WO2020128237A1

WO2020128237A1 - Tread comprising interrupted grooves

Info

Publication number: WO2020128237A1
Application number: PCT/FR2019/053024
Authority: WO
Inventors: Frédéric DOMPROBST
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-12-19
Filing date: 2019-12-11
Publication date: 2020-06-25

Abstract

Disclosed is a tread (1) for a heavy goods vehicle tyre having a rolling surface (10), this tread (1) comprising, close to each of its edges (11), a plurality of open wells (2) on the rolling surface when new, these open wells (2) of depth Pmax being arranged circumferentially with a mean distance D between two consecutive open wells; each open well (2) being delimited by two facing main faces (21, 22), this tread being such that each open well (2) is connected to at least one hidden cavity (32) formed inside the tread, this hidden cavity (32) opening on a main face (21, 22) of said well.

Description

Tread with grooves

interrupted.

The invention relates to the treads for tires of heavy goods vehicles and more particularly the trough arrangements with which these treads are provided, thanks to which both the water drainage performance on the roadway in time rain are made more durable, and driving performance is improved.

DEFINITIONS

By cutting, we mean any cavity or hollow produced in particular by

molding in a tire tread, a cut extending both in the depth of the tread and in a main direction - which is the direction of water flow in the cut during rolling in rainy weather. This main direction corresponds to the largest dimension of the cutout on the running surface.

By open groove means an open cut on a tread surface of a tread coming into contact with the road, this groove being delimited by opposite walls, the average distance between these walls being suitable so that these walls do not come into contact with each other under normal conditions of use of the tire.

By incision is meant a thin cut having a small average width, this average width corresponding to the average distance separating the facing walls delimiting it, and such that, under normal conditions of use of the tire , these walls can come, at least partially, into contact with one another when passing through the region of contact of the tire with the road.

By hidden cavity is meant a cavity formed under the new rolling surface of the tread, this cavity may be intended to form a new groove open on the new rolling surface generated after a predetermined partial wear. A hidden cavity is delimited by two main walls facing each other, these two main walls being interconnected by a lower part forming a bottom and by an upper part in the extension of these main walls radially outwards. In this upper part, an incision can be opened to connect the hidden cavity to the new rolling surface. Viewed in section, a hidden cavity can take any geometric shape such as: circular, rectangular, triangular.

By thickness of material to be used with a tread, is meant

the thickness of the material of this tread can be worn during driving before reaching a legal limit of use, this limit can be identified by wear indicator devices formed in particular in the grooves.

When this limit is reached, an intervention is necessary in order either to reform a new hollow pattern on the tread of the tire or to replace a new tread or even to change the tire.

In the present description, the terms radial or radially are used to indicate a direction which, when taken on the tire, is a direction perpendicular to the axis of rotation of the tire while, when it is taken on a tread alone, it corresponds to the direction of the thickness of said tread.

In addition, the term circumferential is used to indicate a direction which corresponds to a direction tangent to any circle centered on the axis of rotation of the tire. This circumferential direction corresponds to the longitudinal direction of the tread, the latter being produced in the form of a flat strip before it is incorporated into the manufacture of a new tire or the retreading of a worn tire.

The transverse term refers to a direction which is parallel to the

direction of the axis of rotation of the tire. This direction is perpendicular to the radial direction and to the circumferential direction. A direction is said to be oblique when it forms an angle greater than zero with the direction

circumferential or longitudinal on a tread.

PRIOR ART

In known manner, driving conditions in rainy weather require the fastest possible elimination of water between the tread of each tire and the roadway in order to make contact between the material composing the tread and the roadway. The water which is not pushed back on the front or discharged on the sides of the tire returns and partly flows in cutouts formed in the tread, these cutouts taking the form of cavities opening new on the running surface of the tread. These cavities can be oriented in the circumferential direction or the transverse direction or in an oblique direction intermediate between the two previous directions or even in a combination of these directions. By orientation of a cavity is meant the angle made by the direction of its largest dimension on the running surface with for example the circumferential direction on the tire.

Whatever the category of tire, the tread of this tire must offer a performance in drainage of water on the road which is always above a minimum performance called safety performance. In

consequence and taking into account the progressive wear of the tread which progressively reduces the surfaces of the transverse sections of the grooves and the capacity of these grooves to drain a given quantity of liquid, it is usual to make grooves opening onto the surface of bearing in new condition, these grooves extending in the thickness of the strip up to at least a level which corresponds to a legal wear limit requiring the removal of the strip.

The realization of such a plurality of grooves open on the surface of

rolling of a tread, however, has the drawback of reducing the quantity of material for a given tread width and consequently of reducing very considerably the stiffnesses of the tread, which has an impact on the performance in wear. As a result, in order to cope with the stresses to which the strip is subjected during rolling, the person skilled in the art must plan to compensate for these decreases in rigidity by any means at his disposal, in particular by adapting the internal structure of the tire which, of course , is not without impact on the manufacturing cost of the tire itself. These decreases in rigidity can also affect the speed of wear, the regularity of this wear and some of the performance expected during driving.

In addition, there is an increase in the rolling resistance, that is to say an increase in the energy dissipation at each revolution of the wheel, this dissipation being linked to the greatest deformations undergone by the materials. elastomeric forming the tread, which results in a significant increase in the consumption of vehicles equipped with such tires.

To solve at least partially such a problem, it has been proposed in document EP 2323858-B1 to form both grooves and entirely under the running surface of the tread with nine hidden cavities, each hidden cavity, forming a channel, being extended towards the running surface of the new tread by an incision of suitable geometry to promote greater rigidity. With this type of tire, it is possible to renew a greater or lesser part of the initial drainage volume of the grooves when the strip has reached a predetermined level of wear.

It is also known to form what has been described as grooves

undulating (EP2483087 B1) in the thickness of a tread, these grooves having parts open on the rolling surface as new and parts hidden in the thickness of the tread, these parts being interconnected by intermediate parts. To facilitate molding and demolding, an incision is formed connecting the hidden and intermediate parts with the new rolling surface. This arrangement of grooves is of course favorable from a point of view of limiting the reduction in rigidity linked to the presence of recesses in the tread. However, after a certain partial wear the intermediate parts, then the hidden parts alone remain open on the rolling surface in a discontinuous manner, which may require the presence of additional grooves active from partial wear. These additional grooves can result from the transformation of fully formed channels inside the tread.

It has also been proposed in particular in document EP 2379352 B1 to extend hidden cavities by a plurality of cavities opening both in a hidden cavity and on the running surface of the new tread.

Although these provisions are favorable from a performance balance point of view, it has been observed that certain rolling performance still needs to be improved. This is the case with regard to mechanical resistance of the edges of a tire tread for heavy goods vehicles. In fact, the presence of a fully open groove on the running surface in the vicinity of a strip edge can, under certain conditions of use, generate significant mechanical stresses at the bottom of the groove.

SUMMARY OF THE INVENTION

The present invention relates to a solution to this problem of mechanical resistance of the cutouts near the edges of a tread combined with that of reducing the energy loss in the tread at each revolution of the wheel.

To this end, the invention relates to a tread for a tire.

heavy vehicle having a total thickness E corresponding to the total thickness of material to be used in driving. This tread has a new tread surface intended to come into contact with a roadway when rolling a tire provided with this strip. This running surface is gradually renewed with the wear generated by driving on the road.

This tread comprises lateral edges axially defining a tread width.

This tread comprises close to each of its lateral edges:

- A plurality of open wells on the rolling surface new, these open wells of depth Pmax being arranged circumferentially with an average distance D between two consecutive open wells; each well being delimited by two main faces, the two main faces being connected to each other by a bottom, this bottom defining the depth of the well, each well having a maximum opening length Le measured in the direction

circumferential and a transverse width La measuring the distance between the main faces, this width La being less than the maximum opening length Le,

- This tread being characterized in that each open well is connected to at least one hidden cavity formed inside the tread, this hidden cavity being open in a main face of said well. Thanks to this arrangement, it is possible not to have a circumferential continuous groove near the edges and thus to maintain at a relatively high level the rigidity of the tread in new condition while benefiting from a volume. suitable drainage and can be adjusted by the respective volumes of open wells and hidden cavities. Of course, the hidden cavities can form additional transverse or oblique grooves and therefore new active edges in contact with the road, after a predetermined wear causing these cavities to appear on the running surface.

Advantageously, the open wells have on the rolling surface a

opening of elongated shape, the maximum opening length Le being at least equal to twice the dimension of smallest width La, the latter being measured perpendicular to the maximum opening length Le.

In order to make the most of the drainage effect on the shoulders, it is

It is advisable to provide for the permanent presence of at least two open wells on the new rolling surface in the contact imprint on the road, this imprint being obtained for the conditions of use of the tire provided with the tread according to the invention.

For a durability of the running performance on a pavement coated with water until complete wear of the tread, the depth Pmax of the wells is greater than the thickness E of material to be used on the tread.

In an embodiment simplifying the manufacture of the strip

bearing, an open incision on the rolling bearing surface extends to the hidden cavity of an open well and also opens on said well.

In one embodiment of the invention, at least certain cavities

hidden are not open on the outside of the tread and in this case the volume of each of said cavities is adjusted to be sufficient to carry out a drainage of the water present on the roadway in the region of the edges of the tire during driving on pavement covered with water in rainy weather. The volume of all the cavities connected to the wells molded near an edge is chosen as being a percentage of the difference between the volume of a continuous circumferential groove and the sum of the volumes of these wells. This percentage is at least equal to 0.25 and at most equal to 0.50. In one embodiment, it is possible to provide more than one hidden cavity opening onto the same well in order to have good drainage capacity. In order to obtain optimum rigidity of the edge of a tread according to the invention, each hidden cavity is formed as close as possible to the bottom of the well in which it opens.

Advantageously, each hidden cavity has, from an open well, an elongated shape and is oriented to make an angle at least equal to 30 degrees with the circumferential direction corresponding to the arrangement of the plurality of wells open on a edge of the tread.

Even more advantageously, each hidden cavity connected to a well opened on the new rolling surface opens on a lateral face of the tread in order to facilitate the evacuation of liquid drained inside the open well. to which this hidden cavity is connected. A lateral face of a tread corresponds to one of the two faces extending laterally the tread face.

In the latter case, it is advantageous that two hidden cavities opening to the outside are formed to open on a lateral face of the same well, these hidden cavities being oriented in different ways in order to make them insensitive. the operation of these hidden cavities in the direction of rotation of the tire.

In a preferred variant, all the hidden cavities are formed on the same side with respect to the plurality of wells formed axially near the same lateral edge of the tread.

In one embodiment, the tread is suitable for imparting a preferential direction of rotation to the tire provided with this strip. This preferred direction is generally materialized on the tread or on the tire by a visual element or marking such as for example an arrow. In this specific embodiment, the hidden cavity or cavities connected to a well are oriented to promote the flow of water present on a roadway towards the outside of the tread.

Specifically, these hidden cavities are oriented so that, seen in projection on the running surface, the part of each hidden cavity opening into the well between the first in contact with the road. So a flow in the well will be deflected into the cavity at a small angle and less than 45 degrees with the circumferential direction.

In combination with any of the described arrangements of the invention, it is possible to provide for the presence of an incision between the axially open wells near the same lateral edge of the tread, these incisions s 'extending over part of the depth of the strip or up to the depth Pmax of said wells.

The invention also relates to a tire provided with a tread comprising on each of its lateral edges a plurality of open wells in which open hidden cavities formed inside the tread, these cavities hidden or not opening outwards as just described. The tread of this tire may in combination comprise traditional grooves and / or hidden channels intended to form additional grooves after a predetermined partial wear. In such a case, it may be envisaged to open the hidden cavities connected to the open wells in these grooves or these hidden channels.

Other features and advantages of the invention emerge from the

description given below with reference to the accompanying drawings which show, by way of nonlimiting example, embodiments of the subject of the invention

BRIEF DESCRIPTION OF THE DRAWINGS

[Fig 1] Figure 1 shows a first alternative arrangement of the wells

open on a tread, these open wells being formed near a side edge of a tread;

[Fig 2] Figure 2 shows in cross section (according to ll-ll) the variant

shown with Figure 1 in new condition;

[Fig 3] Figure 3 shows a second alternative arrangement of the wells

openings formed near a side edge of a tread having characteristics implying a direction of preferential use when fitted to a tire.

DETAILED DESCRIPTION To facilitate the reading of the figures, the same reference signs are used for the description of variants of the invention when these signs refer to elements of the same nature whether this nature is structural or functional.

Figure 1 shows a first alternative arrangement of the wells open on a running surface, these wells being formed near a side edge of a tread.

In this figure 1 is shown a partial view of a tread 1 of a truck tire having a rolling surface 10 new intended to come into contact with a roadway during driving. The partial view of Figure 1 shows a side edge 11 of this tread.

Near this side edge 11, a plurality of open wells 2 is formed on the rolling surface 10 when new. These open wells 2 are arranged in a circumferential direction with a distance D between two wells. Each of these open wells 2 has an opening 20 on the rolling surface, this opening 20 having, in the example described, a rectangular shape with maximum opening length Le and width La. For the tire of the example of dimension 315 / 70R22.5 the length Le is worth 25 mm and the width La is worth 10 mm, the distance D is worth 30 mm. The dimensions: maximum opening length Le and distance D between two wells, are determined so that there are permanently at least two open wells 2 present in contact with the roadway under the conditions of use.

Each open well 2 is delimited in the thickness of the tread 1 by main faces 21, 22, these main faces comprising end faces 23, 24. The main faces being joined together by a bottom 25. This bottom 25 is at a distance Pmax from the rolling surface 10 when new and in the present case this distance Pmax is greater than the thickness E of material to be used in rolling in order to maintain the presence of a hollow up to with complete wear of the tread.

In addition, there is formed, inside the tread and near each end face 23, 24 of each open well 2, a hidden cavity 32 opening in one of the main faces 21, 22 delimiting this well 2. Overcoming each from these hidden cavities 32, an incision 31 is formed which opens both on the rolling surface 10 and in one of the main faces 21, 22 delimiting the open well 2.

These hidden cavities 32 do not open towards the outside of the strip of

bearing in particular on the lateral parts of the tread as is better visible in FIG. 2 showing in cross section the variant shown with FIG. 1 in the new state.

In this figure 2 we see that a hidden cavity 32 opens in the well 2 as close to the bottom 25 of said well in order to generate an additional drainage volume adding to that of the open well thus compensating for the causes the tread to have no circumferential open groove and continues near its side edges.

This additional volume is less than the volume lacking a groove in the initial state: in fact, the person skilled in the art knows that with a groove it is necessary to provide a larger volume than necessary for new since it is necessary to take account of the wear of the strip and the progressive reduction of the volume available in the groove. With the present invention, it is possible to best adjust the total volume of troughs (including the volume of open wells and that of hidden cavities connected to the wells).

In addition, each hidden cavity 32 generates a new transverse groove after partial wear of the tread, this transverse groove being useful in the last phase of use of the tread.

FIG. 3 shows a second variant of shape and arrangement of the open wells 2 formed near a lateral edge of a tread having specific characteristics implying a direction of preferential use when fitted to a tire ( this direction is indicated in the figure by an arrow R). This preferred direction is generally marked on the tire by a specific sign visible to the user.

In such a case, it is advantageous to orient the hidden cavities 32 of

so as to best use this preferential direction of rotation. The case described shows open wells 2 having on the rolling surface 10 new an opening 20 of oblong shape, the largest of the dimensions denoted Le is measured in the circumferential direction. Near the bottom 25 of each of the open wells 2, a hidden cavity 32 opens at one of its ends through an opening 321 in the well 2, this hidden cavity 32 opening at its other end on one of the lateral faces 12 of the tread through an opening 320 (each lateral face 12 intersecting the tread surface 10 to form an edge 11 of the tread). The presence of this opening 320 makes it possible to further reduce the volume of each hidden cavity to the just necessary to carry out the drainage and the evacuation of the water present on the edge of the tread when in contact with a pavement coated with water. .

Each of the hidden cavities 32 makes an average angle A with the direction

circumferential here equal to 30 degrees with the circumferential direction. The incisions 31 formed between the running surface and the hidden cavities are generally oriented with the same angle A. These incisions are, in the case presented, of wavy geometry both on the surface and in the depth of the strip.

The angle A of each hidden cavity is suitable for promoting the flow of water present on a roadway towards the outside of the tread. Specifically, the hidden cavities 32 are oriented so that, seen in projection on the rolling surface, the projected part of the opening 321 of each cavity hidden in the well enters the first in contact with the road. This arrangement is favorable as soon as the wear of the strip is such that the hidden cavity generates a new groove.

The main direction of the hidden cavity corresponds to the direction of the

length of the hidden cavity according to which a flow of water occurs when driving on a pavement coated with water.

A circumferential groove 4 is shown on the right of Figure 3, it borders here the inner side of the shoulder rib in which the open wells and the hidden cavities are located. In this variant as in the

previous, we see the absence of a circumferential continuous groove

axially between the edges of the tread and said wells.

Of course, the different variants described can be combined with one another depending on the objective sought. The invention is not limited to the two examples presented and various modifications can be made without departing from its scope as defined by the claims. In particular, an incision of suitable geometry can be provided to extend from an open well to another open well, this incision opening onto the rolling surface.

Claims

1. Tread (1) for a heavy-duty vehicle tire having a new tread surface (10) intended to come into contact with a roadway during the rolling of a tire provided with this strip, this tread (1 ) comprising edges (11) axially delimiting a strip width, this tread (1) comprising, near each of its edges (11), a plurality of open wells (2) on the rolling surface as new, these open wells (2) of depth Pmax being arranged circumferentially; each open well (2) being delimited by two main faces (21, 22) connected by a bottom (25) of wells, this bottom (25) defining the depth Pmax of the well, each open well (2) having a maximum length d opening Le measured in the circumferential direction on the running surface and a transverse width La measuring the distance between the main faces (21, 22), this width La being less than the maximum circumferential opening length Le, this tread being characterized in that each open well (2) is connected to at least one hidden cavity (32) formed inside the tread, this hidden cavity (32) opening in a main face (21, 22 ) of said well.

2. Tread (1) according to claim 1 wherein the open wells (2) have, on the rolling surface (10), an opening (20) of elongated shape, the maximum circumferential opening length Le being at less than twice the transverse width La.

3. Tread (1) according to claim 1 or claim 2 wherein there are permanently at least two open wells (2) on the tread surface (10) new in the contact print on the floor , this imprint being obtained for the conditions of use of the tire provided with this tread.

4. Tread (1) according to any one of claims 1 to 3 wherein an incision (31) open on the rolling surface (10) new extends to the hidden cavity (32) of an open well (2) and also opens onto said well.

5. Tread (1) according to any one of claims 1 to 4 wherein each hidden cavity (32) is formed as close as possible to the bottom (25) of the well in which it opens.

6. Tread (1) according to any one of claims 1 to 5 in which each hidden cavity (32) has, from an open well (2), an elongated shape and is oriented to make a mean angle At least 30 degrees with the circumferential direction.

7. Tread (1) according to any one of claims 1 to 6 in which each hidden cavity (32) connected to an open well (2) on the new rolling surface opens on a side face (12 ) of the tread to allow the evacuation of liquid drained inside said open well (2).

8. A tread (1) according to any one of claims 1 to 7 in which all the hidden cavities (32) are formed on the same side with respect to the plurality of wells (2) formed axially near a same side edge (11) of the tread.

9. Tread (1) according to any one of claims 1 to 8 in which the tread is suitable for giving a preferential direction of rotation to the tire provided with this strip, and in which the hidden cavity or cavities (32 ) connected to an open well (2) are oriented in such a way that, seen in projection on the running surface, the part of each hidden cavity opening into the well between the first in contact with the road.

10. Tread (1) according to any one of claims 1 to 9 wherein this tread has no continuous circumferential groove between the plurality of wells axially near an edge and said edge.

11. Tire for heavy goods vehicle provided with a tread (1) according to any one of claims 1 to 10. i