Rear Sprocket Spline Layout for Small-Diameter Torque Transfer
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Solution Overview
Problem
Human-powered vehicle rear sprockets with small outer diameters face challenges in torque transmission strength and smooth shifting operations due to limitations in spline tooth design and chain engagement.
Innovation Solution
The rear sprocket design features a larger maximum spline distance than radial tooth-bottom distance, with spline teeth positioned radially inward from sprocket teeth, and an annular base for improved spline tooth arrangement, allowing for enhanced strength and reduced interference with the drive chain, while specific tooth configurations facilitate smooth shifting operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the sprocket has a small outer diameter, then the vehicle size is reduced, but the strength of the torque-transmitting part deteriorates
Solution Approach 1:
The patent introduces spline teeth that extend in the axial direction (perpendicular to the radial plane of sprocket teeth), creating a three-dimensional torque transmission structure. This allows torque to be transmitted through both radial sprocket teeth and axial spline teeth, effectively increasing the torque transmission capacity without increasing the sprocket's outer diameter.
Solution Approach 2:
The spline teeth are positioned within the radial space defined by the sprocket teeth, with spline crests located radially inward from the tooth outlines. This nested arrangement allows both sprocket teeth and spline teeth to coexist in a compact configuration, maximizing space utilization while maintaining small outer diameter.
2Strength
If the maximum spline distance is increased to improve torque transmission, then the strength of spline teeth is improved, but the radial space for sprocket teeth is reduced
Solution Approach 1:
The patent resolves this contradiction by utilizing the axial dimension for spline tooth development. Instead of increasing radial distance, the spline teeth extend axially with their crests positioned radially inward from the sprocket tooth outlines. This dimensional separation allows both large maximum spline distance for strong spline teeth and adequate radial space for sprocket teeth to coexist.
3Object-affected harmful factors
If the spline teeth are positioned radially inward from sprocket teeth, then interference with drive chain is reduced, but the torque transmission path is lengthened
Solution Approach 1:
The patent addresses this by having spline teeth transmit torque in the axial direction while sprocket teeth handle radial chain engagement. The spline crest position radially inward from tooth outlines prevents chain interference, while the axial extension of spline teeth provides sufficient torque transmission capability without requiring a longer radial path.
Data Source
AI summary
A rear sprocket comprises a sprocket body, a plurality of sprocket teeth, a plurality of spline teeth, a maximum spline distance, and a radial tooth-bottom distance. Each of the plurality of spline teeth has a spline crest. The maximum spline distance is defined from the rotational center axis to the spline crest. The radial tooth-bottom distance is defined from a rotational center axis to one of plurality of tooth bottom center points. The maximum spline distance is larger than the radial tooth-bottom distance. The spline crest of each of the plurality of spline teeth is positioned radially inwardly from the tooth outline of each of the plurality of sprocket teeth in the radial direction.