Tire tread

Abstract

A groove of tire thread having a plurality of first and second portions, each delimited by facing walls spaced apart by a maximum width measured at the tread surface and approaching one another such that, at a depth between 20 and 80% of the total depth they are spaced apart by a width less than the maximum width or facing walls spaced apart by a minimum width measured at the tread and diverge from one another such that, at a depth between 20% and 80% of the total depth of the groove, they are spaced apart from one another by a width greater than the width. A plurality of first and second portions of groove so as to form a continuous passage between all the portions of groove in order to allow liquid to flow in the groove regardless of the level of wear.

Claims

1. A tire tread comprising: a tread surface configured to come into contact with a road surface during running, the tread having a thickness corresponding to a thickness of material to be worn away; and at least one circumferential groove that opens onto the tread surface of the tread having a maximum depth at the tread surface when new, said groove comprising: a plurality of first groove portions, each first groove portion being delimited by first facing walls spaced apart by a first maximum width measured at the tread surface when new, the first facing walls approaching one another such that a first intermediate depth measured from the tread surface is between 20 and 80% of the maximum depth of the at least one groove, the first walls are spaced apart by a first minimum width less than the first maximum width, the first minimum width configured for the first facing walls to come into contact when in a contact patch of the tread surface that is in contact with the road surface, the first walls diverging from one another down to the maximum depth of the at least one groove such that the first facing walls are spaced apart from one another by a first groove-bottom width; and a plurality of second groove portions, each second groove portion being delimited by second facing walls spaced apart by a second minimum width measured at the tread surface when new, the second facing walls diverging from one another such that, a second intermediate depth measured from the tread surface is between 20% and 80% of the maximum depth, the second facing walls are spaced apart from one another by a second maximum width greater than the second minimum width, the second minimum width configured for the second facing walls to come into contact when in the contact patch of the tread surface that is in contact with the road surface at least when new, the second walls delimiting the second groove portion then approaching one another down to the maximum depth of the groove such that they are spaced apart by a second groove-bottom width, wherein the at least one groove is formed by a plurality of said first and second groove portions that are disposed in alternation and continuously one after another to form a continuous passage to allow liquid to flow in the at least one groove regardless of a level of wear, said continuous passage being broken down into two elementary passages disposed radially one above the other, wherein the two elementary passages, when viewed in circumferential direction appear as two continuous circumferential grooves arranged radially one above the other, a maximum width of each groove being less than the first maximum width and greater than the second minimum width.

2. The tire tread according to claim 1, wherein a surface area of respective voids formed by the walls of each elementary passage is at least equal to 25% of a cross-sectional area of a groove having a depth equal to the maximum depth and a constant width equal to the first maximum width.

3. The tire tread according to claim 1, wherein at least one of: a first intermediate height, measured from first groove-bottom width to the first minimum width is between 40 and 60% of the maximum depth, and a second intermediate height, measured from second groove-bottom width to the second maximum width is between 40 and 60% of the maximum depth.

4. The tire tread according to claim 1, wherein the parts of each said first portion of groove and each said second portion of groove in which the facing walls of the groove come into contact have heights, respectively, said heights being greater than zero in order to realize appropriate mechanical support.

5. The tire tread according to claim 1, wherein the first groove portion and the portion second are joined together by connecting regions configured to eliminate geometric discontinuities between the first and second groove portions.

6. The tire tread according to claim 1, wherein a voids volume ratio when new is between 5% and 16%.

7. The tire according to claim 1, wherein the tire is a tire for a heavy-duty vehicle.

8. The tire tread according to claim 1, wherein from a radially inner position to the tread surface: the first facing walls approach each other with first constant but opposite slopes, and then the first facing walls diverge from each other with second constant but opposite slopes, and the second facing walls diverge from each other with third constant but opposite slopes, and then the second facing walls approach each other with fourth constant but opposite slopes.

9. The tire tread according to claim 1, wherein the first maximum width is substantially equal to the first groove-bottom width.

10. The tire tread according to claim 1, wherein the second minimum width is substantially equal to the first minimum width.

Description

DETAILED DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a three-dimensional view of a first variant of a tread having a groove according to the invention;

(2) FIG. 2 shows a view in cross section of the tread shown in FIG. 1 on a section plane, the line of which is indicated by the line II-II;

(3) FIG. 3 shows a view in cross section of the tread shown in FIG. 1 on a section plane, the line of which is indicated by the line III-III;

(4) FIG. 4 shows the two elementary passages formed for drainage in the groove.

DESCRIPTION OF THE FIGURES

(5) To make the figures easier to understand, identical reference signs have been used to denote variants of the invention where these reference signs refer to elements of the same kind, whether structurally or functionally.

(6) FIG. 1 shows a three-dimensional view of a first variant of a tread 1 according to the invention. According to this variant, the tread 1 for a heavy-duty vehicle tire has a thickness E of material to be worn away. This thickness E corresponds to the wear limit at which it becomes necessary to replace the worn tire with a new tire or at the very least to carry out a retreading operation with a new tread.

(7) This FIG. 1 shows a groove 2 opening onto the tread surface 10 when new by way of wide parts that constitute first portions 21 of groove and narrow parts that constitute second portions 22 of groove. The first portions of groove have a maximum width L1 at the tread surface 10 when new and a length D1, while the second portions of groove have a minimum width L2 at the same tread surface and a length D2.

(8) The first portions 21 of groove and second portions 22 of groove are disposed in alternation with one another in the circumferential direction (corresponding to the longitudinal direction) of the tread. This circumferential direction is indicated by the arrow X in FIG. 1.

(9) The corner edges formed at the tread surface by this groove have a plurality of segments connected together in a relatively abrupt manner, that is to say forming an angle of 90 degrees between two consecutive segments. In a variant that is not shown here, it is possible to adapt the geometries of these corner edges such that the connections are softened, notably by providing that the geometries of these connections have continuous gradients (continuous first derivatives).

(10) As can be seen in FIG. 2, which shows a cross section through a first portion 21 of groove, each first portion 21 of groove is limited by facing walls 211, 212 that open onto the tread surface 10 when new, these walls 211, 212 being spaced apart by a maximum width L1 at this tread surface when new. These walls 211, 212 then gradually approach one another into the depth of the tread.

(11) Starting at an intermediate depth H11, which is equal in the example described to 50% of the depth P of the groove and at a height E1, the facing walls 211, 212 are spaced apart from one another by a small spacing L1′ appropriate for these walls to come into contact with one another over this height E1 when in the contact patch in contact with the road.

(12) Next, the walls of the first portions of groove diverge from one another such that, at the bottom 210 of the groove 2, they are at a spacing L1″ equal, in the present case, to the width L1 measured at the tread surface 10 when new.

(13) As far as the second portions 22 of groove are concerned, and as can be seen in FIG. 3, which shows a cross section on a plane, the line of which is indicated by the line III-III in FIG. 1, the facing walls 221, 222 delimiting these second portions of groove are close enough together at the tread surface 10 when new (spacing L2) to come into contact with one another when in the contact patch in contact with the road. Next, these walls 221, 222 diverge gradually from one another so as to be at a maximum spacing L2′ at a depth H21, this latter depth being, in the present case, equal to 50% of the depth P of the groove 2.

(14) In the remaining depth H22, the two walls 221, 222 delimiting the second portions 22 of groove gradually approach one another so as to be at a spacing L2″ at the depth P, that is to say at the bottom 220.

(15) Thus, it has been possible to form at the same time voids with volumes limited to the bare minimum necessary and stiffening the tread by the presence of mechanical bridging in the contact zones between the facing walls. Furthermore, an appropriate surface voids ratio is maintained, regardless of the level of wear of the tread.

(16) Furthermore, and as can be seen clearly in FIG. 4, which shows the two preceding cross sections in superposition, a continuous passage 3 is obtained between the different portions of groove, this passage 3 allowing flow without any discontinuity between the first and second portions of groove, regardless of the level of wear of the tread.

(17) This continuous passage 3 is formed by two elementary passages 31, 32 that are continuous in the main direction of the groove 2 and disjointed in the direction of its depth. The cross-sectional area of each elementary passage 31, 32 is in this case substantially equal to 20% of the total surface area of a groove of depth P and constant width equal to the maximum width L1 of the first portions of groove (this groove is shown schematically in FIGS. 2 to 4 by way of dotted lines). It is clearly apparent that the voids volume has been greatly reduced while maintaining appropriate drainage, regardless of the level of wear, by virtue of this groove geometry.

(18) In the example shown and described, the walls of the first and second portions of groove are formed with flat faces, but these same walls could, of course, be formed with curved faces, satisfying the same design constraints in order to achieve the same result, namely the formation of two elementary drainage passages, one being situated between the tread surface when new and around halfway through the depth P of the groove, the other being situated in the part between halfway through the depth and the bottom of the groove.

(19) In the example shown and described, each first portion of groove and each second portion of groove has a constant cross section. It is of course conceivable for each portion of groove to have a variable geometry in the main direction of flow of the groove, this variable geometry being combined with the definition rules given for said groove.

(20) In another variant, the first and second portions of groove have an identical width at the surface when new but have regions of contact at different depths so as to create at least two passages for drainage.

(21) In the example shown for the understanding of the invention, the connections between portions of groove are made in an abrupt manner. Of course, it is possible for these connections to be realized such that there is a continuity of gradients measured on the level curves. A level curve is understood to be a corner edge formed by the groove at a tread surface in a state of wear of the tread. It has been shown that the first portions are of constant cross section, as is also the case for the second portions of groove. In order to reduce the hydrodynamic pressure head losses, it is advantageous to provide, between each first portion of groove and each second portion of groove, an intermediate region that provides a connection limiting the geometric discontinuities.

(22) The invention also relates to a tire provided with a tread as described and even more particularly to a tread intended to be fitted to a heavy-duty vehicle.

(23) Of course, the invention is not limited to the examples described and shown and various modifications can be made thereto without departing from the scope as defined in the claims.