LOW-NOISE TIRE FOR HEAVY-DUTY VEHICLES

Description

[0001] The present invention relates to a tire for a heavy goods vehicle and concerns its tread, comprising more particularly complex evolving cutouts, that is to say cutouts whose shape evolves during the wear of the tread.

[0002] A tread, made of at least one rubber-based material, is the peripheral part of the tire, designed to wear down upon contact with the ground via a tread surface and to grip the ground. It generally includes a tread pattern, consisting of grooves separating raised elements and thus delimited by two walls of rubber material.

[0003] 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 a direction perpendicular to the axis of rotation of the tire.

[0004] Any cut in the tread, having a center line that is not necessarily straight (i.e., it can be wavy or zigzag), is circumferential, transverse, or oblique. By definition, the center line of a cut is the intersection of its center surface, equidistant from the sides delimiting the cut, with the tread surface. By convention, a cut is said to be circumferential when its center line has a roughly circumferential average direction, that is, forming an average angle of less than 30° with the circumferential direction. A cut is said to be transverse when its center line has a roughly transverse average direction, that is, forming an average angle of at least 60° with the circumferential direction. A cut is said to be oblique when its center line has a roughly oblique average direction, that is, forming an average angle of between 30° and 60° with the circumferential direction.

[0005] As is well known, driving conditions in wet weather for a vehicle, and particularly for a heavy goods vehicle, require rapid evacuation of water from the contact patch between the tread and the road surface. This evacuation ensures direct contact between the tread material and the road surface. Water that is not deflected forward or to the sides of the tire flows away or is partially captured in the grooves formed in the tread. Water evacuation is ensured by these grooves, which form a fluid drainage network that must be effective throughout the tire's service life, from when it is new until it reaches its maximum wear. The maximum wear level, defined by current regulations, is the point at which the tire must be removed from the vehicle for safety reasons.

[0006] Generally, the cutouts that allow water evacuation are essentially wide cutouts called grooves. A groove is wide enough that the opposing material walls defining it do not come into contact with each other when the tread passes over the contact patch, under recommended inflation and load conditions as defined, in particular, by the European Tyre and Rim Technical Organization (ETRTO) standards in its "Standards Manual 2020 - Commercial Vehicle Tyres." The compression and shear deformations of the raised elements defining the groove determine the pressures in contact with the ground and therefore the wear.Moreover, these deformations, by generating hysteretic losses in the tread material, impact rolling resistance, and therefore the vehicle's fuel consumption.

[0007] A tread pattern may also include narrow cuts or incisions. An incision has a width such that the opposing material walls delimiting it come into at least partial contact with each other as the tread passes over the contact patch, under the tire load and pressure conditions specified by the ETRTO as defined above. An incision does not allow water to be evacuated, but, with regard to grip, it has an edge effect in the contact patch, which in particular helps to break up any film of water that may be present on the ground.

[0008] The trade-off for having cutouts in a tread is a reduction in the volume of material to be worn. To limit the reduction in tread material volume resulting from the presence of grooves and incisions, so-called complex cutouts have been proposed. Compared to conventional grooves, which are fully open across the tread surface, these cutouts allow for an increase in tread material volume while still maintaining the cutout volume for water storage beyond a predetermined threshold, regardless of the tire's wear level.

[0009] Treads incorporating such complex cutouts have been described in particular in US documents 2017 / 174008 A1, WO 2018 / 083414 A1, WO2011039194A1, WO2011101495A1, WO2012130735A1, WO2016188956A1, WO2017174925A1, WO2019008276A1, and WO2019122677A1. A complex cutout typically opens discontinuously, at regular or irregular intervals, onto the new tread surface. A complex cutout thus presents external cavities, open to the tread surface and separated from one another in the principal direction of the complex cutout. The main direction of the complex cut often but not necessarily corresponds to the direction of water flow in said complex cut when driving on a water-covered ground.This complex groove pattern includes, in addition to external grooves, internal grooves formed within the tread. These internal grooves are not directly exposed to the tread surface when new and are generally connected to it by grooves. When new, these internal grooves are positioned radially and entirely within the tread surface and are interspersed between the external grooves. The internal grooves can be positioned at various depths within the tread thickness. Furthermore, the external and internal grooves of a single complex groove pattern are interconnected in such a way that continuous water flow within each groove is ensured at all tread wear levels, just as with a conventional continuous groove.On the other hand, the juxtaposition of internal and external cavities not connected to each other, and therefore not allowing fluid flow from one to the other, does not constitute a continuous groove and is therefore not considered a complex cut.

[0010] The combined volume of internal and external cavities in a tread with complex cutouts is generally less than that of all the grooves in a conventional tread. These grooves are fully open across the tread surface when new and have a depth corresponding to the maximum depth of the internal or external cavities. Therefore, a complex tread pattern results in a greater volume of material to be worn. Consequently, such a tread with complex cutouts is more rigid than an equivalent tread with conventional open grooves.

[0011] A tread can include both complex cutouts, opening onto the tread surface intermittently, and classic grooves, opening onto the tread surface along their entire length.

[0012] It is known that any tread pattern with grooves generates rolling noise, resulting from the vibration of air within the grooves as the tread passes over the contact patch with the ground. This air vibration is the source of resonances that generate rolling noise. This phenomenon is particularly noticeable in tread patterns with complex circumferential grooves.

[0013] From a regulatory standpoint, a tire for a heavy vehicle is classified according to its rolling noise, for example, in accordance with UNECE (United Nations Economic Commission for Europe) Regulation No. 117. Therefore, reducing the rolling noise of a tire is a current concern for tire manufacturers.

[0014] The inventors therefore set themselves the objective of reducing the rolling noise of the tread of a heavy vehicle tire comprising complex evolving circumferential cutouts, each consisting of an alternation of external and internal cavities, without degrading the resistance to irregular wear and the robustness against aggressions of the tread.

[0015] This objective was achieved by a tire for a heavy goods vehicle comprising a tread, intended to come into contact with a ground via a tread surface, and comprising at least two juxtaposed complex circumferential cutouts, forming, with a circumferential direction of the tire, an average angle of at most equal to 30°, and separated from each other by a single circumferential row of raised elements, each complex circumferential cut comprising an alternation of external cavities, open to the tread surface and distributed according to a circumferential pitch, and internal cavities, hidden inside the tread when new, two consecutive external and internal cavities respectively being connected to each other, each circumferential row of raised elements, delimited by two juxtaposed complex circumferential cuts, comprising raised elements, two by two separated by incisions, distributed according to a circumferential pitch and each having two ends opening into an external cavity of each of the two juxtaposed complex circumferential cuts, the circumferential distance between the two respective ends of any incision of each circumferential row of raised elements being equal to the circumferential pitch of the incisions,and the circumferential pitch of the external cavities of each of the two juxtaposed complex circumferential cuts being equal to the circumferential pitch of the incisions.

[0016] A first essential characteristic of the invention is that the circumferential distance between the two respective ends of any incision in each circumferential row of raised elements, delimited by two juxtaposed complex circumferential cutouts, is equal to the circumferential pitch of the incisions, that is to say the distance between two consecutive parallel incisions measured along the circumferential direction of the tire.

[0017] This condition implies that, as the tire rolls in the circumferential direction, for a given circumferential row of tread elements, when one end of a groove exits the contact patch, the end of the next groove enters the contact patch. Therefore, the end of a given groove exiting the contact patch is axially aligned with the end of the next groove entering the contact patch. In other words, any axial line of the tread intersects either a single groove or the exiting and incoming ends of two consecutive grooves. This configuration helps reduce tire rolling noise.

[0018] A second essential feature of the invention is that the circumferential pitch of the external cavities of each of the two juxtaposed complex circumferential cuts is equal to the circumferential pitch of the incisions.

[0019] This condition implies that any incision in a given circumferential row of raised elements, delimited by two juxtaposed complex circumferential cuts, opens at each end into an external cavity, forming a constant angle of incidence with the contour of that cavity. The value of this angle of incidence determines the robustness of the incision end zone against damage. Consequently, an identical angle of incidence at each incision end guarantees the same level of robustness against damage across the entire circumference of the tire.

[0020] Preferably the external cavities belonging respectively to two juxtaposed complex circumferential cuts connected by an incision, are offset, from one complex circumferential cut to the other and along the circumferential direction of the pneumatic, by a circumferential offset equal to 0.5 times the circumferential pitch of the external cavities.

[0021] A circumferential offset between the outer cavities of two juxtaposed complex cutouts, equal to half the circumferential pitch of the outer cavities, measured between their respective centers, limits the axial width variation of the circumferential row of raised elements delimited by the two juxtaposed complex cutouts. This, in turn, limits the variation in the volume of material of said circumferential row per wheel revolution along the circumferential direction. This limits the variation in the transverse notch ratio along the circumferential direction, which is beneficial for acoustic performance. By definition, the transverse or axial notch ratio, measured in a given axial plane passing through the tire's axis of rotation, is defined as the ratio between the sum of the axial cross-sections of the cutouts and the total cross-section of the tread assumed to be without cutouts.Moreover, such a circumferential offset guarantees satisfactory uniformity of the tire as well as good resistance to the appearance of irregular wear patterns.

[0022] Advantageously, the circumferential pitch of the external cavities is constant.

[0023] A constant circumferential pitch of the external cavities is advantageous from a manufacturing perspective, as it simplifies the production of the tire mold, which can then be made up of identical elementary patterns with a constant circumferential width. However, a variable circumferential pitch of the external cavities, implying an assembly of elementary patterns with varying circumferential widths, is beneficial from an acoustic standpoint, as it improves the user's subjective perception of noise, especially inside the vehicle.

[0024] Preferably, any incision forms with the line, passing through one of its extremities and tangent to the corresponding external cavity, an angle of at least 70°.

[0025] Such an inclination of the incision at each of its ends opening into an external cavity helps to avoid sharp points of material at the said end of the incision, which makes this area of ​​the sculpture more robust against aggressions and less susceptible to tearing.

[0026] Advantageously, every incision has a thickness, measured on the bearing surface, of at least 0.1 mm. In manufacturing, this minimum thickness guarantees the robustness of the mold elements, called slats, intended to mold said incisions.

[0027] Furthermore, any incision has a thickness, measured on the rolling surface, of no more than 1 mm. Beyond this value, the incision no longer performs its function of blocking the opposing relief elements as effectively, such blocking being necessary to optimize wear and rolling resistance.

[0028] Also advantageously, any complex circumferential cut having a depth, measured along a radial direction of the tire, any incision has a depth, measured along the radial direction of the tire, at least equal to 0.5 times the depth of the complex circumferential cut.

[0029] This minimum tread depth ensures consistent grip on wet or snowy surfaces, thanks to the edge effect of the cuts that remain intact throughout tread wear. Furthermore, from a regulatory standpoint, a minimum tread depth is required for a tire to be labeled "traction," for example, according to the ETRTO standard.

[0030] Furthermore, since any complex circumferential cut has a depth, measured along a radial direction of the tire, any incision has a depth, measured along the radial direction of the tire, no greater than the depth of the complex circumferential cut. Grip on wet or snowy surfaces is thus guaranteed until the complex circumferential cut is completely worn.

[0031] According to a particular and advantageous embodiment, any complex circumferential cutout is delimited by two radial corrugated walls with periodic undulations whose period is equal to the circumferential pitch of the external cavities.

[0032] According to another particular and advantageous embodiment, the tread comprises four juxtaposed complex circumferential cutouts and three circumferential rows of intermediate embossed elements.

[0033] The features of the invention are illustrated by the figures 1 to 4 schematic and not drawn to scale: Figure 1 : Perspective view of a tire tread according to a preferred embodiment of the invention. Figure 2 : Top view of a tire tread according to a preferred embodiment of the invention. Figure 3: Detailed top view of a tire tread according to a preferred embodiment of the invention. Figure 4 : Cross-sectional view, along a radial direction, of an incision opening into a complex tread cut of a tire according to a preferred embodiment of the invention.

[0034] There figure 1is a perspective view of a tread 2 of a tire 1 according to a preferred embodiment of the invention, represented in a cylindrical coordinate system defined by a circumferential direction XX', corresponding to the direction of rotation of the tire, an axial direction YY', parallel to the axis of rotation of the tire, and a radial direction ZZ', perpendicular to the axis of rotation of the tire. The tire 1 for a heavy vehicle comprises a tread 2, intended to come into contact with a ground via a tread surface 3, and comprising, in the embodiment shown, four juxtaposed complex circumferential cutouts (41, 42) and three circumferential rows of intermediate raised elements 5.The complex circumferential cutouts (41, 42) form, with the circumferential direction XX' of the tire, a mean angle of 0°, and are separated in pairs by a single circumferential row of raised elements 5. Each complex circumferential cutout (41, 42) consists of an alternation of external cavities (61, 62), open on the tread surface 3 and distributed according to a circumferential pitch, and internal cavities (71, 72), hidden inside the tread 2 in the new state, two consecutive external (61, 62) and internal (71, 72) cavities respectively being connected to each other.Each circumferential row of relief elements 5, delimited by two juxtaposed complex circumferential cutouts (41, 42), consists of relief elements 5, two by two separated by incisions 8, distributed according to a circumferential pitch and each having two ends opening into an external cavity (61, 62) of each of the two juxtaposed complex circumferential cutouts (41, 42).

[0035] There figure 2This is a top view of a tire tread according to a preferred embodiment of the invention. Each complex circumferential cut (41, 42) is formed by an alternation of external cavities (61, 62), open to the tread surface 3 and distributed according to a circumferential pitch Pc, and internal cavities (71, 72), hidden inside the tread 2 in its new state, two consecutive external (61, 62) and internal (71, 72) cavities being connected to each other. In the embodiment shown, each complex circumferential cut (41, 42) is delimited by two radial corrugated walls with periodic undulations whose period is equal to the circumferential pitch Pc of the external cavities (61, 62).Each circumferential row of relief elements 5, delimited by two juxtaposed complex circumferential cutouts (41, 42), consists of relief elements 5, two by two separated by incisions 8, distributed according to a circumferential pitch Pi and each having two ends (I1, I2) opening into an external cavity (61, 62) of each of the two juxtaposed complex circumferential cutouts (41, 42). According to the invention, the circumferential distance Di between the two respective ends (I1, I2) of any incision 8 of the circumferential row of relief elements 5 is equal to the circumferential pitch Pi of the incisions 8 and the circumferential pitch Pc of the external cavities (61, 62) of each of the two juxtaposed complex circumferential cutouts (41, 42) is equal to the circumferential pitch Pi of the incisions 8.For a given circumferential row of raised elements 5, the end of a given incision 8 is axially aligned with the end of the next incision 8. The external cavities (61, 62), belonging respectively to two juxtaposed complex circumferential cutouts (41, 42) connected by an incision 8, are offset, from one complex circumferential cutout to the other and along the circumferential direction XX' of the pneumatic tube, by a circumferential offset Dc equal to 0.5 times the circumferential pitch Pc of the external cavities (61, 62). The circumferential offset Dc is measured between the respective centers of said external cavities (61, 62). Furthermore, the circumferential pitch Pc of the external cavities (61, 62) is constant.

[0036] There figure 3is a detailed top view of a tire tread according to a preferred embodiment of the invention. In this figure, in particular, is shown an incision 8, having a thickness Ei and separating two consecutive elements of a row of raised elements 5. The incision 8 has two ends (I1, I2) opening into an external cavity (61, 62) of each of the two juxtaposed complex circumferential cutouts (41, 42) and forms with the line (D1, D2), passing through one of its ends (I1, I2) and tangent to the corresponding external cavity (61, 62), an angle (B1, B2) of at least 70°. Such an angle (B1, B2) of the incision 8 at the level of each of its ends (I1, I2) opening into an external cavity (61, 62) makes it possible to avoid sharp points of material at the level of said end of incision, which makes this area of ​​the sculpture more robust against aggressions.

[0037] There figure 4is a cross-sectional view, along a radial direction ZZ', of an incision 8 opening into a complex cut (41, 42) in the tread of a tire according to a preferred embodiment of the invention. Advantageously, the incision 8 has a thickness Ei, measured on the tread surface 3, of at least 0.1 mm and at most 1 mm. A complex circumferential cut (41, 42) having a depth H, measured along a radial direction ZZ' of the tire, the incision 8 advantageously has a depth Hi, measured along the radial direction ZZ' of the tire, of at least 0.5 times the depth H of the complex circumferential cut (41, 42) and at most equal to the depth H of the complex circumferential cut (41, 42).

[0038] The inventors have more specifically studied this invention for a tire of size 275 / 70 R22.5, intended to equip all the axles of an urban bus, and having a load capacity of 3550 kg for an inflation pressure of 9 bars.

[0039] Table 1 below presents the characteristics of a tire according to invention I: [Table 1] Features I Comments Mean angle of the complex circumferential cutouts (61, 62), with respect to the circumferential direction XX' 0° Strictly circumferential complex cutouts Circumferential distance Di between the ends (I1, I2) of an incision 8 31.6 mm Di = Pc Not circumferential Pc of external cavities (61, 62) 31.6 mm Not circumferential Pi of the incisions 8 31.6 mm Pi = Pc Circumferential distance Dc between the respective external cavities (61, 62) of 2 juxtaposed complex circumferential cutouts (41, 42) 15.8 mm Dc = 0.5*Pc Angle of the incisions 8, at their ends, with respect to the circumferential direction XX' 50° relative to XX' Angle determined with respect to the circumferential direction XX', and not with respect to the tangent to the external cavity into which the incision opens Incision thickness Ei 0.4 mm Within the range [0.1 mm; 1 mm] Depth Hi of incision 8 17.3 mm Equal to the depth H of the complex circumferential cut - 0.5 mm

[0040] A rolling noise test, in accordance with UNECE Regulation No. 117, demonstrated a noise level of 71 dB for a tire of size 275 / 70 R22.5 according to the invention.

[0041] The invention is more generally applicable to any tire intended to equip in particular any type of heavy goods vehicle axle, steering, driving or carrying, for road use.

Claims

1. Tyre (1) for a heavy-duty vehicle, comprising a tread (2), intended to come into contact with the ground via a tread surface (3), and comprising at least two juxtaposed complex circumferential cuts (41, 42) which, with a circumferential direction (XX') of the tyre, form a mean angle at most equal to 30°, and which are separated from one another by a single circumferential row of raised elements (5), - each complex circumferential cut (41, 42) comprising an alternation of external cavities (61, 62), which open onto the tread surface (3) and are distributed at a circumferential pitch (Pc), and of internal cavities (71, 72), which are hidden inside the tread (2) when the tread is new, two consecutive respectively external cavities (61, 62) and internal cavities (71, 72) being connected to one another, - each circumferential row of raised elements (5), which is delimited by two juxtaposed complex circumferential cuts (41, 42), comprising raised elements (5), pairs of which are separated by sipes (8), distributed at a circumferential pitch (Pi) and each having two ends (I1,I2) opening into an external cavity (61, 62) of each of the two juxtaposed complex circumferential cuts (41, 42), - the circumferential pitch (Pc) of the external cavities (61, 62) of each of the two juxtaposed complex circumferential cuts (41, 42) being equal to the circumferential pitch (Pi) of the sipes (8). characterized in that the circumferential distance (Di) between the respective two ends (I1, I2) of any sipe (8) in each circumferential row of raised elements (5) is equal to the circumferential pitch (Pi) of the sipes (8).

2. Tyre (1) according to Claim 1, wherein the external cavities (61, 62), belonging respectively to two juxtaposed complex circumferential cuts (41, 42) and connected by a sipe (8), are offset, from one complex circumferential cut to the other and in the circumferential direction (XX') of the tyre, by a circumferential offset (Dc) equal to 0.5 times the circumferential pitch (Pc) of the external cavities (61, 62).

3. Tyre (1) according to one of Claims 1 or 2, wherein the circumferential pitch (Pc) of the external cavities (61, 62) is constant.

4. Tyre (1) according to any one of Claims 1 to 3, wherein any sipe (8) forms, with the straight line (D1, D2) passing through one of its ends (I1, I2) and tangential to the corresponding external cavity (61, 62), an angle (B1, B2) at least equal to 70°.

5. Tyre (1) according to any one of Claims 1 to 4, wherein any sipe (8) has a thickness (Ei), measured on the tread surface (3), at least equal to 0.1 mm.

6. Tyre (1) according to any one of Claims 1 to 5, wherein any sipe (8) has a thickness (Ei), measured on the tread surface (3), at most equal to 1 mm.

7. Tyre (1) according to any one of Claims 1 to 6, any complex circumferential cut (41, 42) having a depth (H), measured in a radial direction (ZZ') of the tyre, wherein any sipe (8) has a depth (Hi), measured in the radial direction (ZZ') of the tyre, at least equal to 0.5 times the depth (H) of the complex circumferential cut (41, 42).

8. Tyre (1) according to any one of Claims 1 to 7, any complex circumferential cut (41, 42) having a depth (H), measured in a radial direction (ZZ') of the tyre, wherein any sipe (8) has a depth (Hi), measured in the radial direction (ZZ') of the tyre, at most equal to the depth (H) of the complex circumferential cut (41, 42).

9. Tyre (1) according to any one of Claims 1 to 8, wherein any complex circumferential cut (41, 42) is delimited by two undulating radial walls with periodic undulations of which the period is equal to the circumferential pitch (Pc) of the external cavities (61, 62).

10. Tyre (1) according to any one of Claims 1 to 9, wherein the tread comprises four juxtaposed complex circumferential cuts (41, 42) and three intermediate circumferential rows of raised elements (5).