WO2018206901A1

WO2018206901A1 - Tyre having a crown comprising a stiffening layer and a high-traction tread

Info

Publication number: WO2018206901A1
Application number: PCT/FR2018/051159
Authority: WO
Inventors: Rémi REYNAL DE ST-MICHEL; 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: FR3066146A3

Abstract

A tyre (1) 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 said yarn-like reinforcing elements form wavelike patterns around said mean direction. Abstract drawing: Figure 2

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 for a road vehicle 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 document WO2012 / 048930 A1 which gives an example of a hooping sheet, located radially at

2017PAT00132WO the outside of two plies 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 locking ply form an angle of between 50 ⁰ and 90 ⁰ with the direction circumferential tire.

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 shear modulus 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 the rubber compounds commonly referred to as soft mixes, 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 efficient especially for tires whose sculpture has grooves oriented rather circumferentially, however, there is a degradation of the acoustic performance of the tire, it proves rather noisy. It seems that the cause is precisely related to the desired stiffening. Indeed, the rigid stiffeners in compression currently available induce too great stiffening.

In a very different field, namely the field of tires for aircraft, the state of the art also knows, from documents EP 2 610 074 A1 and FR 2 518 462 A2, tires comprising reinforcements forming corrugations. . It is known to those skilled in the art that the drift thrust of such tires must be as low as possible, which results in the use of belts of belts oriented quasi-circumferentially, and / or comprising flexible reinforcements in compression, such as multi-filamentary cables made of organic material.

Thus, the document EP 2 610 074 A1 describes a reinforcing ply whose cables have corrugations. The belt band proposed in the application example comprises nylon cables, unable to provide a compressive force. The characteristics of the corrugation are adjusted in order to limit the propagation of the strokes of the tread, and in no case a level of rigidity in compression.

Similarly, FR2518462A2 discloses a similar web in combination with a top belt comprising at least layers of circumferential reinforcements to protect the belt while having a low drift thrust. This is entirely different from the present invention, requiring a cross angle vertex belt.

Unlike aircraft tires, the corrugated reinforcements of the present invention require for their normal operation that the belt plies comprise rigid reinforcements in compression forming with the equatorial plane an angle> 15 °, which is the case of

2017PAT00132WO the vast majority of passenger car tires. Only under this condition that the invention provides the expected benefit in adhesion. Indeed, the combined movement of these two crossed-angle plies causes the compression in the corrugated reinforcements of the invention, increasing the apparent rigidity of the crown reinforcement sufficiently to provide a gain in adhesion, research has shown that a criterion geometrically exposed further ensures this. The apparent rigidity provided by the present invention must also be limited to sufficiently precise values so that the tire is not too noisy, which is facilitated by the adjustment of the corrugations of the reinforcements of the invention.

The objective of the present invention is to propose an improvement to the proposal of WO2016 / 202702 allowing, without the tire becoming too noisy, to achieve a level of rigidity sufficient to contain or prevent any tilting of the block. carving detrimental to the maintenance of a large contact surface of the tire on the ground, so likely to confer good performance of traction and drifting thrust pledge of good handling. .

Brief description of the invention

The invention relates to a tire comprising a crown comprising a belt reinforcement having an axial width W, said belt reinforcement comprising belt plies formed by metal cables arranged parallel to each other, 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 of elastomeric material, the tread comprising a plurality of tread blocks, two axially adjacent tread blocks being separated by a groove extending at least partly circumferentially,

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 form undulations around said average direction.

The term "rigid compression" elements whose Young's modulus in compression in the direction of slenderness of the wire elements is 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

2017PAT00132WO 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 are corrugated. Preferably, the corrugations are in the plane of the layer; this means that the corrugations are located substantially in a plane perpendicular to any plane containing the axis of rotation of the tire. Alternatively, the corrugations are in the plane perpendicular to the plane of the layer or the corrugations form a helix. In addition to the choice of the reinforcing wire element itself, those skilled in the art have additional parameters enabling it to finely adjust the reinforcing effect, namely the "P" pitch of the corrugation around a wire. mean direction "M", and the amplitude "A" thereof. To provide the compression reinforcement performance provided by the invention, advantageously, the corrugation of the reinforcing wire elements has an amplitude (A) and a pitch (P) compatible with the targeted compression rigidity. By way of example, the pitch P of the corrugations is advantageously between 2 and 50 mm. By way of example, the amplitude A of the corrugations is advantageously between 1 and 25 mm. In particular, it is interesting to aim for values such that the P / A ratio ² is greater than 0.3 mm ^-1 .

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 which has been mentioned 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

2017PAT00132WO 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.

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.

The stiffening layer thus has the transverse adhesion advantages described in WO2016 / 202702 while significantly improving the noise emitted by the casing during taxiing.

Thus, the stiffening layer allows the tread to use considerably softer mixtures 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 is thus a material whose use is usually limited to applications in competition only. Note that, while it was already known to use as elastomeric material constitutive of the tread, a material having a low dynamic modulus of shear G * in combination with a reinforcing ply, and that we were so close of the structure proposed by the invention, it is only by adopting the corrugation characteristics specified above that it was possible to significantly improve the acoustic performance of the tire.

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

- Figure 2b shows another configuration where the corrugated reinforcing ply is positioned radially above a shrink layer containing orientation cables close to 0 °;

FIG. 3 is a diagram illustrating the principal parameters of the waviness of the reinforcing wire elements contemplated by the present invention.

2017PAT00132WO Detailed description of the invention

We see in Figure 1 a tire 1 comprising a crown 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 top 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 belt frame of the tire 1 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 reinforcement reinforcements forming, with the circumferential direction an angle at most equal to 5 °. This hooping layer is arranged radially either inside or outside of the stiffening layer 8. The hooping layer 64 comprises a single layer of hoop reinforcements. As an alternative embodiment, the hooping layer 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 1.25mm. The hooping layer 64 is arranged radially at

2017PAT00132WO the outside of the belt plies 62, 63, and is disposed radially inwardly to the stiffening layer 8. The stiffening layer 8 is, in this variant, arranged radially just outside the shrink layer 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 70 of groove 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 makes it possible to limit flexions in the plane and out of plane of the top of the tire under a transverse force by increasing on the one hand the stiffness of the meridian bending of the top (out of plane), this limits the tilting of the blocks of sculptures by bending, and on the other hand increasing the bending rigidity on edge of the crown (in the radial plane).

In FIG. 3, it can be seen that, by way of example, the tire illustrating the invention, of dimension 295/30 R 20, has a corrugation pitch P = 15 mm and an amplitude of corrugation A. = 6 mm. If the use of reinforcing plies having such corrugations is already known per se, for example by the document EP1637354, in the present invention, the orientation of the wire elements is not circumferential; it is to give a double elongation module that the skilled person uses such undulations in a reinforcement hoop; in contrast, in the present invention, given the non-circumferential orientation of said reinforcing wire elements of said stiffening layer 8, the same function provided by this arrangement is quite different. The use of wired elements meridian orientation is also known, for example in the document FR2940183, but in the present invention the wire elements are reinforcing and must be rigid in compression to achieve the objective set by the inventor . The invention of the cited document does not in any way a mechanical effect of the corrugated sheet, unlike that described in this document.

The stiffening layer 8 extends axially over a width WR. By way of example, the width WR is equal to 240 mm for a tire of dimension 295/30 R 20, ie 80% of the width W of the crown reinforcement. Advantageously, the stiffening layer 8 is close to the fiber

2017PAT00132WO mechanical neutral 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, ie the one most requested 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 a particularly 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 layer 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.

2017PAT00132WO A means of concretely adjusting the design of a tire according to a given performance specification is that the shrink layer axially exceeds at least 3 mm and preferably at least 5 mm the edge of the wider (62) belt plies, to enhance the relative extension stiffness 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 layer much more rigid in extension, such as aramid or hybrid cables containing aramid fibers. Yet another means is that this hooping layer consists of several layers of reinforcements at the shoulder, more numerous than in the center of the tire, where the coupling with the stiffening layer 8 already plays this role. Finally, let us quote another way which consists in that the shrinking layer on the shoulders is prestressed, either because it was placed on a manufacturing drum at a shallower radius at 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 dimension 295 / 30R20. The reference tire is a MICHELIN Pilot Super Sport 3 tire. The test tires are all derived from the MICHELIN Pilot Super Sport 3 tire for the non-specific elements of the present invention and for which there is no indication below. The tests were conducted with a PORSCHE 997 carrera 2S at the Charade circuit (Clermont-Ferrand, France). The chronometric results indicated relate to the time required to go around the indicated circuit, starting cold tires. The corrugated stiffening layer used here is composed of metal cables 4.23 with a pitch of 1 mm, waviness amplitude 6mm and period 15mm. The tablecloth width is 240mm.

The table above shows in each case the lap time with and without the corrugated stiffening layer. The reference tire achieves lap time in 2 minutes 12 seconds. The difference is considered significant on this test when a gain of 0.3 seconds is reached.

2017PAT00132WO

Claims

A tire (1) comprising an apex (2) comprising a waist reinforcement having an axial width W, said belt reinforcement comprising belt plies (62, 63) formed by metal cables arranged parallel to one another, forming a 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 (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,

^■ 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,

characterized in that said reinforcing wire elements (80) form undulations around said average direction.

2. The tire (1) according to claim 1, wherein said corrugations are arranged in the plane of the stiffening layer.

3. A tire according to claim 1 or 2, wherein said corrugations have an amplitude (A) and a pitch (P) such that ratio P / A ² is greater than 0.3 mm ^-1 .

4. A tire according to one of claims 1 to 3, wherein said stiffening layer is disposed radially outside the belt frame and axially in 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.

5. A tire according to one of claims 1 to 4, wherein the material constituting the tread (5) has 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.

6. A tire according to one of claims 1 to 5, wherein the Young modulus in compression in the direction of slenderness of the wire elements of the stiffening layer (8) is greater than 1 GPa.

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7. A tire according to one of claims 1 to 6, 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.

8. A tire according to any one of claims 1 to 7, wherein the reinforcing wire elements form with the circumferential direction an angle greater than 85 °.

9. A tire according to one of claims 1 to 8 comprising a shrink layer (64) made of shrink reinforcements, said shrink reinforcements forming, with the circumferential direction an angle at most equal to 5 °.

2017PAT00132WO