Tire Having a Tread Combining Inclined Sipes with a Specific Material

Abstract

Heavy-duty vehicle tire, with tread (1) of thickness E of wearable material and surface (10) for contact with a roadway, tread (1) having a raised element (41, 42) with of sipes (5) circumferentially distributed and inclined. Tread (10) material is an elastomer based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages and on a reinforcing filler predominantly of silica, with a content expressed in phr (parts by weight per hundred parts of elastomers) of greater than 40 and a filler content in phr of greater than 50, and having: a tan(δ)max/(G*25%) ratio at most of 0.065, in which tan(δ) is the measurement, at 60° C., of the loss factor of the tread material, and G*25% is the complex dynamic shear modulus, expressed in MPa, and a deformation at break under tensile testing at least equal to 530%, at a temperature of 60° C.

Claims

1. A tire for a heavy duty vehicle, 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 of wearable material, this at least one raised element being provided with a plurality of sipes distributed in the circumferential direction, these sipes being inclined, namely making an angle other than zero degrees with a radial plane perpendicular to the contact face of the raised element, these inclined sipes extending through the thickness of the tread and 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 of the tread that is intended to be in contact when new with a roadway is an elastomer compound based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages and optionally on at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in case of a blend being present in a majority amount relative to the amount of the other diene elastomer(s) used and on a reinforcing filler consisting predominantly of silica, with a content expressed in phr (parts by weight per hundred parts of elastomers) of greater than 40 and an overall filler content expressed in phr of greater than 50, this material further having the following physical properties: a tan(δ)max/(G*25%) ratio is at most equal to 0.065, in which tan(δ)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(δ), denoted tan(δ)max and measured at 60° C. for the material which, when new, forms the external part of the tread, is less than or equal to 0.10.

4. The tire according to claim 1, wherein the complex dynamic shear modulus G*25% of the material which, when new, forms the external part of the tread, measured at 25% and 60° C. on the outbound cycle, is greater than or equal to 2 MPa.

5. The tire according to claim 1, wherein the material of which the outermost layer (Ce) of the tread when new is made is an elastomer compound based on natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages and optionally on at least one other diene elastomer, the natural rubber or the synthetic polyisoprene in case of a blend being present in a majority amount relative to the amount of the other diene elastomer(s) used and on a reinforcing filler consisting predominantly of a specific silica, with a content expressed in phr (parts by weight per hundred parts of elastomers) of greater than 40 and an overall filler content expressed in phr of greater than 50, which has the following characteristics: (a) a BET specific surface area of between 200 and 240 and preferably between 210 and 230 m2/g; (b) a CTAB specific surface area of between 180 and 220 and preferably between 190 and 210 m2/g; (c) an average particle size (by mass), denoted dw, of from 45 to 75 nm.

6. The tire according to claim 1, wherein the specific silica also has at least one of the following characteristics: a particle size distribution such that dw≥(16 500/CTAB)−30, a porosity that satisfies the criterion L/IF>−0.0025 CTAB+0.85, a content of silanols per unit area, denoted NSiOH/nm2, such that NSiOH/nm2<−0.027 CTAB+10.5.

7. The tire according to claim 1, wherein the sum of the sulfur content and accelerator content of the material which when new forms the external part of the tread is greater than or equal to 2.5 parts by weight per 100 parts by weight of elastomer (phr).

8. The tire according to claim 1, wherein the sulfur content, expressed in phr, is greater than or equal to 1.4.

9. 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.

10. The tire according to claim 1, wherein the angle (A) of the sipes varies from the tread surface progressing towards the inside of the tread.

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

12. The tire according to claim 1, wherein the inclined sipes have a depth which is at least equal to 40% of the wearable thickness of the tread.

13. The tire according to claim 1, wherein the tread comprises at least two layers of materials that are superposed in the radial direction, the material of the layer which when new is radially outermost having the following physical properties: a tan(δ)max/(G*25%) ratio at most equal to 0.065, a strain at break at least equal to 550%, and the material that completes the tread radially on the inside being chosen to be a weak dissipater and such that it has the following physical properties: a tan(δ)max/(G*25%) ratio of less than 0.085, a tan(δ)max value of less than 0.09.

14. The tire according to claim 13, wherein the thickness of the innermost internal layer of the tread is comprised between 10% and 40% of the total thickness of the tread.

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

16. The tire according to claim 1, wherein the tire is intended to equip a steering axle of a heavy-duty vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0088] FIG. 1 depicts a partial view of the tread surface of a tread according to one variant of the invention;

[0089] 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;

[0090] 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

DESCRIPTION OF THE FIGURES

[0091] 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.

[0092] 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.

[0093] 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.

[0094] The circumferential main grooves 2 have a maximum depth equal to 12 mm.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] This same FIG. 2 schematically shows the crown reinforcement 7 of the tire radially beneath the tread 1.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Combined with this tread pattern design, several tread materials were tested and compared. A reference material, denoted T in the table below, and a specific material, denoted M are used as the material for the external layer Ce of the tread.

[0109] The compositions and properties of these materials T and M are listed in the table below (the values of the constituents are expressed in phr, which is, by weight, parts per hundred rubber):

TABLE-US-00001 Component Material Material (phr) T M NR 100 80 BR SBR Tg-48° C. 20 Black N234 42 3 Silica 165G 10 Sil P200 50 Antioxidant 2.5 2.5 (6PPD) Stearic acid 2 2.5 Zinc oxide 3 1 Silane, liquid 0.5 6.25 Sulfur 1 1.5 Accelerator CBS 1.7 1.8 Accelerator TBBS Coaccelerator 0.62 DPG CBS + S 2.7 3.3

[0110] Properties

TABLE-US-00002 G* (25% outward) 1.7 2.3 MPa tan(δ).sub.max 0.15 0.10 tan(δ).sub.max / G*25% 0.088 0.043 strain at break 572 570 under tensile load (%)

[0111] In the above table: [0112] tan(δ).sub.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 measurement of the complex dynamic shear modulus of this material as obtained in accordance with the recommendations of standard ASTM D 5292-96; [0113] the strain at break under tensile load is obtained at a temperature of 60° C. in accordance with the recommendations of French standard NF T 46-002.

[0114] The silica used for the material M has the characteristics reproduced in the table below:

TABLE-US-00003 Silica Zeosil Premium Filler 200 BET surface area (m.sup.2/g) 220 CTAB surface area (m.sup.2/g) 200 d.sub.w (nm) 62 L/IF 0.62 N.sub.SiOH/nm.sub.2 3.90

[0115] The material constituting the internal layer Ci placed radially beneath the external layer Ce of the tread is a customary heavy-duty tire tread material and has the following physical properties: [0116] a tan(δ)max/(G*25%) ratio equal to 0.075, in which tan(δ)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; [0117] a tan(δ)max value equal to 0.085.

[0118] In the table below, the performance obtained with the reference material T used in the tread, this tread being provided with non-inclined sipes, is compared with the test material M used in the tread, this tread being provided or not provided with inclined sipes as described above.

[0119] A value of greater than 100 indicates an improvement expressed as a percentage.

TABLE-US-00004 Tire performance Material T Material M Material M Non-inclined Non-inclined Inclined sipes sipes sipes Rolling resistance 100 108 108 (base 100) Uneven wear (base 100  95 100 100)

[0120] Non-inclined sipes means sipes oriented perpendicular to the tread surface.

[0121] It is found that only the combination of a material M and inclined sipes leads both to an improvement in the rolling resistance and to maintained performance in terms of uneven wear by comparison with the reference tire using the reference material and non-inclined sipes.

[0122] The invention also relates to a tire provided with a tread as claimed and even more particularly to a tire intended to be fitted to the steering axle of a heavy-duty vehicle. In such a case, the tire is provided with a tread which is itself provided with a tread pattern formed of a plurality of circumferential ribs delimiting circumferential grooves.

[0123] Of course, the invention is not limited to the example described and various modifications can be made thereto without departing from the scope as defined by the claims.