and 13 are often unusable after several touchdowns. To replace the unusable touchdown bearings 12 and 13, after disassembling the magnetic bearing device 9 and replacing the bearing, the magnetic bearing device is adjusted while adjusting the clearance between the inner ring and the rotary shaft with high accuracy. Must be reassembled. In order to eliminate the time-consuming disassembling and assembling work, there has been a long-felt demand for a touchdown bearing which has high durability and requires less replacement.

Therefore, it is an object of the present invention to provide a touchdown bearing of a magnetic bearing device having a high durability that can endure many touchdowns.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention eliminates a retainer for holding balls, and instead, a disc-shaped spacer made of lead bronze is loosely fitted between the balls. Have been inserted into. The diameter of the spacer is smaller than the diameter of the ball, and both side surfaces of the spacer are concave surfaces having a radius larger than the radius of the ball, and solid lubrication is applied to at least one of frictional parts that cause rolling friction or sliding friction. It is formed by forming a film.

[0007]

When the rotating member comes into contact with the touchdown surface of the inner ring or the outer ring during the touchdown, the inner ring or the outer ring starts to rotate rapidly, and each ball rapidly starts to rotate and revolve with delay and advance. At this time, since the balls are not restrained by the retainer as in the conventional case, the balls are moved toward and away from each other. When the two balls come close to each other, the two balls come into contact with the concave surfaces on both sides of the spacer, and the minimum ball distance is maintained. At this time, the solid lubricating coating formed on at least one of the frictional or sliding frictional parts is scraped off by a small amount due to contact with the ball, and this becomes a minute lubricating powder that forms the surface of the ball and the inner and outer rings. Is transferred to the transfer surface to form a film having lubricity. When the spacer is not held between the balls, the peripheral surface of the spacer comes into contact with the transfer surface and rubs against the transfer surface, and the solid lubricating coating is directly transferred to the transfer surface. This coating is not lost as long as the supply of lubricating powder continues, and the spacer is made of lead bronze, so the balls,
Good lubrication of the transfer surface and the spacer is maintained over a long period of time.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A touchdown bearing 20 according to the present invention is shown in FIG.
As shown in FIG. 4, the magnetic bearing device 9 is arranged on the outer periphery of the lower end portion 11a of the rotating shaft 11 of the magnetic bearing device 9 of FIG. The bearing 20 is composed of a pair of upper and lower angular contact ball bearings 22 and 24, and is configured to receive both radial load and axial load.

A step portion 24 is formed at the lower end 11a of the rotary shaft 11, and the step portion 24 is an upper angular contact ball bearing 22.
Touches down to the upper end surface 26a of the inner ring 26, and the peripheral surface of the lower end 11a has upper and lower angular contact ball bearings 22, 24.
The inner races 26, 28 are configured so as to touch down on the inner peripheral surfaces thereof. Solid lubricating coatings 29 (shown by thick solid lines in FIG. 1) made of molybdenum disulfide or lead are formed on both upper and lower end surfaces and inner peripheral surfaces of the inner rings 26, 28.
When the magnetic bearing device 9 operates, the rotary shaft 11 is slightly lifted to form a gap C between the step portion 24 and the upper end surface 26a.

Outer rings 30 of the angular ball bearings 22 and 24,
32 is press-fitted to the inner peripheral surface of the fitting hole 34 of the housing 8, and the lower surface of the lower outer ring 32 is supported by a holding ring 36 fixed to the housing 8.

A ball 38 is rollably disposed between the inner and outer rings 28, 30. These balls 38 are the inner ring 2
It is sandwiched between transfer surfaces 40 formed on outer peripheral surfaces 6, 28 and outer peripheral surfaces 30, 32 while a predetermined preload is applied. As shown in FIGS. 1 and 2, disc-shaped spacers 42 are inserted between the balls 38 in the same number as the balls 38 in a loosely fitted state. The spacer 42 is made of lead bronze, and its diameter d is slightly smaller than the diameter D of the ball 38. Further, both side surfaces of the spacer 42 are concave surfaces 44, and when the ball 38 is advanced or delayed, the concave surfaces 44 are formed.
It comes into contact with. If the radius of curvature r of the concave surface 44 is slightly smaller than the radius of curvature R of the ball 38, the ball 38 is in line contact with the peripheral edge of the concave surface 44, which is not preferable. Therefore, the radius of curvature r is slightly larger than R in consideration of the processing error of the concave surface 44.

Next, the operation of the touchdown bearing 20 configured as described above will be described.

The function of the magnetic bearing device is stopped due to disconnection of the power supply system, power failure, etc.
If you touch down on the inner rings 26, 28 of the
8 starts to rotate rapidly. At the same time, the balls 38 suddenly start rotating and revolving. At this time, the balls 38 are not evenly loaded, but some are actually located in the loaded area and some are located in the non-loaded area, which causes the balls 38 to be delayed or advanced. As a result, when the balls 38 come close to each other, the balls 38 are separated from each other by the spacer 42.
The minimum ball spacing is maintained by contacting the concave surfaces 44 on both sides of the. At this time, the coating layer of molybdenum disulfide or lead on the surface of the spacer 42 is scraped off by a minute amount due to contact with the ball, and this becomes a minute lubricating powder and is transferred to the surface of the ball 38 and the transfer surface 40 of the inner and outer rings. To form a coating having lubricity. When the spacer 42 is not sandwiched between the balls 38, the spacer 42 falls onto the transfer surface 40 of the inner and outer rings as shown in FIG. 2 and comes into friction with the contact surface to directly form a lubricating coating on the raceway surface. This coating is not lost as long as the supply of the lubricating powder is continued, and good lubrication between the ball 38, the transfer surface 40 and the spacer 42 is maintained for a long time or over many touchdowns. Further, since the solid lubricating coating 29 of molybdenum disulfide or lead is previously formed on the upper and lower end surfaces and the inner peripheral surfaces of the inner rings 26, 28, the step portion 24 and the lower end portion 11a of the rotating shaft 11 and the inner rings 26, 28 are formed. Good lubrication is also performed between and, and it is possible to prevent such uneven wear.

[0014]

As described above, according to the present invention, the distance between the balls is held in an unconstrained state by the spacers loosely inserted between the balls instead of the conventional cage, so that the touchdown is performed. Even if the ball is delayed or advanced sometimes, the ball and the spacer are not strongly pressed against each other. In addition, since the spacer is coated with molybdenum disulfide or lead to form a solid lubricating film, the lubricity between the ball and the spacer is not only good, but also the coating scattered on contact with the ball or transfer surface. Since a minute powder of the material is transferred as a lubricating powder to the transfer surfaces of the inner and outer rings and the ball surface to form a lubricating film,
Good lubrication between the balls, spacers and transfer surfaces is achieved. Moreover, since the spacer constantly supplies the lubricating powder by contact with the balls or the transfer surface, it is possible to realize a highly durable touchdown bearing that can endure many touchdowns.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a touchdown bearing according to an embodiment of the present invention.

FIG. 2 is a horizontal sectional plan view of the touchdown bearing.

FIG. 3 is a side view of a ball and a spacer.

FIG. 4 is a sectional view of a conventional magnetic bearing device.

FIG. 5A is a vertical sectional view of a conventional touchdown bearing,
(B) is a development view of a conventional cage.

[Explanation of symbols]

20 Touchdown bearing 22,24 Angular contact ball bearing 26,28 Inner ring 29,46 Solid lubricant film of molybdenum disulfide or lead 30,32 Outer ring 38 Ball 40 Transfer surface 42 Spacer 44 Concave surface

Claims (2)

[Claims] 1. A touchdown bearing for supporting a rotating member, which is supported in a non-contact state by a magnetic bearing arranged on a fixed side, in a touchdown state, the rolling member being provided between an inner ring, an outer ring and the inner and outer rings. It is composed of a plurality of movably arranged balls and a plurality of disc-shaped spacers made of lead bronze inserted loosely between the balls, the diameter of the spacers being larger than the diameter of the balls. The touch-down bearing is small and both side surfaces of the spacer are concave surfaces having a radius larger than the radius of the ball, and a solid lubricating film is formed on at least one of frictional portions that cause rolling friction or sliding friction. .. 2. The touchdown bearing according to claim 1, wherein a solid lubricating film is formed on the surface of the spacer.