Note: Descriptions are shown in the official language in which they were submitted.
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1 FIELD OF THE 1 VENTION
2 This invention relates to fiber-reinforced coil
3 springs and more particularly this invention relates to
4 improved fiber-reinforced coil springs especially useful
in applications wherein the spring is subjected to only
6 tension or only compression loads.
7 BACKGROUND OF THE_INVENTION
8 The dependence of the automotive industry on
9 oil as a fuel source is wel~ known. Government, industry
and consumer interests, in increasing fuel erficiency of
11 automotive vehicles to offset the escalating costs of such
12 fuels while concomitantly conserving oil resources, has
13 led to increased searches for new light-weight automotive
14 components which will lead to increased vehicle efficiency
One such application for light-weight, high-strength com-
16 posite structures in motor vehicle applications is in coil17 springs for use in suspension systems and in valve lifters
18 and the like.
19 PRIOR ART
In U.S. Patent 2,852,424, a method for producing
21 a reinforced plastic coil spring is described which in-
22 volves pulling a length of glass roving through a liquid23 resin bath into a flexible tube. The tube is then wound
24 helically aro~nd a mandrel and cured thereon. Subsequent-
ly, the mandrel is removed as well as ~he exterior tubing
26 material, thereby providing a solid glass reinforced plas-
27 tic spring in which the glass is aligned substantially at
28 0 with respect to the center line of the spring wire.
29 In U.S. Pa~ent 3,378,426, an apparatus is dis-
closed for producing a glass fiber-reinforced chemical
31 coil by introducing glass fibers and resin into a rotating
32 drum having an endless mold member on the drum so that the
33 glass resin can be superimposed and molded on the drum and
34 separated from the drum during drum rotation.
Another technique for making a helical spring is
36 disclosed in U.S. Patent 3,728,189. As with the preceding
37 techniques, a spring is produced in which the spring wire
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i5 essentially solid and in which the dominant direction
of the glass fibers in the spring wire is substantially
parallel to the center line of the spring wire.
SUMMP.RY OF' THE INVENTI ON
Briefly stated, the present invention contem-
plates a coil spring formed o~ a continuous unidlrectional
fiber-reinforced tubular xesin member in which substan-
tially all of the continuous fibers are oriented substan-
tially at the same predetermined angle of orientation
with respect to the center line of the tubular mem~er
when co~led or helically wound, In ~eneral, the continu-
ous unidixe~tional ~ibers are oriented substantially at an
angle xanging ~rom between 15 to 75 with respect to the
center line of the helically wound tubular member; however,
in a pre~err~d embodiment of the present invention, the
fibers are oriented at ~rom 30 to 60 with respect to the
~enter line of tbe tubular member of the spring. Most
pre~erably, the continuous unidire~tional fibers are
oriented at bet~-een 43 and 47 with re~peat to the
ce~ter line o~ the helically wound tubular member. The
method comprises forming a coil spr ng consisting
essentially of: a helically wound carbon fiber-reinforced
tubular resin member having from about 50 volume 4 to
about 65 volume % of carbon fibers embedded in said resin,
said carbon fibers being continuous unidirectional fibers,
said fibers being oriented at substantially the same pre-
determined angle of orientation with respect to the center
line of said tubular member, the magnitude of said angle
ranging between from 15~ ~o 75 ~nd the directional
orientation o~ sAid $~bers being such that under conditions
o$ use, the shear load on said spring places the ibers in
tension.
~ Th~ pre~ent in~e~tion also contc~plates 2n
i improv~d m~thod o~ prepar~ng a tubulas co~l spr~ng ~rom
a ~iber-rQin~orced sesln sheet material. ~he
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method comprises forminj a fiber-reinforced tubular resin
coil spring having fibers therein oriented at substantially
the same predetermined angle of orientation comprising:
forming a fiber-reinforced tubular resin spring wire having
a flexible tubing in the center of the spring wire, said
spring wire having fibers therein at a predetermined angle
of orientation with respect to the center line of the spring
wire which angle of orientation differs from the pre-
detenmined angle of orientation in the coilspring; helical-
ly wrapping said spring wire around a mandrel
while simultaneously twisting said spring wire 80 a~ to
redirect the orientation of the fiber3 in the spr~ng wire
at a second predetermined an~le of orientation, whereby
they will be in said first predeterm~.ned angle of orientation:
.after wrappin~ said spring wire a,round said mandrel, wrap-
ping sai~ wire and mandrel with an exterior mold member;
inflatin~ sa~d rubber tu~e withln said spring wire, and
thereafter curing said sprin~ wire at elevat~d temperatures;
removing said flexible tubing in said exker~or mold member
after curin~ whereby a fiber-reinforced tubular resin coil
spring i.s obtained.
These and other embodiment~ of the present ln-
vention will become ~pparent upon further reading of the
speci~ication in conjunction with the accompanying draw-
ings.
BRIEF DESCRIP~ION OF THE DRAWINGS
~igure 1 is a side elevation partly cut away
showing the angle o~ orientation o~ the ~iber ln the
fiber-reinforced helical ~pring o~ the present invention.
~igures 2, 3 and ~ illustrate a preliminary
s~ep in the method of the ~nvention whexein oblong blanks
o~ fiber-reinforced sheet mater$al having unidirectional
fibers are cut in a predetermined pattern to be rolled
upon a mandrel to form a tubular member for use in ~orma-
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1 tion of tubular coil springs in accordance with the pre-
2 sent invention.
3 Figure 5 is an isometric drawing partly in per-
4 spective and partly cut away illustrating the technique
of forming a fiber-reinforced resin wire useful in forming
6 the tubular helical spring of the pre~ent invention.
7 Figure 6 is a cross-sectional view of the pre-
8 ferred number of wrappings of fiber-reinforced sheet
;; 9 material around a mandrel when producing a wire for
tubular spring fabrication in accordance with the present
11 invention.
12 Figure 7 is a diagrammatic illustration of the
13 wrapping of a wire around a mandrel to form the spring of
14 the present invention.
Figure 8 is a cross-se~tion along lines 8-8 of
16 Figure 7
17 DETAILED DESCRIPTION OF THE ~NVENTION
18 Referring now to the drawings, it should be noted
19 that like reference characters designate corresponding
parts throughout the several drawings and views.
21 The coil spring 10 of the present invention is
22 formed from a continuous unidirectional fiber-reinforced
23 tubular resin member in which substantially all of the
24 continuous fibers 11 are oriented at the same or substan-
tially the same predetermined angle of orientation, ~,
26 with respect to the center line 12 of the tubular member.
27 In the practice of the present invention, the
28 unidirectional continuous fibers are selected from typical
; 29 fiber-reinforcing materials, such as boron, carbon,
graphite, glass, polyaramids and mixtures thereof. Pre-
31 ferably, however, the fibers are selected from carbon and
32 graphite fibers, and more particularly carbon and graphite
33 fibers having a Youngs modulus of about 32 x 106 psi and
34 a tensile strength of about 400,000 psi or greater.
As indicated herein, the continuous unidirectional
36 fi~ers are embedded in a resin matrix. In general, any
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1 resin may ~e employed although it is preferred that the
2 resin matrix be a thermosetting resin.
3 Suitable thermosetting resin materials include
4 epoxy and polyester resins.
The epoxy resins are polyepoxides, which are
6 well known condensation products Gr compounds containing
7 oxirane rings with compounds containing hydrox~l groups
8 or active hydrogen atoms such as amines, acids and alde-
9 hydes. The most common epoxy resin compounds are those
of epichlorohydrin and bis-phenol and its homologs.
11 The polyester resins are polycondensation pro-
12 ducts of polybasic acids with polyhydric alcohols. Typi-
13 cal polyesters include polyterePhthalates, such as poly-
14 ethylene terephthalate.
The amount of carbon fiber in the resin is gen-
16 erally in the range of from about 50 to about 65 volume %
17 of fibers in the resin matrix, and preferably between
18 about 60 to 65 volume % of fibers in an epoxy resin
19 matrix.
The magnitude and direction of the angle of
21 orientation, 9, of the unidirectional continuous fibers
22 11 in coil spring 10 depends upon a number of factors
23 including the use to which the coil spring 10 is to be
24 put, the pitch of the coil, the directron Ot the pitch
of the coil, the mean spring diameter, the diameter of
26 the tubular member, and the like. Suffice it to say
27 that when the spring is to be used in compression appli-
28 cations such as in automotive suspension systems, the
29 fibers are directionally orient~d so that the shear load
on the spring places the fibers in tension. For appli-
31 cations where the spring is to be stretched, i.e. loaded
32 in tensior., the fibers are oriented so that the shear
33 load on the spring places the fibers in tension. In
34 general, the magnitude of the angle of orientation of the
continuous unidirectional fibers 11 is between 15 to
36 75 and preferably between about 30 and 60 with respect
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1 to the center line of the helically wound tubular member.
2 Most preferably, in springs for automotive suspension sys-
3 tems, the continuous unidirectional fibers will be ori-
4 ented, for example, at between 43~ and 47 with respect
to the center line of the helically wound tubular member.
6 In the practice of the present invention, coil
7 spring 10 is made from sheets of unidirectional carbon
8 or graphite fibers impregnated with a thermosetting resin.
9 A plurality of such sheets of such unidirectional fiber
impregnated resin sheet material is first cut into the
11 sha~e of a ~redetermined Pattern. Tv~icallv, thr~ ~atterns
12 of material go into forming the tubular coil spring of
13 the present invention. Consequently, the description
14 which follows will make specific reference to three
layers or sheets of resin impregnated fibers; however,
16 it should be appreciated that more or less than this
17 number may be employed.
18 Each of the three layers of resin impregnated
19 continuous unidirectional fibers are cut in the shape
generally of a rectangle. As is shown in Figures 2 to
21 4, the length of the rectangle for each of the three
22 layers of resin impregnated fiber sheet material is the
23 same. Indeed, the length of the rectangular sheet
24 material will be at least as long as that required for
formation into a coil spring of the requisite length.
26 Typically the width of each sheet is different. Thus,
27 as can be seen in Figures 2 to 4, the width, Wl, of sheet
28 14 is narrower than the width, W2, of sheet 15 which in
29 turn $s narrower again than the width of sheet 16.
Each sheet 14, 15 and 16 will have continuous
31 unidirectional fibers 11 oriented at a specific angle
32 with respect to the longitudinal axis of the rectangular
33 sheet material.
34 In fabricating the coil spring, the tubular mem-
ber is first formed by successively and circumferentially
36 wrapping the layers of resin impregnated ~ibers 14, 15
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and 16 on a mandrel 17 ha~ing a resilient tubing 18, such
as a rubber tubing, surrounding the mandrel 17. The dia-
3 meter of the mandrel 17 with its resilient tubing 18 is
4 selected to provide the requisite diameter of the tubular
member for the coil spring~ Since the flat patterns 14,
6 15 and 16 are going to be successively wound around the
7 mandrel 17 with its rubber sleeve 18, it is desirable that
8 the widths Wl, W2 and W3 be sufficient to provide at least
9 a single convolution of material around the mandrel having
the preceding layer applied thereto. Thus, Wl of sheet
11 14 desirably is at least sufficiently wide to accommodate
12 at least one complete turn around mandrel 17 and rubber
13 sleeve 18. Sheet 15 has a sufficient width W2 to provide
14 at least one complete turn about the mandrel containing
sheet 14. Similarly, W3 of sheet 16 is sufficient to
16 provide at least one complete turn around the mandrel
17 containing its layers of sheets 14 and 15. Preferably
1~ the width of each sheet is chosen to provide substantially
19 the same number of a plurality of complete turns around
the mandrel.
21 Wrapping of the sheet materials around the man-
22 drel with its rubber sheath is accomplished very simply
23 by placing the mandrel 17 with its rubber sheath 18 along
24 the lengthwise bottom edge of sheet 14 and thereafter
rolling the mandrel and the sheet material in an upwardly
26 direction such as shown by arrow 19 in Figure 5. Each
27 one of the layers is so successively wrapped around the
28 mandrel.
29 After the three layers of sheet material are
wrapped around the rubber sleeve, the steel mandrel 17 is
31 removed, thereby leaving fiber-reinforced tubular resin
32 member having a rubber tubing in the center thereof. This
33 tubular member with its rubber insert constitutes the
34 spring wire used in fabricating the coil spring of the
present invention. This sprina wire 20 is helically
36 wrapped around a mandrel such as mandrel 21 of Figure 7
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1 which has helical grooves 22 in the circumference thereof
2 of the requisite width and depth to accommodate the dia-
3 meter of spring wire 20. The pitch for the helical
4 grooves 22 will depend upon the desired spring pitch.
Similarly, the diameter of the mandrel 21 will depend
6 upon the desired main spring diameter.
7 In any event, spring wire 20 is wrapped in
8 helical fashion around mandrel 21. During wrapping of
9 the spring wire 20 around mandrel 21, sufficient twist
is given so that the fibers 11 in spring wire 20 will
11 all be oriented at the predetermined desired angle 6
12 with respect to the center line of the helically wound
13 tubulax member. The direction and the amount of twist
14 required will depend, of course, on the angle of orien-
tation of the unidixectional fibers in the flat patterns
16 14, 15 and 16 used in forming spring wire 20. Obviously
17 the direction of twist is chosen to provide the desired
18 predetermined fiber oxientation in the coil spring with
19 minimum displacement of the fibers from their orientation
20 in the spring wire to their orientation in the coil.
21 As was indicated with respect to Figures 2, 3
22 and 4, the flat patterns 14, 15 and 16 are each cut so
23 as to have continuous unidirectional fibers 11 which are
24 oriented at specific angles of orientation ~ 2 and ~3,
25 respectively, of the longitudinal or lengthwise axis of
26 the flat pattern. 61, 62 and 63 are chosen such that if
27 sheets 14, 15 and 16 are formed into a suitable wire 20,
28 upon twistlng wire 20 on mandrel 21 the unidirectional
29 continuous fibers in each of the respective layers 14, 15
30 and 16 will be oriented at the desired angle 6 or the
31 helical spring. Thus, for example, in a particularly pre-
32 ferred embodiment of the present invention, coil spring
33 is provided having a unidirectional ~iber-reinforced tubu-
34 lar resin member in which the continuous fibers are ori-
35 ented substantially at 45 with respect to the center
36 line of the helically wound tubular member. In such
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1 instance, the unidirectional fibers 11 of flat sheet 14
2 will have an angle of orientation of 40 with respect to
3 the lengthwise axis of layer 14. The preferred angle of
4 orientation in that instance for fibers 11 of sheet 15
will be 36 with respect to the lengthwise axis of sheet
6 15. Finally, the angle of orientation of fibers 11 in
7 flat sheet 16 will be 33 with respect to the lengthwise
8 axis of sheet 16.
9 As will be xeadily appreciated, the angles ~1~
42 and ~3 will be chosen depending upon the desired angle
11 that the fibers have in the helical coil and the degree
12 of twist that is to be applied during wrapping of the
13 tubular wire in the form of a coil. More specifically,
14 the change in the angle of orientation of the fibers in
each layer of the wire when the spring wire is twisted
16 once per coil is given by the e~uation:
17 ~ = arc tan r/R
18 where: ~ = change in angle;
19 r = radius of the wire;
R = radius of the coil.
21 From the foregoing equation, it can be seen
22 that twisting the wire causes a larger change in the angle
23 of orientation of the fibers in each layer, the larger the
24 distance of that layer in the wire from the center thereof.
For example, assuming a coil radius of 3 inches and a radi-
26 us of .S inches from the center to the outer layer of the
27 spring wire, then the change in the angle of orientation
28 for the fibers in that outer layer from their original
29 position to their final ~osition upon one twist per coil
is 9.5 since ~ = arc tan .5/3 = 9.5. If the radius of
31 the spring wire to some given inner layer is 0.25, then the
32 fibers in the inner layer under the same circumstances will
33 be displaced 4.8 since ~ = arc tan .25/3 - 4.8.
4 Returning to the process of the present inven-
tion, it can be seen, for example, in Figure 7 that top
36 layer 16 of wire 20 has fibers 11 that, prior to twisting,
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1 are oriented at an angle 63 with res~ect to the center
2 line of the wire 20. Hence, the wire 20 is twisted, for
3 example, in the direction shown by arrow 25 as it is
4 wrap~ed upon mandrel 21. All of the fibers 11 throughout
the wire 20 are substantially oriented at the preferred
6 angle ~.
7 After wrapping the wire 20 around the mandrel,
8 the wire 20 can be held in place by any suitable mold
9 means well known in the art. For example, the wire can
be held in place on the mandrel 21 by an appropriately
11 shaped tool or by wrapping of cellulose acetate tape or
12 sheet material(not shown) which serves in effect as a
13 mold. The rubber tube inside the spring wire 20 is pres-
14 surized in an amount sufficient to facilitate the resin
to flow and to compact during curing. Generally, the
16 pressure will range between 35 to 85 psi and preferably
17 about 65 to 75 psi. The entire assembly is then heated
18 so as to cure ~he resin. The temperature at which the
19 assembly is heated, of course, depends upon a number of
factors, including the resin which is used to impregnate
21 the fibers. These temperatures are well known. Typi-
22 cally, for epoxy resin impregnated fibers, the tempera-
23 ture will be in the range of from about 100C to about
24 180C, and preferably at about 120C. Similarly, the
time for heating will depend on the curing temperatures
26 as well as the resin employed.
27 After heating the assembly, the assembly is next
28 allowed to cool to room temperature, and the external
29 wrapping of cellulose acetate tape and rubber tubing are
removed as well as mandrel 21. The end edges 31 and 32
1 of the wire may be chamfered, if desired, by cutting.
32 To further illustrate the present invention,
33 reference is now made herein to a typical suspension
coil spring for one mode of application. In such an
application, the spring 10 consists of six coils pro-
36 viding a free spring height of 18 inches. The coil
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1 spring 20 will have a spring diameter of 6.15 inches.
2 The tubular member comprising the helical coil 20 will
3 have an outer diameter of one inch and an inner diameter
4 of one-half inch. The angle of orientation ~ of the
continuous carbon fibers will be in the range of from
6 about 43 to 47 and preferably 45.
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