Civil Engineering Tire Carcass Layout for Load and Fatigue Balance
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Solution Overview
Problem
Radial tires for heavy civil engineering vehicles face limitations in load capacity and fatigue resistance due to the rigidity and manufacturing challenges of carcass reinforcement, particularly with high inflation pressures and large diameters, which affect the flexibility and endurance of the tire.
Innovation Solution
A radial tire design featuring two carcass layers with metal reinforcements of smaller diameters (0.17-0.23 mm) arranged to optimize bending behavior, with specific positioning and spacing to balance stress modes and reduce the risk of cracking, allowing for increased flexibility and improved load capacity or reduced pressure without compromising fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the diameter of carcass layer cords is increased to withstand higher inflation pressures and loads, then the load capacity and pressure resistance are improved, but the fatigue resistance deteriorates due to the increased distance from the neutral fiber
Solution Approach 1:
The carcass reinforcement is divided into two separate carcass layers instead of using a single thick layer. Each layer contains cords of optimal diameter positioned at different radial locations, allowing each layer to independently withstand stresses while maintaining fatigue resistance through proper positioning relative to the neutral fiber.
2Strength
If the inflation pressure is increased to increase the maximum load capacity, then the load bearing capability is improved, but the tire stiffness increases reducing its ability to deform and absorb impacts
Solution Approach 1:
The two carcass layers are positioned at different radial distances from the neutral fiber, with the first layer closer to the neutral fiber and the second layer farther away. This segmentation allows the tire to maintain lower inflation pressure while distributing loads across both layers, preserving flexibility for impact absorption while achieving high load capacity.
3Stress or pressure
If the diameter of unit wires in cables is increased to handle higher pressures, then the pressure resistance is improved, but the manufacturing complexity increases due to the difficulty of manufacturing cables with very large numbers of unit metal wires
Solution Approach 1:
Instead of using fewer, thicker unit wires that are difficult to manufacture, the invention uses two layers of cables with a manageable number of unit wires each. This segmentation makes the cables more manufacturable while achieving the required pressure resistance through the combined strength of both layers positioned at optimal locations.
4Ease of manufacture
If a single thick carcass layer is used to reduce manufacturing complexity, then the ease of manufacture is improved, but the flexibility and fatigue resistance deteriorate
Solution Approach 1:
The carcass reinforcement is segmented into two layers with cords of optimal, manageable diameter. This segmentation maintains manufacturing ease compared to a single thick layer, while simultaneously improving flexibility and fatigue resistance by positioning cords at optimal distances from the neutral fiber in each layer.
Data Source
Figure 1
AI summary
A radial-carcass tyre for a civil engineering vehicle comprises two tyre bead cores (2) having a radial height Ht, and a carcass reinforcement formed of two layers. The first, radially innermost layer (1), having a radial height Hdc, is anchored in each of the beads to form a main portion (11) and a turn-over (12). A second carcass layer (3) is radially external to the first layer (1). The free end (A) of the turn-over (12) is at a radial distance from the radially outermost point (21) of the tyre bead core at least equal to 1 and at most equal to 2 times Ht. From the end A of the turn-over (12) to the point B at 85% of the radial height Hdc, the distance between the carcass layers is at least equal to 2 and at most equal to 11 times the diameter of the metal reinforcements of the first carcass layer (1).