WO2014170283A1

WO2014170283A1 - Construction plant tyre tread with variable voids ratio

Info

Publication number: WO2014170283A1
Application number: PCT/EP2014/057548
Authority: WO
Inventors: Murielle DE TULLIO
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2013-04-15
Filing date: 2014-04-14
Publication date: 2014-10-23

Abstract

Tread (1) for a construction plant tyre, this tread made of rubber material being provided with a plurality of raised blocks (21, 22, 23, 24), these blocks having a contact face intended to come into contact with the ground and forming a tread surface, these blocks being delimited by circumferentially oriented grooves (3) and by transversely oriented grooves (4), this tread comprising a median plane that divides the tread axially into two halves of the same width, this tread having an axial width W measured across the tread surface in the new state, this tread comprising a central zone C extending on either side of the median plane, this central zone having a width Wc equal to at least 25% of the axial width W of the tread and at most 75% of that same width W, this central zone having a voids ratio by volume in the new state and axially on either side of the central zone lateral zones B, each lateral zone having a voids ratio by area in the new state, the voids ratio by volume in the new state of the central zone C being at least equal to 50% and at most equal to 65%, the voids ratio by volume in the new state of each lateral zone B being greater than the voids ratio by volume of the central zone in the new state, the difference between these voids ratios by volume being at least equal to 2% and at most equal to 15%.

Description

CIVIL ENGINEER TIRE BEARING ROLL RATE

VARIABLE.

FIELD OF THE INVENTION

The invention relates to a tire tread for civil engineering vehicle (type "off-the-road" in English), this band having a sculpture pattern capable of providing better evacuation of the earth while retaining good properties in adhesion and wear.

Among the uses of civil engineering tires, there is particular use of tires equipping articulated dump trucks ("articulated dump truck" in English). This use is particular since it requires from the vehicles a great capacity of crossing in soft and / or uneven ground.

STATE OF THE ART

Usually, a tire, intended to equip a civil engineering vehicle, is provided with a tread radially outwardly surmounting a crown reinforcement itself surmounting a carcass reinforcement. This tread comprises a sculpture formed by relief elements (ribs or blocks), these relief elements being delimited by a plurality of grooves.

Each element of relief of the tread has a face - said contact face - radially outside the strip, which is intended to come into contact with the ground. The set of contact faces of the elements form a running surface of the strip. The grooves have depths at most equal to the thickness of the band and have geometries, seen in section, suitable for limiting the retention of pebbles and other objects on the ground that can be captured by said grooves during rolling. It is customary to describe a sculpture by a surface hollowing rate calculated as the ratio between the surface of the recesses in the new state and the total surface of the tread in new condition, the latter including the surface of the hollows.

It is also customary to describe a sculpture by a hollow volume ratio calculated as the ratio between the total volume of the troughs in new condition and the tread volume in new condition, the latter volume corresponding to the volume of gum to be used and including the volume of the hollows.

These surface and volume trough levels can be defined for regions of a tread and in particular for the edges of a band.

In the case of the tires of the present invention the overall trough area of the tread is at least equal to 50%.

It is easy to understand that it is necessary, when dimensioning a tread of a tire fitted to a civil engineering vehicle, to combine in the new state at a time a level of hollow rate and a level of hollow volume ratio for shearing an appropriate volume of soil for the purpose of achieving good vehicle traction.

This combination may have consequences on the performance because a too large rate of hollow volume can lead to a significant reduction in stiffness of the tread elements, while a too low rate of trough does not It does not allow to achieve appropriate shear forces in the soil for good traction.

In addition, it is customary that, when driving on soft ground (earth, mud), the relief elements penetrate the ground to shear and thus be able to generate driving forces. It happens that after the passage in the contact, the grooves are then filled with material. To maintain a good traction, it is necessary that these grooves after being filled in the contact can get rid of this material to present a potential for proper adhesion. Indeed, if the grooves remain filled during the next passage in the contact, it becomes difficult for the relief elements to re-enter the ground to develop driving forces. According to the prior art, a tire comprises a tread provided with a plurality of circumferential and transverse orientation grooves (by transverse orientation, it is necessary to understand non-circumferentially that is to say not doing the tire tower), these grooves delimiting a plurality of relief elements having the shape of blocks. Among these blocks, there are two rows of blocks forming the edges axially outside the tread and, between these two edge rows, an intermediate region formed by at least one row of blocks.

In this prior art, the area of the pits in the new state is the same regardless of the circumferential region of the tread (edge region and intermediate region) considered. By circumferential region, it is necessary here to include a circumferential band running around the tire, the width of this band being equal to a fraction of the total width of the band, this fraction being at least equal to 25% and at most 75% o the total width of the strip.

Definitions: A block is a raised element formed on a tread, this element being delimited by recesses or grooves and comprising a contact face, this contact face being intended to come into contact with the ground while taxiing and side faces. Each block includes side faces intersecting the contact face along ridges. There is a front face and a rear face also called leading face and trailing face respectively, these faces being determined in the direction of travel. The front and rear faces delimit transverse grooves. These leading and trailing faces intersect the contact face, respectively, along a leading edge and a trailing edge. The leading edge corresponds to the edge that enters the first in the zone of contact with the ground during the rolling. By radial direction means a direction which is perpendicular to the axis of rotation of the tire (this direction corresponds to the direction of the thickness of the tread).

By transverse or axial direction means a direction parallel to the axis of rotation of the tire. By circumferential direction means a direction that is tangent to any circle centered on the axis of rotation. The circumferential direction is perpendicular both to the axial direction and to a radial direction.

The usual tire rolling conditions or conditions of use are those defined by the standard E.T.R.T.O. ; these conditions of use specify the reference inflation pressure corresponding to the load capacity of the tire indicated by its load index and its speed code. These conditions of use can also be called "nominal conditions" or "conditions of use".

BRIEF SUMMARY OF THE INVENTION [0009] While state-of-the-art treads provide good performance in use, new civil engineering vehicles need to further improve traction and performance performance. soft ground tire treads for civil engineering vehicle.

For this purpose, it is proposed a tread for civil engineering tire, this rubber material strip being provided with a plurality of raised blocks, these blocks having a contact face intended to come into contact with a and forming a rolling surface, these blocks being delimited by grooves of generally circumferential orientation and transversely oriented grooves, this strip comprising a median plane axially dividing the strip into two halves of the same width, this strip having a axial width W measured on the running surface when new (this width corresponds to the maximum width of the region of contact with a flat ground under the conditions of use of the tire).

This band comprises a central portion centered on the equatorial median plane and side portions on either side of the central portion, each lateral portion comprising a single row of blocks arranged in the circumferential direction. By definition, the central portion is delimited axially on the outside by the axially outermost points of the carving elements of the central portion.

This band is such that the central portion has a width Wc equal to at least 25% of the axial width W of the strip and at most 75% of the same width W. In the new state, the central portion and the lateral parts have a cavity rate of their own. This tread is such that the rate of hollow volume in the new state of the central portion is at least equal to 55% and at most equal to 65%, the trough volumetric rate in the new state of each lateral portion is greater than the hollow volume ratio of the central portion in the new state and in that the difference in the amount of hollow volume in the new state between the central portion and each lateral portion is at least equal to 2 % and at most equal to 15%) of the hollow volume ratio of the central part.

Preferably, the degree of depression of each lateral portion is at least equal to 55% o and at most equal to 70%>.

Preferably, the width Wc of the central portion is between 35% and 65% o of the total width of the tread W.

The invention is particularly useful for treads having large thicknesses and more particularly thicknesses greater than 38 mm (by thickness means the maximum height of material that can be used in rolling and which substantially corresponds to the maximum depth of the grooves).

Advantageously, the tread is such that the difference in the level of hollow volume in the new state between the central portion and each lateral portion is at least equal to 5% o and at most equal to 15% >.

According to an advantageous variant, the tread according to the invention is such that the blocks of the central part and of the lateral parts are arranged so that the transverse grooves formed between these blocks are extended at least in part and continuously from the central zone to at least one lateral zone.

Advantageously, the tread according to the invention is such that each transverse groove has a width measured on the running surface in the new state, this width being steadily increasing on each lateral zone.

In a particularly advantageous variant, the tread according to the invention is such that the hollow volume ratio of the central portion and the side portions satisfies, in a worn state corresponding to 50%> of the total height provided for be worn, under the following conditions: [0032] the central part has a hollow volume ratio of at least 50% and at most equal to 65% o,

[0033] there is a gap-volume difference between the central part and each lateral part, this difference being at least equal to 2% and at most equal to 15%, each lateral part having a hollow volume ratio higher than that of the central part.

Other features and advantages of the invention emerge from the description given hereinafter with reference to the single appended figure which shows, by way of non-limiting example, an alternative embodiment of the object of the invention. invention.

BRIEF DESCRIPTION OF THE SINGLE FIGURE [0035] FIG. 1 shows a plan view of a tread according to the invention.

DESCRIPTION OF THE FIGURES

[0036] Figure 1 shows a plan view of a tread 1 for a civil engineering tire size 800/80 R 29.

This tread 1 is provided with a tread comprising four circumferential rows 11, 12, 13, 14 of blocks 21, 22, 23, 24 delimited by circumferential grooves 3 and transverse grooves 4. Of these four rows of blocks, there are two rows of edges 11, 14 and two intermediate rows 12, 13. The depth of the grooves here equal to 40 mm determines the maximum depth available to come shear loose soil and thus obtain improved adhesion and traction.

The tread has a maximum total width W equal in this case to 440 mm. This maximum width corresponds to the width of contact in the conditions of use of the tire on flat ground.

This band 1 is divided into a central portion C and on either side of the central portion of the side portions or B edge portions.

The central portion is centered on the median plane whose trace is marked by the line XX 'on the plane of the single figure showing the tread surface of the tread, the median plane dividing this tread in two halves of the same widths. This central portion comprises two rows of blocks arranged circumferentially, the axially outermost points of these blocks defining a width of the central portion.

In the case in point, the width of the central portion is equal to 50% of the maximum total width W of the strip. Each edge portion has a width equal to 25% of the same total width W.

On the central part the hollow volume ratio is equal to 53%. This means that for a total band volume including the volume of the troughs, the trough volume represents 53% of this total volume.

On each edge portion the hollow volume ratio is equal to 61%. The difference in hollow volume ratio between the central portion and each edge portion is here equal to 8%.

According to this variant, illustrated by the single figure, the transverse grooves 4 defining the blocks of the central region C are continuously extended in the edge portions B so as to facilitate lateral ejection (in the transverse direction). of material entering the grooves of the central region.

In addition to this difference in hollow volume ratio between the central part and the edge parts, the band according to the invention is such that the width of the transverse grooves between the blocks of the edge portions (this width being measured on the running surface in the new state) increases progressively at least from a non-zero distance measured from a plane parallel to the median plane XX 'and passing through the points the axially most outward points of the outer side faces of the blocks of the edge portions of the strip. In this way, it is formed a sort of outward flare facilitating the ejection of the materials introduced during the rolling in the transverse grooves.

Thanks to the invention there has been a significant improvement in traction and adhesion in the field of tire for civil engineering vehicle having a tread of relatively large thickness (ie at least 38 mm) while maintaining a satisfactory wear performance.

Claims

1 tread (1) for civil engineering tire, this rubber material strip being provided with a plurality of raised blocks (21, 22, 23, 24), these blocks having a contact face intended to come into contact with contact with a ground and forming a rolling surface, these blocks being delimited by circumferentially oriented grooves (3) and transversely oriented grooves (4), this band comprising a median plane XX 'axially dividing the strip into two halves of the same width, this strip having an axial width W measured on the running surface when new,

this band comprising a central portion C centered on the equatorial median plane and side portions B on either side of the central portion, each lateral portion comprising a single row of blocks (5) arranged in the circumferential direction, the central portion being defined axially on the outside by the axially outermost points of the carving elements of the central part, this central part having a width Wc equal to at least 25% of the axial width W of the strip and at most 75%> of the same width W,

in the new state, the central part and the lateral parts have a cavity rate of their own,

this tread is such that the level of hollow trough in the new state of the central part is at least equal to 50%> and at most equal to 65%>, the trough volumetric rate at the new state of each Lateral portion is greater than the trough volume level of the central portion in new condition, the difference in trough volume ratio in the new state between the central portion and each lateral portion being at least equal to 2% and at most equal to 15% of the hollow volume of the central part.

2- tread according to claim 1 characterized in that the width of the central portion Wc is between 35%> and 65%> of the total width of the tread W. 3- Tread according to one any one of claims 1 to 2, characterized in that the difference in the ratio of hollow volume in the new state, between the central portion C and each lateral part B, is at least equal to 5% and at most equal to 10%.

4- tread according to any one of claims 1 to 3 characterized in that the blocks of the central and lateral parts are arranged so that the transverse grooves (4) formed between these blocks are extended at least in part and continuously from the central zone C to at least one lateral zone B.

5- tread according to claim 4 characterized in that each transverse groove (4) has a width measured on the running surface in new condition, this width being steadily increasing on each side part outwardly of the band.

6- tread according to one of claims 1 to 5 characterized in that the hollow volume ratio of the central portion C and side B satisfies after wear corresponding to 50% of the total height intended to be worn, under the following conditions :

- the central zone has a hollow volume ratio of not less than 55% and not more than 65%;

- there is a difference in the degree of hollow volume, in the new state, between the hollow volume ratio of the central part and each lateral part, this difference being at least equal to 2% and at most equal to 15%.