U.S. patent application number 09/783182 was filed with the patent office on 2001-10-25 for slip-ring configuration in electric motors and generators, slip-ring body and method for retooling slip-ring bodies.
Invention is credited to Hahn, Ingolf, Meyer, Aloysius, Stadie, Klaus, Vesper, Wolfgang.
Application Number | 20010033117 09/783182 |
Document ID | / |
Family ID | 7632470 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033117 |
Kind Code |
A1 |
Vesper, Wolfgang ; et
al. |
October 25, 2001 |
Slip-ring configuration in electric motors and generators,
slip-ring body and method for retooling slip-ring bodies
Abstract
A slip-ring configuration for electric motors and generators is
provided, in which brushes made of carbon materials and slip rings
of a slip-ring body are electrically conductively connected to each
other. The slip rings include metallic rings of standard
construction as a slip-ring base and an electrically conductive
sliding layer made of a graphite material. The sliding layer has a
thickness which amounts to a maximum of 11% of a radius of the slip
ring and is electrically conductively fastened to the periphery of
the metallic slip-ring base by gluing. A method for retooling
slip-ring bodies having metallic slip rings includes machining the
metallic slip rings and gluing on a sliding layer.
Inventors: |
Vesper, Wolfgang; (Bonn,
DE) ; Stadie, Klaus; (Wachtberg, DE) ; Hahn,
Ingolf; (Bonn, DE) ; Meyer, Aloysius;
(Heroldbach, DE) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
POST OFFICE BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Family ID: |
7632470 |
Appl. No.: |
09/783182 |
Filed: |
February 14, 2001 |
Current U.S.
Class: |
310/232 |
Current CPC
Class: |
H01R 39/085 20130101;
H01R 39/64 20130101; H01R 39/56 20130101 |
Class at
Publication: |
310/232 |
International
Class: |
H02K 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2000 |
DE |
100 09 007.9 |
Claims
We claim:
1. A slip-ring configuration for electric motors and generators,
comprising: a slip-ring body having slip rings to be electrically
conductively connected to brushes made of carbon materials; said
slip rings each having a given radius and a metallic ring of
standard construction acting as a slip-ring base with a periphery;
at least one electrically conductive sliding layer made of a
graphite material; said at least one sliding layer having a
thickness amounting to a maximum of 11% of said given radius and
said at least one sliding layer each electrically conductively
fastened to said periphery of said metallic slip-ring base of a
respective one of said slip rings by gluing.
2. The slip-ring configuration according to claim 1, wherein said
sliding layer is formed of a material having a flexural strength of
at least 30 MPa.
3. The slip-ring configuration according to claim 1, wherein said
sliding layer is formed of an isostatically pressed graphite
material.
4. The slip-ring configuration according to claim 1, wherein said
sliding layer is formed of annular segments.
5. The slip-ring configuration according to claim 4, wherein said
annular segments define joint locations between said annular
segments forming an angle of maximally 75.degree. relative to a
tangent.
6. The slip-ring configuration according to claim 4, wherein said
annular segments have different arc lengths and include a longest
annular segment and a second-longest annular segment, and said arc
length of said longest annular segment is at least 110% of said arc
length of said second-longest annular segment.
7. The slip-ring configuration according to claim 1, wherein said
slip-ring base has an outer surface with edges and a projection at
least at one of said edges.
8. The slip-ring configuration according to claim 7, wherein said
projection at least at one of said edges has a width of between 0.5
mm and 5 mm and a height of between 0.5 mm and 3 mm.
9. The slip-ring configuration according to claim 1, wherein said
sliding layer includes a ring having a circumferential slit at an
angle .beta. relative to a tangent.
10. The slip-ring configuration according to claim 9, wherein said
sliding layer has a circumference, and said angle .beta. is
dimensioned to cause said slit to extend at least once entirely
around said circumference of said sliding layer.
11. The slip-ring configuration according to claim 1, including a
temperature-stable adhesive gluing said sliding layer and said
metallic slip-ring base together, said temperature-stable adhesive
permitting a permanent connection of said sliding layer to said
slip-ring base even during operation of the slip-ring
configuration.
12. The slip-ring configuration according to claim 1, including an
adhesive to which a metal powder is added, said adhesive gluing
said sliding layer and said metallic slip-ring base together.
13. The slip-ring configuration according to claim 1, wherein the
brushes are graphite brushes.
14. The slip-ring configuration according to claim 1, wherein at
least one of said slip rings is not glued to a sliding layer made
of a graphite material.
15. A slip-ring body, comprising: slip rings to be electrically
conductively connected to brushes made of carbon materials; said
slip rings each having a given radius, a metallic ring of standard
construction acting as a slip-ring base with a periphery, and an
electrically conductive sliding layer, said sliding layer of said
slip-ring base of at least one of said slip rings being a sliding
layer made of a graphite material; said sliding layer having a
thickness amounting to a maximum of 11% of said given radius and
said sliding layer electrically conductively fastened to said
periphery of said metallic slip-ring base by gluing.
16. A method for retooling slip-ring bodies in electrical machines,
which comprises: machining a metallic contact layer on an outer
surface of at least one existing metallic slip ring to a depth
corresponding to a thickness of a sliding layer to be applied; and
then applying the sliding layer to the machined outer surface.
17. The method according to claim 16, which further comprises
forming the sliding layer of a material having a flexural strength
of at least 30 MPa.
18. The method according to claim 16, which further comprises
forming the sliding layer of an isostatically pressed graphite
material.
19. The method according to claim 16, which further comprises
forming the sliding layer of annular segments.
20. The method according to claim 19, which further comprises
defining joint locations between the annular segments forming an
angle of maximally 75.degree. relative to a tangent.
21. The method according to claim 19, which further comprises
providing the annular segments with different arc lengths, a
longest annular segment and a second-longest annular segment, and
setting the arc length of the longest annular segment at least at
110% of the arc length of the second-longest annular segment.
22. The method according to claim 16, which further comprises
providing the sliding layer with a ring having a circumferential
slit at an angle .beta. relative to a tangent.
23. The method according to claim 22, which further comprises
dimensioning the angle .beta. to cause the slit to extend at least
once entirely around a circumference of the sliding layer.
24. The method according to claim 16, which further comprises
providing the metallic slip ring with a metallic slip-ring base
having the outer surface; gluing the sliding layer and the metallic
slip-ring base together with a temperature-stable adhesive; and
permitting a permanent connection of the sliding layer to the
slip-ring base even during operation of a slip-ring configuration
due to the temperature-stable adhesive.
25. The method according to claim 16, which further comprises
providing the metallic slip ring with a metallic slip-ring base
having the outer surface; and gluing the sliding layer and the
metallic slip-ring base together with an adhesive to which a metal
powder is added.
26. The method according to claim 16, which further comprises
omitting a sliding layer made of a graphite material from at least
one slip ring.
27. The method according to claim 16, which further comprises:
providing the metallic slip ring with a metallic slip-ring base
having the outer surface; and retaining a projection at least at
one edge of the outer surface of the metallic slip-ring base while
carrying out the step of machining the metallic contact layer in at
least one metallic slip ring.
28. The method according to claim 27, which further comprises
providing the projection with a width of between 0.5 mm and 5 mm
and a height of between 0.5 mm and 3 mm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to slip-ring configurations for
electrical machines, such as electric motors and generators, having
brushes made of carbon materials and slip-ring bodies, wherein the
brushes are electrically conductively connected to slip rings of
the slip-ring bodies. The invention also relates to a slip-ring
body and a method for retooling slip-ring bodies.
[0003] Electric motors and generators with which electrical energy
is converted into rotational energy or, conversely, rotational
energy is converted into electrical energy, require a current
supply to a rotatably disposed coil, which is connected in a
force-locking or form-locking manner to a rotating shaft. A
form-locking connection is one which connects two elements together
due to the shape of the elements themselves, as opposed to a
force-locking connection, which locks the elements together by
force external to the elements. That usually takes place by way of
slip rings which are connected to the rotating shaft, concentric
therewith and conductively connected to stationary brushes, or by
way of pairing brushes with so-called commutators or collectors. In
addition to producing an electrical connection between the
stationary part and the rotating part of the electrical machine,
the commutators or collectors also effect commutation (in
direct-current machines).
[0004] Usually, the slip rings and commutators are formed of metals
such as copper or copper alloys such as, for example, bronze, tin
bronzes, nickel bronze, silver or steel. The slip rings are
connected by insulating fastenings to a hub (rotating shaft) to
form slip-ring bodies, which are insulated with respect to the hub
and with respect to each other. Electrically conductive brushes are
disposed stationarily along the circumference of the slip rings and
are held in contact with the surface of the slip rings by spring
force. In the case of alternating-current motors and generators,
slip rings are required individually or plurally for each
phase.
[0005] The sliding contacts (brushes) generally are formed of
carbon materials, possibly in combination with metals, for example
metal graphite. In order to produce metal graphite, mixtures of
metal powders, in particular copper, tin or lead, are pressed with
graphite, in particular natural graphite, and subsequently hardened
by calcining or sintering.
[0006] In the case of all of those material pairings, wear results
from reciprocal movement as well as from transmission of somewhat
high currents, in which case dust can form from abrasion. On one
hand, that can lead to shortening of a creepage path because of
dirt accumulation and thus to arcing. On the other hand, an eroding
of contacting layers results. There is a necessity for replacing
the brushes and subsequent treatment of a surface of the slip rings
(machining or stripping off of defective spots such as grooves or
the like). In that connection, additional maintenance intervals
result, which are shorter than maintenance intervals of (roller)
bearings, something which causes substantially increased
maintenance costs, above all as a result of additional
down-times.
[0007] It is therefore desirable to keep the abrasion as low as
possible and thus to lessen the frequency of the maintenance work
caused as a result, or to make it at most the same as the frequency
of the maintenance work for the bearings and/or other wearing
parts.
[0008] It is known from East German Patent DD 258 687 A1 and from a
publication entitled VEM Journal 1975, pages 15 ff, that wear is
very low in the case of a pairing of graphite brushes with slip
rings made of graphite. However, that system has the disadvantage
of only permitting small currents to be conducted through the
graphite body of the slip rings because of its specific resistance,
which is relatively high in comparison with metals. When high
currents are conducted, the ohmic heat is unacceptably high. That
can lead to damage to the system. In a slip ring, the introduction
or removal of the current takes place by way of a metal conductor
which extends parallel to the axis of rotation in such a manner
that it is laterally offset with respect thereto and is
electrically conductively connected to the body of the slip ring.
The resistance inside a graphite slip ring is of a similar
magnitude to the contact resistance between a slip ring and a
brush. In the case of a constant induced current in the coil, that
leads to periodic voltage fluctuations in a generator. In a motor,
it leads to an uneven torque, depending on the path length of the
current and thus the active resistance in the slip ring.
[0009] Another construction is known from East German Patent DD 248
909 A1. A slip ring having a metallic slip-ring base and a carbon
sliding ring soldered onto it is described therein. The slip-ring
base is provided with hollow spaces in order to be able to remove
waste heat by ventilation on all sides. The side of the carbon
sliding ring that faces the metallic slip-ring base has to be
metallized in order to ensure a low contact resistance and permit a
soldered joint. Thermal stresses occur as a result of the strong
heating of the structure by the ohmic dissipated energy, as well as
during soldering. An outer portion of the metallic slip-ring base
is therefore preferably provided with recesses for compensation of
thermal stresses.
SUMMARY OF THE INVENTION
[0010] It is accordingly an object of the invention to provide a
slip-ring configuration in electric motors and generators, a
slip-ring body and a method for retooling slip-ring bodies, which
overcome the hereinafore-mentioned disadvantages of the
heretofore-known devices and methods of this general type, which on
one hand lead to as little wear as possible and which on the other
hand allow a sufficiently high current load, in order to permit
systems of that kind to also be used in the high-current range
without an occurrence of strong temperature rises known from the
prior art. A further object is to be able to retrofit existing
machines having metallic slip rings, in such a way that wear
becomes less, with as few parts as possible needing to be
replaced.
[0011] With the foregoing and other objects in view there is
provided, in accordance with the invention, a slip-ring
configuration for electric motors and generators, comprising a
slip-ring body having slip rings to be electrically conductively
connected to brushes made of carbon materials. The slip rings each
have a given radius and a metallic ring of standard construction
acting as a slip-ring base with a periphery. There is at least one
electrically conductive sliding layer made of a graphite material.
The at least one sliding layer has a thickness amounting to a
maximum of 11% of the given radius and each of the at least one
sliding layer is electrically conductively fastened to the
periphery of the metallic slip-ring base of a respective one of the
slip rings by gluing.
[0012] Accordingly, this object is achieved by a slip-ring
construction which includes a metallic ring of standard
construction as a slip-ring base and a sliding layer glued onto
this slip-ring base. The sliding layer preferably is formed of a
carbon material. If a carbon material is used, it is advantageous
to use a graphite material, particularly preferably an
isostatically pressed graphite material. Furthermore, the flexural
strength of the graphite material should preferably amount to at
least 30 MPa (=30 N/mm.sup.2) in order to ensure that the layer
thickness of the carbon material can be kept sufficiently small.
The result of this construction is, on one hand, that the
contact-surface pairing has minimal wear, because the material of
the friction partner of the brushes can be chosen in such a way
that the abrasion between these materials which are moved against
each other is considerably lower than that between a pairing of
metals or a pairing with metal and carbon material for the brushes.
On the other hand, as a result of this construction, the contact
resistance between the metallic base of the slip ring and the
sliding layer is centrosymmetrical.
[0013] In accordance with another feature of the invention, not all
of the slip rings of the slip-ring body are provided with the
sliding layer.
[0014] As is conventional to a person skilled in the art, the
configuration formed of the hub, the insulator (preferably the
insulating covering in the form of a lateral cylinder surface) and
the slip rings, which in the case of the invention are made up of
the metallic slip-ring base and the sliding layer, is referred to
herein as the slip-ring body.
[0015] The thickness of the sliding layer is upwardly limited by
its conductivity (the thicker the sliding layer, which is poorly
conductive in comparison with metals, the higher the resistance
between the terminal lead, which is conductively connected to the
metallic slip-ring base, and the connecting lead at the brushes).
It has proven advantageous to ensure that the thickness of the
sliding layer is not greater than 11% of the radius of the outer
cylindrical or shell surface of the sliding layer.
[0016] The metallic slip-ring base is usually a squat cylindrical
supporting ring which can be constructed in such a way that it is
solid, with (mainly circular) recesses, or a spoked wheel. It is
also possible, and preferred, for the width of the slip-ring base
in the vicinity of the outer cylindrical or shell surface to be
greater in this region than in the rest of the ring. The slip-ring
base is thus given the appearance of a flat ring (which can also
have recesses), on the periphery of which a wide (in the direction
parallel to the axis) lateral cylinder surface like a collar is
preferably formed. A sliding layer with a constant thickness is
electrically conductively fastened on the (outer) lateral surface
of this slip-ring base. This fastening is preferably produced by
conductive gluing. The advantage of gluing is that the electrical
connection has a contact area which is as large as possible. That
lowers the contact resistance and divides the force between the two
materials onto an area which is as large as possible. Heating to
temperatures at which solder melts, which is otherwise required in
the case of the production of a soldered joint, is dispensed with
by gluing. When soldering, particular safety measures, such as
dismantling or putting on a thermal shield, are namely required in
order to avoid damage to the slip-ring base.
[0017] In accordance with a further feature of the invention, the
sliding layer is formed of an electrically conductive graphite
material. Preferably, a graphite material having a flexural
strength of at least 30 MPa is used as the material for the sliding
layer. Furthermore, isostatically pressed graphite material is
preferably used. The thickness of the sliding layer should be kept
as low as possible because of the specific resistance which is
higher in comparison with the metallic slip-ring base. In this
connection, however, it is to be taken into account that, on one
hand, the mechanical stability of the sliding layer decreases with
smaller thickness. On the other hand, the abrasion in connection
with the brushes (that are usually and preferably formed of carbon
materials) is to be determined by the suitable selection of the
material and its thickness in such a way that maintenance
intervals, which become necessary because of the renewing of the
sliding layer, are equal to or greater than the average
rolling-bearing lifetime. Therefore, the thickness of the sliding
layer should not amount to more than 11% of the outer radius of the
slip ring (i.e. of the outer radius of the sliding layer).
Preferably, the thickness of the sliding layer is 10% or less of
this radius, in particular 8% or less, with proportions of 6% and
below or 4% and below being particularly preferred.
[0018] Conductive adhesives are used in order to glue the sliding
layer and the metallic slip-ring base together. These adhesives are
preferably to be chosen in such a way that their temperature
stability is so great that a firm gluing of the sliding layer onto
the metallic slip-ring base is also ensured at the temperatures of
the slip ring that occur during the operation of the slip-ring
configuration. Preferably, however, adhesives which do not have a
suitable inherent conductivity, although to which a metal powder,
preferably copper powder, is added, are also used. It is
particularly preferable if after the depositing of the adhesive
layer, the metal powder is scattered over the coated surfaces in
order to obtain an electrically conductive adhesive connection. The
metal powders being used preferably have a granulation of 0.01 mm
to 0.2 mm. In particular, epoxy-resin adhesives, phenolic-resin
adhesives, cyanate-ester-resin adhesives as well as adhesives based
on polyurethane resins, polyester resins and amine resins, are
counted among the adhesives being used. It is particularly
preferable if phenolic-resin adhesive is used for the slip rings in
accordance with the invention. The layer thickness of the adhesive
on the metal surface of the slip-ring base or on the inside surface
of the sliding layer preferably amounts to between 0.02 mm and 0.2
mm, particularly preferably between 0.05 mm and 0.1 mm. In the
gluing process, sliding-layer segments are placed precisely onto
the supporting slip-ring base and pressed on with even pressure. In
this connection, a gap width between individual segments of the
sliding layer is to be kept as small as possible.
[0019] In accordance with an added feature of the invention,
graphite brushes are used as the sliding partner for the sliding
layer of the slip rings, i.e. brushes made of carbon materials with
a graphitic character. In particular, electrographite and burnt
carbon materials which contain natural graphite are counted among
these materials.
[0020] The fact that the sliding layer, which preferably is formed
of the above-mentioned rigid carbon material, can be renewed
without difficulty when necessary, is to be mentioned as a further
advantage of this construction. In order to do this, it is only
necessary to machine or strip off the remaining sliding layer and
the adhesive layer down to the metal, whereupon a new sliding layer
can then be applied. Changes in the brush position during this
overhaul are not required in this case. In the case of a pure metal
embodiment, the slip ring has to be reworked when worn, without
going below a minimum diameter, or the entire slip ring has to be
exchanged, in which case the brushes also have to be renewed.
[0021] The partial or complete retrofitting of existing machines
having purely metallic slip rings is to be carried out without
difficulty in such a way that the metallic contact layer on the
outer cylindrical or shell surface of the existing slip rings in
the slip-ring body is prepared, preferably worn down, particularly
preferably by machining or stripping off. This is done in such a
way that the sliding layer can be applied in the required thickness
and connected to the remaining metallic slip-ring base by gluing.
The sliding layer can then be reworked if necessary in order to
remove surface irregularities, for example by stripping off or
grinding. The advantage of the embodiment in accordance with the
invention emerges in particular in the case of this retrofitting,
because the thickness (in the radial direction) of the gliding
layer of metallic slip rings is usually great enough to be stripped
off or machined to the required diameter without a loss of
stability. This applies in particular to metallic slip rings which
have two layers in the radial direction, a metallic supporting
layer and a separate outer gliding layer.
[0022] It is of particular advantage to prepare the metallic slip
rings of an existing machine (for example by grinding, turning or
milling) in such a way that at least at one of the edges of the
outer cylindrical or shell surface of the remaining metallic
slip-ring base, a projection (in the direction of the increasing
radius) remains in each case which is preferably 0.5 mm to 5 mm
wide, in particular 1 mm to 3 mm wide, and 0.5 mm to 3 mm high,
preferably 1 to 2 mm high. The sliding layer is glued into the
cylindrical groove which comes about in this way, in such a way
that the sliding layer ends at the projections or preferably
projects above them by up to 5 mm, in particular up to 3 mm.
[0023] In the configuration in accordance with the invention, the
entire slip-ring body can be clamped for overhaul or renewal of the
sliding layer, the slip rings are stripped off or machined down to
the metallic base, and the sliding layer can be replaced
(simultaneously with one or more slip rings).
[0024] In accordance with an additional feature of the invention,
the sliding ring can be formed of a closed ring. However, it is
preferred for the sliding layer to be made up of a plurality of
segments, which are cut from one or more graphite rings. In that
case they are applied to the carrier in at least two segments,
particularly preferably in at least three segments.
[0025] In accordance with yet another feature of the invention, in
this connection, the joint between two adjoining sliding-layer
segments is not made parallel to the axis of rotation (i.e. at
right angles to the tangent), but instead at an angle to the
tangent of a maximum of 75.degree., preferably a maximum of
60.degree., and particularly preferably up to 45.degree.. The word
"tangent" is defined and will be used as follows: "A tangent is
that straight line which borders on the outer cylindrical or shell
surface of the slip-ring and passes perpendicular to the rotational
axis of the electrical machine."
[0026] Therefore, in accordance with a concomitant feature of the
invention, the sliding layer is applied in one piece in the form of
a ring and the latter is slit circumferentially at an angle .beta.
with respect to the tangent. That angle is preferably sized in such
a way that the slit extends at least once around the entire
circumference of the sliding layer. If the sliding layer is applied
in more than one segment, it is advantageous for these segments not
to be sized with the same (arc) length. Instead, the (arc) length
of the longest segment should be at least 110% of the length of the
other (or second-longest) segment. The thickness of the sliding
layer amounts to up to 11% of the outer radius of the slip ring,
preferably a maximum of 5 mm and in particular 4 mm and less.
[0027] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0028] Although the invention is illustrated and described herein
as embodied in a slip-ring configuration in electric motors and
generators, a slip-ring body and a method for retooling slip-ring
bodies, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes
may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the
claims.
[0029] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a fragmentary, diagrammatic longitudinal-sectional
view of a slip-ring body;
[0031] FIG. 2 is an enlarged, fragmentary view of a portion II of
FIG. 1;
[0032] FIG. 3 is an enlarged, fragmentary view similar to FIG. 2,
of an embodiment which is an alternative to FIG. 1;
[0033] FIG. 4 is a cross-sectional view taken along a line IV-IV of
FIG. 1, in the direction of the arrows;
[0034] FIG. 5 is a lateral plan view of a slip-ring body in
accordance with FIG. 4; and
[0035] FIG. 6 is a plan view of a slip-ring body in accordance with
an embodiment that is an alternative to the embodiment of FIG.
4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Referring now to the figures of the drawings in detail and
first, particularly, to FIG. 1 thereof, there is seen a slip-ring
body 11 according to the invention having a total of three slip
rings 10, 10', 10". The slip rings 10, 10', 10" are to be
electrically conductively connected to brushes 13 made of carbon or
graphite materials, although only one brush is shown. The slip
rings are shown in a section taken through the slip-ring body 11
along a plane parallel to an axis of rotation. Metallic rings 2,
2', 2" that are provided as a slip-ring base, are fastened to an
insulating layer 12 which is mounted on a hub 1. A respective
sliding layer 3, 3', 3" in the form of a cylindrical ring is glued
onto a lateral surface of each of these metallic rings 2, 2', 2"
with the aid of an electrically conductive adhesive. This
construction can be seen from FIG. 2, which is an enlargement of a
section of FIG. 1. In this case, a metallic portion of the
slip-ring base 2 is shown, on which the annular sliding layer 3 is
secured by an electrically conductive adhesive 6.
[0037] FIG. 3 illustrates the above-mentioned preferred embodiment,
in which the slip-ring base 2 is constructed in such a way that a
respective projection 4, 4' remains at edges of its outer
cylindrical or shell surface. This is a modified embodiment of the
embodiment shown in FIG. 2 and FIG. 1. In contrast to the
construction shown in FIG. 1, in this case the respective
projection 4 and 4' has been left at both edges of the outer
cylindrical or shell surface of the slip-ring base 2. As a result,
a groove 5 is formed in the center of the outer limiting surface of
the slip-ring base 2, into which the sliding layer can be inserted
in such a manner that it is flush. The electrically conductive
adhesive 6 is brushed onto the slip-ring base 2 at the base of the
groove 5 and the sliding layer 3 is applied and glued to the
slip-ring base 2.
[0038] FIG. 4 shows a section taken along a line IV-IV of FIG. 1.
The sliding layer 3" is glued onto the annular slip-ring base 2"
which is fastened to the insulating layer 12 over the hub 1. A
multi-part construction of the sliding layer 3" which can be seen
in FIG. 4 provides a three-part embodiment with sliding-layer
segments 3".sub.1, 3".sub.2, 3".sub.3 and joint locations 7, 7' and
7".
[0039] FIG. 5 shows a plan view of a slip ring of this type. The
viewing direction of the observer in FIG. 5 is at right angles to
the axis and at right angles to the diameter of the slip ring. The
sliding layer 3 is glued onto the slip-ring base 2 in a plurality
of segments and a joint 8 between two segments of the sliding layer
is visible in FIG. 5. An angle .alpha. of the joint 8 with respect
to the tangent is 60.degree..
[0040] Finally, FIG. 6 shows a further preferred embodiment in a
plan view similar to FIG. 5, in which the ring 3 forming the
sliding layer is slit. An angle .beta. of a slit 9 with respect to
the tangent is preferably chosen in such a way that the slit
extends along a spiral line on a lateral surface of the cylindrical
sliding layer and the length of the slit is greater than the
circumference of the lateral surface. The advantage of this
embodiment is that the ring can be expanded in order to be applied
to the slip-ring base 2 which is fastened to the hub 1. In this
case, if applicable, the ring 3 can be inserted into the groove 5
even over a raised projection 4 or 4' of the slip-ring base (which
is provided in accordance with FIG. 3) without the danger of
breaking. The slit ring or sliding layer 3 is subsequently glued to
the slip-ring base 2 so that it is flush and the width of the slit
9 is as small as possible. The acute angle .beta. (small angle) of
the slit 9 with respect to the tangent further minimizes possible
irregularities or joints and thus reduces abrasion.
[0041] The invention will be further explained by the following
examples:
Comparative Example
[0042] A standard 6 kV-electric motor (type "1LS1 456-4HA60-Z" from
Siemens AG, No. 904 068) having slip rings in accordance with the
prior art made of steel X10Cr13 and associated optimized brushes,
namely metal graphite brushes "RC53" from the company SGL CARBON
GmbH, was used during operation with rated load. The temperature of
the supply air, at the winding, in the slip ring space, at the
brushes and at the slip rings, was determined. The abrasion at the
brushes and the slip rings was determined.
Example
[0043] The slip-ring body of the comparative example (with a
diameter of 280 mm) was clamped centrally onto a turning lathe and
the slip rings made of steel were stripped off or machined to an
outer diameter of 270 mm. Three ring segments being formed of an
isostatically pressed graphite of the type 300 from the company SGL
CARBON GmbH were used having the dimensions: inside diameter 270
mm, outside diameter 282 mm, width 30 mm. The ring segments were
glued onto the smooth surface which resulted from stripping off,
with the aid of a phenolic resin as an adhesive that was filled
with copper powder of the type FFL from the company Norddeutsche
Affinerie (composition: 50% by weight resin, 50% by weight copper
powder). The joint locations between the segments were made with an
inclination of 60.degree.. The slip-ring body was once again
clamped centrally and stripped off or machined to 280 mm outer
diameter. The slip-ring body was reinstalled in the motor. Apart
from this, the brushes were exchanged with graphite brushes of the
type RE65 from the company SGL CARBON GmbH. The same measurements
as in the comparative example were made. The results are summarized
in the table below.
1 Comparison Example Brush RC53 RE65 Sliding layer steel X10Cr13
isographite 300 Brush wear 0.3 mm/100 h <0.05 mm/100 h Ring wear
not measurable not measurable
[0044] Extensive comparisons between the two configurations with
different operating times and different load produced the result
that the temperature of the brushes in the embodiment in accordance
with the invention was on average 13 to 23.degree. C. lower than
that of the comparison, and the temperature of the slip rings was
on average 12 to 18.degree. C. lower than in the comparison. The
lifetime of the components of the electrical machines, such as the
bearings, for example, can be increased due to the lower
temperature load in the slip-ring configuration in accordance with
the invention.
[0045] In comparison, in the case of a comparatively high running
time (a few hundred hours), a clear eroding of the brushes of the
conventional configuration (comparison) was established, while the
configuration in accordance with the invention did not show any
measurable brush wear of the brushes being used. The wear at the
slip rings was not measurable in the case of this short running
time.
[0046] Furthermore, tests with the comparative slip-ring
configuration and the slip-ring configuration in accordance with
the example were carried out on test stands in order to test the
systems under extreme loads. In this connection, the slip-ring
configurations were mounted on a 710 KW motor and turn-on tests in
the form of run-ups with different rotor currents were carried out,
i.e. a very high performance was demanded of them for a short time.
In the case of the comparative slip-ring configuration in
accordance with the background prior art, these tests were able to
be carried out up to a 3.2-fold loading of the rated current,
something which corresponds to a current density per brush of
approximately 32 A/cm.sup.2. However, in this connection, in the
standard embodiment, both the slip rings and the brush gliding
surfaces showed heavy damage as a result of melting (sparking of
the brushes was observed). The slip-ring configuration according to
the invention in accordance with the Example was able to be carried
out up to an approximately 3.5-fold loading of the rated current,
something which corresponds to a current density over the slip-ring
configuration in accordance with the invention of 40 A/cm.sup.2.
Even at this still higher loading, no damage to the slip rings and
brushes (sparking of the brushes) of the configuration in
accordance with the invention could be observed.
[0047] A fundamental advantage of the slip-ring configuration in
accordance with the invention resides in the fact that the slip
rings can be used almost without exchange. On one hand, it is
possible, if necessary, to only renew the sliding layer, although
without significantly affecting the metallic slip-ring base. On the
other hand, the metallic slip rings used heretofore had to be
renewed over time, because in the case of each required maintenance
of the electric machines for exchanging the bearings, they had to
be stripped off or machined in order to even out the formation of
grooves on the slip ring surface.
* * * * *