Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
CO~POSITE TUBULAR ELEMENTS AND METHODS OF FABRICATION
BACKGROUND OF THE INVENTION
The present in~ention relates generally to fiber
reinforced tubular elements such as vehicle drive shafts
and, in particular, to a graphite reinforced luminum drive
shaft and a method for producing such a drive shaft.
Over the past decade, there has been an ongoing
endeavor by the industry to reduce the weight of vehicles
in order to improve fuel economy. In addition to
downsizing and redesigning vehicles to make the most
efficient use of $he available space, a great deal of
attention has been given to constructing various vehicular
components of lighter weight materials. For example, in
the area of drive shafts, it has been proposed to replace
conventional steel drive shafts with lighter weight
aluminum tubes. However, depending on the length of the
drive shaft, and the maximum speed at which the drive shaft
is to be rotated, vibration problems can arise.
While typically the tubular steel or aluminum drive
shafts are adequate to transmit the torsional forces
involved, there is a tendency for a shaft to "whip" or
resonate mechanically when ~he shaft reaches a certain
vehicle speed, typicalIy referred to as a critical speed.
Consequently, in order to overcome the critical speed
limitations of single long drive shafts, typically multiple
sections of shafts are employed. In these instances,
adjacent individual drive shaft sections are connected to
one another by means of a universal joint assembly which in
turn is supported by a bearing mounting unit affixed to the
vehicle frame.
In order to accommodate a longer drive shaft such that
the universal joint assemblies and the bearing mounting
units can be eliminated, it has been proposed to reinforce
metal tubes with a fiber reinforced sleeve portion to
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increase the axial stiffness of the shaft without
substantially increasing its weight. For example, United
States Patent Nos. 4,131,701; 4,173,670; and 4,214,932 all
disclose fiber composite aluminum drive shafts wherein
aluminum tubes are wrapped with alternating layers of
resin-impregnated woven fiberglass cloth and resin-
impregnated fiber reinforcing sheets. The reinforcing
sheets are comprised of continuous unindirectional graphite
~iber layers, with the graphite fibers arranged at angles
between +5 to +20 with respect to the longitudinal axis
of the tube. Another approach to reinforcing a tubular
metallic drive shaft is disclosed in United States Patent
No. 4,272,971, which discloses a drive shaft wherein the
fiber reinforcing layer is applied to the inside surface of
an aluminum`tube.
While the above-discussed fiber-reinforced drive
shafts have satisfactory operating characteristics, they
have been found difficult and expensive to produce on a
high volume production basis.
SUM~.ARY OF THE INVENTION
The present invention relates to a unique fiber
reinforced aluminum drive shaft, along with a unique method
for producing such drive shafts on a production basis.
The drive shaft of the present invention includes a
cylindrical metal tube having a longitudinal axis which, in
the preferred embodiment of the invention, is typically
constructed of aluminum. An isolation layer of cloth
material surrounds the aluminum tube and is adhered to the
outex surface of tne tube. A reinforcing fiber layer also
surrounds the tube and is adhered to the outer surface of
the isolation layer. In accordance with the present
invention, the reinforcing fiber layer includes a plurality
of individual reinforcing graphite fibers which are
orientated parallel to the longitudinal axis of the tube
and are uniformly positioned about the circumference of the
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tube. ~n the above discussed prior art, the graphitefibers were specifically located non-parallel with the
longitudinal axis. Finally, the drive shaft includes a
covering layer of fiber material surrounding the tube and
adhered to the outer surface of the reinforcin~ fiber
layer.
The present invention includes a unique approach to
producing the fiber reinforced drive shafts on a production
basis. In the method of the presen~ invention, a plurality
of cylindrical metal tubes each having a longitudinal axis
are coupled to one another in an end-to-end relationship by
a plurality of joining plastic plug members to form a
longitudinally extending series of metal tubes. The series
of metal tubes are fed along a longitudinal path through an
apparatus for applying the individual layers of the
composite fiber sleeve to the tube.
Initially, the isolation layer of cloth material is
applied around the outer surface of the tube. Next, the
plurality of individual reinforcing fibers are applied
about the circumference of the tube such that the
individual reinforcing fibers are parallel to the
longitudinal axis of the tube~. Next, the covering layer
of fiber material is applied around the outer surface of
the reinforcing fiber layer.
While the individual layers are being applied to the
tube, a vinylester liquid resin material is applied ~o
saturate the individual layers, and the drive shaft having
the saturated layers applied thereto is then passed through
a heated forming die wherein the liquid resin is cured to
firmly adhere the individual layers to the series of tubes.
As the series of tubes having the cured composite sleeve
thereon exits the apparatus, the tubes are severed at each
of the joining plugs to produce a plurality of individual
fiber reinforced drive shafts. In some instances, wherein
a connecting member such as a yoke portion or a splined
shaft is to be welded to the end of the drive shafts, it
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has been found desirable to strip a selected end portion of
the composite reinforcing layer from the drive shaft to
prevent heat damage to the end of the composite sleeve
during the welding operation.
The present invention also concerns alternate methods
of manufacturing the drive shafts.
BRIEF DESCRIPTION OF THE DRA~JINGS
The above, as well as other advan~ages of the present
invention, will become readily apparent to one skilled in
the art from the following detailed description of the
preferred embodiments of the invention when considered in
light of the accompanying drawings, in which:
Fig. 1 is a side elevational view of a fiber
reinforced composite tubular element of the present
invention, shown for use as a drive shaft;
Fig. 2 is a fragmentary sectional view taken along
line 2-2 in Fig. 1 and showing ~he individual layers which
constitute the preferred embodiment of the fiber composite
sleeve;
Fig. 3 is a schematic diagram showing one method of
fabricating the fiber composite tubular element of the
invention on a continuous basis wherein the fiber composite
sleeve is formed and cured about a series of individual
metal tubes temporarily joined together and moving in a
longitudinal path;
Fig. 4 is a side elevational view of a composite fiber
reinforced tubular element produced according t~ the method
schematically illustrated in Fig. 3;
Fiq. 5 is a schematic drawing which illustrates an
alternate method of assembly of the drive shaft wherein
individual previously formed and cured fiber composite
sleeves are slipped over and adhesively secured to an
associated metal tube; and
Fig. 6 is a schematic drawing which illustrates a
further alternate method of manufacture wherein a preformed
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and uncured, resin-saturated fiber reinforcing sleeve is
slipped over a metal tube member and subsequently cured
thereon.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Fig. 1, there is shown a drive shaft
10 which utilizes a composite tubular element embodying the
features of the present invention. The drive shaft 10
incl~des an outer composite fiber reinforcing sleeve 12
which surrounds and is attached to the exterior of a
cylindrical metal tube 14. As illustrated, first and
second connecting members 16 and 18, which are shown as
yoke portions, are connected to opposite ends of the metal
tube 14 for coupling the drive shaft between a drive member
~not shown) and a driven member (not shown). While the
connecting members are shown as yoke portions for
connection to an associated universal joint assembly (not
shown), it will be appreciated that other types of
connecting members such as, for example, a splined shaft
~o end can be used.
The connecting members 16 and 18 are typically secured
to the ends of the metal tube 14 by a welding operation.
To prevent heat damage to the composite sleeve 12 when the
connecting members are attached, the ends of the
reinforcing sleeve 12 are spaced inwardly from the ends of
the metal tube 14 to provide exposed metal end portions 20
and 22. As will appear more fully below, in the preferred
method of manufacture, the reinforcing sleeve 12 is
initially formed along the entire length of the metal tube
14 and is subsequently stripped from the end portions 20
and 22 by severing it circumferentially with a saw, and
peeling it off. In other methods of manufacture, the
reinforcing sleeve 12 is formed so that it initially does
not cover end portions 20 and 22.
Turning now to Fig. 2, there is shown a cross-section
through the tube 14 and the preferred embodiment of the
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composite reinforcing sleeve 12. Typically, the metal tube
14 is a cylindrical aluminum tube fabricated in a
conventional manner. The length, diameter, and wall
thickness of the tube, along with the particular aluminum
alloy from which the tube is formed, may vary from
application to application, depending on the particular
power transmission requirements of the drive shaft. In any
event, the use of the composite reinforcing sleeve 12
having the specific construction of the present invention
has been found to sufficiently increase the axial stiffness
of the aluminum tube such that weight of the tube can be
substantially reduced as compared with a ~ubular aluminum
drive shaft without the reinforcing sleeve.
The composite reinforcing sleeve 12 basically consists
of three sections: an isolation layer 32, a fiber
reinforcing layer 34, and a covering layer 36. As will be
discussed, in the preferred method of manufacture, the
individual layers of the sleeve 12 are bonded to one
another and the tube by a vinylester resin.
The isolation layer 32 includes individual layers 32a,
32b, and 32c. The first isolation layer 32a is composed of
a plurality of longitudinally extending threads of string
material equally spaced about the circumference of the
tube. This layer is not essential to the functioning of
the invention but, as will be discussed, is provided as a
visual indicator to avoid contact of a saw blade (not
shown) with the metal tube 14 when striping the end
portions of ~he reinforcing sleeve 12 as previously
described. In the preferred embodiment of the drive shaft,
the lay~r 32a consists of eight longitudinally extending
polyester strings equally spaced about the circumerence of
the tube.
The second isolation layer 32b is composed of
individual strips of a thin screen-like cloth material
which extend longitudinally and have overlapping lateral
edge portions to completely surround the tube. This layer
functions to isolate the fiber reinforcing layer 34, which
is typically graphite, from the aluminum tube 14, since it
has been found that direct contact between graphite and
aluminum results in undesirable electrolytic corrosion.
The exact width of the individual strips will be dependent
on the number of strips utilized, along with the outside
diameter of the tube. While the number of strips of cloth
material which are utilized to surround the tube can vary
from application to application, in the preferred
embodiment, four individual strips of cloth material are
utilized.
The third isolation layer 32c is similar to the first
layer 32a, and is comprised of a plurality of
longitudinally disposed threads of polyester string
uniformally spaced about the circumference of the tube. In
the preferred embodiment, eight threads are used. Again,
this is not an essential layer, but is provided to form and
hold the strips of cloth material in place on the metal
tube 14. It will be appreciated that, while the isolation
string layers 32a and 32c are shown in Fig. 2 as spacing
the isolation cloth layer 32b from both the tube 14 and the
fiber reinforcing layer 34, there is actually contact
between the layer 32b and the tube 14 and between the layer
32b and the reinforcing layer 34 in the regions between the
spaced apart longitudinally extending threads.
The fiber reinforcing layer 34 is typically comprised
of graphite and includes a plurality of individual and
independent reinforcing fiber strands or "tows" which, in
accordance with the present invention, are preferably
located parallel to the longitudinal axis of the tube, and
uniformly positioned about the isolation layer 32. Each
tow consists of a predetermined number of longitudinally
disposed, individual graphite fibers. The exact number of
tows of graphite which are utilized will depend on the
number of individual fibers located in each tow and the
overall amount of reinforcing which is desired. In one
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preferred embodiment, ~15 longitudinally disposed tows of
graphite fibers are utilized, with each tow being composed
of 36,000 individual fibers of graphite.
The covering or protective layer 36 includes
individual layers 36a, 36b, and 36c, and functions as a
means for retaining the longitudinal graphite strands of
the layer 34 adjacent the metal tube 14. The first
covering layer 36a is comprised of a circumferential
wrapping of fiberglass strands. The number of
circumferential wrappings per given length of the tube
will be dependent on the amount of graphite which has been
applied to the tube, along with the number of individual
glass fibers included in each strand~ In the preferred
embodiment, each strand is composed of 1,800 continuous
glass filaments, and is wrapped about the tube to produce
twenty wraps per longitudinal inch.
The second covering layer 36b is another
circumferential wrapping, similar to that of the first
covering layer 36a, but with polyester string, of a type
similar to that used in the first and third isolation
layers 32a and 32c. It should be noted that the layers
36a and 36b, although illustrated as overlying layers, do
not visually form separate layers, since the strands of
one wrapping will typically fall in between the strands of
the other, so that layers 36a and 36b appear visually as a
single layer.
The third covering layer 36c, which is the outermost
layer of the sleeve 12, is applied similarly to and is
identical in material characteristics to that of the
isolation layer 32b, and provides an outer cloth covering
which produces a smooth outer surface on the drive shaft.
Turning now to Fig. 3, there is shown schematically
an apparatus 40 for forming composite tubular elements of
the type illustrated in Fig. 2 on a continuous basis. As
shown in Fig. 3, a plurality of metal tubes, shown as l~a,
14b, 14c, 14d, are interconnected in an end-to-end
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relationship by a plurality of plug members 42. The plug
members ~2, which typically are constructed of a plastic
material, are shown as double-ended, with a centrally
located protruding annular flange portion 44 having an
outer diameter greater than the outside diameter of the
tubes. As will be discussed, the protruding flange portion
44, after each layer of the composite sleeve has been
applied and cured on the tubes, provides an annular raised
portion in the sleeve which functions as a visual reference
to define the specific location at which the tubes must
sawed apart.
The apparatus 40 includes a plurality of individual
application stations which, as discussed in more detail
below, are utilized to apply the various materials required
to form the composite fiber sleeve on the aluminum tube.
The apparatus also includes a pair of pulling rollers 46
and 48 for pulling the longitudinally extendin~ series of
tubes through the apparatus along a longitudinally
extending path at a predetermined speed.
As shown in Fig. 3, at first station 50, the first
isolation layer 32a of longitudinally extending,
circumferentially spaced apart string is applied. String
from a plurality of rolls 52 passes through a guide means
54 and an application means 56~ which may be pulleys or the
like, into place on the tube 14. Although four rolls are
shown, eight rolls are used in the preferred embodiment of
the invention. Also, while shown as tapered rolls or
spools, the spools used are preferably of the center-feed
type, so that the last turn is on the outside, and
additional rolls can be connected without interrupting the
process.
Then, at a second station 58, the second isolation
layer 32b of strips of cloth material is applied. As
shown, the layer 32b is applied in four segments. At the
second station 58, the material of the second layer 32b is
applied from rolls 60 and 62. While not shown in the
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drawings, the rolls 62 are preferably located along a line
which is perpendicular to the line along which the rolls 60
are located. The individual strips are urged into
conformance with the shape of tube 14 by a conical
preformer 64.
Next, at a third station 66, the third isolation layer
32c of string is applied to form the cloth layer 32b around
the tube 14. As with the first station 50, the string from
a plurality of rolls 68 passes through a guide means 70 and
an application means 72 into position around the tube 14.
At a fourth station 74, approximately half of the
fiber reinforcing layer 34 is applied. A set of rolls 76,
although shown as six in number for simplicity, actually
number approximately half of the total number of graphite
tows to be applied. The tows supplied from the rolls 76
pass through individual apertures in a forming ring 78 into
conformance with the shape of the tube 14. Then, at a
fifth station 80, a resin mixture is supplied from a tank
82 through a line 84 to a dispensing end 86, from which it
l 20 coats the first half of the fiber reinforcing layer 34 and
the underlying isolation layer 32.
The resin mix contained in the tank 82 is~preferably a
vinylester resin mix of the type available under the trade
name Derakane. A suitable resin mixture is available from
Dow Chemical of Joliet, Illinois under part number 411-35.
In addition, any conventional resin mixture may be used,
although it should be selected from among those that remain
flexible after curing. Although not shown in the drawings,
a catalyst or hardener can be mixed with the resin mixture
shortly before application of the mixture to the partially
formed sleeve~
At a sixth station 88, the remainder ~f the desired
number of graphite tows are applied from a set of rolls 90
through a forming ring 92 into conformance with the tube 14
3S and, at a seventh station 94, are again coated with the
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resin mixture from the ~ank 82, through a line 96 and a
dispensing end 98.
An eighth station 100 and a ninth station 102 include
a spinner head 104 having rolls 106 and 108 for
circumferentially wrapping covering layers 36a and 36b
respectively. Of course, more than one such spinner head
104 may be provided, and more than a single roll can be
used to apply the layers 36a and 36b. As illustrated, the
head 104 contains the fiberglass material of the first
covering layer 36a on the roll 106 and the polyester string
material of the second covering layer 36b on the roll 108.
As previously described, the layers 36a and 36b are
circumferential wrappings which, in the preferred
embodiment, are applied at a rate of approximately twenty
per inch. At a tenth station 110, the resin mix from the
tank 82 is again applied, through a line 112 and a
dispensing end 114.
Then, at an eleventh station 116, the final layer, the
third covering layer 36c, is applied. A set of rolls 118
contain cloth material identical to that contained by the
rolls 60, which material is urged into conformance with the
tube 14 by a conical performer 120. A set of rolls 122
contain cloth material identical to that contained on the
rolls 62, which material is urged into conformance with the
tube 14 by a conical entrance 124 of a heated forming die
126. ~s was ~he case with the rolls 60 and 62, the rolls
118 and 122 are preferably located along lines
perpendicular to one another. The forming die 126 not only
forms the surface of the continuous drive shaft assembly,
but also provides appropriate heat input to effect a rapid
cure of the resin mixture as the series of drive shafts are
pulled through the apparatus 40.
The continuous chain of composite tubular elements 10
is then cut apart at protruding flange portions 48, and
stripped in a manner as described above to form exposed
metal end portions 20 and 22, to which appropriate
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connecting members can be attached by conventional welding.
The composite tubular element produced by the method of
Fig. 3 is shown in Fig. 4 prior to the attachment of the
connecting members.
It will be appreciated that other methods can be
utilized to produce a fiber-reinforced aluminum drive shaft
embodying the principal features of the present invention.
Fox example, Fig. 5 schematically illustrates a method
wherein a stiff, performed, precut and previously cured
reinforcing sleeve 130 of a predetermined length is
provided, with an internal diameter slightly larger than
the external diameter of the metal tube 14. As illustrated
in Fig. 5, the reinforcing sleeve 130 is slipped into
position over a metal tube 132, to which a layer of glue
134 has been applied.
Various types of glues or bonding agents may be used
for the glue 134. One such structural adhesive which can
be used is commercially known as Metalbond 1133, and is an
elastomer modified epoxy material sold by the Narmco
division of Celanese Corp, New York, New York. Such
adhesives may be applied by brushing or spraying.
Fig. 6 illustrates schematically a further alternate
method of making a composite tubular element according to
the invention, in which a fiber-reinforced sleeve 140
saturated with uncured resin, but made to appropriate
length, is slipped over a metal tube 142 and is
subsequently cured to bond the sleeve 140 to the metal tube
142. If desired, an appropriate structural adhesive may be
used to assist in bonding the sleeve to the tube. In Fig.
6, the fiber-reinforced sleeve 140 is formed on a mandrel
148, and is saturated with resin from a tank 150 through a
line 152 and a dispensing end 15g, or by any other
convenient means, such as brushing or spraying. As
illustrated, the reinforcing sleeve 140 includes three
layers, an inner layer of isolation material applied by
rolls 156, an intermediate layer of longitudinally
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extending reinforcing fiber applied by rolls 158, and an
outer layer of covering6material applied by rolls 160~
As shown in Fig.-~, there is a supply of metal tubes
142, onto each of which a reinforcing sleeve member 140 is
placed by sliding it off mandrel 148 and onto the tube 142,
wherein it is urged into position by applying
circumferentially forces 162 in any convenient manner, such
as by drawing a forming die over it. Then, the reinforcing
member 140 is cured in place on the metal tube 142, either
by the passage of time without application of heat, or by
the application of heat in any convenient manner.
The precise embodiment of the reinforcing sleeve used
in the methods illustrated in Figs. 5 and 6 may differ from
the construction shown in Fig. 2 and produced by the method
of Fig. 3. For example, the first and third isolation
layers 32a and 32c of Fig. 2, which provide a visual
indicia for stripping the ends of the sleeve in the method
of Fig. 3, would not be required in the methods of Figs. 5
and 6, since the reinforcing sleeves are formed to length
before application to the metal tube. In addition~ in some
instances, the second isolation layer 32b may also not be
necessary, since the glue used to retain a previously
formed cured or uncured reinforcing sleeve to a metal tube
may by itself provide a suitable isolation layer between
the graphite and the aluminum. Also, the outer most
covering layer 36c of Fig. 2, which is provided to form a
smooth exterior surface is not an absolutely necessity, nor
is the use of two di~ferent materials, shown as covering
layers 36a and 36b to retain the primary reinforcing fiber
layer 34 in place.
In accordance with the provisions of the patent
statutes, the composite tubular element of the present
invention, along with the methods of producing the tubular
element, have been illustrated and described in its
preferred embodiments. However, it will be appreciated
tha~ numerous modifications and variations of the disclosed
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invention will be apparent to one skilled in the art,
including re-arrangement in the ordering of layers and the
addition or omission of layers, and may be made without
departing from the scope of the attached claims.
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