Heavy-duty off-road tires with sidewalls that are protected from attack

Abstract

The present invention relates to a tire (1) for heavy vehicles intended for off-road use, the purpose of which is to protect its sidewall (2) from mechanical attack. The sidewall (2) comprises a plurality of protrusions (6) distributed circumferentially on the sidewall outer surface (21). All protrusions (6) have an average thickness (E), an average circumferential length (A), and an average radial height (C), and are separated from adjacent protrusions by an average circumferential pitch (P). According to the invention, the average circumferential length (A) is equal to at least 20% of the average circumferential pitch (P), the average circumferential pitch (P) is equal to at most 20% of the free outer diameter (De), the average thickness (E) is equal to at least 0.2% of the free outer diameter (De), the radial distance (D) is equal to at most 50% of the section height (H), and the average radial height (C) is equal to at least 2% of the section height (H).

Description

[Technical Field]

[0001] The present invention relates to tires for heavy vehicles intended for off-road use, such as construction plant vehicles or military vehicles, intended to travel on uneven, stony ground, and more particularly to the sidewalls of such tires. [Background technology]

[0002] By definition, the circumferential or longitudinal direction is the direction of rotation of the tire, the axial or lateral direction is the direction parallel to the tire's axis of rotation, and the radial direction is the direction perpendicular to the tire's axis of rotation.

[0003] Generally, a tire has two sidewalls, which connect the tread to two beads. The tread is positioned around the tire's circumference and is intended to wear down as the tire is driven. The beads are intended to securely attach the tire to the rim.

[0004] More specifically, the sidewall typically comprises, axially from the outside to the inside of the tire: at least one outer layer of rubber material that is in contact with the atmosphere and that generally has a collection of concave or convex markings on its outer surface; a carcass reinforcement that comprises at least one layer of metal reinforcement coated with a rubber material; and at least one inner layer of rubber material that is intended to come into contact with inflation gases when the tire is mounted on a rim and inflated.

[0005] A recurring problem with tires for heavy vehicles used in off-road applications is mechanical attack from stones and other blunt objects, such as metal objects, present on the ground when traveling over uneven, unpaved terrain. Such mechanical attack essentially concerns the tread and sidewall of the tire. With regard to the sidewall in particular, such mechanical attack is prone to cause cracks that can propagate into the tire sidewall, leading to damage to the tire carcass and causing the tire to burst, which may then require removal from the vehicle.

[0006] To combat the initiation and propagation of cracks in the sidewall, for example, Japanese Patent No. 4202168 (B2) and European Patent No. 3523141 (B1) propose incorporating circumferentially distributed protrusions on the outer surface of the sidewall. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent No. 4202168 (B2) [Patent Document 2] European Patent No. 3523141(B1) Summary of the Invention [Problem to be solved by the invention]

[0008] The inventors set themselves the objective of reducing the sensitivity to mechanical attacks of the sidewalls of tires intended to be fitted to heavy vehicles for off-road use by selecting an optimized circumferential distribution of the sidewall protrusions. [Means for solving the problem]

[0009] This object is achieved by means of a tire for heavy vehicles intended for off-road use, comprising two sidewalls respectively connecting a tread intended to come into contact with the ground to two beads intended to come into contact with the rim, - the tire has an axis of rotational symmetry, a free outer diameter measured on the tire not mounted on a rim and not inflated, and a section height within the meaning of the "European Tyre and Rim Technical Organisation" standard, at least one sidewall has, on its outer sidewall surface in contact with the atmosphere, a plurality of protrusions that protrude in relief relative to the outer sidewall surface and are distributed circumferentially around the tire; all protrusions have an average thickness measured perpendicular to the sidewall outer surface, an average circumferential length measured at the mid-thickness of the protrusions in an axial plane parallel to the axis of rotational symmetry, and an average radial height measured at the mid-thickness of the protrusions in a circumferential plane perpendicular to the axis of rotational symmetry; - all protrusions are positioned radially relative to the tread edge at a radial distance measured at the mid-thickness of the protrusion at a point corresponding to the maximum thickness of the protrusion; two successive protrusions are circumferentially separated by an average circumferential distance measured at the mid-thickness of said protrusions in an axial plane; the average circumferential pitch separating two successive protrusions is the sum of the average circumferential length of the protrusions and the average circumferential distance between two successive protrusions; the average circumferential length is at least equal to 20% of the average circumferential pitch, - the mean circumferential pitch is equal to a maximum of 20% of the free outer diameter, the average thickness is at least equal to 0.2% of the outer free diameter, - the radial distance is equal to a maximum of 50% of the section height, - The average radial height is equal to at least 2% of the cross-sectional height.

[0010] The invention essentially consists in protecting the sidewalls of tires intended for off-road driving from mechanical attacks by means of a circumferential distribution of protrusions optimized in terms of their average size, their average circumferential distribution pitch and their radial positioning relative to the tread, with the aim of providing an effective protection but without excessively increasing the total volume of the protrusions in order to minimize the amount of material.

[0011] From a geometrical standpoint, every protrusion has an average thickness measured perpendicular to the outer sidewall surface, an average circumferential length measured at the mid-thickness of the protrusion in an axial plane parallel to the axis of rotational symmetry, and an average radial height measured at the mid-thickness of the protrusion in a circumferential plane perpendicular to the axis of rotational symmetry. Because protrusions are generally not strictly parallelepipedal and can have relatively complex shapes, it is useful to characterize their geometry in terms of an average dimension measured at the mid-thickness of the protrusion. The aforementioned average dimensions need not necessarily be the same for all protrusions, but usually are.

[0012] The radial distance of a protrusion relative to the tread edge characterizes its position on the sidewall, and the radial distance does not necessarily have to be the same for all protrusions, but usually is.

[0013] The average circumferential pitch separating two consecutive lobes is defined as the sum of the average circumferential length of the lobes and the average circumferential distance between two consecutive lobes, and characterizes the density of the raised material around the wheel. The circumferential pitch is generally constant, although not enforced.

[0014] According to the invention, the average circumferential length is at least equal to 20% of the average circumferential pitch, in other words, the lobe volume fraction, defined as the ratio between the average circumferential length of the lobes and the average circumferential pitch separating two consecutive lobes, is at least equal to 20%, thereby ensuring a sufficient amount of rubber material to protect the sidewall.

[0015] Furthermore, according to the invention, the average circumferential pitch is equal to a maximum of 20% of the free outer diameter, which ensures a uniform and sufficiently dense distribution of the protrusions and, as a result, effective protection all around the circumference.

[0016] Furthermore, according to the invention, the average thickness is equal to at least 0.2% of the outer free diameter, this feature ensuring that the thickness of the rubber material is sufficient to possibly push aside obstacles and limit attacks from them.

[0017] According to another essential feature of the invention, the radial distance is at most equal to 50% of the section height, which condition allows the projection, and thus the associated protection, to be positioned radially in the sidewall area relatively close to the ground where foreign objects tend to attack it.

[0018] According to another essential feature of the invention, the average radial height is equal to at least 2% of the cross-sectional height, this condition making it possible to have protrusions that are resistant to any chunking that may result from an attack.

[0019] Advantageously, the average circumferential length is at least equal to 20% of the average circumferential pitch. This minimum material volume fraction ensures even more effective protection.

[0020] Also advantageously, the average circumferential pitch is at most equal to 18% of the outer free diameter. The lower the average circumferential pitch, i.e. the higher the density of the projections, the more effective the all-round protection will be.

[0021] Even more advantageously, the average thickness is equal to at least 0.25% of the outer free diameter. The higher the average thickness, the better the protection.

[0022] Advantageously, the radial distance is equal to at most 30% of the section height: the closer the protrusion is to the ground, the higher the probability that it will function effectively against an attack.

[0023] Also advantageously, the average radial height is equal to at least 4% of the cross-sectional height: the higher the average radial height, the greater the resistance of the protrusion to chunking.

[0024] Even more advantageously, the average radial height is at most equal to 25% of the cross-sectional height, preferably at most 20% of the cross-sectional height. This limitation of the radial height of the protrusions makes it possible to strictly minimize the volume of rubber material and the temperature rise in the sidewall, which tends to lead to its degradation.

[0025] The features of the present invention are illustrated by Figures 1-4, which are schematic and not to scale. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a side view of a portion of a tire according to the present invention. [Figure 2] 1 is a top view of a portion of a tire according to the present invention. [Figure 3] 1 is a side view of a complete tire according to the present invention; [Figure 4] 1 is a half-meridian section of a tire according to the invention, inflated and compressed; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] Figure 1 shows a side view of a portion of a tire according to the invention. The tire 1 for heavy vehicles intended for off-road use comprises two sidewalls 2 each connecting a tread 3 intended to come into contact with the ground to two beads 4 intended to come into contact with the rim 5. Figure 1 is illustrated in a cylindrical reference system, in which the circumferential or longitudinal direction XX' is the direction of rotation of the tire, the axial or transverse direction YY' is the direction parallel to the axis of rotation of the tire and the radial direction ZZ' is the direction perpendicular to the axis of rotation of the tire. The tire 1 has an axis of rotational symmetry YY', an outer free diameter De measured on the tire 1 not mounted on a rim 5 and not inflated, and a section height H in the sense of the "European Tyre and Rim Technical Organisation" standard. The sidewall 2 of Figure 1 is provided, on its outer sidewall surface 21 in contact with the atmosphere, with a plurality of protrusions 6 which protrude in relief relative to the outer sidewall surface 21 and are distributed circumferentially in the circumferential direction XX' of the tire. Every protrusion 6 has an average thickness E (not shown in FIG. 1 ) measured perpendicular to the sidewall outer surface 21, an average circumferential length A measured at the mid-thickness of the protrusion in an axial plane XY parallel to the axis of rotational symmetry YY′, and an average radial height C measured at the mid-thickness of the protrusion in a circumferential plane XZ perpendicular to the axis of rotational symmetry YY′. Every protrusion 6 is positioned radially relative to the tread edge at a radial distance D measured at the mid-thickness of the protrusion at a point corresponding to the maximum thickness of the protrusion. Two consecutive protrusions 6 are circumferentially separated by an average circumferential distance B measured at the mid-thickness of the protrusion in the axial plane XY. The average circumferential pitch P separating two consecutive protrusions 6 is the sum of the average circumferential length A of the protrusions 6 and the average circumferential distance B between two consecutive protrusions 6. According to the invention, the average circumferential length A is equal to at least 20% of the average circumferential pitch P, the average circumferential pitch P is equal to at most 20% of the free outer diameter De, the average thickness E is equal to at least 0.2% of the free outer diameter De, the radial distance D is equal to at most 50% of the cross-sectional height H, and the average radial height C is equal to at least 2% of the cross-sectional height H.

[0028] 2 is a top view of a portion of a tire according to the invention. This view shows in more detail the positioning of the protrusions 6, which protrude in relief relative to the outer surface 21 of the sidewall 2 and radially inward of the tread 3. It also illustrates the average thickness E of the protrusions 6, measured perpendicularly to the outer sidewall surface 21, their average circumferential length A, their average circumferential distance B, and their average circumferential pitch P, which is the sum of the average circumferential length A and the average circumferential distance B, all measured in the axial plane XY at the mid-thickness of the protrusions 6, i.e., at an axial distance E / 2 from the outer sidewall surface 21. In the illustrated embodiment, the cross section of the protrusions 6 in the axial plane XY has a substantially trapezoidal shape, which is particularly effective in terms of protection. The sides of the trapezoid connect to its base and are connected to the sidewall by chamfer radii with an appropriate inclination relative to the direction perpendicular to the outer sidewall surface and an optimized radius.

[0029] 3 is a side view of a complete tire according to the invention, showing in more detail the circumferential distribution of the projections 6 at regular intervals, positioned radially inward of the tread 3, in the radially outer portion of the sidewall 2 of the tire 1.

[0030] 4 is a half-side meridian section of an inflated and compressed tire according to the invention. This figure particularly shows the function of the protrusions 6, which project in relief relative to the outer sidewall surface 21 when the tire 1, mounted on the rim 5 and inflated, is compressed, protecting the sidewall 2, extending between the tread 3 and the bead 4, from obstacles 7. The outline of the protrusions 6 before the tire is compressed is shown by the dotted lines.

[0031] Table 1 below presents an example of features according to the invention for a tire of size 59 / 80R63 intended to be fitted to a heavy construction plant vehicle of the dump truck type. [Table 1] TIFF2025532369000002.tif83139 [Explanation of symbols]

[0032] 1. Off-road tires for large vehicles 2 Sidewall 3 Tread 4 beads 5 rims 6 Protrusion 21 Outer sidewall A Average circumferential length of protrusion B Average circumferential distance between two consecutive lobes C Average radial height of the protrusion D Radial distance of protrusion from tread edge De Tire free outer diameter H Tire section height P Average circumferential pitch of protrusions XX' Circumferential or longitudinal direction YY' axial or lateral direction ZZ' Radial

Claims

1. A tire (1) for heavy vehicles intended for off-road use, comprising two sidewalls (2) respectively connecting a tread (3) intended to come into contact with the ground to two beads (4) intended to come into contact with a rim (5); said tire (1) having an axis of rotational symmetry (YY'), a free outer diameter (De) measured on said tire (1) not mounted on said rim (5) and not inflated, and a section height (H) within the meaning of the "European Tyre and Rim Technical Organisation" standard, At least one sidewall (2) has, on its outer sidewall surface (21) in contact with the atmosphere, a plurality of protrusions (6) that protrude in relief relative to said outer sidewall surface (21) and are distributed around the periphery in the circumferential direction (XX') of the tire; All of said projections (6) have an average thickness (E) measured perpendicular to said sidewall outer surface (21), an average circumferential length (A) measured at the mid-thickness of said projections in an axial plane (XY) parallel to said axis of rotational symmetry (YY'), and an average radial height (C) measured at the mid-thickness of said projections in a circumferential plane (XZ) perpendicular to said axis of rotational symmetry (YY'), all of said projections (6) are positioned radially relative to the tread edge at a radial distance (D) measured at the mid-thickness of said projections at a point corresponding to the maximum thickness of said projections; two successive protrusions (6) are circumferentially separated by an average circumferential distance (B) measured at the mid-thickness of said protrusions in the axial plane (XY); an average circumferential pitch (P) separating two consecutive protrusions (6) is the sum of the average circumferential length (A) of the protrusions (6) and the average circumferential distance (B) between the two consecutive protrusions (6); a tire (1) characterized in that the average circumferential length (A) is equal to at least 20% of the average circumferential pitch (P), the average circumferential pitch (P) is equal to at most 20% of the outside free diameter (De), the average thickness (E) is equal to at least 0.2% of the outside free diameter (De), the radial distance (D) is equal to at most 50% of the section height (H), and the average radial height (C) is equal to at least 2% of the section height (H).

2. Tyre (1) according to claim 1, wherein said average circumferential length (A) is equal to at least 25% of said average circumferential pitch (P).

3. Tyre (1) according to claim 1 or 2, wherein said mean circumferential pitch (P) is at most equal to 18% of said outside free diameter (De).

4. Tyre (1) according to any one of claims 1 to 3, wherein said average thickness (E) is equal to at least 0.25% of said outside free diameter (De).

5. Tyre (1) according to any one of claims 1 to 4, wherein said radial distance (D) is at most equal to 30% of said section height (H).

6. Tyre (1) according to any one of claims 1 to 5, wherein said mean radial height (C) is equal to at least 4% of said section height (H).

7. Tyre (1) according to any of the preceding claims, wherein said mean radial height (C) is at most equal to 25% of said section height (H), preferably at most equal to 20% of said section height (H).

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