Tyre with improved grip for heavy vehicles

Abstract

The invention relates to a tyre (1) for a trailer of a heavy vehicle and is intended to improve its grip performance on the snowfield without compromising its mechanical strength in terms of scratch stress. According to the invention, the tread (2) having at least one complex circumferential cut (7) in the middle portion (4) comprises a first type of transverse cuts (referred to as transverse through sipes (81)) and / or a second type of transverse cuts (referred to as blind transverse cuts (82)), said transverse through sipes (81) having a thickness (E1) at most equal to 0.8 mm, a depth (P1) at least equal to 20% of the maximum cut depth (H), the blind transverse cut-out (82) stops near the outer cavity (71), has a thickness (E2) at least equal to 1 mm, a depth (P2) at most equal to 20% of the maximum cut-out depth (H), and a distance (D2) from the outer cavity (71) at least equal to 3 mm, and the blind transverse cut-out (82) stops near the outer cavity (71), has a thickness (E2) at least equal to 1 mm, a depth (P2) at most equal to 20% of the maximum cut-out depth (H), and a distance (D2) from the outer cavity (71).

Description

Technical Field

[0001] The present invention relates to a tyre for a heavy vehicle, more particularly for a trailer of a heavy vehicle, and to a tyre tread, more particularly comprising complex and gradually changing cuts, the shape of which gradually changes as the tread gradually wears. Background Art

[0002] The tread, made of at least one rubber material, is the peripheral portion of the tire, which is intended to wear and grip the ground when in contact with the ground through the tread surface. It generally comprises a tread pattern consisting of cuts 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 the direction perpendicular to the axis of rotation of the tire.

[0004] Any cut in the tread (where the line is not necessarily a straight line, i.e. the center line may be wavy or zigzag) is circumferential or transverse. By definition, the center line of the cut is the intersection between its mean surface (equidistant from the wall defining the cut) and the surface of the tread. By convention, the cut is said to be circumferential when the center line of the cut has a substantially circumferential mean direction (i.e. a direction that forms an average angle of less than 45° with the circumferential direction). The cut is said to be transverse when the center line of the cut has a substantially transverse mean direction (i.e. a direction that forms an average angle of at least 45° with the circumferential direction).

[0005] It is well known that wet weather driving conditions for vehicles, and more particularly for heavy vehicles, require rapid drainage of water present in the contact patch of the tread with the road surface. This drainage ensures that the material constituting the tread is in direct contact with the road surface through the tread surface. Water that is not pushed to the front or to the sides of the tyre flows or is partially collected in the cuts formed in the tread. The drainage of water is ensured by the cuts, which form a fluid flow network that needs to be effective throughout the service life of the tyre, from new to its maximum wear state. The maximum wear state specified by current regulations is the wear state beyond which it is necessary to remove the tyre from the vehicle for safety reasons.

[0006] The cutouts that enable water to drain are generally wide cutouts called grooves. The width of the grooves is such that the opposing material walls delimiting the grooves do not contact each other when the tread enters the contact patch when the tire is subjected to the recommended inflation and load conditions defined in particular by the "Manual of Standards 2021 - Commercial Vehicle Tyres" of the European Standard of the "European Tyre and Rim Technical Organization" or "ETRTO". The compression and shear deformations of the raised elements delimiting the grooves influence the pressure in the contact patch and therefore the wear. In addition, these deformations affect the rolling resistance by generating hysteresis losses in the tread material and therefore the fuel consumption of the vehicle.

[0007] The tread may also include narrow cuts or sipes. The width of the sipes is such that, under the tire load and pressure conditions specified by ETRTO as described above, the opposing material walls delimiting the sipes at least partially contact each other when the tread enters the contact patch. The sipes cannot drain water, but in terms of grip, they have an edge effect in the contact patch, which is particularly capable of breaking up a film of water that may be present on the ground.

[0008] Corresponding to the presence of incisions in the tread, they reduce the volume of material that can be worn away. In order to limit the reduction in the volume of tread material that can be worn away caused by the presence of grooves and sipes, so-called complex incisions have been proposed that are able to increase the volume of tread material relative to conventional grooves that open completely onto the tread surface, while causing the volume of the incisions for storing water to exceed a predetermined threshold, whatever the level of wear of the tire.

[0009] Treads comprising such complex incisions are particularly described in documents WO2011039194A1, WO2011101495A1, WO2012130735A1, WO2016188956A1, WO2017174925A1, WO2019008276A1 and WO2019122677A1. When brand new, the complex incisions lead to the tread surface at regular or irregular intervals in a generally discontinuous manner. Therefore, the complex incisions have external cavities that lead to the tread surface and are separated from each other in the main direction of the complex incisions. The main direction of the complex incisions is usually (although not necessarily) the direction in which water flows in the complex incisions when driving on a ground covered with water. In addition to the external cavity, the complex incision also includes an internal cavity, which is formed inside the tread, does not directly lead to the tread surface when brand new, and is usually connected to the tread surface by a sipe. These internal cavities are located completely radially inside the tread surface in a new state and between the external cavities. The internal cavities may be located at different depth levels within the thickness of the tread. Furthermore, the external cavities and the internal cavities of the same complex incision are interconnected so that the continuity of the flow of water in each complex incision is ensured in any state of wear of the tread, as in the case of a conventional continuous groove. On the other hand, the juxtaposition of internal and external cavities that are not connected to each other and therefore do not allow the flow of fluid from one cavity to the other does not constitute a continuous groove and is therefore not considered a complex incision.

[0010] The volume of all the internal and external cavities present in a tread with complex cuts is generally smaller than the volume of all the grooves present in a conventional tread that is completely open to a new tread surface, and the depth corresponds to the maximum depth of the internal or external cavities, which means that for complex cuts, the volume of material that can be worn away is greater. Therefore, such a tread including complex cuts is also more rigid than an equivalent tread including conventional open grooves.

[0011] The tread may include both complex cuts that open to the tread surface intermittently and conventional grooves that open to the tread surface throughout their entire length.

[0012] Consider the specific case of tires for trailers of heavy vehicles: their treads generally (although not necessarily) comprise between four and seven circumferential rows of raised elements. For this type of tread, complex circumferential cuts have been envisaged, such as those described above, which are interposed in particular between two circumferential rows of consecutive raised elements but not at the edges of the tread. In other words, these complex circumferential cuts are preferably located in the middle portion of the tread.

[0013] It is known that tires for trailers of heavy vehicles are subject to severe lateral loads when the vehicle makes sharp turns, especially at roundabouts. In such conditions of driving in a curve, the tire is subject to side sliding forces, subjecting the tread to severe loads, especially at its edges. This is why such treads include a solid circumferential edge row, which usually consists of a continuous rib, without any cuts.

[0014] It is also known that tyres for trailers of heavy vehicles need to have high grip properties, in particular under adverse driving conditions, for example when driving on snow. A known solution is to provide a tread with transverse sipes, the orientation of which is optimized with respect to the desired grip direction. Usually, the transverse sipes, which form by convention an average angle of at least 45° with the circumferential direction of the tyre, have a transverse component effective with respect to the longitudinal grip and a longitudinal component effective with respect to the transverse grip. The effectiveness of such transverse sipes with respect to grip is based on the indentation effect achieved by the outer corners of the sipes forming an indentation on the ground. As mentioned above, these transverse sipes are located in the middle part of the tread and are usually not contained in the edge rows that are subject to very high mechanical loads. Summary of the invention

[0015] The inventors therefore set themselves the object of providing a tire for trailers of heavy vehicles with a tread comprising gradually varying complex cuts to improve its gripping properties, in particular on snow, without compromising its mechanical strength in terms of lateral sliding loads.

[0016] This object has been achieved by a tyre for heavy vehicles, comprising a tread intended to come into contact with the ground via a tread surface, the tread comprising a central portion and two lateral portions,

[0017] - the median portion is separated from each lateral portion by a circumferential cutout forming an average angle of less than 45° with the circumferential direction of the tyre,

[0018] - the intermediate portion comprises at least one complex circumferential incision making an average angle of less than 45° with the circumferential direction of the tyre,

[0019] - when the tyre is new, at least one complex circumferential incision comprises an alternation of external cavities opening onto the tread surface and internal cavities concealed inside the tread and connected to the tread surface by a circumferential sipe, two consecutive cavities (respectively the external cavity and the internal cavity) being connected to one another,

[0020] - the intermediate portion comprises a plurality of transverse cuts having at least one transverse portion making a mean angle at least equal to 45° with the circumferential direction of the tire,

[0021] - the tread has a maximum cut depth,

[0022] a plurality of transverse cuts including transverse cuts of the first type (called transverse through-sipes) intersecting at least one complex circumferential cut between two consecutive external cavities and each having a thickness at most equal to 0.8 mm and a depth at least equal to 20% of the depth of the maximum cut, each transverse through-sipe being at a distance of at least 7 mm from the nearest external cavity of said complex circumferential cut,

[0023] - and / or multiple transverse cuts include a second type of transverse cuts (called blind transverse cuts), which stop near the external cavity of the complex circumferential cut and each have a thickness of at least 1 mm and a depth of at most 20% of the maximum cut depth, each blind transverse cut being at a distance of at least 3 mm from the external cavity.

[0024] The tread of the tire according to the invention thus essentially comprises a central portion having at least one complex circumferential incision, the surface shape of which, as it opens onto the tread surface, changes gradually as the tire wears, and which, when the tire is new, comprises one or the other or both of the two types of transverse incisions described above.

[0025] A first type of transverse incisions consists of transverse through-sipes, that is to say of a sipe that passes through a complex transverse incision outside the external cavity of said complex circumferential incision. When the tyre is new, the portion of the external cavity that opens onto the tread surface has a larger dimension, generally with a minimum dimension at least equal to 7 mm. The intermediate portion connecting two consecutive external cavities generally consists of a narrow incision, called a circumferential sipe, having a thickness generally at most equal to 1 mm and extending the internal cavity radially outwards. Thus, a transverse through-sipe intersects a circumferential sipe that extends the internal cavity radially outwards and circumferentially connects two consecutive external cavities.

[0026] The transverse through-cutting sipe has a thickness at most equal to 0.8 mm and a depth at least equal to 20% of the maximum incision depth. The transverse through-cutting sipe is therefore present on the tread surface at least until 20% of the tread is worn. According to the invention, the transverse through-cutting sipe intersects the complex circumferential incision, more specifically the circumferential sipe connecting two consecutive external cavities to each other, and at a distance from the nearest external cavity at least equal to 7 mm.

[0027] During so-called side slip transverse loading of the tire tread, this minimum distance of 7 mm limits the risk of crack initiation and propagation between the transverse through-cut sipe and the nearest external cavity and, accordingly, the risk of tread chipping damage.

[0028] The second type of transverse cuts involves blind transverse cuts that stop near the external cavity. Compared to the transverse through-cuts of the first type, the blind transverse cuts have a greater thickness (at least equal to 1 mm) and a smaller depth (at most equal to 20% of the maximum cut depth). In addition, the minimum distance of the blind transverse cuts relative to the nearest external cavity (which is equal to 3 mm) is smaller than the minimum distance of the transverse through-cuts relative to the nearest external cavity.

[0029] As in the case of the transverse through-sipes, this minimum distance of 3 mm limits the risk of crack initiation and propagation between the transverse through-sipes and the nearest external cavity during so-called side slip transverse loading of the tire tread, and therefore limits the risk of tread chipping damage. It can be noted that the blind transverse cuts (which are thicker than the transverse through-sipes, but not as deep as the transverse through-sipes) can be closer to the external cavity, since the risk of cracking that may occur is lower.

[0030] Advantageously, in case the plurality of transverse cuts comprises a transverse through-sipe of the first kind, the thickness of each transverse through-sipe is at least equal to 0.4 mm.This minimum sipe thickness is essentially the result of technical constraints concerning the manufacture of the metal sipe blade used to mould said sipes.

[0031] Still more advantageously, in the case where the plurality of transverse cuts comprises transverse through-cut sipes of the first type, the depth of each transverse through-cut sipe is at most equal to the maximum cut depth. The deeper the sipe, the longer its corner effect on the grip is retained as the tire wears, thus providing a durable grip throughout the life of the tire. However, deeper sipes contribute to local flexibility of the tread pattern of the tread, which may reduce the wear life and may impair the performance of said tread pattern in terms of chipping.

[0032] Preferably, in the case where the plurality of transverse cuts comprises transverse through-slots of the first type, the distance between each transverse through-slot and the nearest external cavity is at least equal to 10 mm. The greater the minimum distance between a transverse through-slot and the nearest external cavity, the lower the risk of cracking, since the crack has to propagate over a greater distance.

[0033] Advantageously, in the case where the plurality of transverse cuts comprises blind transverse cuts of the second type, the thickness of each blind transverse cut is at least equal to 2 mm. A greater minimum thickness enables to reduce the risk of crack initiation at the ends of the blind transverse cuts near the external cavity.

[0034] Still more advantageously, in the case where the plurality of transverse cuts comprises blind transverse cuts of the second type, each blind transverse cut has a thickness at most equal to 5 mm, preferably at most equal to 4 mm. The greater the thickness of the blind transverse cut, the greater the road noise generated, and therefore the greater the benefit of limiting this thickness.

[0035] Advantageously also, in the case where the plurality of transverse cuts comprises blind transverse cuts of the second type, the depth of each blind transverse cut is at least equal to 10% of the maximum cut depth. When the tyre is new, the blind transverse cuts need to be deep enough to have a significant corner effect on grip.

[0036] According to a particular embodiment, in the case where the plurality of transverse incisions comprises blind transverse incisions of the second type, at least one blind transverse incision comprises a first transverse portion forming with the circumferential direction of the tire an average angle of at least 45° and a blind end portion forming with the circumferential direction of the tire an average angle of less than 45°, preferably less than 30° and more preferably less than 25°. Thus, the blind end portion is circumferential within the meaning of the convention defined above. In this particular embodiment, the blind transverse incision comprises a first transverse portion forming with the circumferential direction an average angle of at least 45°. This first transverse portion is extended by a second circumferential blind end portion forming with the circumferential direction an average angle of less than 45°. Thus, the blind transverse incision has a median line broken at two different angles, the average angle of the blind end portion being a design parameter that allows adjusting the minimum distance between the blind end and the nearest external cavity.

[0037] Advantageously, the circumferential spacing between two consecutive transverse incisions of the plurality of transverse incisions is at least equal to 10 mm, preferably at least equal to 20 mm. The circumferential spacing is the maximum circumferential distance measured between two consecutive transverse incisions (not necessarily of the same kind). Below 10 mm, the circumferential spacing becomes too small and the number of transverse incisions increases, in particular increasing the risk of road noise and tread chipping.

[0038] Advantageously, the circumferential spacing between two consecutive transverse cuts of the plurality of transverse cuts is at most 50 mm, preferably at most 35 mm. Above 50 mm, the circumferential spacing becomes too large and the number of transverse cuts decreases, especially the grip on snow. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] By way of illustration, not drawn to scale Figure 1 and Figure 2 The features of the present invention are described as follows:

[0040] - Figure 1 : a top view of a portion of the tread of a tire according to the invention,

[0041] - Figure 2 : circumferential median cross-section of a portion of the tread of a tire according to the invention. DETAILED DESCRIPTION

[0042] Figure 1: is a top view of a portion of a tread 2 of a tyre 1 according to the invention, more specifically a tyre of size 245 / 70R17.5. The tyre 1, intended to be mounted on a heavy vehicle, more specifically a trailer of a heavy vehicle, comprises a tread 2, intended to come into contact with the ground via a tread surface 3, said tread 2 comprising a central portion 4 and two lateral portions 5. The central portion 4 is separated from each lateral portion 5 by a circumferential incision 6 which, in the embodiment illustrated, forms an average angle equal to 0° with the circumferential direction XX' of the tyre. The central portion 4 comprises a single complex circumferential incision 7 which forms an average angle equal to 0° with the circumferential direction XX' of the tyre. When the tyre is brand new, the complex circumferential incision 7 comprises an alternation of external cavities 71 opening onto the tread surface 3 and internal cavities 72 which are concealed inside the tread 2 (at the circumference of the tread surface 3). Figure 1 The intermediate portion 4 comprises a plurality of transverse cuts (81, 82), at least one portion of which forms an average angle of 60° with the circumferential direction XX' of the tire. The maximum cut depth H of the tread 2 ( Figure 1 The plurality of transverse cuts (81, 82) comprises a first type of transverse cuts (called transverse through-cuts 81), which intersect the complex circumferential cut 7 between two consecutive external cavities 71 and each have a thickness E1 equal to 0.6 mm and a depth P1 equal to 4 mm (31% of the maximum cut depth H). The distance D1 between each transverse through-cut slit 81 and the closest external cavity 71 of the complex circumferential cut 7 is equal to 10 mm. The plurality of transverse cuts (81, 82) also comprises a second type of transverse cuts (called blind transverse cuts 82), which stop near the external cavity 71 of the complex circumferential cut 7 and each have a thickness E2 equal to 2 mm and a depth P2 equal to 2 mm (16% of the maximum cut depth H). The distance D2 between each blind transverse cut 82 and the external cavity 71 is equal to 3 mm. Each blind transverse incision 82 comprises a first transverse portion 821 forming an average angle B1 of 60° with the circumferential direction XX' of the tire and a blind end portion 822 forming an average angle B2 of 25° with the circumferential direction XX' of the tire. The circumferential spacing Pc between two consecutive transverse incisions of the plurality of transverse incisions (81, 82) (respectively between the transverse through-cutting sipe 81 and the blind transverse incision 82) is equal to 35 mm.

[0043] Figure 2is a circumferential median cross section of a portion of the tread 2 of the tire 1 according to the present invention. The circumferential median cross section is taken from Figure 1 The cross-sectional plane AA corresponds to the median circumferential plane XZ passing through the middle of the tread and passing through the complex circumferential incision 7 along its centerline. When the tire is brand new, the complex circumferential incision 7 located in the middle part 4 of the tread 2 comprises an alternation of external cavities 71 and internal cavities 72, the external cavities 71 leading to the tread surface 3, the internal cavities 72 hidden inside the tread 2 and connected to the tread surface 3 by a circumferential sipe 721, two consecutive cavities (respectively the external cavities 71 and the internal cavities 72) being connected to each other. In the illustrated embodiment, the depth H of the complex circumferential incision 7 extending radially from the tread surface 3 corresponds to the maximum incision depth. Figure 2 Two blind transverse cuts 82 with a depth P2 are depicted in dashed lines (since they do not open into the plane XZ). A transverse through-cut sipe 81 with a thickness E1 and a depth P1 is also depicted in cross section.

[0044] The inventors have studied the invention more specifically for a tyre 1 of size 245 / 70R17.5, intended to be mounted on an axle of a trailer for a heavy vehicle having a maximum load capacity equal to 2725 kg at an inflation pressure equal to 9 bar.

[0045] Table 1 below summarizes the characteristics of the tire I according to the invention studied by the inventors:

[0046] [Table 1]

[0047]

[0048]

[0049] The results of the performance tests carried out on the size 245 / 70R 17.5 studied above show that the expected results are met. In particular, the grip on snow, tested according to the method described in Annex 7 of UNECE Regulation No. 117, is significantly improved, with traction increased by 35% compared to the reference Michelin tire 245 / 70R 17.5X MULTI T2. In addition, the performance in terms of wet grip measured according to the method described in Annex 5 of UN Regulation No. 117 and road noise measured according to the method described in Annex 3 of UN Regulation No. 117 are comparable to the reference tire. Finally, the performance in terms of chipping resistance is being confirmed in customer driving tests.

Claims

1. A tyre (1) for a heavy vehicle, said tyre (1) comprising a tread (2) intended to come into contact with the ground via a tread surface (3), said tread (2) comprising a central portion (4) and two lateral portions (5), - said central portion (4) is separated from each lateral portion (5) by a circumferential cutout (6) forming an average angle less than 45° with the circumferential direction (XX') of the tyre, - said intermediate portion (4) comprises at least one complex circumferential incision (7) forming with the circumferential direction (XX') of the tyre an average angle of less than 45°, - when the tyre is new, the at least one complex circumferential incision (7) comprises an alternation of external cavities (71) opening onto the tread surface (3) and internal cavities (72), the external cavities (71) opening onto the tread surface (3), the internal cavities (72) being concealed inside the tread (2) and connected to the tread surface (3) by means of circumferential sipes (721), two consecutive cavities being connected to each other, the two consecutive cavities being respectively the external cavity (71) and the internal cavity (72), - the intermediate portion (4) comprises a plurality of transverse cuts (81, 82) having at least one transverse portion forming with the circumferential direction (XX') of the tyre a mean angle (T, B1) at least equal to 45°, - the tread (2) has a maximum cut depth (H), It is characterized in that The plurality of transverse cuts (81, 82) include transverse cuts of a first type, which are referred to as transverse through-cuts (81), which intersect at least one complex circumferential cut (7) between two consecutive external cavities (71) and each have a thickness (E1) of at most 0.8 mm and a depth (P1) of at least 20% of the maximum cut depth (H), each transverse through-cut (81) being at a distance of 100 mm from the nearest external cavity (71) of the complex circumferential cut (7). The distance (D1) is at least 7 mm, and / or the multiple transverse incisions (81, 82) include a second type of transverse incision, which is called a blind transverse incision (82), and the blind transverse incision (82) stops near the external cavity (71) of the complex circumferential incision (7), and each has a thickness (E2) of at least 1 mm and a depth (P2) of at most 20% of the maximum incision depth (H), and the distance (D2) between each blind transverse incision (82) and the external cavity (71) is at least 3 mm.

2. The tire (1) according to claim 1, wherein the plurality of transverse cuts (81, 82) comprises transverse through-cut sipes (81) of a first type, wherein: The thickness (E1) of each transverse through-cutting groove (81) is at least equal to 0.4 mm.

3. The tire (1) according to any one of claims 1 or 2, wherein the plurality of transverse cuts (81, 82) comprises transverse through-cut sipes (81) of a first type, wherein: The depth (P1) of each transverse through-cut groove (81) is at most equal to the maximum cut depth (H).

4. The tire (1) according to any one of claims 1 to 3, wherein said plurality of transverse cuts (81, 82) comprises transverse through-cutting sipes (81) of a first type, wherein: The distance (D1) between each transverse through-cut groove (81) and the nearest outer cavity (71) is at least equal to 10 mm.

5. The tire (1) according to any one of claims 1 to 4, said plurality of transverse cuts (81, 82) comprising second type blind transverse cuts (82), wherein: The thickness (E2) of each blind transverse cut (82) is at least equal to 2 mm.

6. Tyre (1) according to any one of claims 1 to 5, said plurality of transverse incisions (81, 82) comprising second type blind transverse incisions (82), wherein: The thickness (E2) of each blind transverse cut (82) is at most equal to 5 mm, preferably at most equal to 4 mm.

7. Tyre (1) according to any one of claims 1 to 6, said plurality of transverse incisions (81, 82) comprising second type blind transverse incisions (82), wherein: The depth (P2) of each blind transverse incision (82) is at least equal to 10% of the maximum incision depth (H).

8. Tyre (1) according to any one of claims 1 to 7, said plurality of transverse incisions (81, 82) comprising second type blind transverse incisions (82), wherein: At least one blind transverse incision (82) comprises a first transverse portion (821) forming with the circumferential direction (XX') of the tire an average angle (B1) of at least 45°, and a blind end portion (822) forming with the circumferential direction (XX') of the tire an average angle (B2) of less than 45°, preferably less than 30°, and more preferably less than 25°.

9. The tire (1) according to any one of claims 1 to 8, wherein: The circumferential spacing (Pc) between two consecutive transverse cuts of the plurality of transverse cuts (81, 82) is at least equal to 10 mm, preferably at least equal to 20 mm.

10. The tire (1) according to any one of claims 1 to 9, wherein: The circumferential spacing (Pc) between two consecutive transverse cuts of the plurality of transverse cuts (81, 82) is at most equal to 50 mm, preferably at most equal to 35 mm.

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