Asymmetric Bead Core Structure for Pneumatic Tire Stress Management

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Solution Overview

Problem

The existing pneumatic tire designs for light trucks face durability issues at the bead portion due to stress concentration on the carcass layer when rolling under load, particularly at the corner of the bead core, leading to potential failure and reduced durability.

Innovation Solution

The pneumatic tire incorporates a bead core with a specific structure featuring two central layers of equal metal wire circumferential portions, with upper and lower layers having one fewer portion than the central layers, dispersing stress and enhancing durability. This configuration reduces the number of turned-up carcass layers, maintaining durability while improving cost performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a two-ply carcass structure is employed with a typical bead core with a quadrangular or hexagonal cross-sectional shape, then cost is reduced, but stress concentrates at the corner portion of the bead core leading to failure of the carcass cords and reduced durability

Engineering Contradiction:

ImprovecostVSAvoiddurability of the carcass layer at the bead portion

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The bead core is designed with an asymmetric cross-sectional shape where the number of metal wire circumferential portions varies by layer. The central layers have a maximum number of circumferential portions (e.g., 6), while the upper and lower layers have one fewer portion (e.g., 5). This asymmetric configuration eliminates corner portions that concentrate stress, thereby improving durability while maintaining cost-effectiveness with a two-ply carcass structure.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

Different layers of the bead core are designed with different numbers of metal wire circumferential portions to address local stress distribution needs. The central layers have more portions to provide structural support where needed, while the upper and lower layers have fewer portions to avoid stress concentration at corners. This localized variation in structure optimizes both durability and cost performance.

Inventive Principle:

Principle #3Local quality

2Strength

If the number of metal wire circumferential portions is increased in all layers, then structural strength is improved, but stress concentration at corner portions increases leading to carcass cord failure

Engineering Contradiction:

Improvestructural strength of the bead coreVSAvoiddurability against stress concentration

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The bead core employs an asymmetric design where central layers have a maximum number of circumferential portions (providing structural strength) while upper and lower layers have one fewer portion (eliminating stress-concentrating corners). This asymmetric configuration maintains overall structural strength while preventing stress concentration that would lead to carcass cord failure.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The bead core is segmented into multiple layers with different numbers of metal wire circumferential portions. The central layers (with maximum portions) and upper/lower layers (with one fewer portion) are segmented to distribute stress appropriately, providing structural strength where needed while avoiding stress concentration in other areas.

Inventive Principle:

Principle #1Segmentation

3Reliability

If two turned up carcass layers are provided at the bead portion, then durability of the carcass layer is improved, but manufacturing cost and complexity increase

Engineering Contradiction:

Improvedurability of the carcass layer at the bead portionVSAvoidnumber of turned up carcass layers

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The asymmetric bead core design with varying numbers of metal wire circumferential portions by layer eliminates stress concentration at corner portions. This allows the use of a single turned up carcass layer instead of two, maintaining durability while reducing manufacturing complexity and cost.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The invention changes the structural parameters of the bead core (number of circumferential portions per layer) to achieve stress distribution optimization. This parameter change enables the use of fewer turned up carcass layers (one instead of two) while maintaining the required durability, thereby reducing complexity and cost.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11413909B2Pneumatic tire

Publication Date: 2022.08.16 THE YOKOHAMA RUBBER CO LTD

AI summary

A pneumatic tire includes a bead core including circumferential portions made of metal wire bundled in rows disposed at each bead portion; and a carcass layer turned up at end portions around the bead cores from a tire inner side to an outer side; the bead cores including at least two central layers centrally located in a tire radial direction, at least one upper layer outward of the central layers in the radial direction, and at least one lower layer inward of the central layers in the radial direction; a number of the circumferential portions made of metal wire in the central layers is equal to each other and a maximum value; and a number of the circumferential portions made of metal wire in the upper layer(s) and the lower layer(s) being reduced by one from the maximum value for each layer away from the central layers.