TIRE COMPRISING A TREAD

Abstract

A tire comprises a directional tread (10), said tread comprising a central axis (12) and two edges (14A, 14B) a tread width W being greater than or equal to 140 mm, said tread (10) comprising a plurality of patterns (13) which succeed one another in the circumferential direction, each pattern having a pitch P, the patterns (13) delimiting a plurality of oblique grooves (16A, 16B), each oblique groove extending from one of the edges (14A, 14B) of the tread as far as the central axis (12). In a central part of the tread centered on the central axis (12) and of a width corresponding to 80% of the width W of said tread, all or some of the oblique grooves (16A, 16B) of the plurality of oblique grooves have a prescribed slenderness ratio, and all or some of the patterns comprise at least one sipe and have a prescribed sipes density SD.

Claims

1.-16. (canceled)

17. A tire comprising a directional tread, the tread comprising a central axis and two edges flanking the central axis and determining a tread width W, the tread width W being greater than or equal to 140 mm, the tread comprising a plurality of patterns which succeed one another in a circumferential direction, each pattern having a pitch P, the patterns delimiting a plurality of oblique grooves, each oblique groove extending from one of the edges of the tread in the direction of the central axis but without reaching the central axis, wherein, in a central part of the tread centered on the central axis and of a width corresponding to 80% of the width W of the tread, all or some of the oblique grooves of the plurality of oblique grooves have a slenderness ratio E between 0.85 and 1.5, the slenderness ratio corresponding to a ratio between a projected length Lpx of the oblique groove in the circumferential direction and half the width of the central part of the tread, such that $E=\frac{\mathrm{Lpx}}{0.4*W},$ and wherein all or some of the patterns comprise at least one sipe, a sipes density SD in all or some of these patterns being between 10 mm.sup.−1 and 70 mm.sup.−1, the sipes density SD corresponding to a ratio between a sum of a projected length lpyi of the at least one sipe in an axial direction to a product of the pitch P of the pattern and of the width W of the tread, all then multiplied by 1000, such that $\mathrm{SD}=\frac{\underset{i=1}{\overset{n}{.Math.}}\mathrm{lpyi}}{P*W}*1000,$ where n is a number of sipes in the pattern and lpvi is a projected length of the nth sipe.

18. The tire according to claim 17, wherein the tread comprises different pattern types Mj, where j is greater than or equal to 2, the patterns belonging to the one same pattern type having the one same pitch, the pitch between patterns belonging to two different pattern types being different, and wherein a mean sipes density SDmean is between 10 mm.sup.−1 and 70 mm.sup.−1, the mean sipes density SDmean corresponding to a mean of the sipes densities SDj of the patterns of the different pattern types Mj over an entire circumference of the tread, the mean sipes density SDmean being weighted according to a number of patterns Nj per pattern type Mj and according to a pitch Pj of the patterns belonging to that pattern type Mj over the circumference of the tread, such that $\mathrm{SDmean}=\frac{\underset{j=1}{\overset{m}{.Math.}}\left(\mathrm{SDJ}*\mathrm{NJ}*\mathrm{Pj}\right)}{\underset{j=1}{\overset{m}{.Math.}}\left(\mathrm{Nj}*\mathrm{Pj}\right)},$ where m is the number of different pattern types, SDj is the sipes density in a pattern belonging to the pattern type Mj, Pj is the pitch of the patterns belonging to the pattern type Mj, and Nj is the number of patterns belonging to the pattern type Mj.

19. The tire according to claim 17, wherein the sipes density SD is greater than 25 mm.sup.−1, less than 50 mm.sup.−1, or both greater than 25 mm.sup.−1 and less than 50 mm.sup.−1.

20. The tire according to claim 17, wherein the sipes density SD is between 30 mm.sup.−1 and 40 mm.sup.−1.

21. The tire according to claim 17, wherein the tread comprises at least one tread main groove and a width Ws of the tread main groove is determined such that a ratio CSR of a sum of the widths Ws of the at least one tread main groove to the width W of the tread is less than or equal to 0.15.

22. The tire according to claim 17, wherein each pattern comprises a set of blocks comprising at least one block, and wherein the at least one block has a maximum radial height Hmax when new that is between 5.5 mm and 9 mm.

23. The tire according to claim 22, wherein the at least one block is made of a rubbery material, and wherein a composition of the rubbery material has a glass transition temperature Tg between −40° C. and −10° C. and a dynamic complex shear modulus G* measured at 60° C. between 0.5 MPa and 2 MPa.

24. The tire according to claim 22, wherein a composition of the at least one block comprises an elastomer compound, the elastomer compound containing a modified diene elastomer containing at least one functional group comprising a silicon atom, the silicon atom being situated within a main chain of the elastomer, including ends of the chain.

25. The tire according to claim 24, wherein the modified diene elastomer containing a functional group comprising a silicon atom is a modified elastomer containing at least one silanol functional group situated at one end of the main chain of the modified elastomer.

26. The tire according to claim 24, wherein the functional group is selected from a silanol functional group and a polysiloxane group having a silanol end.

27. The tire according to claim 24, wherein the modified diene elastomer containing a functional group comprising a silicon atom is a modified elastomer containing, within its structure, at least one alkoxysilane group bonded to the modified elastomer via the silicon atom, and at least one functional group comprising a nitrogen atom.

28. The tire according to claim 26, wherein the modified diene elastomer is predominantly functionalized in the middle of the chain by an alkoxysilane group bonded to the two branches of the modified diene elastomer via the silicon atom.

29. The tire according to claim 26, wherein the modified diene elastomer exhibits at least two of the following characteristics: the functional group comprising a nitrogen atom is a tertiary amine; the functional group comprising a nitrogen atom is borne by the alkoxysilane group via a spacer group defined as an aliphatic C1-C10 hydrocarbon-based radical; and the alkoxysilane group is a methoxysilane or an ethoxysilane, optionally partially or completely hydrolyzed to give silanol.

30. The tire according to claim 24, wherein the modified diene elastomer is a butadiene/styrene copolymer.

31. The tire according to claim 24, wherein the modified diene elastomer exhibits a glass transition temperature within a range extending from −105° C. to −70° C.

32. The tire according to claim 17, wherein the tire has a 3PMSF winter certification, the certification being indicated on a sidewall of the tire.

Description

[0054] The present invention will be understood better upon reading the detailed description of embodiments that are given by way of entirely non-limiting examples and are illustrated by the appended drawings, in which:

[0055] FIG. 1 is a schematic view showing part of a tread of a tyre according to the invention, according to a first embodiment;

[0056] FIG. 2 is an impression of the tread of FIG. 1;

[0057] FIG. 3 is part of the impression of FIG. 2, centred on an oblique groove;

[0058] FIG. 4 is part of the impression of the tread of FIG. 2, said figure being centred on a first pattern of pitch P1;

[0059] FIG. 5 is part of the impression of the tread of FIG. 1, said figure being centred on a second pattern of pitch P2;

[0060] FIG. 6 is part of the impression of the tread of FIG. 1, said figure being centred on a third pattern of pitch P3;

[0061] FIG. 7 is an impression of a tread of a tyre according to the invention, according to a second embodiment.

[0062] The invention is not limited to the embodiments and variants presented and other embodiments and variants will become clearly apparent to a person skilled in the art.

[0063] In the various figures, elements that are identical or similar bear the same reference. Thus, the references used to identify elements on the tread are used together in order to identify these same elements on the impression made of said tread.

[0064] FIG. 1 partially depicts a tread according to a first embodiment of the invention. This tyre comprises a tread 10 and two sidewalls 11A, 11B flanking said tread 10. The sidewalls 11A, 11B form the lateral parts of the tyre. Each sidewall at its end comprises a bead intended to be seated on a rim of a wheel. The sidewalls 11A, 11B define the tread 10 at a first edge 14A and a second edge 14B. The first edge 14A and the second edge 14B flank a central axis 12 of the tread 10. This first edge 14A and this second edge 14B determine a tread width W. This tread width here is greater than 140 mm. The tread 10 also comprises a central part centred on the central axis 12 and the width of which corresponds to 80% of the width W of said tread 10. This central part is delimited by a third edge 15A and a fourth edge 15B. The tread 10 comprises a plurality of patterns 13 which succeed one another in the circumferential direction X.

[0065] On the tread, each pattern 13 comprises a set of blocks here comprising a first block 171, a second block 172, a third block 173, a fourth block 174 and a fifth block 175. The first block 171 extends from the first edge 14A of the tread 10, as far as a first oblique cut 231. The second block 172 extends from the first oblique cut 231, as far as a second oblique cut 232. The third block 173 extends on either side of the central axis 12 between the second cut 232 and a third cut 233. The fourth block 174 extends from the third cut 233, as far as a fourth cut 234. The fifth block 175 extends from the fourth cut 234, as far as the second edge 14B. The first block 171 and the fifth block 175 extend beyond the limits 14A and 14B of the tread 10. The regions of the first block 171 and fifth block 175 which are outside the tread are not intended to come into contact with the ground under normal running conditions.

[0066] The first block 171, the second block 172, the third block 173, the fourth block 174 and the fifth block 175 are delimited, at least in part, by oblique grooves 16A, 16B. In the tread of FIG. 1, the oblique grooves 16A, 16B extend respectively from the first edge 14A and from the second edge 14B in the direction of the central axis 12 but without reaching said central axis. These oblique grooves 16A, 16B encourage the removal of water from the tread when running on a wet road surface. Each block 171, 172, 173, 174, 175 respectively comprises a first sipe 181, a second sipe 182, a third sipe 183, a fourth sipe 184, a fifth sipe 185 and a sixth sipe 186 to improve the grip of the tyre on snowy ground. More particularly, the first sipe 181 extends from the first edge 14A as far as one sipe end of the first sipe 181. The second sipe 182 extends from the first oblique cut 231 as far as the second oblique cut 232. The third sipe 183 extends from the second oblique cut 232 as far as one end of the third sipe 183. The fourth sipe 184 extends from one end of the fourth sipe 184 as far as the third oblique cut 233. The fifth sipe 185 extends from the third oblique cut 233 as far as the fourth oblique cut 234. The sixth sipe 186 extends from one end of the sixth sipe 186 to reach the second edge 14B of the tread.

[0067] Each sipe 181, 182, 185, 186 divides the associated block 171, 172, 174, 175 into two parts of roughly identical width. In the third block 173, the length of the sipes 183 and 184 is limited. The third sipe 183 and the fourth sipe 184 thus do not extend as far as the central axis 12.

[0068] FIG. 2 depicts an impression of the tread of FIG. 1.

[0069] This impression has been made dynamically under conditions as described hereinabove. The recessed “voids” elements such as the oblique grooves 16A, 16B, and the sipes 181, 182, 183, 184, 185, 186 are represented in white. The blocks 171, 172, 173, 174, 175 are illustrated in black. From this impression, it is possible to determine a slenderness ratio E of the oblique grooves (FIG. 3) and a sipes density SD for the sipes in the blocks 171, 172, 173, 174, 175 (FIGS. 4 to 6).

[0070] FIG. 3 thus depicts part of the impression of FIG. 2, centred on an oblique groove 16A. In the tread, this oblique groove 16A begins from the first edge 14A and stops before reaching the central axis 12.

[0071] It is possible to determ ine a slenderness ratio E for the oblique groove 16A in the central part of the tread, namely to determine the level of its inclination in this central part. As has already been specified, the central part is delimited in part by the third edge 15A. The slenderness ratio E is determined from a projected length Lpx of the oblique groove 16A in the circumferential direction X and half the width of the central part of the tread, 0.8*W/2, such that

[00004]$E=\frac{\mathrm{Lpx}}{0.4*W}.$

More particularly, the projected length Lpx is measured between a first point A and a second point B. The point A is determined at the intersection between a midline 19 of the oblique groove 16A and the third edge 15A. The midline 19 of the oblique groove 16A divides said oblique groove 16A into two oblique half-grooves of the same width. The point B is determined at the intersection between the midline 19 of the oblique groove 16A and the end of the oblique groove 16A. The slenderness ratio E is here comprised between 0.85 and 1.5 and preferably between 0.87 and 1.1.

[0072] Each pattern 13 has a pitch P. This pitch P is determined as being the distance between the centres of two adjacent oblique grooves flanking the blocks 171, 172, 173, 174, 175. It will be noted that, in the example of the embodiment of FIG. 1, the tread 10 comprises three pitches P1, P2, P3 having different values.

[0073] FIGS. 4, 5 and 6 illustrate three patterns of the one same tread, belonging to three different pattern types having different pitches P1, P2, P3. FIG. 4 thus illustrates a first pattern having a first pitch P1. As has already been described, the first pattern comprises the first block 171, the second block 172, the third block 173, the fourth block 174 and the fifth block 175. The first block 171 comprises the first sipe 181. The second block 172 comprises the second sipe 182. The third block 173 here comprises the third sipe 183 and the fourth sipe 184. The fourth block 174 comprises the fifth sipe 185. The fifth block 175 comprises the sixth sipe 186. For each sipe, it is possible to determine a projected sipe length in the axial direction Y. The first sipe 181 thus has a first projected length lpy11, the second sipe 182 has a second projected length lpy12, the third sipe 183 has a third projected length 1pyl3, the fourth sipe 184 has a fourth projected length 1pyl4. The fifth sipe has a fifth projected length Lpyl5. The sixth sipe has a sixth projected length Lpyl6. It is possible to determine a first sipes density SD1 in the set of blocks of pitch P1 comprising the first block 171, the second bloc 172, the third block 173, the fourth block 174, the fifth block 175. This first sipes density SD1 corresponds to the ratio between the sum of projected lengths lpy11, lpy12, lpy13, lpy14, lpy15, and lpy16 of the sipes 181, 182, 183, 184, 185 and 186 to the product of the pitch P1 of the pattern and of the width W of the tread, all then multiplied by 1000, such that

[00005]$\mathrm{SD}1=\frac{\left(\mathrm{lpy}11+\mathrm{lpy}12+\mathrm{lpy}13+\mathrm{lpy}14+\mathrm{lpy}15+\mathrm{lpy}16\right)}{P1*W}*1000.$

[0074] FIG. 5 illustrates a second pattern having a second pitch P2. The second pitch P2 has a higher value than the first pitch P1. As was the case with the first pattern, it is possible to determine a second sipes density SD2. This second sipes density SD2 is calculated from the projected lengths lpy21, lpy22, lpy23, lpy24, lpy25, lpy26 of the sipes 181, 182, 183, 184, 185, 186 belonging to the blocks 171, 172, 173, 174, 175. This second sipes density SD2 thus corresponds to the ratio between the sum of projected lengths lpy21, lpy22, lpy23, lpy24, lpy25, and lpy26 of the sipes 181, 182, 183, 184, 185 and 186 to the product of the pitch P2 of the pattern and of the width W of the tread, all then multiplied by 1000, such that

[00006]$\mathrm{SD}2=\frac{\left(\mathrm{lpy}21+\mathrm{lpy}22+\mathrm{lpy}23+\mathrm{lpy}24+\mathrm{lpy}25+\mathrm{lpy}26\right)}{P2*W}*1000.$

[0075] FIG. 6 illustrates a third pattern having a third pitch P3. The third pitch P3 has a higher value than the second pitch P2. As was the case with the first pattern and the second pattern, it is possible to determine a third sipes density SD3. This third sipes density SD3 is calculated from the projected lengths lpy31, lpy32, lpy33, lpy34, lpy35, lpy36 of the sipes 181, 182, 183, 184, 185, 186 belonging to the blocks 171, 172, 173, 174, 175. This third sipes density SD3 thus corresponds to the ratio between the sum of projected lengths lpy31, lpy32, lpy33, lpy34, lpy35, and lpy36 of the sipes 181, 182, 183, 184, 185 and 186 to the product of the pitch P3 of the pattern and of the width W of the tread, all then multiplied byl000, such that

[00007]$\mathrm{SD}3=\frac{\left(\mathrm{lpy}31+\mathrm{lpy}32+\mathrm{lpy}33+\mathrm{lpy}34+\mathrm{lpy}35+\mathrm{lpy}36\right)}{P3*W}*1000.$

[0076] In the embodiment of FIGS. 1 to 6, the tread comprises an arrangement of N1 patterns of pitch P1, N2 patterns of pitch P2, and N3 patterns of pitch P3. It is thus possible to determine a mean sipes density SDmean corresponding to the mean of the sipes densities SD1, SD2, SD3 of the patterns of pitch P1, P2, P3 over the entire circumference of the tread. The mean sipes density SDmean is thus weighted according to the number of patterns N1, N2, N3 per pattern type and the pitch P1, P2, P3, such that:

[00008]$\mathrm{SDmean}=\frac{\left(\mathrm{SD}1*N1*P1+\mathrm{SD}2*N2*P2+\mathrm{SD}3*N3*P3\right)}{N1*P1+N2*P2+N3*P3}.$

[0077] The patterns of pitch P1, P2, P3 are arranged randomly on the tread so as to limit the emergence of tyre noise during running. Thus, for a tyre of size 205/55 R 16, patterns of pitch P1, P2 and P3 may be arranged relative to one another as follows: P1 P1 P2 P1 P2 P2 P2 P2 P1 P1 P2 P1 P1 P1 P2 P2 P3 P2 P2 P3 P2 P1 P2 P2 P1 P1 P1 P1 P2 P1 P2 P1 P1 P1 P1 P2 P1 P1 P2 P2 P3 P3 P3 P2 P2 P3 P3 P3 P3 P3 P2 P2 P1 P2 P2 P3 P2 P1 P2 P2 P1 P2 P3 P2 P2 P1 P2 P2 P2 P1 P1 P1 P2 P3 P2 P1. Such an arrangement would then comprise 21 patterns of pitch P1, 35 patterns of pitch P2 and 13 patterns of pitch P3. As has already been specified, a pitch P is determined as being the distance between the centres of two adjacent oblique grooves flanking a block. In order to determine, with precision, the values for the pitches P1, P2 and P3, these are measured in groups of patterns belonging to the same pattern type, for example in P1 P1 P1, P2 P2 P2 and P3 P3 P3 pattern groups.

[0078] In one preferred embodiment, the mean sipes density SDmean is comprised between 10 mm.sup.−1 and 70 mm.sup.−1.

[0079] In one preferred embodiment, the mean sipes density SDmean is greater than 25 mm.sup.−1 and/or less than 50 mm.sup.−1.

[0080] In another preferred embodiment, the mean sipes density SDmean is comprised between 30 mm.sup.−1 and 40 mm.sup.−1.

[0081] It will be noted that the third blocks 173 of the different patterns are bonded to one another. All of these third blocks thus form a rib of material which extends all the way along the circumference of the tyre.

[0082] FIG. 7 illustrates a second embodiment of the invention in which the tread 10 further comprises a tread main groove of width Ws. This width Ws is measured in the axial direction Y. From this width Ws, it is possible to determine a contact area ratio of the tread main groove, called CSR, corresponding to the ratio of the width Ws of the tread main groove to the width W of the tread, such that

[00009]$\mathrm{CSR}=\frac{W_s}{W}.$

In one preferred embodiment, the contact area ratio CSR is less than or equal to 0.15.

[0083] For all the embodiments illustrated in FIGS. 1 to 7, each block is formed from a rubbery material. In one preferred embodiment, the composition of this rubbery material exhibits a glass transition temperature Tg comprised between −40° C. and −10° C. and preferably between −35° C. and −15° C. and a shear modulus measured at 60° C. comprised between 0.5 MPa and 2 MPa, and preferably between 0.7 MPa and 1.5 MPa.

[0084] In one preferred embodiment, the composition of the rubbery material of the blocks is based on at least: [0085] an elastomer matrix comprising more than 50% by weight of a solution SBR bearing a silanol functional group and an amine functional group; [0086] −20 to 200 phr of at least one silica; [0087] a coupling agent for coupling the silica to the solution SBR; [0088] 10 to 100 phr of a hydrocarbon-based resin having a Tg of greater than 20° C.; [0089] 15 to 20 phr of a liquid plasticizer.

[0090] The solution SBR in this preferred embodiment is a copolymer of butadiene and styrene, prepared in solution. The characteristic feature thereof is that it bears a silanol functional group and an amine functional group. The silanol functional group of the solution SBR bearing a silanol functional group and an amine functional group may for example be prepared by hydrosilylation of the elastomer chain by a silane bearing an alkoxysilane group, followed by hydrolysis of the alkoxysilane functional group to give a silanol functional group. The silanol functional group of the solution SBR bearing a silanol functional group and an amine functional group may equally be introduced by reaction of the living elastomer chains with a cyclic polysiloxane compound as described in EP 0 778 311. The amine functional group of the solution SBR bearing a silanol functional group and an am ine functional group may for example be introduced by initiating polymerization using an initiator bearing such a functional group. A solution SBR bearing a silanol functional group and an amine functional group may equally be prepared by reacting the living elastomer chains with a compound bearing an alkoxysilane functional group and an amine functional group according to the procedure described in patent application EP 2 285 852, followed by hydrolysis of the alkoxysilane functional group to give a silanol functional group. According to this preparation procedure, the silanol functional group and the amine functional group are preferably situated within the chain of the solution SBR, not including the ends of the chain. The reaction producing the hydrolysis of the alkoxysilane functional group borne by the solution SBR to give a silanol functional group may be carried out according to the procedure described in patent application EP 2 266 819 A1 or else by a step of stripping the solution containing the solution SBR. The amine functional group can be a primary, secondary or tertiary amine functional group, preferably a tertiary functional group.

[0091] It will also be noted that the blocks have a relatively low maximum radial height Hmax when new. This radial height is comprised between 5.5 mm and 9 mm, and preferably between 6 mm and 7.5 mm. This relatively low radial height could compromise grip on wet ground. Thus, by virtue of the invention, the radial height is compensated for by the high slenderness ratio of the tread and by the characteristics of the material used containing the solution SBR. That allows the tyre to maintain good grip on wet ground over time.

[0092] The invention is not limited to the embodiments and variants presented and other embodiments and variants will become clearly apparent to a person skilled in the art.

[0093] Thus, FIGS. 1 to 7 show embodiments in which the tread comprises at least three different pitch types. As a variant, the tread comprises a single pitch type P. The tyre is thus said to be monopitch. The sipes density SD thus corresponds to the sum of the projected lengths of the sipes in the axial direction Y to the product of the pitch P of the pattern and of the width W of the tread, all then multiplied by 1000, sucn that

[00010]$\mathrm{SD}=\frac{\underset{i=1}{\overset{n}{.Math.}}\mathrm{lpyi}}{P*W}*1000,$

where n is the number of sipes in the pattern and lpy1 is the projected length of the nth sipe. The sipes density is comprised between 10 mm.sup.−1 and 70 mm.sup.−1. Preferably, the sipes density SD is greater than 25 mm.sup.−1 and/or less than 50 mm.sup.−1. Preferably, the sipes density SD is comprised between 30 mm.sup.−1 and 40 mm.sup.−1.

[0094] FIG. 7 thus shows a tread 10 comprising a single central tread main groove. As a variant, the tread comprises a number of tread main grooves greater than 1. As a result, the CSR corresponds to the ratio of the sum of the widths of the tread main grooves to the width of the tread, such that

[00011]$\mathrm{CSR}=\frac{\underset{j>1}{\overset{m}{.Math.}}{W}_{\mathrm{sj}}}{W},$

where m is the number of tread main grooves in the tread and Wsj is the width of the jth tread main groove. The CSR for a tread comprising at least two tread main grooves is less than or equal to 0.15.

[0095] Thus, as illustrated in FIGS. 1 to 7, the central rib of material formed by the third blocks has a small width overall. As a variant, the width of this central rib of material corresponds to at least a third of the width W of the tread.