U.S. patent application number 11/672651 was filed with the patent office on 2007-06-07 for windshield wiper system with tubular drive arm and cavity.
This patent application is currently assigned to VALEO ELECTRICAL SYSTEMS, INC.. Invention is credited to Harry Charles JR. Buchanan.
Application Number | 20070124888 11/672651 |
Document ID | / |
Family ID | 32107160 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070124888 |
Kind Code |
A1 |
Buchanan; Harry Charles
JR. |
June 7, 2007 |
WINDSHIELD WIPER SYSTEM WITH TUBULAR DRIVE ARM AND CAVITY
Abstract
This invention relates to windshield wiper system which utilizes
a flexible drive arm for withstanding bending loads applied to a
wiper. The drive arm may be made of a pull-molded composite
material having a relatively low modulus of elasticity and a
relatively high elongation factor. The flexible arm twists in the
presence a bending load and undergoes rapidly progressing elastic
buckling when the bending load exceeds a predetermined amount.
Inventors: |
Buchanan; Harry Charles JR.;
(Auburn Hills, MI) |
Correspondence
Address: |
MATTHEW R. JENKINS, ESQ.
2310 FAR HILLS BUILDING
DAYTON
OH
45419
US
|
Assignee: |
VALEO ELECTRICAL SYSTEMS,
INC.
3000 University Drive
Auburn Hills
MI
48326
|
Family ID: |
32107160 |
Appl. No.: |
11/672651 |
Filed: |
February 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10919588 |
Aug 17, 2004 |
7174598 |
|
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11672651 |
Feb 8, 2007 |
|
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|
10281488 |
Oct 28, 2002 |
6833682 |
|
|
10919588 |
Aug 17, 2004 |
|
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|
Current U.S.
Class: |
15/250.351 |
Current CPC
Class: |
B60S 1/3848 20130101;
B60S 1/32 20130101; B60S 1/3415 20130101; B60S 1/3427 20130101;
B60S 1/3463 20130101 |
Class at
Publication: |
015/250.351 |
International
Class: |
B60S 1/32 20060101
B60S001/32; B60S 1/34 20060101 B60S001/34 |
Claims
1-8. (canceled)
9. A windshield wiper system comprising: a drive motor; a drive arm
coupled to said drive motor; and a wiper blade also coupled to said
drive arm for wiping a windshield when said drive motor is
energized; said drive arm being made of a composite material and
being generally curved in cross-section and an internal cavity
extending along its length.
10. The windshield wiper system as recited in claim 9 wherein said
generally curved cross-section defines a shape that is elliptical,
concave or one side of said arm is generally flat.
11. The windshield wiper system as recited in claim 10 wherein the
cross-section defines a concave shape.
12-16. (canceled)
17. The windshield wiper system as recited in claim 9 wherein said
drive arm comprises: a tubular member defining said cross-section
and said cavity comprising an internal cavity extending initially
forward along a longitudinal axis; and said tubular member
comprising a wiper axis for connection of a wiper thereto and a
motor axis for connection of a drive motor thereto; said wiper axis
being selected to cause a bending of said tubular member about said
longitudinal axis when said bending force is applied thereto.
18. The windshield wiper system according to claim 17 wherein said
tubular member experiences an elastic buckling when said bending
force exceeds a predetermined amount.
19-20. (canceled)
21. The windshield wiper system according to claim 17 wherein said
tubular member being naturally curved in the absence of a bending
force on said wiper axis.
22. The windshield wiper system according to claim 21, said tubular
member flattens out such that at least a portion of said
cross-sectional shape becomes generally flat.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a windshield wiper system and,
more particularly, to a windshield wiper system which utilizes a
reciprocating, flexible arm comprising a for driving a windshield
wiper.
[0002] An example of a prior art windshield wiper drive link and
system is shown in Buchanan et al., U.S. Pat. No. 6,148,470, which
is incorporated herein by reference and made a part hereof. A
windshield wiper system, as taught therein, is particularly useful
for driving in snow or in mud, under conditions wherein an
accumulation of foreign material may cause a sudden blockage of the
wiper block. When this happens, the windshield wiper motor may
generate a momentarily large driving torque in an attempt to
overcome the blockage. That in turn may cause permanent damage to
one or more components of the wiper system.
[0003] A flexible arm, as taught in Buchanan et al., reduces the
risk of such damage by constructing the wiper drive arm from a
material which tolerates compression loads up to a predetermined
limit. Below that limit, known as the critical buckling load limit,
the drive arm simply compresses by an amount proportional to the
force of the load. However, upon reaching the critical buckling
load limit, the arm gives way by pronounced elastic buckling. The
buckling effectively prevents any further increase in the load
being applied to wiper system components, and does so without
permanent injury to the drive arm. Once the blockage has been
removed, manually or otherwise, the flexible arm simply pops back
into its original configuration.
[0004] As further taught in Buchanan et. al. U.S. Pat. No.
6,148,470, the flexible drive arm may be interposed between a drive
motor and a pair of drive plates. The drive plates in turn apply
drive torques cooperatively to a pair of wiper blades. The flexible
drive arm preferably is made from a composite material of a type
described in Table I of the patent. Four specific materials are
taught, including a molded glass laminate, a molded epoxy resin,
and two pull-molded polyesters having oriented glass fibers.
[0005] As further disclosed in Buchanan et al, the flexible drive
arm may be generally elongated and generally rectangular in
cross-section. The patent teaches that the flexible drive arm could
have other cross-sectional geometries, such as elliptical or
circular, and in one described configuration could have a length of
at least about 250 mm. Notches could be fabricated in the flexible
drive arm in order to adjust the bending stress at which elastic
buckling occurs. The patent observes that a suitable flexible drive
arm should have a design strength such that buckling is not
expected to occur in the face of a compression load less than about
30 percent greater than the normally expected maximum running load
for a comparably sized steel or rigid link that does not flex.
[0006] The prior art also includes a windshield wiper for an
aircraft, as shown, for example in Rogers et. al (U.S. Pat. No.
4,318,201). That patent teaches a flexible drive arm for a
windshield wiper wherein the cross-section varies from end to end
in order to control the onset of elastic buckling. The Rogers
patent also discloses the use of a glass fiber composite for
construction of a flexible drive arm for a windshield wiper.
SUMMARY OF THE INVENTION
[0007] This invention improves the performance of a windshield
wiper by providing it with a flexible drive arm supported by a
hollow tube extending from a motor to a wiper arm. The tube
preferably has a normally unstressed sideward curvature for
relaxation along a windshield when the wiper axis rests on a curved
portion thereof. The cross-section of the hollow tube has an
off-center shear center. As the wiper axis moves to a flat portion
of the windshield, the contact of the wiper against the windshield
generates a sidewardly directed bending (unbending) force which
stresses and straightens out the drive arm along a cross-sectional
width. The straightening of the drive arm sets up internal bending
stresses which flatten the hollow tube thereby progressively
decreasing the moment of inertia about the longitudinal axis.
Transverse blocking results in elastic buckling when the sidewardly
applied bending force reaches a predetermined level. That in turn
relieves the stress on the windshield drive motor and wiper
components when the wiper system or arm becomes blocked.
[0008] In one aspect, this invention comprises a drive arm for a
windshield wiper comprising a tubular member having a preselected
cross-section and an internal cavity extending initially forward
along a longitudinal axis, with a curvature extending laterally
from said longitudinal axis; and said tubular member comprising a
wiper axis for connection of a wiper thereto and a motor axis for
connection of a drive motor thereto; and said wiper axis being
selected to cause a bending of said tubular member about said
longitudinal axis when a bending force is applied thereto.
[0009] In another aspect, this invention comprises a windshield
wiper system comprising a drive motor, a drive arm coupled to said
drive motor; and a wiper blade also coupled to said drive arm for
wiping a windshield when said drive motor is energized; said drive
arm being made of a composite material and being generally curved
in cross-section and an internal cavity extending along its
length.
[0010] Other objects and advantages of the invention will be
apparent from the following description, the accompanying drawings
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a sketch of two cooperatively installed windshield
wiper systems, one of which is stalled by blockage material;
[0012] FIG. 2 is an isometric drawing of a flexible drive arm;
[0013] FIG. 3 is a drawing of a cross-section of a first embodiment
of a flexible drive arm, taken at a lightly stressed station
thereof;
[0014] FIG. 4 is a drawing of a cross-section of a second
embodiment of a flexible drive arm;
[0015] FIG. 5 is a drawing of a cross-section of the flexible drive
arm embodiment of FIG. 3, taken at a heavily stressed station
thereof;
[0016] FIG. 6 is a schematic illustration of braiding of
pull-molded composite material about the surface of a flexible
drive arm;
[0017] FIG. 7 is a plan view of a drive arm in accordance with an
embodiment of the invention;
[0018] FIG. 8 is a side view of the drive arm shown in FIG. 7,
illustrating the curvature of the side arm;
[0019] FIG. 9 is a cross-sectional view taken along the line 9-9 in
FIG. 8;
[0020] FIG. 10 is a cross-sectional view taken along the line 10-10
in FIG. 8;
[0021] FIG. 11 is a cross-sectional view taken along the line 11-11
in FIG. 8;
[0022] FIG. 12 is a cross-sectional view taken along the line 12-12
in FIG. 8;
[0023] FIG. 13 is a view of the drive arm having one end mounted to
a shaft of a motor, with the second end having a wiper blade
mounted thereon and in operative engagement with a windshield;
[0024] FIG. 14 is a cross-sectional view taken along the line 14-14
in FIG. 13;
[0025] FIG. 15 is a cross-sectional view taken along the line 15-15
in FIG. 13;
[0026] FIG. 16 is a cross-sectional view taken along the line 16-16
in FIG. 13;
[0027] FIG. 17 is a cross-sectional view taken along the line 17-17
in FIG. 13;
[0028] FIG. 18 is another view of the drive arm as it engages
debris on a windshield;
[0029] FIG. 19 is a sectional view taken along the line 19-19 in
FIG. 18;
[0030] FIG. 20 is a cross-sectional view taken along the line 20-20
in FIG. 18;
[0031] FIG. 21 is cross-sectional view taken along the line 21-21
in FIG. 18;
[0032] FIG. 22 is another view of the wiper arm shown in FIG. 18 as
a motor continues to drive the arm;
[0033] FIG. 23 is a cross-sectional view taken along the line 23-23
in FIG. 22;
[0034] FIG. 24 is a cross-sectional view taken along the line 24-24
in FIG. 22;
[0035] FIG. 25 is a cross-sectional view taken along the line 25-25
in FIG. 22;
[0036] FIG. 26 is another view of the wiper arm illustrated in FIG.
22;
[0037] FIG. 27 is a cross-sectional view taken along the line 27-27
in FIG. 26;
[0038] FIG. 28 is a cross-sectional view taken along the line 28-28
in FIG. 26;
[0039] FIG. 29 is a cross-sectional view taken along the line 29-29
in FIG. 26;
[0040] FIG. 30 is a view illustrating a tube in a mold prior to
inflation or enlargement;
[0041] FIG. 31 is a view similar to FIG. 30 where the tube has been
inflated to mold the material to a shape which will define the
drive arm;
[0042] FIG. 32 is a view illustrating various directional
components for facilitating an understanding the Moment of Inertia
to be calculated as described;
[0043] FIG. 33 is a view of another embodiment of the
invention;
[0044] FIG. 34 is a cross-sectional view taken along the line 34-34
in FIG. 33;
[0045] FIG. 35 is a cross-sectional view taken along the line 35-25
in FIG. 33;
[0046] FIG. 36 is a cross-sectional view taken along the line 36-36
in FIG. 33;
[0047] FIG. 37 is a cross-sectional view taken along the line 37-37
in FIG. 33;
[0048] FIG. 38 is a cross-sectional view taken along the line 38-38
in FIG. 33; and
[0049] FIG. 39 is a cross-sectional view taken along the line 39-39
in FIG. 39.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0050] Referring now to FIG. 1, there are illustrated two
windshield wiper systems, 10, 10, each of which has a wiper 14,
connected to a flexible drive arm 12 at a pivotal joint 16. Wipers
14, 14 each comprise a wiper blade (not illustrated), suitably
supported by its associated pivotal joint 16. For this purpose, the
wipers 14, 14 may be fitted with spines (also not illustrated)
assembled in well known whiffletree or flat blade arrangements. A
pair of drive motors 18, 18 cause flexible drive arms 12, 12 to
carry wipers 14, 14 across windshield 20 in reversing arc-like
paths 24, 24, so as to remove debris therefrom. For ease of
illustration, the motors 18, 18 are shown coupled to the arms 12,
12, but it should be understood that drive linkage (not shown) may
be employed to couple the arms 12, 12 to a single motor 18 or
multiple motors 18, 18.
[0051] Still referring again to FIG. 1, the flexible drive arm 12
on the right hand side of the windshield 20 is shown to be working
against a relatively unyielding pack 22 of foreign matter or
debris. This produces a relatively high stress which tends to be
transferred to the associated motor 18. In accordance with this
invention, wear and tear on the motor is reduced by twisting the
flexible drive arm to reduce the stiffness thereof and sharply
achieve elastic buckling upon occurrence of the predetermined
bending force. The principal structural component of a flexible
drive arm 12 is a hollow tube 32, manufactured from a composite
material, as hereinafter described. It should also be understood
that the arm 12 may be solid as shown in the embodiment illustrated
in FIGS. 33-39.
[0052] The geometry of a tube 32 is illustrated in FIG. 2.
Preferably, tube 32 is fitted with an elastomeric hose 47, as shown
in cross-section in FIG. 3. Tube 32 is characterized by a
cross-section having an off-center shear center 37. Tube 32 is
secured to motor axis 26 by a stamping or casting (not illustrated)
and extends from motor axis 26 to a wiper axis 28 in an initial
direction indicated by a longitudinal axis 30 as illustrated in
FIG. 2. Wiper 14 is attached to tube 32 along wiper axis 28. Wiping
loads are transferred from wiper 14 to tube 32 along that axis. As
further shown in FIG. 2, tube 32 has a pronounced sideward
curvature which carries it laterally away from longitudinal axis
30. The total amount of this curvature is indicated on FIG. 2 by
the angle .alpha.. That is the non-stressed, rest configuration of
tube 32, where no bending force is transmitted from wiper 14 to
tube 32. When the arm 12 is installed in operative relationship to
a windshield, the arm 12 flattens and reduces the moment of inertia
in the "out-of-plane" bending. The arm 12 experiences lateral
bending load as the arm 12 sweeps across the windshield 20.
[0053] In the rest condition shown in FIG. 2, wiper 14 rests
lightly against the curving contour of the windshield 20. However,
when wiper 14 traverses a substantially planar windshield region,
the windshield 20 reacts against wiper 14, thereby creating a
bending force, which is transmitted along wiper axis 28 to tube 32.
That produces a bending force, F, which stresses tube 32, causing
flexible drive arm 12 to straighten out in the direction of
longitudinal axis 30. The bending force acting in the plane of the
angle may be calculated from the following equation: F = 3 .times.
EI .times. .times. .delta. L 3 = KS ##EQU1## where .times. :
.times. .times. K = 3 .times. EI L 3 ##EQU1.2## where: [0054] k is
the spring constant of the flexible drive arm [0055] E is the
modulus of elasticity of the flexible drive arm [0056] I is the
moment of inertia about the major axis [0057] * is the deflection
in the direction of the major axis [0058] L is the length of the
flexible drive arm.
[0059] The value of the moment of inertia depends upon the position
and the direction of a reference axis about which the moment of
inertia is calculated. For example, FIG. 32 depicts a rectangular
cross-section 83 having a height h and a base b. Assume that this
rectangular cross-section is made up of elemental areas, dA, having
directional components dX and dY and that the Moment of Inertia,
I.sub.x, is to be calculated about the x-axis. The value of I.sub.x
is given by the equation; which can be expanded to: I x = .intg. -
h 2 h 2 .times. y 2 .function. [ .intg. o b .times. .times. d x ]
.times. .times. d y ##EQU2## or ##EQU2.2## I x = b .times. .intg. -
h 2 h 2 .times. y 2 .times. .times. d y ##EQU2.3## This .times.
.times. gives .times. : ##EQU2.4## I x = b 3 .times. y 3 .times. |
h 2 - h 2 = b 3 .function. [ ( h / 2 ) 3 - ( - h / 2 ) 3 ] = b 3
.function. [ h 3 8 + h 3 8 ] = bh 3 12 ##EQU2.5##
[0060] Consequently, flexible drive arm 12 is sufficiently stiff to
carry a bending force which varies in proportion to the minor axis
length. As flexible drive arm 12 bends toward longitudinal axis 30,
tube 32 generates a shear flow causing a bending stress that
flattens tube 32 about its shear center 37. The twist angle, so
produced, is indicated by the Greek letter .beta. in FIG. 5.
Twisting of tube 32 tends to flatten out the cross-section thereof,
as illustrated in FIGS. 22-28, which in turn causes a substantial
reduction in the moment of inertia, I. This reduces the stiffness
of tube 32, as well as the force calculated by the above noted
equation, so that elastic buckling occurs rapidly upon occurrence
of the predetermined force. It will be understood that the location
of shear center 37 is shown only approximately. The actual position
is situated at a point such that a hypothetical shear load,
equivalent to the actual distributed shear load, would produce a
twist, .beta., when directed therethrough. Most preferably, the
cross-section varies along the length of tube 30.
[0061] In the embodiment described, the arm 12 comprises a
slenderness ratio, L/r of at least 50, but not more than 600,
[0062] where: L is the length of the arm 12; and
[0063] "r" is the least radius of gyration of the cross-section
(I=ar.sup.2), where I is the moment of Inertia and a is the area of
the cross-section.
[0064] In prior art wiping systems of the cantilever beam type the
drive arm is oftentimes shaped such that aerodynamic wind forces of
increasing speed tend to press the arm into the glass with lower
intensity. Also, with such prior art systems the arm tip force
normally increases at the tip as the beam is deflected. The present
invention compensates for such increases by providing a beam
cross-section having a moment of inertia affording a substantially
constant tip force through the working deflection. In the preferred
embodiment, flexible drive arm 12 has an off-center shear center 37
which reduces arm twisting due to torsional loads about wiper axis
28. In one preferred embodiment the off-center shear center may
appear as a `smile` or upwardly curved (as viewed in FIG. 2)
cross-section (See FIGS. 3-5). The material has high elongation
properties and will allow for major deformation without breaking. A
frozen blade might twist the structure and the arm flex out of
plane, breaking loose the ice.
[0065] In a typical prior art wiping system the arm would deflect
0-3 inches or 75 mm. The deflection is caused by the rise and fall
of the arm during the wiping action. In some cases there is no
elastic buckling. Another embodiment is where the arm 12 is a one
piece solid or tubular construction that is generally U-shaped in
cross-section. This cross-sectional shape is similar to a
cross-sectional shape of a steel carpenter's rule. This embodiment
produces the desired elastic buckling.
[0066] The drawing of FIG. 2 includes a series of lines
representing spaced stations along a flexible drive arm 12. FIGS. 3
and 5 illustrate the cross-sections thereof appearing at stations
32 and 34 respectively. These cross-sections decrease in scale and
also flatten down as flexible drive arm 12 approaches station 32
from the direction of motor axis 26. This cross-sectional
flattening is quite reminiscent of the snapping action of a
sidewardly bowed steel rule when extended beyond a certain critical
length and is due in part to the relative lengths of minor axis 83
and major axis 85.
[0067] As illustrated in FIGS. 3 and 5, a flexible drive arm 12 may
comprise a thin elastomeric hose 45 encased within a glass/fiber
composite tube 33. Hose 45 provides a passage for supplying washer
fluid to the wiping blade (not illustrated). More preferably,
however, a flexible drive arm 12 has a configuration 50, as
illustrated in FIG. 4. This particular embodiment features a fluid
supply hose 47 encased within a tube 51 and supported by a foam
core 52. Preferably, drive arms 12, 12 are manufactured from a
fiber-reinforced plastic material, produced by a well known process
called "pull-molding". Broad background teachings regarding
pull-molding may be found by reference to U.S. Pat. No. 6,253,411
B1 (Aichele et al.), the disclosure of which is hereby incorporated
herein. This invention generally follows prior art teachings, such
may be found in the patent produces a pull-molded strand of
glass/plastic composite. It should be understood that the strands
may be glass, carbon or other suitable fiber. That strand (not
illustrated herein) is stored on a suitable reel until required. At
that time a large batch of flexible drive arms may be produced in a
joined, end-to-end, arrangement, withdrawing pull-molded composite
material from the reeled strand, as required. Individual drive arms
12 may be sawed off from the linked arrangements at such time as
may be convenient. It has been found particularly convenient to
store the still-joined flexible drive arms on a large reel and to
separate them just prior to shipment from the factory. It will be
appreciated that the entire process could be consolidated at a
single site, but it is feasible to parcel out parts thereof to
separate contractors.
[0068] FIGS. 33-39 illustrates another embodiment of the invention.
Notice the arm 13 is a solid uniaxial pull-molded wiper arm with
diecast terminations 61 and 62 which are crimped onto the ends
thereof as shown. It should be appreciated that the end or fitting
61 comprises an opening 63 for mounting onto a drive motor 18 (FIG.
1). The fitting 62 may be a shaft or post for receiving a wiper
blade 14 (FIG. 1). In the embodiment being described, the post 62
may be situated in an opening 65 and then riveted onto the drive
arm 13. In the embodiment being described, this arm 13 is a right
hand wiper arm which would be situated on the right hand wiper
motor 18 (as viewed in FIG. 1). Note the cross-sectional
transitions (FIG. 34-39) of the pull-molded wiper arm 13.
[0069] The arm 13 comprises the following dimensions:
TABLE-US-00001 Dimensions Measurement (FIGS. 33-39) (mm) D.sub.1
3.71 D.sub.2 36.98 D.sub.3 3.89 D.sub.4 36.2 D.sub.5 6.13 D.sub.6
23.11 D.sub.7 7.78 D.sub.8 18.24 D.sub.9 8.2 D.sub.10 17.13
D.sub.11 12.53 D.sub.12 10.54 D.sub.13 55 D.sub.14 615 D.sub.15 640
D.sub.16 150 D.sub.17 110 d.sub.18 50 D.sub.19 240
[0070] It should be appreciated that the arm 13 may be of solid
construction with fiber orientation, for example, the longitudinal
direction of the arm 13. The arm 13 may comprise one or more of the
features described earlier herein relative to the other
embodiments, such as a channel or tube through which wiper fluid
may flow and the like.
[0071] Advantageously, the invention provides a lightweight, yet
strong, drive arm having a relatively low modulus of elasticity and
a relatively high elongation factor. Another advantage of the
invention is that the flexible arm twists in the presence of a
compressive load and undergoes rapidly progressing elastic buckling
when the compressive load exceeds a predetermined amount such as
when the wiper blade 14 (FIG. 1) encounters debris on the
windshield and the drive arm 12, 13, experiences a bending force
that is greater than the maximum blade frictional force. The simple
one-piece construction and elasticity of the drive arm 12, 13
provides a lightweight, yet strong, drive arm that facilitates
using fewer number of components and parts which can become
unusable if overfatigued.
[0072] In the preferred embodiment the overall process for making a
flexible drive arm includes the steps of: [0073] 1. Preparing a
mold having an internal cavity characterized by spaced
cross-sections of generally one of the configurations shown in
FIGS. 1-39. [0074] 2. If desired, placing a tube in the cavity to
provide a pathway through drive arm 12, 13. [0075] 3. Placing
flexible filler material inside the cavity to support the hose and
to provide a form for building the flexible drive arm 12 or 13.
[0076] 4. Foam cores are formed, for example, by inflating tube 51
(FIG. 31) to press foam against mold walls 53a and 53b (FIG. 31).
[0077] 5. The successive cores are placed on a shipping roll (not
shown) for transport. [0078] 6. Fiber (glass, carbon, etcetera) is
woven over each core as described herein. [0079] 7. Woven cores are
places on shipping roll (not shown) for transport. [0080] 8.
Shipping roll of woven, end-to-end cores are unrolled from roll.
[0081] 9. Woven cores are subject to resin bath to provide
resin-coated core. [0082] 10. Resin-coated core placed in mold.
[0083] 11. Mold heats and cures resin-coated core. [0084] 12. Cured
cores removed from molds. [0085] 13. Successive cores are cut
apart. [0086] 14. End fittings are crimped onto ends of core to
provide drive arm 12. [0087] 15. Plastic or other material (not
shown) may be optionally over-molded over joints (not shown)
between fittings and drive arm 12.
[0088] Braiding of the pull-molded strand proceeds as illustrated
in FIG. 6. During braiding, a plurality of strips of pull-molded
working material are fed to an automatic braiding machine which
braids them into tubes having a generally crescent-shaped
cross-section. At some locations along flexible drive arms 12, 12,
the cross-sections may resemble the familiar "smiley face" commonly
appearing on the contemporary American scene. Alternatively, they
may be elliptical, or even concave on one side with the opposing
side being generally flat. The braiding machine creates a triaxial
braid at a braiding angle, .gamma., which varies along the length
of the arm. This optimizes torsional stability and provides a
reduced stiffness perpendicular to the fibers, thereby minimizing
arm pressure variance as the arm tip rises and falls during the
wiping of the windshield glass.
[0089] The tube walls comprise about twenty-one percent by weight
of a thermosetting polyester resin, seventy-five percent by weight
of 113E-Glass Roving and four percent by weight of a suitable
filler. It should be appreciated that the percentages may vary from
those mentioned, which are presented for purposes of illustration
only. In its unbraided state the working material has the following
preferred monotonic properties: [0090] Elastic Modulus 43 GPa (6.2
Mpsi) [0091] Ultimate strength of 11400 Mpa (165 ksi); [0092]
Strain at fracture=2.6%, [0093] Specific Gravity=1.92
[0094] This composite material may be strained about 10 times as
much as spring steel and is able to withstand a relatively large
deflection without fracture. It is important that the ends of
flexible drive arms 12, 12 be properly terminated in order to deal
with high stress concentrations applied along motor axis 26 and
wiper axis 28. Bolt holes in the braided material along motor axis
26 and wiper axis 28 would fray and eventually fail, if made to
carry the stress of ordinary nut and bolt attachments. Therefore
this invention joins drive arms 12, 12 to other parts by means of
thermoplastic or thermoset overmolded, ductile steel, aluminum,
zinc or other metallic die cast stampings. A part to be joined to a
drive arm 12 is formed around and inside the pull-molded arm. Since
the space between the steel stamping and the fiberglass structure
is small, any "Plastic Creep" effect is minimal, and the stress is
transferred effectively between parts.
[0095] The braid illustrated in FIG. 6 is a structure is similar to
the weave of a sock or a Chinese torture finger tube, only woven
and placed continuously on a reel, perhaps over a foam core. It
should be understood that the braid could be straight in a
longitudinal direction along its length or even straight in a
vertical direction (as viewed in FIG. 6) or any combination
thereof.
[0096] Note in FIG. 30 that the drive arm 12 could also be formed
by alternative methods. For example, an elastometric tube 51 may be
placed in a mold 53. Foam 55 or other suitable forming material is
situated around tube 51, as illustrated in FIG. 30. The tube 51 is
then expanded by gas, such as air or water against walls 53a and
53b of mold 53 (as shown in FIG. 31) to provide an arm 12. The arm
12 may then be processed with one or more of the steps 3-12
described earlier herein. It is envisioned that the tube 51 may
then be deflated and subsequently used to provide a passageway or
channel for washer fluid through the arm 12.
[0097] FIGS. 7-24 illustrate further features of an embodiment of
the invention having the characteristics described.
[0098] FIG. 7 illustrates a plan or top view of the composite wiper
arm as described earlier herein relative to FIG. 2. Note the
generally curved shape illustrated in FIG. 8 which facilitates
providing the aforementioned tip force which facilitates
maintaining the wipers 14 against the windshield 15. FIGS. 9-12
illustrate various cross-sectional views of the arm in an
embodiment of the invention when the arm is at rest. These shapes
are further illustrated in FIGS. 13-17.
[0099] FIGS. 18-24 illustrate a general change in the
cross-sectional shape when the wipers engage the debris 22 (FIGS. 1
and 13). FIGS. 14-16 illustrate the cross-sectional shape of the
arm 12 when it first engages the debris 22.
[0100] As the motor 18 (FIG. 17) continues to drive the arm 12 in
the direction of arrow A in FIG. 17, the arm experiences increased
torque and begins to twist in the manner illustrated and described
herein. Note that the leading edge 12a begins to move toward the
debris 22 as shown and the trailing edge moves away from the
windshield as illustrated in FIG. 18. This slight twist and
movement of the arm is also experienced at the cross-sectional
areas illustrated in FIGS. 19 and 20.
[0101] FIG. 22 illustrates a more exaggerated twisting motion as
the motor 18 continues to attempt to drive the arm 14 in the
direction of arrow A. Further twisting of the arm is illustrated
and FIGS. 22-24 further show the movement of the leading and
trailing edges 12a and 12b, respectively. It is important to note,
as illustrated in FIGS. 22 and 23 and described earlier herein,
that the cross-sectional shape of the arm changes from the
generally curved shape shown, for example, in FIGS. 18 and 19, to a
generally flatter shape illustrated in FIGS. 22 and 23. This
feature of the invention facilitates distributing the encountered
load forces and torque across the length of the arm 12 which in
turn facilitates accommodating the elastic buckling which would
normally severally damage the wiper arms used in the past.
[0102] While the systems and methods herein described, and the
forms of apparatus for carrying these systems and methods into
effect, constitute one embodiment of this invention, it is to be
understood that the invention is not limited to these precise
methods and forms of apparatus, and that changes may be made in
either without departing from the scope of the invention, which is
defined in the appended claims.
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