Composite Cord Reduces Bending Stiffness in Runflat Tires
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Solution Overview
Problem
Conventional pneumatic tire overlays face challenges in achieving optimal balance between hoop reinforcing effects and elongation properties to ensure ride comfort and handling performance, particularly in reducing belt package stiffness while maintaining performance characteristics.
Innovation Solution
A composite cord construction featuring an aramid yarn twisted helically around a nylon yarn, with specific linear density ranges and twist directions, is used in the overlay ply to reduce the gauge and bending stiffness of the belt structure, enhancing ride comfort without compromising other tire performance parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a strong cord with high modulus is used in the overlay ply to provide hoop reinforcing effects, then the reinforcing strength is improved, but the bending stiffness increases and ride comfort deteriorates
Solution Approach 1:
The patent uses a hybrid cord construction combining aramid yarns (high modulus, 70-90% of total linear density) with nylon or polyester yarns (lower modulus, 10-30% of total linear density). This composite structure provides both the hoop reinforcing strength from the aramid and the elongation properties from the nylon/polyester, reducing bending stiffness by 35% while maintaining handling performance.
Solution Approach 2:
The patent specifies precise parameter ranges: aramid yarn linear density of 200-800 dtex, nylon/polyester yarn linear density of 50-200 dtex, and cord count of 10-25 ends per cm in the overlay ply. These parameter optimizations balance the reinforcing effects with elongation properties to achieve reduced bending stiffness while maintaining ride comfort and handling characteristics.
2Ease of operation
If the overlay ply gauge is reduced to improve ride comfort, then the bending stiffness decreases and ride comfort improves, but the hoop reinforcing effects may be compromised
Solution Approach 1:
The hybrid cord construction allows the overlay ply to use lower gauge (reduced thickness) while maintaining reinforcing strength through the high-modulus aramid component. The aramid yarns provide the necessary hoop strength even at reduced ply gauge, while the lower-gauge construction inherently reduces bending stiffness to improve ride comfort.
Solution Approach 2:
The patent applies different material properties to different components of the cord: aramid yarns (70-90% linear density) provide localized high-strength reinforcement, while nylon/polyester yarns (10-30% linear density) provide localized elongation and flexibility. This local differentiation allows reduced overall ply gauge while maintaining both strength and comfort.
3Strength
If a hybrid cord with break point at 2-3% elongation is used, then the hoop reinforcing effects are optimized, but the tire cannot expand sufficiently into toroidal shape during molding and bending stiffness is excessive
Solution Approach 1:
The patent uses a hybrid cord where aramid yarns (70-90% linear density) provide the hoop reinforcing effects with a break point at 2-3% elongation, while nylon or polyester yarns (10-30% linear density) contribute elongation capacity allowing the tire to expand into toroidal shape during molding. The lower-modulus nylon/polyester components increase overall cord elongation beyond what aramid alone could provide.
Solution Approach 2:
The patent optimizes the ratio of high-modulus to lower-modulus yarns (70-90% aramid to 10-30% nylon/polyester by linear density) to adjust the break point elongation. This parameter optimization allows the cord to maintain strong hoop reinforcing effects while achieving sufficient elongation for tire molding and bending flexibility.
Data Source
AI summary
A composite cord for use in a pneumatic tire is disclosed. The cord (30) comprises one or two aramid or nylon first yarn(s) (34) twisted helically about one nylon or aramid second yarn (32). The first yarn(s) has/have a linear density in a range of from 500 dtex to 800 dtex and the second yarn has a linear density in a range of from 200 dtex to 800 dtex. Also a tire (10) comprising such a cord (30) in a ply is disclosed. Preferably, the cord (30) is used in an overlay ply (26) of a runflat tire.