Bicycle Gearshift Actuation Device Closed-Loop Indexing
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Solution Overview
Problem
Existing actuation devices for bicycle gearshifts are limited in the number of toothed wheels they can support due to the restricted stroke of the control cable, which restricts the number of gear ratios and requires a larger excursion of the rear derailleur, exceeding the radial space available in the casing.
Innovation Solution
The actuation device features a cable-winding bush with a closed-loop fastening track and multiple stop positions, allowing for increased angular positions and stroke length, enabling operation with a greater number of toothed wheels by optimizing the indexing angles and using two pointers to distribute forces effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of toothed wheels is increased to provide more gear ratios, then the number of gear ratios is improved, but the stroke of the control cable must be increased which exceeds the radial space available in the casing
Solution Approach 1:
The patent transforms the linear stroke requirement into angular rotation by introducing a rotary member with a closed-loop fastening track. The control cable is converted from linear motion to rotational motion around the rotary member, allowing multiple gear ratios to be achieved through angular displacement rather than linear extension, thus avoiding the radial space constraint in the casing.
Solution Approach 2:
The rotary member is mounted within the existing casing structure, with the closed-loop fastening track nested around the rotary member. The control cable is wound around the rotary member in a compact manner, effectively nesting the cable path within the available radial space while still providing sufficient stroke for multiple gear ratios.
2Adaptability or versatility
If the stroke of the control cable is increased to support more toothed wheels, then the number of gear ratios is improved, but the rear derailleur excursion exceeds the available radial space
Solution Approach 1:
The patent converts the linear excursion requirement of the rear derailleur into angular rotation of the rotary member. By winding the control cable around the rotary member in a closed-loop configuration, the system achieves the necessary cable stroke through multiple rotations rather than linear extension, thereby reducing the radial excursion of the rear derailleur within the casing.
Solution Approach 2:
The rotary member introduces dynamic rotational motion to the previously static linear cable system. The closed-loop fastening track allows the control cable to dynamically wind and unwind around the rotary member, providing variable stroke lengths as needed for different gear ratios without requiring proportional increases in derailleur excursion.
3Reliability
If two pointers are used to distribute forces on the fastening track, then reliability is improved, but the device complexity increases
Solution Approach 1:
The two pointers are integrated into a single rotary member component, with both pointers fixed to the same rotating element. This merging approach allows force distribution across two engagement points on the fastening track while maintaining a unified structural component, thereby improving reliability without proportionally increasing device complexity.
Data Source
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AI summary
The invention relates to an actuation device (10) of the control cable of a bicycle gearshift comprising a casing (11), a cable-winding bush (13) mounted in the casing (11) rotatable about a rotation axis (X) in a first angular direction (A) between a first and a last angular position and in a second angular direction (B) between the last and the first angular position, a rotary member (14) mounted in the casing in a rotary manner about the rotation axis (X) and a stationary member (18) mounted in a non-rotary manner in the casing (11), wherein one from the two members is provided with at least one first pointer (15) engaged on a fastening track (19) formed on the other member, the fastening track (19) extending along a closed loop path and comprising at least one first plurality of stop positions (20) engageable in sequence by the pointer (15), the cable-winding bush (13) passing from one angular position to an adjacent angular position following the passage of the pointer (15) from one stop position to an adjacent stop position, each stop position being angularly spaced from an adjacent stop position by a respective indexing angle (C), a first stop position (20a) that determines the first angular position of the cable-winding bush (13) being angularly spaced from the next stop position (20b) by an indexing angle (C) equal to the indexing angle (C) necessary to make the cable-winding bush (13) rotate from the penultimate angular position to the last angular position.