EP4347278A1

EP4347278A1 - Heavy goods vehicle tyre with complex tread pattern

Info

Publication number: EP4347278A1
Application number: EP22732291.4A
Authority: EP
Inventors: Fabien Marlier; Tony Zivkovic
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2021-05-31
Filing date: 2022-05-23
Publication date: 2024-04-10
Also published as: FR3123250A1; WO2022254120A1; CN117355425A

Abstract

The present invention relates to a tyre for a heavy goods vehicle that has a complex tread pattern, and aims to improve the resistance of its tread to irregular wear. The tyre (1) comprises a tread (2) comprising at least one complex circumferential cut-out (6), consisting of alternating external cavities (7) and internal cavities (8), each external cavity (7) having a length (L1). According to the invention, the length (L1) of any external cavity (7) is at least equal to 1.5% and at most equal to 12% of the outer diameter (D) of the tyre (1), measured on the tyre when new and free.

Description

Tire for a heavy-duty vehicle with complex tread pattern

[0001] The subject of the present invention is a tire for a heavy vehicle and relates more particularly to its tread, comprising complex cutouts emerging in a discontinuous manner, at regular or irregular intervals, on the running surface at the new condition of the tire.

[0002] A tread, consisting of at least one rubber-based material, is the wearing part of the tire, located at its periphery and intended to be worn when it comes into contact with the ground by means of a running surface. It most often includes a tread pattern which is a combination of cutouts, or hollows, and elements in relief, of the block type or of the rib type, intended essentially to ensure satisfactory performance in grip, more particularly on wet road surfaces.

[0003] The geometrical characteristics described in this document are defined in a cylindrical marker associated with the tire. By convention, 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 cutout has an average line that is not necessarily rectilinear, which may be wavy or zigzag, and having an average circumferential, transverse or oblique direction. By convention, a cutout is said to be circumferential when its average line has an average circumferential direction, i.e. forms, with the circumferential direction, an average angle of less than 30°. A cutout is said to be transverse when its average line has an average transverse direction, that is to say forms, with the circumferential direction, an average angle at least equal to 60°. A cutout is said to be oblique when its mean line has an oblique mean direction, i.e. forms, with the circumferential direction, a mean angle between 30° and 60°.

[0005] In known manner, the conditions of driving a vehicle in rainy weather, and more particularly those of a heavy vehicle, require rapid evacuation of the water present in the contact surface between the tread and the pavement. This Evacuation makes it possible to ensure direct contact of the material constituting the tread with this roadway by G through the running surface. The water that is not pushed forwards or the sides of the tire runs off or is partially captured in the cutouts formed in the tread. [0006] Water is evacuated by the cutouts which form a fluid flow network which must be effective throughout the life of the tire, from its new condition to its worn condition. maximum. The maximum state of wear, fixed by the regulations in force, is the state of wear from which the tire must be removed from the vehicle for safety reasons. [0007] Generally, the cutouts allowing the evacuation of water are essentially wide cutouts called grooves. A groove has a width such that the walls of material facing it delimiting it do not come into contact with each other, during the passage of the tread in the contact surface, when the tire is subject to recommended inflation and load conditions as defined in particular by the European standards of the “European Tire and Rim Technical Organization” or “ETRTO” in its “Standards Manual 2020 - Commercial Vehicle Tyres” (2020 Standards Manual - Commercial Vehicle Tyres). The compression and shear deformations of the elements in relief delimiting the groove condition the pressures in contact with the ground and therefore the wear. In addition, these deformations, by generating hysteretic losses in the material of the tread, impact the rolling resistance, and therefore the fuel consumption of the vehicle.

[0008] A tread may also comprise narrow cutouts or incisions. An incision has a width such that the facing material walls delimiting it come into contact at least partially with each other, during the passage of the tread in the contact surface, under the conditions load and tire pressure specified by the ETRTO and seen previously. An incision does not make it possible to evacuate the water, but, vis-à-vis the grip, has an edge effect in the contact with the ground, which makes it possible in particular to break a film of water possibly present on floor. [0009] To limit the reduction in the volume of material to be worn out of the tread resulting from the presence of grooves and incisions, so-called complex cutouts have been proposed which, compared to usual grooves, are entirely open on the running 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 pneumatic.

[0010] Treads comprising such complex cutouts have been described in particular in the documents WO 2011039194, WO 2011101495, WO 2012130735, WO 2016188956, WO 2019008276 and WO 2019122677. A complex cutout emerges discontinuously, at intervals regular or not, on the running surface when new. Each complex cutout has external cavities, open to the tread surface and separate from each other in the main direction of the complex cutout. The main direction of the complex cutout often, but not necessarily, corresponds to the direction of water flow in said cutout when driving on ground covered with water. This complex cutout includes, in addition to the external cavities, internal cavities formed inside the tread and usually connected to the tread surface by incisions. These internal cavities are positioned radially and completely inside the running surface when new, and interposed between the external cavities. The internal cavities can be positioned at different levels of depth in the thickness of the strip. In addition, the continuity of the water flow in each complex cut-out, when new, is generally ensured by connecting portions, or connecting channels, between two consecutive external and internal cavities respectively. The assembly formed by the external cavities, the internal cavities and the connecting channels thus forms a continuous groove. On the other hand, the juxtaposition of internal and external cavities not linked together, and therefore not allowing a flow of fluid from one to the other over the entire circumference of the tire, does not constitute a continuous groove and is therefore not considered as a complex groove.

[0011] The volume of all the internal cavities, the external cavities and the connecting channels, present in a tread with complex cutouts, is less than that of all the grooves, present in a conventional tread. , open entirely on the running surface when new 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 when new due to the presence of the grooves.

[0012] A tread pattern can comprise both complex cutouts, emerging on the running surface intermittently, and conventional grooves, emerging on the running surface over their entire length.

[0013] It has been observed on tire treads for heavy vehicles, comprising complex circumferential cutouts positioned axially close to the edges of the tread, the appearance of forms of irregular wear in waves, in the width and in the thickness of the tread. These forms of irregular wear generate vibrations when driving the vehicle, which can degrade comfort, in particular for the tires mounted on the steering axle at the front of the vehicle. This degradation of driving comfort results in early removal of tires, before they are completely worn out, which leads to an economic loss for carriers.

[0014] Consequently, the inventors have set themselves the objective of improving the resistance to irregular wear of a tire tread for a heavy vehicle, comprising complex circumferential cutouts formed by an alternation of external cavities, internal cavities and connecting channels between external cavities and internal cavities, that is to say to delay as much as possible the appearance of forms of irregular wear on said tread.

[0015] This objective has been achieved by a tire for a heavy-duty vehicle comprising a tread, intended to come into contact with the ground via a running surface, comprising cutouts delimiting elements in relief,

-at least one cutout being a complex circumferential cutout, having an average line extending along a circumferential direction of the tire and consisting, when the tire is new, of an alternation of external cavities, opening onto the running surface, and internal cavities, not opening onto the running surface, two consecutive outer and inner cavities respectively being interconnected by a connecting channel,

-each external cavity having, along the average line, a length, measured at the level of the tread surface of the tire in the new and free state, -the length of any external cavity being at least equal to 1.5% and at most equal at 12% of the outside diameter of the tyre, measured on the tire in new and free condition.

[0016] In order to delay as far as possible the appearance of forms of irregular wear induced by a complex circumferential cutout in a tread, said complex circumferential cutout being constituted, when the tire is new, by an alternation of external cavities and internal cavities, two consecutive external and internal cavities respectively being interconnected by a connecting channel, the inventors have demonstrated that the length of any external cavity, measured at the level of the tread surface of the tire when new and free, is essentially understood, in relative value with respect to the outer diameter of the tire, measured on the tire in the new and free condition, in the interval [1.5%; 12%]. The external cavity length and external diameter measurements of the tire are carried out on the tire in new condition, that is to say not worn, and free, that is to say not mounted on a rim and not inflated.

[0017] Indeed, the alternation of external cavities and internal cavities in a complex circumferential cutout leads to a variation of the rigidities along said circumferential cutout, in the thickness of the tread, and therefore a variation of the pressures and slips in the contact of the tread with the ground, at the origin of the appearance of forms of irregular wear.

[0018] The range of values of the ratio between the external cavity length and the external diameter of the tire thus guarantees more even wear, that is to say without the forms of irregular wear generated by the alternation of cavities respectively internal and external.

[0019] Preferably, the length of any external cavity is at most equal to 10% of the external diameter of the tire. Below this value, the variation in rigidities, due to the alternation of external cavities and internal cavities, is particularly optimized. [0020]Advantageously, the tire having a tread surface portion in contact with a flat ground of average length when the tire in new condition is mounted on a recommended rim, inflated to a recommended pressure and subjected to a recommended vertical load , the respectively recommended rim, pressure and vertical load being defined by the European standards of the European Tire and Rim Technical Organization, the length of any external cavity is at least equal at 5% and at most equal to 55% of the average length of the portion of running surface in contact with the ground. The range of values [5%; 55%] of the ratio between the length of the external cavity and the average length of the area of contact of the tire with the ground, under standard conditions of use, guarantees satisfactory grip performance on wet ground.

[0021] Preferably, the length of any external cavity is at most equal to 45% of the average length of the running surface portion in contact with the ground.

Advantageously, each internal cavity having, along the mean line, a length, measured at the level of a radially outer section of said internal cavity, the length of any external cavity is at least equal to 70% and at most equal to 130% of the length of any internal cavity. In order to guarantee the most even wear possible as well as the most effective grip on wet ground, thanks to the water storage capacity in the internal cavities of the tread, it is necessary to have a distribution balanced between the open volume of the external cavities and the hidden volume of the internal cavities, that is to say between the length of the external cavity and the internal cavity.

Advantageously, each external cavity having, perpendicular to the mean line, a transverse surface, and each internal cavity having, perpendicular to the mean line, a transverse surface, the transverse surface of any external cavity is at least equal to 50% and at most equal to 150% of the cross-sectional area of any internal cavity. Under these conditions, a regular flow of fluid, through the alternation of external cavities and internal cavities is thus possible, because there are no significant areas of stricture of the complex cutout, during the passage of a cavity external to an internal cavity. Preferably, the cross-sectional area of any external cavity is at least equal to 80% and at most equal to 140% of the cross-sectional area of any internal cavity. The balanced distribution of the cross-sectional surfaces of the external cavities and internal cavities guarantees an even flow of fluid in the complex cutout. [0025] The tire having, when new, an axial tread width and at least one lateral complex circumferential cutout, the center line of which is positioned at an axial distance from a median circumferential plane of the tire, intersecting the tire into two symmetrical portions, the axial distance of the lateral complex circumferential cutout is advantageously at least equal to 25% and at most equal to 45% of the axial width of the tread. Such a lateral complex circumferential cutout is thus axially positioned in a lateral portion of the tread. In this lateral portion, plumb with such a lateral circumferential cutout, the crown of the tire generally comprises only a rubber portion, since the axially outer end of the crown reinforcement is generally axially inside said cutout circumferential edge. Consequently, a lateral tread portion is softer than the central tread portion, which generates more slippage in contact with the ground and therefore more forms of irregular wear. Thus, a complex lateral circumferential cutout, in addition to its variation in intrinsic rigidities due to the alternation of external cavities and internal cavities, capable of locally generating slippage, is axially positioned in a zone of high potential slippage. In conclusion, for these two reasons, it is particularly sensitive to forms of irregular wear, and is therefore a particularly advantageous object of application of the invention.

The characteristics of the invention are illustrated by Figures 1, 2, 3, 4A, 4B and 4C schematic and not shown to scale:

-Figure 1: Perspective view of a tire tread according to the invention

-Figure 2: Top view of a tire tread according to the invention -Figure 3: Footprint on the ground of a tire tread according to the invention -Figure 4A: Perspective view of a portion of complex circumferential cutout of a tire tread according to the invention -Figure 4B: Respective meridian sections of an external cavity (AA) and an internal cavity (BB) of a complex circumferential cut-out portion of a tire tread according to the invention

-Figure 4C: Circumferential section (C-C) of a complex circumferential cut-out portion of a tire tread according to the invention

[0027] Figure 1 is a perspective view of a tire tread 2 according to the invention. The tread 2 of a tire 1 for a heavy vehicle, intended to come into contact with the ground via a running surface 3, comprises cutouts 4 delimiting elements in relief 5. In the case of the embodiment shown, it comprises three complex circumferential cutouts 6, ie a median complex circumferential cutout and two lateral complex circumferential cutouts, two by two separated by a groove-type circumferential cutout. Each complex circumferential cutout 6, having an average line extending along a circumferential direction of the tire, is constituted, when the tire is new, by an alternation of external cavities 7, opening onto the running surface 3, and cavities internal (not shown), not opening onto the running surface 3.

[0028] Figure 2 is a top view of a tire tread 2 according to the invention. In FIG. 2, the tire 1, when new, has an axial tread width Wt, and comprises three complex circumferential cutouts 6: two lateral complex circumferential cutouts 6, the respective mean line of which is positioned at a distance axis Yd of a median circumferential plane XZ of the tire, cutting the tire into two symmetrical portions, and a median complex circumferential cutout 6, the middle line of which is positioned in the median circumferential plane XZ. Advantageously, the axial distance Yd of the lateral complex circumferential cutout 6 is at least equal to 25% and at most equal to 45% of the axial tread width Wt. Furthermore, any external cavity 7 has a length L1, measured along the mean line of the corresponding complex circumferential cutout 6, at the level of the running surface 3 of the tire in the new and free state. [0029] Figure 3 is a footprint of a tire tread 2 according to the invention, that is to say the contact surface with a flat ground of an inflated and crushed tire. Said contact surface is a portion of tread surface in contact with a flat ground of average length Le, when the tire 1 in new condition is mounted on a recommended rim, inflated to a recommended pressure and subjected to a recommended vertical load . According to an advantageous embodiment of the invention, the length L1 of any external cavity 7 is at least equal to 5% and at most equal to 55% of the average length Le of the portion of running surface in contact with the ground. . Preferably, the length L1 of any external cavity 7 is at most equal to 45% of the average length Le of the portion of running surface in contact with the ground.

[0030] FIG. 4A is a perspective view of a complex circumferential cut-out portion 6 of a tread 2 of a tire according to the invention. The complex circumferential cutout 6, having an average line extending along a circumferential direction XX' of the tire, is formed, when the tire is new, by an alternation of external cavities 7, opening onto the rolling surface 3, and of internal cavities 8, not opening onto the running surface 3, two consecutive external 7 and internal 8 cavities respectively being interconnected by a connecting channel 9. Each external cavity 7 has, along the mean line of the complex circumferential cutout 6, a length L1, measured at the level of the running surface 3 of the tire when new and free. Each internal cavity 8 having, along the mean line, a length L2, measured at the level of a radially outer section of said internal cavity 8. According to the invention, the length L1 of any external cavity 7 is at least equal to 1.5% and at most equal to 12% of the outside diameter D of the tire 1, measured on the tire in the new and free condition. Preferably, the length L1 of any external cavity 7 is at most equal to 10% of the outer diameter D of the tire 1. Two meridian sections, in a meridian plane YZ defined by the axial direction YY' and a radial direction ZZ', are produced respectively at an external cavity 7 (A-A) and at an internal cavity 8 (BB), and are the subject of FIG. 4B. A circumferential section (CC), in a circumferential plane XZ defined by the circumferential direction YY' and a radial direction ZZ', is made at the level of the line average of a portion of complex circumferential cutout 6, and is the subject of FIG. 4C.

[0031] FIG. 4B represents two respective meridian sections of an external cavity 7 (A-A) and of an internal cavity 8 (B-B) of a portion of complex circumferential cut-out 6 of a tread 2 of a tire along the 'invention. As seen above, two consecutive external 7 and internal 8 cavities respectively are interconnected by a connection channel 9. Advantageously, each external cavity 7 having, perpendicularly to the mean line, a transverse surface SI, and each internal cavity 8 having, perpendicularly at the mean line, a transverse surface S2, the transverse surface SI of any external cavity 7 is at least equal to 50% and at most equal to 150% of the transverse surface S2 of any internal cavity 8. Preferably the transverse surface SI of any external cavity 7 is at least equal to 80% and at most equal to 140% of the transverse surface S2 of any internal cavity 8.

[0032] FIG. 4C is a circumferential section (C-C) of a complex circumferential cut-out portion 6 of a tire tread according to the invention. Advantageously the length L1 of any external cavity 7 is at least equal to 70% and at most equal to 130% of the length L2 of any internal cavity 8.

The inventors have more particularly studied this invention for a tire of size 315/70R22.5, intended to equip a steering axle for a heavy vehicle and having a load capacity of 4000 kg for an inflation pressure equal to 9 bars.

Table 1 below shows the compared characteristics of a tire according to the invention I and a reference tire R:

[Table 1]

[0035] The inventors measured the variations in the radius of the tire, over its entire circumference, at the level of the ribs delimiting a lateral complex circumferential cutout, after 75,000 km of travel, and observed maximum amplitudes of local variations in the radius of the tire respectively equal to 0.7 mm for the reference tire R, and to 0.3 mm for the tire according to the invention I, hence a reduction in amplitude of 43%, and therefore a significant reduction in the forms of irregular wear in this portion lateral and at this mileage.

Claims

1. Tire (1) for a heavy vehicle comprising a tread (2), intended to come into contact with the ground by G through a running surface (3), comprising cutouts (4) delimiting elements embossed (5),

-at least one cutout (4) being a complex circumferential cutout (6), having an average line extending along a circumferential direction (XX') of the tire, and consisting, when the tire is new, of an alternation of external cavities (7), opening onto the rolling surface (3), and internal cavities (8), not opening onto the rolling surface (3), two consecutive external (7) and internal (8) cavities respectively being interconnected by a connecting channel (9),

-each external cavity (7) having, along the mean line, a length (Ll), measured at the level of the tread surface (3) of the tire in the new and free state, characterized in that the length (Ll) of any external cavity (7) is at least equal to 1.5% and at most equal to 12% of the external diameter (D) of the tire (1), measured on the tire in new and free condition.

2. Tire (1) according to claim 1, in which the length (L1) of any external cavity (7) is at most equal to 10% of the external diameter (D) of the tire (1) ·

3. Tire (1) according to one of claims 1 or 2, having a tread surface portion in contact with a flat ground of average length (Le) when the tire (1) in new condition is mounted on a recommended rim, inflated to a recommended pressure and subjected to a recommended vertical load, the rim, the pressure and the respectively recommended vertical load being defined by the European standards of the "European Tire and Rim Technical Organization". of the wheel), in which the length (Ll) of any external cavity (7) is at least equal to 5% and at most equal to 55% of the average length (Le) of the portion of rolling surface in contact with floor.

4. A tire (1) according to claim 3, in which the length (L1) of any external cavity (7) is at most equal to 45% of the mean length (Le) of the tread surface portion in contact with the floor.

5. A tire (1) according to any one of claims 1 to 4, each internal cavity (8) having, along the mean line, a length (L2), measured at the level of a radially outer section of said internal cavity ( 8), in which the length (L1) of any external cavity (7) is at least equal to 70% and at most equal to 130% of the length (L2) of any internal cavity (8).

6. A tire (1) according to any one of claims 1 to 5, each external cavity (7) having, perpendicular to the mean line, a transverse surface (SI), and each internal cavity (8) having, perpendicular to the average line, a cross-sectional area (S2), in which the cross-sectional area (SI) of any external cavity (7) is at least equal to 50% and at most equal to 150% of the cross-sectional area (S2) of any internal cavity (8).

7. A tire (1) according to claim 6, in which the transverse surface (SI) of any external cavity (7) is at least equal to 80% and at most equal to 140% of the transverse surface (S2) of any cavity. internal (8).

8. A tire (1) according to any one of claims 1 to 7, the tire (1) having in new condition an axial tread width (Wt) and a lateral complex circumferential cutout (6), the middle line is positioned at an axial distance (Yd) from a median circumferential plane (XZ) of the tire (1), cutting the tire (1) into two symmetrical portions, in which the axial distance (Yd) of the complex circumferential cutout side (6) is at least equal to 25% and at most equal to 45% of the axial tread width (Wt).