Bicycle Sprocket Shift Assist Tooth Design
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Solution Overview
Problem
Existing multistage sprocket assemblies for bicycles face challenges in smooth chain shifting due to the lack of effective mechanisms to facilitate axial movement of the chain between sprockets, leading to inefficient gear changes.
Innovation Solution
The design incorporates a shift assist recess and shift assist teeth on the larger diameter sprocket, which allow the chain to deviate axially and engage properly with the outer or inner link plates, ensuring reliable shifting by positioning the chain centers on a tangent and using projecting portions to maintain pitch alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sprocket designs are used without shift assist features, then the structure remains simple, but the chain shifting process becomes difficult and unreliable
Solution Approach 1:
The sprocket tooth is segmented into multiple functional zones: a root portion with a recess for chain engagement, a projecting portion for guiding chain movement, and a trailing portion for maintaining engagement. This segmentation allows each zone to perform a specific function in the shifting process, improving reliability without requiring a completely new sprocket design
Solution Approach 2:
The projecting portion of the tooth acts as an intermediary element between the chain and the sprocket body. It guides the chain laterally during shifting and provides a transition path for the chain to move from one sprocket to another, facilitating reliable shifting while maintaining a relatively simple overall structure
2Adaptability or versatility
If the chain path is positioned far from the sprocket center, then the gear ratio range increases, but the chain shifting distance increases making shifting more difficult
Solution Approach 1:
The invention introduces lateral movement of the chain as an additional dimension to the shifting process. Instead of only moving the chain radially between sprockets, the projecting portion guides the chain to move laterally outward during the transition, creating a two-dimensional shifting path that reduces the effective shifting distance and improves ease of operation while maintaining a wide gear ratio range
3Manufacturing precision
If the chain is forced to shift directly between sprockets without assist features, then the mechanism remains simple, but misalignment and improper engagement occur
Solution Approach 1:
The root portion recess and projecting portion are positioned to perform preliminary actions during the shifting process. The recess initially engages the chain to stabilize it, and the projecting portion pre-guides the chain's lateral movement before the chain fully engages the next sprocket. This preliminary action ensures precise alignment and proper engagement without requiring complex adjustment mechanisms
Data Source
AI summary
A sprocket comprises a sprocket body and a plurality of sprocket teeth extending radially outwardly from a root portion of the sprocket body. The sprocket body has a first side surface and a second side surface, wherein a root portion side surface of the root portion defines a root portion plane at the first side surface of the sprocket body. A shift assist recess is formed in the root portion below a first sprocket tooth at the first side surface of the sprocket body, and a second sprocket tooth has a projecting portion that extends laterally outwardly from the root portion plane at the first side surface of the sprocket body.