Tread for a Heavy-Duty Vehicle Tire

Abstract

Tread (1) for a heavy-duty vehicle tire having, when new, a tread surface (10), with at least one evolving cut (2) comprising a part (22) hidden inside the tread which is delimited by opposing walls (221, 222) distant from one another by a maximum width Lc. The part (22) being extended towards the tread surface (10) by a sipe (21), opening into the hidden part (22) to be offset from one of the walls (221, 222) delimiting the hidden part to form a bridge situated radially over said hidden part (22). The tread having a plurality of grooves (4) open when new onto the tread surface (10), these grooves (4) opening into an evolving cut (2) to form a connecting region (41), the tread (1) further comprising, in at least 50% of the connecting regions (41, 42), a protuberance (5) extending over the entire height Hc of the hidden part (22) and over a maximum thickness Ep so as to act as a support for the bridge (211) situated radially over the hidden part (22) in the connecting region (41).

Claims

1. A tread for a heavy-duty vehicle tire having, when new, a tread surface intended to come into contact with a roadway during running, this tread comprising at least one evolving cut of maximum depth Pc, this evolving cut comprising at least one part hidden inside the tread, this hidden part, of height Hc, and delimited by opposing walls distant from one another by a maximum width Lc, this hidden part being extended towards the tread surface by a sipe opening onto this tread surface, this sipe opening into the hidden part in such a way as to be offset from one of the walls delimiting the hidden part in order to form at least one bridge of material situated radially over said hidden part, this tread further comprising a plurality of grooves open when new onto the tread surface, these open grooves having, when new, a depth Pg and a mean width Lg on the tread surface and comprising two ends, these open grooves opening at least at one of their ends into an evolving cut to form a connecting region, wherein in the tread, a protuberance is formed locally on the wall of the hidden part of the evolving cut in at least 50% of the connecting regions, this protuberance extending over the entire height Hc of the hidden part and over a total length L measured in the main direction of the hidden part and over a maximum thickness Ep so as to act as a support for the bridge of material situated radially over the hidden part in the connecting region.

2. The tread according to claim 1, wherein said protuberance is formed in each connecting region of the tread.

3. The tread according to claim 1, wherein the maximum thickness Ep of the protuberance is at least equal to the width of the bridge of material situated radially over the hidden part in the connecting region.

4. The tread according to claim 1, wherein the protuberance has a transverse cross section that is such that the opening onto the hidden part is at least equal to 20% of the cross-sectional area of the hidden part.

5. The tread according to claim 1, wherein each protuberance comprises lateral parts extending on each side of the connecting region to form parts of variable thickness so as to limit the disruption to flow in the hidden part of the evolving cut.

6. The tread according to claim 1, further comprising a bridge of material is formed in the groove and open onto the tread surface, this the bridge of material having a height Hp comprised between 30% and 70% of the depth Pg of the open groove and a length Lp measured in the direction of the open groove which is at most equal to 75% of the length Lr of said open groove.

7. The tread according to claim 1, wherein at least one evolving cut comprises a hidden part which is wavy in the direction of the thickness of the tread.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] FIG. 1 shows an overview of the exterior surface of a first variant of a tread when new according to the invention;

[0032] FIG. 2 shows a partial cross section on a plane of section of which the line is depicted as II-II in FIG. 1;

[0033] FIG. 3 shows a partial cross section on a plane of section of which the line is depicted as III-III in FIG. 1;

[0034] FIG. 4 shows the tread surface of the tread of the first variant after partial wear;

[0035] FIG. 5 shows a view in cross section of a second variant according to the invention.

DESCRIPTION OF THE FIGURES

[0036] The first variant illustrating the invention relates to a tread 1 of a tire of size 11 R 22.5 to equip a heavy-duty vehicle. This tread 1 comprises, as can be seen in FIG. 1, a tread surface 10 intended to come into contact with the roadway during running.

[0037] This tread 1 comprises two evolving cuts 2 of circumferential direction opening onto the tread surface when new via sipes 21 of a width that is suitable for their opposing walls to come into at least partial contact when they enter the contact patch in which the tire is in contact with the roadway. The mean width of these sipes 21 on the tread surface 10 when new is, in this instance, equal to 1 mm. These two evolving cuts 2 between them delimit a central region 3 extending on each side of the midplane of the tread, the line of which is indicated by the direction XX′ in FIG. 1. On each side of this central region 3 there are formed circumferential ribs 7 that axially delimit the tread 1.

[0038] Each evolving cut 2 has a maximum depth Pc equal to 19 mm and comprises a hidden part 22 forming a channel that is completely hidden beneath the tread surface when new 10. Each hidden channel 22 is intended to form a new groove open onto the tread surface of the tread after a predetermined amount of partial wear.

[0039] In this instance, and as can be seen in FIG. 2 which shows a transverse cross section on a plane of which the line in FIG. 1 is indicated by II-II, the hidden part 22 is of substantially rectangular cross section with a height Hc (here equal to 7 mm) and a maximum width Lc (here equal to 4.5 mm). This hidden part 22 comprises two opposing walls 221, 222, these walls being connected by a bottom 220 radially on the inside and by a top 223 radially on the outside. In the instance described, the sipe 21 cuts the top 223 of the hidden part 22 into two parts of equal width. It can be discerned that there are formed, on either side of the sipe 21, bridges of material 211, 212, each bridge of material coming into contact with the opposing bridge of material as the sipe 21 closes as it enters the contact patch in which it is in contact with the roadway.

[0040] Furthermore, FIG. 1 shows that the tread comprises a plurality of open grooves 4 on the tread surface when new 10, these open grooves 4 being oriented transversely, namely parallel to the axial direction of the tire (perpendicular to the direction identified by the axis XX′ in FIG. 1). Each transverse open groove 4 has a width Lg on the tread surface when new 10 equal to 12 mm, and a depth Pg equal to 19 mm.

[0041] Each one of these transverse open grooves 4 ends at the evolving cuts 2 at its two ends to form two connecting regions 41, 42. These connecting regions 41, 42 allow a circulation of fluid inside the transverse open grooves 4 and inside the hidden parts 22 of the evolving cuts.

[0042] FIG. 3 shows, in a plane of section the line of which is identified by III-III in FIG. 1, the presence, in each connecting region, of a protuberance 5 formed on the lateral wall 221 of the hidden part 22 (the other wall 222 having been eliminated locally by the presence of the transverse groove 4). In the case described, this protuberance 5 occupies the entirety of the width of the bridge of material 211 still present (the other bridge of material having been eliminated by the presence of the transverse groove 4) and has a thickness Ep that is constant over its entire height. Thus, an opening 230 onto the hidden part 22 is maintained, placing the transverse open groove 4 and said hidden part 22 in communication.

[0043] In this way, this protuberance 5, without completely closing the hidden part 22, offers mechanical support to the bridge of material 211 that there is between the hidden part 22 and the tread surface 10 in the region 41 of connection between the evolving cut 2 and the transverse open groove 4.

[0044] Studying FIG. 4, which shows a view of the tread surface after partial wear that is sufficient that the hidden parts have become open onto the tread surface and are forming new circumferential grooves, it may be seen that the protuberance 5 has a maximum thickness Ep (in this instance: 2.25 mm) equal to half the maximum width Lc of the hidden part and that it has a total length L (here equal to 11.5 mm), the latter length being measured at its base on the surface of the wall 221 of the hidden part 22. This same protuberance 5 has a front lateral face 50 occupying the entire width of the transverse groove 4 in this instance. This front lateral face 50 is extended on each side by end lateral faces 51, 52 which are inclined and connected to the wall 221 of the hidden part 22 of the evolving cut.

[0045] The numerical values are given only by way of illustration of the example described, and it is of course possible for a person skilled in the art to adapt each of these dimensions to suit the technical requirements in each specific instance.

[0046] In this first variant, there has also been provided a bridge 6 of material formed from the bottom 40 of each transverse groove 4 and rising up over a height Hp equal in the example described to 50% of the depth of the groove 4 when new (namely 9.5 mm) as can be seen notably in FIG. 3. The length Lp of this bridge of material 6, measured in the main direction of the transverse groove 4, is, in the example described, of the order of 50% of the length Lr of said transverse groove. In order to adapt the local stiffnesses, it is possible to provide this bridge of material with a sipe parallel to the walls delimiting the open groove in which the bridge is formed. This same sipe may extend into the protuberance formed in the region of connection between the open groove and the hidden part of the evolving cut.

[0047] That which has been described for one end of the transverse open groove 4 is also found at the other end.

[0048] A second variant is shown in FIG. 5, where the sipe 21 extending the hidden part 22 towards the tread surface 10 when new is offset on the top face 223 of said hidden part 22. In this variant, the bridges of material 211, 212 formed on each side of the sipe 21 and radially on the outside of the hidden part 22 of the evolving cut 2 do not have the same width P1, P2. In the example described, the width P1 of the bridge of material 211 which remains in the region of connection with the transverse open groove 4 is greater than the width P2 of the other bridge of material 212.

[0049] In order to enjoy sufficient mechanical support while at the same time maintaining a suitable opening onto the hidden part 22, a protuberance 5 is formed which occupies the entire width P1 of the bridge of material 211 at the top 223 of the hidden part and a width Es on the bottom of said hidden part, this width Es being substantially equal to 50% of the width P1 of the bridge of material 211. The protuberance 5 comprises a lateral face 50 facing the open groove 4 which is an undercut. The maximum width Ep of the protuberance 5 is here equal to the width P1 of the bridge 211. The lateral face 50 which here is planar and inclined may of course be adapted and adopt a convex or concave shape.

[0050] As a preference, as depicted in FIG. 1, a protuberance 5 is formed in each of the connecting regions (41, 42) of the tread. However, depending on the configuration of the tread, a certain number of connecting regions may also not be provided with such a protuberance provided that at least 50% of the connecting regions are actually provided with same.

[0051] In a variant which has not been depicted here, the protuberance may be formed in such a way as to widen in the direction towards the bottom of the hidden part; in this last variant, the risk of foreign bodies such as stones becoming caught in the hidden part is reduced.

[0052] The invention is not restricted to the two examples described and various modifications can be made thereto without departing from its scope as defined in the claims. In particular, that which has been described in respect of circumferential evolving cuts could be applied to any other orientation, and notably to a transverse or oblique orientation. Likewise, grooves which are open when new onto the tread surface could be oriented obliquely with respect to the direction of the evolving cuts.