JPS5833936B2 - magnetic bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-contact magnetic bearing, and is particularly suitable as a magnetic bearing for a high-speed rotating body device.

FIG. 1 shows the structure of a conventionally known magnetic bearing device.

1 is a high-speed rotating body.

Reference numeral 2 denotes a rotating side magnet of the magnetic bearing, which is attached to the shaft 4 by a ring 3.

The stationary magnet 5 is arranged concentrically outside the rotating magnet 3 in the radial direction so as to be magnetized with the same polarity in the axial direction at the same height as the rotating magnet 3, and is fixed to the mounting plate 6. .

The magnetic bearing with this configuration has a radial centripetal force (radial spring constant) in the radial direction due to the repulsive force of the ring-shaped magnets 2 and 5, and its characteristics are as shown by the broken line in FIG. When the heights of the side magnet 5 and the rotating side magnet match (the axial displacement is zero), the repulsive force between the magnets is at its maximum, and the value of the radial spring constant is also at its maximum.

However, when the rotating magnet is displaced up and down in the axial direction, the value of its radial spring constant rapidly decreases.

Generally, in the case of a high-speed rotating body, the rotating body contracts in the axial direction as the rotational speed increases due to centrifugal force, so the rotating side magnet attached to the rotating body via the upper shaft also moves in the axial direction.

Therefore, as described above, the value of the radial spring constant of the magnetic bearing becomes small.

For this reason, with the one shown in FIG. 1, it is difficult to suppress the whirling vibration that occurs when the rotating body becomes critical.

In addition, the radial spring constant becomes small near the rated rotation speed, making the magnetic bearing disadvantageous for earthquake resistance.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a magnetic bearing that can increase the radial spring constant with a simple structure, and in which the radial spring constant does not change due to axial movement of one of the magnets. .

A feature of the present invention is that the axial length of one of a pair of magnets arranged concentrically and facing each other in the radial direction is longer than the axial length of the other magnet, and the longer magnet The magnetic plate is disposed on at least one magnetic pole surface in the axial direction of the magnetic plate.

As a magnetic bearing whose radial spring constant changes little due to the movement of the magnet in the axial direction, the one shown in FIG. 2 can be considered.

In FIG. 2, parts that are the same as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

The difference between FIG. 2 and FIG. 1 is that the axial height h2 of the stationary magnet 5 is longer than the axial height hl of the rotating magnet 3.

In general, a magnetized magnet can be replaced with an equivalent current as shown in the principle explanatory diagram of FIG.

Therefore, the radial force of the magnetic bearing can be determined from the Biot-Savart formula as the electromagnetic force acting between the circular currents 7.8 and 9,10.

In the magnetic bearings shown in Figures 1 and 2, a spring constant of (to) works at 7 and 9 and 8 and 10, and (to) at 7 and 10 and 8 and 9.
The spring constant of g) is obtained, but the characteristics of the magnetic bearing are determined between 8 and 9, which are the closest in radial direction.

According to this principle, in the conventional Figure 1, when the rotating side magnet is displaced in the axial direction, the decrease in the radial force values of 7 and 9.8 and 10 and 7 and 10 is small, but 8, which determines the spring force.
The radial force between and 9 is greatly reduced.

For this reason, in the one shown in FIG. 1, the radial spring constant decreases rapidly with respect to axial displacement.

On the other hand, in the case of FIG. 2, the height of the stationary side magnet in the axial direction is longer than that of the rotating side magnet, so even if the rotating side magnet is displaced in the axial direction, the effect of the displacement on the radial force is small.

Therefore, the radial force between currents 8 and 9 and other currents remains almost the same as before the displacement with respect to axial displacement, so as shown by the solid line in Figure 4, the radial spring constant is Even if there is a considerable displacement in the direction, the value will hardly change.

The present invention adds the function of increasing the radial spring constant to the function obtained by the magnetic bearing shown in FIG. 2.

A preferred embodiment of the present invention will be described below with reference to FIG. 5.

In the magnetic bearing of this embodiment, a stationary magnet 5 is attached to a mounting plate 4 as shown in FIG. 1, and a rotating magnet 2 is fixed to a rotating shaft 2 as shown in FIG.

The length of the fixed side magnet 5 in the axial direction is longer than the length of the rotating side magnet 2 in the axial direction as in FIG. 2.

A magnetic plate 11 is attached to the magnetic pole surface in the axial direction of the long fixed side magnet 5, for example, to the N pole surface at the upper end.

By providing the magnetic plate 11, the magnetic plate 11 acts like a mirror, and the two rotating side magnets and the fixed side magnet 5A, which are virtual images of the rotating side magnet 2 and the fixed side magnet 5,
This occurs at a position symmetrical to the rotating magnet 2 and the stationary magnet 5.

Therefore, the rotating side magnet 2 and the stationary side magnet 5 are aligned in the axial direction.
It produces the same function as the state in which it is arranged in pairs.

This leads to increasing the radial spring constant of the magnetic bearing with a simple structure.

The radial spring constant of this embodiment is approximately equal to the sum of the radial spring constant between the rotating side magnet 2 and the stationary side magnet 5 and the radial spring constant between the coaxial side magnet 2 and the rotating side magnet 2A.

These radial spring constants are positive (stable).

Actually, it is necessary to consider the radial spring constant between the rotating magnet 2 and the fixed magnet 5A and the radial spring constant between the rotating magnet 2A and the fixed magnet 5.

These radial spring constants are negative (
(unstable), which reduces the sum of the two radial spring constants mentioned above.

However, the feed value of the value plus the negative radial spring constant is
This value is extremely small compared to the absolute value O of the radial spring constant between the rotating side magnet 2 and the rotating side magnet 2A, and may be ignored.

Also, in this example, similar to the magnetic bearing shown in FIG.
Even if the rotating magnet 2 moves in the axial direction, the radial spring constant hardly changes.

According to this embodiment, the radial spring constant becomes large, and the value of the radial spring constant hardly changes with respect to the axial displacement, so it is possible to suppress the run-out vibration that occurs when the rotating body passes through the critical rotation speed. can be operated stably up to high speeds.

Earthquake resistance will also be improved. FIG. 6 shows a magnetic bearing according to another embodiment of the present invention.

In this embodiment, the length of the rotating side magnet 2 in the axial direction is made longer than that of the fixed side magnet 5, and the magnetic plate 11 is attached to the rotating side magnet 2.
It is placed on the lower magnetic pole surface.

In this embodiment as well, the same effects as in the above-mentioned embodiment can be obtained.

The magnetic plate may be attached to one pole face of the magnet Q) or to both of them.

According to the present invention, a large radial spring constant can be obtained with a simple structure, and the radial spring constant hardly changes even if the magnet is displaced l in the axial direction.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a conventional magnetic bearing, Figure 2 is a vertical cross-sectional view of a magnetic bearing that is an improved version of the magnetic bearing shown in Figure 1, and Figure 3 is a vertical cross-sectional view of a magnetic bearing that is an improved version of the magnetic bearing shown in Figure 1.
The figure is an explanatory diagram showing the principle of the magnetic bearing shown in Figure 2, and Figure 4 shows the radial spring constant against axial displacement in Figures 1 and 2.
FIG. 5 is a longitudinal cross-sectional view of a magnetic bearing according to a preferred embodiment of the present invention, and FIG. 6 is a longitudinal cross-sectional view of another embodiment of the present invention. 2...Rotating side magnet, 2'...Virtual image of rotating side magnet, 3...Protection ring, 4...
Shaft, 5, 5'...Fixed side magnet, 5'/-...
...Virtual image of fixed side magnet, 6...Mounting plate, 7.8
, 9.10... Circular current, 11... Magnetic plate N, S... Polarity, hl... Axial height of rotating side magnet, h2・・・・・・Axial height of fixed side magnet.

Claims (1)

[Claims] 1. In a magnetic bearing in which a pair of ring-shaped magnets having different diameters are arranged concentrically (opposing each other in the radial direction), the length in the axial direction of one of the magnets arranged oppositely is: longer than the length in the axial direction of the other magnet;
A magnetic bearing in which a magnetic plate is arranged on at least one magnetic pole surface in the axial direction of the long magnet.