Tire having specified carcass reinforcement for a two-wheeled vehicle

Abstract

A tire for a two-wheeled motorized vehicle includes a tread joined by two sidewalls to two beads, the tread having first and second elastomer compositions, crown reinforcement, radially inside tread having a crown layer having mutually parallel circumferential reinforcers forming an angle at most equal to 5° to the circumferential direction, a carcass reinforcement, radially inside crown reinforcement, having turnup. Carcass reinforcement includes mutually parallel reinforcers, and wrapped, in each bead, from the inside to the outside of the tire, about bead wire in order to form turnup having free end E.sub.2. Carcass reinforcement includes crown portion and lateral portion, crown portion extending axially between first and second ends E.sub.2, E′.sub.2, E.sub.2 and E′.sub.2 being symmetric to equatorial plane P of the tire, lateral portion extending symmetrically to equatorial plane P radially towards the inside, from radially outermost end E.sub.2 to fourth end E.sub.4 disposed at the bead wire.

Claims

1. A tire for a two-wheeled motorized vehicle of the motorcycle type, comprising: a—a tread, of half-width L, that is joined by two sidewalls to two beads, said tread comprising a first elastomer composition and a second elastomer composition, b—a crown reinforcement, radially inside the tread, comprising a crown layer comprising mutually parallel circumferential reinforcers that are coated with an elastomer composition and form an angle that is at most equal to 5° with respect to the circumferential direction, c—a carcass reinforcement, radially inside the crown reinforcement, comprising a turned-up carcass layer, wherein the turned-up carcass layer comprises mutually parallel reinforcers that are coated with an elastomer composition, and being wrapped, in each bead, from the inside to the outside of the tire, about a bead wire in order to form the turnup comprising a free end E.sub.2, wherein the turned-up carcass layer of the carcass reinforcement has a thickness M without the turnup, the turned-up carcass layer comprising a crown portion and a lateral portion, wherein the crown portion extends axially between a first end E.sub.2 and a second end E′.sub.2, E.sub.2 and E′.sub.2 being symmetric with respect to the equatorial plane P of the tire, wherein the lateral portion extends symmetrically with respect to the equatorial plane P radially towards the inside, from the radially outermost end E.sub.2 to a fourth end E.sub.4 disposed at the bead wire, wherein, in the lateral portion, the reinforcers of the radially inner carcass reinforcement form, with the circumferential direction, an angle A.sub.3 of between 55° and 70° at the end E.sub.2 increasing to an angle of between 70° and 80° at the end E.sub.4, the reinforcers of the radially outer carcass reinforcement forming an angle A.sub.4 of the same absolute value as but of opposite sign to the angle A.sub.3, wherein the carcass reinforcement comprises an elastomer composition having a modulus of rigidity MA10 at 10% elongation of between 9 and 15 MPa and a modulus of rigidity MA100 at 100% elongation of between 4 and 7 MPa, wherein the crown portion comprises a central first part that is symmetric with respect to the equatorial plane and extends from the end E.sub.1 axially outside the end E.sub.2 to said equatorial plane, said central first part comprising reinforcers that form, with the circumferential direction, an angle A.sub.1 that is constant and greater than 80°, and wherein the crown portion comprises a lateral second part which extends, symmetrically with respect to the equatorial plane, from the end E.sub.1 to the end E.sub.2, said lateral second part comprising reinforcers that form, with the circumferential direction, a first angle A.sub.2 of greater than 80° at the end E.sub.1 decreasing to a second angle of between 55° and 70° at the end E.sub.2, such that the first angle and the second angle form, between one another, a difference in angle A.sub.2 of greater than or equal to 15°, wherein a layer of uncoupling elastomer composition is disposed between and directly adjacent to the radially inner carcass reinforcement and the respective turnup from the end E.sub.1 to an end E.sub.3, the end E.sub.3 being radially inside the end E.sub.2 and radially outside the end E.sub.4, such that the end E.sub.2 is equidistant from the ends E.sub.1 and E.sub.3.

2. The tire according to claim 1, wherein said uncoupling elastomer composition has a modulus of rigidity MA10, at 10% elongation, of between 3 and 7 MPa, and a modulus of rigidity MA100, at 100% elongation, of between 1.5 and 4 MPa.

3. The tire according to claim 1, wherein the tread comprises a first part P.sub.1 and a second part P.sub.2 that are juxtaposed at a fifth end E.sub.5 common to said parts, said parts P.sub.1 and P.sub.2 being disposed symmetrically with respect to the equatorial plane, said first part P.sub.1 being central and having an axial half-width L.sub.0, between the equatorial plane P and the end E.sub.5, at least equal to 0.55L and at most equal to 0.8L, and comprising a central layer of the first elastomer composition C.sub.1, said second part being lateral and having a half-width L.sub.1 disposed between the end E.sub.5 and the axial end of the nominal section width L and equal to L-L.sub.0, and comprising a layer of the first elastomer composition C.sub.1 radially inside a layer of the second elastomer composition C.sub.2.

4. The tire according to claim 3, wherein the first elastomer composition C.sub.1 has a modulus of rigidity MA10 at 10% elongation of between 3.5 and 5 MPa and a modulus of rigidity MA100 at 100% elongation of between 1 and 1.7 MPa.

5. The tire according to claim 3, wherein the second elastomer composition C.sub.2 has a modulus of rigidity MA10 at 10% elongation of between 2.5 and 4 MPa and a modulus of rigidity MA100 at 100% elongation of between 1 and 1.3 MPa.

6. The tire according to claim 3, wherein the first elastomer composition C.sub.1 in the two parts P1 and P2 occupies between 0.65 and 0.8 times the complete volume of the tread.

7. The tire according to claim 1, wherein the layer of uncoupling elastomer composition has a thickness greater than 0.7 M.

8. The tire according to claim 1, wherein the crown portion has an axial half-width at least equal to 0.7 times and at most equal to 0.85 times the axial width of the tread half-width L.

9. The tire according to claim 1, wherein the lateral portion has a radial height H.sub.2, H.sub.2 being the radial height between the ends E.sub.2 and the radially innermost point of the ends of the beads, at least equal to 0.55 times and at most equal to 0.65 times the height of the meridian section of the tire.

10. The tire according to claim 1, wherein the reinforcers of the turned-up carcass layer are made of textile.

11. The tire according to claim 1, wherein the reinforcers of the crown reinforcement are made of textile.

12. The tire according to claim 1, wherein the reinforcers of the turned-up carcass layer are made of polyester or nylon.

13. The tire according to claim 1, wherein the reinforcers of the crown reinforcement are made of aramid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantageous details and features of the invention will become apparent below from the description of embodiments of the invention with reference to FIGS. 1 and 2 and from the following examples, wherein, in the figures:

(2) FIG. 1 shows a meridian half section of a tire, and

(3) FIG. 2 shows the graph representing the range of change of the angle formed, with the circumferential direction, by the reinforcers of the carcass layer with a turnup, along its curved abscissa comprised between the equatorial plane and the end of the turnup.

(4) In order to make them easier to understand, FIGS. 1 and 2 are not drawn to scale.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 shows a tire 1 comprising a tread 2 connected by two sidewalls 3 to two beads 4, a crown reinforcement 5, radially inside the tread 2, comprising at least one crown layer, a carcass reinforcement 6, radially inside the crown reinforcement 5, comprising at least one turned-up carcass layer 61. The turned-up carcass layer 61 comprises, at the sidewall, reinforcers that are mutually parallel and is wrapped, in each bead 4, from the inside to the outside of the tire, around a bead wire 7 to form a turn-up 8 at the bead wire 7.

(6) The crown portion 611 of the turned-up carcass layer 61 extends axially between a first and a second end E.sub.2 and E′.sub.2, (not shown) which are symmetric with respect to the equatorial plane P. The axial half-width L.sub.3 is between 0.7 and 0.85 times the axial half-width L of the tread, defined between the two axial ends of the tread surface. The crown portion 611 is thus centred with respect to the equatorial plane P of the tire, defined by the respectively circumferential X and radial Z directions.

(7) The lateral portion 612 of the turned-up carcass layer 61 extends, in the sidewall 3, radially towards the inside, from a radially outermost first end E.sub.2 to a second end E.sub.4 disposed at the bead wire 7. It also extends axially inside the turnup 8. The radial height H.sub.2 between the first and second ends E.sub.2 and E.sub.4 is between 0.55 times and 0.65 times the design section height H, measured between the point on the tread surface that is positioned in the equatorial plane and the radially innermost point of the bead 4.

(8) The turnup 8 extends radially towards the outside from the radially innermost end E.sub.4 of the lateral portion 612 as far as the free end E.sub.2 of the turnup 8.

(9) A layer of uncoupling elastomer composition C.sub.3 is disposed between the radially inner carcass reinforcement and the turnup 8 of the carcass reinforcement from the free end E.sub.1 to an end E.sub.3. This uncoupling elastomer composition has a rigidity of between 5 and 7 MPa at 10% elongation. The use of this uncoupling composition makes it possible to avoid decohesion of the radially inner carcass reinforcement and the turnup 8 of this carcass reinforcement.

(10) The tread 2 comprises a first part P.sub.1 and a second part P2 that are juxtaposed at a fifth end E.sub.5. The parts P.sub.1 and P.sub.2 are disposed symmetrically with respect to the equatorial plane P.

(11) The part P.sub.1 is central and has an axial half-width L.sub.0 comprised between the plane P and the end E.sub.5 of between 0.55L and 0.65L. This part P.sub.1 comprises a single layer C.sub.1 of elastomer composition having a modulus of rigidity MA10 at 10% elongation of between 3 and 5 MPa.

(12) The part P.sub.2 is disposed towards the axially outer ends of the tread of half-width L.sub.1. This part P.sub.2 comprises two layers C.sub.1 and C.sub.2. The radially outer first layer C.sub.1 has an elastomer composition having a modulus of rigidity MA10 at 10% elongation of between 3 and 5 MPa and a modulus of rigidity MA100 at 100% elongation of between 1 and 1.7 MPa. The radially inner second layer C.sub.2 has an elastomer composition having a modulus of rigidity MA10 at 10% elongation of between 2.5 and 4 MPa and a modulus of rigidity MA100 at 100% elongation of between 1 and 1.3 MPa.

(13) The proportion by volume of the layer C.sub.1 over the two parts P.sub.1 and P.sub.2 with respect to the complete volume of the tread 2 is between 0.65 and 0.8.

(14) FIG. 2 shows the range of change of the angle A formed, with the circumferential direction X, by the reinforcers of the turned-up carcass layer, as a function of the curved abscissa value s, comprised between the point M of the equatorial plane and the end E.sub.1 of the turnup. The curve C.sub.max is the envelope curve of maximum angle. The curve C.sub.min is the envelope curve of minimum angle. The curve C is a standard example of how the angle changes, as a function of the curved abscissa value along the turned-up carcass layer. Positive values for the angle correspond to the changes in the angle along the crown portion and the lateral portion, respectively. Negative values for the angle correspond to changes in the angle along the turn-up 8.

(15) The first portion of the range of change corresponds to that part of the crown portion 611 that is comprised between the points M and E.sub.1, for which the reinforcers form, with the circumferential direction X, a substantially constant angle A.sub.1 of between 80° and 90°.

(16) The second portion of the range of change corresponds to that part of the crown portion that is comprised between the end E.sub.1 and the end E.sub.2, for which the reinforcers form, with the circumferential direction X, an angle A.sub.2 that decreases from the end E.sub.1 to the end E.sub.2.

(17) The third portion of the range of change corresponds to the lateral portion 612 comprised between the ends E.sub.2 and E.sub.4, for which the reinforcers form, with the circumferential direction X, an angle A.sub.3 that increases, from the radially outermost first end E.sub.2 to the radially innermost end E.sub.4, from an angle at least 10° smaller than the substantially constant angle A.sub.1 formed, with the circumferential direction, by the reinforcers of the crown portion 611.

(18) The fourth portion of the range of change corresponds to the turnup 8, for which the reinforcers form, with the circumferential direction X, an angle A.sub.4, of opposite sign to the angle A.sub.3, formed by the reinforcers of the lateral portion 612. This angle A.sub.4 decreases, in terms of absolute value, from a maximum angle of between 70° and 80° at the end E.sub.4 of the lateral portion 612 until it reaches a minimum angle of between 60° and 70° at the end E.sub.2 of the turnup 8.

(19) The invention has been studied more particularly on the 180/55 ZR 17 and 190/50 ZR 17 sizes. The values derived from these sizes are set out in Table I below.

(20) TABLE-US-00001 TABLE I 180/55 ZR 17 190/50 ZR 17 H  106 mm 112.5 mm  H.sub.2 65.6 mm 67.8 mm H.sub.2/H 0.62 0.60 L.sub.0 56.2 mm 60.7 mm L.sub.1 34.8 mm 36.3 mm L.sub.2 63.9 mm 67.5 mm L.sub.3 71.5 mm 75.2 mm L   91 mm   97 mm L.sub.0/L 0.62 0.63 Thickness layer C.sub.3 0.94M 0.94M Angle A.sub.1 82° 82° Angle A.sub.3 at the end E.sub.2 64° 62° Angle A.sub.3 at the end E.sub.4 74° 74° Volume C.sub.1 1050 cm3.sup.  1133 cm3.sup.  Volume C.sub.2  432 cm3  448 cm3 Volume C.sub.1/total volume 70.85% 71.66%

(21) In this tire size under study, the reinforcers of the turned-up carcass layer are made of polyester, while the reinforcers of the circumferential crown layer are made of aramid.

(22) The cornering stiffness of this size was compared with the respective cornering stiffnesses of a first reference size R.sub.1 and a second reference size R.sub.2. The first reference size R.sub.1 comprises a carcass reinforcement, made up of a single carcass layer at 90°, and a crown reinforcement, made up of a single circumferential crown layer. The reference R.sub.1 is the reference for stability in a straight line. The second reference size R.sub.2 comprises a carcass reinforcement, made up of two crossed carcass layers at 65°, and a crown reinforcement, made up of a single circumferential crown layer. The reference R.sub.2 is the reference for stability in a curve.

(23) The results obtained are presented in Table II below:

(24) TABLE-US-00002 TABLE II Reference R.sub.1 Reference R.sub.2 Invention Cornering stiffness 100 110 100 with a zero camber angle Cornering stiffness 100 120 130 with a camber angle equal to 30°

(25) The tire size under study has levels of cornering stiffness that are at least equivalent to the best performing reference, whether riding in a straight line with a zero camber angle or in a curve with a high camber. It has a cornering stiffness that is rather low in a straight line and rather high in a curve.

(26) The invention should not be understood as being limited to the description of the examples above and extends notably to tires that can have carcass reinforcements in which no carcass layer has a turnup. The lateral portion of carcass without a turnup is then not axially inside a turnup but axially inside an independent portion of carcass layer anchored in the bead.