Tire Having a Tread Combining Inclined Sipes with a Specific Material

Abstract

Tyre for a heavy-duty vehicle, this tyre comprising a tread (1) having a thickness E of wearable material and a tread surface (10) intended to come into contact with a roadway, this tread (1) having, on at least one raised element, a plurality of inclined sipes (5) extending into the thickness of the tread, these inclined sipes (5) having suitable widths such that they close up at least partially when they enter the contact patch in contact with the roadway. The tire being formed from a material having, a tan()max/(G*25%) ratio is at most equal to 0.065, in which tan()max is the measurement, at 60 C., of the loss factor of the material of which the tread is made, and G*25% is the complex dynamic shear modulus, expressed in MPa, anda deformation at break under tensile testing which is at least equal to 530%, this value being obtained at a temperature of 60 C.

Claims

1. A tire for a heavy-duty vehicle, this tyre comprising a tread having a thickness E of wearable material and a tread surface intended to come into contact with a roadway, this tread having at least one raised element, this raised element having a contact face forming part of the tread surface, lateral faces intersecting the contact face along edge corners, each raised element having a height at least equal to the thickness E of wearable material, this at least one raised element comprising a plurality of sipes distributed in the circumferential direction, these sipes being inclined, namely making an angle (A) other than zero degrees with a radial plane (ZZ) perpendicular to the contact face of the raised element, these inclined sipes intersecting the contact face of the raised element to form edge corners, these inclined sipes having suitable widths such that they close up at least partially when they enter the contact patch in contact with the roadway, wherein the material which, when new, forms the radially external part (Ce) of the tread and is intended to be in contact, when new, with a roadway, is chosen such that it has the following physical properties: a tan()max/(G*25%) ratio is at most equal to 0.065, in which tan()max is the measurement, at 60 C., of the loss factor of the material of which the tread is made, and G*25% is the complex dynamic shear modulus, expressed in MPa, of this material as obtained according to the recommendations of standard ASTM D 5292-96, and a deformation at break under tensile testing that is at least equal to 530%, this value being obtained at a temperature of 60 C. according to the recommendations of French standard NF T 46-002.

2. The tire according to claim 1, wherein the deformation at break under tensile testing of the material which, when new, forms the radially external part (Ce) of the tread is at least equal to 570%.

3. The tire according to claim 1, wherein the maximum value of tan(), denoted tan()max and measured at 60 C. for the material which, when new, forms the external part (Ce) of the tread, is less than or equal to 0.10.

4. The tire according to claim 1, wherein the angle (A) of inclination of the inclined sipes with respect to a radial plane is at least equal to 5 degrees and at most equal to 20 degrees.

5. The tire according to claim 1, wherein the angle of the inclined sipes varies from the tread surface progressing towards the inside of the tread.

6. The tire according to claim 1, wherein the inclined sipes have widths at most equal to 2 mm.

7. The tire according to claim 1, wherein each inclined sipe has a depth which is at least equal to 40% of the thickness E of wearable material of the tread.

8. The tire according to claim 1, wherein the tread comprises, when new, an external layer (Ce) formed from a material having the following physical properties: a tan()max/(G*25%) ratio at most equal to 0.065, a strain at break at least equal to 530%, and, radially on the inside of this external layer (Ce), an internal layer (Ci) formed from a material chosen to be a weak dissipator and having the following physical properties: a tan()max/(G*25%) ratio of less than 0.085, a tan()max value of less than 0.09.

9. The tire according to claim 8, wherein the inclined sipes extend in the external layer (Ce) and at most into 10% of the thickness of the internal layer (Ci).

10. The tire according to claim 8, wherein the thickness of the innermost internal layer (Ci) of the tread is comprised between 10% and 40% of the total thickness of the tread.

11. The tire according to claim 1, wherein each inclined sipe is provided with a widening at its end furthest towards the inside of the tread.

12. The tire according to claim 1, wherein the inclined sipes in the thickness of the tread have plots on the tread surface when new which are inclined so as to make a mean angle (B) other than zero with respect to the axis of rotation of the tyre.

13. The tire according to claim 1, wherein certain raised elements are provided with short inclined sipes that open only onto a lateral wall of these raised elements.

14. The tire according to claim 1, for attachment to a steering axle of a heavy-duty vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0063] FIG. 1 depicts a partial view of the tread surface of a tread according to one variant of the invention;

[0064] FIG. 2 depicts a view in transverse section of the crown part of the tire on a plane of section the plot of which is indicated by II-II in FIG. 1;

[0065] FIG. 3 shows a view in cross section of the tread shown in FIG. 1 on a plane of section the plot of which is indicated by III-III;

[0066] FIG. 4 shows another variant of the tread according to the invention in cross section.

DESCRIPTION OF THE FIGURES

[0067] In order to make the figures easier to understand, identical reference signs have been used to describe variants of the invention where these reference signs refer to elements of the same kind, whether structurally or functionally.

[0068] FIG. 1 depicts part of the tread surface 10 of a tread 1 of a heavy-duty tire (315/70R22.5), the said tread surface being intended to come into contact with a roadway when the tire is running.

[0069] In this variant of tire according to the invention, it may be seen that this tire, intended to be fitted to the steered axle of a heavy-duty vehicle, comprises a tread 1 which when new has two main grooves 2 of circumferential orientation (indicated by the direction XX in FIG. 1), these main grooves 2 being entirely open onto the tread surface 10 when new. These main grooves 2 have a depth when new which is slightly greater than the thickness E of tread material to be worn away, so as to ensure a lasting performance, notably in rainy weather (in this instance, the thickness E is equal to 10.5 mm). The thickness E of wearable material is determined as being the thickness beyond which the tread has to be renewed by re-capping or the tire has to be changed, the remaining depth of the grooves and voids having reached a pre-set limit value.

[0070] The circumferential main grooves 2 have a maximum depth equal to 12 mm.

[0071] Furthermore, the tread 1 comprises three wavy grooves 3 oriented mainly in the circumferential direction. These wavy grooves 3 are formed of a plurality of parts 31 opening onto the tread surface of the tread when new, these open parts being extended into the tread by hidden parts 31 (visible in FIG. 2) hidden inside the thickness of the tread.

[0072] The grooves together delimit two edge ribs 41 axially on the outside of the tread and, between these edge ribs 41, four intermediate ribs 42.

[0073] FIGS. 2 and 3 show partial sections through the tire of which part of the tread surface is shown in FIG. 1. Visible in these FIGS. 2 and 3 are the layers that make up the tread: an external layer Ce, positioned radially on the outside and intended to come into contact with the roadway when new, this external layer Ce surmounting an internal layer Ci which in theory is not intended to come into contact with the roadway as long as the user does not exceed the predefined wear limit.

[0074] The material of which the external layer Ce of the tread is made has the following physical properties:

[0075] a tan()max/(G*25%) ratio equal to 0.050, in which tan()max is the measurement, at 60 C., of the loss factor of the material of which the tread is made, and G*25% is the complex dynamic shear modulus, expressed in MPa, of this material as obtained according to the recommendations of standard ASTM D 5292-96;

[0076] a deformation at break under tensile testing that is equal to 630%, this value being obtained at a temperature of 60 C. according to the recommendations of French standard NF T 46-002.

[0077] A material of this kind is described in particular in document WO 2017/103495 A1 (see in particular the composition denoted CA1 in the exemplary embodiments described in that document).

[0078] The material of which the internal layer Ci placed radially beneath the external layer Ce of the tread is made has the following physical properties:

[0079] a tan()max/(G*25%) ratio equal to 0.075, in which tan()max is the measurement, at 60 C., of the loss factor of the material of which the tread is made, and G*25% is the complex dynamic shear modulus, expressed in MPa, of this material as obtained according to the recommendations of standard ASTM D 5292-96;

[0080] a tan()max value equal to 0.085.

[0081] The material of which the internal layer Ci is made is a conventional material employed to form a tread of a heavy-duty tire.

[0082] FIG. 2 shows a transverse section through the crown part of the tire shown in FIG. 1, this transverse section being taken in a plane containing the axis of rotation (parallel to the direction YY) and of which the plot in FIG. 1 is indicated by II-II.

[0083] This sectional view shows the superposition of an external layer Ce and of an internal layer Ci of the tread 1. The external layer Ce has a thickness E1 equal to 12 mm, and the internal layer Ci has a thickness E2 equal to 3 mm. The thickness E of wearable material in this instance is equal to 10.5 mm.

[0084] The circumferential main grooves 2 and the circumferentially oriented wavy grooves 3 are formed in the external layer Ce by moulding, these grooves delimiting edge ribs 41 and intermediate ribs 42. In the case of the wavy grooves 3 it is possible to distinguish groove parts 31 that are open onto the tread surface 10 when new and groove parts 31 that are hidden beneath the tread surface 10 when new. Sipes 32 extend the groove parts 31 that are open onto the tread surface 10 down to a depth equal to the depth of the circumferential main grooves 2. The hidden groove parts 31 are extended towards the tread surface 10 when new by sipes 32 that make the tire easier to mould and to demould. The hidden groove parts 31 extend in the thickness of the tread down to a depth equal to that of the circumferential main grooves 2.

[0085] This same FIG. 2 schematically shows the crown reinforcement 7 of the tire radially on the inside of the tread 1.

[0086] FIG. 3 shows a partial cross section of an intermediate rib 42, this section being taken on a plane perpendicular to the axis of rotation and the plot of which is indicated by III-III in FIG. 1.

[0087] This intermediate rib 42 is provided with a plurality of inclined sipes 5 opening onto the two lateral faces of the intermediate rib 42 and having, on the tread surface 10, as is visible in FIG. 1, a zigzag plot. Furthermore, each of these sipes is inclined, in the plane of FIG. 1, at a constant mean angle B to the axial direction indicated by the direction YY in FIG. 1, this mean angle B in this instance being equal to 25 degrees. This mean angle B is obtained as the angle made by the segment connecting the start and end of the plot of a sipe on the tread surface with respect to the axis of rotation indicated by the direction YY. In the example described, only the sign of this mean angle B changes from one rib to another.

[0088] All of the sipes 5 have a mean width equal to 0.8 mm allowing the walls delimiting them to come into even partial contact.

[0089] These sipes 5 are also, and as can be seen in FIG. 3, inclined in the thickness of the tread at a constant angle A with respect to a radial plane passing through the mean plot of the sipe on the tread surface when new. By definition, a radial plane is a plane which contains the axis of rotation. In FIG. 3, the plot of a radial plane passing through the sipe at the tread surface is represented by the direction ZZ. The angle of inclination in the depth of the tread is 15 degrees here. The magnitude of this angle A is the same for all the inclined sipes formed on the four intermediate ribs and is constant through the depth of the tread.

[0090] The inclined sipes 5 comprise a rectilinear part 5, ending in an enlargement 5 of maximum width equal to 2 mm. These inclined sipes 5 extend as far as a depth equal to 11 mm, which is less than the thickness of the external layer Ce but greater than the thickness of wearable material E in this instance so as to maintain the presence of these sipes throughout the service life of the tire.

[0091] In FIG. 1 it may be seen that the ribs 41, 42 flanking the circumferential main grooves 2 are also provided with a plurality of short sipes 6 opening only onto these main grooves 2. These short sipes 6 contribute as is known to improving the wearing performance of the tire. These short sipes 6 are both inclined with respect to the axis of rotation (direction YY) and inclined in the thickness of the tread with respect to the radial direction (ZZ) in the same way as the inclined sipes 5 formed on the intermediate ribs and described hereinabove. It must be understood here that the short sipes 6 are oriented in the same way as the inclined sipes 5 but not necessarily with the same magnitude of angle.

[0092] In another variant, shown in FIG. 4, each inclined sipe 5 has an inclination A that varies in the thickness of the tread; this inclination A is equal to 12 degrees in the vicinity of the end 51 of the sipe 5 on the tread surface when new 10 and equal to 0 degrees at its other end 52 inside the tread. The variation in inclination is regular with depth. In this example, as in the previous example, the tire has a preferred direction of rotation indicated by the arrow R in this FIG. 4. Thus, the inclined sipes are formed such that they have their ends furthest towards the inside of the tread in front compared with their end 51 on the tread surface when new. These sipes 5 have, in the depth, a mean inclination equal to 6 degrees, this mean inclination being given by the angle A* that the segment PQ connecting the starting point of the sipe 5 on the tread surface 10 and the point furthest towards the inside of the sipe makes with the direction (ZZ) of a radial plane in the section plane considered in FIG. 4.

[0093] Although the invention has been illustrated by means of these two variants, nothing should limit it to these described examples, and various modifications can be made thereto without departing from the scope as defined by the claims. In particular, the tire may have a tread of which the raised elements are blocks rather than ribs, or a combination of blocks and ribs.