Bicycle Crankset Crown Pin Geometry for Reliable Outer-Link Shifting
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Solution Overview
Problem
Existing bicycle crankset pins fail to prevent inner link gearshifting, leading to incomplete gear changes and chain drop issues due to their circular surface design, which allows inner links to engage with the pin, disrupting the intended outer link gearshifting mechanism.
Innovation Solution
The pin features an inclined first surface portion on its second face, angled between 60° and 70°, preventing inner link contact and ensuring only outer links engage, along with anti-rotation abutment and chain-engagement surfaces to maintain proper orientation and engagement with the chain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the pin has a circular surface design, then the pin can engage with both inner and outer links of the chain, but this causes inner link gearshifting which leads to incomplete gear changes and chain drop issues
Solution Approach 1:
The pin surface is designed with different local qualities: an inclined first surface portion (at 60°-70° to the longitudinal axis) that prevents inner link engagement, and a second surface portion that is substantially perpendicular to the longitudinal axis that allows outer link engagement. This local differentiation ensures reliable outer link gearshifting while blocking inner link interference.
Solution Approach 2:
The pin breaks the symmetry of the circular surface design by introducing an inclined surface portion at a specific angle (60°-70°) relative to the longitudinal axis. This asymmetric geometry creates directional selectivity, allowing the pin to differentiate between inner links (blocked by the inclined surface) and outer links (engaged by the perpendicular surface).
2Ease of operation
If the pin surface is perpendicular to the longitudinal axis, then outer link gearshifting is facilitated, but inner links can still contact the pin causing gearshifting attempts
Solution Approach 1:
The inclined first surface portion acts as a preliminary anti-action mechanism that prevents inner links from making contact with the pin before they can interfere with the gearshifting process. By angling this surface at 60°-70° to the longitudinal axis, the design proactively blocks inner link approach while maintaining the perpendicular second surface for normal outer link operation.
3Adaptability or versatility
If the pin allows inner link contact, then the chain can potentially engage, but this disrupts the intended outer link gearshifting mechanism
Solution Approach 1:
The pin surface is designed with different local qualities: an inclined first surface portion (at 60°-70° to the longitudinal axis) that prevents inner link engagement, and a second surface portion that is substantially perpendicular to the longitudinal axis that allows outer link engagement. This local differentiation ensures reliable outer link gearshifting while blocking inner link interference.
Data Source
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AI summary
The invention relates to a pin (110) for a crown of a bicycle crankset, the pin (110) comprising: - a mounting portion (20) extending along a longitudinal axis (X) of the pin (110) and configured to be fixed to said crown, said mounting portion (20) having a first dimension (21a) along a transversal direction (Y) perpendicular to said longitudinal axis (X); - a chain engaging portion (30) associated with said mounting portion (20) and having a second dimension (21b) greater than said first dimension (21a) along said transversal direction (Y). Said chain engaging portion (30) comprises a first face (32) facing towards said mounting portion (20) and configured to engage a plate of a link of a bicycle chain, and a second face (34) facing on the opposite way with respect to said mounting portion (20). Said second face (34) comprises at least one first surface portion (136) inclined with respect to said longitudinal axis (X) by a first angle smaller than 90°, said first angle being measured in a longitudinal section plane of the pin (110) that contains said longitudinal axis (X) and is perpendicular to said transversal direction (Y).