Bicycle Chainring Tooth Profile for Low-Friction Chain Realignment
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Solution Overview
Problem
Existing bicycle chainrings with alternating wide and narrow teeth suffer from abrupt realignment, leading to increased wear and reduced pedaling efficiency due to high outer chain link side loads and friction, as the wide teeth abruptly widen from their tip to midpoint and maintain width until the root, causing rapid wear and misalignment issues.
Innovation Solution
The design features wide teeth with a maximum axial width that fills less than 80% of the link space, with a gradual transition from the tip to the root, and a second width that is at least 90% of the link width, allowing for a more gradual realignment and reduced wear by minimizing contact surface area and friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wide teeth are configured to fill at least 80% of the link space width, then chain misalignment is reduced, but chain wear and friction increase due to abrupt realignment
Solution Approach 1:
The tooth profile is designed with varying width characteristics at different locations: the upper portion (first region) has a width that fills approximately 80-95% of the link space to provide precise alignment, while the lower portion (second region) has a reduced width of 40-60% of link space to minimize friction and wear during the power transfer phase. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The tooth is segmented into distinct functional regions: a first region extending from the tooth tip to a first radial position with width optimized for alignment (80-95% of link space), and a second region from the first radial position to the root with reduced width (40-60% of link space). This segmentation allows the tooth to perform different functions at different heights, reducing both misalignment and excessive friction simultaneously.
2Reliability
If wide teeth maintain constant width from midpoint to root, then chain realignment is achieved, but wear increases due to large contact surface area
Solution Approach 1:
The tooth width is locally optimized: the first region (upper portion) maintains a width of 80-95% of link space to ensure reliable chain retention and alignment, while the second region (lower portion) reduces width to 40-60% of link space to minimize material wear. This local quality differentiation allows the tooth to provide sufficient retention where needed while reducing wear in the high-contact region.
Solution Approach 2:
The tooth profile transitions dynamically in width along its height, creating a tapered effect where the width varies radially. This dynamic width variation means the tooth presents different effective widths at different radial positions, reducing the overall contact surface area with the chain while maintaining alignment capability in the upper region where chain engagement is most critical.
3Ease of operation
If multiple tooth faces are used for chain engagement, then chain realignment capability is improved, but friction and wear increase at transition zones
Solution Approach 1:
The tooth profile creates different engagement characteristics at different heights: the upper first region provides gentle guidance with optimized width (80-95% of link space) for initial chain capture and alignment, while the lower second region with reduced width (40-60% of link space) minimizes friction during the power transfer phase. This local differentiation reduces the need for aggressive multi-face transitions.
Data Source
AI summary
A bicycle chainring may have a plurality of first teeth that fit within the narrow link spaces in a drive chain, and a plurality of second teeth that fit within the wide link spaces in a drive chain. Each second tooth may have a first width that is greater than the its tip width at a location that is between about 40% and about 60% of the tooth height and a second width that is greater than the first width and is between the first plane and the root. A first transition portion may be on a first side of the second tooth and may extends between a first edge that is at the tip and extends in an edge direction that is substantially parallel to the central plane and a second edge that is disposed at the second plane and extends in the edge direction.