WO2018020153A1

WO2018020153A1 - Tyre with composite sub-layer

Info

Publication number: WO2018020153A1
Application number: PCT/FR2017/052081
Authority: WO
Inventors: Pascal Prost; Bertrand Daval; David Dean; Yasufumi NAKASHIMA; Sébastien RIGO
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2016-07-28
Filing date: 2017-07-26
Publication date: 2018-02-01
Also published as: FR3054486A3

Abstract

Tyre (1) having a sub-layer (7) arranged radially on the outside of the crown reinforcement (5) and radially on the inside of the tread (6), comprising filamentary reinforcers (70) embedded in a matrix (71) made of an elastomeric material, different from the tread material, the said filamentary reinforcers (70) being oriented at least in part in a direction that has a radial component.

Description

PNEUMATIC UNDERCOAT COMPOSITE

Field of the invention

The present invention relates to tires, and more particularly to a tire whose performance in terms of rolling resistance and road behavior are 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 CP is a plane perpendicular to the axis of revolution 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 equatorial plane of the tire, in the axial direction."

State of the art

As we know, tires for road applications, and especially tires for passenger vehicles, make an essential contribution to vehicle performance in terms of resistance or rolling (and therefore energy efficiency of vehicles), adhesion, dynamic response for the guidance of vehicles (especially cornering) and wear (and therefore overall cost of use of vehicles). Among the parameters of tire design, the skilled person knows the importance of the choice of the constituent material of the tread and the constituent material of the underlayer. An example of an underlayer, that is to say a layer of rubber inserted between the crown reinforcement and the tread material, is described in the document FR 2 954 333. In general, underlayment materials so as to improve the rolling resistance of the tire with a low hysteretic material or to stiffen the tread shear, but with rigidities remaining modest so as not to oppose the flattening of the tread. tread of the tire in the area of contact with the ground.

However, the lower the rigidity, the better the response drift of the tire on the steering load of the vehicle. Indeed, schematically, one can consider that the stack of rubber layers radially outside the crown reinforcement as a series of springs in series. This is why we seek despite all to avoid introducing too low module materials to not penalize drift rigidity. This may be contrary to the objective of minimizing rolling resistance. Even in the highest stiffness variants, the dynamic shear modulus G * of a sub-layer material is generally much less than 8 MPa, even when the best performance in behavior is sought. In the present specification, it should be pointed out that the dynamic shear modulus G * considered is the dynamic shear modulus G * measured at 23 ° C., and under an alternating shear stress at a frequency of 10 Hz and at 10% of deformation.

[0006] Document WO 2015/170615 also discloses a tire comprising a base layer, that is to say an underlayer, formed by two materials superimposed radially. The modulus of the tread material and the value of tg δ (tangent delta) thereof are lower than the values of the same parameters of the underlayer material in contact with the tread material, that is, that of the two outermost layers radially. The material modulus of the radially inner layer of the underlayer materials and the tg δ value thereof are lower than the values of the same parameters of the underlayer material in contact with the tread material. However, a tire made according to this teaching does not bring progress in the balance of performance.

The invention aims to provide a better dynamic response in drifting thrust on steering bias without degrading the rolling resistance of the tire. Brief description of the invention

The invention relates to a tire having an axis of rotation and a median plane perpendicular to the axis of rotation, and comprising: · a crown reinforcement,

A tread radially outside the crown reinforcement, the tread comprising a contact face intended to come into contact with the roadway during the running of the tire, the tread comprising a tread pattern comprising at least a groove delimited radially inwards by a groove bottom, the tread radially extending from said contact face to the bottom of the groove, the tread being constituted by a tread material free of reinforcement filament,

An underlayer disposed radially outwardly of the crown reinforcement and radially inwardly of the tread,

wherein the underlayer comprises filamentary reinforcements embedded in a matrix of elastomeric material, said filamentary reinforcements being oriented at least partly in a direction having a radial component.

The proposed solution is therefore to form a composite underlayer by incorporating filamentary reinforcements in a matrix formed by a rubber mixture of very low modulus. By indicating that said filamentary reinforcements are oriented at least partly in a direction having a radial component, it is intended to give them a particular function that can be summarized as follows: these reinforcements are integrated so that they are not not operative in the absence of biasing of the tire in longitudinal and / or axial force (directions generally designated X (longitudinal direction) and Y (axial direction)); that is to say, preferably they should not be stretched or at least if they are, they should not develop a significant tensile force; these reinforcements are also integrated so that they are tensioned by the shear of the underlayer and are therefore operative when the tire develops a significant longitudinal or axial force. Description of the Figures

The invention is now described with the aid of the accompanying drawing in which:

- Figure 1 shows a meridian half-section of a tire according to one embodiment of the invention;

- Figure 1a is a zoom on a specific element of the present invention, in the same state as in Figure 1;

- Figure lb is a zoom on the same element in another state;

- Figure 2 shows an alternative embodiment of the invention. Detailed description of the invention

We see in Figure 1 a tire 1 shown in an axial half of only one side of the equatorial plane CP. We see two beads 2, one of the two sides 3 connected to a bead 2. The tire has a vertex 4. The top 2 comprises a crown reinforcement 5 and a tread 6. The tread extends axially from one shoulder 60 to the other shoulder. The tread comprises a contact face 61 intended to come into contact with the roadway during the rolling of the tire. The tread is essentially the wear layer of the tire. The tread 6 generally comprises a sculpture formed by sculpting blocks 63 separated by furrows 62 oriented substantially circumferentially. Each groove 62 is bounded radially inwards by a groove bottom 620. Radially, the tread, at least the wear portion thereof, goes from the contact face 61 to the groove bottom 620 (under deduction of residual tread depth required by regulatory provisions).

The crown 4 also comprises an underlayer 7 arranged radially outwardly of the crown reinforcement 5 and radially inwardly of the tread 6. Referring to FIGS. 1a and 1b, there is seen in more detail than the sub-layer 7. -layer 7 comprises filamentary reinforcements 70 embedded in an elastomeric matrix 71. In the following, we discuss the materials used for the underlayer 7. These filamentary reinforcements 70 are non-stretched in Figure la. When a biasing F oriented in the axial direction Y appears, the filamentary reinforcements 70 are stretched as shown in FIG. 1b. It would be the same when there appears a bias oriented in the direction X, as well as for any combination of orientations along the X and Y directions. The underlayer 7 is arranged radially directly on the crown reinforcement 5. As known in itself, the crown reinforcement comprises layers of cables or monofilament reinforcements generally coated with a thin layer of rubber. In the context of this by the accuracy that the underlayer 7 is arranged radially directly on the crown reinforcement 5, it is indicated that it is in contact with the cables or reinforcements, without regard to their rubber coating.

[0013] Preferably, the material of the elastomeric matrix 71 has a dynamic shear modulus G * of less than 1.5 MPa, and preferably less than 0.5 MPa, and very advantageously, less than 0.3 MPa. Recall that for sub-layers of usual configuration, that is to say mono-material and extending axially from one shoulder to the other of the tire, the material has a dynamic shear modulus G * in general between 1.5 MPa and 2.5 MPa. Furthermore, it is preferable that the material of the matrix is weakly hysteretic, to achieve a rolling resistance of the tire as low as possible. This hysteresis is evaluated by the value of tg δ measured at 23 ° C. at 10 Hz and under an alternating shear deformation of 10%. Preferably, this value is less than 0.2 and very advantageously, the value of tg δ is of the order of 0.1. Thus, the low modulus of this material and its low tg δ can further reduce hysteretic losses due to a lower rolling resistance.

An example of a suitable formulation for the material of the matrix 71, dynamic shear modulus G * equal to 0.2 MPa is as follows:

Table 2

The formulations are given in mass (ie, percentage of the elastomer mass). As for the filamentary reinforcements 70, preferably, they are made of textile material of extension module greater than 100 MPa and more preferably greater than 1 GPa; these filamentary reinforcements 70 are glued to allow the connection with the gum. A textile reinforcement is advantageous because it generally has a low compression modulus which gives the reinforced underlayer the low rigidity sought in the situation where said reinforcements are not stretched in the absence of tire stresses. An example of glue is "RFL" glue. By way of example, it is possible to use a 3D fabric composed of aramid yarns of title 167/2 with a density of 100 threads / dm arranged less radially in the underlayer, or at least partly radially. Recall that "3D fabric" means a structure based on filament reinforcement developing in space, that is to say in 2 dimensions which are the main dimensions of a layer (or a sheet or a sheet) and in addition in a third dimension corresponding to a thickness, the latter dimension being rather small compared to the other two. An example of such 3D fabric is commercially available from the catalog of the manufacturer ASAHI KASEl, under the reference AKE64334. This is a polyesther fabric whose characteristics are given in Table 2 below:

Table 2

Reference AKE64334

Dimension Width x length x 215cm x 44m x 2.4mm

thickness

Yarn (% weight ratio) Before PET 55dtex / 18f (20%)

Nylon medium lOOdtex / lf

(60%)

Rear PET 55dtex / 18f (20%)

Weight (g / m) 400

Break Strength (N) * Length 509

Elongation rupture (%) * Length 47

Break Strength (N) * Width 190

Elongation breaking (%>) * Width 97

Toughness toughness (kPa) 784

Boulouchage (Pilling) (level) 5

Stiffness (N) 328

Residual strain in (%) 4.6

cyclic compression

Residual deformation in (%) 3,6

compression

Compression stiffness (%) 16

Compressive stress at 50% N 315

Permeability to air cc / cm ² sec 682 This polyester fabric provides the filamentary reinforcements 70; it may be impregnated in any suitable manner by the mixture constituting the elastomeric matrix 71.

As to the material of the tread, it may be of any nature but emphasize that the invention is particularly advantageous to use in combination with a tread material (that is to say the wear layer) of rigidity greater than the rigidity of the matrix of the underlayer. Advantageously, the tread matrix is used with a rubber compound whose dynamic shear modulus G * is less than 5.0 MPa and preferably less than 2.5 MPa. As a rule of good practice, the material of the matrix 71 is an elastomeric material different from the tread material.

The following table 3 gives an example of a tread formulation:

Table 3

The formulations are given in mass; "Phr" means part by weight per 100 parts of elastomer, with:

(a) SBR with 27% styrene, -1,2: 5% butadiene, cis-1,4: 15%, trans -1,4: 80% Tg -48 ° C

(b) "Zeosill l65MP" silica of the company Solvay BET surface area 160m ² / g

(c) Silane TESPT "SI69" from Evonik

(d) Shell Flexon 630 TDAE Oil

(e) Escorez 2173 Resin from Exxon Company

(f) Antioxidant "Santoflex 6PPD" from the company Solutia

(g) "Santocure CBS" accelerator from Solutia The dynamic shear modulus G * after vulcanization is 1.8 MPa.

testing

Two controls were used: a first tire RI having a tread made with a mixture whose dynamic shear modulus G * is equal to 3.0 MPa, and whose underlayer is formed by a first mixture Ml having a dynamic shear modulus G * of 2.0 MPa; a second tire R2 comprising a tread made with a mixture identical to the case of the tire R and an underlayer 7 made with a mixture M2 having a dynamic shear modulus G * of 0.2 MPa. A test tire T, according to the invention, comprises a tread made with a mixture identical to the tires R1 and R2 and an underlayer 7 made with the fabric described above, impregnated with the second mixture M2 having a dynamic modulus. shearing G * vallant 0.2 MPa. The values of rolling resistance (kg / T) and drift rigidity Dz (N / °) are brought back to base 100 for the indicators RI and R2 and expressed as a value with respect to the base 100 for the tires according to the invention. . The drift stiffness measurement of a tire makes it possible to evaluate the road behavior of a vehicle by its ability to react during a driving call or to take the path of a turn. This drift rigidity is measured on equipment and consists in rolling a tire mounted on a rim and inflated to a nominal pressure on an adhered metal strip, by means of a "Fiat Track" type machine. The measurement is made when the tire is traveling at 80 km / h with a series of stresses varying the load, drift and camber conditions. Rolling resistance can be measured in accordance with ISO28580.

Table 1

Note that the invention allows a displacement of the performance compromise between rolling resistance and rigidity drift; it allows a very significant improvement in rolling resistance (a higher figure corresponding to a lower rolling resistance) at the cost of a drop in rigidity drift quite acceptable for applications to passenger vehicles where the desired performance is mainly the comfort of driving. Note that an advantage of the invention is that one can use standard materials for treads, namely materials whose dynamic shear modulus G *, measured at 23 ° C, and under shear stress alternating at 10 Hz at 10% deformation is less than 5 MPa, and more preferably less than 2.5 MPa.

FIG. 2 represents an alternative embodiment in which the sub-layer 7 has interruptions 73, in particular under the grooves 62, where the underlayer can be considered as less useful for the behavior insofar as it does not is not facing areas of the tread touching the ground; these interruptions 73 to further improve the rolling resistance.

The skilled person, tire designer, may adopt alternative embodiments in which the tread itself comprises a plurality of different materials superimposed radially and / or juxtaposed axially.

Claims

A tire (1) having an axis of rotation and a median plane (CP) perpendicular to the axis of rotation, and comprising:

· A crown reinforcement (5),

A tread (6) radially outside the crown reinforcement (5), the tread comprising a contact face (61) intended to come into contact with the roadway during the rolling of the tire, the tread comprising a tread having at least one groove (62) delimited radially inwardly by a groove base (620), the tread radially extending from said contact face (61) to the bottom of the tread groove (620), the tread being made of a tread material free of filament reinforcement,

An underlayer (7) disposed radially outwardly of the crown reinforcement (5) and radially inwardly of the tread (6),

characterized in that the sub-layer (7) comprises filamentary reinforcements (70) embedded in a matrix (71) of elastomeric material, said filamentary reinforcements (70) being oriented at least partly in a direction having a radial component.

2. Pneumatic tire (1) according to claim 1, characterized in that the dynamic shear modulus G *, measured at 23 ° C, and under an alternating shear stress at 10 Hz at 10% of deformation, of the material of the matrix (71) is less than 1.5 MPa.

Pneumatic tire (1) according to claim 1, characterized in that the dynamic shear modulus G *, measured at 23 ° C., and under an alternating shear stress at 10 Hz at 10%> of deformation, of the material of the matrix (71) is less than 0.5 MPa.

4. A tire (1) according to claim 1, characterized in that the dynamic shear modulus G *, measured at 23 ° C, and under an alternating shear stress at 10 Hz to 10%> deformation, the material of the matrix (71) is less than 0.3 MPa.

5. Tire (1) according to one of the preceding claims, characterized in that the value of tg δ measured at 23 ° C at 10 Hz and under an alternating shear deformation of 10%> of the material of the matrix (71) is less than 0.2.

Pneumatic tire (1) according to claim 5, characterized in that the value of tg δ measured at 23 ° C at 10 Hz and under an alternating shear deformation of 10% of the material of the matrix (71) is order of 0.1.

7. Pneumatic tire (1) according to one of claims 1 to 6, characterized in that said filamentary reinforcements (70) are textile.

8. Pneumatic tire (1) according to one of claims 1 to 6, characterized in that said filamentary reinforcements (70) are polyesther.

9. Pneumatic tire (1) according to one of claims 1 to 6, characterized in that said filamentary reinforcements (70) are included in a 3D fabric.

10. Tire (1) according to one of the preceding claims, characterized in that the dynamic shear modulus G *, measured at 23 ° C, and under an alternating shear stress at 10 Hz to 10%) deformation, the tread material (6) is less than 5 MPa.