Bicycle Sprocket Axial Tooth Width Variation for Shifting
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Solution Overview
Problem
Current bicycle sprockets lack efficient gear-shifting mechanisms, leading to interference issues and unintentional disengagement of the bicycle chain, particularly during upshifting and downshifting, which affects the performance and reliability of the drivetrain.
Innovation Solution
The bicycle sprocket design incorporates shifting facilitation areas with axially recessed portions and tooth-free gaps, along with chain-engaging teeth of varying widths and positions, to facilitate smooth gear changes and reduce chain disengagement, featuring a hub engagement structure for secure attachment to the bicycle hub assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sprocket design with uniform teeth width is used, then manufacturing is simple, but gear-shifting efficiency is poor and chain disengagement occurs
Solution Approach 1:
The sprocket teeth are designed with varying axial widths where different teeth have different engagement characteristics. Specifically, teeth at positions favorable for chain engagement have larger axial widths, while other teeth have smaller widths. This local differentiation optimizes chain retention at critical positions without requiring complex modifications to the entire sprocket structure.
Solution Approach 2:
The invention introduces axial width variation as an additional design dimension beyond the traditional uniform tooth geometry. By varying the axial width of teeth in the axial direction, the sprocket creates differentiated engagement zones that improve chain retention during shifting operations without adding mechanical complexity.
2Reliability
If sprocket body axial width is increased to improve chain retention, then chain disengagement is reduced, but weight increases
Solution Approach 1:
Instead of uniformly increasing the axial width of the entire sprocket body, the invention applies increased axial width only to specific teeth at positions where chain engagement is critical. This localized approach maintains chain retention reliability while minimizing the overall weight increase of the sprocket.
Solution Approach 2:
The sprocket teeth are segmented into different types based on their axial widths. Teeth at positions favorable for chain engagement have larger axial widths, while other teeth have smaller widths. This segmentation allows the sprocket to achieve reliable chain retention only where needed, rather than throughout the entire structure.
3Ease of operation
If gear-shifting mechanism is simplified, then device complexity is reduced, but shifting facilitation and precision are poor
Solution Approach 1:
The sprocket design incorporates teeth with varying axial widths at different circumferential positions to create favorable engagement conditions for chain shifting. This local differentiation in tooth geometry provides built-in shifting facilitation without requiring additional mechanical components or complex shifting mechanisms.
Solution Approach 2:
The varied tooth widths themselves serve the dual function of both chain engagement and shifting facilitation. The teeth at positions with larger axial widths automatically provide the necessary engagement characteristics for smooth shifting, making the sprocket structure self-sufficient for both functions without external assistance.
Data Source
AI summary
A bicycle sprocket has a rotational center axis. The bicycle sprocket comprises a sprocket body and a chain engagement structure. The sprocket body has an axial width defined in an axial direction parallel to the rotational center axis. The chain engagement structure is arranged on a radially outer periphery of the sprocket body. The chain engagement structure includes at least one shifting facilitation area and a plurality of chain-engaging teeth. The at least one shifting facilitation area is configured to facilitate changing gears. The plurality of chain-engaging teeth include at least two neighboring chain-engaging teeth each including a chain-engaging portion configured to engage with a bicycle chain. The chain-engaging portion has an axial chain-engaging width defined in the axial direction. The axial chain-engaging width is larger than the axial width of the sprocket body.