Bicycle Rear Cogset Assembly for Balanced Torque and Rigidity
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Solution Overview
Problem
Modern bicycle gear systems with a large number of sprockets face stress inhomogeneity and risk of deformation due to overhanging cogsets, leading to irregular operation and structural yielding.
Innovation Solution
A sub-assembly for a bicycle rear wheel with a sprocket-carrying body and cogset mounted coaxially through a coupling profile, where specific adimensional indices (P1, P2, and K) are calculated to optimize torque transmission and rigidity, allowing for a larger number of sprockets without compromising structural solidity, with preferred values of K between 2 and 4, Ls between 25 and 34 mm, Sest between 7 and 8 mm, and Sest/Sint between 2 and 4.5.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the cogset has a greater axial extension with respect to the sprocket-carrying body (overhanging configuration), then the number of sprockets can be increased, but the stress distribution becomes inhomogeneous and structural yielding may occur
Solution Approach 1:
The patent applies parameter changes by optimizing the adimensional indices P1, P2, and K that characterize the geometric relationships between the coupling profile and cogset. Specifically, it defines P1 = Ls/Lc (coupling profile length to sprocket-carrying body length ratio), P2 = Lc/Lp (sprocket-carrying body length to cogset length ratio), and K = P1×P2. By constraining these parameters within specific ranges (P1 ≥ 0.3, P2 ≥ 0.7, K between 2-4), the patent achieves both increased sprocket count and maintained structural integrity, resolving the contradiction between quantity and strength.
2Strength
If the coupling profile axial length Ls is increased to improve torque transmission, then the axial space available for sprockets is reduced
Solution Approach 1:
The patent resolves this contradiction through parameter optimization by establishing that Ls should be between 25-34 mm, which corresponds to P1 = Ls/Lc being at least 0.3. This parameter range ensures sufficient torque transmission capability while maintaining adequate axial space for the cogset. The balanced design achieves both objectives simultaneously rather than prioritizing one at the expense of the other.
3Quantity of substance
If the sprocket-carrying body length Lc is increased to accommodate more sprockets, then the device complexity and axial space requirements increase
Solution Approach 1:
The patent optimizes Lc to be between 31-40 mm (with P2 = Lc/Lp between 0.7-1.0) to accommodate increased sprocket quantities while controlling device complexity. By setting K = P1×P2 between 2-4, the patent achieves a balanced configuration that accommodates more sprockets without excessive axial space requirements, resolving the contradiction between quantity and complexity.
Data Source
Figure 1
Figure 2
AI summary
This sub-assembly for a bicycle rear wheel, formed by a sprocket-carrying body (14) and a cogset (20) mounted coaxially on the sprocket-carrying body (14) through shape engagement, is sized so as to respect the condition: K=P1*P2 wherein P1 = Ls / Lp and P2 = Lc / (Sint + Sest). In this way, a good compromise is obtained between the ability to house a relatively large number of sprockets and the structural solidity of the sub-assembly.