Motorbike tire with specified carcass and crown reinforcements

Abstract

A tire of the “bias belted” type for a motorbike comprises: a tread (2) connected by two sidewalls (3) to two beads (4). A crown reinforcement (5) is radially on the inside of the tread (2) and comprises at least one crown layer (51, 52), such a crown layer (51, 52) comprising mutually parallel reinforcers. A carcass reinforcement (6) is radially on the inside of the crown reinforcement (5) and comprises at least two carcass layers (61, 62, 63), each comprising mutually parallel reinforcers, and crossed from one carcass layer to the next. The reinforcers of each crown layer (51, 52) form, with the circumferential direction (XX′), an angle between 15° and 25° in the equatorial plane (XZ), and the reinforcers of each carcass layer (61, 62, 63) form, with the circumferential direction (XX′), an angle between 40° and 50° in the equatorial plane (XZ).

Claims

1. A motorbike tire, comprising: a tread connected by two sidewalls to two beads; a crown reinforcement radially on the inside of the tread and comprising at least one crown layer; each of said at least one crown layer comprising mutually parallel reinforcers forming, with the circumferential direction of the tire, an angle at least equal to 15° and at most equal to 25° in the equatorial plane; a carcass reinforcement radially on the inside of the crown reinforcement and comprising at least two carcass layers each connecting the two beads to one another; each carcass layer comprising mutually parallel reinforcers forming, with the circumferential direction, an angle at least equal to 40° and at most equal to 50° in the equatorial plane, and crossed from one carcass layer to the next, wherein at least two of the at least two carcass layers are turned-up carcass layers wound, in each bead, from the inside towards the outside of the tire around a bead wire to form a turnup comprising a free end, wherein a respective radially outermost turnup of the at least two turned-up carcass layers is at least partially in contact with a radially innermost crown layer of the at least one crown layer along the region of overlap between the respective axial end of the radially innermost crown layer and the respective free end of the radially outermost turnup, and wherein a curvilinear width of the region of overlap between the respective axial end of the radially innermost crown layer and the respective free end of the radially outermost turnup is at most equal to 0.6 times a curvilinear half-width of the crown layer, wherein the curvilinear half-width of the radially innermost crown layer is measured along a curvilinear abscissa of the radially innermost crown layer between the respective axial end and a middle of the said radially innermost crown layer, and wherein the free end of the respective turnup of every turned-up carcass layer is axially on the inside and radially on the outside of the respective axial end of every crown layer.

2. The tire according to claim 1, wherein said at least one crown layer has an axial width between its two axial ends in which the angle of the reinforcers thereof is constant over the entire axial width of the crown layer.

3. The tire according to claim 1, wherein the at least one crown layer is at least two crown layers of which the respective reinforcers are crossed from one crown layer to the next.

4. The tire according to claim 3, wherein the respective reinforcers of two successive crown layers are crossed from one crown layer to the next forming, with the circumferential direction angles that are equal in terms of absolute value.

5. The tire according to claim 1, wherein the reinforcers of said at least one crown layer are made of textile.

6. The tire according to claim 1, wherein the reinforcers of said at least one crown layer are made of polyester.

7. The tire according to claim 1, wherein the reinforcers of at least a first of said at least one crown layer are made of polyester and the reinforcers of at least a second of said at least one crown layer are made of aromatic polyamide.

8. The tire according to claim 1, wherein the respective radially outermost turnup is radially on the inside of the radially innermost crown layer in the region of overlap.

9. The tire according to claim 1, wherein the curvilinear width of the region of overlap is at least equal to 0.2 times the curvilinear half-width of the radially innermost crown layer.

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

11. The tire according to claim 1, wherein, the tread being made is of an elastomeric compound, wherein the elastic modulus at 10% elongation of the elastomeric compound of the tread is at least equal to 6.5 MPa and at most equal to 9 MPa at 23° C., and at least equal to 5 MPa and at most equal to 6 MPa at 100° C.

12. The tire according to claim 1, the sidewalls of the tire being made of an elastomeric compound, wherein the elastic modulus at 10% elongation of the elastomeric compound of the sidewalls is at least equal to 8 MPa at 23° C.

13. The tire according to claim 1, wherein the reinforcers of said at least one crown layer are made of aromatic polyamide or of aliphatic polyamide or of polyester.

14. The tire according to claim 1, wherein the reinforcers of each carcass layer are made of polyester or of nylon.

15. The tire according to claim 1, wherein the curvilinear width of the region of overlap is equal to 0.45 times the curvilinear half-width of the radially innermost crown layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1: a meridian section of a tire according to a first embodiment of the invention,

(3) FIG. 2: a meridian section of a tire according to a second embodiment of the invention, of “shoulder lock” type,

(4) FIG. 3: a graph indicating the change in lateral stiffness of a tire according to the invention as a function of the cornering stiffness thereof, for various angles of crown layer reinforcers and carcass layer reinforcers.

(5) FIG. 4: a graph indicating the change in lateral stiffness of a tire according to the invention as a function of the cornering stiffness thereof, in an embodiment of the “shoulder lock” type, for various values of overlap.

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

DETAILED DESCRIPTION OF THE DRAWINGS

(7) FIG. 1 depicts a meridian half-section of a tire 1 for a motorized two-wheeled vehicle of the motorbike type according to the invention, the section being taken on a meridian plane (YZ) passing through the axis of rotation of the tire of axial direction (YY′), the tire 1 being symmetric about the equatorial plane (XZ) passing through the middle of the tread 2 and perpendicular to the axis of rotation of the tire. In this meridian half-section, the tread 2 is connected by the sidewall 3 to the bead 4. The crown reinforcement 5 radially on the inside of the tread 2 comprises two crown layers (51, 52) having axial ends (F.sub.1, F.sub.2). The reinforcers of each crown layer (51, 52) form, with the circumferential direction (XX′), an angle at least equal to 15° and at most equal to 25° in the equatorial plane (XZ). The carcass reinforcement 6 radially on the inside of the crown reinforcement 5 comprises three carcass layers (61, 62, 63) of which two are turned-up carcass layers (61, 62) and one is a carcass layer (63) without a turnup. The two turned-up carcass layers (61, 62) are wound around the bead wire (7) to form respective turnups (81, 82) having free ends (E.sub.1, E.sub.2). The reinforcers of each carcass layer (61, 62, 63) form, with the circumferential direction (XX′), an angle at least equal to 40° and at most equal to 50° in the equatorial plane (XZ).

(8) FIG. 2 depicts a meridian half-section of a tire 1 for a motorized two-wheeled vehicle of the motorbike type according to the invention, in an embodiment of “shoulder lock” type. In this meridian half-section, the tread 2 is connected by the sidewall 3 to the bead 4. The crown reinforcement 5 radially on the inside of the tread 2 comprises two crown layers (51, 52) having axial ends (F.sub.1, F.sub.2). The reinforcers of each crown layer (51, 52) form, with the circumferential direction (XX′), an angle at least equal to 15° and at most equal to 25° in the equatorial plane (XZ). The carcass reinforcement 6 radially on the inside of the crown reinforcement 5 comprises two turned-up carcass layers (61, 62) wound around the bead wire 7, to form respective turnups (81, 82) having free ends (E.sub.1, E.sub.2). The turnup (81) of the turned-up carcass layer (61) axially nearest to the inside in the sidewall (3) is at least partially in contact with the crown layer (51) of curvilinear half-width (l.sub.1), along a region of overlap (91), comprised between the axial end (F.sub.1) of the crown layer (51) and the free end (E.sub.1) of the turnup (81) over a curvilinear width (a.sub.1). The ratio a.sub.1/l.sub.1 characterizes said overlap. The turnup (82) of the turned-up carcass layer (62) axially furthest towards the outside in the sidewall 3 has its free end (E.sub.2) radially on the inside of the axial end (F.sub.1) of the crown layer (51). The reinforcers of each carcass layer (61, 62) form, with the circumferential direction (XX′), an angle at least equal to 40° and at most equal to 50° in the equatorial plane (XZ).

(9) FIG. 3 is a graph indicating the change in lateral stiffness L, expressed in daN/mm, of a tire according to the invention as a function of the cornering stiffness D thereof, expressed in daN/°, for various angles A.sub.S of crown layer reinforcers. More specifically, each curve is determined for a given angle A.sub.S of crown layer reinforcers. Three curves are depicted here, these respectively corresponding to crown layer reinforcer angles A.sub.S of 15°, 22° and 28° respectively. For each crown layer reinforcer angle value A.sub.S, the lateral stiffness L and the cornering stiffness D are determined for carcass layer reinforcer angle values A.sub.C able successively to adopt values of 65°, 60°, 55°, 50°, 45°, 40°, 35° and 28°. The curves thus obtained pass through a maximum of lateral stiffness L as a function of cornering stiffness D. The inventors set themselves a minimum cornering stiffness value D.sub.min and a minimum lateral stiffness value L.sub.min order to determine the optimum value ranges for the angles A.sub.S of the crown layer reinforcers and the angles A.sub.C of the carcass layers, that allow the lateral stiffness L to be maximized for a sufficient cornering stiffness D. This graph shows that the ranges of angles A.sub.S respectively of [15°, 25°], for the crown layer reinforcers, and of angles A.sub.C of [40°, 50°], for the carcass layer reinforcers, make it possible to achieve optimum levels of lateral stiffness L and of cornering stiffness D.

(10) FIG. 4 is a graph indicating how the lateral stiffness L, expressed in daN/mm, of a tire according to the invention in an embodiment of the “shoulder lock” type changes as a function of its cornering stiffness D, expressed in daN/°, for given crown layer and carcass layer reinforcer angles. The variable parameter is the curvilinear width of overlap a.sub.1, or, more specifically, the ratio a.sub.1/l.sub.1 between the curvilinear width of overlap a.sub.1 and the curvilinear half-width l.sub.1 of the crown layer 51, as depicted in FIG. 2. The respective lateral L and cornering D stiffnesses are determined for an a.sub.1/l.sub.1 ratio that can adopt the values of 0%, 15%, 30%, 45% and 55%. The curve indicated has a maximum lateral stiffness L for an a.sub.1/l.sub.1 ratio equal to 45%.

(11) The invention has been devised more particularly for a motorbike tire of size 160/70B17. A reference tire was compared against a tire according to the invention, in an embodiment of “shoulder lock” type as depicted in FIG. 2.

(12) The reference tire comprises a carcass reinforcement with two turned-up carcass layers the polyester reinforcers of which form, with the circumferential direction, an angle of 28° in the equatorial plane. The free end of the turnup of the turned-up carcass that is axially furthest towards the inside in the sidewalls is positioned a radial distance of 50 mm, radially on the outside of the radially innermost point of the bead wire. The free end of the turnup of the turned-up carcass that is axially outermost in the sidewalls is positioned at a radial distance of 42 mm, radially on the outside of the radially innermost point of the bead wire. The crown reinforcement of the reference tire comprises two crown layers the aramid reinforcers of which form, with the circumferential direction, an angle of 28° in the equatorial plane. In this reference design, the lateral stiffness of the tire is equal to 24 daN/mm, whereas the cornering stiffness is equal to 67 daN/°.

(13) The tire according to the invention, in an embodiment of “shoulder lock” type as depicted in FIG. 2, comprises a carcass reinforcement with two turned-up carcass layers the reinforcers of which are made of polyester and form, with the circumferential direction, an angle equal to 45° in the equatorial plane. The free end of the turnup of the turned-up carcass axially furthest towards the inside in the sidewalls is positioned at a radial distance of 76 mm, radially on the outside of the radially innermost point of the bead wire. The region of overlap between this first turnup and the crown layer in contact is equal to 20 mm. The free end of the turnup of the turned-up carcass axially furthest towards the outside in the sidewalls is positioned at a radial distance of 70 mm, radially on the outside of the radially innermost point of the bead wire. There is no region of overlap between this second turnup and a crown layer. The crown reinforcement of the tire according to the invention moreover comprises two crown layers of which the aramid reinforcers form, with the circumferential direction, an angle of 22° that is constant across the axial width of the crown layer. In this design according to the invention, the lateral stiffness of the tire is equal to 27 daN/mm, namely +3 daN/mm in comparison with the reference, whereas the cornering stiffness is equal to 72 daN/°, namely +5 daN/° with respect to the reference.