Tire Bead Design with Localized Rubber Moduli
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Solution Overview
Problem
High-load index passenger vehicle tires with existing designs face challenges in reducing rolling resistance while maintaining industrial robustness and cost-effectiveness, particularly due to the difficulty in preventing rubber movement during curing and the high cost of using rubber compositions with low elastic modulus for optimized apex and outer strip geometries.
Innovation Solution
A tire design featuring a single carcass reinforcement with a shortened turn-up, an apex made from a rubber composition with an elastic modulus greater than 40 MPa, and an outer strip with moduli less than or equal to 15 MPa, positioned to optimize thickness variations and reduce manufacturing costs while maintaining rolling resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If rubber compositions with low elastic modulus are used for optimized apex and outer strip geometries to reduce rolling resistance, then rolling resistance is reduced, but industrial robustness deteriorates due to difficulty in preventing rubber movement during curing
Solution Approach 1:
The patent applies different elastic modulus requirements to different parts of the bead structure: the apex uses high elastic modulus rubber (≥40 MPa) for stability during curing, while the outer strip uses low elastic modulus rubber (≤15 MPa) for rolling resistance reduction. This local differentiation allows each component to fulfill its specific function without compromising overall performance.
Solution Approach 2:
The bead structure is segmented into distinct functional zones: the apex (with high modulus rubber for structural stability) and the outer strip (with low modulus rubber for energy loss reduction). This segmentation allows independent optimization of each zone's material properties to resolve the contradiction between curing stability and rolling resistance.
2Loss of energy
If thick outer strips are used to optimize geometry for reduced rolling resistance, then rolling resistance is reduced, but manufacturing productivity deteriorates due to increased rubber movement during curing
Solution Approach 1:
The outer strip is designed with specific thickness constraints (Ep(r) ≤ 3.5 mm and gradient ≤ 0.25 mm/mm) to balance its dual role: maintaining sufficient thickness for rolling resistance optimization while limiting it enough to prevent excessive movement during curing, thereby ensuring manufacturing productivity.
3Strength
If traditional stiff apexes are used in high-load index tires, then load-bearing capacity is maintained, but rolling resistance increases
Solution Approach 1:
The apex is designed with high elastic modulus rubber (≥40 MPa) to maintain stiffness for load-bearing capacity while being positioned and dimensioned to work in conjunction with the low-modulus outer strip, achieving both strength requirements and reduced rolling resistance through material property differentiation.
Data Source
AI summary
Tire comprising two beads comprising an annular reinforcing structure, a carcass reinforcement anchored in the two beads so as to form a main portion and a wrapped-around portion, each wrapped-around portion extending radially outwards as far as an end situated at a radial distance DEC that is less than or equal to 10% of the radial height H of the tire; each bead comprising an apex made of a rubber composition having an elastic modulus greater than 40 MPa, extending radially as far as a radial distance DEE1 comprised between 10% and 15% of the height H; each bead further comprising an outer strip made of a rubber composition 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, extending at least between 20% and 25% of the height H, the apex having an axial thickness E(r) that is substantially a linear function of r, r denoting the distance with respect to the radially innermost point of the annular structure, wherein the entity formed by the apex and outer strip has a thickness ET(r) such that, in the range of distances r comprised between 25 and 45% of the height H of the tire, the variation in thickness∂ET(r)∂ris negative and has an absolute value that is greater than or equal to 0.25 mm/mm over at least 4% of the height H; and wherein said annular structure has a maximum axial width DE such that the ratioET(r)max-DEET(r)max,where ET(r)max is the maximum value of the thickness ET(r), is less than 10%.