Technical Field
[0001] The present invention relates generally to slip ring and wire brush assemblies and,
more particularly, to the use of noble metal materials forming a surface layer of
a wire brush.
Background Art
[0002] Slip ring assemblies are well known in the prior art and generally comprise a rotating
conductive ring in contact with a non-rotating brush mounted in a suitable brush holder.
The brush is often a monolithic wire element comprising a gold alloy brush wire or
a gold plated wire running against a gold plated ring. Gold or other noble metals
are highly preferred since it has been known for some time that to achieve performance
over long periods of time (years) with contact resistance variations in the low milliohm
levels, noble metals and noble metal alloys must be used in the electrical contact
zone rather than base metals.
[0003] Gold alloy brush wires can be expected to operate for long periods of time with minimal
contact resistance variations. However, gold alloy wires are relatively expensive
since the gold content is high.
[0004] Gold plated wires are also known and tend to be less expensive than gold alloy wires
since the gold plating covers a less expensive base metal. However, the gold plating
is susceptible to cracking, especially when the gold plated brush wire is bent to
a particular radius of curvature for certain types of applications. Additionally,
from a manufacturing standpoint, the manufacture of plated wires require a more substantial
capital investment in view of the need for plating baths and equipment, and also create
environmental disposal problems and additional related expense.
Disclosure of the Invention
[0005] It is accordingly an object of the present invention to improve the structural integrity
of brush wires having noble metal coverings.
[0006] Another object is to improve wear characteristics of noble metal covered brush wires.
[0007] Yet another object is to improve the structural integrity and wear characteristics
of noble metal covered brush wires relative to platted wires while lowering costs
relative to noble metal alloy wires.
[0008] This present invention relates to a slip ring and brush assembly including a slip
ring in sliding contact with a brush wire. In a broad sense, the invention relates
to an improvement wherein the brush wire includes a first material forming at least
part of a wire core and a second material forming an outer layer metallurgically bonded
to the first material.
[0009] In the preferred embodiment, the invention relates to a slip ring and brush assembly
for transmitting electrical energy between a conductor and a shaft. One of the conductor
and shaft is stationary while the other is rotating. The assembly comprises a noble
metal covered slip ring surface formed on the shaft and at least one brush wire in
contact with the noble metal covered slip ring surface and coupled to the conductor.
In accordance with the invention, the brush wire includes a conductive core, an optional
metal barrier layer covering the core, and a noble metal surface layer metallurgically
bonded to one of the barrier layer and core.
[0010] The feature of metallurgically bonding the noble metal surface layer to the underlying
core, either directly or through an intermediate metallurgically bonded barrier layer,
advantageously results in better brush forming by providing intimate attachment conditions
at the atomic level that minimizes cracking or peeling of the precious metal surface
relative to prior art plating techniques. Brush wires formed with the metallurgically
bonded noble metal surface also tend to be less expensive than gold or noble metal
alloy wire by reducing the gold or noble metal content while retaining the same precious
metal contact at the ring/brush interface for low noise and wear.
[0011] The brush wire according to the present invention utilizes an optional metal barrier
layer to prevent diffusion between the conductor core and noble surface layer depending
on the selection of materials between which diffusion may be a problem. In situations
where a noble metal barrier layer is utilized, the barrier layer is preferably metallurgically
bonded to the conductor core and the noble metal surface layer is in turn metallurgically
bonded to the barrier layer.
[0012] In one preferred embodiment according to the invention, the brush wire comprises
a copper center core, preferably Beryllium copper, with a nickel clad overlay barrier
followed by a gold cladding on the outer surface of the nickel barrier.
[0013] Still other objects and advantages of the present invention will become readily apparent
to those skilled in this art from the following detailed description, wherein only
the preferred embodiments of the invention are shown and described, simply by way
of illustration of the best mode contemplated of carrying out the invention. As will
be realized, the invention is capable of other and different embodiments, and its
several details are capable of modifications in various obvious respects, all without
departing from the invention. Accordingly, the drawing and description are to be regarded
as illustrative in nature, and not as restrictive.
Brief Description of Drawings
[0014]
Fig. 1 is a detailed longitudinal cross-section of an exemplary brush assembly utilizing
novel brush wires constructed in accordance with the present invention;
Fig. 2 is an exploded perspective view taken along the line 2-2 of Fig. 1 of one of
the brush wires;
Fig. 3 is a side elevational view of one of the brush wires; and
Fig. 4 is a detailed side view of a multifilament brush assembly.
Best Mode for Carrying out the Invention
[0015] FIG 1. is an exemplary illustration of a slip ring and brush assembly, generally
designated with reference numeral 10, in which a series of brush wires 12 are in sliding
contact with a slip ring surface 14 formed on a rotating slip ring assembly 15. The
respective surfaces of the brush wires 12 and slip ring surface 14 are preferably
gold covered to achieve good wear characteristics, low electrical resistance and increase
current density as is well known. However, in accordance with the unique features
set forth below, each brush wire 12 includes a surface layer 16 in the form of a gold
cladding layer 16a that is metallurgically bonded in the preferred embodiment to an
underlying conductive core 16b, either directly or through a diffusion layer 16c (see
FIG. 2) that in turn is metallurgically bonded to the core. In this manner, the advantages
of gold-on-gold low contact resistance are achieved while avoiding either the higher
likelihood of fatigue and failure problems associated with gold plating, or the increased
costs of gold alloy wire with their higher gold content.
[0016] Assembly 10 is representative of a large class of brush wire and slip ring assemblies
in which the rotating conductive slip ring assembly 15 is contacted by a non-rotating
brush 12 mounted in a suitable brush holder to provide flow paths for electrical power
or signal. In FIG. 1, assembly 10 comprises a cylindrical housing 20 in which a pair
of bearings 22 and 24 are disposed at opposite ends of slip ring assembly 15 to rotatably
support one end of a rotating shaft 28. A series of brush wires 12 are disposed in
axially spaced location in respective contact with annular grooves 30 formed along
the length of the slip ring assembly 15.
[0017] More specifically, upper and lower sets of axially sets 12a and 12b of axially spaced
identical brush wires 12 are mounted to respective upper and lower brush blocks 32
and 34 that provide for proper wire positioning in sliding or rotating contact with
the slip ring assembly grooves 30. As best depicted in Fig. 1, each brush block assembly
32 and 34 extends the length of the slip ring assembly 15 and has opposite ends in
respective contact with bearings 22 and 24 to properly position the bearings within
the assembly 10. The brush blocks 32 and 34 are also used for positioning and locating
the lead wires 36, and provide lead exits as known in the art. The lead wires 36 are
retained in position in relation to the brush block assemblies 32, 34 by utilizing
a potting material 38 disposed between the outer surface of each brush block and the
inner surface wall of the housing 20. A retainer ring 40 disposed in a recessed proximal
end of the housing 20 is used to axially fix the brush block assemblies 32, 34 relative
to the rotating shaft 28 while an end cap 42 closes off the distal end of the assembly
10 through which the lead wires 36 extend.
[0018] The foregoing construction of assembly 10 is conventional with the exception of the
composition of brush wires 12. As best depicted in Fig. 2, each brush wire 12 in the
preferred embodiment includes a surface layer 16 in the form of a cladding layer 16a
that is metallurgically bonded to an underlying conductive core 16b preferably through
a diffusion layer 16c. The cladding layer 16a is preferably made of a noble material,
such as gold. The feature of metallurgically bonding the outer layer 16a either to
the underlying core 16b or diffusion layer 16c provides much better attachment conditions
than previously achieved with gold or noble metal plating due to the tendency of plated
materials to wear faster as a result of the inferior attachment conditions between
the plated layer and substrate inherent in plating technology. This inherent disadvantage
of plating is particularly noticeable and disadvantageous in products relying upon
one or more brush wires in sliding or rotating contact with an associated slip ring
assembly.
[0019] Brush wires 12 constructed in accordance with the unique features of the present
invention tend to offer similar performance (i.e. in terms of wear rates and longevity)
provided by high gold content and therefore higher priced gold alloy brush wires but
without the concomitant costs. The noble metal clad brush wire 12 of the invention
also offers the ability to provide better conductivity than gold alloy wire of similar
dimension by being bonded to a center core material 16b selected to have better conductivity
then a pure gold alloy. The ability to bond the cladding layer 16a to a center core
16b of a different material enables the resulting brush wire 12 to have superior mechanical
properties in relation to gold alloy wires depending on the selection of the center
core material.
[0020] The feature of using noble metal clad wires also offer better formability as compared
to plated wires as a result of superior bonding attachment provided by metallurgical
bonding relative to plating. This improved formability is evidenced by fewer incidences
of cracking or peeling of the surface layer 16a which is particularly useful when
the brush wire is bent on a tight radius. The noble metal clad wires of the invention
have particularly advantageous benefits when used in brush wires having, for example,
a horse shoe shape of the type depicted in Fig. 3 as is used in the assembly 10 of
the preferred embodiment.
[0021] The invention is not limited to the use of gold but is intended to cover other noble
metals. The invention is also applicable to brush wires used with sliding or rotating
contacts in which a surface material forming an outer layer is metallurgically bonded
to a core material, with or without an intermediate cladding layer, so that the benefits
of metallurgical bonding as described above may be realized that would otherwise not
be realized by attachment of such surface material with plating techniques.
[0022] The invention is applicable to the use of both monofilament and multifilament materials
forming the individual brush wires and brush wire assemblies.
[0023] In the preferred embodiment, each wire 12 is formed with a gold outer layer 16a that
is metallurgically bonded to the diffusion layer 16c (e.g. Nickel) in turn metallurgically
bonded to the core 16b (e.g. Beryllium copper). Under certain circumstances, depending
on the selection of materials forming the outer cladding layer 16a and core 16b, a
diffusion layer 16c is unnecessary in which case the outer layer is metallurgically
bonded to the core.
[0024] Figure 4 is a detailed side view of a multifilament brush assembly 100 that may comprise
a plurality of filaments 102 which made be in the 1 to 25 mil size and which are held
in a unitary relationship by means of a collar 104. The collar 104 may comprise the
end portion of a wire insulation, or maybe a separate tube element specifically designed
to hold the fibers 102 in a selectively shaped bundle. As shown, the fibers 102 extend
from the collar 104 a sufficient distance to enable them to be in tangential contact
with the slip ring surface, as well know (see e.g. U.S. Patent No. 4,398,113).
[0025] In accordance with the invention, each fiber 102 is constructed in a manner similar
to that described above in connection with brush wire 12. That is, each fiber 102
is preferably in the form of a cladding layer that is metallurgically bonded to an
underlying conductive core preferably through a diffusion layer. The cladding layer
is preferably made of a noble material, such as gold. As in the case of brush wire
12, the feature of metallurgically bonding the outer layer either to the underlying
core or to a diffusion layer (in turn metallurgically bonded to the core) provides
much better attachment conditions than previously achieved with gold or noble metal
plating as described above.
[0026] It will be readily seen by one of ordinary skill in the art that the present invention
fulfills all of the objects set forth above. After reading the foregoing specification,
one of ordinary skill will be able to effect various changes, substitutions of equivalents
and various other aspects of the invention as broadly disclosed herein. It is therefore
intended that the protection granted hereon be limited only by the definition contained
in the appended claims and equivalents thereof.
1. A slip ring and brush assembly for transmitting electrical energy between a conductor
and a shaft, one of said conductor and shaft being stationary and the other of said
conductor and shaft being a rotating structure, the assembly comprising:
a noble metal covered slip ring surface formed on the shaft and at least one brush
wire in contact with said noble metal covered slip ring surface and coupled to the
stationary conductor, wherein said at least one brush wire includes a conductive core,
an optional metal barrier layer covering the core, and a noble metal surface layer
metallurgically bonded to one of said barrier layer and core.
2. The slip ring and brush assembly of claim 1, further comprising said metal barrier
layer being formed of a material preventing diffusion between said conductive core
and said noble surface layer.
3. The slip ring and brush assembly of claim 2, wherein said metal barrier layer is metallurgically
bonded to said conductor core.
4. The slip ring and brush assembly of claim 2, wherein said conductive core is copper,
said barrier layer is nickel and said noble metal surface layer is gold.
5. The slip ring and brush assembly of claim 1, wherein said brush wire is smoothly curved
along at least a portion of the length thereof.
6. The slip ring and brush assembly of claim 1, wherein said brush wire is drawn to a
predetermined size.
7. The slip ring and brush assembly of claim 6, wherein said brush wire is formed without
any heat treatment after drawing.
8. The slip ring and brush assembly of claim 1, wherein said brush wire is a single monofilament
wire.
9. The slip ring and brush assembly of claim 1, wherein said brush wire includes a bundle
of filaments each having said conductive core, said optional metal barrier layer covering
the core, and said noble metal surface layer metallurgically bonded to one of said
barrier layer and core.
10. The slip ring and brush assembly of claim 1, wherein said slip ring surface is plated.
11. The slip ring and brush assembly of claim 1, wherein said slip ring surface is metallurgically
bonded or plated to an underlying surface.
12. The slip ring and brush assembly of claim 1, wherein said conductive core is a beryllium
copper center core, said barrier layer is a nickel clad barrier layer, and said noble
metal surface layer is a gold cladding layer.
13. The slip ring and brush wire assembly of claim 12, wherein the diameter of the beryllium
copper center core approximately is 0.007 inch with a nickel clad barrier of about
75-150 micro inch and a gold cladding of approximately 100-500 micro inch on the outer
surface of said nickel barrier.
14. In a slip ring and brush assembly including a slip ring in sliding contact with a
brush wire, the improvement wherein said brush wire includes a first material forming
at least part of a core and a second material forming an outer layer metallurgically
bonded to said first material.