Bicycle Crank Assembly Segmentation for Weight Reduction
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Solution Overview
Problem
Conventional bicycle crank assemblies with one-piece crank arms are heavy and lack sufficient rigidity when a crank axle is fixed, making it difficult to reduce weight while maintaining structural integrity.
Innovation Solution
A bicycle crank assembly design featuring a hollow crank axle with two outer shell members and supporting members that provide rigidity through press-fitting and adhesive fixation, allowing for a space between the shell members to reduce overall weight and enhance structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a one-piece crank arm structure is used, then the structure is simple and easy to manufacture, but the weight is heavy and rigidity is insufficient
Solution Approach 1:
The crank arm is divided into multiple pieces (first crank arm piece and second crank arm piece) that are connected together, allowing weight reduction while maintaining structural integrity. The segmentation enables the use of thinner, lighter materials while preserving the necessary strength through proper connection design.
2Device complexity
If a one-piece crank arm structure is used, then the structure is simple, but the rigidity at the crank axle fixing portion is insufficient
Solution Approach 1:
The crank arm is segmented into multiple pieces with dedicated connection portions that provide enhanced rigidity at the crank axle fixing location. The segmentation allows for optimized structural design where rigidity is concentrated where needed without increasing overall complexity.
Solution Approach 2:
The connection portions between crank arm pieces are designed with specific local characteristics to provide enhanced rigidity at the crank axle fixing portion. The local quality of the connection structure is optimized to ensure sufficient strength without requiring the entire crank arm to be more complex or heavy.
3Weight of moving object
If multiple piece crank arm structure is used, then the weight is reduced, but the complexity of ensuring sufficient rigidity increases
Solution Approach 1:
The crank arm is divided into multiple pieces with standardized connection portions that simplify the overall structure. The segmentation allows for modular assembly while maintaining rigidity, reducing the complexity of ensuring sufficient strength compared to a one-piece design that would require thicker, heavier sections.
Solution Approach 2:
The connection portions are designed with specific local characteristics that provide enhanced rigidity where needed. This localized approach to quality optimization allows the majority of the crank arm to be lighter while maintaining overall structural integrity, thereby reducing the complexity of weight reduction.
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 design achieves reduced weight and maintained rigidity by supporting the crank axle with external and internal mounting surfaces, ensuring the crank axle fixing portion has sufficient rigidity and allowing for efficient weight reduction.
Implementation Method 1
the first and second outer shell members are fixed to the crank axle by being fitted together with the crank axle
Implementation Method 2
A bicycle crank assembly design featuring a hollow crank axle with two outer shell members and supporting members that provide rigidity through press-fitting and adhesive fixation
Data Source
AI summary
A bicycle crank assembly is basically provided with a crank axle, a first outer shell member, a second outer shell member, a first crank axle supporting member and a second crank axle supporting member. The crank axle has an end portion with an external mounting surface and an internal mounting surface. The first and second outer shell members are arranged relative to each other with a space being formed between the first and second outer shell members. The first crank axle supporting member is disposed on the first outer shell member and supports the external mounting surface of the crank axle. The second crank axle supporting member is disposed on the first outer shell member and supports the internal mounting surface of the crank axle.