Coaxial Electromechanical Rear Derailleur for Positioning Accuracy
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Solution Overview
Problem
Conventional rear derailleurs for bicycles suffer from instability, lack of precision, and susceptibility to ghost shifting due to varying frame tolerances and increased lever forces, especially with modern sprocket clusters having a large number of sprockets and gear ratio spreads, leading to tilting and positioning inaccuracies.
Innovation Solution
An electromechanical rear derailleur with a base member and movable member connected by a pivot mechanism, allowing coaxial mounting on the rear wheel axis, featuring a stable straight parallelogram four-bar linkage and a worm gear drive, which is securely attached to the frame without direct referencing, minimizing frame tolerances and protecting sensitive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of sprockets is increased to achieve larger gear ratio spread, then the versatility of the drivetrain is improved, but the lever forces increase causing the rear derailleur to tilt and positioning accuracy deteriorates
Solution Approach 1:
The patent transitions from conventional non-coaxial mounting to coaxial mounting of the rear derailleur on the rear wheel axis. This dimensional change in mounting configuration eliminates the tilting problem caused by increased lever forces, maintaining positioning accuracy even with large gear ratio spreads of 500% or more achieved through 11-13 sprocket clusters
Solution Approach 2:
The patent employs a composite structure combining a straight parallelogram four-bar linkage mechanism with coaxial mounting. This composite design provides both the mechanical advantage to handle increased lever forces from multiple sprockets and the positional stability required for precise chain guiding across the expanded gear range
2Adaptability or versatility
If separate derailleur hangers are used to accommodate different frame designs, then the adaptability to various frames is improved, but the positioning accuracy deteriorates due to additional tolerances
Solution Approach 1:
The patent extracts and eliminates the separate derailleur hanger component from the system. By implementing direct coaxial mounting of the rear derailleur on the rear wheel axis, the design removes the additional tolerance interface, achieving positioning accuracy independent of frame manufacturing variations while maintaining adaptability through the coaxial mounting configuration
Solution Approach 2:
The patent merges the functions of the derailleur hanger and the rear derailleur mounting into a single integrated coaxial mounting system. This consolidation eliminates the intermediate tolerance stack-up between hanger and derailleur, directly referencing the rear wheel axis for precise and consistent positioning
3Adaptability or versatility
If the dimensions of the rear derailleur are increased to accommodate more sprockets, then the adaptability to modern sprocket clusters is improved, but the stability deteriorates due to increased leverage forces
Solution Approach 1:
The patent applies coaxial mounting that repositions the rear derailleur directly on the rear wheel axis, changing the dimensional relationship between the derailleur and the sprocket cluster. This configuration creates more favorable leverage conditions that stabilize the system even as derailleur dimensions increase to accommodate 11-13 sprocket clusters with large gear ratio spreads
Solution Approach 2:
The patent employs a straight parallelogram four-bar linkage mechanism that maintains parallel motion of the chain guide relative to the sprocket cluster. This geometric configuration ensures stable chain guiding and reduces lateral forces on the derailleur body, enhancing stability despite increased size requirements for modern multi-sprocket configurations
4Ease of manufacture
If conventional non-coaxial mounting is used, then the ease of manufacture is improved, but the positioning accuracy deteriorates due to frame tolerance dependence
Solution Approach 1:
The patent implements coaxial mounting that references the rear wheel axis rather than the frame, changing the reference dimension for positioning. This approach maintains manufacturing simplicity while eliminating dependence on frame tolerances, as the rear wheel axis provides a more stable and precise reference for derailleur positioning
Data Source
AI summary
The disclosure describes an electromechanical rear derailleur for coaxial mounting on a rear wheel axis. The rear derailleur has a base member, a pivot mechanism, a movable member having a chain guiding arrangement, and an electromechanical drive for driving the pivot mechanism. The pivot mechanism connects the base member to the movable member. The chain guiding arrangement is connected to the movable member for rotation about an axis of rotation. The base member comprises a first connection end, which can be mounted coaxially with the rear wheel axis, and a second connection end for coupling with the pivot mechanism.