WO2018206900A1

WO2018206900A1 - Tyre having a crown comprising a stiffening layer and a high-traction tread

Info

Publication number: WO2018206900A1
Application number: PCT/FR2018/051158
Authority: WO
Inventors: Rémi REYNAL DE ST-MICHEL; Bertrand Daval; Frédéric Perrin
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2017-05-12
Filing date: 2018-05-11
Publication date: 2018-11-15
Also published as: FR3066147A3

Abstract

A tyre (1) having a crown (2) comprising a belt reinforcement with an axial width W, a tread (5) made of an elastomeric material, the tread comprising a plurality of tread pattern blocks (50), two axially adjacent tread pattern blocks being separated by a groove (7) extending at least in part circumferentially, a stiffening layer consisting of yarn-like reinforcing elements with compression rigidity, said yarn-like reinforcing elements being oriented in a mean direction forming an angle of between 50° and 90° with the circumferential direction C, wherein the yarn-like reinforcing elements are fragmented when moving along their mean direction into fragments with an overlapping amplitude "R" between circumferentially adjacent fragments.

Description

PNEUMATIC WITH A TOP COMPRISING A RIGIDIFICATION LAYER

AND A HIGH ADHESIVE TREAD

Field of the invention

The present invention relates to tires, and more particularly to a tire whose adhesion performance is improved.

In general, a tire is an object having a geometry of revolution with respect to an axis of rotation. A tire comprises two beads intended to be mounted on a rim; it also comprises two flanks connected to the beads, a top having a tread intended to come into contact with the ground, the top having a first side connected to the radially outer end of one of the two sidewalls and having a second side connected to the radially outer end of the other of the two sides.

The constitution of the tire is usually described by a representation of its constituents in a meridian plane, that is to say a plane containing the axis of rotation of the tire. The radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to any meridian plane. In what follows, the expressions "radially", "axially" and "circumferentially" respectively mean "in a radial direction", "in the axial direction" and "in a circumferential direction" of the tire. The terms "radially inner or radially outer" mean "closer or farther away from the axis of rotation of the tire in a radial direction". The equatorial plane is a plane perpendicular to the axis of rotation of the tire, positioned axially so as to cut the surface of the tread substantially halfway between the beads. The terms "axially inner, respectively axially outer" mean "closer or more distant respectively, the median plane of the tire in the axial direction."

State of the art

To improve the transverse adhesion performance of tires whose tread comprises a plurality of circumferential grooves, WO201 1/073022 A1 proposes to have, under the carcass ply and even under the inner sealing layer, a reinforcing ply comprising elements of cable type oriented substantially axially. However, the reinforcing effect of such a structure is limited and such a structure may be insufficiently enduring. The state of the art also knows the

2017PAT00155WO WO2012 / 048930 A1 which gives an example of a hooping sheet located radially outside two sheets composed of monofilament steel reinforcements, forming with the carcass ply the typical triangulation of the radial-ply tires, and in which the reinforcements of the hooping web forms an angle between 50 ⁰ and 90 ⁰ with the circumferential direction of the tire.

[0005] By the documents FR 1 187 336 A, US 5 052 458 A and FR 2 098 334, the state of the art also knows tires having layers provided with fractionated elements.

To improve the adhesion of a tire, it has also been proposed in WO2016 / 202702 to use in combination an elastomeric material constitutive of the tread of low dynamic modulus shear G * and a web of rigidification consisting of rigid reinforcing wire elements in compression, said reinforcing wire elements forming, with the circumferential direction, an angle of between 50 ° and 90 °. Thus, the objective is to combine a very good adhesion of the tread on the ground which is the prerogative of rubber compounds commonly referred to as soft mixtures, with a slight bending of the tread of the tire seen in meridian section. , that is to say with a small tilting of the sculpture blocks, to maintain a large surface contact with the ground.

If such a choice is very powerful especially for tires whose sculpture has grooves oriented rather circumferentially, however, there is a deterioration of the acoustic performance of the tire, it proves rather noisy. It seems that the cause is precisely related to the desired stiffening.

The objective of the present invention is to provide an improvement to the document proposal to achieve a level of rigidity sufficient to contain or prevent any tilting of carving block detrimental to maintaining a large contact surface of the tire on the ground, without the tire getting too noisy.

Brief description of the invention

The invention particularly relates to a tire having two beads, two flanks connected to the beads, and a vertex.

The invention relates to a tire comprising a crown comprising a belt reinforcement having an axial width W, the belt reinforcement comprising a stack of at least two plies coupled with a carcass ply, said at least two webs being constituted by metal cables, said metal cables forming an angle with the

2017PAT00155WO circumferential direction between + 10 ° and + 40 ° for one of these plies and between -10 ° and -40 ° for the other of these plies, the tire comprising:

A tread made of elastomeric material, the tread comprising a plurality of tread blocks, two axially adjacent tread blocks being separated by a groove extending at least partially circumferentially, the material constituting the tread ( 5) having a dynamic shear modulus G *, at 60 ° C and under an alternating stress at 10 Hz of 0.7 MPa, less than 1.1 MPa.

A stiffening layer consisting of rigid reinforcing wire elements in compression, said reinforcing wire elements being oriented in a mean direction forming an angle of between 50 ° and 90 ° with the circumferential direction C,

characterized in that said reinforcing wire elements are fractionated by moving along their mean direction, forming overlapping fragments of amplitude "R" between circumferentially adjacent fragments.

The term "rigid compression" elements whose Young's modulus in compression in the direction of slenderness of the wire elements is typically greater than 1 GPa, and preferably 10 GPa. For example, the wire reinforcing elements are constituted by metal cables. The wire reinforcing elements can also be monofilaments. They can also be formed by rigid assembly in compression of organic fibers, or inorganic fibers such as glass fibers, carbon, aramid type fibers, embedded in a sufficiently rigid matrix. The section of the monofilaments may be circular or flattened, for example of elliptical or rectangular section.

It has been indicated that, according to the invention, the reinforcing wire elements of said stiffening layer are fractionated. Compression is transmitted from cable to cable by shearing rubber between cables. Ideally, the number of cables interrupted at the same time must be as small as possible to optimize the deformations in the inter-cable rubber. In practice, to make manufacturing more robust, cutting two cables at a time ensures that there will always be at least one interrupted.

Thus, in addition to the choice of the reinforcing wire element itself, the skilled person has additional parameters allowing him to finely adjust the reinforcing effect, namely the laying step "P" of the fractionation layer (distance measured perpendicular to their large dimension between two adjacent fragments, see Figure 3), the amplitude "R" of the overlap between adjacent fragments. The term "adjacent fragments" means pieces of wire elements parallel to each other, located at the same radial level, and arranged circumferentially adjacent to each other. The wired reinforcing elements are therefore interrupted regularly in their length. The characteristics of this interruption are adapted to the pitch "P" and can

2017PAT00155WO also to the rigidity of the rubber mixture coating said reinforcing wire elements, in order to achieve the mechanical properties targeted for the stiffening layer.

[0014] Preferably, all the circumferentially adjacent fragments have an overlap. Advantageously, the circumferentially adjacent fragments have an overlap at least once in four. The amplitude "R" may be variable within the stiffening layer, especially when two or more cables are cut at a time. The covering "R" is advantageously of length between 2 and 40 mm.

Another important parameter is the axial separation distance between the cables. Indeed, in compression, the cables tend to approach axially from each other, which can lead to bracing and therefore to over-stiffening, detrimental to the performance of the tire. It is important that the space between two adjacent fragments of wire element is sufficient not to close during a compression deformation under stress of use of the tire. Let's agree that "The" is the axial separation distance between the cables and "The" is the length of a fragment. In particular, it is interesting to aim for values such that the ratio is greater than 5%.

Preferably, said stiffening layer is disposed radially outside the belt frame and axially under at least one groove of the tread; advantageously, said stiffening layer extends axially at least over a width WR at least 50% of the axial width W of the belt reinforcement.

Thus, the stiffening layer makes it possible to use for the tread mixtures considerably softer than in tires for passenger vehicles and this without significant harm neither for their longevity kilometer nor for their acoustic performance. The constituent material of the tread according to one of the objects of the invention is thus a material whose use is usually limited to applications in competition only.

Brief description of the figures

The objects of the invention are now described with the aid of the accompanying drawing, in which:

- Figure 1 shows very schematically (without respecting a specific scale), a radial section of a tire according to one embodiment of the invention;

- Figure 2a schematically shows a partial view in the radial direction, with skinned, the top of the tire shown in Figure 1 wherein the fractional reinforcement ply is positioned radially immediately above the crown belt plies;

2017PAT00155WO FIG. 2b shows another configuration in which the fractionated reinforcement ply is positioned radially above a hooping sheet containing orientation cables close to 0 °;

FIG. 3 is a diagram illustrating the main parameters of the fractionation of the reinforcement elements targeted by the present invention;

FIGS. 4a and 4b illustrate two variant embodiments of the invention.

Detailed description of the invention

We see in Figure 1 a tire 1 comprising a vertex 2, two sides 3 each connected to a bead 4. The top 2 is connected on each side to the radially outer end of each of the two sides. The top 2 comprises a tread 5. FIG. 1 shows an equatorial plane EP, plane perpendicular to the axis of rotation of the tire, situated halfway between the two beads 4 and passing through the middle of the belt reinforcement. ; FIG. 1 also indicates, by arrows placed just above the tread 2, on the equatorial plane EP, the axial X, circumferential C and radial Z directions.

Each bead comprises a bead 40; a carcass ply 41 (also visible in FIG. 2) is wound around each bead wire 40. The carcass ply 41 is radial and is in a known manner constituted by cables (in this case of implementation, cables textiles) arranged substantially parallel to each other and extending from one bead to the other such that they form an angle between 80 ° and 90 ° with the equatorial plane EP.

The vertex 2 comprises (see FIGS. 1 and 2) a belt reinforcement comprising said carcass ply 41 and two belt plies 62, 63. In a very conventional manner, the belt plies 62, 63 are formed by cables Metallic arranged parallel to each other. As is well known, the reinforcing elements formed by the cables of the carcass ply 41 and the cables of the waist plies 62, 63 are oriented in at least three different directions so as to form a triangulation. The waist reinforcement is of axial width W, the latter being measured from one axial end to the other of the widest (62) of the belt plies, that is to say the widest of the plies forming a triangulation with the carcass ply or layers.

The tread 5 comprises a plurality of carving blocks 50. Two axially adjacent carving blocks 50 are separated by a groove 7 extending at least partly circumferentially; each groove 7 is delimited radially inwardly by a bottom groove 70.

The tire 1 reinforcing belt comprises a shrink web 64 consisting of shrink reinforcements formed by organic fibers or aromatic polyamide or aramid or are formed of hybrid cables containing aramid fibers, said reinforcing reinforcements

2017PAT00155WO forming, with the circumferential direction an angle at most equal to 5 °. This layer is arranged indifferently radially inside or outside of the stiffening layer 8. The hooping sheet 64 comprises a single layer of hoop reinforcements. As an alternative embodiment, the hooping web consists of several layers of hoop reinforcements.

According to the invention, the tire 1 comprises a stiffening layer 8 that can be seen in Figures 1, 2a and 2b; this is formed, according to a particular embodiment of the invention, by steel cables. The steel cables are 4.26 cables, arranged at a 90 ° angle with a pitch of 1.25 mm. The hooping web 64 is disposed radially outside the belt plies 62, 63, and is disposed radially inwardly of the stiffening layer 8. The stiffening layer 8 is, in this variant, arranged radially just at the outside the shrink web 64. The stiffening layer 8 is arranged radially and axially under the (or, according to the embodiments, under at least one) groove 7 of the tread 5, thus under the bottom groove 70 7.

The reinforcing wire elements of said stiffening layer 8 (here, the cables) are oriented essentially in the meridian direction: the applicant's experiments show that the stiffening effect according to the invention is substantially obtained with an angle between 50 ° and 90 °, and preferably an angle greater than 85 °. The stiffening layer as proposed by the invention has indeed two main functions:

- Make a bending beam type "composite sandwich beam" working with the carcass ply; the layer must therefore have an angle close to the carcass ply to reinforce the stiffness of meridian bending of the crown;

- increase the bending stiffness on edge of the crown reinforcement, by increasing the shear stiffness of the layer in its plane; this is maximum for a 45 ° layer angle.

The angle range indicated above thus limits the bending in the plane and off plan of the tire top under a transverse force by increasing the meridian bending stiffness of the top (off plane) on the one hand, this limits the tilting of the blocks of sculptures by bending, and on the other hand increasing the bending rigidity on the top edge (in the radial plane).

In Figure 3, we see the step of fractionation P, the recovery amplitude R, the gap "The" between fractions and the length of fraction "The". For example, for a tire of size 225/45 R 17, for a wire rope comprising 4 filaments of 0.26 mm, values giving good performance are P = 1, 25mm, R = 19.5mm, Le = 6mm; we deduce Le = 45mm. In FIG. 3 as well as in FIG. 4a, it is seen that only one reinforcing element is interrupted at a time circumferentially, while in FIG. 4b it is seen that are interrupted.

2017PAT00155WO two reinforcing elements both circumferentially. In both variants, the compression is transmitted from cable to cable by shearing the rubber present between cables.

The diameter of the reinforcing elements ( _O1 |) targeted by the present invention is preferably greater than 0.2 mm. This lower limit is intended to prevent buckling in compression during the solicitations of the tablecloth in use.

So as not to increase the volume of the tire, the stiffening layer according to the invention can advantageously replace the materials present in general at the base of the tread. Generally found under the groove bottom a layer of an elastomeric material of the order of 2 mm which brings a protection of the belt frame to the aggressions suffered by the tire in use. The stiffening layer of the present invention can provide sufficient protection against these attacks, which allows, if not eliminate, at least to reduce the thickness of said layer of elastomeric material discussed above, for example reduce at most 1, 5 mm instead of 2 mm or even up to a thickness of at least 0.5 mm. This reduction in thickness also makes it possible to increase the shear stiffness of the tread and thus to contribute to improving the transverse handling of the vehicle.

It should be noted that the stiffening layer is generally a semi-finished comprising not only the steel cables but also a so-called calendering rubber. This is generally the case for all plies, whether it is the carcass ply or plies, the belt plies, the hooping ply: they consist of wired, monofilamentary or cabled reinforcing elements coated with gum. calendering binding them together to form a manufacturing semi-finished; the calendering gum is of generally selected composition to meet both the requirements of the manufacturing process and also to provide the tire as a finished product with suitable characteristics. Recall in passing that there are manufacturing processes where the removal of belt ply cords is made yarn by thread on a blank tire under construction, without going through the stage of manufacturing a semi-finished as a calendered tablecloth; the invention is compatible with such a method. All these considerations are only a reminder of technical data well known to those skilled in the art and are not part of the invention.

The stiffening layer 8 extends axially over a width WR. By way of example, the width WR is 140 mm for a 225/45 R 17 tire, ie 70% of the width W of the crown reinforcement. Advantageously, the stiffening layer 8 is close to the mechanical neutral fiber of the structural assembly formed by the crown 2 of the tire. In another embodiment, at least 70% of said width WR of the stiffening layer is disposed on one side of the median plane EP, namely the side intended to be mounted on the outside of the vehicle;

2017PAT00155WO say the one most solicited in turns taken at high speed. In certain implementations of the invention, the tire is then asymmetrical. However, this is not imperative, the tire according to the invention can very well be axially symmetrical. Preferably, the stiffening layer extends over a width WR at least 50% of the axial width W of the belt reinforcement and preferably at least 70%. Advantageously, the stiffening layer extends over a width WR at most 100% of the axial width W of the belt reinforcement.

The invention finds an especially interesting application when the grooves 7 or some of them extend circumferentially. It may very well be grooves that are not oriented exactly circumferentially but may be oblique with respect to the equatorial plane EP; as the means of the invention make it possible to effectively combat the tendency to tilt of sculpture blocks and the tendency to bend the crown when the tread is soft rubber in order to promote adhesion, and that the flexion of the crown and the tilting of the sculpture is particularly detrimental to tire stresses in the transverse direction, the invention finds a particularly advantageous field of application in the presence of grooves at least partially circumferentially oriented. Of course, there may furthermore be grooves oriented mainly axially, and in this case the invention makes it possible to combat the tilting of the sculpture blocks 50 in the event of longitudinal stress, originating from a large torque, for example when braking 'emergency. The stiffening layer 8 is part of the belt frame of the tire 1; the stiffening layer 8 is in direct connection with the belt plies 62, 63 and with the hooping web 64. This makes it possible to stiffen the crown 2 and effectively limits or even prevents the tilting of the tread blocks 50 from the tread 5.

The addition of the stiffening layer 8 contributes to a strong mechanical coupling with the belt plies 62 and 63 forming a dimensionally stable triangle, particularly in the center of the tire, when the coupling is well established. Thus, when the tire is centrifuged, the center of the tire in the vicinity of the equatorial plane EP does not deform while the shoulders undergo a deformation (or radial extension) under the effect of inertial forces. This difference in radial extension under the effect of centrifugation then causes a certain fragility of the tire at high speeds and can cause premature failure of the tire. Consequently, in a particularly advantageous embodiment, the invention comprises a hoop particularly adapted to prevent any significant radial extension according to the maximum speed level that is fixed for the tire.

One way of concretely adjusting the design of a tire according to a given performance specification is that the shrink web exceeds axially by at least 3 mm and preferably by at least 5 mm. the edge of the widest (62) tablecloth

2017PAT00155WO belt, to reinforce the stiffness of relative extension of the tire to the shoulders. We will return to this aspect with the description of the fifth variant embodiment below. Another means is to use materials constituting the hooping web much more rigid in extension, such as aramid or hybrid cables containing aramid. Yet another means consists in that this hooping web is made up of several layers of reinforcements at the shoulder, more numerous than at the center of the tire, where the coupling with the stiffening layer 8 already plays this role. Finally, let us quote another way that is that the shoulder shrink web is prestressed, either because it was placed on a manufacturing drum at a lower radius to the shoulders than in the center, before conformation of the tire in the vulcanization press, either because it was placed on a drum of tension manufacture with a tension higher than the shoulders than in the center.

tests

The invention has been tested by making tires in the 225/45 R dimension 17. The reference tire is a MICHELIN Pilot Sport 3 tire. The test tires are all derived from the MICHELIN Pilot Sport 3 tire for the elements. non-specific of the present invention and for which there is no indication below. The vehicle used is a Renault ® Clio RS ™. The chronometric results indicated concern the time necessary to go around the indicated circuit, starting cold tires, average over 3 laps. The fractional stiffening layer used here is composed of 4.26 cables at a pitch of 1.25mm, split into 45mm pieces spaced 6mm along their alignment.

The table above shows in each case the chronograph with and without the fractional stiffening layer. The reference tire achieves a time in 2 minutes 21, 8 seconds. The difference is considered significant on this test when a gain of 0.3 seconds is reached.

2017PAT00155WO

Claims

Pneumatic tire (1) comprising a crown comprising a waist reinforcement having an axial width W, the belt reinforcement comprising a stack of at least two plies coupled with a carcass ply, said at least two plies being constituted by metal ropes said metal cables forming an angle with the circumferential direction between + 10 ° and + 40 ° for one of these plies and between -10 ° and -40 ° for the other of these plies, the tire comprising:

^■ - a tread band (5) of elastomeric material, the tread comprising a plurality of tread blocks (50), two axially adjacent tread blocks being separated by a groove (7) extending at least partially circumferentially , the material constituting the tread (5) having a dynamic shear modulus G *, at 60 ° C and under an alternating stress at 10 Hz of 0.7 MPa, less than 1.1 MPa,

^■ a reinforcing layer of wire elements rigid reinforcement in compression, said wire reinforcement elements being oriented in a mean direction forming an angle of between 50 ° and 90 ° with the circumferential direction C,

A tire according to claim 1, wherein all circumferentially adjacent fragments have an overlap.

The tire of claim 1, wherein the circumferentially adjacent fragments have at least one overlap at all.

Tire according to one of claims 1 to 3, wherein the cover "R" is of length between 2 and 40 mm.

Tire according to one of claims 1 to 4 wherein, "Le" being the axial separation distance between the cables and "Le" being the length of a fragment, the ratio ^ is greater than 5%.

2017PAT00155WO Tire according to one of claims 1 to 5, wherein said stiffening layer is arranged radially outside the belt frame and axially under at least one groove (7) of the tread, and extends axially at least over a width WR at least 50% of the axial width W of the belt reinforcement.

7. A tire according to one of claims 1 to 6, wherein the Young's modulus in compression in the direction of slenderness of the wire elements of the stiffening layer (8) is greater than 1 GPa.

8. A tire according to one of claims 1 to 7, wherein the stiffening layer (8) is covered by a layer of an elastomeric material (55) of at least 0.5 mm and at most 1.5 mm between the groove bottom and said stiffening layer.

9. A tire according to any one of claims 1 to 8, wherein the reinforcing wire elements form with the circumferential direction an angle greater than 85 °.

10. A tire according to one of claims 1 to 9 comprising a shrink layer (64) made of shrink reinforcements, said shrink reinforcements forming, with the circumferential direction an angle at most equal to 5 °.

2017PAT00155WO