Tire including a tread provided with incisions including wide portions and narrow portions

Abstract

Tyre comprising a tread, this tread including a rolling surface (12) intended to come into contact with the ground, at least one circumferential row of upstanding elements (11), these upstanding elements (11) being separated from one another in the circumferential direction by incisions (20) of transverse or substantially transverse orientation, each incision (20) of transverse or substantially transverse orientation leading onto the rolling surface (12) and having a depth P, each incision (20) forming, on the rolling surface of the tyre when new, two facing edges (21, 22), these edges (21, 22) delimiting at least one narrow portion (30) of the incision, i.e. a portion having a mean width LE less than or equal to 2 mm, and at least one wide portion (40) of the incision, i.e. a portion having a mean width LL greater than 2 mm, these wide and narrow portions being disposed alternately, each narrow portion (30) and each wide portion (40) extending the full depth P of the incision (20), each narrow portion (30) having a volume uniformly distributed over the full depth P of the incision, each wide portion (40) having a volume for the most part between half the depth P of the cut-out and the depth P, this tread being characterized in that the following condition is satisfied:
0.90E/R<(sum LE)/Pr<1.10E/R, in which: (sum LE) is the sum of the mean widths LE of the narrow portions of all the incisions separating the upstanding elements of the same row on a circle centred on the rotation axis of the tyre, R is the mean radius of the circle centred on the rotation axis on the rolling surface of the row concerned when new and Pr is the mean perimeter of the circle centred on the rotation axis and passing through a circumferential series of incisions in accordance with the invention, E is the mean thickness of the tread at the level of the row concerned.

Claims

1. A tire comprising a tread, comprising: a rolling surface intended to come into contact with the ground, at least one circumferential row of upstanding elements, these upstanding elements being separated from one another in the circumferential direction by incisions of transverse orientation, each incision of transverse orientation leading onto the rolling surface and having a depth P at most equal to a value E of the tread, each incision forming on the rolling surface of the tire, when new, two facing edges, these edges delimiting at least one narrow portion of the incisions having a mean width LE less than or equal to 2 mm, and at least one wide portion of the incisions having a mean width LL greater than 2 mm, these wide and narrow portions being disposed alternately, each narrow portion and each wide portion extending the full depth P of the incision, each narrow portion having a volume uniformly distributed over the full depth P of the incision, each wide portion having a volume between half the depth P of the cut-out and the depth P, wherein the following condition is satisfied:
0.90(E/R)<(sumLE)/Pr<1.10(E/R), wherein: (sum LE) is the sum of the mean widths LE of the narrow portions of all the incisions separating the upstanding elements of the same row on a circle centered on the rotation axis of the tire, R is the mean radius of the circle centered on the rotation axis on the rolling surface of the row concerned when new and Pr is the mean perimeter of the circle centered on the rotation axis and tangential to the upstanding elements, E is the mean thickness of the tread at the level of the row concerned.

2. The tire according to claim 1, wherein a greatest volume of each wide portion (the volume measured between half the depth and the bottom of the incision) is at least equal to 1.10 times the volume of said wide portion situated between the rolling surface and half the depth of the incision.

3. The tire according to claim 2, wherein the greatest volume of each wide portion is at least equal to 1.20 times the smallest volume of the same wide portion.

4. The tire according to claim 1, wherein each wide part of an incision has a constant width LL and a length DL increasing with depth, this length DL being measured in the direction of the incision on the rolling surface, this direction corresponding to the direction of a straight line segment joining the end points of this incision on this surface.

5. The tire according to claim 1, wherein each wide part of an incision has a width increasing regularly between the rolling surface when new and the bottom of the incision.

6. The tire according to claim 1, wherein each wide part of an incision has a constant width between the rolling surface when new and a depth P1 greater than half the depth P of the incision, this part of constant width being extended to the depth P by a part having a width greater than the width of the part of constant width.

7. The tire according to claim 1, wherein at least some wide portions are provided with studs at the bottom of the incision.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will be better understood thanks to the description of the drawings, in which:

(2) FIG. 1 shows a tread comprising two rows of elements each provided with incisions in accordance with the invention;

(3) FIG. 2 represents diagrammatically an incision in accordance with a first variant of the invention;

(4) FIG. 3 represents diagrammatically an incision in accordance with a second variant of the invention;

(5) FIG. 4 represents diagrammatically an incision in accordance with a third variant of the invention;

(6) FIG. 5 represents diagrammatically an incision in accordance with a fourth variant of the invention;

(7) FIG. 6 represents diagrammatically an incision in accordance with a fifth variant of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(8) To facilitate the reading of the figures, the same reference signs may be employed for the description of variants of the invention provided that these reference signs refer to elements of the same structural or functional kind.

(9) FIG. 1 shows a tire embodiment comprising two circumferential rows 1 of upstanding elements 2, these rows 1 being separated from one another by a circumferential groove 3. These rows 1 form circumferential ribs provided with a plurality of incisions 20 in accordance with the invention; these incisions 20 have a substantially transverse orientation, i.e. they are inclined at a mean angle equal to 15 to the direction of the rotation axis of the tire. These incisions 20 delimit with the circumferential grooves a plurality of upstanding elements 11. Each incision 20 comprises alternating narrow parts 30 having a width LE and wide parts 40 having a width greater than the width LE. Each incision 20 is inclined at a mean angle A equal to 15 degrees to the transverse direction (indicated by the direction YY in FIG. 4).

(10) Each substantially transversely oriented incision (20) leads onto the rolling surface (12) and has a depth P at most equal to the thickness E of the tread measured at the level of the row concerned. Each incision (20) forms on the rolling surface of the tire when new two facing edges (21, 22), these edges (21, 22) delimiting at least one narrow portion (30) of the incision, i.e. a portion having a mean width LE less than or equal to 2 mm, and at least one wide portion (40) of the incision, i.e. a portion having a mean width LL greater than 2 mm. These wide and narrow portions are disposed alternately, a narrow portion being followed by a wide portion. Each narrow portion (30) extends the full depth P of the incision (20) and has a volume uniformly distributed over the entire depth P of the incision. Each wide portion (40) extends the full depth P of the incision (20) and has a volume that is not uniformly distributed and is for the most part between half the depth P of the cut-out and the depth P.

(11) To limit deformation of the upstanding elements 11 on coming into contact with a road when rolling, the number and width of the incisions 20 of each row 1 are determined as a function of the perimeter Pr of a circle centred on the rotation axis of the tire and tangential to the external surface of each rib (the trace of this circle is indicated by a straight line segment D). This perimeter is preferably measured over the median part of each row 1 and on the rolling surface of the tire when new (i.e. before any rolling and wear).

(12) In the present casecorresponding to a 205/55R16 tirethe sum of the widths LE of the narrow parts of the cut-outs of the same rib satisfy the following condition:
0.90E/R<(sum LE)/Pr<1.10E/R, in which: R is the mean radius of the circle centred on the rotation axis on the rolling surface of the row concerned when newin the present case R=316 mm; Pr is equal to the perimeter of this same circlein the present case Pr=1985 mm; E is the mean thickness of the tread at the level of the row concernedin the present case E=10 mm; (sum LE) is the sum of the mean widths LE of the narrow parts of all the incisions separating the upstanding elements of the same row on a circle centred on the rotation axis of the tirein the present case, LE=0.6 mm and (sum LE)=60 mm.

(13) Each row comprises one hundred incisions disposed with a pitch equal to 8 mm.

(14) FIG. 2 shows one variant of an incision in accordance with the invention. FIG. 2 shows only part of the rolling surface, namely the part on the upstanding element 11. This upstanding element 11 comprises a cut-out or incision 20 in accordance with the invention, this incision leading onto the rolling surface 12 and having a depth P slightly less than the thickness E of the tread. By cut-out is meant a hollow space of a tread delimited by walls of rubber mixture or any other material forming the tread and leading onto the rolling surface, where it forms two facing edges. In the present case, the incision 20 is delimited by a first wall 201 and a second wall 202; the first wall 201 is plane while the second wall 202 is formed of a plurality of plane parts 221, 222, some of these plane parts 221 being parallel to the first wall 201 of the incision 20 and the other parts 222 being perpendicular to the first wall 201.

(15) The incision 20 shown forms two facing edges 21 and 22 on the rolling surface 12 of the tire when new. The edge 21 has a rectilinear tracedefining the length of the incision 20while the other edge 22 has a trace formed of rectilinear edge sections, some of the sections being parallel to the edge 21 and others perpendicular to that same edge 21. LE is the smallest mean distance separating the sections of the edge 22 parallel to the edge 21.

(16) These edges 21, 22 delimit in the case shown five narrow parts 30 of the incision 20, i.e. parts having a mean width LE less than or equal to 2 mm, and four wide parts 40 of the incision 20, i.e. parts having a mean width LL greater than 2 mm, these wide and narrow portions being disposed alternately, each narrow portion 30 and each wide portion 40 extending the full depth P of the cut-out 20.

(17) Moreover, it is seen that between the rolling surface when new and a depth P1 less than P the narrow portions 30 and wide portions 40 do not change geometry, whereas from this depth P1 and as far as the depth P the wide parts 40 have a width LL that is greater than the width LL of the wide parts between the rolling surface when new and the depth P1. Here the width LL is approximately 30% greater than the width LL.

(18) In the present case, the depth P1 represents substantially two thirds of the depth P.

(19) In this manner, each wide part 40 has a volume for the most part between half the depth P of the cut-out and the depth P. In other words more than 50% of the available volume of each wide part is located between the depth P1 and the depth P of the cut-out.

(20) Example of values for a 205/55R16 tire:

(21) Thickness E=10 mm

(22) Depth of cut-out P=8 mm

(23) Depth P1=5 mm

(24) Width of narrow part LE=0.6 mm

(25) Width of wide part LL (between rolling surface and depth P1)=2 mm

(26) Width of wide part LL (between depth P1 and total depth P)=3 mm

(27) In a second variant of the invention, shown in FIG. 3, the geometry of the wide parts 40 of the incisions 20 is modified. In fact, each wide part 40 retains the same width LL over the entire depth P of the incision 20 but each wide part has a width measured parallel to the rectilinear edge 21 (i.e. parallel to the length of the incision 20) that varies as a function of depth and in the present case increases regularly with depth in order for the volume of each wide part to be for the most part situated between half the depth P of the incision 20 and the depth P. By altering the geometry of the wide parts it is easy to have a greater or lesser part of the volume of each wide part between 50% of the depth P and said depth P. To limit stress concentrations the bottom of the incision may be provided over its entire length with an additional part in the form of a circular section channel as in the prior art. This volume of the additional part is not taken into account to evaluate the volume of the wide part of the incision.

(28) In a third variant of the invention, shown in FIG. 4, the geometry of each wide part 40 of a cut-out 20 is modified relative to that of each wide part of the incisions shown in FIGS. 2 and 3. Here, each wide part 40 retains the same length DL measured parallel to the rectilinear edge 21 and has a width LL measured perpendicularly to the rectilinear edge 21. This width LL varies regularly, increasing with depth in order for the volume of each wide part to be for the most part situated between half the depth P of the cut-out 20 and the depth P.

(29) FIG. 5 shows an incision 20 in accordance with a fourth variant of the invention, this variant reproducing on each wall 201, 202 delimiting an incision 20 the non-plane geometry of a wall of the incision shown in FIG. 2. In this fourth variant, the incision 20 is formed of a plurality of wide parts 40 and narrow parts 30 and the volume of the wide parts is for the most part situated between 50% and 100% of the total depth of the incision. Another variant (not shown here) could in the same manner as the first variant employ the geometry of the non-plane wall of the incision shown in FIG. 2 or the non-plane wall of the incision shown in FIG. 4.

(30) FIG. 6 represents an incision 20 in accordance with a fifth variant of the invention that is relatively close to the incision shown in FIG. 3 and in which studs 5 are provided at the bottom of the incision 200 in some of the wide parts 40 to protect said bottom. As shown in this variant, the incision 20 comprises at its two ends 20, 20 wide parts 40 leading into grooves and it may not be necessary to provide these wide parts with studs on the groove bottom at the ends; as shown in this figure, any foreign body introduced into one or the other of these wide parts can migrate toward a lateral groove and consequently not remain in place. Of course, the reduction of volume consequent upon the presence of these studs 5 must be compensated in order to satisfy the necessary condition that the volume of the wide parts is for the most part under 50% of the depth P of the incision 20.

(31) The examples described refer to incisions in which the lengths of each narrow part and each wide part are substantially equal; of course, it is within the competence of the person skilled in the art to adapt the dimensions of the narrow and wide parts according to what is required, notably in terms of performance.

(32) Similarly, the variants shown and described in the present document may be combined in the same tire as a function of the intended objective.

(33) Finally, the invention is not limited to the examples described and shown to which various modifications may be made without departing from the scope defined by the claims.