Tire Element

Abstract

A non-pneumatic tire intended to be mounted on a rim and fitted to a lightweight vehicle, and the subject of the present invention is more specifically a tire element, which is able to be wound onto a rim. To increase the load-bearing capability, the tire element (1) has two stiffening portions (6) at least partially not joined together, and each stiffening portion (6) extends in the open main interior cavity (5), from a transition zone between the bead (4) and the sidewall (3) as far as the vicinity of the middle of the crown (2), and delimits, with a portion of tire element (7) facing the said stiffening portion (6), a closed secondary interior cavity (8).

Claims

1. A tire element, able to be wound onto a rim to constitute a non-pneumatic tire for a lightweight vehicle, the tire element comprising: tire a hollow tubular body having a longitudinal midline (L.sub.m) of length L and comprising at least one polymer material, tire a crown, intended to come into contact with the ground, and connected by two sidewalls to two beads which are intended to collaborate with the rim, the assembly consisting of the crown, the two sidewalls and the two beads delimiting an open main interior cavity, wherein the tire element further comprises two stiffening portions at least partially disjointed with respect to one another in the open main interior cavity, so as to have mechanical behaviours that are essentially independent, wherein each stiffening portion extends in the open main interior cavity, from a transition zone between the bead and the sidewall as far as the vicinity of the middle of the crown, and delimits, with a portion of tire element facing the said stiffening portion, a closed secondary interior cavity, such that the main interior cavity is divided into two closed secondary cavities, separated from one another by a third secondary cavity open at the beads.

2. The tire element according to claim 1, wherein the two stiffening portions are symmetrical with respect to a longitudinal midplane (XZ), passing through the middle of the crown and containing the longitudinal midline (L.sub.m) of the tire element.

3. The tire element according to claim 1, wherein each portion of the tire element facing a stiffening portion having, in any transverse plane (YZ) perpendicular to the longitudinal midline (L.sub.m) of the tire element, a transverse curvature C.sub.0, wherein each stiffening portion has, in any transverse plane (YZ), a transverse curvature C.sub.1 that has the opposite orientation to the transverse curvature C.sub.0 of the portion of tire element facing the stiffening portion (6).

4. The tire element according to claim 1, wherein the tire element is made of a single polymer material.

5. The tire element according to claim 4, wherein the polymer material of which the tire element is made has a Shore hardness at least equal to 70.

6. The tire element according to claim 5, wherein the polymer material of which the tire element is made is a thermoplastic elastomer material or a vulcanized thermoplastic material.

7. The tire element according to claim 1, wherein the tire element has a curved longitudinal midline (L.sub.m) having a monotonic radius of curvature R.

8. The tire element according to claim 1, wherein each bead comprises a longitudinal groove opening onto an interior face of a bead, facing the open main interior cavity, and extending along the entire length L of the tire element.

9. A method for producing a tire element according to claim 1, comprising a step of hot-extruding the hollow tubular body that constitutes the tire element.

10. The method according to claim 9 tire, comprising a step of hot-extruding the hollow tubular body that constitutes the tire element, using an extrusion nozzle that has a curved longitudinal mean line (L.sub.m) with a monotonic radius of curvature R.

11. A method for producing a tire element according to claim 7, comprising a step of hot-extruding the hollow tubular body that constitutes the tire element.

Description

[0034] The invention is illustrated in the figures referenced hereinbelow, which are not to scale and are described below:

[0035] FIG. 1A: Cross section through a tire element according to the invention.

[0036] FIG. 1B: Perspective view of a tire element according to the invention.

[0037] FIG. 1C: Side view of a tire element according to the invention.

[0038] FIG. 2: Cross section through a non-pneumatic tire which is obtained by winding a tire element according to the invention, in a compressed state.

[0039] FIG. 3A: Partial perspective view of a non-pneumatic tire in the process of being created, by winding a tire element according to the invention onto a rim.

[0040] FIG. 3B: Partial perspective view of a non-pneumatic tire obtained by winding a tire element according to the invention onto a rim.

[0041] FIG. 4: A schematic diagram of a method for hot-extruding a curved tire element according to a preferred embodiment of the invention.

[0042] FIG. 1A depicts a cross section, in a transverse plane YZ, of a tire element according to the invention. The tire element 1 is a hollow tubular body comprising at least one polymer material. It comprises a crown 2, intended to come into contact with the ground, and connected by two sidewalls 3 to two beads 4 which are intended to collaborate with a rim (not depicted). The assembly consisting of the crown 2, the two sidewalls 3 and the two beads 4 delimits an open main interior cavity 5. According to the invention, the tire element 1 comprises two stiffening portions 6 at least partially not joined together, and each stiffening portion 6 extends in the open main interior cavity 5 from each bead 4 as far as the crown 2 and delimits, with a portion of tire element 7 facing the said stiffening portion 6, a closed secondary interior cavity 8. In the preferred embodiment depicted, the two stiffening portions 6 are symmetrical with respect to the longitudinal midplane XZ, passing through the middle of the crown 2 and containing the longitudinal midline L.sub.m (depicted in FIG. 1C) of the tire element 1. Furthermore, each stiffening portion 6 has, in the transverse plane YZ, a transverse curvature C.sub.1 that has the opposite orientation to that of the transverse curvature C.sub.0 of the portion of tire element 7 facing the stiffening portion 6. Finally, each bead 4 comprises a longitudinal groove 41 opening onto an interior face 42 of a bead, facing the open main interior cavity 5, and extending along the entire length L of the tire element 1. FIG. 1B is a perspective view of a tire element according to the invention, the cross section of which is depicted in FIG. 1A. Finally, FIG. 1C is a side view of a tire element according to the invention, in the particular instance in which the tire element 1 has a curved longitudinal midline L.sub.m having a monotonic radius of curvature R.

[0043] FIG. 2 is a cross section, in a transverse plane YZ, of a non-pneumatic tire obtained by winding a tire element according to the invention, in a compressed state. In addition to the elements depicted in FIG. 1A there are a rim 10, on which the tire element is wrapped in order to form a non-pneumatic tire, and a clamping insert 9, the ends of which are positioned in the longitudinal grooves 41 of each bead 4 so as to ensure optimal clamping of the beads 4 to the rim 5. This clamping insert 9, in the case depicted, has the form of a tape extending circumferentially, in the direction XX, over the entire circumference of the non-pneumatic tire. As the non-pneumatic tire mounted on its rim 10 is compressed onto the ground, the stiffening portions 6 come into contact with one another and, by bearing against one another via their respective exterior faces, increase the stiffness of the non-pneumatic tire with respect to compression.

[0044] FIG. 3A is a partial perspective view of a non-pneumatic tire in the process of being created, by winding a tire element according to the invention onto a rim 10. The tire element 1, cut to a length L substantially equal to the circumference of the rim 10 and provided with a clamping insert, in the form of a tape 9, is applied progressively to the rim 10, with the beads being fitted against the rim flanges. FIG. 3B is a partial perspective view of a non-pneumatic tire obtained by winding a tire element according to the invention onto a rim and depicts the final state of the mounting thus achieved.

[0045] Finally, FIG. 4 is a schematic diagram of a method for hot-extruding a curved tire element 1, according to a preferred embodiment of the invention. FIG. 4 schematically describes the device for performing the step of hot-extruding the hollow tubular body that constitutes the tire element 1, using an extrusion nozzle 11 that has a curved longitudinal mean line L.sub.m with a monotonic radius of curvature R. The curved tire element 1 obtained therefore has a longitudinal mean line L.sub.m that is curved with a monotonic radius of curvature R and is easy to wind onto a storage reel while awaiting the production of a non-pneumatic tire.

[0046] The invention has been studied more particularly for the case of a non-pneumatic tire for a bicycle of size 37-622, according to the designation of the ETRTO standard.

[0047] Such a non-pneumatic bicycle tire has a section width, in the direction YY, equal to 37 mm and a section height, in the direction ZZ, equal to 39 mm. It is intended to be mounted on a rim having a diameter equal to 622 mm Each stiffening portion of the tire element has a thickness equal to 3 mm and a curvilinear length, comprised between its interface with the bead and its interface with the crown, equal to 22 mm. Furthermore, each stiffening portion of the tire element has an interface with the bead which is positioned, in the direction ZZ, at a distance, from the end of the bead, equal to 3 mm, and has an interface with the crown which is positioned, in the direction YY, at a distance, with respect to the longitudinal midplane XZ, equal to 2 mm. The polymer material of which the tire element is made is a vulcanized thermoplastic material having a Shore A hardness equal to 86, measured at 23 C., and a cure temperature of between 175 C. and 230 C. Finally, the tire element has a curved longitudinal midline having a monotonic radius of curvature R equal to approximately 300 mm.

[0048] The inventors have demonstrated that the stiffening of the non-pneumatic tire leads to a significant reduction in the radial deformation of the crown, or deflection. The deflection changes from 15 mm, for a reference non-pneumatic tire without a stiffening portion, to a deflection of 5 mm for a non-pneumatic tire according to the invention, with two stiffening portions, which is to say that the deflection is reduced by a factor of 3, for the same applied load.