Caterpillar made of elastomer material

Details Caterpillar made of elastomer material Caterpillar made of elastomer material

2001-07-26

2003-08-26

Morano, S. Joseph (Department: 3617)

Wheel substitutes for land vehicles

Endless belt having nonmetallic track or tread

Track formed of endless flexible belt

C305S157000, C305S179000, C264S273000

Reexamination Certificate

active

06609770

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention concerns caterpillars made of rubber for vehicles, and more particularly the reinforcement of the said caterpillars.
In what follows, “elastomer material” means a material comprising at least one elastomer that can be reinforced with at least one filler such as carbon black; diene elastomers, polyurethane and thermoplastic rubbers among others are examples of elastomer materials.
A caterpillar for a vehicle generally comprises:
a strip forming a closed loop along a longitudinal direction of given width (in a transverse direction), with an inside and an outside surface, the said strip being mainly composed of at least one elastomer material;
on the outside surface of the strip, a plurality of relief elements intended to make contact with the ground in order to ensure good traction of the vehicle fitted with the said caterpillar, the said relief elements themselves also being made of an elastomer material;
on the inside of the strip, a plurality of teeth made of an elastomer material, comprising lateral faces and front and rear faces (the latter spaced apart in the longitudinal direction), these teeth being designed at least to guide the caterpillar in order to ensure good coupling between the caterpillar and the vehicle fitted therewith.
In addition, and bearing in mind the stresses to which a caterpillar fitted to a vehicle is subjected, it is known to provide inside the strip at least one reinforcement armature that ensures dimensional stability of the caterpillar in the longitudinal direction corresponding to the direction of the loop formed by the said caterpillar. This reinforcement armature generally consists of a plurality of cables arranged in the longitudinal direction or at a relatively small angle thereto, so as to confer upon the strip an appropriate extension rigidity in the longitudinal direction sufficient to resist the forces encountered in use.
It is also known to add a supplementary reinforcement armature comprising a stack of plies each formed of a plurality of reinforcing cables or cords arranged parallel to one another and which may cross over from one layer to the next.
Among vehicles fitted with elastomer caterpillars, there are two families depending on the function fulfilled by the teeth of the said caterpillars. In a first family the teeth only have a guiding function, i.e. once the caterpillar has been fitted on a vehicle, the teeth fit between the sides of two wheels of the vehicle to ensure good solidarity between the caterpillar and the vehicle. This solution, however, results in more or less severe wear of the lateral faces of the teeth that ensure guidance by contact with the sides of the guide wheels; if this wear becomes too pronounced, it is possible that under the transverse forces occurring while rounding a bend, the teeth will come out of their recess between the sides of the guide wheels and that the trajectory of the vehicle will then become uncontrollable.
In a second family of vehicles with caterpillars, the teeth play a dual role of guiding and of transmitting the caterpillar drive forces. The caterpillar is driven by at least one wheel positioned inside the caterpillar and having a plurality of transversely orientated bars that form a kind of “squirrel cage”, each tooth that guides and moves the caterpillar fitting between two bars of the said wheel. Each bar of the drive wheel makes contact with the front face of a tooth, and this exerts contact stresses on the said face and produces shear stresses within the said tooth. These stresses may be the cause of wear on the front faces of the teeth (or the rear faces in the case of movement in reverse) and may therefore weaken the said teeth or even tear them off under the effect of repeated shearing. As described for the first family of vehicles, the teeth also guide the vehicle by virtue of the contact between their lateral faces and the drive wheels; the said lateral faces therefore also undergo more or less pronounced wear.
To reduce wear caused by friction on the lateral faces of the teeth, U.S. Pat. No. 5,984,438 proposes to provide each guiding tooth with a thermoplastic resin insert that emerges on at least one of the lateral faces of the said teeth.
Another solution is to make the teeth with relatively large volume so that a large amount of material has to be worn away before it becomes necessary to change the caterpillar. It has been found, however, that during the operation of molding inside a metallic mold, the temperature rise causes rubber materials to expand by much more than the expansion of the metallic mold; this large difference between the expansions gives rise to defects at the level of the strip's reinforcement armatures and in particular the armature whose reinforcing elements are essentially longitudinal. In effect, at each guiding tooth the expansion of the elastomer material in contact with the mold induces a bulge away from the mold that modifies the path of the armature; the armature then shows a plurality of undulations at each tooth which, during use under high tension and owing to the numerous successive cycles of curvature variation undergone by the said armature in use, increases the fatigue of the reinforcement in the said armature.
It should be mentioned that the solution proposed U.S. Pat. No. 5,989,438 does not solve this last problem because, short of replacing the entire volume of each tooth by an insert, the difference of the elastomer's expansion relative to that of the mold metal will still result in a modification of the geometry of the reinforcement armature.
On the other hand, it is the large volume of the teeth relative to the thickness of the strip which determines the cross-linking time of the said strip: to reach a satisfactory level of cross-linking at all points in the teeth (i.e. one that gives optimum physical characteristics), a longer time is needed than the time just needed to ensure proper cross-linking of the strip, and this is more costly in the industrial context.
In what follows, “guide tooth” will be used without differentiation to mean a tooth of a caterpillar of the first or second family, as described above.
SUMMARY OF THE INVENTION
One purpose of the invention is to propose an elastomeric caterpillar for a vehicle that does not show the disadvantages indicated earlier and in particular a caterpillar whose guide teeth are designed to reduce the cross-linking time without thereby distorting the reinforcement armatures.
To that end, a caterpillar comprises:
a strip forming a closed loop of width L having an inside surface and an outside surface separated by its thickness E, the said strip consisting mainly of at least one elastomer material and being reinforced by at least one longitudinal reinforcement armature whose reinforcing elements are arranged essentially in the longitudinal direction of the strip;
a plurality of relief elements projecting from the outside surface, these relief elements being intended to contact the ground to ensure good traction of the vehicle fitted with the said caterpillar;
a plurality of guide teeth with average height H projecting from the inside surface, these guide teeth comprising lateral faces and front and rear faces in the longitudinal direction;
at least one insert positioned inside each guide tooth; the said caterpillar being characterized in that:
each insert positioned within each guide tooth has a generally hollow shape forming a free space, the function fulfilled by this insert being to absorb most of the expansion of the elastomer of the guide tooth during the molding and cross-linking of the caterpillar, and to reduce the curing time of the elastomer by homogenizing the range of temperatures within the tooth.
Preferably, the hollow volume inside each inset is at least equal to the supplementary expansion volume of the elastomer.
In the caterpillar according to the invention, the presence of at least one insert having a generally hollow shape, i.e. one which reserves a volume that can be reduced by the expansion of the elastomer duri

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