Pneumatic Tire Bead Stiffness via Curved Carcass Geometry
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Solution Overview
Problem
Pneumatic tires face a challenge in reducing weight and rolling resistance while maintaining desired stiffness, as the use of small apices leads to inevitable reduction in bead stiffness, and additional apices to improve stiffness compromise the weight and rolling resistance benefits.
Innovation Solution
A pneumatic tire design featuring a carcass ply with a specific shape and configuration, including a main body portion between the tread and sidewall, a pair of turned-up portions, and rubber reinforcing layers between the carcass and clinches, which contribute to reduced weight and rolling resistance while ensuring desired stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a small apex is used to reduce weight and rolling resistance, then weight and rolling resistance are reduced, but bead stiffness is inevitably reduced
Solution Approach 1:
The invention applies local quality by creating a specific geometric configuration of the main body portion with different curvature radii in different zones. The first zone (from boundary portion to apex outer end) has a smaller curvature radius to provide stiffness, while the second zone (from apex outer end to turned-up portion end) has a larger curvature radius to reduce weight. This local differentiation allows the structure to have varying stiffness characteristics in different regions, maintaining bead stiffness where needed while reducing overall weight.
Solution Approach 2:
The invention utilizes curvature principles by defining the main body portion shape using specific curvature radii (R1 and R2). The rounded, curved geometry of the main body portion with controlled curvature radii creates an optimized structural form that balances stiffness and weight. The specific curvature configuration allows the material distribution to provide structural support while minimizing mass.
2Strength
If a second apex is provided between carcass and clinch to improve stiffness, then bead stiffness is improved, but the effect of reducing weight and rolling resistance diminishes
Solution Approach 1:
Instead of adding a second apex structure, the invention achieves stiffness enhancement through local geometric optimization of the main body portion. By controlling the curvature radius R1 in the first zone to be within a specific range (0.05H to 0.15H where H is the height from bead base line to apex outer end), the structure provides adequate stiffness support locally without requiring additional apex elements that would increase weight.
Solution Approach 2:
The invention changes the geometric parameters of the main body portion, specifically the curvature radii R1 and R2, to optimize the balance between stiffness and weight. By setting R1 within a specific range and R2 to be 0.2H to 0.4H, the structure achieves the desired mechanical properties through parameter optimization rather than through additional structural elements.
3Weight of moving object
If the main body portion has a specific shape with controlled curvature radii, then stiffness is maintained and weight is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The invention defines specific parameter ranges for the curvature radii (R1: 0.05H to 0.15H, R2: 0.2H to 0.4H) that balance manufacturing feasibility with performance requirements. These parameter ranges are optimized to be sufficiently restrictive to ensure performance but not so tight as to make manufacturing prohibitively difficult. The use of relative proportions (as fractions of H) rather than absolute values provides some flexibility in manufacturing.
Data Source
AI summary
In a tire 2, a length from a center in an axial direction of a boundary between a core 30 and an apex 32 of each bead 10 to an outer end PA of the apex 32 is not less than 10 mm and not greater than 15 mm. In a state where the tire 2 is mounted on a normal rim and an internal pressure of the tire 2 is adjusted to a normal internal pressure, a shape of a main body portion 36, of a carcass ply 34, which is located in a zone from a boundary portion between a tread 4 and each sidewall 6 to the outer end PA of each apex 32 is represented by a single circular arc, and a diameter of the circular arc is not less than 75% and not greater than 90% of a cross-sectional height of a carcass 14.