Tire Tread Comprising Wavy Grooves and Sipes

Abstract

Tread with longitudinally oriented grooves (31, 41, 42) at least one is wavy (31) opening onto tread surface (10), at least one rib (21) oriented in the longitudinal direction and delimited by (31) with external cavities (311) opening to tread surface and internal cavities (312) hidden within the thickness of the tread, cavities (311) opening onto the surface (10) when new with a contour (310) having farthest-spaced endpoints A and B separated by a distance Lm, the rib (21) of width Ln having transverse sipes (5), made at a mean pitch Pi, where the length Lm of contour (310) of cavity (311) is equal to or greater than an integer multiple N of the pitch Pi times an amount at most equal to 25% of this integer multiple N of the pitch Pi, when new, N+1 transverse sipes (5) of rib (21) open into cavity (311) bordering the rib.

Claims

1. A tire tread comprising a tread surface, a thickness of material to be worn away during running, this tread being provided with a tread pattern formed by at least two longitudinally oriented grooves opening onto the tread surface of the tread, and of which at least one is a wavy groove, this tread comprising at least one rib oriented in the longitudinal direction of the tread and delimited by said at least one wavy groove, each wavy groove comprising external cavities opening onto the tread surface and internal cavities hidden within the thickness of the tread, the external cavities of each wavy groove opening onto the tread surface when new with a contour of which the longitudinally farthest-spaced endpoints (A, B) are separated by a longitudinal distance Lm, this distance Lm measuring the maximum longitudinal length of the contour of each external cavity, each external cavity having a depth Ho, the rib of width Ln comprising a plurality of transverse sipes, which is to say sipes oriented at 45 degrees or more to the longitudinal direction, made at a mean pitch Pi, the depth of these transverse sipes being at least equal to the depth Ho of the external cavities of the wavy groove delimiting said rib, wherein: the longitudinal length Lm of the contour of the external cavity is equal to or greater than an integer multiple N of the pitch Pi times an amount at most equal to 25% of this integer multiple N of the pitch Pi, when new, N+1 transverse sipes of the one same rib open into each open cavity bordering said rib, one of these transverse sipes opening near the end point A of the contour (310) at a distance D1 from this point A, another transverse sipe opening near the other end point B of the contour at a distance D2 from this point B, the difference between the two distances D1 and D2 being at most equal to 5 mm.

2. The tread according to claim 1, wherein the total voids volume ratio when new is at most equal to 13%.

3. The tread according to claim 1, wherein the tread comprises several intermediate ribs and edge ribs, the latter axially flanking the intermediate ribs, each intermediate rib being delimited by at least one wavy groove and being provided with a plurality of transverse sipes, and on each intermediate rib: the longitudinal length Lm of the contour of the opening of each external cavity onto the tread surface is equal to or greater than an integer multiple N of the pitch Pi of the transverse sipes times an amount at most equal to 25% of this integer multiple N of the pitch Pi, when new, N+1 transverse sipes of the one same rib open into each open cavity bordering said rib, one of these sipes opening near the end point A of the contour at a distance D1 from this point A, another sipe opening near the other end point B of the contour at a distance D2 from this point B, the difference between the two distances D1 and D2 being at most equal to 5 mm.

4. The tread according to claim 1, wherein the multiple N is identical for all the intermediate ribs.

5. The tread according to claim 1, wherein the distance D1 is equal to the distance D2 for all the ribs.

6. The tread according to claim 1, wherein the open cavities of the wavy grooves are offset from one another so that these external cavities do not come into contact with the road surface at the same time.

7. The tread according to claim 1, wherein the transverse sipes are offset on the intermediate ribs and the open cavities on the wavy grooves in a way suitable for the transverse sipes and these open cavities to come into the contact patch successively.

8. The tread according to claim 1, wherein at least one thin blade of rubbery material is formed at the ends of the contour of the external cavities, each thin blade being attached to at least one of the walls delimiting each external cavity.

9. The tread for a heavy duty vehicle provided with a tread according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0048] FIG. 1 depicts a view of the surface of a tread of a heavy duty vehicle of a first variant of the invention, for which N is equal to 1;

[0049] FIG. 2 shows a view in section on a plane of which the line in FIG. 1 is identified as II-II;

[0050] FIG. 3 shows a view in section on a plane of which the line in FIG. 1 is identified as III-III;

[0051] FIG. 4 shows a view of the surface of another variant of a tread for a tire of a heavy duty vehicle according to the invention and for which N is equal to 2.

DESCRIPTION OF THE FIGURES

[0052] In order to make the figures easier to understand, identical reference signs may be used to describe different variants of the invention where these reference signs refer to elements of the same kind, whether this be in terms of structure or in terms of function.

[0053] With reference to FIG. 1, the first variant of the invention describes a tread 1 having a tread surface 10 intended to be in contact with a road surface when a tire provided with said tread is running. This tread 1 has a thickness of material to be worn away during running, in which thickness cuts, grooves or sipes are formed.

[0054] FIG. 1 shows the view of the tread surface 10 of this tread, this tread comprising three circumferentially oriented grooves 31, 41, 42 (running in the circumferential direction indicated by the line XX′). These three grooves delimit two intermediate circumferential ribs 21, 22 and two edge ribs 20, 25 axially on the outside. Two of these grooves 41, 42 are cuts that are open over their entire length onto the tread surface of the tread when new. These two grooves 41, 42 have the same mean width La and a depth Ha (visible in FIG. 3). These two grooves flank a third wavy groove 31, undulating into the thickness of the tread.

[0055] This wavy groove 31 comprises external cavities 311 opening onto the tread surface 10 and internal cavities 312 hidden within the thickness of the tread. The internal cavities 312 are connected to the open external cavities 311 by linking cavities 313 (visible in FIG. 2) ensuring continuity of a flow of fluid in the groove when new and until a predetermined level of partial wear is reached.

[0056] The external cavities 311 of each wavy groove open onto the tread surface 10 when new and are bounded by a contour 310 of rectangular shape elongate in the circumferential direction and of which the the farthest-spaced endpoints A and B are separated by a longitudinal distance Lm, this distance Lm measuring the maximum length, in the longitudinal direction, of the rectangular contour of each external cavity 311. Each external cavity 311 has a mean width Lo, equal in the variant described to the width La of the other grooves, and a depth Ho, this depth corresponding to the level of tread wear for which the external cavities 311 disappear.

[0057] To facilitate the moulding and demoulding of the tread, the formation of circumferential sipes 314, opening onto the tread surface 10 and into the hidden cavities 312 and into the linking cavities 313, is planned.

[0058] Each of the two intermediate ribs 21, 22 of the tread is delimited both by a groove 41 or 42, that is open over its entire length, and by the wavy groove 31.

[0059] The intermediate ribs 21, 22 have the same width Ln that measures the shortest width between the grooves delimiting them. The maximum width of these intermediate ribs is equal to the sum of this shortest width and half the width of the external cavities 311.

[0060] Moreover, each of the intermediate ribs 21, 22 is provided with a plurality of transverse sipes 5 which in this instance make an angle of 90 degrees with the circumferential direction XX′. These sipes 5 are arranged on each intermediate trip 21, 22 with the same mean pitch Pi. The depth of these sipes is equal to the maximum depth Hc of the hidden cavities of the wavy groove. This maximum depth Hc of the hidden cavities 312 being equal to the depth Ha of the open grooves 41, 42. In this variant, two sipes 5 open into each open cavity.

[0061] Furthermore, the Tread is Such that: [0062] the longitudinal length Lm of the contour of each external cavity of the wavy groove 31 is in this example slightly greater than the pitch Pi of the transverse sipes 5, by the order of 10%; [0063] when new, two sipes 51, 52 of the one same intermediate rib 21, 22 open into each open cavity 311 bordering said rib, a sipe 51 opening near one end A of the rectangular contour 310 corresponding to a corner of said rectangle, namely at a non-zero distance D1 from this point A, the other sipe 52 opening near the other end point B of the rectangular contour, namely at a non-zero distance D2 from this point B. The distances D1 and D2 are equal in the example described and their sum is equal to 10% of the pitch Pi.

[0064] FIG. 2 shows a view in section on a plane of which the line in FIG. 1 is identified as II-II.

[0065] FIG. 3 shows a view in section on a plane of which the line in FIG. 1 is identified as III-III.

[0066] In this first variant, the sipes on each intermediate rib have the same layout with respect to the external cavities of the wavy grooves.

[0067] By virtue of this arrangement of the transverse sipes 51, 52 and of the external cavities 311 of the wavy groove 31, it is possible to create a tread having a satisfactory level of grip, notably when running on ground covered with water, and that does not develop uneven wear while at the same time limiting running noise. Furthermore, this tread reduces the risk of the initiation of cracks associated with picking up a stone.

[0068] FIG. 4 shows the tread surface of a tread 1 of a heavy duty tire of size 315/70 R 22.5.

[0069] This tread 1 has a width W equal to 265 mm and a thickness of material to be worn away equal to 11 mm; it is provided with a tread pattern formed of five circumferentially oriented grooves and obliquely oriented sipes.

[0070] This tread comprises three wavy grooves 31, 32, 33 in its thickness and, interposed between these wavy grooves, two open grooves 41, 42, open, over their entire length, onto the tread surface 10 when new.

[0071] The open grooves 41, 42 that are open over their entire length have a depth of 12 mm and a width equal to 8 mm.

[0072] The wavy grooves 31, 32, 33 comprise external cavities 311, 321, 331 which are open onto the tread surface when new, and internal cavities hidden within the tread, these external and internal cavities being connected to one another by linking cavities. The mean width of these cavities is equal to 8 mm. Each external cavity 311, 321, 331 has a depth equal to 6 mm. Furthermore, a sipe 314, 324, 334 of width 0.6 mm connects each hidden cavity to the linking cavities formed on each side of the hidden cavity. The innermost point of the wavy grooves are at a depth equal to 12 mm.

[0073] The dimensions given for the wavy groove 31 are also found on the other wavy grooves 32, 33. The external cavities 311 have a contour 310 on the tread surface 10 when new that is of elongate rectangular shape with a maximum length Lm that is equal in this variant to 77 mm (this length measures the distance between the points A and B situated at the end of this contour corresponding to the points of connection to the circumferential sipes 314). These external cavities 311 are arranged in the circumferential direction at a pitch equal to 154 mm.

[0074] The tread pattern of the tread thus delimits four intermediate ribs 21, 22, 23, 24 and two edge ribs 20, 25, these latter axially delimiting the width W of the tread. Each intermediate rib is delimited by a wavy groove and by a groove that is open over its entire length.

[0075] The grooves are arranged in such a way that the intermediate ribs all have the same minimum width Ln equal to 34 mm.

[0076] This tread has a volume voids ratio when new of 12.5%

[0077] Furthermore, each intermediate rib comprises a plurality of sipes 5 of oblique overall orientation which are mutually parallel on the one same rib and arranged at a mean pitch Pi (corresponding to the mean distance between two sipes measured in the circumferential direction); in this instance this pitch Pi is equal to 33 mm.

[0078] The overall orientation of a sipe 5 is obtained as being the angle made by a segment of straight line passing through the endpoints of the sipe with the transverse direction—indicated by the axis YY′ in the plane of FIG. 4. These sipes 5 are made on all the intermediate ribs with an overall orientation that makes a mean angle—in terms of absolute value—equal to 15 degrees to the transverse direction. Furthermore, these sipes 5 are arranged on the intermediate ribs in order to give the tread pattern of the tread 1 a directional nature, the sipes 5 on one half of the tread having the one same orientation, whereas on the other half the angle of orientation is of opposite value.

[0079] In order to obtain a good level of performance in terms of grip, notably on ground covered with water, without developing uneven wear and while at the same time limiting running noise, three sipes 5 open onto each external cavity 311 of the wavy grooves. Of these three sipes 5, the two sipes 51, 52 closest to the ends A and B of the contour of each external cavity 311 are situated at respective distances D1 equal to 7.1 mm, and D2 equal to 3.9 mm, from said ends A and B.

[0080] By positioning these sipes 51, 52 as close as possible to the ends A and B of the contour 310 of each external cavity 311, and by limiting the difference between these distances, it is, surprisingly, possible to solve the mentioned problems and also limit the risk of initiating cracks as a result of picking up a stone.

[0081] The invention described with the support of two variants is of course not restricted to these variants alone, and various modifications can be made thereto while still remaining within the scope defined by the claims.