Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-04-01
2004-08-24
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S268000
Reexamination Certificate
active
06781269
ABSTRACT:
TECHNICAL FIELD
The present invention relates to axial magnetic bearing apparatus as follows. That is, in the axial magnetic bearing apparatus, a rotary disc made of a magnetic material is fixedly attached to a rotating shaft of rotating apparatus such as an electric generator, an electric motor, or the like. Electromagnetic stators each having an electromagnetic coil for generating magnetomotive force are fixed to casings respectively so as to be located with very small distances from the rotary disc. A displacement sensor for measuring axial displacement of the rotating shaft is provided. Magnetic attraction force is made to act between the rotary disc and the electromagnetic stators in accordance with an output signal from the displacement sensor, so as to bear the rotating shaft at a target position distant from the electromagnetic stators and in non-contact therewith.
BACKGROUND ART
FIG. 8
shows a background-art general example of so-called axial magnetic bearing apparatus for bearing a rotating shaft of rotating apparatus such as an electric generator, an electric motor, or the like, in a thrust direction by use of magnetism. In the drawing, the reference numeral
1
represents a rotating shaft, to which a rotary disc
2
made of a magnetic material is fixedly attached. The rotary disc
2
usually has sleeves
6
formed on opposite sides of the rotary disc
2
so as to make the fixation of the rotary disc
2
to the rotating shaft
1
firm. The reference numeral
10
represents each of ring-like electromagnetic coils formed by winding coated copper wire around the rotating shaft
1
with a required and adequate number of turns. Each of the electromagnetic coils
10
is incorporated in an electromagnetic stator
7
having an inside magnetic pole tooth
11
and an outside magnetic pole tooth
12
. The reference numeral
8
represents each of ring-like housings which forms a magnetic circuit portion for corresponding one of the electromagnetic stators
7
. The electromagnetic coils
10
are received in coil slots
9
formed symmetrically with respect to the rotation axis of the ring-like housings
8
. The electromagnetic stators
7
are paired and disposed in opposition to each other with respect to a collar
22
so as to have suitable very small distances from the rotary disc
2
respectively on opposite sides of the rotary disc
2
. Thus, the electromagnetic stators
7
are attached to the casings
23
.
This axial magnetic bearing apparatus is controlled as follows. That is, axial displacement of the rotating shaft
1
is measured by a not-shown displacement sensor. On the basis of an output signal from this displacement sensor, electric currents to the electromagnetic coils
10
are adjusted to suitably vary magnetic attraction force acting between the rotating disc
2
and the inside magnetic pole teeth
11
of the electromagnetic stators
7
and between the rotating disc
2
and the outside magnetic pole teeth
12
of the electromagnetic stators
7
. Thus, the rotating shaft
1
is borne at a target position distant from the electromagnetic stators
7
and in non-contact therewith.
However, in the structure of the above-mentioned axial magnetic bearing apparatus generally used in the background art, for example, magnetic circuits as shown in
FIG. 9
are formed among the two electromagnetic stators
7
a
and
7
b
and the rotary disc
2
by selecting the polarities of the electric currents flowing into the electromagnetic coils
10
. At this time, there are two magnetic circuits
13
formed between the respective electromagnetic stators
7
and the rotary disc
2
, and a magnetic circuit
14
formed between the two electromagnetic stators
7
a
and
7
b
opposed to each other with respect to the rotary disc
2
. Here, the magnetic circuits
13
are magnetic circuits which contribute to magnetic attraction force required for the position control of the axial magnetic bearing, but the magnetic circuit
14
is a magnetic circuit which does not contribute to the magnetic attraction force at all.
As a result, the magnetic attraction force generated by each of the electromagnetic stators
7
decreases so that the support stiffness of the axial magnetic bearing apparatus decreases.
Incidentally, the reason why the support stiffness decreases due to the generation of the magnetic circuit
14
is, for example, disclosed in Japanese Patent Laid-Open No. 122896/1993. Therefore, the description of the reason is omitted here.
Thus, an invention for improving this defect is, for example, disclosed in Japanese Patent Laid-Open No. 122896/1993.
FIG. 11
shows this background-art improved axial magnetic bearing apparatus. In the drawing, one rotary disc piece
3
made of a magnetic material has an L-shaped sectional structure with a sleeve
6
. A pair of such rotary disc pieces
3
are opposed to each other on their contra-sleeve sides, and a disc
5
of non-magnetic material is sandwiched like a layer between the rotary disc pieces
3
. Thus, one rotary disc
2
is formed. Electromagnetic stators
7
are disposed respectively with suitable very small distances from the rotary disc
2
on opposite sides of this rotary disc
2
so as to be opposed to each other with respect to a collar
22
. Thus, the electromagnetic stators
7
are attached to casings
23
.
Accordingly, a magnetic circuit
14
which is formed through the two electromagnetic stators
7
opposed to each other with respect to the rotary disc
2
and which does not contribute to magnetic attraction force is eliminated. On the other hand, independent magnetic circuits
13
are formed between the respective electromagnetic stators
7
and the rotary disc
2
. Thus, the performance of position control of the axial magnetic bearing apparatus is improved.
Now, generally, axial magnetic bearing apparatus is often used as a support mechanism for a high-speed rotating body. It is difficult to realize such a support mechanism by a mechanical contact type bearing. In the high-speed rotating body, the natural frequency of the first-order bending mode of a rotor is important when the dimensions and shape of the rotor are designed. It is requested to design the rotor to have a natural frequency as high as possible. To this end, the strength and mass of the rotary disc
2
and the fixation stiffness between the rotating shaft
1
and the rotary disc
2
often become critical in the axial magnetic bearing apparatus which generally has a maximum outer diameter in the rotor shape. It is therefore necessary to pay close attention to the design of the rotor shape, particularly the design of the shape of the rotary disc
2
of the axial magnetic bearing apparatus.
Generally, when a rotor makes a rotary motion, centrifugal force F [N] as shown in the following expression acts on the rotating body, and the magnitude thereof is in proportion to the mass and the outer diameter of the rotating body.
F=mr&ohgr;
2
Provided that m designates the mass [Kg] of the rotating body, r designates the outer radius [m] of the rotating body, and &ohgr; designates the rotation angular velocity [rad/sec].
The rotary disc
2
of the above-mentioned improved axial magnetic bearing apparatus (
FIG. 11
) in the background art has two rotary disc pieces
3
. Each of the rotary disc pieces
3
has an L-shaped sectional structure with a sleeve
6
. The two rotary disc pieces
3
are opposed to each other on their contra-sleeve sides, and a non-magnetic disc
5
is sandwiched between the rotary disc pieces
3
so as to form one rotary disc. Thus, the two rotary disc pieces
3
and the non-magnetic disc
5
are independent of one another, and not locked to one another. As shown in
FIG. 12
, at the time of high speed rotation, centrifugal force
24
acts on the rotary disc
2
and the non-magnetic disc
5
. Thus, the rotary disc
2
has a maximum outer diameter at rotation-axis-direction positions of angular portions
4
of the rotary disc pieces
3
. As a result, larger centrifugal force acts on the rotary disc
2
Lam Thanh
Mitsubishi Denki & Kabushiki Kaisha
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