Coaxial Rear Derailleur Assembly for Frame-Independent Shifting
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Solution Overview
Problem
Conventional rear derailleurs face issues with positioning accuracy due to frame tolerances, instability, and susceptibility to unintended shifting, particularly with increasing sprocket counts and lever forces, exacerbated by non-coaxial mounting and slant parallelogram mechanisms.
Innovation Solution
A rear derailleur design for coaxial mounting on the rear wheel axle, featuring a base element with two axially spaced arms for stable alignment, a straight parallelogram four-bar linkage, and a hub guide for precise assembly, eliminating frame referencing and incorporating an adapter for secure attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a separate derailleur hanger is used to attach the derailleur to the frame, then the derailleur can be mounted independently of the frame, but the additional component introduces tolerances that negatively impact positioning accuracy and the hanger is prone to damage under increased leverage forces
Solution Approach 1:
The patent removes the separate derailleur hanger component entirely, integrating the mounting function directly into the frame structure. The derailleur base element is mounted coaxially to the rear axle through the frame dropout, eliminating the intermediate hanger that introduced tolerances and vulnerability to damage.
Solution Approach 2:
The mounting function previously separated in the derailleur hanger is merged with the frame dropout structure. The base element connects directly to the frame through the dropout, combining the mounting and positioning functions into a single integrated arrangement that reduces component count and tolerance accumulation.
2Quantity of substance
If the derailleur dimensions are increased to accommodate large sprocket clusters, then more sprockets can be accommodated, but increased leverage forces occur that a replaceable derailleur hanger cannot adequately absorb
Solution Approach 1:
The patent establishes a rigid, damage-resistant mounting structure from the beginning that can handle increased leverage forces. The coaxial mounting through the frame dropout creates a stable foundation that prevents the base element from bending or breaking under the higher forces generated by large sprocket clusters.
Solution Approach 2:
The frame dropout acts as an intermediary structure that transfers the increased leverage forces from the derailleur directly to the frame. This rigid connection path allows the frame to absorb the forces rather than the replaceable hanger, enabling the use of larger sprocket clusters.
3Device complexity
If conventional derailleurs are directly attached to the frame and referenced to it, then the mounting is simplified, but manufacturing tolerances of the frame directly affect the derailleur positioning accuracy
Solution Approach 1:
The rear axle serves as an intermediary reference that is more stable and precise than the frame. By mounting the base element coaxially to the rear axle through the dropout, the system uses the axle's precise positioning to establish the derailleur's location, reducing sensitivity to frame manufacturing tolerances.
Solution Approach 2:
The patent changes the reference dimension from frame-based (lateral attachment) to axle-based (coaxial mounting). This dimensional shift allows the derailleur position to be defined by the rear axle's precise location rather than the frame's less precise mounting surfaces.
4Manufacturing precision
If an angled pivoting mechanism (slant parallelogram) is used in coaxially mounted derailleurs, then the derailleur can be mounted coaxially, but vertical impacts can cause movement of the pivoting mechanism and lead to unintended shifting
Solution Approach 1:
The patent uses an asymmetric, non-parallelogram linkage mechanism where the inner and outer linkage arms have different lengths and pivot at different angles. This asymmetric design prevents the mechanism from moving vertically under impact, as the unequal arm configurations create different mechanical responses to vertical forces, eliminating the ghost shifting problem.
Solution Approach 2:
The patent changes the geometric parameters of the linkage mechanism from a symmetric parallelogram with equal arm lengths to an asymmetric configuration with different arm lengths and pivot angles. This parameter change fundamentally alters the mechanism's response to vertical impacts, preventing unintended shifting while maintaining coaxial mounting.
Data Source
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AI summary
The invention relates to a rear derailleur for coaxial mounting on a rear wheel axle. The derailleur comprises a base element, a pivoting mechanism, a movable element, and a chain guide assembly. The pivoting mechanism connects the base element to the movable element. The chain guide assembly is rotatably connected to the movable element about a pivot axis. The base element includes a first connecting end, which can be mounted coaxially with the rear wheel axle, and a second connecting end for coupling with the pivoting mechanism.