Airless tyre with optimised supporting structure

Abstract

The present invention relates to an airless tyre (1) having a supporting structure (3) that is optimised with respect to mechanical strength and buckling resistance. The supporting structure (3) comprises at least two coaxial undulating annular elements (6) forming pairs and being interconnected at their respective extrema (M; N) by means of a connection interface (7). According to the invention, the path (C) of any corrugated annular element (6), in any circumferential plane (XZ), is a continuous and differentiable curve, and the straight line (D) connecting the respective ends (I; J) closest to one another of the two consecutive connection interfaces (7), forms, with each of the radial straight lines (DI, DJ) respectively passing through one of the ends (I; J), an angle (AI; AJ) that is at least equal to 35°.

Description

Airless pneumatic with an optimized load-bearing structure

[0001] The present invention relates to an airless tire, intended for a vehicle, and more particularly concerns its supporting structure.

[0002] A conventional tire, subjected to the internal pressure of an inflation gas, generally air, has load-carrying, force-transmission between the ground and the vehicle, and shock-absorption capabilities that make it a preferential choice for use on a vehicle. However, a risk inherent in conventional tires is a more or less rapid loss of pressure, in the event of an impact or driving over a perforating object, which could result in the vehicle being immobilized.

[0003] To eliminate this risk of pressure loss, alternative solutions to conventional tires have been developed, such as, for example, solid tires. A solid tire, which carries the load by compressing its structure, does not offer the performance advantages previously described for a conventional tire. In particular, a solid tire is generally heavy and rigid, therefore with a lower shock absorption capacity. In addition, it often has a lower load capacity and lower endurance, due to greater heating in use. Therefore, a solid tire is used only for specific vehicles, such as, for example and not exhaustively, handling equipment.

[0004] An airless tire, or more generally a tire without inflation gas, is another known alternative solution, which carries the load thanks to structural components and which has performance comparable to that of a conventional tire. An airless tire, mounted on a hub or rim, is sometimes called a "non-pneumatic elastic wheel".

[0005] Such an airless tire has been described, by way of examples, in documents WO 2003018332A1, FR 2964597A1, WO 2012102932A1, WO 2018101937A1, WO 2018102303A1, WO 2018102560A1, WO 2018125186A1.

[0006] In the following, the circumferential or longitudinal direction means the direction of rotation of the tire, the axial or transverse direction means the direction parallel to the axis of rotation of the tire and the radial direction means a direction perpendicular to the axis of rotation of the tire.

[0007] An airless tire generally comprises, radially from the inside to the outside: - a supporting structure, intended to structurally carry at least part of the load and to cooperate with a rim or a hub, - a shear strip, intended to transmit rolling forces to the supporting structure by shear and to contribute at least in part to carrying the load, -and a tread, designed to transmit rolling forces to the shear band, to be worn and to guarantee the grip of the tire on the ground.

[0008] For example, Michelin North America has been marketing for several years a complete assembled solution, consisting of an airless tire, as previously described, and a wheel, under the name MICHELIN® TWEEL®. This technical solution is mainly composed, radially from the outside to the inside, of a tread, a shear band, a load-bearing structure, consisting of highly resistant polyresin spokes and a hub made of two reinforced steel parts.

[0009] The supporting structure most often comprises, radially from the inside to the outside, means for connection with a rim or a hub, radial elements or spokes, and means for connection with a shear band. However, the supporting structure does not generally delimit a sealed internal cavity intended to contain a pressurized gas, as in a conventional tire. Consequently, an airless tire does not need to have a sealed connection with respect to a rim or a hub. Such a supporting structure comprising radial elements is described, for example, in document EP 3519204B 1.

[0010] Other load-bearing structure configurations have also been proposed. A load-bearing structure comprising an array of interconnected polygonal cells has been described in US 9004127B2. A load-bearing structure comprising interconnected metallic corrugated annular elements has also been proposed in WO 2020139682A1.

[0011] The inventors set themselves the objective of proposing an airless tire with a load-bearing structure comprising a plurality of corrugated annular elements interconnected, capable of carrying a high load, ensuring good mechanical strength of the interfaces of the supporting structure with the interface elements, such as a shear band and a rim, and ensuring satisfactory buckling strength of said supporting structure.

[0012] This objective has been achieved by an airless pneumatic tire for a vehicle, having an axis of rotation defining an axial direction, and comprising, radially from the inside to the outside, a supporting structure intended to cooperate with a rim or a hub, a shear band and a tread, -the supporting structure comprising at least two coaxial corrugated annular elements, -any corrugated annular element extending circumferentially over the entire circumference, and forming, in any circumferential plane perpendicular to the axis of rotation, a trace having a constant radial amplitude and a constant circumferential period, -two consecutive corrugated annular elements being interconnected at their respective extrema by means of a connection interface, extending over an angular sector, -each connection interface having a radial thickness, measured between the extrema of the two consecutive corrugated annular elements, and having a circumferential length, corresponding to the arc of the angular sector and measured between two ends of said connection interface, - the trace of any corrugated annular element comprising a set of portions, each delimited by two points respectively radially aligned with the respective ends, closest to each other, of two consecutive connection interfaces, -the trace of any wavy annular element, in any circumferential plane, being a continuous and derivable curve -and the straight line connecting the respective ends, closest to each other, of two consecutive connection interfaces, forming, with each of the radial lines passing respectively through one of said ends, an angle at least equal to 35°.

[0013] According to a first essential characteristic of the invention, the trace of any undulating annular element, in any circumferential plane, is a continuous and derivable curve. In other words, this curve does not include any angles, which allows to have interconnections not reduced to a point, both at the level of the internal interfaces between the corrugated annular elements and at the level of the external interfaces with the rim or the tread, which guarantees good mechanical resistance of these interfaces.

[0014] According to a second essential characteristic of the invention, the straight line connecting the respective ends, closest to each other, of two consecutive connection interfaces, forms, with each of the radial lines passing respectively through one of said ends, an angle at least equal to 35°. This angle, bounded below, makes it possible to adjust the rigidity of the corrugated annular element as well as its resistance to buckling.

[0015] Preferably, each straight line, tangent to the trace at a point radially aligned with a connection interface end, forms, with the straight line, tangent to the trace at the nearest extremum, an angle at most equal to 20°. This limitation of the angle of tangency to the trace, directly above a connection interface end, makes it possible to have admissible stresses in the connection interfaces between two consecutive corrugated annular elements.

[0016] Still preferably, any portion of said trace, delimited by two points respectively radially aligned with the respective ends, closest to each other, of two consecutive connection interfaces has a curvilinear length at least equal to 1.015 times the distance between said points. Such a portion of said trace is thus delimited by two consecutive connection interfaces, respectively positioned at two consecutive extrema, and therefore corresponds to the free part of each corrugated annular element. It is an elementary portion, duplicated periodically over the entire circumference, which defines the mechanical behavior of each corrugated annular element. The specified minimum value of curvilinear length makes it possible to guarantee optimization of the rigidity of the corrugated annular element and its buckling resistance.

[0017] Advantageously, the supporting structure being constituted by the circumferential juxtaposition of Nm elementary patterns each extending over an angular sector Am=2*Pi / Nm, the angular sector over which any connection interface is circumferentially extending is at most equal to 0.5 times the angular sector over which any elementary pattern of the supporting structure extends circumferentially. Beyond the minimum value of the specified angular sector, the connection interface has a curvilinear length too large, which complicates the manufacture by stamping of a corrugated annular element. Indeed, in this particular case of manufacture by stamping, a connection interface that is too long circumferentially would imply a top portion of the corrugated annular element that is too flat, requiring connections to the free portions with small radii of curvature, likely to induce deformations and excessively high localized stresses in these connection zones. This phenomenon is all the more damaging in the case of a composite corrugated annular element made up of a juxtaposition of blades.

[0018] Also advantageously the number Nm of elementary patterns of the supporting structure is at least equal to 5. This minimum number of elementary patterns per wheel revolution guarantees, when rolling, a homogeneous circumferential distribution of rigidities and stability with respect to buckling.

[0019] Advantageously, the number Nm of elementary patterns of the supporting structure is at most equal to 40. This maximum number of elementary patterns per wheel turn allows this design to be used for any type of tire intended to be mounted on a rim with a diameter between 13 inches and 63 inches.

[0020] According to an advantageous embodiment of the connection interface, the radial thickness of any connection interface is at most equal to the radial amplitude of the trace, preferably at most equal to 0.5 times the radial amplitude of the trace. Beyond this maximum value of radial thickness of the connection interface, the corrugated annular elements are not sufficiently deformable to be able to obtain the targeted radial deformation, or deflection, of the tire.

[0021] According to a preferred embodiment of the material constituting a corrugated annular element, any corrugated annular element comprises at least one material having a secant Young's modulus, measured at 0.2% elongation, at least equal to 50 MPa. This minimum Young's modulus value contributes to achieving the desired levels of rigidity.

[0022] According to a preferred variant of the preferred embodiment of the constituent material of a corrugated annular element, the at least one material of any corrugated annular element is a composite material, consisting of reinforcing elements coated in a polymer matrix and arranged in the circumferential direction of the tire. Such a composite material with circumferential reinforcing elements makes it possible to achieve a tire mass comparable to that of a conventional tire. In addition, the circumferential direction of the reinforcing elements is particularly suited to the mechanical stresses of the tire when rolling.

[0023] According to particular embodiments of the reinforcing elements, the reinforcing elements are polyethylene (PET), glass or carbon fibers.

[0024] According to particular embodiments of the polymer matrix for coating the reinforcing elements, the polymer matrix is ​​a thermoplastic material, such as a polycarbonate or a polyphthalamide, a polyamide such as a nylon, a copolymer.

[0025] According to a preferred embodiment of the material of the connection interface, any connection interface comprises at least one material having a secant Young's modulus, measured at 0.2% elongation, at least equal to 1 MPa.

[0026] According to particular embodiments of the material of the connection interface, at least one material of the connection interface is a vulcanized rubber, a thermoplastic material, or an elastomeric thermoplastic material. In the preferred case of a composite corrugated annular element as previously described, the materials mentioned above have a Young's modulus less than or equal to that of the material constituting the polymer matrix coating the reinforcing elements, which guarantees good deformability of the tire, in particular in the axial direction. In the general case, these types of material allow satisfactory adhesion to the corrugated annular elements.

[0027] The characteristics of the invention are illustrated by schematic figures 1 and 2, not shown to scale: -Figure 1: Overall side view of an airless tire according to the invention -Figure 2: Detailed side view of a portion of an airless tire according to the invention.

[0028] Figure 1 is an overall side view of an airless tire 1 according to the invention. The airless tire 1, intended to equip a vehicle, has an axis of rotation RR' defining an axial direction YY', and comprises, radially from the inside to the outside, a supporting structure 3 intended to cooperate with a rim or a hub 2, a shear band 4 and a tread 5. In the case shown, the supporting structure 3 is constituted circumferentially by the circumferential juxtaposition of ten elementary patterns each extending over an angular sector Am=2*Pi / 10, and is constituted radially by three coaxial corrugated annular elements 6. Any corrugated annular element 6 extends circumferentially over the entire circumference, and forms, in any circumferential plane XZ perpendicular to rotation axis RR', a trace C having a constant radial amplitude A and a constant circumferential period P. Two consecutive corrugated annular elements are interconnected at their respective extrema (M; N) by means of a connection interface 7, extending over an angular sector Ai.Each connection interface 7 has a radial thickness Ei, measured between the extrema (M; N) of the two consecutive corrugated annular elements 6, and having a circumferential length Li, corresponding to the arc of the angular sector Ai and measured between two ends (I; J) of said connection interface 7. According to the invention, the trace C of any corrugated annular element 6, in any circumferential plane XZ, is a continuous and derivable curve.

[0029] Figure 2 is a detailed side view of a portion of an airless tire according to the invention. Knowing that the trace C, shown in Figure 1, comprises a set of portions C1, each delimited by two points (I1; J1) respectively radially aligned with the respective ends (I; J), closest to each other, of two consecutive connection interfaces. Figure 2 represents such a portion C1 with two half-connection interfaces each having a curvilinear length Li / 2. The circumferential juxtaposition of this set of portions C1, combined with the two half-connection interfaces, makes it possible to constitute a corrugated annular element within the meaning of the invention.According to the invention, the straight line D connecting the respective ends (I; J), closest to each other, of two consecutive connection interfaces, forms, with each of the radial straight lines (DI, DJ) passing respectively through one of said ends (I; J), an angle (AI; ​​AJ) at least equal to 35°. Preferably, each straight line (Tu; TJI), tangent to the trace C at a point (Il; Jl), radially aligned with an end (I; J) of the connection interface 7, forms, with the straight line (TM; TN), tangent to the trace C at the nearest extremum T (M; N), an angle (Bu; BJI) at most equal to 20°. Still preferentially, the portion Cl of said trace C, delimited by two points (Il; Jl) respectively. radially aligned with the respective ends (I; J), closest to each other, of two consecutive connection interfaces has a curvilinear length at least equal to 1.015 times the distance between said points (Il; Jl).

[0030] The inventors have more particularly studied this invention for a tire of dimension 235 / 65 R16, intended to carry a nominal load equal to 1450 kg. This study tire has a different design from that of the tire shown in Figure 1, in terms of the number of coaxial corrugated annular elements and the number of circumferential elementary patterns.

[0031] Table 1 below shows the characteristics of the study tire: [Table 1]

[0032] Table 2 below shows the geometric characteristics specific to each corrugated annular element, also called a blade, with blade 1 corresponding to the most radially outer blade and blade 5 corresponding to the most radially inner blade: [Table 2]

Claims

Claims 1. Airless tire (1) for a vehicle, having an axis of rotation (RR') defining an axial direction (YY'), and comprising, radially from the inside to the outside, a supporting structure (3) intended to cooperate with a rim or a hub (2), a shear band (4) and a tread (5), - the supporting structure (3) comprising at least two coaxial corrugated annular elements (6), - any corrugated annular element (6) extending circumferentially over the entire circumference, and forming, in any circumferential plane (XZ) perpendicular to the axis of rotation (RR'), a trace (C) having a constant radial amplitude (A) and a constant circumferential period (P), -two consecutive wavy annular elements (6) being interconnected at their respective extrema (M; N) by means of a connection interface (7), extending over an angular sector (Ai), -each connection interface (7) having a radial thickness (Ei), measured between the extrema (M; N) of the two consecutive corrugated annular elements (6), and having a circumferential length (Li), corresponding to the arc of the angular sector (Ai) and measured between two ends (I; J) of said connection interface (7), -the trace (C) of any corrugated annular element (6) comprising a set of portions (Cl), each delimited by two points (Il; Jl) respectively radially aligned with the respective ends (I; J), closest to each other, of two consecutive connection interfaces (7), characterized in that the trace (C) of any corrugated annular element (6), in any circumferential plane (XZ), is a continuous and derivable curve and in that the straight line (D) connecting the respective ends (I;J), the closest to each other, of two consecutive connection interfaces (7), forms, with each of the radial lines (Di, Dj) passing respectively through one of said ends (I; J), an angle (Ai; Aj) at least equal to 35°.; 2. Airless tire (1) according to claim 2, in which each straight line (Tu; TJI), tangent to the trace (C) at a point (Il; Jl), radially aligned with a end (I; J) of the connection interface (7), forms, with the straight line (TM; TN), tangent to the trace (C) at the level of the nearest extremum (M; N), an angle (Bu; BJI) at most equal to 20°.

3. Airless tire (1) according to one of claims 1 or 2, wherein any portion (Cl) of said trace (C), delimited by two points (Il; Jl) respectively radially aligned with the respective ends (I; J), closest to each other, of two consecutive connection interfaces (7) has a curvilinear length (Li) at least equal to 1.015 times the distance between said points (Il; Jl).

4. Airless tire (1) according to any one of claims 1 to 3, the supporting structure being constituted by the circumferential juxtaposition of Nm elementary patterns each extending over an angular sector Am=2*Pi / Nm, in which the angular sector (Ai) on which any connection interface (7) is circumferentially located is at most equal to 0.5 times the angular sector (Am) on which any elementary pattern of the supporting structure (3) extends circumferentially.

5. Airless tire (1) according to claim 4, in which the number Nm of elementary patterns of the supporting structure (3) is at least equal to 5.

6. Airless tire (1) according to one of claims 3 or 4, in which the number Nm of elementary patterns of the supporting structure (3) is at most equal to 40.

7. Airless tire (1) according to any one of claims 1 to 6, wherein the radial thickness (Ei) of any connection interface (6) is at most equal to the radial amplitude (A) of the trace (C), preferably at most equal to 0.5 times the radial amplitude (A) of the trace (C).

8. Airless tire (1) according to any one of claims 1 to 7, wherein each corrugated annular element (6) comprises at least one material having a secant Young's modulus, measured at 0.2% elongation, at least equal to 50 MPa.

9. An airless tire (1) according to claim 8, wherein the at least one material of any corrugated annular element (6) is a composite material, consisting of reinforcing elements coated in a polymer matrix and arranged in the circumferential direction of the tire.

10. Airless tire (1) according to claim 9, wherein the reinforcing elements are polyethylene (PET), glass or carbon fibers.

11. Airless tire (1) according to claim 9, in which the polymer matrix is ​​a thermoplastic material, such as a polycarbonate or a polyphthalamide, a polyamide such as a nylon, a copolymer.

12. Airless tire (1) according to any one of claims 1 to 11, wherein any connection interface (7) comprises at least one material having a secant Young's modulus, measured at 0.2% elongation, at least equal to 1 MPa.

13. Airless tire (1) according to claim 12, wherein at least one material of the connection interface (7) is a vulcanized rubber, a thermoplastic material, or an elastomeric thermoplastic material.

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