Bicycle Toothed Crown Recess Layout for Low Weight and Torque Strength
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Solution Overview
Problem
Bicycle toothed crowns for racing bicycles face a challenge in achieving lightness without compromising structural strength, particularly at areas stressed by torque from the crank arm and chain engagement, where existing designs often prioritize thickened portions over weight reduction.
Innovation Solution
Incorporating strategically placed lightening recesses on the annular body of the toothed crown, specifically at angular portions stressed by the chain during maximum pedaling efforts, while maintaining structural integrity by avoiding recesses on axially inner surfaces and optimizing tooth count and coupling portion arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thickened portions are provided on the axially outer surface of the toothed crown to reinforce structural strength at high-stress areas, then the structural strength is improved, but the weight of the toothed crown increases significantly
Solution Approach 1:
The patent applies local quality by providing thickened portions only at specific high-stress areas (coupling portions and certain tooth regions) rather than uniformly throughout the toothed crown. This allows the structure to have enhanced strength precisely where needed while maintaining lighter weight in less critical areas, resolving the contradiction between overall strength and weight reduction.
2Weight of moving object
If lightening recesses are provided on the axially inner surface of the toothed crown to reduce weight, then the weight is reduced, but the structural strength at stressed areas is compromised
Solution Approach 1:
The patent avoids providing lightening recesses on the axially inner surface at high-stress areas, instead concentrating thickened portions at these locations. This local differentiation ensures that weight reduction through lightening recesses does not compromise the structural integrity at critical stress points, while still achieving overall weight reduction in less stressed regions.
3Strength
If the axial thickness of the toothed crown is increased to improve resistance to torque stresses, then the structural strength is improved, but the weight and material usage increase
Solution Approach 1:
The patent increases axial thickness locally at coupling portions and specific tooth regions where torque stresses are highest, rather than uniformly increasing the thickness of the entire toothed crown. This targeted approach improves resistance to torque stresses at critical locations while minimizing material usage and overall weight.
Solution Approach 2:
The toothed crown is segmented into regions of different axial thicknesses, with thickened portions at high-stress areas and thinner sections elsewhere. This segmentation allows optimized material distribution that balances structural requirements with weight and material efficiency.
Data Source
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AI summary
The invention relates to a toothed crown (100) for a bicycle crankset. The toothed crown (100) comprises an annular body (101) extending about a rotation axis (O) and comprising an axially inner surface, an axially outer surface (140) and a reference plane (R) on which the rotation axis (O) lies and a longitudinal axis of a right crank arm coupled with the toothed crown (100) is intended to lie. The annular body (101) has a maximum axial thickness equal to the distance between two main planes parallel to one another and orthogonal to the reference plane (R). The maximum axial thickness is defined at at least one first angular portion (141, 142) of the annular body (101). Such an angular portion comprises a first lightening recess (181, 182) formed on said axially outer surface (140) and that extends circumferentially between two delimiting planes (K, L) passing through the rotation axis (O) and inclined with respect to the reference plane (R) by a first angle comprised between about 21° and about 27°, the extreme values being included, and by a second angle comprised between about 67° and about 73°, the extreme values being included, respectively. Said first angle and second angle are measured on said axially outer surface (140) moving angularly in the clockwise direction from the reference plane (R).