TREAD FOR HEAVY VEHICLE TIRE

Abstract

The tread has a total width W and two main grooves. The main grooves divide the tread into a middle region and edge regions. The middle region has an axial width Lm that is 45% to 70% of the total width W. The volume void ratio of the tread when new is less than 17%. An internal surface extends parallel to the tread surface when new and is in contact radially with the innermost points of the deepest main grooves. The middle part has a plurality of transverse sipes, each of which has a depth at least equal to the depth of the main grooves. The transverse sipes open into the main grooves. The middle region has a volume void ratio when new that is less than half the total volume void ratio of the tread, and at least one circumferential channel appears when the tread becomes part worn.

Claims

1. A tread for a heavy vehicle tire, comprising: said tread having a total width W and being provided with two main grooves of circumferential overall orientation, said main grooves dividing said tread into three regions including a middle region (M) and two edge regions (B) axially on each side of said middle region, said middle region (M) having an axial width Lm at least equal to 45% and at most 70% of the total width W of said tread, said tread having a total void volume V0 when new, said middle part of this tread having a total void volume Vm when new, said volume void ratio of said tread when new is less than 17%, said void ratio being calculated as a ratio between said total void volume V0 and a total volume including all voids and evaluated between said tread surface when new and an internal surface extending in said tread parallel to said tread surface when new, said internal surface being in contact radially on an inside with innermost points of deepest ones of said main grooves, said middle part comprising a plurality of transverse or oblique sipes having a depth at least equal to 75% of the depth of said main grooves, said transverse or oblique sipes opening into said main grooves delimiting said middle region (M) and being formed at a mean spacing Pm, wherein said middle region has a volume void ratio when new less than half said total volume void ratio of said tread when new and in that at least one continuous circumferential channel is formed under said tread surface when new so that it appears when said tread becomes part worn and forms a new groove.

2. The tread according to claim 1 wherein said edge regions are circumferentially continuous ribs with no sipes or grooves at all.

3. The tread according to claim 1 wherein said edge regions are provided with transversely or obliquely oriented sipes arranged at a mean spacing Ps, said mean spacing Ps being greater than said mean spacing Pm of said sipes in said middle region.

4. The tread according to claim 3 wherein said edge regions are provided with transversely or obliquely oriented sipes arranged at a mean spacing Ps, said mean spacing Ps being at least greater than 1.25 times said mean spacing Pm of said sipes in said middle region.

5. The tread according to claim 1 further including, in said middle region, at least two circumferential sipes, said at least two circumferential sipes extending into said tread by widened parts forming channels, said channels forming new grooves when said tread reaches a predetermined level of part wear.

6. The tread according to claim 1 wherein at least one channel formed in said middle region appears at the latest when a degree of part wear reaches 60% of said depth of said main grooves.

7. The tread according to claim 1 wherein said volume void ratio of said tread when new is less than 10% and wherein said volume void ratio of said middle region when new is at most equal to 3%.

8. A tire provided with a tread according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0040] FIG. 1 is a plan view of a tread pattern design for a tread according to one alternative form of the disclosure;

[0041] FIG. 2 is a view in cross section on a plane perpendicular to the plane of FIG. 1 and passing through the line II-II;

[0042] FIG. 3 is a plan view of a tread pattern design for a tread according to another alternative form of the disclosure;

[0043] FIG. 4 shows a cross section on a plane perpendicular to the plane of FIG. 3 and passing through the line

DESCRIPTION OF THE FIGURES

[0044] In order to make the figures easier to understand, the same reference signs are used for describing alternative forms of the disclosure where these reference signs refer to elements of the same nature, whether this be a structural or indeed a functional nature.

[0045] FIG. 1 is a partial plan view when new of a tread pattern design for a tread according to a first alternative form of the disclosure.

[0046] The tread 1 according to the disclosure is intended to form part of a tire of size 315/70 R22.5 intended to equip the drive axle of a heavy vehicle. This tread 1 has a tread surface 10 when new which is shown partially in FIG. 1. This tread has a width W measured in the axial direction and equal to 270 mm.

[0047] This tread 1 comprises a directional tread pattern design that imposes a direction of running. This tread pattern design comprises two main grooves 2 of circumferential overall orientation and having a geometry that zigzags slightly about the circumferential direction; these main grooves 2 open onto the tread surface 10 when new and are formed on each side of the equatorial midplane indicated by its line XX in this figure. These two main grooves 2 between them delimit a middle region M of which the width Lm measured between the axially innermost walls of the main grooves 2 is equal in this instance to 159 mm (namely 59% of the total width W). These main grooves 2 have a mean width equal to 9 mm on the tread surface when new and a width of 4 mm at a maximum depth equal to 13.5 mm.

[0048] Formed axially on the outside of each main groove 2 is an edge region B provided with a plurality of oblique grooves 3. These oblique grooves 3 delimit a plurality of blocks 31 that have no sipes at all.

[0049] The middle region M further comprises three circumferentially oriented sipes 41, 42, 43 opening onto the tread surface when new, each of these sipes being extended into the thickness of the tread by channels 51, 52, 53 respectively, these channels being intended to form new grooves when the tire becomes part worn. These channels are visible in FIG. 2 which shows a cross section through the tread.

[0050] In the case of this first alternative form, the total volume void ratio when new is equal to 9.6% whereas the volume void ratio of the middle region when new is equal to 3.0%. The total volume void ratio is calculated when the tread is new by summing the volumes of the circumferential grooves and the transverse grooves and the volumes of the channels.

[0051] Furthermore, the middle region is provided with a plurality of oblique sipes 6 forming a general V-shaped pattern between the two circumferential grooves. These oblique sipes are arranged at a mean spacing Pm equal to 25.1 mm. These oblique sipes 6 have a mean width equal to 0.6 mm and open into the main grooves 2 and into the circumferential sipes 6 of the middle region M. Furthermore, these oblique sipes 6 open into the channels 51, 52, 53 formed in the thickness of the tread.

[0052] FIG. 2 is a view in cross section on a plane perpendicular to the plane of FIG. 1 and of which the line in this FIG. 1 is depicted by the line II-II.

[0053] In this FIG. 2 it may be seen that the middle channel 52 forms a new groove when part-wear reaches 48% whereas the other new grooves are formed by the other channels 51, 53 when part-wear reaches 56%. These percentages of wear are evaluated with respect to the wearable thickness PMU of material. The central channel 52 has a mean width of 4.5 mm and a total height of 7 mm. The other two channels 51, 53 have a width of 4.5 mm and a height of 6 mm. The innermost points of these channels 51, 52, 53 are at the same depth in the tread as the innermost points of the main grooves 2.

[0054] In another alternative form shown in FIG. 3 and FIG. 4, a tread 1 according to the disclosure for a heavy vehicle tire of size 11R22.5 comprises two circumferential main grooves 2 dividing the tread width-wise into a middle region M of width Lm equal to 121 mm (namely 54% of the total width W of the tread) and edge regions B of width equal to 42 mm. These main grooves 2 have a mean width equal to 13 mm and a depth equal to 15.5 mm. The relief angle on the walls of the grooves is equal to 16 degrees with respect to a direction perpendicular to the tread surface 10.

[0055] The middle region M further comprises two rectilinear sipes 6 of circumferential orientation opening onto the tread surface 10 when new, each of these sipes being extended into the thickness of the tread by the channels intended to form new grooves after 51% wear is reached (this percentage is measured with respect to the wearable thickness PMU of material). Each channel has a mean width equal to 5 mm and a height equal to 8 mm.

[0056] Furthermore, the middle region M is provided with a plurality of oblique sipes 6 in a general zigzag pattern between the two main grooves 2. These oblique sipes 6 open into the main grooves and intersect the circumferential sipes 41, 42. These oblique sipes 6 are arranged with a mean spacing Pm equal to 28.7 mm. Each oblique sipe 6 extends into the thickness of the tread as far as a channel 51, 52, these channels being intended to form new grooves after a predetermined degree of partial wear is reached.

[0057] Formed at each intersection between an oblique sipe 6 and a circumferential sipe 41, 42 is a radially directed well 7 itself connected to an underlying channel (well diameter equal to 5 mm).

[0058] In the case of this second alternative form, the total volume void ratio is equal to 9.37% whereas the volume void ratio of the middle region is equal to 2.77%. The total volume void ratio is calculated when the tread is new by summing the volumes of the circumferential main grooves 2 and the volumes of the channels 51, 52 and those of the radial wells 7 and of the sipes 41, 42, 6.

[0059] Formed axially on the outside of each main groove 2 is an edge region B that has no sipe or groove at all.

[0060] FIG. 4 shows a cross section on a plane perpendicular to the plane of FIG. 3, this plane passing through the line IV-IV visible in FIG. 3. It may be seen that two channels 51, 52 are molded in the middle part, these channels being intended to form new grooves when the tread becomes part worn so as to ensure lasting performance in terms of the removal of any water that may be present on the roadway.

[0061] Of course, the disclosure is not restricted to the examples described and depicted and various modifications can be made thereto without departing from the scope defined by the claims.