Bicycle Sprocket Tooth Geometry to Prevent Chain Wear Blocking
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Solution Overview
Problem
Individual chain wheels for bicycle front crank arrangements experience material abrasion in load flanks due to the drive chain rollers, leading to potential blocking of the chain and increased wear, which can impede smooth operation over time.
Innovation Solution
The design incorporates teeth with a first and second group, featuring load flanks with geometric profiles that allow for unobstructed disengagement even under wear, including shallow load flank angles and recesses to prevent edge formation and ensure continuous chain slipping, reducing contact forces and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the load flanks of the teeth are made as steep as possible to prevent chain jumping, then the chain is secured against radial outward jumping, but material abrasion occurs in the load flanks leading to edge formation that impedes chain slipping
Solution Approach 1:
The patent changes the geometric parameters of the load flanks by introducing rounded edges at the top of the load flanks and providing relief grooves. This modifies the contact geometry between the chain rollers and tooth surfaces, transforming the steep, sharp-edged load flanks into rounded profiles that distribute contact pressure and prevent edge formation during wear.
Solution Approach 2:
The patent applies preliminary action by pre-forming rounded edges and relief grooves on the load flanks before the chain begins to wear the teeth. This preliminary geometric modification ensures that as wear occurs during operation, the rounded profiles and grooves guide the wear process to maintain smooth surfaces rather than forming blocking edges.
2Reliability
If steep load flanks are used to prevent chain jumping, then chain security is improved, but wear-induced edges block the drive chain after extended operation
Solution Approach 1:
The patent modifies the load flank geometry by rounding the top edges and adding relief grooves, changing the wear pattern from edge-forming to surface-distributing. This parameter change ensures that the teeth maintain their chain-securing function throughout the extended service life without developing blocking edges.
Solution Approach 2:
The patent converts the harmful effect of wear into a beneficial outcome by designing rounded load flank edges that, as they wear down, maintain smooth contact surfaces rather than forming sharp edges. The relief grooves similarly convert wear into a beneficial distribution pattern that prevents material buildup and edge formation.
3Object-generated harmful factors
If the load flanks are designed with shallow angles to reduce wear, then material abrasion is reduced, but the chain may jump radially outward over the teeth
Solution Approach 1:
The patent optimizes the load flank angle parameter to an intermediate value that balances chain retention and wear resistance. The rounded edges and relief grooves are added to this optimized angle to provide both secure chain engagement and reduced wear, achieving a compromise that satisfies both requirements.
Solution Approach 2:
The patent creates a composite geometric structure on the tooth surface by combining the load flank surface, rounded edges, and relief grooves into a unified profile. This composite structure integrates the chain-retaining function of the load flank with the wear-reducing functions of the rounded edges and grooves.
Data Source
AI summary
An individual chain wheel for a bicycle front crank arrangement for engaging in a drive chain includes a plurality of teeth formed on a circumference of the chain wheel and having a first and a second group of teeth. The teeth of the second group of teeth are arranged in an alternating manner between the teeth of the first group of teeth. Each tooth has a load flank via which force is transmitted between an adjacent roller of the drive chain and the respective tooth. Each tooth of the first group may also have at least one profile with an opening in the vicinity of the flank, in which a portion of an inner link plate of the drive chain, which portion protrudes beyond the roller, engages.