Wheel substitutes for land vehicles – Endless belt having nonmetallic track or tread – Track formed of endless flexible belt
Patent
1996-08-12
1997-10-21
Stormer, Russell D.
Wheel substitutes for land vehicles
Endless belt having nonmetallic track or tread
Track formed of endless flexible belt
305185, B62D 5518
Patent
active
056789033
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a resilient suspension device for a vehicle and more particularly to a short track wheel comprising a resilient band entraining a pair of rollers.
BACKGROUND OF THE INVENTION
Conventional tracked suspension devices utilize a pair of outer rollers and a number of intermediate support rollers. This type of tracked device is relatively complex and exhibits high rolling resistance.
Tracked devices using resilient endless bands are known, and examples of such devices are disclosed in U.S. Pat. No. 2,055,932 to Kitchen, U.S. Pat. No. 4,386,809 to Lapsys, and in the present inventor's prior U.S. Pat. No. 4,957,332. The bands or tracks of such devices function as a resilient suspension device which provide an extensive area of contact between the track and the supporting surface.
However, the load supporting capacity of the known devices is limited. It would be desirable if a resilient track wheel was capable of supporting a large vehicle load while providing a large area of contact between the track and supporting surface.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a track wheel with a large load carrying capacity while also having a large footprint in soft ground.
A further object of one embodiment of the invention is to provide a track wheel with small overall size and small mass while also having a relatively large footprint in soft ground.
The load supporting capacity of a spring track is mainly a function of its material properties, its curvatures and its length. In the present inventor's prior U.S. Pat. No. 4,957,332, the limit of the track curvature and length is expressed in terms of a track arc angle between rollers of 15.degree., or greater. It has now been determined that tracks with a relatively small arc, and specifically with an arc smaller than 15.degree., can support a heavy load provided the longitudinal curvature radius is less than 20 times the transverse curvature radius. The flatter, or large radius small arc portion between rollers provides an increased surface contacting area, or footprint.
It has also been found that the load on a track wheel, with preferred radii, can be increased until the track segment, with highest bending load, is bent straight, beyond which the track buckles. The resistance to bending of a thin, dual curved band, such as employed by the present invention, is dependant on the transverse and longitudinal curvatures of the band, and properties of the material used. Specifically, the track band will bend to a straight segment at maximum load, when R/r=E/12S, where R and r are the radii of the initial, or unloaded, longitudinal and transverse curvatures, respectively, and E is the Modulus of Elasticity of the material, and S is the highest acceptable material stress (yield point). With R/r radii ratios higher than 1/12 times the E/S ratio, the band will deflect beyond a straight line, and buckle, before the yield point is reached and the load is less than the maximum possible load.
In accordance with the present invention there is provided a self supporting spring track for mounting on a pair of load bearing rollers, said track comprising a continuous resilient band having a preformed transverse and longitudinal curvature for resisting flattening to a larger radius under load but substantially free to bend to a smaller radius of curvature for passage around said rollers, and wherein the radius of said transverse curvature is substantially equal to the radius of said rollers, and the radius of said longitudinal curvature is from 2.2 to 20 times the radius of said transverse curvature, in the unmounted and unconfined state of the track.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side elevational view of a track wheel of this invention.
FIG. 2 is a side view of an unmounted band for the track wheel of FIG. 1.
FIG. 3 is an end view of the track of FIG. 2.
FIG. 4 is a side view of the band of FIG. 2, at reduced scale, shown with the loop cut.
DESCRIPTION OF THE PREFERRED
REFERENCES:
patent: 2055932 (1936-09-01), Kitchen
patent: 2661249 (1953-12-01), Bonmartini
patent: 3619012 (1971-11-01), Bizier et al.
patent: 4378133 (1983-03-01), Trautwein
patent: 4386809 (1983-06-01), Lapsys
patent: 4957332 (1990-09-01), Batelaan
Bitner Ronald G.
Stormer Russell D.
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