Tyre for off-road heavy vehicles, comprising sidewalls with anti-attack protection

Abstract

The invention relates to a tyre (1) for off-road heavy vehicles and seeks to protect its sidewalls (2) from mechanical attacks. The sidewall (2) comprises a plurality of protrusions (6) distributed in the circumferential direction on the sidewall outer surface (21). Each projection (6) has an average thickness (E), an average circumferential length (A) and an average radial height (C), and is spaced apart from adjacent projections by an average circumferential pitch (P). According to the invention, the average circumferential length (A) is at least equal to 20% of the average circumferential pitch (P), the average circumferential pitch (P) is at most equal to 20% of the free outer diameter (De), the average thickness (E) is at least equal to 0.2% of the free outer diameter (De), the radial distance (D) is at most equal to 50% of the cross-sectional height (H), and the average radial height (C) is at least equal to 2% of the cross-sectional height (H).

Description

Technical Field

[0001] The present invention relates to tyres for off-road heavy vehicles, such vehicles being intended to travel on uneven and rocky terrain, such as construction site vehicles or military vehicles. The invention relates more particularly to the sidewalls of such tyres. Background Art

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

[0003] Generally, a tire includes two sidewalls, which are two side parts that connect the tread to two beads, respectively. The tread is located at the outer circumference of the tire and wears when the tire is running. The beads are intended to ensure that the tire is mounted on the rim.

[0004] More specifically, axially from the outside to the inside of the tire, the sidewall generally comprises: at least one outer layer of rubber material, which is in contact with the atmospheric air and generally comprises a combination of recessed or raised markings on the outer surface; a carcass reinforcement, which comprises at least one layer of metal reinforcement wrapped in rubber material; and at least one inner layer of rubber material, which is intended to be in contact with the inflation gas when the tire is mounted to the rim and inflated.

[0005] A recurring problem with tires for heavy vehicles used off-road is that, when driving on uneven and non-asphalted surfaces, the tires are subject to mechanical attack from stones and other blunt objects (e.g. metal objects) on said surface. Such mechanical attack is mainly associated with the tread and sidewalls of the tire. More specifically with respect to the sidewalls, such mechanical attack may initiate cracks that may propagate to the sidewalls of the tire and cause damage to the tire carcass, which can easily lead to a tire blowout, so that the tire needs to be removed from the vehicle.

[0006] In order to prevent the initiation and propagation of cracks in the sidewall, it is proposed, for example, in documents JP 4202168 B2 and EP 3523141 B1 to include circumferentially distributed protrusions on the outer surface of the sidewall. Summary of the invention

[0007] The aim that the inventors set themselves was to reduce the sensitivity of the sidewalls of a tyre intended to be mounted on a heavy vehicle for off-road use to mechanical attack by choosing an optimized circumferential distribution of the sidewall protrusions.

[0008] This object is achieved by a tyre for heavy vehicles used off-road, comprising two sidewalls connecting a tread intended to come into contact with the ground, respectively, to two beads intended to come into contact with the rim,

[0009] - the tyre has an axis of rotation, a free outside diameter and a section height within the meaning of the European Tyre and Rim Technical Organisation standards, the free outside diameter being measured on the tyre not mounted on a rim and not inflated,

[0010] - at least one sidewall comprises, on an outer surface of the sidewall in contact with atmospheric air, a plurality of protrusions, said plurality of protrusions protruding relative to the outer surface of the sidewall and distributed circumferentially in the circumferential direction of the tire,

[0011] each lug has a mean thickness, measured perpendicularly to the outer surface of the sidewall, a mean circumferential length, measured at the mid-thickness of the lug in an axial plane parallel to the axis of rotation, and a mean radial height, measured at the mid-thickness of the lug in a circumferential plane perpendicular to the axis of rotation,

[0012] - each lug is radially positioned relative to an end of the tread at a radial distance measured at a point at mid-thickness of the lug corresponding to its maximum thickness,

[0013] - two consecutive protuberances are circumferentially separated by an average circumferential distance measured in an axial plane at the mid-thickness of said protuberances,

[0014] - the average circumferential pitch separating two consecutive protrusions is the sum of the average circumferential length of a protrusion and the average circumferential distance between said two consecutive protrusions,

[0015] - the average circumferential length is at least equal to 20% of the average circumferential pitch,

[0016] - the average circumferential pitch is at most equal to 20% of the free outer diameter,

[0017] - an average thickness at least equal to 0.2% of the free outer diameter,

[0018] - a radial distance at most equal to 50% of the section height,

[0019] - The average radial height is at least equal to 2% of the cross-sectional height.

[0020] The invention consists essentially in protecting the sidewalls of a tyre intended for off-road driving from mechanical attack by means of a circumferential distribution of protuberances which optimizes the average size of the protuberances, the average circumferential pitch of their distribution and the radial positioning of the protuberances relative to the tread. The objective is to have a total volume of protuberances sufficient to provide effective protection but not too large in order to minimize the amount of material.

[0021] From a geometric point of view, each protrusion has an average thickness, measured perpendicular to the outer surface of the sidewall, an average circumferential length, measured at the mid-thickness of the protrusion in an axial plane parallel to the axis of rotation, and an average radial height, measured at the mid-thickness of the protrusion in a circumferential plane perpendicular to the axis of rotation. The protrusion is usually not a strict parallelepiped, but may have a relatively complex shape, so it is helpful to geometrically characterize it by the average size measured at the mid-thickness of the protrusion. The aforementioned average size is usually (although not necessarily) the same for all protrusions.

[0022] The radial distance of a lug relative to the tread end characterizes its position on the sidewall. The radial distance is usually (although not necessarily) the same for all lugs.

[0023] The average circumferential pitch separating two consecutive lugs (defined as the sum of the average circumferential length of a lug and the average circumferential distance between said two consecutive lugs) characterizes the density of the lug material around the wheel.The circumferential pitch is usually (although not necessarily) constant.

[0024] According to the invention, the average circumferential length is at least equal to 20% of the average circumferential pitch. In other words, the protrusion content calculated by volume (defined as the ratio between the average circumferential length of the protrusion and the average circumferential pitch separating two consecutive protrusions) is at least equal to 20%, thereby ensuring a sufficient amount of rubber material to protect the sidewall.

[0025] Also according to the invention, the average circumferential pitch is at most equal to 20% of the free outer diameter, thereby ensuring that the projections are evenly and sufficiently densely distributed and thus provide effective protection over the entire circumference.

[0026] Still according to the invention, the average thickness is at least equal to 0.2% of the free outer diameter. This feature ensures that the rubber material has sufficient thickness to be able to push aside obstacles and limit attacks from said obstacles.

[0027] According to another essential feature of the invention, the radial distance is at most equal to 50% of the section height. This circumstance enables the protrusions and the associated protection to be positioned radially in a sidewall region relatively close to the ground where foreign bodies liable to attack the tyre are present.

[0028] According to another essential characteristic of the invention, the average radial height is at least equal to 2% of the cross-sectional height. This condition enables the protrusion to resist any chipping that may result from an attack.

[0029] Advantageously, the average circumferential length is at least equal to 25% of the average circumferential pitch.A minimum material content by volume ensures a more effective protection.

[0030] Likewise advantageously, the average circumferential pitch is at most equal to 18% of the free outer diameter. A smaller average circumferential pitch, ie a greater density of protrusions, further improves the protective effect around the entire circumference.

[0031] More advantageously, the average thickness is at least equal to 0.25% of the free outer diameter. The greater the average thickness, the better the protection effect.

[0032] Advantageously, the radial distance is at most equal to 30% of the height of the section.The closer the protrusion is to the ground, the higher the probability that the protrusion will be effective in resisting an attack.

[0033] Likewise advantageously, the average radial height is at least equal to 4% of the cross-sectional height. The greater the average radial height, the greater the resistance of the protrusion to chipping.

[0034] Also advantageously, the average radial height is at most equal to 25% of the cross-sectional height, preferably at most equal to 20% of the cross-sectional height. This limitation of the radial height of the protrusions makes it possible to limit to a strict minimum the volume of rubber material and the temperature rise in the sidewalls, which is liable to cause their degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention is characterized by the following Figures 1 to 4 The following drawings are schematic and not drawn to scale:

[0036] - Figure 1 : side view of a portion of a tyre according to the invention,

[0037] - Figure 2 : a top view of a portion of a tire according to the invention,

[0038] - Figure 3 : A side view of the entire tire according to the invention,

[0039] - Figure 4 : Meridian half-section view of the tire after inflation and compression according to the present invention. DETAILED DESCRIPTION

[0040] Figure 1 is a side view of a portion of a tyre according to the invention. A tyre 1 for off-road heavy vehicles comprises two sidewalls 2 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 respectively. Figure 1 is depicted 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 a direction parallel to the axis of rotation of the tire and the radial direction ZZ' is a direction perpendicular to the axis of rotation of the tire.

[0041] The tyre 1 has an axis of rotation YY′, a free outer diameter De (measured on the tyre 1 not mounted on the rim 5 and not inflated) and a section height H within the meaning of the “European Tyre and Rim Technical Organisation” standard. Figure 1 The sidewall 2 in the embodiment includes a plurality of protrusions 6 on a sidewall outer surface 21 in contact with atmospheric air. The plurality of protrusions 6 protrude relative to the sidewall outer surface 21 and are circumferentially distributed in the circumferential direction XX′ of the tire.

[0042] Each protrusion 6 has an average thickness E( Figure 1 ), an average circumferential length A and an average radial height C, the average thickness E being measured perpendicular to the outer surface 21 of the sidewall, the average circumferential length A being measured at the middle thickness of the protrusion in an axial plane XY parallel to the axis of rotation YY', and the average radial height C being measured at the middle thickness of the protrusion in a circumferential plane XZ perpendicular to the axis of rotation YY'. Each protrusion 6 is radially positioned relative to the tread end at a radial distance D, the radial distance D being measured at a point corresponding to the maximum thickness of the protrusion at the middle thickness of the protrusion. Two consecutive protrusions 6 are circumferentially separated by an average circumferential distance B, which is measured at the middle 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 protrusion 6 and the average circumferential distance B between the two consecutive protrusions 6. According to the present invention, the average circumferential length A is at least equal to 20% of the average circumferential pitch P, the average circumferential pitch P is at most equal to 20% of the free outer diameter De, the average thickness E is at least equal to 0.2% of the free outer diameter De, the radial distance D is at most equal to 50% of the cross-sectional height H, and the average radial height C is at least equal to 2% of the cross-sectional height H.

[0043] Figure 2 is a top view of a portion of a tire according to the present invention. The figure more specifically shows the position of a protrusion 6 protruding relative to the outer surface 21 of the sidewall 2 and radially located on the inner side of the tread 3. The figure also depicts the average thickness E of the protrusion 6, the average circumferential length A of the protrusion 6, the average circumferential distance B and the average circumferential pitch P, the average thickness E is measured perpendicular to the outer surface 21 of the sidewall, the average circumferential pitch P is the sum of the average circumferential length A and the average circumferential distance B, and the features A, B and P are all measured in the axial plane XY at the middle thickness of the protrusion 6 (i.e. at an axial distance E / 2 from the outer surface 21 of the sidewall). In the depicted embodiment, the cross section of the protrusion 6 in the axial plane XY has a substantially trapezoidal shape, which is particularly effective from the perspective of protection. The side of the trapezoid connecting its bottom has an appropriate inclination relative to the direction perpendicular to the outer surface of the sidewall, and is connected to the sidewall by a fillet with an optimized radius.

[0044] Figure 3is a side view of the entire tire according to the invention. The figure shows more specifically the constant pitch circumferential distribution of the protrusions 6 located radially outside the sidewall 2 of the tire 1 and radially inside the tread 3 .

[0045] Figure 4 1 is a meridian half-section view of a tire according to the present invention after inflation and compression. The figure specifically shows that when the tire 1 mounted on the rim 5 and inflated is compressed, the sidewall 2 extending between the tread 3 and the bead 4 is protected from the obstacle 7 by the protrusion 6 protruding relative to the sidewall outer surface 21. Before the tire is compressed, the outer contour of the protrusion 6 is indicated by a dotted line.

[0046] Table 1 below shows an example of the characteristics of a tyre according to the invention, of size 59 / 80R63 and intended to be mounted on a heavy construction site vehicle of the tipper type:

[0047] [Table 1]

[0048]

Claims

1. A tyre (1) for a heavy vehicle for off-road use, comprising two sidewalls (2) 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), respectively, the tyre (1) has an axis of rotation (YY'), a free outer diameter (De) and a section height (H) within the meaning of the "European Tyre and Rim Technical Organization" standard, the free outer diameter (De) being measured on the tyre (1) not mounted on the rim (5) and not inflated, - at least one sidewall (2) comprises, on its outer sidewall surface (21) in contact with atmospheric air, a plurality of protuberances (6), said plurality of protuberances (6) protruding relative to the outer sidewall surface (21) and distributed circumferentially in the circumferential direction (XX') of the tire, - each lug (6) has a mean thickness (E) measured perpendicularly to the sidewall outer surface (21), a mean circumferential length (A) measured at the mid-thickness of the lug in an axial plane (XY) parallel to the axis of rotation (YY'), and a mean radial height (C) measured at the mid-thickness of the lug in a circumferential plane (XZ) perpendicular to the axis of rotation (YY'), - each lug (6) is radially positioned relative to an end of the tread at a radial distance (D) measured at a point at the mid-thickness of the lug corresponding to the maximum thickness of the lug, - two consecutive protuberances (6) are circumferentially separated by an average circumferential distance (B), said average circumferential distance (B) being measured in the axial plane (XY) at the mid-thickness of said protuberances, the average circumferential pitch (P) separating two consecutive protrusions (6) is the sum of the average circumferential length (A) of a protrusion (6) and the average circumferential distance (B) between said two consecutive protrusions (6), It is characterized in that The average circumferential length (A) is at least equal to 20% of the average circumferential pitch (P), the average circumferential pitch (P) is at most equal to 20% of the free outer diameter (De), the average thickness (E) is at least equal to 0.2% of the free outer diameter (De), the radial distance (D) is at most equal to 50% of the cross-sectional height (H), and the average radial height (C) is at least equal to 2% of the cross-sectional height (H).

2. The tire (1) according to claim 1, wherein: The average circumferential length (A) is at least equal to 25% of the average circumferential pitch (P).

3. The tire (1) according to any one of claims 1 or 2, wherein: The average circumferential pitch (P) is at most equal to 18% of the free outer diameter (De).

4. The tire (1) according to any one of claims 1 to 3, wherein: Said average thickness (E) is at least equal to 0.25% of the free outer diameter (De).

5. The tire (1) according to any one of claims 1 to 4, wherein: Said radial distance (D) is at most equal to 30% of the cross-sectional height (H).

6. The tire (1) according to any one of claims 1 to 5, wherein: The average radial height (C) is at least equal to 4% of the cross-sectional height (H).

7. The tire (1) according to any one of claims 1 to 6, wherein: Said average radial height (C) is at most equal to 25% of the cross-sectional height (H), preferably at most equal to 20% of the cross-sectional height (H).

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