Composite Bicycle Front Sprocket for Cross-Chaining Stiffness
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Solution Overview
Problem
Traditional bicycle front sprockets, being flat and made from metals, suffer from low lateral stiffness, leading to inefficiencies and mechanical issues due to lateral pull from cross-chaining in bikes with multiple rear gears, and have high material waste in manufacturing.
Innovation Solution
A composite front sprocket assembly using a metallic outer assembly and a carbon fiber reinforced nylon or plastic center assembly, with a crank drive ring, that is injection molded or compression molded, providing increased stiffness and integrating with crank arms without external fastening, reducing material waste and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional metal front sprockets are used, then strength is adequate, but lateral stiffness is low leading to drive efficiency loss
Solution Approach 1:
The patent applies composite materials by combining a metal outer assembly with a carbon fiber reinforced polymer center assembly. The carbon fiber reinforcement provides high lateral stiffness to resist chain pull forces, while the metal outer assembly maintains strength and durability. This composite structure resolves the contradiction by achieving both adequate strength and high lateral stiffness that neither material could provide alone.
Solution Approach 2:
The patent applies local quality by using different materials in different regions of the sprocket. The center assembly uses carbon fiber reinforced polymer for lateral stiffness where chain pull forces are applied, while the outer assembly uses metal for strength and wear resistance where teeth engage the chain. This localized material selection optimizes each region for its specific functional requirements.
2Strength
If traditional subtractive manufacturing processes are used, then metal strength is maintained, but material waste is high
Solution Approach 1:
The patent uses composite materials formed through additive or formative processes rather than subtractive machining. The metal outer assembly and polymer center assembly can be manufactured separately and joined, or formed as an integrated composite piece, significantly reducing material waste compared to machining solid metal sprockets while maintaining the necessary strength properties.
Solution Approach 2:
The patent changes the manufacturing parameters from traditional metal machining to composite material forming processes. By transitioning to injection molding or compression molding for the polymer components and potential additive manufacturing or forging for the metal components, the process achieves high material utilization efficiency while maintaining structural integrity and strength requirements.
3Ease of manufacture
If flat plate structure is used, then manufacturing is simple, but lateral stiffness is insufficient under cross-chaining loads
Solution Approach 1:
The patent employs composite materials where the carbon fiber reinforced polymer center assembly provides exceptional lateral stiffness despite a relatively simple flat plate geometry. The carbon fiber orientation and distribution within the polymer matrix deliver high stiffness-to-weight ratio and resistance to lateral chain pull forces, achieving the required performance without complex structural features.
Solution Approach 2:
While the overall structure remains relatively flat for manufacturing simplicity, the patent incorporates curved or contoured features in the outer assembly and tooth geometry to optimize load distribution and enhance lateral stiffness. The metal outer assembly may feature curved profiles that provide structural reinforcement while maintaining ease of manufacture through forming processes.
Data Source
AI summary
Methods and apparatus for a composite bicycle front sprocket are disclosed herein. One embodiment discloses a composite bicycle front sprocket assembly having an outer assembly of a first material. The bicycle front sprocket assembly also has a center assembly of a second material. The center assembly is disposed at least partially within the outer assembly. The center assembly is irremovably coupled with the outer assembly. The center assembly is irremovably coupled with the outer assembly without an external fastening device to irremovably couple the center assembly with the outer assembly.