Bicycle Rear Derailleur Parallelogram Linkage for High Tooth Ratio Shifting
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Solution Overview
Problem
Existing bicycle drive arrangements face challenges in shifting the drive chain between rear sprockets with a large difference in the number of teeth, leading to issues such as chain flexing or getting stuck, due to variable free chain lengths, which are not optimal for all sprockets.
Innovation Solution
A drive arrangement utilizing a parallelogram four-bar linkage to maintain a constant free chain length between the chain guide roller and the active sprocket, achieved by adjusting the distances between the chain guide roller axes and the tensioning pivot axis, ensuring sufficient chain capacity and ground clearance, with an optimal angle range of 55° to 60° between connecting planes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the free chain length between the chain guide roller and the active sprocket is made long, then the chain can accommodate sprockets with larger diameter differences, but the chain flexes instead of transferring to adjacent sprockets during shifting
Solution Approach 1:
The patent employs a dynamic tensioning device with a parallelogram four-bar linkage that automatically adjusts the chain guide roller position along the sprocket axis based on the active sprocket's diameter. This dynamic adjustment maintains an optimal free chain length for reliable shifting while accommodating sprockets with large diameter differences, resolving the contradiction between adaptability and shifting reliability.
2Manufacturing precision
If the free chain length is made short, then shifting precision is improved, but the chain acts as a rigid body and the rear derailleur gets stuck between the chain guide roller and the sprocket
Solution Approach 1:
The dynamic tensioning device with parallelogram four-bar linkage automatically adjusts the chain guide roller position to maintain an optimal free chain length. This prevents the chain from acting as a rigid body during shifting, allowing smooth chain transfer to adjacent sprockets without the rear derailleur getting stuck, thus resolving the contradiction between shifting precision and operation smoothness.
3Adaptability or versatility
If a high tooth ratio between largest and smallest rear sprocket is used, then the drive arrangement can handle varying terrain conditions, but the shifting process becomes problematic due to large diameter differences
Solution Approach 1:
The patent uses a dynamic tensioning device with parallelogram four-bar linkage that automatically adjusts the chain guide roller position according to the active sprocket's diameter. This maintains optimal chain tension and free chain length across all sprockets, enabling reliable shifting even with a high tooth ratio (e.g., 50 teeth on largest sprocket) between largest and smallest sprockets, thus resolving the contradiction between terrain adaptability and shifting reliability.
4Ease of operation
If the chain guide roller is positioned closer to the sprocket, then shifting to larger diameter sprockets is facilitated, but the free chain length becomes too short causing rigid body behavior
Solution Approach 1:
The dynamic tensioning device with parallelogram four-bar linkage automatically adjusts the chain guide roller position along the sprocket axis based on the active sprocket's diameter. When shifting to larger sprockets, the roller positions closer to facilitate chain transfer, while the system maintains sufficient free chain length to prevent rigid body behavior, resolving the contradiction between ease of operation and chain flexibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for reliable shifting between sprockets with a large difference in teeth, maintaining consistent shifting behavior and sufficient chain guiding capacity, even with a large number of sprockets and significant differences in sprocket diameters, ensuring smooth operation uphill and downhill.
Implementation Method 1
a parallelogram four-bar linkage (34) connecting the attachment part (26) with the moving part (32) of the rear chain guide (24)
Data Source
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AI summary
A drive arrangement for a bicycle comprises a front chainring (20), a plurality (12) of coaxial rear sprockets (14, 16, 18), a circulating drive chain (22) which is in meshing engagement with a selected active sprocket and with the chainring (20), and a rear chain guide (24) with a tensioning derailleur (32, 40), wherein the tensioning derailleur (32, 40) has a tensioning device (40) with two chain guide rollers (42, 44) having chain guide roller axes (F42, F44) that are parallel to each other and to the common sprocket axis (R), wherein the rear chain guide (24) has a mounting part (26) that is fixed with respect to the sprocket axis (R) and a moving part (32) that is movably connected to the mounting part by a parallelogram four-bar linkage (34), wherein the four linkage axes (G1, G2, G3, G4) of the parallelogram four-bar linkage (34) regardless of the selected relative position of the tension derailleur (32,40) are aligned orthogonally to the pinion axis (R), wherein the constant first distance (L) of the chain guide roller axis (F42) closer to the pinion is shorter than the constant second distance (H) of the chain guide roller axis (F44) further from the pinion is shorter than the tensioning swivel axis (S), and a first connecting plane (E1) containing the chain guide roller axis (F42) closer to the pinion and the tensioning swivel axis (S) forms an angle of most preferably 55° to 60° with a second connecting plane (E2) containing the chain guide roller axis (F44) further from the pinion and the tensioning swivel axis (S).