Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-04-29
2004-12-14
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216006
Reexamination Certificate
active
06831385
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a structure of a magnetic bearing that supports a rotor without making contact, particularly a stator core for a homo-polar type of magnetic bearing, and a method of manufacturing it.
2. Prior Art
A turbo compressor can be made larger in capacity and smaller in size than a reciprocating or screw compressor, and can be easily made to an oil-free type. Therefore, turbo compressors are used often as general-purpose compressors in applications such as a compressed air source for factories, a source of air for separation, and other various processes.
Conventionally, gas bearings, sliding bearings and magnetic bearings have been used to support a high-speed rotating shaft of a high-speed motor that is connected directly to and drives a turbo compressor. In particular, a homo-polar magnetic bearing can be used to support a rotor (rotating shaft) in a contact free manner that rotates to form the high speed shaft of a high speed motor by passing magnetic flux through the shaft to produce an electromagnetic sucking force which causes the shaft to float, this being one type of radial magnetic bearing for use with shafts that rotate at a high speed (for instance, 100,000 min
−1
or more).
FIGS. 1A and 1B
show typical schematic viewes of a conventional homo-polar magnetic bearing. In these figures, a homo-polar magnetic bearing
1
is composed of a rotor
3
that is arranged at the axial center of a casing
2
and parallel to it in the axial direction and can rotate at a high speed, U-shaped stator cores
4
installed inside the casing
2
with gaps between the outer surface of the rotor
3
, and coils
5
that are placed around the toothed ends of the stator cores
4
.
In addition, a plurality of stator cores (4 cores in
FIGS. 1A and 1B
) are disposed equally spaced in the circumferential direction with gaps between the outer surface of the rotor
3
. Although not illustrated, stator cores
4
are arranged in the axial direction of the rotor
3
in at least 2 locations with a predetermined distance between them. Consequently, the rotor can rotate stably at a high speed. A stator core
4
is made of laminated steel sheets each of which is manufactured with an insulating adhesive material applied to its surface to bond to an adjacent thin steel sheet, and these are bonded one after another to obtain a predetermined length. As shown in
FIGS. 1A and 1B
, the direction A in which the laminated steel sheets
4
(lamination) are bonded is arranged to be perpendicular to the axial direction Z of the rotor
3
.
As described above, in the homo-polar magnetic bearing
1
, since the toothed ends of the stator cores
4
that surround the rotor
3
are close to each other in the axial direction and as the coils
5
produce the N and S poles of an electro magnet, the homo-polar magnetic bearing
1
can float the shaft in a contact free manner and support the rotor
3
by the sucking force of the toothed ends located opposite each other. Therefore, the direction of this homo-polar magnetic field is parallel to the centerline of the rotor and on the outer surface of the rotor
3
as shown by the dashed arrow lines in FIG.
1
B.
FIG. 1C
is a schematic view that shows a conventional process for assembling laminated steel sheets to form a conventional stator core. Normally, the stator core
4
of the homo-polar magnetic bearing
1
is manufactured by making thin rectangular steel sheets
4
a
coated with an insulating material, by a method such as punching, and assembling these punched steel sheets
4
a
one after another, to produce a laminated stator core
4
.
However, when the inner surfaces of the aforementioned stator cores
4
(laminated steel sheets) are cut by a rotary cutting process, a large cutting load is applied to the edges of the laminated steel sheets
4
a
in a lateral direction, so the tips of the laminated steel sheets
4
a
are bent, and the insulating material is crushed in the direction of rotation by the above-mentioned bending load, which is a practical problem. Consequently, the steel sheets contact each other resulting in an increase in the eddy currents in the stator unit, so another problem occurs due to the reduced levitation force applied to the rotor
3
, poor rotating characteristics, etc. Still another problem is that the laminated material is peeled away by the edge of the cutting tool. Even if the above-mentioned process of cutting in a lathe is replaced by using a vertical boring machine etc. to cut the inner surfaces of laminated steel sheets, because there are gaps between adjacent steel sheets, there is the additional problems that smooth cutting and true roundness cannot be easily ensured.
On the other hand, the inventors of the present invention have proposed the homo-polar magnetic bearing apparatus configured as shown in
FIGS. 2 and 3
, with the aim of improving the characteristics of conventional homo-polar magnetic bearings (unpublished Japanese patent application No. 88402/2000). According to this magnetic bearing apparatus, adjacent N poles or S poles are connected together in the circumferential direction, or are located close to each other with a small gap between them. The homo-polar magnetic bearing with this configuration has the advantage that it is capable of greatly reducing the production of eddy currents and the heat and eddy current losses generated in the rotor.
However, if the stator cores
4
of the homo-polar magnetic bearing shown in
FIGS. 2 and 3
are produced using laminated steel sheets with small eddy current losses, as shown in
FIG. 1
, the laminated steel sheets become so thin in the peripheral web
4
b
that they fail, crush or peel when processed, which is a practical disadvantage.
More explicitly, in the homo-polar magnetic bearing with the structure shown in
FIGS. 2 and 3
, the stator cores
4
are connected together circumferentially or located close to each other, so the distribution of magnetic flux in the rotor is more uniform and losses can be reduced. Conversely, however, if stator cores
4
in which the tips are connected together are formed with a conventional laminated structure, the laminated steel sheets are so small in the portions where adjacent magnetic poles are connected together that the laminated structure may collapse when the cores are machined, therefore, it is very difficult to machine the cores without detaching, crushing or peeling the laminations.
Another problem in a conventional apparatus is that amorphous materials cannot be used because they are difficult to laminate, despite the advantages of having a high electrical resistance and permeability, so the choice of electromagnetic sheet steel is restricted.
Next, the structure of a conventional homo-polar radial magnetic bearing is described in more detail than before by referring to
FIGS. 4 and 5
.
FIG. 4
a
is a front view of a conventional homo-polar radial magnetic bearing, and
FIG. 4
b
is the corresponding side sectional elevation.
FIG. 5
is an isometric view of the stator core of a conventional homo-polar radial magnetic bearing.
The homo-polar radial magnetic bearing
1
is provided with a casing
2
, a plurality of electromagnetic components
13
and a rotating shaft
3
. The rotating shaft
3
is made of a material which is magnetic at least on the surface thereof, with an outer diameter of D1 and a length determined by the rotor. The rotor
3
is disposed coaxially with the centerline of the casing
2
, parallel thereto in the longitudinal direction, and is supported so that it can rotate freely. The plurality of electromagnetic components
13
support the rotor
3
so that it can rotate freely, and are arranged around the rotor
3
. For instance, four electromagnetic components are connected together to form a set, and sets of electromagnetic components
13
support the rotor
3
at 2 locations. At each supporting location,
4
electromagnetic components are equally spaced around the rotor.
The electromagnetic components
13
are pro
Hasegawa Kazumitsu
Kuwata Gen
Ozaki Shin-ichi
Sugitani Noriyasu
Takahashi Toshio
Aguirrechea J.
Griffin & Szipl, P.C.
Ishikawajima-Harima Heavy Industries Co. Ltd.
Nguyen Tran
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