Alternating-Tooth Bicycle Chainring for Rough-Terrain Chain Retention
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Solution Overview
Problem
Managing chain engagement and tension on chainrings, especially in geared bicycles riding over rough terrain, is challenging due to severe changes in chain tension and potential frame damage from chainring contact with the chainstay.
Innovation Solution
A solitary chainring design with alternating teeth configurations, including a first group with outboard protrusions and a second group with rectangular cross-sections, and recesses to securely engage the drive chain, enhancing chain guidance and tension management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional chainring design is used, then the structure is simple, but the chain engagement is unreliable under severe tension changes and rough terrain conditions
Solution Approach 1:
The chainring teeth are divided into two distinct groups: a first group with outboard protrusions and a second group with inboard recesses. This segmentation allows each group to perform a specialized function - the protrusions engage with outer chain links while the recesses engage with inner chain links - thereby improving chain engagement reliability without requiring a completely complex new design
Solution Approach 2:
Different regions of the teeth are given different geometries to optimize local engagement characteristics. The outboard sides of first group teeth have protrusions for engaging outer chain links, while the inboard sides have recesses for engaging inner chain links. This local differentiation of tooth geometry improves chain retention under varying tension conditions
2Force
If the chainring is allowed to contact the chainstay under high load, then the frame experiences elastic deformation, but this can lead to damage to the frame and chainring
Solution Approach 1:
The alternating tooth configuration with protrusions and recesses creates a more compliant engagement interface that can accommodate frame elastic deformation under high load. The design anticipates frame flexing and provides a chainring geometry that maintains chain engagement even when the frame deforms, preventing damage by allowing controlled movement rather than rigid contact
3Device complexity
If a solitary chainring design is used, then the drivetrain is simplified, but chain tension management becomes challenging over rough terrain
Solution Approach 1:
The tooth geometry parameters are specifically designed with alternating patterns of protrusions and recesses. This parameter variation in tooth shape creates natural chain tension management by providing engagement features that accommodate the dynamic tension changes occurring during rough terrain riding, eliminating the need for additional tension management devices
Data Source
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AI summary
A solitary chainring (50) of a bicycle front crankset for engaging a drive chain, including a plurality of teeth (52) formed about a periphery of the chainring, the plurality of teeth (52) consisting of an even number. The plurality of teeth (52) includes a first group of teeth (58) and a second group of teeth (60) arranged alternatingly between the first group of teeth (58). The first group of teeth (58) and the second group of teeth (60) are equal in number. Each of the first and second group of teeth include an outboard side (54) and an inboard side (56) opposite the outboard side (54) and each tooth of the first group of teeth (58) includes at least a first protrusion on the outboard side (54) thereof and each tooth of the second group of teeth (60) are free of the first protrusions on the outboard side (54) and the inboard side (56).