Note: Descriptions are shown in the official language in which they were submitted.
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There has lon~ been a controversy over the relative abilities of
wheels and tracks as motive supporting means for mobile vehicles. ~enerally
speakin~, ~any heavier duty vehicles such as military vehicles, and some
industrial vehicles, have utilized articulated tracks since they have pro-
vided a broader ~footprint~ of contact with the ground, resulting in lower
per unit area pressure and weight distribution, generally increased traction,
and the ability to support heavy loads. Such vehicles have been seen to
hold advantages over wheeled vehicles, particularly for off-road or rough
terrain environments. Ilowever, an inherent drawback has been the relatively
high weight of the track itself, and the required suspension system, and
the relatively high number of moving parts which have been required. The
latter factor has of course given rise to increased costs in manufacturing,
lower reliability, and higher maintenance costs, not to mention breakdowns
at inopportune moments such as in combat situations.
~ number of years ago it was proposed to utilize loops formed of
flexible material and curved much in the nature of a carpenter's rule so as
to provide an approach to resolve some of the aforementioned problems
inherent with tracks. An example of prior art proposals or publications
in this regard are:
French patent 1,443,364 Levame
British patent 413,729 Kitchen
United States patent 2,061,249 Bonmartini
German patent 97,243 Egerton
"The Mobile Lander with Elastic Loop Suspension" published in
Deutsche Luft-und Raumfahrt Forschungsbericht June 1975,
pgs 289-308, by Wolfgang Trautwein
None of the approaches suggested in the referenced patents has, to
applicant's knowledge, proven successful, perhaps because various support-
ing technologies had not been developed to the point where refinements in
t;l~
design and materials were possible to render practical the full
potential inherent in the approachO
It is also noted in recent years that endless, flexible
loop, tracks have been provided for snowmobiles though these are
for reasons which will be hereinafter set forth, not analogous
to the instant invention~ Applicant, recognizing the advantages
inherent in a loop track approach, has developed and operated a
track as herein disclosed which obviates the disadvantages of
the conventional track while retianing its desirable features
and has provided a lower cost, higher reliability, structure
which should find broad application not only in military,
industrial, and other off-road vehicles, but also for on-road
and lighter-weight commercial designsO
According to the present invention there is provided
a loop track adapted to provide motive support for vehicles
comprising: at least two concentric composite cores, each of ::
said cores being formed of filaments bound together by a suitable
binder; a plurality of stud bands extending transversely of said
cores; engagement means secured to the ends of each of said stud
bands to receive sprocket teeth; and protective means connected
to the ends of said stud bands providing a cover for and consti-
tuting a part of said engagement meansO
Preferably, the cores are formed so as to assume a
"barrel" shape, iOeO, having slightly smaller diameter at their
edges than at the center portion of the core so that the track
has a generally concavo-convex transverse cross sectionO The
track is preferably circular rather than elliptical in its un-
stressed condition.
As desired, thick rubber or other flexible tread
material may be provided in the outer surface of the outer core.
Any kind of composite fibrous or filamentous core
which is impregnated with resin to maintain shape and provide
strength in support of the fibers may be employedO Applicant
has found that choice of fibers and resin would depend upon the
requirements of a particular application, though it has been
found that glass or graphite fibers impregnated with epoxy
resin have generally been found to be optimumO
The outer surface of the outer core may, if desired,
be provided with a tread of rubber or other desired material to
provide for increased traction, reduced mechanical shock to the
assembly, a more quiet operation and longer useful lifeO The
tread may be of any desired pattern or configuration, including
an essentially smooth or unconvoluted surfaceO However, a
tread having greater thickness at the outer edges of the fiber-
glass cores than in the center will provide for a generally
- flattened footprint and a more even distribution of ground pres-
sure while assisting in retaining the concavo-convex cross
section of the coresO
The loop track is preferably suspended or sprung from
a vehicle by the use of at least one swing arm being rotatably
journaled onto a frame, normally contained substantially within
the loop track, and having a load roller journaled in the upper
portion of the swing arm which normally presses downwardly onto
the loop track, thus tending to force the loop into a more elon-
gate positionO The rotatable nature of the swing arm provides
for a compensating pressed engagement of an idler sprocket also
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mounted bctween the swing arms, which automaticallY tends to
follow the slack in the loop providing constant engagement with
the loop trackO Of importance is the fact that dampers can be
used to damp the swing arm motion thus providing damping to the
total suspension system~
The loop track mechanism, being stiff and inherently
circular, provides an obvious springiness or flexibility on
supporting a vehicle, and depending upon the nature of manufac-
ture, can provide support to considerable weight, applicant
having tested such a laminated core loop track to support at
least 750 pounds. Larger units can support many times this
weightO The loop's flexibility is augmented by the fact that
the drive sprockets and idler sprockets are located some dis-
tance away from the ground or other supporting surface for the
vehicle on which it is mounted, thus allowing the inherent flex-
: ibility of the loop core to support the weight of the vehicle
without allowing the drive and idler sprockets or other rollers
to come into contact with the ground. This eliminates the "bogey
wheels" which have been necessary to maintain normal tracks on
tracked vehicles and
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to provide for a more uniform extension of vehicle weight into contact withthe ground. lhis ground contact is provided and maintained in the loop
track mechanism due to the inherent flexibility of the loop track, thus
affording a considerable reduction in weight, number of moving parts, cost,
and an increase in reliability. Thus, load distribution of a vehicle is
transmitted to the loop track through two upper idler wheels and is distri-
buted uniformly over a large footprint on the opposite side of the loop.
The two curved segments at the front and rear of the loop track
act as suspension "springs" providing large vertical deflection under
dynamic loads. The loop track's inherent stiffness along the ground contact
area has the effect of providing an infinite number of bogey wheels. The
distribution of ground pressure provides excellent traction, especially in
hill climbing modes and marginal terrain environment such as loose soil
or fine sand, mud, or the like. This feature, in addition to the lower
weight, has led many to conclude thatthe loop tracks of the invention would
offer excellent motive means for extraterrestrial vehicles. This is
especially attractive in view of the fact that a loop track suspensioD is
estimated to reduce unspring mass by approximately 40% over current track
suspension mechanisms.
Another feature of the loop track resides in the fact that the
flexibility and mounting as described provides a vertical as well as a
horizontal resiliency and this adds to driver/passenger comfort in any type
o vehicle where ground contact shocks are transmitted substantially undamp-
ened to such personnel. It would be expected that damage to a loop track
could be sustained to a much greater extent before catastrophic failure occ-
urs because of the fact that, compared to the normal track with its closely
fitting parts, nicks and damage caused by bullets, mines, rocks, and the
like would tend to cut only a relatively few fibers of the many provided,
109;~1S
while the inherent tensilestrength and flexibility of the remaining fibers
would constitute a highly sustaining backup strength to resist complete
failure. In this r~gard J. C. Shuart, in an article "The Role of Reinforced
Plastics in Leaf Springs" in the Journal of Springs, April 1967, showed -
that glass fiber reinforced epoxy, compared to quenched and tempered steel,
maintained more than twice the strength as steel.
Inherently, the by-product of lower weight, fewer moving parts,
and lowered running resistance is lowered fuel consumption and energy saving
which could be a significant factor as loop tracks come to be adopted for
a broad range of vehicle applications.
Also, applicant has found that the stud bands and mounting
mechanism to be hereinafter described provide sprocket engagement means
which eliminates the necessity for apertures to be punched which would
otherwise be provided in a loop track mechanism. Such apertures would be
expected to significantly degrade the strength of any material of which the
loop cores were made.
In keeping with the above description, the following figures are
provided to illustrate one embodiment of the invention which will be describ-
ed in greater detail hereinafter:
FIGURE 1 is an isometric view of a loop track mechanism,
FIGURE 2 is a cross sectional view of one portion of a loop track
showing the manner of engagement of a sprocket assembly,
FIGURE 3 is a side view of a loop track mechanism,
FIGURE 4 is a top view of a loop track mechanism,
FIGURE 5 illustrates a mandrel and the first step in the process
of winding a fiber reinforced composite,
FIGURE 6 illustrates a second step in the process of winding
wherein cross plys are wrapped around an inner core of
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circumferential plys,
FIGURE 7 shows a third step of the core manufacturing process in
which additional circumferential fibers are used to
secure the cross plys,
FIGURE 8 illustrates a final manufacturing step in which the core
is heat cured in the desired "barrel" shape, and
FIGURE 9 is a side view of a loop track mounted by the use of a
swing arm with load rollers onto a support mechanism
generally internal of the loop.
With reference to the accompanying drawings Figure 1 shows a
loop track 1 in isometric view which is seen to generally consist of an
inner fiber reinforced composite core 2 and an outer fiber reinforced com-
posite core 3. A description of one preferred process by which such
filament wound cores may be made will be hereinafter detailed.
~he composite cores are formed in such manner as to originally
and normally maintain a circular shape. They are formed in a concavo-convex
"barrel" shape so that the ID at the outer edges of the core is somewhat
less than the ID at the center of the core. This shape has been found to
enhance the suspensional and flexibility properties of the cores and to
provide, in addition to needed strength, a more evenly distributed weight
per unit area of the core. The outer diameter of the inner core and the
inner diameter of the outer core members are manufactured in such a way that
they will fit concentrically with tolerances close enough to provide a proper
` fit.
The embodiment herein described incorporates two composite cores.
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In other embodiments depending upon the thickness of individual cores and
the application to which a particular loop track is to be put, a large
number of such cores could be secured together.
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Sandwiched between the composite or filamentary cores 2 and 3 are
a plurality of transversely extending stud bands 4. Stud bands 4 are general-
ly flat, elongate members terminating at each end in t~reads 5, it being
noted that the portion of the stud band between the flat middle portion
and the ~reads 5 is formed so as to provide a thickened annular shoulder
6. A thin layer 7 of resilient, isolating material is provided between stud
bands 4 and the cores 2 and 3 as a means of securing the stud bands 4 to
the composite core members 2 and 3. ~his strain isolating layer is a
resilient material that adheres to the stud band and to the composite cores.
Such protective coating may also be provided on the inner surface of inner
core 2. The outer surface of outer core 3 is provided with a tread 8 of
rubber to provide for increased traction, reduced mechanical shock to the
assembly, a more quiet operation and longer useful life. Tread 8 has greater
thickness at the outer edges of the fiberglass cores than in the center
to provide for a generally flattened footprint and a more even distribution
of ground pressure while assisting in retaining the concavo-convex cross
section of the cores. As shown in Figure 2, reinforcement 9 is provided in
tread 8, to additionally enhance strength, not only in the tread but also
of the entire loop track assembly. Such a reinforcement assists in prevent-
ing expansion of tread 8 and improves adherence and cohesiveness of the
other elements of the loop track.
The end caps 10, which may be forgings or sections of extrusions
of aluminum or other desired material, are provided with a protective
cover flange 11 which is adapted to extend over the linking mechanism to
be described. On the other "side" of central wall 12 are upper and lower
channels formed by lower leg 13, middle leg 14, and upper leg 15. Central
wall portion 12 is provided with a pair of apertures essentially in the cen-
ter of the lower channel formed between middle leg 14 and lower leg 13, the
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apertures being adapted to receive threaded ends 5 and thickened annular
shoulders 6 of stud bands 4~ The channel formed between middle leg 14
and lower leg 13, in addition to accommodat:ing stud bands 4, also is sized
to permit tight engagement of the "sandwich" formed by composite cores 2
and 3 and the strain isolating coatings 7 which may be provided between the
stud bands and the cores.
~he remaining channel formed between middle leg 14 and upper leg
15 of end cap 10 is adapted to receive outwardly extending shoulder 16,
which in this embodiment is integrally formed, of tread portion 8. Thus,
tread 8, in addition to being bonded to outer core 3, is also attached to
the assembly by the aforementioned engagement of outwardly extending shoulder
16 within the aforementioned upper cha~nel.
From the above description, it will be seen that stud bands 4 are
attached in isolated pairs through interengagement with end caps 10.`~ This
serves the function of maintaining the stud bands in relatively constant
circumferential spacement insofar as the individual pairs are concerned.
To provide complete e~ual spacement between all stud bands, inner chain
~ links 17 are provided which are generally flat link members containing
apertures near their end portions. The apertures are spaced apart the same
distance as the apertures in central walls 12, and when placed over threaded
portions 5 of one of the two stud bands held together by each end cap, thus
provide a link which rotatably interengages all of the stud bands 4 together.
It is preferable to utilize stress washers 18 in making the aforementioned
connection.
Each of the threaded portions 5 of stud bands 4 is provided with
protective caps 20 and With internal threads to engage upon threads 5. End
caps 20 are provided with retainer shoulders 21 onto which are positioned
outer links 22 which are alte m ately arranged onto the stud hands 4 to pro-
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vide a linking means complimentary to the function of central wall 12 with
inner llnks 17. It is desirable to utilize stress washers 23 in mo~mting
the outer links 22.
Rotatable bearing rollers 24 are journalled between inner links
17 and outer links 22, thus providing a more flexible engagement surface
for sprocket teeth 25 to engage.
~ rive sprocket 26 journalled on drive shaft 27 is provided with
an annular shoulder 28 which is adapted to engage with lower leg 13 of end
caps 10 in providing additional support for the stud band core combinational
assemblies.
The mechanism described thus provides a protective cover for
the linking mechanisms, and inherently, through easy to manufacture and
assemble parts, provides means to further enhance the structural integrity
between the inner and outer cores 2 and 3, and stud bands 4. Inner links 17
provide a means for absorbing stress and allowing stud bands 4 to remain
in circumferential equidistant relationship.
Turning now to a consideration of Figures 5, 6, 7 and 8, a descrip-
tion of the preferred method of manufacturing inner and outer filament wound
cores is presented. With reference to Figure 5 a winding machine shaft 30
is provided with ad~ustable spokes 31 which accommodate attachment of a
segmented male mandrel 32 which is in turn provided with an extension ring
33, annular in shape, providing a mounting surface over which cross plys of
fibrous material 34 may be positioned. Cross plys 35 may be positioned
with respect to the longitudinal axis of winding machine shaft 30 either
parallel to the shaft, or in selected biased angles there between, all as
required to suit the requirements of a given application. A plastic liner
35 is also provided over at least a portion of the outer circumferential
surface of extension ring 33, although this may be omitted.
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After placement of cross plys 34 on the mandrel, the win~ing
machi.ne shaft is rotated so as to continuously receive circumferential fibers
36. Various winding machines known to the prior art or within the skill
of one familiar with the art can be utilized to provide rotational movement
of the mandrel while at the same time providing for movement in an axial
direction so that circumferential fibers 36 are wound onto the mandrel simil-
ar to a fishing line evenly wounding onto a reel. Circumferential fibers
36 may be laid onto the mandrel with a simultaneous implacement of a binder
or impregnant material, or such material may be later provided in a manner
known to the art. After sufficient circumferential fibers 36 are laid onto
the mandrel forming a thickness as desired, the cross ply layer 34 is, as
shown in Figure 6, folded or wrapped around what has then become an "inner"
core of longitudinal plys or fibers and is secured to it in a suitable
manner utilizing adhesives, clamps, or the inherent properties of the binder/
impregnant if used.
Applicant has found that a desirable manner of securement involves
providing an additional layer or layers of circumferential fibers, thus
constituting an outer layer 37 of such fibers which has the dual advantage of
containment of the cross PlY layer for further processing and adding strength
to the composite.
In an alternate method of core winding the inner cross plys 34 are
wound to the correct width of the loop core without extensions by simultane-
ous rotation and fast axial motion of the winding machine as known to the
prior art of winding bias plys. After the desired number of inner cross
plys are wound the winding machine is programmed to wind the circumferential
fibers 36 on the mandrel. The outer cross plys 34 are subsequently wound in
the same manner as described above for the inner cross plys.
This alternate winding method shows promise to reduce manufacturing
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costs and is more amenable to ~uantity production.
Figure 8 shows the core member removed from the male mandrel 32
and placed within a f~male mandrel 38, the core member being secured to
the female mandrel by the plastic liner 35 which is secured to the female
mandrel for example by a vacuum. Thus, the latter is held in desired shape
during the cycle in which the impregnant is cured as consistent with the
properties and characteristics of the particular impregnant.
After two or more of the cores constructed in accordance with the
aforementioned process are completed, they are assembled with the stud bands
and other hardware to constitute a loop track having essentially constant
concavo-convex cross section, and normally circular configuration.
Core assembly is begun by assembling the next largest core within
the largest core. This is accomplished by using a fixture to deform the
smaller oore into a shape similar to a cardioid. m is makes it possible to
readily insert a smaller core into the larger. The smaller core is then
allowed to assume its normal shape, thus fitting properly within the larger
core. By this process additional smaller cores can be successively inserted,
if required, to build a loop track of the desired strength and number of
cores.
Ccnposite cores constructed as above described may be used in
providing "run-flat" ¢apability for conventional automative tires. When the
inflatable tire is blown the core provides a supportive strength. This of
course minimizes inJuries that occur from sudden tire decompression and
allows the vehicle to proceed to a point of repair o~ safety.
Figure 9 shows a loop track constructed in accordance with the
above description and which is provided, primarily within the loop track,
with the base frame 40 which could be a part of a vehicle chassis.
Drive wheel 41 is rotatably journalled within the loop track
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between the side panels of base frame 40, clrive wheel 41 being provided
with gear teeth thus constitut~ g a pair of drive sprockets 42, the teeth
of which interengage in the manner described above with the loop track
mechanism. Motive means to drive the drive wheel and drive sprocket 41 and
li2 is not shown and is considered to be within the skill of the art.
Obviously, such means could be an internal ccmbustion engine, electric motor,
etc. coupled to the drive wheel through state-of-the art power trains.
Rotatably journalled between the side walls of base frame 40 in
a position to exert the welght of the vehicle chassis is passive load roller
lo 43.
At the opposite end of base frame 40 and journalled between its
side walls is a swing arm 45. Swing arm 45 is preferably journalled between
the side walls 44 of base frame 40 through a rotary shock absorber 46.
Swing arm 45 primarily constitutes a pair of end walls 47, portions of each
of which extend upwardly and outside the periphery of loop track 1, thus
being positioned to have journalled therebetween an active load roller 48.
Load rollers 43 and 48 may be identical in construction and are
seen to provide an inner axial surface which may rest or roll on the auter
periphery of end caps 10. The rollers are provided at each end with roller
flanges 49, which serve the i,mportant function of providing a means to pre-
vent edgewise movement of,the loop tr,ack,thus supp~ementing the sprocket-loop
track engagement in transmitting side loads, thereby materially increasing
its stability.
Noting that swing arm end walls 47 are generally triangulate in
shape, the remaining "apex" area of the end walls are adapted to journal
therebetween an idler sprocket 50 which is constructed in a manner similar
to drive sprocket 42 and which in the same manner is provided with teeth
whioh interengage with the link mechanism described above.
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Normally circular loop track l is shown in Figure 3 in its mounted
position in generally elliptical form thus having been compressed by any
suitable means to the desired shape and being held in such Porm by load
rollers 43, 48, drive sprocket 42, and idler sprocket 50. Such compression
of the loop track. provides for more even distribution of weight per unit
area over the portion of the loop track in contact with the ground than
would be the case if its shape remained in a more circular form
Each of the sprockets 42 and 50 is thus positioned near the middle
of the end portions of the ellipse forned by the loop track and inherently
enable the track to flex vertically as obstacles and pressures are encounter-
ed. Further, the curvature of the loop track. and the aforementioned mounting
of the sprockets above-ground provide for a certain degree of longitudinal
flexibility that is inherent in such a loop track mounting system. The
latter is enhanced by the fact that swing arm 45 adJusts automatically to
the elongations and contractions of the loop track as it is operated. Thus,
as greater G-loads are transmitted from the vehicle through base frames 40
into the loop track, swing arm 47 assumes the function of a lever which is
primarily fulcrumed about the axis of active load roller 48 which at the
same time exerts greater compressive force on the loop track l. This lever
funotion causes swing arm 47 to carry or force idler sprockets 50 generally
outwardly to accc0modate the changing ellipticity of the loop track, to
maintain constant engagement of both sprockets with the loop track, thus
maintaining relatively constant tension and preventing the track from becom-
ing disengaged from the sprocket. As pressure or G forces are released, the
reverse would of course take place and the loop track would assume a more
circular form.
Thus, the inherent flexibility of the loop track l and its mount-
ing through base frame 40 utilizing swing arms 45, provides a high strength,
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lig~t-weight, re:Latively low cost, durabLe mechanism which may be used at
high and low speeds over rough as well as smooth terrain exerting low unit
area ground pressure and providlng, often cruciaL, increased comfort for
riders and a low shock environment for equipment.
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