Tyre tread for a heavy goods vehicle comprising stone-expelling and noise-preventing projections

Abstract

The present invention relates to a tyre of which at least one longitudinal groove (6) comprises a longitudinal distribution of projections (7), which is transverse from a recess (72) in the wall (61, 62) of the groove. Each projection has a free end (71) which is positioned at a transverse distance d1 from the opposite side wall (61, 62) of the groove, the distance being at least equal to 0.4 times the average width W of the groove (6). The height H' of the free end is at least equal to 0.7 times the depth H of the longitudinal groove (6). Each projection (7) has, at its free end (71), a longitudinal thickness L1 which is at least equal to 1 mm. Each projection (7) is positioned facing a side wall portion (61, 62) without a projection (7).

Description

Description Title • Heavy vehicle tire tread including anti-noise and stone guard protrusions

[0001] The present invention relates to a tire tread and a tire for a heavy vehicle, intended to carry heavy loads and to roll on stony ground or on tarred ground, and, more particularly, a tire for a civil engineering vehicle of the mobile crane type, intended to move from one site to another to lift heavy loads and this in particular for tires whose nominal rim radius is equal to 22.5 inches.

[0002] A tread comprises at least one rubber-based material and is intended to constitute the peripheral part of a tire and to be worn when its rolling surface comes into contact with a ground.

[0003] A tread can be defined by three dimensions: a depth, in a radial direction, a width, in a transverse direction, and a length, in a longitudinal direction. When a tread is integrated into the tire, the transverse direction is also called the axial direction, because it is parallel to the tire's axis of rotation, and the longitudinal direction is also called the circumferential direction, because it is tangent to the tire's circumference in the tire's rolling direction.

[0004] To guarantee in particular satisfactory performance in longitudinal grip, under engine torque and braking torque, and in transverse grip, it is necessary to form, in the tread, a sculpture which is a more or less complex system of cutouts, or hollows, separating elements in relief in relation to a base surface.

[0005] In the case of a tire tread for a heavy civil engineering vehicle, the raised elements are generally ribs or blocks. A raised element is a volume of rubber material delimited by a contact face, contained in the tread surface, by a bottom surface and by lateral faces connecting the contact face to the bottom surface. A rib is a circumferential relief element delimited by two adjacent longitudinal hollows, also called longitudinal grooves or more simply grooves, by adjacent we mean that there is no longitudinal groove between two adjacent grooves. Blocks are relief elements having a circumferential length smaller than the circumferential length of the tire, most often smaller than a circumferential length of contact patch measured at nominal pressure and nominal load. Blocks can be arranged so as to constitute longitudinal rows of blocks, these rows being two by two separated by longitudinal grooves.A longitudinal hollow has a mean line, not necessarily rectilinear, having at each point a tangent forming an angle between 0° and 45° with the longitudinal direction. Furthermore, within the same longitudinal row of blocks, the blocks are most often separated in pairs by transverse hollows. A transverse hollow has a mean line, not necessarily rectilinear, having at each point a tangent forming an angle between 0° and 45° with the transverse direction. Thus, the longitudinal and transverse hollows respectively form a network of cutouts separating the blocks.

[0006] The tread of a tire is most often characterized geometrically by a transverse width of the tread, in the transverse direction, and a radial depth, in a radial direction. The transverse width of the tread is defined as the transverse width of the contact surface of the tread of the new tire with a smooth ground, such as a tarred ground, when the tire is subjected to nominal pressure and load conditions recommended, for example, by the standard of the "European Tyre and Rim Technical Organization" or ETRTO (European Tyre and Wheel Technical Organization). The radial depth is defined, by convention, as the maximum radial depth measured in the hollows, corresponding to the maximum radial block height.In the case of a tire for a civil engineering vehicle of the mobile crane type, and by way of example, the transverse width of the tread is at least equal to 300 mm and the radial thickness is at least equal to 12 mm.

[0007] The usual driving conditions for a tire for a heavy vehicle such as a mobile crane are generally mixed, both off-road, on stony ground, and on-road, on tarred ground.

[0008] When the tire rolls on stony ground, its tread is likely to retain stones in its longitudinal and transverse hollows, and in particular at the intersection zones between a longitudinal hollow and a transverse hollow. These stones retained by the hollows of the tread are then likely to create perforations in the tread, which can lead to damage to the crown reinforcement of the tire, radially inside the tread, and, ultimately, to a rupture of said crown reinforcement making the tire unusable. Stone ejection devices, in the form of protuberances of suitable shape and size, have been described in documents EP 3178669, WO 0132448 and WO 2009082394.

[0009] When the tire rolls on a tarred surface, at higher speed, its tread is likely to generate noise, in particular due to the presence of longitudinal hollows in which airborne sound waves propagate. Devices for damping these sound waves, usually called anti-noise devices, often in the form of flexible obstacles forming at least a partial barrier in the longitudinal hollows, have been described in documents WO 2013171172 and WO 2012001031.

[0010] When driving on tarmac at higher speeds, the tires must also allow for proper drainage of any water that may be present on the road. Unlike purely off-road vehicles, cranes can travel at 80 km / h on asphalt roads. Noise barriers in the grooves are obstacles to this drainage and can impair grip on wet roads.

[0011] The inventors set themselves the objective of improving, for a tire, particularly for heavy vehicles for mixed use on construction sites on unpaved ground and on the road, both its ability to not retain stones in its grooves, during use on construction sites, its ability to absorb the noise it generates, during use on the road and its ability to evacuate water in the event of road driving on wet ground.

[0012] This objective has been achieved by a tire for a vehicle comprising a tread, intended to come into contact with a ground via a rolling surface and comprising cutouts delimiting raised elements extending from a bottom surface in a radial direction, -at least one cutout being a longitudinal groove, delimited by two facing side walls connected to each other by a groove bottom, and extending over the entire circumferential length L of the tread in a longitudinal direction (XX'), -each longitudinal groove having a depth H, measured between the tread surface and the groove bottom in a radial direction (ZZ'), and an average width W, measured between the two side walls in the tread surface in a transverse direction (YY'), -at least one longitudinal groove comprising a longitudinal distribution of protuberances, - each protrusion extending transversely from a recess in a wall of the longitudinal groove towards the opposite wall of said groove, the recess having a longitudinal length LA in a longitudinal direction (XX') and a transverse width TA, in the transverse direction (YY') towards the inside of the longitudinal groove, - each protuberance having a free end positioned at a transverse distance dl from the opposite side wall of the groove, at least equal to 0.4 times the average width W of the longitudinal groove, - each protuberance extending radially outwards from the bottom of the groove over a height H', at its free end, at least equal to 0.7 times the depth H of the longitudinal groove, - each protuberance having at its free end a longitudinal thickness L1 at least equal to 1 mm, - each protuberance being positioned opposite a portion of side wall without protuberance.

[0013] The tread according to the invention essentially comprises, in at least one longitudinal groove, a longitudinal distribution of protuberances, each protuberance extending from a recess capable of containing water in order to compensate the presence of the protuberance on the storage of water in the groove. This protuberance has the function of an anti-noise barrier. A noise barrier contributes to the damping of airborne sound waves propagating in the longitudinal groove, when the tire rolls on a tarred ground. To be effective, this protuberance must have a height H' at least equal to 0.7 times the depth H of the longitudinal groove in which it is positioned. The free end of these protuberances does not have a particular rigidity function, however it is necessary that it resists rolling on stony ground, therefore the free end of the protuberances must have a longitudinal thickness L1 at least equal to 1 mm. The objective of the invention being to have an operation of these protuberances preserving the grip performance on wet ground, it is appropriate that they do not disturb the flow of water in the groove.Thus the protrusion must not extend into the groove by more than 60% of the average width W of the groove. The average width W will be measured on the new tire free at the level of the rolling surface and outside the portions provided with protrusions and their recesses. Similarly, to avoid disturbing the flow of water in the groove, the area of ​​the groove opposite the protrusion and its recess must not contain any protrusion which could hinder the flow of water in the groove. Thus each protrusion is positioned opposite a portion of side wall without protrusion. This portion without protrusion is of a longitudinal length at least equal to the longitudinal length LA of the recess from which the protrusion extends. Its limits correspond to the orthogonal projections on the walls of the groove of the longitudinal ends of the recess.

[0014] The depth H of the groove is the maximum depth measured between the rolling surface and the radially innermost point of the groove bottom, in the longitudinal mid-plane of the longitudinal groove. The height H' of the protuberance corresponds to a maximum height of the protuberance from the bottom of the hollow from which the height H is measured. The height of the protuberance can vary in the transverse and / or longitudinal directions. A height H' of protuberance at least equal to 0.7 times the depth H of the longitudinal groove aims to guarantee the presence of the protuberance over almost the entire depth of the groove, for good noise barrier effectiveness.

[0015] A recess in a groove forms a hollow in the wall of a groove. Between two adjacent protrusions and their associated recesses, apart from the cutouts, the grooves usually form repetitive rectilinear or undulating patterns. It is easy for a person skilled in the art to perceive the repetitive pattern of the groove, its undulation and therefore to perceive the beginning and the end of a recess associated with a protrusion, in particular with the transition zones between the groove and its longitudinal walls and the walls of the recess making a substantially different angle of at least 30° with respect to the wall of the groove. If the junction between the walls of the groove and those of the recess is a sharp edge, the measurement of the longitudinal length LA of the recess will be made between the sharp edges.If this junction is made by the connecting radius of a rounding, the longitudinal length LA of the recess will be made in such a way that half of the length of the rounding will be considered as part of the groove and the other half as part of the recess. The measurement of the transverse width of the recess will be made between the straight line joining the two longitudinal ends of the recess and the point on the wall of the recess that is furthest away. These measurements will take place at the level of the rolling surface.

[0016] The objective of the recess being to compensate for the presence of the protuberance in half of the groove, a preferred solution is that the longitudinal length LA of the reinforcement of each protuberance is at least equal to 0.7 times the average width of the groove W and at most equal to 1.3 times the average width of the groove W.

[0017] According to the same principle, an advantageous solution is that the transverse width TA of the reinforcement of each protuberance is at least equal to 0.2 times the average groove width W and at most equal to 0.8 times the average groove width W.

[0018] These LA and TA values ​​provide a good balance between the rigidity of the raised element, the volume of rubber to be worn for wear performance and the volume of hollows to store water when driving on wet ground.

[0019] The recess must free up space to store water. It must therefore not be mainly filled by the volume of the protuberance. Thus, each protuberance has an average longitudinal thickness L1M at most equal to 50% of the longitudinal length LA of the recess, preferably at most equal to 20% of the longitudinal length LA of the recess. The average longitudinal thickness L1M is the average of the measurements of the longitudinal thickness of the protrusion on the most radially outer part of each protrusion, between their two transverse ends from its free end to the closest of the following two points: either its other transverse end, or the point of the protrusion located at a transverse distance equal to W-dl from the free end. In the case of a continuous protrusion crossing the raised element, the thickness of the protrusion at the raised element does not influence the performance of the protrusion at the groove.

[0020] A depression creates a hollow in a groove wall, thus creating two parts in the groove wall on either side of the depression. The depression itself has a wall connecting the two parts of the groove wall and also the rolling surface at the bottom of the groove. This connection can be made by a substantially radial wall to maximize the volume of the depression and its capacity to store water. However, such a configuration poses two problems. The first is that this depression is conducive to the storage of gravel which can crack the bottom of the groove up to the first metallic or textile reinforcement elements of the tire exposing them to the effect of the water present on the rolling surface and whose effect is negative on the endurance of the tire. The second problem is that the depression creates a stiffness differential on the raised element which can generate irregular wear.To overcome these problems, it is advantageous for each recess to be connected to the furrow by inclined walls forming an average angle B with the radial direction (ZZ') and for the average angle B to be at most equal to 65°. The angle B ultimately depends on the furrow width and the transverse width TA of the recess. According to the invention, it is important that the walls of the recess, when inclined, do not obstruct the flow of water in the furrow and are therefore such that their height is at most zero at the level of the wall opposite the protuberance. For this, angle B must be at most equal to the arctangent of (W+TA) / H.

[0021] A sloping wall in the recess allows for a more gradual transition of the rigidity of the relief element and therefore limits uneven wear at the recess. These sloping walls also prevent stones from sinking too deeply into the sculpture and thus act as a stone chaser. A stone chaser has the function of promoting the ejection of stones retained in the hollows, when rolling the tire on stony ground, and of preventing them from damaging the bottom of the furrow.

[0022] For an optimal effect on noise, a preferred solution is that each protuberance of the longitudinal groove extends radially over a height H' at least equal to 90% of the depth H of the longitudinal groove.

[0023] The protuberances are placed against one or other of the side walls, and two consecutive protuberances, in the longitudinal direction, not necessarily placed against the same side wall, are spaced apart by a pitch P, the longitudinal distance between said two protuberances.

[0024] All geometric characteristics described are measured on a tire tread in new condition.

[0025] According to a preferred embodiment, the protuberances of the longitudinal groove are alternately placed against one or the other of the side walls. This alternating positioning of the protuberances on one and the other of the walls means that two consecutive protuberances are not placed against the same wall, but in contact with facing walls. This alternation guarantees almost complete closure of the longitudinal groove, by overlapping the protuberances positioned on facing walls, and therefore an almost total barrier to the propagation of sound waves. Given the flow speed of the water and its viscosity, this arrangement does not constitute an obstacle in the contact area for the evacuation of the water and therefore allows good adhesion.

[0026] Advantageously, the protuberances of the longitudinal groove are spaced two by two by a pitch P at most equal to 0.1 times the circumferential length L of the tread. Knowing that, when the tire is subjected to nominal load and pressure conditions, the contact area of ​​the tread with the ground has a longitudinal length of the order of 0.1 times the length L of the tread, this condition implies the presence of at least two protuberances in the contact area closing the longitudinal groove in the contact area and thus avoiding the formation of a pipe, between the tread and the ground, likely to generate noise. It should be noted that the pitch P between two consecutive protuberances is not necessarily constant.

[0027] In the particular case of a tire comprising at least one transverse groove, an advantageous solution is that said at least one transverse groove connects two recesses of two protuberances of two adjacent longitudinal grooves delimiting a raised element. In this case, the volume of the transverse groove is added to the volume of the recess, allowing better storage and better circulation of water in the contact area. In such a case, the transverse width TA of the recess will be at most equal to the width of the raised element in the case of a full-depth transverse groove. If the transverse groove is not full-depth, then there is a wall of the recess ensuring the transition between the groove bottom and the raised bottom of the groove, which will allow the calculation of the transverse width TA of the recess.

[0028] The characteristics of the invention are illustrated by schematic figures 1 to 5, not shown to scale: -Figure 1: Top view of a portion of tread according to the invention, -Figure 2: Perspective view of a protrusion of a longitudinal tread groove according to the invention, and cross-sectional view of a protrusion of a longitudinal tread groove according to the invention with an angle B close to 45°, -Figure 3: Perspective view of a protrusion of a longitudinal tread groove according to the invention, and cross-sectional view of a protrusion of a longitudinal tread groove according to the invention with an angle B close to 5°, -Figure 4: Top view of a portion of tread comprising transverse grooves according to the invention, Figure 5: Perspective view of a protrusion of a longitudinal tread groove comprising transverse grooves according to the invention, and cross-sectional view of a protrusion of a longitudinal tread groove comprising transverse grooves according to the invention with an angle B close to 45°.

[0029] Figure 1 and 4 are top views of a portion of tread 1 according to the invention. The tread 1 of a tire for a heavy vehicle, intended to come into contact with a ground via a tread surface 2, comprises cutouts 3 delimiting raised elements 4 made of rubber extending from a bottom surface 5 in a radial direction ZZ'. The cutouts 3 of the tread 1 are either longitudinal grooves 6 of average width W, or hollows transverse 8 only present in figure 4. In the embodiment shown, on the four longitudinal grooves 6, each delimited by two side walls 61 and 62 facing each other connected to each other by a groove bottom 63, and extending over the entire length of the tread 1 in a longitudinal direction XX', each groove comprises a longitudinal distribution of protuberances 7 alternately leaning against one and the other of the side walls 61 or 62, two consecutive protuberances positioned respectively on two side walls 61 and 62 facing each other being spaced apart by a pitch P. The pitch P is variable but this is not a necessity of the invention. Each protrusion 7 is positioned in a recess 72 and has a free end 71. Each protrusion 7 is positioned opposite a portion of side wall 61, 62 without protrusion 7.

[0030] Figure 4 differs in that transverse grooves 8 join two recesses 72 of two protuberances 7 of two adjacent longitudinal grooves 6 delimiting a relief element 4.

[0031] Figures 2, 3 and 5 show a perspective view of a protrusion 7 of a longitudinal groove 6 of the tread according to the invention and a cross-sectional view of a protrusion 7 of a longitudinal groove 6 of the tread according to the invention. The protrusion 7 of the longitudinal groove 6 of depth H extends transversely from a recess 72 in a wall 61, 62 of the longitudinal groove 6 towards the opposite wall of said groove, the recess 72 having a longitudinal length LA in the transverse direction XX' and a transverse width TA, in the transverse direction YY' towards the inside of the longitudinal groove. Each protrusion comprises a free end 71, extending radially outwards from the groove bottom 63 positioned on the bottom surface 5 at a height H'. Each free end 71 is positioned at a transverse distance dl from the opposite side wall of the groove, at least equal to 0.4 times the average width W and preferably at most equal to 0.6 times the average width W. This makes it possible to adjust the compromise between noise performance for which the distance dl must be minimal and wet grip performance for which the distance dl must be maximal.

[0032] The free end 71 has a thickness L1 and the protuberance 7 an average thickness L1M shown as equal in the figures. Each recess 72 is connected to the groove 6 by inclined walls 721 forming an average angle B with the radial direction ZZ' . B is close to 45° in figures 2 and 5, 5° in figure 3. Figure 5 illustrates a possible version of the invention when a transverse groove 8 connects two reinforcements on either side of the relief element 4.

[0033] The inventors have more particularly studied this invention for a tire of dimension 445 / 75R22.5 intended to be mounted on a specific type of mobile crane, comprising a tread having a sculpture with anti-noise and stone-plough protrusions, in accordance with the invention. According to the ETRTO standard, such a tire must be capable of carrying a load of at least 6000 kg, when inflated to a pressure of at least 8 bars. This dimension ultimately aims to carry a load of 6500 kg for a pressure of 9 bar and must therefore pass the associated standards.

[0034] For the tire according to the invention, the depth H of the groove is equal to 15 mm, H' being equal to H and its width W equal to 16 mm. The free end of the protuberances are located at a distance dl from the opposite wall equal to 7.8 mm. The thickness L1 of the free end of the protuberance is equal to 2.2 mm, its average thickness L1M is equal to 1.5 mm. The length LA of the recess is 17.1 mm for a depth TA of 8.6 mm and it extends into a transverse groove with a depth of 4 mm joining another recess on the same raised element on the adjacent groove. The walls 712 of the recess make an angle B with the direction ZZ' equal to 55°. The protrusions 7 of the longitudinal groove 6 are alternately placed against one or other of the side walls of the longitudinal groove with a minimum pitch equal to 27 mm.

[0035] The tire of the example studied has an outside diameter equal to 1238 mm, which corresponds to a developed tread length L equal to 3885 mm. The tread comprises, in each of its longitudinal grooves and over its entire length L, 96 anti-noise and stone guard protrusions alternately positioned on the walls opposite the longitudinal groove, constituting 48 pairs of protrusions forming 48 anti-noise barriers. When this tire is inflated to a pressure equal to 9 bars and subjected to a load equal to 6500 kg, the contact area of ​​its tread contains, for a given longitudinal groove, 3 pairs of protrusions, each forming an anti-noise barrier extending over almost the entire width of the longitudinal groove.

[0036] The tire has passed the "coast by" noise standard of the European Union's RI 17 regulation. According to expert knowledge, the protrusion allows for a gain of 1 dB(A). Note that larger crane tires do not need to pass this type of standard.

[0037] Furthermore, the tire has passed the “Wet Grip” standard of the European Union’s RI 17 regulation.

Claims

Claims 1. Tyre for a vehicle comprising a tread (1), intended to come into contact with a ground via a rolling surface (2) and comprising cutouts (3) delimiting raised elements (4) extending from a bottom surface (5) in a radial direction (ZZ'), -at least one cutout (3) being a longitudinal groove (6), delimited by two side walls (61, 62) facing each other connected to each other by a groove bottom (63), and extending over the entire circumferential length L of the tread (1) in a longitudinal direction (XX'), -each longitudinal groove (6) having a depth H, measured between the rolling surface (2) and the groove bottom (63) in a radial direction (ZZ'), and an average width W, measured between the two side walls (61, 62) in the rolling surface (2) in a transverse direction (YY'), -at least one longitudinal groove (6) comprising a longitudinal distribution of protuberances (7), - characterized in that each protuberance (7) extends transversely from a recess (72) in a wall (61, 62) of the longitudinal groove (6) towards the opposite wall of said groove, the recess (72) having a longitudinal length LA in a longitudinal direction (XX') and a transverse width TA, in the transverse direction (YY') towards the inside of the longitudinal groove (6), - in that each protuberance has a free end (71) positioned at a transverse distance dl from the opposite side wall (61, 62) of the groove, at least equal to 0.4 times the average width W of the longitudinal groove (6), - in that each protuberance (7) extends radially outwards from the bottom of the groove (63) over a height H', at its free end, at least equal to 0.7 times the depth H of the longitudinal groove (6), - in that each protuberance (7) has at its free end (71) a longitudinal thickness L1 at least equal to 1 mm, - and in that each protuberance (7) is positioned opposite a portion of side wall (61, 62) without protuberance (7).

2. Tire according to claim 1, in which the longitudinal length LA of the reinforcement (72) of each protuberance (7) is at least equal to 0.7 times the average width W of the groove (6) and at most equal to 1.3 times the average width W of the groove (6).

3. Tire according to one of claims 1 or 2 in which the transverse width TA of the reinforcement (72) of each protuberance (7) is at least equal to 0.2 times the average width of the groove W and at most equal to 0.8 times the average width W of the groove (6).

4. Tire according to any one of the preceding claims in which each protuberance (7) has an average longitudinal thickness L1M at most equal to 50% of the longitudinal length LA of the recess, preferably at most equal to 20% of the longitudinal length LA of the recess.

5. Tire according to any one of the preceding claims in which each protuberance has a free end (71) positioned at a transverse distance dl from the opposite side wall (61, 62) of the groove, at most equal to 0.6 times the average width W of the groove (6).

6. Tire according to any one of the preceding claims, in which each recess (72) is connected to the groove (6) by inclined walls (721) forming an average angle B with the radial direction (ZZ') at most equal to 65°.

7. Tire according to any one of the preceding claims in which each protuberance (7) of the longitudinal groove (6) extends radially over a height H' at least equal to 90% of the depth H of the longitudinal groove (6).

8. A tire according to any one of the preceding claims, in which the protrusions (7) of the longitudinal groove (6) are alternately placed against one or other of the side walls (61) of the longitudinal groove (6).

9. A tire according to any one of the preceding claims, two consecutive protuberances (7), not necessarily attached to the same side wall (61), being spaced apart by a pitch P, in which the protuberances (7) of the longitudinal groove (6) are spaced two by two by a pitch P at most equal to 0.1 times the circumferential length L of the tread (2), preferably at most equal to 0.05 times the circumferential length L of the tread (2).

10. A tire according to any one of the preceding claims, comprising at least one transverse groove (8), wherein said at least one transverse groove (8) connects two recesses (72) of two protuberances (7) of two adjacent longitudinal grooves (6) delimiting a raised element (4).

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