Note: Descriptions are shown in the official language in which they were submitted.
~a~ 4~
The present inven-tion to an elec-tromagnetic bearing for
supporting the ends of rotors rota-ting at high speeds of the
type which cornprises a disc armature integral wi-th the rotor
and an annular fixed armature located a-t a sma].l dlstance from
the disc armature in such a manner -that a small axial air gap
is formed, -the said fixed armature comprising exication
windings and a ferromagnetic coreO
The mounting of a shaft rotating with the assistance of
axial an~/or radial electromagnetic suspension has a number of
advantages in that frietion is suppressed and the inertia and the
rigidity of the shaft ean be increased since the eleetromagnetic
suspension is not affected by the diameter of the shaft.
Aecordingly, vibration is redueed at high speedsO In addition,
the eontrol of electromagnetic bearlngs with the help of
detectors for the positioning of the shaft enablesthe shaft
to be maintained in position against axial and/or radial
displacement forces.
~ he operation of axial eleetromagnetic beariIlgs poses,
however, a certain number of problemsO In effeet, the dise
armature, whieh eonstitutes the rotor of the bearing, rotates
at a very high speed and cannot be made of a laminated material
because the meehanieal strength would be too weak. Aeeordingly,
large Eddy eurrents are in~ueed in the interior of the body
of the disc and these eause damping which lead to a limita-tion
in the pass band of the associated eontrol.
It has been proposed, to reduce -the size of the Eddy currentc;
that radial slots be eut in -th~ periphery of the disc in the form
of teethO Such an arrangement eertainly reduees ~ddy currents
but the cllt-away portions lead to.too great a reduction in
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the mechanical strength. In effect, at high ro-tational speeds,
the exagera-ted stress appearing at the root of -the teeth can
cause rup-turing of the disc.
The object of the present invention is to remedy the
aforementioned inconveniences and notably to reduce the Eddy
currents appearing in the disc of an axial elec-tromagnetic
bearing without causing a notable diminution of the mechanical
strength of the said disc.
~ ccording to the present invention there is provided
an axial electromagne ic bearing for supporting the end of a
- shaf-t rotating at high speed comprising an armature in the form
of a disc attached to the shaft and an annular fixed armature
located a short distance from the disc to define a small axial
air gap therebetween, the said fixed armature comprising
excitation windings and a ferromagnetic core, and the bearing
bearing characterised in that radial grooves are provided in the
peripheral portion of the disc armature facing the fixed armature.
Thus, these radial yrooves cut the Eddy currents from --
which it follows that the damping and thus the weakening of the
control of the axial bearing are reduced. Moreover, the mechan-
ical strength of the disc integral with the rotating shaft
magnetically s~spended is not substantially reduced and the disc
can withstand high rotational speeds. In effect, the thickness
of the disc is reduced in localised zones but there is no
discontinuity in the edge of the disc.
Preferably, the said grooves are regularly spaced in
the said peripheral portion of the disc armature.
In one particular emhodiment of the invention, when the
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axial bearing comprises a disc armature disposed between two
fixed annular armatures, the radi.al grooves are provided in the
two aces of the disc i.n the peripheral portion thereof faci.ng
the annular armatures.
Preferably, the radial grooves provided i.n each of the faces
of the disc are regularly spaced arld out ~f phase in relation
to the grooves provided in the opposite face of the disc.
Preferably also, each groove in each face of the disc is
disposed an equal distance from the two nearest grooves situated
on the opposite face of the disc.
The grooves permit a maximum efficiency to be attained when
they are out of phase by a half cycle, that is to say when
each groove on one face of the disc is diametrically opposite
to a groove on the other side of the disc.
The preserit invention will now be described by way of
exa~ple with reference to the accompanying drawing in which:-
Fig. 1 is a cross section on the line I-I of ~igure 2
showing a bearing according to thé invention; and
Fig. 2 is a side view of a disc forming the rotor armature
of -the axial bearing of ~igure 1.
As can be seen in ~igure 1, a disc 1 comprises the rotor
armature of an electromagnetic axial ~earlng. ~he disc 1 is
located between two annular stator armatures 2 and ~ comprising
repsectively a ferromagnetic core 2a, ~ and excitation windings
2b1 3b. The disc 1, integral with a rotating shaft 8, has two
frorlt faces 6 and 7 and an end face 9. Grooves 4 and 5
respectively are provided in the faces 6 and 7 of the disc 1
in the peripheral porti.on thereof situa~ed facing -the annular
stator armatures 2 arid 3 respectively7 As can be seen in Figure 2,
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the radial grooves 4, 5 respectively are regularl~ spaced at
the periphery of the disc 1 and -the grooves in one of the faces
are out of phase in relation to the grooves provided in the
opposite face. Preferabl~, each groove 4, 5 on each face 6, '7
of the disc 'l is located an equal distance from two grooves
5, 4 which are situated the nearest to it on the opposite face
7, 6 respectively.
As sho~Jn in Figure 1, each groove 4, 5 respectively of a
face 6, 7 respectively of the disc 1 is diame-trically opposite
a grQove 5, 4 respectively on the opposite face 7, 6 of the disc 1
Thus, the grooves of one of the faces are out of phase b~r a
half-cycle in relation to the grooves of the other face.
~ he rin~s 2a, 3a comprising the ferromagnetic core of the
stator armature 27~ and which are coaxial to the shaft 8 Cc~l be
made in one piece but are preferably made of bundles of isolated
laterall~ disposed sheets or of laminated iron sheets in order
to reduce the heating of the electromagnetic portions and ~he
loss caused by Eddy currents,
The air gaps 10 and 11 between t-he stator armatures 2 and 3
respectively and the disc armature 1 of the axial electromagnetic
bearin~ are controlled and regulated with the help of axial
detectors, not shown, in relation to the axial position of the
shaft 8. '~hese axial dete,c-tors regulate the excita-tion of the
axial bearing in such a manner as to maintain constantly the
air gaps lQ and 11.
'l`he disc 1 can be formed with an aperture ~2 at its centre
and be moun-ted coaxially on -the shaft 8, as shown in ~igures 1
and 2, or can comprise an abutment on the shaft 8 in the fashion
of -the horizontal cxoss-piece of a 'l1-shape~
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It is to be noted that, in accordance wi-th the present
invention~ the end face 9 of the disc 1 is not cu-t and always
has a thicknc~ss or width A. ~he thickness of the disc 1 is only
reduced at the ].evel of the grooves 4 and 5 with respect to
the end face 9 of -the disc 1. The grooves 4 and 5 can have
different configurations but advantageously the profile of the
bottom 14, 15 of the grooves 4, 5 is curved so tha-t the forming
of the grooves is facilitated and the efficiency can be the
greatest possible with relation to a removal of the least
material and so that the profile of the grooves can correspond
substantially to the field lines of the induced magnetic field.
As is well known, diverse modification and additions can be
made by persons skilled in the art to the apparatus which is
described above strictly by way of non--limiting example without
limiting the scope of protection of the invention.
