U.S. patent application number 09/771918 was filed with the patent office on 2002-08-01 for composite bow mono-leaf spring.
Invention is credited to Greco, Giovanni.
Application Number | 20020101012 09/771918 |
Document ID | / |
Family ID | 25093329 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020101012 |
Kind Code |
A1 |
Greco, Giovanni |
August 1, 2002 |
COMPOSITE BOW MONO-LEAF SPRING
Abstract
A fiberglass composite monoleaf bow spring for use in a vehicle
chassis system capable of multi-linear response when compressed.
The fiberglass composite monoleaf bow spring extends longitudinally
below a vehicle frame and is secured at each end of the vehicle
frame typically using a pair of pinned end attachments and is
secured in the middle to an axle. The spring has a central upwardly
curved region introduced between two downwardly curved regions that
are introduced between two more upwardly curved regions. The spring
can be made using either a pre-preg process or three-dimensional
weaving process. By varying the curvature either the upwardly
curved regions or downwardly curved regions, or by varying the
length and width of the bow spring, the rate of displacement along
each portion of the multi-linear deflection response curve may be
controlled.
Inventors: |
Greco, Giovanni; (Canton,
MI) |
Correspondence
Address: |
Steven W. Hays
Artz & Artz, PC
Suite 250
28333 Telegraph Road
Southfield
MI
48034
US
|
Family ID: |
25093329 |
Appl. No.: |
09/771918 |
Filed: |
January 29, 2001 |
Current U.S.
Class: |
267/36.1 |
Current CPC
Class: |
F16F 2224/0241 20130101;
F16F 1/185 20130101 |
Class at
Publication: |
267/36.1 |
International
Class: |
F16F 001/18 |
Claims
What is claimed is:
1. A monoleaf bow spring comprising: a central concave region; a
pair of convex regions, one of said pair of convex regions located
adjacent to one side of said central concave region and the other
of said pair of convex regions located adjacent to the other side
of said central concave region; and a pair of outer concave
regions, each of said concave regions having an attachment region,
wherein one of said pair of outer concave regions is located
adjacent to said one of said pair of convex regions and the other
of said pair of outer concave regions is located adjacent to said
other of said pair of convex regions.
2. The monoleaf bow spring of claim 1, wherein the monoleaf bow
spring is symmetrical about a vertical axis running through the
middle of said central concave region.
3. The monoleaf bow spring of claim 1, wherein said central concave
region curves upward at a first angle relative to a horizontal
axis.
4. The monoleaf bow spring of claim 3, wherein said first angle is
between approximately ten degrees and sixty degrees relative to
said horizontal axis.
5. The monoleaf bow spring of claim 1, wherein the monoleaf bow
spring is asymmetrical about a vertical axis running through the
middle of said central concave region.
6. The monoleaf bow spring of claim 1, wherein the monoleaf bow
spring is comprised of a fiberglass composite material.
7. The monoleaf bow spring of claim 1, wherein one of said pair of
convex regions curves downward at a second angle relative to a
second horizontal axis, said second angle being between zero and
forty-five degrees relative to said second horizontal axis; wherein
the other of said pair of convex regions curves downward at a third
angle relative to a third horizontal axis, said third angle being
between zero and forty-five degrees relative to said third
horizontal axis; wherein one of said pair of outer concave regions
curves upward at a fourth angle relative to a fourth horizontal
axis, said fourth angle being between ten and eighty degrees
relative to said fourth horizontal axis; and wherein the other of
said pair of outer concave regions curves upward at a fifth angle
relative to a fifth horizontal axis, said fifth angle being between
ten and eighty degrees relative to said fifth horizontal axis.
8. The monoleaf bow spring of claim 1, wherein said outer concave
regions each have an integral pinned end attachment for securing
the monoleaf spring to a vehicle frame of a vehicle chassis
system.
9. The monoleaf bow spring of claim 9, wherein each of said an
integral pinned end attachments comprises a molded-in pinned end
attachment.
10. The monoleaf bow spring of claim 1, wherein said monoleaf
spring achieves a multi-linear deflection response when compressed
under a load demand.
11. A method for making a composite monoleaf bow spring for use in
a chassis system, the method comprising the steps of: three
dimensional weaving a plurality of glass fibers into a preform;
placing said preform into a mold; adding a first quantity of
curable resin to said preform to form a composite; molding said
composite to a desired shape, said desired shape comprising a
middle upwardly curved region, a pair of downwardly curved regions,
and a second pair of upwardly curved regions, said second pair of
upwardly curved regions each having a pinned end attachment; and
removing said composite from said mold.
12. The method of claim 11, wherein the step of three dimensional
weaving a plurality of glass fibers onto a preform comprises the
step of weft knitting a plurality of E-type glass fibers into a
preform.
13. The method of claim 11, wherein the step of three dimensional
weaving a plurality of glass fibers onto a preform comprises the
step of warp knitting a plurality of E-type glass fibers into a
preform.
14. The method of claim 11, wherein the composite spring having
said desired shape has a multi-linear spring rate when
compressed.
15. The method of claim 11, wherein the step of adding a first
quantity of curable resin to said preform comprises the step of
adding a first quantity of curable epoxy resin to said preform.
16. The method of claim 11 further comprising the step of securing
each end of the composite bow mono-leaf spring to a vehicle frame
and securing said middle upwardly curved region of the composite
bow mono-leaf spring to an axle.
17. The method of claim 16, wherein the step of securing each end
of the composite bow mono-leaf spring to a vehicle frame comprises
the steps of: comolding a pinned end attachment into each end of
the composite bow monoleaf spring; inserting a bolt through one of
said pinned end attachments and through a front pair of holes in a
vehicle frame to secure one of said pinned end attachment to said
vehicle frame; inserting a second bolt through the other of said
pinned end attachments and through a back pair of holes in said
vehicle frame to secure said other of said pinned end attachments
to said vehicle frame.
18. The method of claim 16, wherein the step of securing each end
of the composite bow mono-leaf spring to a vehicle frame comprises
the steps of: comolding a pinned end attachment into each end of
the composite bow monoleaf spring, each of said pinned end
attachments having a bolt secured within said pinned end
attachment; inserting one of said pinned end attachments through a
front pair of holes in a vehicle frame to secure said one of said
pinned end attachments to said vehicle frame; and inserting the
other of said pinned end attachments through a back pair of holes
in said vehicle frame to secure said other of said pinned
attachments to said vehicle frame.
19. A method for making a composite monoleaf bow spring for use in
a chassis system, the method comprising the steps of: stacking a
plurality of layers of pre-preg tape on top of each other, wherein
each of said plurality of layers is comprises of a plurality of
unidirectional fibers and a quantity of polymer resin; and
compacting and heating said plurality of layers to a first desired
shape, said first desired shape comprising a middle upwardly curved
region, a pair of downwardly curved regions, and a second pair of
upwardly curved regions, said second pair of upwardly curved
regions each having a pinned end attachment.
20. The method of claim 19 further comprising the step of securing
each end of said pinned end attachments to a vehicle frame and
securing said middle upwardly curved region to a vehicle axle.
Description
[0001] support the weight of the car while still allowing
suspension travel (movement).
[0002] Leaf springs are commonly made of flat plates or strips of
spring steel bolted together. Recently, fiberglass has replaced
steel in longitudinal leaf springs because it significantly reduces
weight. Flat plates or strips allow for a sharper dual rate spring
effect than currently available monoleaf springs. However, in
currently available systems, a number of plates must be coupled
together to get a desired bi-linear response.
[0003] It is thus highly desirable to design a monoleaf spring
wherein the material systems used and geometry of the component
will achieve multi-linear response.
SUMMARY OF THE INVENTION
[0004] It is thus an object of the present invention to create a
monoleaf spring for use in a chassis system that achieves
multi-linear response.
[0005] The monoleaf spring is designed having a central curved
region introduced between two oppositely curved outer regions. The
spring preferably is designed wherein each end of the spring has an
open region for coupling with the chassis mount locations.
Alternatively, each end region is coupled to the chassis mount
locations with a separate end piece.
[0006] Other objects and advantages of the present invention will
become apparent upon considering the following detailed description
and appended claims, and upon reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows a rear chassis system having a composite bow
mono-leaf spring according to one preferred embodiment of the
present invention;
[0008] FIG. 2 shows a close-up of the attachment point of the
composite bow mono-leaf spring to the vehicle frame of FIG. 1
rotated 90 degrees relative to FIG. 1;
[0009] FIG. 3 shows the composite bow mono-leaf spring of FIG.
1;
[0010] FIG. 4 is a top view of FIG. 3; and
[0011] FIG. 5 illustrates a normalized force versus displacement
curve for the composite bow-mono leaf spring of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0012] Referring now to FIG. 1, a chassis system 10 having a
composite bow leaf spring 12 according to a preferred embodiment is
depicted. The illustrated adaptation in FIG. 1 is for the rear of a
vehicle. The spring 12 extends longitudinally below the vehicle
frame 16 and has a pinned end attachment 18, 20 at each end of the
spring for attachment to the vehicle frame 16. A close-up view of
the end attachments is described below in FIG. 2. In addition, the
spring 16 is center attached to the axle (not shown) in a manner
that is similar to a conventional Hotchkiss suspension. A pair of
shock absorbers 24 may also be connected to the vehicle frame 16
and the axle in a manner similar to a typical Hotchkiss suspension
to dampen up and down motions.
[0013] Referring to FIG. 2, a close-up of one of the end attachment
points of the spring 12 to the vehicle frame is depicted. The
spring 12 has a pinned end attachment 26 co-molded into each end
that can accept a bolt 38 that is inserted through the pinned end
attachment 26 either before or after the spring 12 is molded. The
vehicle frame has a pair of holes 30, 32 for accepting and securing
the bolt 38. Depending upon the characteristics of the chassis
system containing the spring 12, a shackle (not shown) may be
needed to help secure the spring 12 to the vehicle frame 16.
[0014] As seen in FIGS. 3 and 4, the composite mono-leaf spring 12
generally has a wave-type design that is preferably symmetrical
about a central, vertical axis 50. Extending from a middle upwardly
curved region 52, or central concave region, towards the end
regions 54 outwardly are a pair of downwardly curved regions 56, or
outwardly convex regions, and second pair of upwardly curved
regions 58, or outer concave regions. Depending upon the spring
rate requirements, the amount of curve in the middle upwardly
curved region 52, the downwardly curved regions 56, or the second
pair of upwardly curved regions 58 may be increased or decreased.
Preferably, the middle upwardly curved region 52 curves upward at
an angle between ten and sixty degrees relative to a horizontal
axis perpendicular to center vertical axis 50, with a larger angle
relative to the horizontal axis corresponding to a spring 12 having
higher load capacity characteristics. Further, the pair of
downwardly curved regions 56 preferably curve at an angle downward
between zero and forty-five degrees relative to a horizontal axis
56b passing through their respective pivot points 56a, and the
second pair of upwardly curved regions 58 preferably curve upward
at an angle upward between ten and eighty degrees relative to a
horizontal axis 58b passing through their respective pivot points
58a.
[0015] The spring 12 has a pair of molded in pin end attachments 28
for securing the spring 12 to the vehicle frame. Of course, in
alternative arrangements, the shape of the pin end attachments 28
may be modified in any number of arrangements depending upon how
the spring 12 will ultimately be secured to the vehicle frame 16
and still come within the spirit and scope of the present
invention.
[0016] As depicted in FIG. 4, the width w of the spring 12 is
consistent throughout the length 1 of the spring 12. The width w is
a function of the spring rate desired for the spring 12.
[0017] Fiberglass leaf springs are preferable to metal leaf springs
for a number of reasons. First, fiberglass leaf springs 12 such as
in FIG. 1 have a strength that is approximately five times greater
than average cold rolled steel.
[0018] Second, this extra strength allows for a greater range of
loads available for using the monoleaf fiberglass leaf springs 12
of the present invention. FIG. 5 illustrates a force versus
displacement (deflection) curve for the composite spring 12 of FIG.
1.
[0019] Third, as FIG. 5 illustrates, the composite spring 12 of
FIG. 1 achieves not just bi-linear response, but actually a
multi-linear response. Referring now to FIG. 5, the displacement of
the spring 12 along line 300 between approximately 0 and 10% of its
normalized load corresponds to a first slope of approximately 10%
normalized load per 20% normalized displacement, or 1/2. Between
20% and 66% normalized displacement, this slope decreases to a
second slope of approximately 1/1. Between 66% and 100% normalized
displacement, this slope decreases further to a third slope of
approximately 1.5/1. Thus, the amount of reaction force necessary
to displace the spring along its normalized load scale changes as
the amount of force is increased. Here, three actual different
levels of linear response are achievable along a normalized plot
for load versus deflection of the composite spring as depicted in
FIG. 1. By modifying the amount of curve in either middle upwardly
curved region 52, downwardly curved regions 56, or upwardly curved
regions 58, or any combination thereof, or by modifying the
thickness or width of the composite material, the spring rate
characteristics of the spring 12 along the first slope, second
slope, or third slope may be increased or decreased as desired.
Further, these changes may affect the location in the plot as
depicted in FIG. 5 of the rate changes from the first slope to
second slope or the second slope to third slope. Finally, these
changes may also increase of decrease the number of possible linear
responses from three as depicted in FIG. 5 to some other
number.
[0020] Minor modifications to the amount of curve in the middle
upwardly curved region 52, the downwardly curved regions 56, the
second pair of upwardly curved regions 58, the thickness of the
composite, and/or the width of the composite spring allow the
spring to be used under a wide variety of load demands, ranging
from small pick up trucks having a load capacity of about 1000
pounds and a displacement of approximately 200 mm to a heavy duty
truck having a load capacity of 2500 pounds and a deflection of
approximately 350 mm. Of course that the load requirements may
exceed that of a heavy-duty truck, and the composite spring 12 of
the present invention can be designed to accommodate this
additional stress. The composite spring 12 as depicted in FIG. 1 is
thus ideal for use in a light truck chassis system.
[0021] To produce the composite spring 12, two preferred methods
are currently contemplated. One method is to make the springs 12
out of layers of pre-preg tape. The pre-preg tape consists of
unidirectional glass fibers with uncured resin surrounding them.
The layers can be stacked on top of each other until a desired
thickness is achieved. The layers are then compacted and heated,
typically between 80 and 170 degrees Celsius, for a predetermined
amount of time, to cure the resin. The amount of time necessary to
cure the resin is a function of the curing temperature. As the
temperature is increased, the amount of time necessary decreases.
In a preferred embodiment, an epoxy resin is used to cure the
layers and E-type fiberglass comprises the unidirectional glass
fibers.
[0022] Another preferred method for making the springs 12 is
3-dimensional (3D) weaving. In this method, multiple spools of
glass fiber feed fiber into a weaving machine that loops the glass
fiber across the width and through the thickness, with a majority
of the fibers running in the machine direction along the length of
the beam preform. These preforms are then placed in a mold and
injected with resin using an RTM process. This method allows the
springs 12 to have integral pivots, as slits can be left in the
preform allowing bushings or other inserts to be inserted in them.
Again, as above, an epoxy resin is contemplated as the curing
resin.
[0023] While the invention has been described in terms of preferred
embodiments, it will be understood, of course, that the invention
is not limited thereto since modifications may be made by those
skilled in the art, particularly in light of the foregoing
teachings. For example, while the spring 12 preferably has a
symmetrical design, it is contemplated that the spring 12 may be
asymmetrical depending upon the requirements of the chassis system.
Further, the number of downwardly curved regions 56 and upwardly
curved regions 58 extending in each direction from the middle
upwardly curved region 52 may be increased from one on each side of
the middle upwardly curved region 52 and still be within the spirit
of the present invention.
* * * * *