CA1093615A - Loop track mobility system - Google Patents

Abstract

ABSTRACT
This invention involves a filament wound composite core which is combined with one or more additional cores to produce a loop track characterized by transverse curvature and stud bands extending between the sandwiched or laminated cores and which extend to provide sprocket engage-ment means for transferring motive power to the loop track, and a system for mounting the novel loop track on a vehicle.

Description

;15 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 ~s . ~,-,, lV~ 15 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-,. ~ ' ~ ' , lV~3~;15 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 105~

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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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 constituting a part of said engagement means.

2. A loop track adapted to provide motive support for a vehicle as claimed in claim 1 and which is normally circular in unstressed condition and which has a generally concavo-convex transverse cross section.

3. 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, protective means connected to the ends of said stud bands providing a cover for and constituting a part of said engagement means, said loop track being generally concavo-convex in transverse cross section and normally circular in unstressed condition, a base frame located at least partially within the circum-ference of said cores, a drive sprocket journaled on said base frame and interconnecting with said engagement means, a first load roller journaled on said frame and exerting compressive pressure on the outer circumferential surface of said cores, a swing arm rotatably journaled on said base frame within said cores and having end walls extending beyond the periphery of said cores, a second load roller journaled between said end walls and exerting pressure against the outer periphery of said cores, an idler sprocket journaled within the periphery of said cores between said end walls and interconnecting with said engagement means, whereby the compressive pressure exerted on said cores by said load rollers, and the extensive forces exerted against the inner periphery of said cores by said drive wheel and said idler sprocket accommodate a flexible, generally elongate operational configuration of said cores.

4. A loop track adapted to provide motive support for vehicles as claimed in claim 3 and in which said swing arm is journaled onto said base frame through a rotatable shock absorver.

5. A loop track adapted to provide motive support for a vehicle as claimed in claim 2 and which includes an elastic strain isolating adhesive layer between said stud bands and said cores.

6. A loop track adapted to provide motive support for a vehicle comprising:
at least two concentric, composite cores, each of said cores formed of filaments bound together by a binder and comprising a number of layers of continuous, circum-ferentially wound filaments, at least one layer of cross-filaments substantially enclosing and positioned at a biased angle relative to said circumferential fibers, at least one layer of circumferentially wound filaments extending around the outer periphery of said cross-filaments, the inner diameter of the edges of each of said cores being less than the inner diameter of the central portion of said cores, thus to provide a barrel shape to said cores, a plurality of stud bands extending transversely of said cores, the ends of each of said stud bands terminating in a thread-ed portion having a thickened annular shoulder between said threads and the generally flat section extending between said cores, end caps comprising a central wall portion with two apertures therein, a protective cover flange extending outwardly from said central wall portion over the threaded ends of said stud bands, at least two legs extending inwardly from said central wall and defining a channel, a portion of each of said cores and adjacent pairs of stud bands inserted and contained respectively in said channels of each of said end caps, with the annular shoulders of adjacent stud bands inserted in the apertures in the central wall of said caps, a flexible tread secured to the outer peripheral surface of the outer core, inner link members inserted over the threads and positioned next to the annual shoulders and between stud bands of adjacent end caps, thus to constitute, in alternate conjunction with said central walls, the inner links of a chain providing spacing between said stud bands, a protective cap having end retainer shoulders threadably engaging the ends of said stud bands, and generally flat outer links journaled on said protective caps, providing connection between adjacent pairs of stud bands near their outer ends.

7. A loop track adapted to provide motive support for vehicles as claimed in claim 6 in which said cores are normally circular in unstressed condition, and which includes bearing rollers journaled on said protective caps between said inner and outer links.