Tyre for heavy vehicle and having tread with improved robustness

Abstract

The aim of the invention is to improve the robustness of the tread (1) of a heavy vehicle tyre, said tread comprising at least two composite cutouts (5), each cutout (5) having alternating outer cavities (6) and narrow portions (7). According to the invention, for any sipe (9) connecting two outer cavities (6) respectively belonging to two adjacent composite cuts (5), the distance (D) between each intersection (I1, I2) of the sipe (9) and each outer cavity (6) and the bisecting plane (P) of the outer cavity (6) is at least equal to 25% and at most equal to 50% of the length (Le) of the outer cavity (6), a first intersection (I1) with the outer cavity (6) of the first composite incision (5) is located near the front end (E1) of the outer cavity (6) and a second intersection (I2) with the outer cavity (6) of the second composite incision (5) is located near the rear end (E2) of the outer cavity (6).

Description

Technical Field

[0001] The present invention relates to a tire for a heavy vehicle intended to travel on an asphalt road surface, and more particularly to the tread of said tire. Background Art

[0002] The tread is located at the periphery of the tire and is intended to wear when it comes into contact with the ground through the tread surface. The tread is composed of at least one rubber-based material. The tread generally includes a tread pattern, which is a combination of incisions or voids and raised elements and is particularly intended to ensure satisfactory performance in terms of grip (more particularly grip on a wet road surface).

[0003] It is well known that rainy driving conditions for vehicles (more particularly heavy vehicles) require rapid drainage of the water present in the contact patch between the tire tread and the road surface. This drainage ensures that the material constituting the tread is in direct contact with the road surface through the tread surface. The water that is not pushed forward or to the sides of the tire flows into the incisions formed in the tread or is partially collected in the incisions formed in the tread.

[0004] The drainage of water is ensured by the incisions, and the fluid flow network formed by the incisions preferably needs to be durable, that is, effective throughout the entire service life of the tire (from a brand-new tire to its maximum wear state). The maximum wear state is defined by current regulations, and for safety reasons, tires exceeding this state need to be removed from the vehicle.

[0005] For a tire for a heavy vehicle, when the tire is brand-new, the available void volume in the contact patch is generally relatively high. The available void volume is understood as the void volume that can be filled with the water present on the road surface. The void volume leading to the tread surface is evaluated when the tire is under the recommended inflation and load conditions as particularly defined by the "European Tyre and Rim Technical Organization" or "ETRTO" in its "Standard Manual 2022 - Commercial Vehicle Tires".

[0006] In the incisions, a distinction is made between sipes and grooves. Under the tire load and pressure conditions specified by ETRTO, the width of the sipes is such that when the tread enters the contact patch, the opposing walls of the material defining the sipes are at least partially in contact with each other: thereby limiting the deformation of the opposing parts of the material and thus limiting wear. In contrast, the grooves are wider, and when the tread enters the contact patch, the material parts defined by the grooves can deform without contacting each other. These deformations generated by the material parts during compression and shear processes increase the wear of the tread. In addition, when grooves are present, the increase in deformation leads to an increase in the hysteresis loss of the tread, thereby increasing the rolling resistance and thus increasing fuel consumption.

[0007] In order to limit the reduction in the volume of the tread material due to the presence of grooves, so-called compound cuts have been proposed, which can increase the volume of the tread material compared to ordinary grooves that lead completely to the tread surface, while meeting the volume of water storage voids above a given threshold, regardless of the degree of tire wear.

[0008] Treads including such compound cuts are described in particular in documents WO 2011039194 A1, WO 2011101495 A1, WO 2012130735 A1 and WO 2020030667 A1. When brand new, the compound cuts lead to the tread surface in a discontinuous manner, at regular or irregular intervals. Each compound cut has external cavities that lead to the tread surface and are separated from each other in the main direction of the compound cut. When driving on a water-covered ground, the main direction of the compound cut corresponds to the direction in which water flows in the cut. In addition to the external cavities, the compound cut also includes internal cavities that are formed inside the tread and are generally connected to the tread surface through sipes. These internal cavities are located entirely inside the brand new tread surface in the radial direction and are between the external cavities. The internal cavities can be located at different depth levels in the tread thickness. Furthermore, in each brand new compound cut, the continuity of water flow (or fluid flow in a broader sense) is ensured through the connection between the external cavities and the internal cavities. Therefore, the connection between the internal cavities and the external cavities forms a continuous groove, independent of the local direction of the internal cavities or the external cavities. In contrast, juxtaposed internal cavities and external cavities are not connected to each other, so they do not allow fluid to flow from one cavity to another around the entire circumference of the tire, and thus do not constitute a continuous groove.

[0009] For a tread with compound cuts, the volume of all cavities (internal cavities and external cavities) is smaller than the volume of grooves that lead completely to the tread surface when brand new, and has a depth corresponding to the maximum depth of the internal cavities or the external cavities. Therefore, the presence of the compound cuts can limit the reduction in the stiffness of the brand new tread associated with the presence of grooves.

[0010] The tread pattern can have both compound cuts (leading to the tread surface intermittently) and conventional grooves (leading to the tread surface along their entire length).

[0011] However, it has been found that the mere presence of compound cuts does not achieve the level of grip under traction and braking required for certain heavy vehicles. Therefore, it is advisable to combine these compound cuts with slotted grooves leading to a completely new tread surface (i.e., grooves inclined with respect to the main direction of the grooves). These slotted grooves create additional edge lengths in the tread surface, enabling good traction levels and satisfactory grip to be obtained under so-called "slippery" conditions, particularly on a water-covered ground.

[0012] However, the presence of the grooves weakens the tread, which may cause the rubber blocks to break and flower, and has an adverse effect on the performance in terms of grip and wear.

[0013] Tread damage generally starts with the germination of cracks in the material, resulting in exceeding the fracture stress or fatigue limit of the material. In both cases, the preferred areas for crack germination are areas of stress concentration, corresponding to local geometries characterized by a small radius of curvature or an angle with a small angular opening. This is especially true for the grooves, which have a small thickness, usually at most equal to 2 mm, meaning that the grooves have a small radius of curvature at their bottom, and the connection of the compound cuts associated therewith is usually inclined with respect to the main direction of the main cut, with a small angular opening, to optimize the noise generated.

[0014] Generally, the problem of crack germination is encountered in two cases: during the manufacturing process of the tire (i.e., when demolding after curing), or during the use of the tire.

[0015] During the demolding process of the tire after curing, the tread pattern elements that are difficult to demold, especially the hidden internal cavities of the compound cuts, exert a radial traction force on the tread, which may cause the stress in the stress concentration area to possibly exceed the fracture stress of the material. As the number and width of the hidden internal cavities increase, the difficulty of demolding and the associated risk of breaking and flowering also increase.

[0016] When the tire is in use, driving over blunt objects may also cause the fracture stress of the material to be exceeded. In addition, repeated drift stress or torque transmission stress may cause them to exceed the fatigue limit over time.

[0017] Those skilled in the art are familiar with adding small cavities with a sufficient radius of curvature at the bottom of the grooves to achieve a stress lower than the fracture stress at the bottom of the grooves, thereby avoiding the germination of cracks. On the other hand, the tread has a lower stiffness, with a risk of reduced wear performance, the tread demolding is more complex, and the cost of producing the mold parts for molding the tread is higher.

[0018] Those skilled in the art have also identified other risks, which are related to the combination of the compound cut and the tool groove of the external cavity leading to the compound cut. In particular, the relative position of the external cavity between multiple compound cuts and the relative position of the inclined tool groove may generate additional noise phenomena and / or cause uneven tread wear.

[0019] In addition to the above-mentioned disadvantages related to the presence of the inclined tool groove leading to the compound cut, those skilled in the art have also found that the presence of the compound cut in the tread increases the risk of stones being trapped and remaining in the external cavity of the compound cut, which may also cause cracks in the tread. Summary of the Invention

[0020] Therefore, the object set by the inventor for himself is to improve the crack resistance and chipping resistance of the tread including the combination of the compound cut and the tool groove connecting the compound cuts, while limiting the generation of noise and ensuring a satisfactory compromise among the performances in terms of wear, grip, and rolling resistance.

[0021] This object has been achieved by a tire for heavy vehicles, which includes a tread designed to contact the ground through the tread surface and includes cuts defining raised elements.

[0022] - The tread has a thickness measured perpendicular to the tread surface, and the thickness is equal to the depth of the deepest cut.

[0023] - The tread includes at least two adjacent compound cuts, and when the tire is new, each compound cut includes alternating external cavities and narrow parts.

[0024] - Each external cavity has a length measured at the tread surface between a front end intended to first contact the ground and a rear end intended to last contact the ground along the traveling direction of the tire, and the front end and the rear end are located on the average line of the external cavity.

[0025] - The external cavity has a width measured perpendicular to the average line of the external cavity and a height measured perpendicular to the tread surface, and the maximum value of the width is at least equal to 6 mm.

[0026] - Each narrow part has a width measured perpendicular to the average line of the narrow part and a height measured perpendicular to the tread surface, and the width is at most equal to the width of the external cavity and at most equal to 2 mm.

[0027] - The narrow part is radially inwardly continued by an internal cavity, and the internal cavity has a width measured perpendicular to the average line of the internal cavity and a height measured perpendicular to the tread surface.

[0028] - At least one siped extends from a first intersection with the outer cavity of the first compound cut to a second intersection with the closest outer cavity of a second compound cut adjacent to the first compound cut,

[0029] - The siped has a width measured perpendicular to the average line of the siped and a height measured perpendicular to the tread surface, and the width is at most equal to 2 mm,

[0030] - The distance between each intersection of the siped with each outer cavity and a plane that bisects the outer cavity and is perpendicular to the average line of the outer cavity and equidistant from the front end and the rear end of the outer cavity is at least equal to 25% of the length of the outer cavity and at most equal to 50% of the length of the outer cavity,

[0031] - The first intersection of the siped with the outer cavity of the first compound cut is located near the front end of the outer cavity,

[0032] - The second intersection of the siped with the closest outer cavity of the second compound cut is located near the rear end of the outer cavity.

[0033] The main feature of the present invention lies in optimizing the position of the siped connecting the two closest outer cavities in two adjacent compound cuts.

[0034] According to the first basic feature, the distance between each intersection of the siped with each outer cavity and a plane that bisects the outer cavity and is perpendicular to the average line of the outer cavity and equidistant from the front end and the rear end of the outer cavity is at least equal to 25% of the length of the outer cavity and at most equal to 50% of the length of the outer cavity. In other words, the siped leads to the outer cavity rather than to the narrow area where the inner cavity continues radially inwards.

[0035] During the tire manufacturing process, more particularly at the end of the curing step in the mold, this position of the siped has the advantage of avoiding cracks at the bottom of the siped when the closest inner cavity is demolded. When the tire is in motion, due to the greater local flexibility of the tread given by the grooves, this position of the grooves is conducive to discharging stones that may get stuck at one end of the outer cavity to which the siped leads.

[0036] According to the second and third basic features of the present invention respectively, the first intersection of the siped with the outer cavity of the first compound cut is located near the front end of the outer cavity, and the second intersection of the siped with the closest outer cavity of the second compound cut is located near the rear end of the outer cavity.

[0037] By optimizing the offset between the respective outer cavities of two adjacent compound cuts, this respective positioning of the siped ends relative to each outer cavity to which it leads can both limit the noise generated by the siped and limit uneven wear of the outer cavity.

[0038] Advantageously, the direction of the groove with respect to the plane bisecting the outer cavity has an average inclination angle, which is defined as the slope of the straight line passing through the two intersection points of the groove and the outer cavity. The average inclination angle is at least equal to 10° and at most equal to 45°, preferably at least equal to 20° and at most equal to 35°. The average inclination angle of the groove being within this range helps to limit the noise generated by the groove.

[0039] Also advantageously, the groove has an incident angle with respect to the plane bisecting each outer cavity at the intersection point, which is defined as the slope of the straight line tangent to the groove at the intersection point. The incident angle is at most equal to the average inclination angle. This incident angle characterizes the position of the average line of the groove relative to the edge of the outer cavity and thus defines the angular sector of the material portion bounded by the groove and the edge of the outer cavity. Therefore, the smaller the incident angle, the smaller the acute angle formed by the angular sector of the material portion, thereby reducing the risk of local chipping at the edge of the outer cavity near the intersection of the outer cavity and the groove.

[0040] Also advantageously, each groove has a constant height. The constant height avoids any geometric singularities at the bottom of the groove, such as discontinuities or bridges, because these singularities may be sites of stress concentration, which may lead to local cracking at the bottom of the groove and thus cause local chipping.

[0041] Advantageously, the height of each groove is at least equal to the height of the narrow part. Therefore, when the tire wears, at least before the inner cavity appears on the tread surface, the grooves on the tread surface are still visible, thus ensuring the durability of the tread grip when the tire wears.

[0042] Advantageously, the bottom radius of each outer cavity is at least equal to 2 mm. As shown above, the larger the bottom radius, the stronger the anti-cracking property.

[0043] Advantageously, the width of each inner cavity is at least equal to 5 mm. A wide enough cavity allows water storage and / or water flow evacuation, which is beneficial for obtaining satisfactory grip on wet ground at an advanced wear level corresponding to the presence of inner cavities on the tread surface.

[0044] Also advantageously, the height of each inner cavity is at least equal to 5 mm. As mentioned above, a high enough cavity allows water storage and / or water flow evacuation, which is beneficial for obtaining satisfactory grip on wet ground at an advanced wear level corresponding to the presence of inner cavities on the tread surface.

[0045] Advantageously, the bottom radius of each inner cavity is at least equal to 2 mm. As in the case of the outer cavity, the larger the bottom radius, the stronger the anti-cracking property. Since the inner cavity usually has sufficient width, it is easy to imagine that the inner cavity has a large bottom radius.

[0046] According to a preferred embodiment, all the incisions are compound incisions, which makes it possible to optimize the compromise between wear, grip and rolling resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The features of the invention are illustrated schematically Figures 1 to 6 in the figures, which are not shown to scale:

[0048] - Figure 1 : Overall top view of a tread intended for a steering axle according to a first embodiment of the invention,

[0049] - Figure 2 : Partial top view of the tread according to a first embodiment of the invention,

[0050] - Figure 3 : Circumferential cross-sectional view of a part of the compound incision of the tread according to a first embodiment of the invention,

[0051] - Figure 4 : Cross-sectional view along the groove leading to the compound incision of the tread according to a first embodiment of the invention,

[0052] - Figure 5 : Overall top view of a tread intended for a driven axle according to a second embodiment of the invention,

[0053] - Figure 6 : Partial top view of the tread according to a second embodiment of the invention. DETAILED DESCRIPTION

[0054] Figure 1 is an overall top view of a tread 1 intended for a steering axle of a heavy vehicle according to a first embodiment of the invention. The tread 1 is intended to come into contact with the ground through the tread surface 2 and includes incisions 3 that define raised elements 4. The tread 1 has a thickness E measured perpendicular to the tread surface 2, and this thickness E is equal to the depth of the deepest incision 3, and this thickness E is shown in Figure 3 . Figure 1 The shown tread 1 includes five pairs of adjacent compound incisions 5, and when the tire is new, each compound incision 5 includes alternating outer cavities 6 and narrow portions 7, and each compound incision 5 has an average line M extending in the circumferential direction XX' of the tire. As Figure 3 and Figure 4 shown, each narrow portion 7 of each compound incision 5 is continued radially inwards by an inner cavity 8. Each outer cavity 6 of a given compound incision 5 is connected to two outer cavities 6 of any compound incision 5 adjacent to said compound incision 5 through two grooves 9.

[0055] Figure 2 , Figure 3 and Figure 4A first embodiment of the present invention is described in detail. Figure 2 is a partial top view of the tread according to the first embodiment of the present invention. Figure 3 is a circumferential cross-sectional view A-A of a part of the composite cut of the tread according to the first embodiment of the present invention. Figure 4 is a cross-sectional view B-B along the groove leading to the composite cut of the tread according to the first embodiment of the present invention. Each outer cavity 6 has a length Le measured between a front end E1, which is intended to first contact the ground along the running direction R of the tire at the tread surface 2, and a rear end E2, which is intended to last contact the ground. The front end E1 and the rear end E2 are located on the average line Me of the outer cavity 6. The outer cavity 6 has a width We measured perpendicular to the average line Me of the outer cavity 6 and a height He measured perpendicular to the tread surface 2, and the maximum value of the width We is at least equal to 6 mm. Each narrow portion 7 has a width Ws measured perpendicular to the average line Ms of the narrow portion 7 and a height Hs measured perpendicular to the tread surface 2, and the width Ws is at most equal to the width We of the outer cavity 6 and at most equal to 2 mm. The narrow portion 7 continues radially inward by an inner cavity 8, which has a width Wc measured perpendicular to the average line of the inner cavity and a height Hc measured perpendicular to the tread surface 2. Each groove 9 extends from a first intersection point I1 with the outer cavity 6 of the first composite cut 5 to a second intersection point I2 with the closest outer cavity 6 of the second composite cut 5 adjacent to the first composite cut 5. The groove 9 has a width Wi measured perpendicular to the average line Mi of the groove 9 and a height Hi measured perpendicular to the tread surface 2, and the width Wi is at most equal to 2 mm. According to a first feature of the present invention, the distance D between each intersection point (I1, I2) of the groove 9 with each outer cavity 6 and a plane P that bisects the outer cavity 6 perpendicular to the average line Me of the outer cavity 6 and is equidistant from the front end E1 and the rear end E2 of the outer cavity 6 is at least equal to 25% of the length Le of the outer cavity 6 and at most equal to 50% of the length Le of the outer cavity 6. According to a second feature of the present invention, the first intersection point I1 of the groove 9 with the outer cavity 6 of the first composite cut 5 is located near the front end E1 of the outer cavity 6. According to a second feature of the present invention, the second intersection point I2 of the groove 9 with the closest outer cavity 6 of the second composite cut 5 is located near the rear end E2 of the outer cavity 6. As Figure 2 shown, the groove 9 has an average inclination angle Am with respect to the plane P that bisects the outer cavity 6, and the average inclination angle Am is defined as the slope of the straight line passing through the two intersection points (I1, I2) of the groove with the outer cavity 6. Advantageously, the average inclination angle Am is at least equal to 10° and at most equal to 45°. Also as Figure 2As shown, the cutter grooves 9 have an incident angle (A1, A2) at the intersection points (I1, I2) with respect to the plane P that bisects each external cavity 6, and the incident angle (A1, A2) is defined as the slope of the line tangent to the cutter groove 9 at the intersection points (I1, I2). Advantageously, the incident angle (A1, A2) is at most equal to the average inclination angle Am. In Figure 2 In the particular case shown, the angles Am, A1, and A2 are equal.

[0056] The subject of the second embodiment of the present invention is the tread 1 of a tire intended to be mounted on the trailing axle of a heavy vehicle and is described in Figure 5 and Figure 6 described in. Figure 5 is an overall top view of a tread according to the second embodiment of the present invention intended for the trailing axle of a heavy vehicle. Figure 6 is a partial top view of the tread according to the second embodiment of the present invention. The above introduction remains valid in this case. The second embodiment of the present invention differs from the first embodiment in that each composite cut has an average line forming a broken line, and its direction is substantially transverse to the traveling direction of the tire.

[0057] The inventors have conducted more specific research on the present invention. The tire according to the first embodiment I1 of the present invention is for the steering axle of a heavy vehicle and has a size of 315 / 70R 22.5; the tire according to the second embodiment I2 of the present invention has a size of 295 / 80R 22.5 and is for the trailing axle.

[0058] Table 1 below shows the characteristics of the tested treads:

[0059] [Table 1]

[0060]

[0061]

[0062] The road tests conducted on the above exemplary embodiments show that the treads designed according to the present invention for the steering axle or the trailing axle of a heavy vehicle exhibit a favorable compromise in terms of performance among wear, rolling resistance, and wet grip. During the manufacturing and use of the tread demolding, the robustness of the composite cuts and the accessory cutter grooves has been significantly improved, and it is easier to discharge the stones that may be trapped in the external cavities.

Claims

1. Tire for a heavy vehicle, said tire comprising a tread (1), said tread (1) being intended to come into contact with the ground via a tread surface (2) and comprising incisions (3) defining raised elements (4), - The tread (1) has a thickness (E) measured perpendicular to the tread surface (2), said thickness (E) being equal to the depth of the deepest incision (3), - The tread (1) comprises at least two adjacent composite incisions (5), and when the tire is brand new, each composite incision (5) comprises alternating external cavities (6) and narrow portions (7), - Each external cavity (6) has a length (Le) measured at the tread surface (2) between a front end (E1) intended to first come into contact with the ground and a rear end (E2) intended to last come into contact with the ground along the running direction (R) of the tire, said front end (E1) and said rear end (E2) being located on the average line (Me) of the external cavity (6), - The external cavity (6) has a width (We) measured perpendicular to the average line (De) of the external cavity (6) and a height (He) measured perpendicular to the tread surface (2), and the maximum value of said width (We) is at least equal to 6 mm, - Each narrow portion (7) has a width (Ws) measured perpendicular to the average line (Ms) of the narrow portion (7) and a height (Hs) measured perpendicular to the tread surface (2), said width (Ws) being at most equal to the width (We) of the external cavity (6) and at most equal to 2 mm, - The narrow portion (7) is radially inwardly continued by an internal cavity (8), said internal cavity (8) having a width (Wc) measured perpendicular to the average line of the internal cavity (8) and a height (Hc) measured perpendicular to the tread surface (2), - At least one siped (9) extends from a first intersection point (I1) with the external cavity (6) of the first composite incision (5) to a second intersection point (I2) with the closest external cavity (6) of the second composite incision (5) adjacent to the first composite incision (5), - The siped (9) has a width (Wi) measured perpendicular to the average line (Mi) of the siped (9) and a height (Hi) measured perpendicular to the tread surface (2), said width (Wi) being at most equal to 2 mm, It is characterized in that The distance (D) between each intersection point (I1, I2) of the siped (9) with each external cavity (6) and a plane (P) that bisects the external cavity (6) perpendicular to the average line (Me) of the external cavity (6) and is equidistant from the front end (E1) and the rear end (E2) of the external cavity (6) is at least equal to 25% of the length (Le) of the external cavity (6) and at most equal to 50% of the length (Le) of the external cavity (6), and the first intersection point (I1) of the siped (9) with the external cavity (6) of the first composite incision (5) is located near the front end (E1) of said external cavity (6), and the second intersection point (I2) of the siped (9) with the closest external cavity (6) of the second composite incision (5) is located near the rear end (E2) of said external cavity (6).

2. The tire according to claim 1, wherein the sipes (9) have an average inclination angle (Am) with respect to the plane (P) bisecting the outer cavity (6), and the average inclination angle (Am) is defined as the slope of the straight line passing through the two intersection points (I1, I2) of the sipe and the outer cavity (6), where, The average inclination angle (Am) is at least equal to 10° and at most equal to 45°, preferably at least equal to 20° and at most equal to 35°.

3. The tire according to claim 2, wherein the grooves (9) have an angle of incidence (A1, A2) with respect to the plane (P) bisecting each outer cavity (6) at the intersection points (I1, I2), the angle of incidence (A1, A2) being defined as the slope of the line tangent to the groove (9) at the intersection points (I1, I2), where The incident angles (A1, A2) are at most equal to the average inclination angle (Am).

4. The tire according to any one of claims 1 to 3, wherein, Each cutter groove (9) has a constant height (Hi).

5. The tire according to any one of claims 1 to 4, wherein, The height (Hi) of each cutter groove (9) is at least equal to the height (Hs) of the narrow part (7).

6. The tire according to any one of claims 1 to 5, wherein, The width (Wc) of each internal cavity (8) is at least equal to 5 mm.

7. The tire according to any one of claims 1 to 6, wherein, The height (Hc) of each internal cavity (8) is at least equal to 5 mm.

8. The tire according to any one of claims 1 to 7, wherein, The incisions (3) are all composite incisions.

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