Variable Stiffness Spoke for Non-Pneumatic Tires
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Solution Overview
Problem
Existing non-pneumatic deformable structures lack a method to effectively control vertical stiffness and manage stress distribution, particularly in varying load applications, as they rely on adjusting mechanical properties and dimensions of the outer band, which affects contact pressure and is not efficient in achieving desired levels of initial vertical load versus deflection stiffness.
Innovation Solution
Varying the spoke excess length and employing a recurved spoke profile with three primary curvatures, two convex and one concave, to control vertical stiffness and reduce stress concentration, allowing for adjustable initial and final stiffness levels while minimizing excess length and peak stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high initial vertical stiffness is used to limit static vertical deflection under heavy loads, then the load support capability is improved, but the ability to roll easily over obstacles when lightly loaded is worsened
Solution Approach 1:
The patent implements dynamic stiffness characteristics through the recurved spoke profile with three primary curvatures. Under heavy static loads, the spoke geometry provides high stiffness to limit deflection. Under light loads and dynamic conditions like rolling over obstacles, the same geometry allows greater flexibility and easier deformation, enabling easy rolling without requiring separate structures for different load conditions.
Solution Approach 2:
The patent uses a recurved spoke profile with three primary curvatures (two convex and one concave) instead of straight or simple curved spokes. This complex curvature geometry creates non-linear stiffness characteristics that adapt to different load magnitudes, providing high stiffness when needed and flexibility when appropriate.
2Loss of substance
If the spoke excess length is minimized to reduce material usage, then the manufacturing cost is reduced, but the stress concentration in the spoke elements increases
Solution Approach 1:
The patent optimizes the spoke excess length parameter to achieve a balance between material usage and stress concentration. Rather than simply minimizing excess length, the invention identifies an optimal range that provides sufficient material to distribute stresses while avoiding excessive material consumption, thereby reducing both manufacturing cost and peak stress simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method allows for adjustable vertical stiffness and reduced stress concentration, enabling the non-pneumatic deformable structure to handle high static loads effectively while maintaining flexibility for lighter loads, and reduces peak stress by up to 36% with a more efficient design.
Implementation Method 1
employing a recurved spoke profile with three primary curvatures, two convex and one concave, to control vertical stiffness and reduce stress concentration
Implementation Method 2
each of said spoke elements has a curvilinear length greater than the length of a straight line segment extending from a point of connection of said outer end of said spoke element with the outer annular band to a point of connection of said inner end of said spoke element to the inner hub
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~5
AI summary
The invention described herein provides a non-pneumatic deformable structure having a variable stiffness spoke assembly that provides a method of adjusting the vertical stiffness. The structure comprises an outer annular band having a predetermined stiffness, a set of spoke elements having an outer end and an inner end, where the outer end is connected to the outer band, with the spoke element extending inward and having its inner end connected to a hub, the hub being configured to attach the structure to a vehicle axle or other apparatus capable of rotation about an axis. Each of the spoke elements has a curvilinear length greater than the length of a straight line segment extending from a point of connection of the outer end of the spoke element with the outer annular band to a point of connection of the inner end of the spoke element to the hub. The outer end of said spoke element is tangent to the straight line segment, and the inner end of said spoke element is tangent to the straight line segment.