Crank Assembly Chain-Drop Control Protrusion
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Solution Overview
Problem
Human powered vehicle crank assemblies face issues with chain drop-off into the space between the crank arm and sprocket, leading to inefficiency and potential damage, particularly when the chain disengages from the sprocket teeth.
Innovation Solution
The crank assembly incorporates chain-drop control protrusions with through bores and chamfered portions to prevent the chain from entering the space between the crank arm and sprocket, while maintaining weight savings and ensuring rigidity, and can be adapted with additional features like threaded portions for versatility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chain-drop control protrusions are added to prevent chain from entering the space between crank arm and sprocket, then chain drop-off is prevented and reliability is improved, but device complexity increases
Solution Approach 1:
The chain-drop control protrusion is designed as a separate component that can be attached to the crank arm or sprocket, rather than integrating it into the main structure. This segmentation allows the protrusion to be added only where needed to prevent chain drop-off, without requiring redesign of the entire crank assembly, thus improving reliability while minimizing increase in device complexity
Solution Approach 2:
The chain-drop control protrusion acts as an intermediary element between the chain and the critical space between crank arm and sprocket. It physically blocks the chain from entering this space without requiring direct modification of the crank arm or sprocket structures, thereby preventing chain drop-off with minimal structural changes
2Reliability
If solid chain-drop control protrusions are used to prevent chain entry, then chain drop-off is prevented, but weight of the crank assembly increases
Solution Approach 1:
The chain-drop control protrusion incorporates a through bore, creating a porous or hollow structure instead of using solid material. This reduces the weight of the protrusion itself while maintaining its structural integrity and its ability to prevent the chain from entering the critical space, thus improving reliability without significantly increasing the weight of the moving crank assembly
Solution Approach 2:
The protrusion uses a through bore to change the density and mass parameters of the component. By creating a hollow structure with reduced material volume, the weight parameter is decreased while the functional parameter (chain drop-off prevention) is maintained through the preserved external geometry and positioning
3Reliability
If chain-drop control protrusions are added to restrict chain movement, then chain drop-off is prevented, but manufacturing complexity increases
Solution Approach 1:
The protrusion is designed as a separate attachable component with a standardized attachment interface (such as a through bore for bolting or riveting). This segmentation allows the protrusion to be manufactured independently using simple processes, and then attached to the crank arm or sprocket, avoiding complex integrated manufacturing and improving ease of manufacture while maintaining chain drop-off prevention functionality
Solution Approach 2:
The protrusion serves as an intermediary component that can be attached to existing crank arm or sprocket structures without requiring modification of the base components' manufacturing processes. This approach maintains the simplicity of manufacturing the main crank assembly parts while adding the chain-drop control function through a separate, easily manufactured element
Data Source
AI summary
A crank assembly comprises a crank arm, a front sprocket unit, and at least one chain-drop control protrusion. The at least one chain-drop control protrusion is configured to inhibit a drive chain from getting into a space provided radially inwardly from the at least one control protrusion and between the crank arm and the front sprocket unit in the axial direction. The at least one chain-drop control protrusion is configured to be provided to at least one of an axially inwardly facing crank-surface of the crank arm and an axially outwardly facing sprocket-surface of the front sprocket unit. The at least one chain-drop control protrusion has a through bore.