Heavy-duty vehicle tire with improved tread wear

Abstract

The present invention aims to improve the resistance to irregular wear of a tire tread for a heavy goods vehicle, comprising at least three complex cutouts (31, 32, 33). According to the invention, they are arranged relative to each other, in a first direction (D1), such that the middle (I) of any external cavity (41) of a first cutout (31), interposed between a second and a third cutout (32, 33), is aligned, in a second direction (D2) with the respective middles (J, K) of the incisions (42) of the second and third cutouts (32, 33), and such that the middle (L) of any incision (42) of the first cutout (31) is aligned, in the second direction (D2), with the respective middles (M, N) of the external cavities (43) of the second and third cutouts (32, 33).Furthermore, the incisions (52) separating two consecutive blocks (51) are parallel to each other, and distributed, according to the first direction (D1), according to a constant average pitch (Pi). Abstract figure: Fig.1.

Description

Title of the invention: Heavy goods vehicle tire with improved tread wear

[0001] The present invention relates to a tire for a heavy goods vehicle, intended to run on tarmacked roads, and more particularly concerns its tread.

[0002] A tread, located at the periphery of the tire and intended to be worn when it comes into contact with a ground via a rolling surface, is made of at least one rubber-based material. It generally comprises a sculpture which is a combination of cutouts, or hollows, and raised elements, intended in particular to ensure satisfactory grip performance, more particularly on a wet road surface.

[0003] As is known, the driving conditions of a vehicle in wet weather, and more particularly those of a heavy goods vehicle, require rapid evacuation of the water present in the contact surface between the tread of the tire and the road surface. This evacuation ensures direct contact of the material constituting the tread with this road surface via the rolling surface. The water which is not pushed towards the front or the sides of the tire flows away or is partly captured in the cutouts formed in the tread.

[0004] Water evacuation is ensured by the cutouts which form a fluid flow network which must preferably be durable, that is to say effective throughout the entire period of use of the tire between its new condition and its maximum state of wear. The maximum state of wear, set by the regulations in force, is the state from which the tire must be removed from the vehicle for safety reasons.

[0005] Heavy goods vehicle tires generally have a relatively large available void volume in the contact patch when new. Available void volume means a void volume that can be filled by water present on the road surface. The void volume opening onto the rolling surface is evaluated when the tire is subjected to recommended inflation and load conditions as defined in particular by the European standards of the “European Tyre and Rim Technical Organization” or “ETRTO” in its “Standards Manual 2022 - Commercial Vehicle Tyres”.

[0006] Among the cutouts, a distinction is made between incisions and grooves. The incisions have a width such that the facing material walls delimiting them come into contact at least partially with each other, when the tread passes through the contact surface, under the load and pressure conditions of the tire specified by the ETRTO: which limits the deformations of the facing material portions and therefore the wear. On the other hand, the grooves, which are wider than the incisions, delimit portions of material which can deform without coming into contact with each other, when the tread passes through the contact surface. These deformations of the material portions, in compression and in shear, contribute to an increase in the wear of the tread.Furthermore, in the case of the presence of grooves, an increase in deformations generates an increase in hysteretic losses of the tread, therefore in rolling resistance and, consequently, higher fuel consumption.

[0007] To limit the reduction in the volume of material of the tread resulting from the presence of grooves, so-called complex cutouts have been proposed which make it possible, compared to conventional grooves, which are entirely open over the tread surface, to increase the volume of material of the tread while respecting the hollow volume for water storage beyond a determined threshold, whatever the level of wear of the tire.

[0008] Treads comprising such complex cutouts have been described in particular in documents WO 2011039194 A1, WO 2011101495 A1, WO 2012130735 A1, WO 2020030667 A1 and WO2020058622 A1. A complex cutout opens discontinuously, at regular or irregular intervals, onto the new tread surface. Each complex cutout has external cavities, open onto the tread surface and separate from each other in the main direction of the complex cutout. The main direction of the complex cutout corresponds to the direction of flow of water in said cutout when rolling on ground covered with water. This complex cutout comprises, in addition to the external cavities, internal cavities formed inside the tread and generally connected to the tread surface by incisions.These internal cavities are positioned radially and completely inside the tread surface in the new condition, and interposed between the external cavities. The internal cavities can be positioned at different depths in the thickness of the tread. In addition, the continuity of the flow of water, or more generally of fluid, in the new condition, in each complex cut is ensured by the connection between the external and internal cavities respectively. The connections between the internal and external cavities thus form a continuous groove, independently of the local orientation of the internal or external cavities. On the other hand, the juxtaposition of unconnected internal and external cavities between . them, and therefore not allowing fluid flow from one to the other around the entire circumference of the tire, does not constitute a continuous groove.

[0009] For a tread with complex cutouts, the volume of all the cavities, internal and external, is reduced compared to that of grooves fully open on the new tread surface and having a depth corresponding to the maximum depth of the internal or external cavities. The presence of complex cutouts thus makes it possible to limit the reduction in rigidity of the tread in the new condition linked to the presence of the grooves.

[0010] A tread sculpture may comprise both complex cutouts, opening onto the tread surface intermittently, and conventional grooves, opening onto the tread surface over their entire length.

[0011] However, it has been found that the mere presence of complex cutouts does not make it possible to achieve the level of grip in traction and braking required on certain heavy goods vehicles and that it is advisable to combine these complex cutouts with oblique incisions, i.e. inclined relative to the main direction of the grooves, opening onto the running surface in the new condition. These oblique incisions generate, in the running surface, an additional length of edges, making it possible to achieve a good level of traction and satisfactory grip in so-called "slippery" conditions, particularly on ground covered with water.

[0012] The appearance of irregular wear patterns has also been observed on tire treads for heavy vehicles, comprising complex cutouts. These irregular wear patterns generate vibrations when the vehicle is running, which can degrade comfort, particularly for tires mounted on the steering axle at the front of the vehicle. This deterioration in driving comfort can be a cause for early removal of a tire, before it is completely worn. In addition, the presence of irregular wear patterns can lead to complete wear of certain parts of the tread, while other parts are only partially worn, resulting in removal of the tire with a large volume of residual wear material. Early removal of a tire results in an economic loss for the user.

[0013] The causes of initiation of irregular wear are often linked to geometric singularities of the tread pattern which induce pressure differentials in the contact area of ​​the tire with the ground. These geometric singularities are inherent in the design choices of recent tread patterns, generally comprising a network of complex, substantially circumferential cutouts and substantially transverse incisions generating heterogeneous tread blocks of different shapes and dimensions.

[0014] Therefore the inventors set themselves the objective of improving the resistance to irregular wear of a tire tread for a heavy goods vehicle, including complex circumferential cutouts, consisting of alternating external cavities and internal cavities, and transverse incisions, i.e. to delay as much as possible the appearance of irregular wear patterns on said tread.

[0015] This objective has been achieved by a tire for a heavy goods vehicle comprising a tread, intended to come into contact with a ground via a rolling surface, comprising, in a first direction tangent to the rolling surface, at least three exclusively complex cutouts, -each complex cutout being constituted, at least in the new state of the tire, by an alternation of external cavities, open on the tread surface, and incisions, extended radially towards the inside of the tread by internal cavities, two consecutive external and internal cavities respectively being connected to each other, - two consecutive complex cutouts being separated by a row of adjacent blocks in pairs and separated by an incision opening at each of its two ends into external cavities of the two consecutive complex circumferential cutouts, - the at least three complex cutouts being two by two equidistant and arranged in relation to each other, according to the first direction, -such that the middle of the largest dimension of any external cavity of a first complex cutout, interposed between a second and a third complex cutout adjacent to said first complex cutout, is aligned, in a second direction with the respective middles of the incisions of the second and third complex cutouts, closest to said external cavity of the first complex cutout, -and such that the middle of any incision of the first complex cut is aligned, in the second direction, with the respective middles of the respective largest dimensions of the external cavities of the second and third complex cuts, closest to said incision of the first complex cut, -and the incisions separating two consecutive blocks of the same row of blocks being parallel to each other, and distributed, according to the first direction, according to a constant average pitch.

[0016] The invention is essentially characterized, on the one hand, by the alignment, in a second direction, of the respective middles of the external cavities and the incisions of three consecutive complex cutouts parallel to each other and oriented in a first given direction, and, on the other hand, by a circumferential distribution, according to a constant pitch, blocks of the rows separating two consecutive complex cuts. This design allows to obtain a homogeneous distribution of the blocks separating the complex cuts both in the first and second directions, guaranteeing a balanced distribution of ground contact pressures, favorable to a later appearance of irregular wear forms.

[0017] Advantageously, the first direction in which any complex cutout extends forms, with a circumferential direction, an angle at most equal to 70°. This condition therefore excludes complex cutouts forming an angle of less than 30° relative to the axial direction, i.e. substantially transverse cutouts.

[0018] Also advantageously, the second direction forms, with the first direction, an angle at least equal to 45°. This angle defines the positioning of the mean line of the incision separating two blocks, relative to the edge of the external cavity, and consequently defines the angular sector of the portion of material delimited by the incision and the edge of the external cavity. Thus, the higher this angle, the less the angular sector of the portion of material forms a sharp angle, which reduces the risk of local tearing at the edge of the external cavity, in the vicinity of its intersection with the incision.

[0019] Advantageously, the tread having an axial width, measured in an axial direction, between a first and a second edge of the tread, and each external cavity of a complex cutout having a smaller dimension called width, measured on the tread surface between two walls of said external cavity, the width of any external cavity is at least equal to 2% and at most equal to 7% of the axial width of the tread. In this range of values, the external cavity allows, on wet ground, the evacuation of the quantity of water necessary for good grip. In addition, the width of this cavity is sufficiently small to have a compact and rigid tread, the low deformations of which limit the dissipation of energy, and, consequently, the rolling resistance.

[0020] Also advantageously, each incision of a complex cutout having a smaller dimension called width, measured on the rolling surface between two walls of said incision, the width of any incision is at most equal to 2 mm. Below 2 mm, the walls of the incision no longer necessarily come into contact and no longer ensure their blocking and stiffening function between the rows of blocks.

[0021] Still advantageously, each incision separating two adjacent blocks of the same row of blocks having a smaller dimension called width, measured on the rolling surface between two walls of said incision, the width of any incision is at most equal to 2 mm. As seen previously, below 2 mm, the walls of the incision no longer necessarily come into contact and no longer ensure their blocking and stiffening function between the blocks of the same row.

[0022] According to a preferred embodiment of the invention, the first direction according to which extends any complex cut is circumferential. This is the optimal embodiment for the use of a tire according to the invention on the steering axle of a heavy goods vehicle.

[0023] According to a first advantageous variant of the preferred embodiment with a first circumferential direction, the tread having an axial width, measured in an axial direction, between a first and a second edge of the tread, the at least three circumferential complex cutouts are distributed, in the axial direction, according to a constant average axial pitch at least equal to 10% and at most equal to 25% of the axial width of the tread. This range of axial pitch values ​​between two complex circumferential cutouts makes it possible to obtain a satisfactory compromise between the endurance and grip performance of the tread. Below 10%, the number of complex cutouts becomes too high, which limits the endurance of the tread which is then very cut, therefore more fragile.Beyond 25%, the number of complex cutouts is insufficient with regard to wet grip, because the water evacuation potential is limited, and insufficient with regard to transverse grip on dry ground, because the edge effect of the complex circumferential cutouts is then limited.

[0024] According to a second advantageous variant of the preferred embodiment with a first circumferential direction, the tread having a circumferential length, measured in the circumferential direction, at the center of the tread surface, the constant average circumferential pitch between two consecutive incisions is at least equal to 0.5% and at most equal to 2% of the circumferential length of the tread. The technical effect described with respect to the axial pitch of the complex circumferential cutouts is transposable to that of the circumferential pitch of the transverse incisions between blocks. Thus this range of circumferential pitch values ​​between two incisions makes it possible to obtain a compromise between the endurance and grip performances of the tread. Below 10%, the number of incisions becomes too high, which limits the endurance of the tread which is then very cut, therefore more fragile.Beyond 25%, the number of incisions is insufficient with regard to longitudinal adhesion, because the edge effect of the incisions is then limited.

[0025] According to a preferred variant of the preferred embodiment with a first circumferential direction, the tread comprises at least four, preferably five, complex circumferential cutouts. This configuration guarantees a satisfactory compromise between the grip and the endurance of the tread, in particular in terms of block tearing.

[0026] The characteristics of the invention are illustrated by schematic figures 1 and 2, not shown to scale: -[Fig.l]: Partial front view of a tire tread according to a preferred embodiment of the invention, -[Fig.2]: Circumferential sectional view of a complex circumferential cutout of a tread according to the preferred embodiment of the invention of [Fig.l].

[0027] [Fig. 1] is a partial front view of a tread 2 of a tire 1 according to a preferred embodiment of the invention. The tread 2, intended to come into contact with a ground via a tread surface 20, comprises, in a first circumferential direction DI tangent to the tread surface 20, three central complex circumferential cutouts (31, 32, 33), and two edge complex circumferential cutouts (not referenced in [Fig. 1]). Each complex circumferential cutout (31, 32, 33) is constituted, in the new state of the tire, by an alternation of external cavities 41, open on the tread surface 20, and incisions 42, extended radially towards the inside of the tread 2 by internal cavities 43 (see [Fig. 2]),two consecutive external cavities 41 and internal cavities 43 respectively being connected to each other. The width Wcc of any external cavity 41 is equal to 5% of the axial width W of the tread 2, for the central complex circumferential cutouts, and to 2.5% of said axial width W, for the edge complex circumferential cutouts, therefore, in both cases at least equal to 2% and at most equal to 7% of said axial width W. The width Wic of any incision 42 is equal to 0.6 mm, therefore at most equal to 2 mm. Two consecutive complex circumferential cutouts (31, 32, 33) are separated by a row of blocks 51 two by two adjacent and separated by an incision 52 opening at each of its two ends into external cavities 41 of the two consecutive complex circumferential cutouts. The width Wi of any incision 52 is equal to 0.4 mm, therefore at most equal to 2 mm. According to the invention the three complex circumferential cutouts (31, 32,33) are two by two equidistant and arranged with respect to each other, along the first circumferential direction D1, such that the middle I of the largest dimension of any external cavity 41 of a first complex circumferential cutout 31, interposed between a second and a third complex circumferential cutout (32, 33) adjacent to said first complex circumferential cutout 31, is aligned, along a second direction D2 with the respective middles (J, K) of the incisions 42 of the second and third complex circumferential cutouts (32, 33), closest to said external cavity 41 of the first complex circumferential cutout 31, and such that the middle L of any incision 42 of the first complex circumferential cutout 31 is aligned, along the second direction D2, with the respective middles (M,N) of the respective largest dimensions of the external cavities 43 of the second and third complex circumferential cutouts (32, 33), the most, close to said incision 42 of the first complex circumferential cutout 31. Still according to the invention, the incisions 52 separating two consecutive blocks 51 of the same row of blocks are parallel to each other, and distributed, according to the first circumferential direction D1, according to a constant average pitch Pi (see [Fig.2]) equal to 0.9% of the circumferential length of the tread (not shown), therefore at least equal to 0.5% and at most equal to 2% of said circumferential length. The second direction D2 forms, with the first circumferential direction D1, an angle B equal to 80°, therefore at least equal to 45°. The three complex circumferential cutouts (31, 32, 33) are distributed, in the axial direction YY', according to a constant average axial pitch Pd equal to 16% of the axial width W of the tread 2, therefore at least equal to 10% and at most equal to 25% of said axial width W.

[0028] [Fig. 2] is a circumferential sectional view of a complex circumferential cutout of a tread 2 according to the preferred embodiment of the invention of [Fig. 1]. The complex circumferential cutout 31, adjacent to the complex circumferential cutout 32, is constituted, in the new state of the tire, by an alternation of external cavities 41, open on the tread surface 20, and incisions 42, extended radially towards the inside of the tread 2 by internal cavities 43, two consecutive external cavities 41 and internal cavities 43 being connected to each other. [Fig. 2] also shows, in circumferential section, a row of blocks 51 two by two adjacent and separated by an incision 52 opening at each of its two ends into external cavities 41 of the two consecutive complex circumferential cutouts.The incisions 52 separating two consecutive blocks 51 have a width Wi and are distributed, according to the first circumferential direction Dl, according to a constant average pitch Pi.

[0029] The inventors have more particularly studied this invention for a tire for a heavy goods vehicle in the dimension 315 / 70 R 22.5.

[0030] Table 1 below shows the characteristics of the tread of the tire according to the invention shown in Figures 1 and 2 previously described. [Tables 1] Characteristics I Comments Axial tread width W 269 mm Circumferential tread length 3187 mm Angle A of the first direction DI of a complex cut relative to the circumferential direction XX' 0° Less than 70° Average pitch Pd between two consecutive complex circumferential cuts 43mm 16% of W Axial width Wcc of an external cavity 41 of a complex circumferential cut 14 mm (central cut) and 7.2 mm (edge ​​cut) 5% of W and 2.5% of W Axial width Wic of an incision 42 of a complex circumferential cut 0.6 mm Less than 2 mm Average pitch Pi between two incisions 52 separating two adjacent blocks 51 29.5mm 0.9% of the circumferential tread length Angle B of an incision 52 separating two adjacent blocks 51 with respect to the circumferential direction XX' 80° Greater than 45° Axial width Wi of an incision 52 separating two adjacent blocks 51 XX' 0.4 mm Less than 2 mm

[0031] The rolling tests, carried out on the embodiment described above, showed a significant improvement in the robustness of the tread with respect to the forms of wear, that is to say a later appearance of the forms of irregular wear.

Claims

Claims

1. A tire (1) for a heavy goods vehicle comprising a tread (2), intended to come into contact with a ground via a rolling surface (20), comprising, in a first direction (Dl) tangent to the rolling surface (20), at least three exclusively complex cutouts (31, 32, 33), -each complex cutout (31, 32, 33) being constituted, at least in the new state of the tire, by an alternation of external cavities (41), open on the rolling surface (20), and incisions (42), extended radially towards the inside of the tread (2) by internal cavities (43), two consecutive external (41) and internal (43) cavities respectively being connected to each other, -two complex cutouts (31, 32,33) consecutive being separated by a row of blocks (51) two by two adjacent and separated by an incision (52) opening at each of its two ends into external cavities (41) of the two consecutive complex circumferential cutouts, characterized in that the at least three complex cutouts (31, 32, 33) are two by two equidistant and arranged relative to each other, in the first direction (D1), in such a way that the middle (I) of the largest dimension of any external cavity (41) of a first complex cutout (31), interposed between a second and a third complex cutout (32, 33) adjacent to said first complex cutout (31), is aligned, in a second direction (D2) with the respective middles (J, K) of the incisions (42) of the second and third complex cutouts (32, 33), closest to said external cavity (41) of the first complex cutout (31),and such that the middle (L) of any incision (42) of the first complex cutout (31) is aligned, along the second direction (D2), with the respective middles (M, N) of the respective largest dimensions of the external cavities (43) of the second and third complex cutouts (32, 33), closest to said incision (42) of the first complex cutout (31), and in that the incisions (52) separating two consecutive blocks (51) of the same row of blocks are parallel to each other, and distributed, along the first direction (D1), according to a constant average pitch (Pi).,

2. A tire according to claim 1 wherein the first direction (Dl) along which any complex cut (31, 32, 33) extends, forming, with a circumferential direction (XX'), an angle at most equal to 70°.

3. Tire according to one of claims 1 or 2 in which the second direction (D2) forms, with the first direction (D1), an angle (B) at least equal to 45°.

4. A tire according to any one of claims 1 to 3, the tread (2) having an axial width (W), measured in an axial direction (YY'), between a first and a second edge of the tread (21, 22), and each external cavity (41) of a complex cutout (31, 32, 33) having a smaller dimension called width (Wcc), measured on the tread surface (20) between two walls of said external cavity (41), wherein the width (Wcc) of any external cavity (41) is at least equal to 2% and at most equal to 7% of the axial width (W) of the tread (2).

5. A tire according to any one of claims 1 to 4, each incision (42) of a complex cutout (31, 32, 33) having a smallest dimension called width (Wic), measured on the rolling surface (20) between two walls of said incision (42), wherein the width (Wic) of any incision (42) is at most equal to 2 mm.

6. A tire according to any one of claims 1 to 5, each incision (52) separating two adjacent blocks (51) of the same row of blocks having a smaller dimension called width (Wi), measured on the rolling surface (20) between two walls of said incision (52), in which the width (Wi) of any incision (52) is at most equal to 2 mm

7. 111111. A tire according to any one of claims 1 to 6 wherein the first direction (Dl) along which any complex cutout (31, 32, 33) extends is circumferential.

8. A tire according to claim 7, the tread (2) having an axial width (W), measured in an axial direction (YY'), between a first and a second edge of the tread (21, 22), in which the at least three circumferential complex cutouts (31, 32, 33) are distributed, in the axial direction (YY'), according to a constant average axial pitch (Pd) at least equal to 10% and at most equal to 25% of the axial width (W) of the tread (2).

9. A tire according to one of claims 7 or 8, the tread (2) having a circumferential length, measured in the circumferential direction, (XX'), at the center of the tread surface (20), in which the constant average circumferential pitch (Pi) between two consecutive incisions (52) is at least equal to 0.5% and at most equal to 2% of the circumferential length of the tread (2).

10. A tire according to any one of claims 7 to 9 wherein the tread (2) comprises at least four, preferably five, complex circumferential cutouts (31, 32, 33).

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