Pneumatic Radial Tire Reinforcement Layer Design
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Solution Overview
Problem
Heavy-duty tires with a low aspect ratio of 60% or less face issues with fatigue break and separation at the edge portions of the circumferential-direction reinforcement layer due to high cord tension, which restricts the width of the reinforcement layer and reduces high-speed durability, and large shear strain causes separation in cross belt layers.
Innovation Solution
A pneumatic radial tire design featuring at least two cross belt layers with a circumferential-direction reinforcement layer of smaller width, where the cross belt layers are separated at the outer sides, and steel cords with different elongation at break are used, with a center portion having a lower elongation and outer portions having a higher elongation, to increase the reinforcement layer width and reduce fatigue break and shear strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the cross belt layers are laminated to be in direct contact with each other at outer sides of the circumferential-direction reinforcement layer, then the width of the circumferential-direction reinforcement layer is restricted, but the total width is restricted which reduces high-speed durability
Solution Approach 1:
The cross belt layers are segmented into different width regions: they overlap with the circumferential-direction reinforcement layer in the central region but are separated at the outer sides. This segmentation allows the reinforcement layer to extend wider without requiring continuous cross belt coverage, thereby improving high-speed durability while maintaining structural integrity.
Solution Approach 2:
Different regions of the cross belt layers have different functions: the central region provides reinforcement where it contacts the circumferential-direction reinforcement layer, while the outer regions are separated to allow the reinforcement layer to extend wider. This local differentiation optimizes both high-speed durability and structural width.
2Device complexity
If the cross belt layers are laminated to be in direct contact with each other at outer sides of the circumferential-direction reinforcement layer, then the structure is simplified, but large shear strain causes separation in cross belt layers
Solution Approach 1:
The cross belt layers are segmented into overlapping and separated regions. By separating the outer sides of the cross belt layers, the shear strain concentration at the edges is reduced, preventing cord-rubber separation while maintaining a relatively simple overall structure.
Solution Approach 2:
Instead of having the cross belt layers extend beyond the circumferential-direction reinforcement layer (which would create harmful stress concentrations), the layers are deliberately separated at the outer sides. This converts the potential harm of edge stress into a beneficial design feature that reduces shear strain and prevents separation.
3Strength
If the circumferential-direction reinforcement layer has increased width, then high-speed durability is improved, but fatigue break occurs at edge portions due to high cord tension
Solution Approach 1:
Different types of steel cords with different elongation at break are used in different regions of the circumferential-direction reinforcement layer. High-elongation cords are placed at the outer side portions where fatigue resistance is critical, while low-elongation cords are used in the center portion where strength is prioritized. This local differentiation allows the layer to be wider without suffering from edge fatigue break.
Solution Approach 2:
The circumferential-direction reinforcement layer uses a composite structure of two types of steel cords with different properties (different elongation at break). This composite approach allows optimization of each region: the center region benefits from high strength low-elongation cords, while the outer regions benefit from high-elongation cords that resist fatigue break, enabling the layer to achieve both increased width and improved fatigue resistance.
Data Source
AI summary
Provided is a pneumatic radial tire: that includes a circumferential-direction reinforcement layer having a width increased with fatigue break of the circumferential-direction reinforcement layer being suppressed at edge portions thereof; and that suppresses separation in each of cross belt layers at edge portions thereof. A pneumatic radial tire according to the present invention is a pneumatic tire including: at least two cross belt layers disposed on an outer circumferential side of a carcass layer in a tread portion; and at least one circumferential-direction reinforcement layer disposed between these cross belt layers, a width of the circumferential-direction reinforcement layer being smaller than that of each cross belt layer. The pneumatic radial tire is configured so that: the cross belt layers are separated away from each other at outer sides respectively of end positions, in a width direction, of the circumferential-direction reinforcement layer; the circumferential-direction reinforcement layer includes steel cords of two types which differ in elongation at break; and the steel cord having relatively small elongation at break is disposed in a center portion of the circumferential-direction reinforcement layer, whereas the steel cord having relatively large elongation at break is disposed in each of outer side portions of the circumferential-direction reinforcement layer.