Linear Derailleur Spatial Linkage Path
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Solution Overview
Problem
Traditional bicycle derailleurs with 2-dimensional planar 4-bar linkages suffer from non-linear linkage paths, leading to varying angular relationships between pulley axes and the wheel axis, which results in undesirable forces, increased wear, and limited design freedom, making it difficult to achieve a compact and efficient shifting mechanism.
Innovation Solution
A linear derailleur mechanism utilizing an over-constrained spatial 6R linkage, such as a Sarrus linkage, which maintains pulley axes parallel to the wheel axis throughout its range of motion, allowing for concentric or eccentric mounting and reducing complexity and weight by ensuring a rectilinear path for the floating link.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a planar 4-bar linkage parallelogram is used in the derailleur, then the mechanism can shift the chain between cogs, but the resultant path is non-linear causing the pulley axes angle to vary relative to the wheel axis, creating undesirable forces and increased wear
Solution Approach 1:
The patent transitions from a 2D planar 4-bar linkage to a 3D spatial linkage mechanism. By introducing the vertical dimension and using skew links with axes not parallel to each other, the mechanism achieves a linear resultant path while maintaining the parallelogram's basic function. This dimensional expansion allows the pulley axes to remain parallel to the wheel axis throughout the range of motion, eliminating the angular variation problems of planar linkages.
2Adaptability or versatility
If the parallelogram linkage mounting location is constrained, then the linkage path is limited, but this leaves little freedom for frame designers and limits packaging options
Solution Approach 1:
By moving from planar to spatial configuration, the patent provides mounting freedom in three dimensions rather than being constrained to a single plane. The skew links can be mounted at various locations and orientations on the frame, allowing frame designers greater flexibility in positioning the derailleur while maintaining the desired linear path characteristics.
3Manufacturing precision
If additional complex features such as pulley wheels and extended links are added to achieve optimum linkage path and actuation ratio in a parallelogram mechanism, then the path can be optimized, but weight and complexity increase
Solution Approach 1:
The patent extracts and eliminates the need for additional complex features like pulley wheels and extended links by fundamentally changing the linkage geometry to a spatial configuration. The linear path and optimized actuation ratio are achieved through the inherent geometry of the skew links rather than through added components, thereby reducing weight while maintaining precision.
Data Source
AI summary
A derailleur system is provided that moves the derailleur cage in a substantially rectilinear path. The derailleur is mounted to a frame having a gear cassette mounted thereon. The gear cassette includes an axis of rotation. The derailleur includes a drive member engaging the gear cassette. The derailleur is positioned on the frame adjacent the gear cassette, and including a spatial linkage having a stationary link, a floating link, and a cage assembly having two pulleys each defining an axis of rotation. The drive member engages each of the pulleys. The path of the floating link is substantially linear through substantially its entire range of motion and variously aligns at least one of the pulleys with the gear cassette.