Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-03-26
2004-12-14
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06831384
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on and hereby claims priority to German Application No. 100 47 583.3 filed on Sep. 26, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magnetic bearing.
2. Description of the Related Art
Magnetic bearings allow moving parts to be mounted free from any contact or wear. They therefore do not require any lubricants and can be of a low-friction design. What are known as active magnetic bearings, with electromagnets, require an active position control, which controls the currents of the supporting magnets and counteracts deviations of the rotor body from its intended position by position sensors and a control loop. What are known as passive magnetic bearings, on the other hand, stabilize their position by themselves, so that no active position control is necessary.
U.S. Pat. No. 4,072,370 A discloses a passive magnetic bearing with an arrangement of permanent magnets both on the stator and on the rotor.
Furthermore, there are known passive magnetic bearings in which only one of the bearing parts is formed by permanent-magnetic elements and the other bearing part includes a superconductor. The permanent-magnetic elements induce shielding currents when there is a change in position, as a consequence of changes in the field in the superconductor. The resulting forces may be repelling or attracting, but are always directed in such a way that they counteract the deflection from the intended position. Consequently, an inherently stable bearing can be achieved and it is possible to dispense with a complex and fault-susceptible control. However, cooling of the superconductor material is required. Magnetic bearings with superconductors are described, for example, in U.S. Pat. No. 5,196,748 A and EP 0 322 693 A.
DE 44 36 831 C2 then discloses a further passive magnetic bearing with a high-temperature superconductor. This known magnetic bearing includes a first bearing part, which is connected to a rotor shaft, and a second bearing part, which is arranged on a stator and surrounds the first bearing part. One of the two bearing parts has the high-temperature superconductor. The other bearing part includes an arrangement of permanent-magnetic elements arranged adjacent to one another. The magnetization of neighboring permanent-magnetic elements is opposite to one another. The interspaces between respective pairs of permanent-magnetic elements are filled with ferromagnetic material to concentrate the magnetic flux emerging from the permanent-magnetic elements on the side facing the other bearing part. As a result, great bearing rigidity (stability) is obtained.
In a configuration according to DE 44 36 831 C1, the permanent magnets are provided in a hollow-cylindrical arrangement on the inner bearing part and the superconductor is arranged as a hollow-cylindrical structure on the inner side of a hollow-cylindrical support body of the outer bearing part. Cooling channels for passing through liquid nitrogen are formed in the support body to cool the superconductor. In another configuration, the high-temperature superconductor is arranged on the inner bearing part on the rotor shaft, a cooling channel being provided in the rotor shaft for the liquid nitrogen to cool the high-temperature superconductor. The permanent-magnetic elements with the ferromagnetic intermediate elements may be axially arranged in relation to the rotor shaft one behind the other in the form of thin rings or else be axially stretched out and arranged one behind the other in the circumferential direction, respectively with alternating magnetization.
In DE 44 36 831 C2, a material with an energy product (B*H)
max
of at least 20 MGOe, in particular a neodymium(Nd)-iron(Fe)-boron(B) alloy or a samarium (Sm)-cobalt (Co) alloy, is proposed as the permanent-magnetic material. The permanent-magnetic material may also be cooled to increase its coercive field strength.
The permanent-magnetic materials used in the known magnetic bearings to achieve the high magnetic fields are themselves exposed to considerable forces by the high magnetic fields. With the permanent magnets arranged on the rotating bearing part, centrifugal forces additionally act on the permanent magnets. These forces may then lead to the detachment of individual magnetic particles, in particular from the brittle permanent magnets produced power-metallurgically by sintering or pressing, or even to the rupture of the permanent magnets, in particular in the case of permanent loading and material fatigue. This can, however, bring about considerable damage or even complete destruction of the magnetic bearing.
EP 0 728 956 A1 then discloses a magnetic bearing with a superconductor on the stator and an arrangement of permanent magnets on the rotor and also a bearing gap between the superconductor and the permanent magnets. The permanent magnets are formed in an annular manner and arranged concentrically in relation to the axis of rotation of the rotor. Annular, soft-magnetic flux guiding elements are provided between the individual annular permanent magnets. The annular permanent magnets, on the other hand, are formed from a magnetic sintered material with a high energy product, in particular a samarium-cobalt or a neodymium-iron-boron magnetic material. In order to prevent a rupture of these sintered permanent magnets, in particular at high rotational speeds, a reinforcing ring of a glass-fiber or synthetic-fiber reinforced plastic is then arranged around the outermost ring of the arrangement of magnets and radially holds the arrangement of the annular permanent magnets together under a radial pressure.
A similar arrangement is also known from Patent Abstracts of Japan with respect to JP 09 049 523 A.
EP 0 413 851 A1 discloses a bearing ring for magnetic bearings for use in magnet-mounted vacuum pumps with arrangements of permanent magnets on the rotor and the stator. Iron-neodymium-boron magnets or cobalt-samarium magnets are proposed as permanent magnets. This known magnetic bearing includes, on the rotating shaft, bearing rings which respectively include a hub ring, a ring of permanent magnets and a reinforcing ring. The reinforcing rings have the task of avoiding destruction of the permanent rings being caused by the high centrifugal forces and preferably are formed of high-grade steel.
Patent Abstracts of Japan with respect to JP 08 200 368 A further discloses a magnetic bearing with a superconductor on the outer-lying stator and an arrangement of permanent magnets on the inner-lying rotor. The arrangement of permanent magnets includes a number of permanent magnets in the form of segments of a ring lying adjacent to one another in the circumferential direction and combining with one another to form a closed ring. Arranged around the outer periphery of all the ring-segment-like permanent magnets is a holding ring, to avoid the permanent magnets being ruptured by the great centrifugal forces at high rotational speeds. Also provided is a thrust ring, which presses the holding ring radially inward against the outer faces of the permanent magnets. The permanent magnets are not spaced apart from one another but touch one another. Flux guiding elements are not provided between the permanent magnets.
In the case of known magnetic bearings in which radial holding devices are provided for the permanent magnets, however, the supporting forces of the bearing or the load-bearing capacity of the bearing are reduced. This is because, in the case of the known magnetic bearings, the radial holding devices are arranged between the permanent magnets and the associated flux guiding elements, if any, on the one hand and the bearing gap on the other hand and, as a result, reduce the magnetic flux density effective in the bearing gap and with the superconductor, since the bearing gap must not become less than a specific minimum width.
SUMMARY OF THE INVENTION
The invention is therefore based on an object of protecting the magneti
Ries Günter
Steinmeyer Florian
Mullins Burton
Siemens Aktiengesellschaft
Staas & Halsey , LLP
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