Tyre Bead Crack Control via Stiffness Gradient
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Solution Overview
Problem
Existing tire designs face challenges with increased mass and volume due to bead fillers, leading to decreased rolling efficiency, and are prone to cracks at the body ply endings, especially in 'low turn-up' tires, which reduces durability and requires complex construction methods.
Innovation Solution
A tire design using a pair of elastomeric material strips with varying stiffness, where a softer strip is adjacent to the body ply and a harder strip is wrapped around the bead bundle, creating a stiffness gradient that directs crack propagation parallel to the turn-up, increasing durability and allowing for reduced abrasion gum strip thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bead filler is used to increase bead stiffness, then the tyre mechanical durability is improved, but the mass and volume of the tyre increase, decreasing rolling efficiency
Solution Approach 1:
The bead filler is designed with non-uniform thickness, being thicker at the base of the turn-up and thinner towards the apex. This local variation in quality provides enhanced stiffness where most needed (at the bead bundle interface) while reducing overall mass compared to a uniform thickness filler.
Solution Approach 2:
The invention changes the geometric parameters of the bead filler, specifically using a thickness that varies from 2-5mm at the base to 1-3mm at the apex. This parameter optimization maintains the necessary stiffness for durability while minimizing the volume and mass of the filler material.
2Reliability
If a bead filler is used to increase bead stiffness, then the tyre mechanical durability is improved, but the volume of the tyre increases, decreasing rolling efficiency
Solution Approach 1:
The bead filler concentrates its volume where it is most structurally needed - at the base of the turn-up where the body ply is folded over the bead bundle. The thinner apex reduces unnecessary volume in regions where stiffness requirements are lower, optimizing the volume-stiffness relationship.
Solution Approach 2:
The bead filler is constructed as a composite structure combining the elastomeric material with reinforcing cords (such as steel or textile cords) arranged in specific patterns. This composite approach provides high stiffness with reduced volume compared to solid elastomeric fillers.
3Ease of manufacture
If the body ply is folded at the turn-up, then the tyre structure is formed, but cracks may form at the body ply endings, reducing tyre lifetime
Solution Approach 1:
The bead filler is positioned beforehand to cushion and protect the body ply ending at the turn-up. This pre-positioned filler absorbs and distributes the mechanical stresses that would otherwise concentrate at the folded ply, preventing crack initiation before they can occur during service.
Solution Approach 2:
The bead filler acts as an intermediary element between the rigid bead bundle and the flexible body ply. It mediates the stress transfer in the turn-up region, reducing the friction and mechanical shock between the folded ply layers, thereby preventing crack formation.
4Strength
If a traditional bead filler configuration is used, then bead stiffness is achieved, but the construction process requires pre-assembly of fillers with bead bundles, increasing complexity
Solution Approach 1:
The invention merges the bead filler application with the body ply laying operation. The filler is applied directly to the body ply in the turn-up region before the ply is folded over the bead bundle, eliminating the need for separate pre-assembly of filler-bundle units and simplifying the construction process.
Solution Approach 2:
The bead filler is designed to be self-positioning during the tyre construction process. Its placement on the body ply and its deformation during the folding operation automatically position it in the correct location and shape, eliminating the need for complex pre-assembly fixtures or operations.
Data Source
AI summary
A tyre including two toroidal bead portions housing an annular bead bundle (121); a toroidal body ply, folded, about a respective bead bundle forming a respective turn-up; two bead fillers, each in contact with a respective bead bundle and at least partly enclosed by a respective turn-up, and two elastomeric crack control members, one for each bead portion. Each crack control member extends at a body ply ending, and each crack control member is made by a couple of strips having a differentiated stiffness along their transversal section, with a lower stiffness at a first strip adjacent to the body ply ending and a higher stiffness at a second strip in contact with the respective bundle, so that the first lower stiffness strip defines a preferential propagation path for any tyre crack originating at the body ply folded ending.