Tread for a heavy goods vehicle tire

Abstract

Tread (1) for a heavy-duty vehicle tire having a total thickness corresponding to the thickness of material to be worn away during running, this tread having, in the new state, a tread surface (10) intended to come into contact with a roadway when running. The tread comprises at least one hidden cavity (2) forming a new groove opening onto the tread surface after a predetermined amount of partial wear. Cavity (2) comprises two opposite lateral walls (21, 22) connected together by bottom (23) radially towards the inside and by crown part (24) radially towards the outside. Crown part (24) is provided with a plurality of fine grooves (25) extending radially towards the outside from crown part (24) delimiting the cavity and extending in a direction that makes an angle at least equal to 40 degrees with the main direction of cavity (2).

Claims

1. A tread for a heavy-duty vehicle tire having a total thickness corresponding to the thickness of material to be worn away during running, the tread having, in the new state, a tread surface adapted to come into contact with a roadway when running, the tread comprising at least one axially extending hidden cavity configured to form a new groove opening onto the tread surface after a predetermined amount of partial wear, the hidden cavity comprising two opposite lateral walls connected together by a bottom radially towards the inside and by a crown part radially towards the outside, a sipe that extends from the tread surface to the at least one axially extending hidden cavity, the sipe dividing the crown part radially towards the outside; wherein the at least one axially extending hidden cavity open towards an outside at respective lateral edges of the tread, wherein the crown part of the hidden cavity is provided with a plurality of fine grooves, the depth of which extends radially towards the outside from the crown part delimiting the cavity, said fine grooves extending in a direction that makes an angle at least equal to 40 degrees with the axially extending main direction of the cavity, the main direction of a cavity corresponding to the direction of flow of a liquid inside this cavity when it is open onto the tread surface and forms a new groove, wherein the fine grooves are spaced apart from one another between one and five times a width of the hidden cavity; and at least one circumferentially extending groove having alternating open grooves and hidden circumferential portions configured to form a new circumferential groove opening onto the tread surface after a predetermined amount of partial wear, wherein the hidden circumferential portions have axially extending fine grooves, wherein a first axial end of each axially extending fine groove extends radially towards the tread surface and a second axial end of each axially extending fine groove, axially opposite the first axial end, extends radially away from the tread surface.

2. The tread according to claim 1, wherein the fine grooves formed in the crown part delimiting the hidden cavity have a maximum depth at least equal to 1 mm and at most equal to 5 mm.

3. The tread according to claim 1, wherein the fine grooves formed in the crown part delimiting the hidden cavity are oriented at an angle substantially equal to 90 degrees to the main direction of the hidden cavity.

4. The tread according to claim 1, wherein the fine grooves continue on a part of the walls delimiting the sipe.

5. The tread according to claim 4, wherein the height over which said fine grooves extend along the sipe is at most equal to 3 mm.

6. The tread according to claim 1, wherein the fine grooves extend as far as a lateral wall of the hidden cavity and are continued on this lateral wall over a height at most equal to 3 mm.

7. The tread according to claim 1, wherein respective lateral ends of the at least one axially extending hidden cavity are radially inclined towards the tread surface.

8. The tread according to claim 7, wherein the respective lateral ends of the at least one axially extending hidden cavity are configured as grooves that open onto the tread surface.

9. The tread according to claim 1, wherein a maximum width of the hidden cavity is equal to 5 mm and a height of the hidden cavity is equal to 6 mm.

10. The tread according to claim 1, wherein the hidden cavity is situated beneath the tread surface at a first distance and the hidden cavity has a height, wherein the first distance and the height are equal.

11. The tread according to claim 1, wherein each of the crown parts is inclined at an angle of 15 degrees.

12. The tread according to claim 1, wherein the fine grooves have a depth at least equal to 5% of the thickness of material to be worn away and at most equal to 30% of the thickness of material to be worn away.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a partial view of the edge of a tread comprising a plurality of channels formed entirely beneath the tread surface in the new state, these channels being oriented transversely, i.e. parallel to the axis of rotation of the tire provided with this tread;

(2) FIG. 2 shows a moulding element intended to mould a channel as shown in FIG. 1;

(3) FIG. 3 shows the element from FIG. 2 in cross section on a plane III-III;

(4) FIG. 4 shows a variant of a channel according to an embodiment of the invention that is continued towards the tread by a sipe and comprises a plurality of small incisions formed in the upper part of the channel;

(5) FIG. 5 shows a variant of the invention applied to a wavy groove having a succession of parts that are open onto the tread surface in the new state and hidden parts.

DETAILED DESCRIPTION OF THE FIGURES

(6) The first variant illustrating the invention is shown in FIG. 1 and relates to a tread 1 of a tire for a heavy-duty vehicle, this tread 1 having, in the new state, a tread surface 10 intended to come into contact with a roadway. This tread 1 comprises hidden channels 2 under the tread surface 10 that are intended, after the tread has been partially worn away, to form new grooves that open onto the tread surface. In the present case, these channels 2 are oriented transversely, that is to say in a direction AA′ corresponding to the transverse or axial direction of a tire provided with this tread. The transverse direction is coincident with the axis of rotation of the tire. As can be seen in FIG. 1, these channels 2 open towards the outside at the lateral edges of the tread 1. Each channel 2 comprises two opposite lateral walls 21, 22, the distance between these lateral walls defining the width Lc of the channel. These lateral walls 21 and 22 are connected together by a channel bottom 23 in the innermost part and by a crown part 24 in the part closest to the tread surface 10.

(7) Located in each of the channels 2 and in the crown part 24 are a plurality of fine grooves 25 with a maximum depth equal to 4 mm, these fine grooves 25 being oriented obliquely with respect to the main direction of the channels 2. In the present case, the main direction of the channels corresponds to the transverse or axial direction on the tread (indicated by the line AA′ in FIG. 1).

(8) Each channel 2 is situated beneath the tread surface 10 of the tread 1 at a distance Hs and has a total height Hc. In the present case, these two heights Hs and Hc are substantially the same. The thickness of tread material to be worn away corresponds more or less to the sum of the heights Hs and Hc.

(9) Each of these channels 2 can be moulded by virtue of a moulding element as shown in part in FIG. 2.

(10) Apparent on the moulding element 20 shown in FIG. 2 is a main body 200, this main body 200 having two lateral faces 201, 202 connected by a part 203 that moulds the bottom of the channel and a crown part 204 that moulds the upper part of the channel, this crown part 204 being intended to be situated between the channel and the tread surface of the tread while the tread is being moulded. The maximum distance between the crown part and the bottom is equal to the height Hc of the channel moulded with this moulding element 20.

(11) Apparent in the crown part 204 of the moulding element are a plurality of protuberances 205 that are distributed across the entire width of this crown part 204 and at a mean orientation that makes an angle B equal to 45 degrees with the main direction of the moulding element in this example; the main direction of the moulding element corresponds to the direction of the length of the element that is indicated by a direction AA′ in the drawing. In the present case, this direction is coincident with the transverse direction of the tread. Of course, these channels 2 can be moulded in oblique directions with respect to the transverse direction.

(12) These protuberances 205 have a maximum height equal to 2 mm and are intended to mould fine grooves with a maximum width equal to 1.5 mm and a maximum depth equal to 2 mm, these fine grooves opening into the cavity moulded by the body 200 after the tread has been moulded. These protuberances 205 are spaced apart by a mean distance P of between one and five times the maximum width Lm of the moulding element 20. In the present case, the mean distance P is equal to the maximum width Lm separating the parallel faces 201, 202 of the moulding element.

(13) The fine grooves moulded by this moulding element are not cut grooves oriented in the main direction of the channel so as to cause the appearance of a new groove, as is described in the document EP1015261 B1, but rather grooves that modify the local stiffness across the entire width of the crown part of the channel. By virtue of this modification, it is possible to improve to make wear more regular.

(14) FIG. 3 shows a cross section of the moulding element 20 from FIG. 2 on a section plane, the line of which is indicated by the line in FIG. 2. Visible in this cross section is the crown part 204 having protuberances 205 for moulding fine grooves in the tread, these protuberances being spaced apart by a distance P.

(15) FIG. 4 shows a variant of the invention in which a channel 2 is continued towards the tread surface 10 by a sipe 4. In this variant, the crown part 24 of the channel 2 is subdivided on either side of the sipe 4 into two crown parts 241, 242. Each of these crown parts is inclined at an angle G equal to 15 degrees in the example, so as to form an angle of 150 degrees therebetween. Also formed in each of these crown parts 241, 242 are a plurality of transversely oriented fine grooves 25. These fine grooves 25 make an angle of 90 degrees with the main direction of the hidden cavity corresponding to the direction perpendicular to the plane of FIG. 4. These fine grooves 25 extend somewhat over the walls 41, 42 delimiting the sipe 4 and over the lateral faces 21, 22 delimiting the cavity 2.

(16) The combination of the presence of a plurality of fine grooves 25 and the inclination of the crown parts 241, 242 is particularly effective on the wearing surface.

(17) The third variant, shown in FIG. 5, relates to a tread 1 for a heavy-duty vehicle tire of size 315/70R22.5.

(18) This tread has, in its thickness, at least one groove referred to as wavy, this wavy groove 3 having an alternation of groove parts 31 that open onto the tread surface 10 in the new state and hidden cavities 32 that are intended to open onto the tread surface after a predetermined amount of wear in order to form new grooves. These open groove parts 31 and hidden cavity parts 32 are connected together by connecting parts 33 that ensure continuity of the flow of fluids in the wavy groove in the new state, this flow taking place in the main direction of the groove. This type of wavy groove is described in the patent EP2483087-B1, to which reference is made in particular for the figures.

(19) The maximum width of the hidden cavity 32 is equal to 5 mm and its height is equal to 6 mm.

(20) In order to make it easier to mould and demould this wavy groove 3, a sipe 4 is also formed that extends between each hidden cavity 32 and each connecting part 33 for connecting to the tread surface 10 in the new state. The sipe 4 has a width equal to 0.6 mm and is delimited by walls that are able to come into at least partial contact with one other under use conditions.

(21) Each hidden groove 32 comprises two opposite lateral walls, these lateral walls being connected together by a lower part forming a bottom radially on the inside and by an upper part radially on the outside. The upper part is divided into two parts that are continued by walls delimiting the sipe 4.

(22) In order to improve the wearing surface radially above the hidden cavities and thus to achieve more regular wear over the entire tread surface, a plurality of fine grooves 35 are formed in the upper part of each hidden cavity, said fine grooves 35 being oriented in the present case so as to make an angle of 90 degrees with the main direction of the groove 3, this main direction corresponding to the direction of the flow of water in the groove 3 in wet weather.

(23) These fine grooves indent the walls delimiting the sipe 4 over a small height (1.5 mm). Furthermore, these same fine grooves 35 continue over a small height (1.5 mm) on the walls delimiting each hidden cavity 32 widthwise. These fine grooves 35 are disposed parallel to one another at a spacing equal to 6 mm.

(24) After the tread has been partially worn away, and before the fine grooves 35 appear at the tread surface of the tread, the absence of material associated with the presence of these fine grooves causes localized flexibility in the vicinity of the cavity, making it possible to ensure more regular wear.

(25) The invention is not limited to the examples described and various modifications can be made thereto by a person skilled in the art without departing from the scope as defined in the claims.