TIRE FOR A CITY BUS WITH SIDEWEAR INDICATOR FOR BETTER VISIBILITY

Description

[0001] The present invention relates to a tire for a heavy vehicle for urban use, more particularly an urban bus, and concerns a sidewall of such a tire.

[0002] Generally, a tire consists of two sidewalls, which are two lateral sections connecting a tread to two beads. The tread is positioned around the circumference of the tire and is designed to wear down as the tire is driven. The beads are designed to secure the tire to a rim.

[0003] More specifically, a sidewall usually comprises, from the outside to the inside of the tire, at least one outer layer of rubber material, in contact with atmospheric air and generally comprising, on an outer face, a set of recessed or raised markings, a carcass reinforcement comprising at least one layer of metallic or textile reinforcements coated in a rubber material, and at least one inner layer of rubber material, intended to be in contact with the inflation gas when the tire is mounted and inflated on its rim.

[0004] It is well known that urban bus tires are characterized by their thick sidewalls, meaning they have an outer layer of rubber material thick enough to allow for some abrasion before the carcass reinforcement is exposed to friction against curbs. Indeed, the sidewalls of an urban bus tire are regularly subjected to friction against curbs during the bus's stopping and starting maneuvers. This friction causes abrasion of the outer sidewall layer, and when this layer is completely worn, it leads to degradation of the carcass reinforcement, potentially resulting in a burst, which is detrimental to the safety of people near the urban bus.Therefore, it is essential to be able to estimate the remaining thickness of the outer sidewall layer during the use of the tire in order to decide either to turn the tire over on its rim, to expose the other sidewall, or to replace it.

[0005] Estimating the remaining thickness of the outer sidewall layer at a given date is most often achieved through a visual inspection of the sidewall to assess the presence or absence of at least one wear indicator formed within the sidewall. A wear indicator is generally a cavity cut into the outer sidewall layer from an outer face of the sidewall; this cavity can have a variable shape. Various embodiments of such a wear indicator have been described, as examples, in documents KR 101981887B1, EP 3251958B1, JP 2014180904A, WO 2013118657A1, CN 201380726, JP 2003200717A, and EP 0726173B1. Other documents, such as DE 10 2018 211248 A1, EP 3261858 A1 and JP H04 129808 A, also provide technical instruction on wear indicators.

[0006] However, visually inspecting a wear indicator is not always easy due to insufficient contrast between the wear indicator and the surrounding sidewall, particularly in the case of direct visual inspection with the naked eye. Consequently, the presence or absence of a wear indicator often results from the observer's subjective assessment.

[0007] The inventors have also set themselves the objective, for a tire for heavy vehicles, in particular for urban buses, including at least one sidewall wear indicator, of improving the visibility of the sidewall wear indicator, and of allowing an easy correlation between the observation of the wear indicator and the remaining thickness of the outer sidewall layer.

[0008] This objective was achieved by a tire for heavy vehicles for urban use comprising two sidewalls connecting a tread, intended to come into contact with the ground, respectively to two beads, intended to come into contact with a rim, at least one sidewall comprising, on an outer sidewall face in contact with atmospheric air, at least one wear indicator recessed relative to the outer sidewall face, any wear indicator having a section opening onto the outer sidewall face containing an inscribed circle whose diameter decreases continuously with the wear of the sidewall, any wear indicator having a non-smooth inner wall, comprising a distribution of raised or recessed elements relative to the inner wall, and / or a textured relief relative to the inner wall, such that said inner wall visually contrasts with the outer sidewall face, the raised or recessed elements relative to the inner wall being striations, and the raised or recessed striations relative to the inner wall being distributed radially in a pitch enabling the residual depth of the wear indicator to be determined at a given level of sidewall wear.

[0009] For a tire intended for use on a heavy vehicle for urban use, such as a city bus, the invention essentially proposes to provide at least one of its sidewalls, which may come into contact with a curb, with at least one wear indicator comprising a through-surface containing an inscribed circle whose diameter decreases continuously with sidewall wear. An inscribed circle is understood to be a circle tangent internally to the contour of the through-surface. The diameter of the circle, that is, the portion of the through-section that it delimits, decreases continuously as the outer layer of the sidewall wears away.

[0010] Also crucially, the inner wall of the wear indicator provides visual contrast thanks to: either raised or recessed elements relative to the inner wall, such as, for example and not limited to, striations, or a raised texture such as, for example and not limited to, a "velvet" type texture made up of strands and / or blades, as described for example in documents WO 2007045425 and WO 2011036061, or a combination of the two preceding means.

[0011] These two types of features, present on the inner wall, have a dual function: on the one hand, to allow the determination, at any level of sidewall wear, of the residual depth of the hollow cavity constituting the wear indicator, i.e. the residual thickness of the outer sidewall layer in rubbery material in which the wear indicator is hollowed out, and, on the other hand, to guarantee a good contrast between the wear indicator and the portion of sidewall that surrounds it, and, consequently, a better visibility of the wear indicator guaranteeing a better reliability of the determination of the residual thickness of the outer sidewall layer.

[0012] It should be noted that the wear indicator extends from an outer sidewall face into the interior of an outer sidewall layer composed of a rubbery material, without reaching the internal carcass reinforcement within said outer sidewall layer, which consists of metal or textile reinforcements encased in a rubbery material. Thus, when the sidewall abrasion reaches the bottom of the wear indicator, the carcass reinforcement remains protected from external damage by a thin layer of rubbery material.

[0013] According to the invention, the raised or recessed elements relative to the inner wall are striations. The striations have the advantage of visually differentiating the inner wall of the wear indicator from the surrounding flank portion, and of creating a geometric discretization of the wall allowing the measurement of the evolution of the cavity depth.

[0014] According to the invention, the raised or recessed grooves relative to the inner wall are radially distributed at a pitch that allows the residual depth of the wear indicator to be determined at a given sidewall wear level. The spacing between two consecutive grooves thus makes it possible to measure the variation in abraded thickness between these two grooves.

[0015] According to a first preferred embodiment, the through-section of any wear indicator has a circular contour in the new condition of the sidewall. A circular contour is a simple and robust shape from a wear perspective. In this particular case, the contour of the through-section is therefore coincident with the inscribed circle. The new condition of the sidewall is the initial, unabraded state of the sidewall, before any grinding and therefore before any reduction in the thickness of the outer sidewall layer.

[0016] According to a second preferred embodiment, the open section of any wear indicator has a contour comprising at least two lobes in the new condition of the flank. A multi-lobed contour is a slightly more visually distinctive shape than a circular contour.

[0017] Advantageously, the open cross-section of any wear indicator has a shape that evolves according to the wear of the sidewall. In other words, the shape of the open cross-section's contour changes with the level of wear. Thus, a given contour shape can correspond to a given remaining thickness and thus characterize it. For example, when new, the contour may have a multilobed shape, and at mid-wear, a circular shape.

[0018] Advantageously, the diameter of the circle inscribed in the surface of the wear indicator, in the new condition of the sidewall, is at least 10 mm. Below 10 mm, the features present on the inner wall of the wear indicator, such as raised or recessed elements or the textured surface, become less visible as the outer layer of the sidewall wears away, because the size of the surface area decreases. This makes it more difficult to determine the remaining thickness of the outer layer of the sidewall.

[0019] Furthermore, the diameter of the circle inscribed in the surface opening, in the new condition of the sidewall, is at most 70 mm. Above 70 mm, the initial surface opening becomes too large, and the size of the wear indicator risks causing localized wear on the sidewall due to an excessive lack of material.

[0020] According to a first variant of an embodiment of the inner wall of the wear indicator, the texture of the non-smooth inner wall of the wear indicator comprises strands. According to document WO 2011036061, typically and by way of example, the average cross-sectional diameter of a strand is between 0.03 mm and 0.5 mm. The strand density is at least 5 strands / mm². The roughness Rz of the texture made up of strands is between 5 µm and 30 µm.

[0021] According to a second embodiment of the wear indicator's inner wall, the texture of the non-smooth inner wall of the wear indicator comprises blades. A texture blade is most often substantially smaller than the wall striations described previously. Document WO 2011036061 describes a texture composed of a plurality of blades that are substantially parallel to each other. Typically, and by way of example, the average width of a blade is between 0.03 mm and 0.5 mm. The pitch between two consecutive blades is at most 0.5 mm. The roughness Rz of the blade texture is between 5 µm and 30 µm.

[0022] Advantageously, at least one sidewall includes, on an outer face of the sidewall, at least two wear indicators recessed relative to the outer face of the sidewall. The presence of at least two wear indicators makes it possible to measure the remaining thickness of the outer sidewall layer at two different locations and to average the measurements thus obtained.

[0023] Even more advantageously, two consecutive wear indicators are positioned circumferentially along meridian planes forming an angle of at least 90° between them, to have residual thickness measurements sufficiently distributed around the perimeter of the side.

[0024] The features of the invention will be better understood with the help of the figures 1 à 6C , not shown to scale: Figure 1 Perspective view of a tire for an urban bus including a wear indicator according to the invention Figure 2A Cross-sectional view of a tire for an urban bus including a wear indicator according to the invention Figure 2B : Meridional cross-sectional view of a portion of the flank (detail A of the figure 2A ) Figure 3 : Cross-sectional view of a wear indicator according to the invention Figure 4A Front view of a wear indicator according to the invention having a circular open section with concentric circular grooves raised relative to the inner wall Figure 4B Front view of a non-conforming wear indicator having a circular open cross-section with raised straight grooves relative to the inner wall Figure 4C Front view of a wear indicator not according to the invention having a circular open section with a raised texture on the bottom of the inner wall Figure 4D Front view of a wear indicator having a circular contoured through-section with concentric circular grooves raised relative to the inner wall and a texture between the grooves Figure 5A Front view of a wear indicator with a multilobed (4 lobes) open cross-section Figure 5B Front view of a multi-lobed (4-lobe) wear indicator with a raised texture on the inner wall. Figure 6A Front view of a wear indicator with a multilobed (4-lobe) open cross-section in its new condition on the sidewall Figure 6B Front view of a wear indicator with a multilobed (4-lobe) open cross-section showing partial wear on the sidewall Figure 6C Front view of a wear indicator with a multilobed (4-lobe) open cross-section showing a greater degree of partial wear on the flank than the figure 6B .

[0025] There figure 1 is a perspective view of a tire 1 for an urban bus comprising a wear indicator 6 according to the invention. The tire 1 comprises two sidewalls 2 connecting a tread 3 intended to come into contact with a ground, respectively to two beads 4, intended to come into contact with a rim 5.

[0026] There figure 2A is a meridional cross-sectional view of a tire 1 for an urban bus comprising a wear indicator 6 according to the invention. This view represents half of the meridional cross-section of the tire. The sidewall 2 comprises, on an outer sidewall face 21 in contact with atmospheric air, a wear indicator 6 recessed in a layer of rubber material axially external to a carcass layer reinforcement 8 wrapped around each bead 4 mounted on the rim 5. The figure 2B is a meridional cross-sectional view of a portion of flank 2 (detail A of the figure 2A ), comprising a wear indicator 6 opening onto the axially external face of flank 21, in the new condition of flank 2. The wear indicator 6 has a section opening 61 onto the external face of flank 21, containing an inscribed circle of diameter D and an inner wall 62 extending to a depth P.

[0027] There figure 3 This is a meridional cross-sectional view of a wear indicator 6 according to the invention. The meridional profile of the example shown is a portion of a circle of radius r. The wear indicator 6 has a section 61 opening onto the outer face of the flank 21, containing an inscribed circle 7 whose diameter (D0, D1, D2, D3) decreases continuously with the wear of the flank 2, this wear being characterized by a decreasing depth (P0, P1, P2, P3). The wear indicator 6 has a non-smooth inner wall 62, comprising a distribution of elements 63 in relief or recess relative to the inner wall 62, such that said inner wall 62 visually contrasts with the outer face of the flank 21.

[0028] There figure 4A is a front view of a wear indicator 6 having a through section 61 with a circular outline and concentric circular striations 63 raised relative to the inner wall 62. The figure 4B is a front view of a wear indicator 6 having a through section 61 with a circular outline and straight striations 63 raised relative to the inner wall 62. The figure 4C is a front view of a wear indicator 6 having a circularly contoured through section 61 with a raised texture 64 on the bottom of the inner wall 62. The figure 4D is a front view of a wear indicator 6 having a through section 61 with a circular contour combining concentric circular striations 63 raised relative to the inner wall 62 and a texture 64 between the striations.

[0029] There figure 5A is a front view of a wear indicator 6 having a through section 61 with a multilobed contour (4 lobes) and an inner wall 62. The figure 5B is a front view of a wear indicator 6 with a multilobed contour (4 lobes) with a texture 64 raised on the bottom of the inner wall 62.

[0030] There figure 6A is a front view of a wear indicator 6 having a through section 61 with a multilobed contour (4 lobes) in the new condition of the sidewall, before any abrasion of the sidewall. The figure 6B is a front view of a wear indicator 6 having a through section 61 with a multilobed contour (4 lobes) in a state of partial wear of the flank. The figure 6C is a front view of a wear indicator 6 having a through section 61 with a multilobed contour (4 lobes) at a partial wear state of the flank greater than that of the figure 6B .

[0031] The invention was studied more specifically in the case of a 275 / 70R22.5 X Michelin Incity tire, intended for use on an urban bus. For such a tire, the recommended inflation pressure is 9 bar, the recommended static load is 3550 kg, and the recommended maximum speed is 100 km / h.

[0032] Two types of wear indicators were tested: one with a circular cross-section and the other with a four-lobed cross-section. In both cases, when the sidewall is new, the diameter of the circle inscribed in the cross-section is 22 mm, and the depth of the wear indicator is 5 mm. The first type features circular grooves, spaced at 2 mm intervals, with a height of 0.5 mm and a thickness of 5 mm, and / or includes a texture. The second type may or may not include a texture. Analysis of these wear indicators at various sidewall wear levels, particularly using a suitable optical system, showed that they provided good visual contrast against the rest of the sidewall and allowed for reliable determination of wear depth.

Claims

1. Tyre (1) for a heavy vehicle intended for urban use comprising two sidewalls (2) connecting a tread (3), which is designed to come into contact with the ground, respectively to two beads (4), which are designed to come into contact with a rim (5), - at least one sidewall (2) comprising, on an outer face (21) of the sidewall in contact with the atmospheric air, at least one wear indicator (6) recessed relative to the outer face (21) of the sidewall, characterized in that each wear indicator (6) has an open section (61) on the outer face (21) of the sidewall containing an inscribed circle (7), the diameter (D) of which decreases continuously as the sidewall (2) wears down, in that each wear indicator (6) has a non-smooth inner wall (62), comprising a distribution of elements (63) raised or recessed relative to the inner wall (62), and / or a texture (64) raised relative to the inner wall (62), such that said inner wall (62) contrasts visually with the outer face (21) of the sidewall, in that the elements (63) raised or recessed relative to the inner wall (62) are grooves, and in that the grooves (63) raised or recessed relative to the inner wall (62) are distributed radially at a pitch enabling the residual depth of the wear indicator (6) to be determined at a given wear level of the sidewall (2).

2. Tyre (1) according to Claim 1, in which the open section (61) of each wear indicator (6) has a circular contour when the sidewall (2) is new.

3. Tyre (1) according to Claim 1, in which the open section (61) of each wear indicator (6) has a contour comprising at least two lobes when the sidewall (2) is new.

4. Tyre (1) according to any one of Claims 1 to 3, in which the shape of the open section (61) of each wear indicator (6) changes as the sidewall (2) wears down.

5. Tyre (1) according to any one of Claims 1 to 4, in which the diameter (D) of the inscribed circle (7) in the open section (61) is at least 10 mm when the sidewall is new.

6. Tyre (1) according to any one of Claims 1 to 5, in which the diameter (D) of the inscribed circle (7) in the open section (61) is at most 70 mm when the sidewall is new.

7. Tyre (1) according to any one of Claims 1 to 6, in which the texture (64) of the non-smooth inner wall (62) of the wear indicator (6) comprises plies.

8. Tyre (1) according to any one of Claims 1 to 7, in which the texture (64) of the non-smooth inner wall (62) of the wear indicator (6) comprises strips.

9. Tyre (1) according to any one of Claims 1 to 8, in which at least one sidewall (2) has at least two wear indicators (6) on an outer face (21) of the sidewall that are recessed relative to the outer face (21) of the sidewall.