JPS63289318A - Radial ball bearing for protection in magnetic bearing device - Google Patents

Abstract

PURPOSE:To reduce centrifugal force acting on balls and improve durability of a bearing in the case of touch down by making the diameter of the pitch circle of a radial ball bearing for protection smaller than its normal average diameter. CONSTITUTION:In case of high speed touch down, as thickness te of an outer ring 13 is large, expansion of the outer ring 13 itself generated by a centrifugal force at rotation is small, and as a change of clearance inside of the bearing is small, its rotation is smooth. Deformation of the outer ring 13 generated in the case of making contact with a rotor becomes smaller, because thickness te of the outer ring 13 is large, and its rotation becomes smoother, because unreasonable force does not act on balls 11. Rigidity of the outer ring 13 becomes higher, because number of balls is increased by making the diameter Da of each ball 11 smaller. As the diameter dp of a pitch circle is small, orbital speed of the ball 11 becomes smaller and centrifugal force acting on the ball 11 also becomes smaller at rotation. Therefore, durability of the bearing 10 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a protective radial ball bearing in a magnetic bearing device, such as a vacuum pump.

Prior art and its problems FIG. 2 shows an example of a conventional magnetic bearing device, in which a cylindrical rotor (2) is arranged around a vertical fixed shaft (1). The rotor (2) has radial magnetic bearings (3) (4) and axial magnetic bearings (5) provided on the fixed shaft (1).
) (6) in a non-contact state, for example 3000
Rotates at a high speed of about 0 rpm.

Protective radial ball bearings (7) (8) are installed at two locations above and below the fixed shaft (1) to receive the rotor (2) when it is stopped.
) is provided. A total pressure bearing is used for each protective bearing (7) (8) to increase the load capacity, and its inner ring (7a
) (8a) is fixed to the fixed shaft (1). When the rotor (2) is rotating normally, there is a gap of, for example, about 0.1 to several IIl [11] between the rotor (2) and the protective bearings (7) and (8). And the rotor (2
) is stopped, the rotor (2) is moved to the protective bearing (7).
) (8), the rotor (2) contacts and is received by the outer ring (7b) (sb) of the magnetic bearing (3) (4) (
5) It is designed to prevent damage to items such as (6) by contacting them. Note that this operation in which the rotor is stopped by being received by the protective bearing is called touchdown.

By the way, if the magnetic bearing device stops under normal conditions,
Since the rotor (2) is gradually decelerated and reaches a fairly low speed, it contacts the protective bearings (7) (8) and touches down at a low speed, so the protective bearings (7) and (8) will not be damaged. do not have. On the other hand, if the magnetic bearings (3) (4) (5) ([i) stop working due to a power outage or other failure, the rotor (2) rotating at high speed will 8) to touch down at high speed,
In particular, in the case of magnetic bearing devices for vacuum pumps, protective bearings (
7) (8) is in vacuum (e.g. 10-2 to 10-3T)
orr) with a rapid rise and high speed rotation (for example, d
mn>300×104). For this reason, in the conventional protective bearings (7) (8), balls (7c) (8c)
) and raceway surfaces are severely worn and have poor durability, and the protective bearing (7) (8) is damaged during one high-speed touchdown.
There were problems such as damage to the

In addition to the type of magnetic bearing device in which a cylindrical rotor rotates around a fixed shaft as described above, there is also a type in which a rotor shaft rotates inside a cylindrical fixed case. In this case, protective bearings are provided at two locations on the upper and lower sides of the case, and when the shaft stops, the shaft contacts and is received by the inner ring of the protective bearing, but there is a problem similar to that described above.

An object of the present invention is to provide a highly durable protective radial ball bearing that solves the above problems.

Means for Solving the Problems The protective radial ball bearing according to the present invention is a magnetic bearing device in which a rotating part is supported and rotated by a magnetic bearing in a non-contact state with respect to a fixed part, and when the rotating part is stopped, the rotating part is This is a protective radial ball bearing that is provided at multiple locations on a fixed part to receive the protection, and is characterized in that the pitch circle diameter is smaller than the average diameter.

Operation During high-speed touchdown, if the rotating part contacts the raceway of the protective radial ball bearing while still rotating at high speed, this raceway also starts rotating at high speed, but the pitch circle diameter of the protective radial ball bearing is equal to the average diameter. Because they are smaller, they are more durable and less susceptible to damage. That is, since the pitch circle diameter is small, the revolution speed of the ball is small. Therefore, the centrifugal force acting on the ball during touchdown is reduced, improving the durability of the bearing. Furthermore, since the pitch circle diameter is small, the outer ring has a large wall thickness. Particularly when the outer ring rotates in contact with the rotor during touchdown, if the outer ring is thick, the expansion of the outer ring itself due to centrifugal force during rotation is small, and the change in the bearing internal clearance (radial clearance) is small. Therefore, the rotation is smooth. Since the outer ring is thicker, the outer ring deforms less when it comes into contact with the rotor, and no unreasonable force is applied to the balls, resulting in smooth rotation.

Therefore, by making the pitch circle diameter smaller than the average diameter, the durability of the protective radial ball bearing is improved.

Embodiment FIG. 1 shows a specific example of a protective radial ball bearing for a magnetic bearing device.

This bearing (10) is a total pressure bearing, and the diameter Da of the balls (11) is smaller than that of a normal radial ball bearing, and the inner ring (1
The wall thickness ti of 2) is thin, and the wall thickness te of the outer ring (13) is thick. Therefore, the diameter (pitch circle diameter) dp of the circle passing through the center (0) of the ball (11) is the inner diameter (
It is considerably smaller than half (average diameter) dm of the sum of the bearing inner diameter) d and the outer diameter (bearing outer diameter) D of the outer ring (13). To give an example of these dimensions, the bearing inner diameter d is 90+nm.
, bearing outer diameter 115mm+, average diameter dm 102.5
mm, the wall thickness ti of the inner ring (12) is 3 mm-, the outer ring (1
3) Thickness te is 6mm 5 pitches Circle diameter dp is average diameter dm
Make the ball 2.5mm smaller to 100mm, and make the ball (11)
The diameter Da is set smaller than the normal 6.747m+n.

The radius of curvature (groove radius) ri of the raceway groove (14) of the inner ring (12) is larger than normal, for example, about 0.55D.
It is a.

When this bearing (10) is used in a magnetic bearing device of the type in which a cylindrical rotor rotates around a fixed shaft as shown in FIG. 2, the inner ring (12) is fixed to the fixed shaft.

When the rotor is rotating normally, the rotor is supported by the magnetic bearing in a non-contact state, and there is an appropriate clearance between the rotor and the outer ring (13) of the bearing (10).
) has stopped.

In the case of high-speed touchdown, the rotor rotating at high speed contacts the outer ring (13) of the bearing (10), and the outer ring (13) also starts rotating at high speed. For this reason, in conventional bearings, the outer ring starts rotating at high speed with a very sudden rise, and the maximum rotational speed of the outer ring is close to the rotational speed of the rotor. As a result, the bearing is damaged as described above.

However, in the case of the above-mentioned bearing (lO), as explained below, it has high durability and can prevent such damage.

That is, first of all, since the wall thickness te of the outer ring (13) is increased, the expansion of the outer ring (13) itself due to centrifugal force during rotation is small, and the change in the bearing internal clearance (radial clearance) is small, so the rotation is It's smooth. Then, the outer ring (1
By increasing the wall thickness te of 3), the deformation of the outer ring (13) when it comes into contact with the rotor is reduced, and the balls (
Since no unreasonable force is applied to 11), rotation becomes smooth.

Moreover, since the diameter Da of the balls (11) is reduced to increase the number of balls, the rigidity of the outer ring (13) is increased.

In addition, since the pitch circle diameter dp is small, the ball (1
The revolution speed of 1) becomes smaller, and the centrifugal force acting on the ball (11) during rotation also becomes smaller. Therefore, the durability of the bearing (10) is improved.

Furthermore, in the bearing (10) described above, since the groove radius r i (=0.55 Da) of the inner ring (12) is large, the following effects are achieved. First, when the rotor contacts the outer ring (13) of the bearing (10) during Sochi down in the evening,
The bearing (10) is tilted, but by increasing the groove radius ri, the allowable tilt angle becomes larger, and the bearing (10)
Excessive stress will no longer occur inside. In the case of the same inclination angle, the larger the groove radius ri, the smaller the difference in revolution speed of the ball (11) and the smoother the rotation. In addition, by increasing the groove radius ri, the contact surface pressure between the ball (11) and the raceway groove (14) increases, making it easier for the ball (11) to rotate normally from the beginning when starting up to high-speed rotation. . Note that the above effect can be achieved if the groove radius ri is approximately 0.53 to 0.58 Da.

The above bearing (10) can also be used in a magnetic bearing device in which the rotor shaft rotates inside a cylindrical fixed case. In this case, the outer ring (13) is fixed to the fixed case, and the rotor shaft contacts the inner surface of the inner ring (12). In this case as well, substantially the same effects as above are achieved.

Although a total pressure bearing is shown in the above embodiment, the present invention can also be applied to a ball bearing with a cage.

Effects of the Invention According to the protective radial ball bearing in the magnetic bearing device of the present invention, since the pitch circle diameter is smaller than the average diameter, it has high durability and can prevent damage during high-speed touchdown as described above. can.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of the main part of a protective radial ball bearing showing an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view showing a magnetic bearing device incorporating a conventional protective radial ball bearing. (10)... Radial ball bearing for protection, (11)...
Ball, (12)...inner ring, (13)...outer ring, dp.
...Pitch circle diameter, dm...average diameter. ” ni

Claims (1)

[Scope of Claims] In a magnetic bearing device that supports and rotates a rotating part in a non-contact state with a magnetic bearing with respect to a fixed part, protection is provided at multiple locations on the fixed part to receive the rotating part when the rotating part stops. A radial ball bearing for protection in a magnetic bearing device, characterized in that the pitch circle diameter is smaller than the average diameter.