Tire with improved beads
View Patent ↗Tire having two beads each comprising an annular reinforcing structure and a carcass reinforcement which is anchored in the two beads by being wrapped around the annular reinforcing structure so as to form, in each bead, a main portion and a wrapped-around portion, wherein each bead comprises an apex situated between the main portion and the wrapped-around portion of the carcass reinforcement, and an outer strip positioned axially on the outside of the carcass reinforcement and of the apex, the apex and the outer strip being made of a rubber compound that has an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that: G″[MPa]≦0.2·G′[MPa]−0.2 MPa, the elastic and viscous moduli being measured at 23° C.; wherein the entity formed by the apex and the outer strip has a thickness E(r), the thickness E(r) varying such that, in the range of distances r comprised between 25 and 45% of the height H of the tire, the variation in thickness ∂ E ( r ) ∂ r is less than or equal to −0.25 mm/mm over at least 4% of the height H of the tire, that, in the range of distances r comprised between 15 and 35% of the height H, the variation in thickness ∂ E ( r ) ∂ r is greater than or equal to 0.20 mm/mm over at least 2% of the height H of the tire, and that, in the range of distances r comprised between 10 and 20% of the height H of the tire, the variation in thickness ∂ E ( r ) ∂ r is greater than or equal to −0.10 mm/mm and less than or equal to 0.0 mm/mm over at least 5% of the height H of the tire.
1. A tire comprising:
two beads adapted to come into contact with a mounting rim, each bead comprising at least one annular reinforcing structure;
two sidewalls extending the beads radially outwards, the two sidewalls meeting in a crown comprising a crown reinforcement surmounted by a tread;
at least one carcass reinforcement extending from the beads through the sidewalls as far as the crown, the carcass reinforcement comprising a plurality of carcass reinforcing elements and being anchored in the two beads by being wrapped around the annular reinforcing structure so as to form, within each bead, a main portion and a wrapped-around portion, each wrapped-around portion extending radially outwards as far as an end situated a radial distance DRR from the innermost point of the annular reinforcing structure of the bead, the radial distance DRR being greater than or equal to 10% of the radial height H of the tire;
wherein each bead comprises an apex, the apex being situated radially on the outside of the annular reinforcing structure and at least partially between the main portion and the wrapped-around portion of the carcass reinforcement, the apex extending radially outwards from the radially innermost point of the annular reinforcing structure of the bead as far as a radial distance DRB from said radially innermost point, the radial distance DRB being greater than or equal to 20% and less than or equal to 30% of the radial height H of the tire,
wherein each bead further comprises an outer strip positioned axially on the outside of the carcass reinforcement and of the apex, each outer strip extending radially between a radially inner end of the outer strip and a radially outer end of the outer strip, the radially inner end of the outer strip being situated at a distance DRI from the radially innermost point of the annular reinforcing structure of the bead, the radial distance DRI being less than or equal to 20% of the radial height H of the tire, the radially outer end of the outer strip being situated at a distance DRL from the radially innermost point of the annular reinforcing structure of the bead, the radial distance DRL being greater than or equal to 25% of the radial height H of the tire,
wherein the outer strip is made of a rubber compound that has an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that:
G ″[MPa]≦0.2· G ′[MPa]−0.2 MPa,
the elastic and viscous moduli being measured at 23° C.;
wherein an entity formed by the apex and the outer strip has a thickness E(r), this thickness corresponding to the length of the intersection of the direction perpendicular to the main portion of the carcass reinforcement with said entity, r denoting the distance separating intersection of the direction perpendicular to the main portion of the carcass reinforcement from the radially innermost point of the annular reinforcing structure, the thickness E(r) varying such that
(1) in the range of distances r comprised between 25% and 45% of the height H of the tire, a variation in thickness
∂
E
(
r
)
∂
r
is less than or equal to −0.25 mm/mm over at least 4% of the height H of the tire,
(2) in the range of distances r comprised between 15 and 35% of the height H of the tire, the variation in thickness
∂
E
(
r
)
∂
r
is greater than or equal to 0.20 mm/mm over at least 2% of the height H of the tire, and
(3) in the range of distances r comprised between 10 and 20% of the height H of the tire, the variation in thickness
∂
E
(
r
)
∂
r
is greater than or equal to −0.10 mm/mm and less than or equal to 0.00 mm/mm over at least 5% of the height H of the tire.
2. The tire according to claim 1 , wherein the radial distance DRR between the end of the wrapped-around portion of the carcass reinforcement and the radially innermost point of the annular reinforcing structure of the bead is less than or equal to 20% of the radial height H of the tire.
3. The tire according to claim 1 , wherein the radial distance DRL between the radially outer end of the outer strip and the radially innermost point of the annular reinforcing structure of the bead, is greater than or equal to 30% and less than or equal to 45% of the radial height H of the tire.
4. The tire according to claim 1 , wherein the apex is made of a rubber compound having an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that:
G ″[MPa]≦0.2 ·G ′[MPa]−0.2 MPa,
the elastic and viscous modulus values being measured at 23° C.
5. The tire according to claim 1 , wherein, in the range of distances r comprised between 25% and 45% of the height H of the tire, the variation in the thickness
∂
E
(
r
)
∂
r
is less than or equal to −0.3 mm/mm over at least 4% of the height H of the tire.
6. The tire according to claim 1 , wherein the portion of the tire that is axially outside the outer strip is made of a rubber compound that is different from the rubber compound of which the outer strip is made and has a thickness EE(r) varying such that a variation in thickness
∂
EE
(
r
)
∂
r
is greater than or equal to −0.20 mm/mm and less than or equal to 0.20 mm/mm for r values that are comprised between r =ri+0.20·(re−ri) and r=ri+0.85·(re−ri), where “ri” designates the r value of the radially inner end of the outer strip and “re” designates the r value of the radially outer end of the outer strip.