Tire comprising a protective reinforcement

Abstract

The invention relates to a tire with a radial carcass reinforcement comprising a crown reinforcement, itself radially capped with a tread comprising at least two circumferentially continuous cutouts, the said tread being connected to two beads via two sidewalls. According to the invention, the crown reinforcement comprises at least one axially discontinuous layer consisting of at least two bands each formed of at least one multilayer laminate, the said laminate comprising at least one multiaxially stretched thermoplastic polymer film positioned between and in contact with two layers of rubber composition, and, in a meridian plane, the axial ends of each of the said bands being respectively axially on the outside of each of the axially outermost points of one same circumferentially continuous cutout.

Claims

1. A tire with radial carcass reinforcement, made up of at least one layer of metal reinforcing elements, the tire comprising: a crown reinforcement, a tread radially capping the crown reinforcement, comprising at least two circumferentially continuous cutouts, two beads connected to the tread via two sidewalls, wherein the crown reinforcement comprises at least one axially discontinuous layer consisting of at least two bands axially distant from one another, and each formed of at least one multilayer laminate, wherein the laminate comprises at least one multiaxially stretched thermoplastic polymer film positioned between, and in contact with, two layers of rubber composition, and wherein, in a meridian plane, axial ends of each of the bands are respectively axially on the outside of each of the axially outermost points of one same circumferentially continuous cutout, wherein the axial distance between an axial end of a band and the axially outermost point of the circumferentially continuous cutout axially closest to the end of the band is between 4 and 12 mm; wherein at least one band is disposed radially beneath at least one circumferentially continuous cutout; and wherein the thermoplastic polymer is a polyester, the crown reinforcement of the tire comprises at least two multilayer laminates positioned in contact with one another circumferentially to form a circumferentially continuous band, and the ends of the at least two multilayer laminates in the circumferential direction have a cutout that makes with the circumferential direction an angle substantially equivalent to that of the reinforcing elements of the crown reinforcing layer radially closest to the at least two laminates.

2. The tire according to claim 1, wherein the bands forming the axially discontinuous layer have widths of between 20 and 40 mm.

3. The tire according to claim 1, wherein the thermoplastic polymer film has, whatever direction of tension is considered, an extension modulus denoted E that is greater than 500 MPa.

4. The tire according to claim 1, wherein the thermoplastic polymer film has, whatever direction of tension is considered, a maximum tensile stress denoted max which is greater than 80 MPa.

5. The tire according to claim 1, wherein the thermoplastic polymer film has, whatever direction of tension is considered, an elongation at break denoted Ar which is greater than 40%.

6. The tire according to claim 1, wherein the thermoplastic polymer film is heat stabilized.

7. The tire according to claim 1, wherein the polyester is a polyethylene terephthalate or a polyethylene naphthalate.

8. The tire according to claim 1, wherein the thickness of the thermoplastic polymer film is between 0.05 and 1 mm.

9. The tire according to claim 1, wherein the thickness of each layer of rubber composition is between 0.05 and 2 mm.

10. The tire according to claim 1, wherein the crown reinforcement is formed of at least two working crown layers of inextensible reinforcing elements which are crossed from one layer to the other, making with the circumferential direction angles of between 10 and 45.

11. The tire according to claim 1, wherein the crown reinforcement comprises at least one layer of circumferential reinforcing elements.

12. The tire according to claim 1, wherein the crown reinforcement further comprises a triangulation layer formed of metal reinforcing elements that make with the circumferential direction angles of greater than 60.

Description

(1) Other advantageous details and features of the invention will become apparent hereinafter from the description of some exemplary embodiments of the invention given with reference to FIGS. 1 to 4 which depict:

(2) FIG. 1 a meridian view of a diagram of a tire according to the invention,

(3) FIG. 2 a schematic depiction of a half view of the tire of FIG. 1, which is extended symmetrically about the axis XX that represents the circumferential median plane or equatorial plane,

(4) FIG. 3 a schematic depiction of a view in cross section of a laminate according to the invention,

(5) FIG. 4 a schematic depiction of the junction between two laminates.

(6) For simplicity of understanding, the figures have not been drawn to scale.

(7) In FIG. 1, the tire 1, of size 315/70 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3 around bead wires 4. The carcass reinforcement 2 is formed of a single layer of metal cords. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped by a tread 6.

(8) As illustrated in FIG. 2, the crown reinforcement 5 is formed radially from the inside outwards: of a first working layer 51 formed of non-wrapped inextensible metal cords 11.35 which are continuous over the entire width of the ply, oriented at an angle of 18, of a layer 52 of circumferential reinforcing elements formed of metal cords made of steel 2123, of bimodulus type, of a second working layer 53 formed of non-wrapped inextensible metal cords 11.35 which are continuous over the entire width of the ply, oriented at an angle of 18 and which are crossed with the metal cords of the first working layer, of an axially discontinuous layer made up of six bands 7 each formed of at least one multilayer laminate according to the invention. Just three bands have been depicted in FIG. 2 which corresponds to a half-view of the tire 1 of FIG. 1.

(9) The multilayer laminate that makes up the six bands 7 is itself made up of a multiaxially stretched thermoplastic polymer film positioned between two layers of rubber with which it is in contact.

(10) The tread comprises six grooves 8 or cutouts which are circumferentially continuous and radially superposed with the six bands 7, in accordance with the invention.

(11) Each of the bands 7 has a width of 30 mm. The width of the bands 8 is, according to the invention between 20 and 40 mm.

(12) The axially outer ends 9 and 10 of a band 7 are axially distant from the axially outermost points 11 and 12 of the grooves 8 by a distance d equal to 10 mm, and which is therefore between 4 and 12 mm according to the invention.

(13) The multilayer laminate that makes up the six bands 7 as illustrated in greater detail in FIG. 3 consists of a biaxially stretched PET film 71 of thickness e.sub.1 equal to around 0.35 mm, sandwiched between two layers 72, 73 of rubber composition of thickness e.sub.2 equal to around 0.4 mm, the laminate 9 therefore having an overall thickness (e.sub.1+2e.sub.2) of around 1.15 mm. The rubber composition used is a composition that is conventional in the calendering of metal belting plies for pneumatic tire covers based on natural rubber, carbon black, a vulcanizing system and the usual additives. Adhesion between the PET film and each layer of rubber is ensured by a glue of the RFL type which has been applied in the known way as indicated earlier.

(14) FIG. 4 very schematically illustrates the junction between two segments 7a and 7b that make up a band 7 over one revolution of the wheel, each of the segments covering a sector of around 180 in this particular instance. To make the figure easier to understand, the edges of the two segments have been offset slightly. After curing, the ends of the segments 7a and 7b remain radially superposed over a length l of 5 mm measured in the circumferential direction CC.

(15) According to the invention, the end of the segments 7a and 7b is oriented at an angle equal to 18 with respect to the circumferential direction CC that is identical to the angle formed by the reinforcing elements of the working layer 53 with respect to the circumferential direction.

(16) The multiaxially stretched thermoplastic polymer film has, whatever direction of tension is considered, the following mechanical properties: an extension modulus E higher than 500 MPa; a maximum tensile stress .sub.max higher than 100 MPa; a plastic deformation threshold Yp of between 5 and 10%; an elongation at break denoted Ar greater than 50%.

(17) The quality of the protection conferred by the multilayer laminate can be assessed in what is known as a penetration test which involves measuring the resistance to penetration by a penetration probe. The principle behind this test is well known and described for example in standard ASTM F1306-90.

(18) During comparative penetration tests the following were tested: on the one hand, a multilayer laminate as described hereinabove; and on the other hand, for comparison, a layer of reinforcing elements usually used as a protective layer in heavy goods vehicle tires. It is made up of metal reinforcing elements laid parallel to one another in a plane, at a laying spacing of around 2.5 mm. The reinforcing elements are coated in two layers of calendering rubber to form on the back of the cords a thickness equal to e.sub.2, namely around 0.4 mm.

(19) The reinforcing elements of this layer habitually used as a protective layer are multistrand ropes of so-called 60.35 or 320.35 construction, which means to say ropes each made up of three strands of two threads of diameter 0.35 mm, assembled with one another by cabling to form elastic metal cords. The overall diameter (or envelope diameter) of these cords is around 1.4 mm which means that the final metal fabric has an overall thickness of around 2.2 mm.

(20) The metal penetration probe used is of cylindrical shape (diameter 4.50.05 mm), conical at its end (cone angle of 302) and truncated to a diameter of 1 mm. The composite test specimen tested (multilayer laminate according to the invention or control metal fabric) was fixed to a metal support 18 mm thick which was pierced, in line with the penetration probe, with a hole of diameter 12.7 mm in order to allow the penetration probe to pass freely through the perforated test specimen and its backing plate.

(21) In order to characterize resistance to penetration, the force-displacement curve of the above penetration probe (fitted with sensors connected to the tensile test machine) passing through the test specimen at a velocity of 10 cm/min was recorded.

(22) The table below provides detail of the measurements recorded, the base 100 being adopted for the control composite: the bending modulus represents the initial gradient of the force-displacement curve; the penetration force is the maximum force recorded before the tip of the penetration probe penetrated the test specimen; the elongation at penetration is the relative elongation recorded at the instant of penetration.

(23) TABLE-US-00001 Thickness Bending Force at Elongation at (mm) modulus penetration penetration Control 2.20 100 100 100 Invention 1.15 93 92 103

(24) From studying this table it will be noted that the multilayer laminate according to the invention, despite having a thickness reduced practically by half by comparison with the control solution and despite the absence of reinforcing threads, has a resistance to penetration that is almost equivalent to that of the conventional metal fabric.

(25) Running tests were carried out on tires produced according to the invention as depicted in the figures, and others using so-called reference tires.

(26) The reference tires differ from the tires according to the invention through the presence of a protective layer as described hereinabove in place of the axially discontinuous layer consisting of six bands 7 each formed of at least one multilayer laminate.

(27) Drum running endurance tests were carried out on a test machine that imposed a load of 4415 daN and a speed of 40 km/h on the tires. The tests were carried out on the tires according to the invention under conditions identical to those applied to the reference tires. Running was stopped as soon as the tires began to show degradation.

(28) The tests thus carried out showed that the distances covered in each of these tests are substantially the same for the tires according to the invention and for the reference tires; the distances covered are of the order of 250 000 km.

(29) Moreover, for the size considered during the testing, the mass of the laminate is approximately twelve times lighter than that of a protective layer and leads to a saving of around 3.5% on the mass of the tire.

(30) Likewise, the cost of the laminate is at least three times less expensive than that of the layer of reinforcing elements and leads to a saving of around 3% on the cost price of the tire.