Coaxial Rear Gearshift Mechanism for Accurate Sprocket Alignment
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Solution Overview
Problem
Existing rear gearshift mechanisms face issues with positioning accuracy due to varying derailleur hangers, increased lever forces, susceptibility to damage, and incorrect gearshifts, particularly with large sprocket assemblies and oblique parallelograms, which are complicated to set and prone to undesired gearshifts.
Innovation Solution
A rear gearshift mechanism with a base element having two spaced-apart arms for coaxial installation, a linkage mechanism with orthogonal pivot axles, and a chain guide arrangement, which stabilizes the mechanism parallel to the sprocket plane, reduces tilting, and is independent of frame tolerances, using an adapter for secure fastening and orthogonal pivot axles to prevent undesired gearshifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a separate derailleur hanger is used to fasten the gearshift mechanism, then the mechanism can be installed on the frame, but positioning accuracy deteriorates due to varying hanger positions and additional tolerances
Solution Approach 1:
The invention removes the separate derailleur hanger component entirely and integrates the fastening function directly into the base element of the gearshift mechanism. The base element now includes an axle opening that receives the rear-wheel axle directly, eliminating the intermediate hanger component that caused positioning variations and tolerance accumulation.
Solution Approach 2:
The fastening function previously performed by the separate derailleur hanger is merged into the base element itself. The base element now serves both as the structural foundation for the gearshift mechanism and as the mounting interface that directly attaches to the rear-wheel axle, consolidating multiple functions into a single component.
2Adaptability or versatility
If exchangeable derailleur hangers are used, then adaptability to different frames is improved, but stability deteriorates due to susceptibility to damage and inadequate accommodation of lever forces
Solution Approach 1:
The base element is pre-designed with an integrated axle opening and fastening structure that is optimized from the outset to accommodate the rear-wheel axle directly. This preliminary integration ensures that the fastening structure is inherently stable and capable of withstanding lever forces without requiring separate, potentially fragile hanger components.
3Ease of operation
If the gearshift mechanism is fastened to the frame, then installation is enabled, but positioning accuracy worsens due to dependency on frame tolerances
Solution Approach 1:
The invention extracts the dependency on frame tolerances by changing the reference point from the frame to the rear-wheel axle. The base element's axle opening is designed to center on the rear-wheel axle directly, making the positioning independent of frame manufacturing variations and dropout alignment tolerances.
Data Source
AI summary
A bicycle gearshift mechanism has a base element, a pivot mechanism, a movable element, and a chain guide arrangement. The pivot mechanism connects the base element to the movable element. The chain guide arrangement is connected, rotatably about a rotary axle, to the movable element. The base element comprises a first attachment end, which is coaxial with respect to the rear-wheel axle or axis, and a second attachment end for coupling to the pivot mechanism.