Bicycle Gearshift Actuation Device with Extra-Stroke Clearance
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Solution Overview
Problem
Existing actuation devices for bicycle gearshifts often fail to ensure reliable upward gearshifting, resulting in 'refused gearshifting' where the transmission chain does not engage the toothed wheel with a larger diameter.
Innovation Solution
An actuation device with a coupling providing a predetermined circumferential clearance corresponding to a gearshifting extra-stroke angle between the cable-winding bush and the indexing bush, allowing an additional rotation stroke to ensure proper engagement with the next larger toothed wheel during upward gearshifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional coupling between cable-winding bush and indexing bush is used, then the device structure is simple, but upward gearshifting reliability is poor due to refused gearshifting
Solution Approach 1:
The coupling is pre-configured with a circumferential clearance corresponding to an extra-stroke angle, which is established during manufacturing. This preliminary geometric configuration ensures that when upward gearshifting is actuated, the cable-winding bush automatically rotates through the additional extra-stroke angle before the indexing bush engages, guaranteeing reliable chain engagement with the larger diameter toothed wheel without requiring complex control mechanisms.
2Reliability
If the cable-winding bush is directly connected to the indexing bush, then the mechanism is simple, but the chain may not engage the larger diameter toothed wheel properly
Solution Approach 1:
The coupling's circumferential clearance parameter is specifically designed to correspond to a predetermined extra-stroke angle. This parameter change from a direct connection (zero clearance) to a controlled clearance connection modifies the rotational kinematics, allowing the cable-winding bush to rotate through an additional angle range that ensures the chain has sufficient travel to engage the larger diameter toothed wheel reliably.
3Reliability
If a coupling with circumferential clearance is introduced, then gearshifting reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The circumferential clearance with the specific extra-stroke angle correspondence is established as a preliminary geometric feature during coupling manufacturing. By pre-configuring this clearance parameter, the design converts a potential precision challenge into a manufacturable feature that can be controlled through standard machining tolerances, while ensuring the functional reliability of gearshifting through the built-in geometric relationship.
Data Source
AI summary
A bicycle control cable actuation device having: a casing, configured for fixing to bicycle handlebars, a cable-winding bush, on which the control cable is wound and which is angularly mobile in the casing about a main axis of the device, an indexing bush that is coaxial to and associated with the cable-winding bush to removably hold the cable-winding bush in predetermined positions that are angularly spaced from each other by predetermined indexing angles, a manoeuvring mechanism, operative on the cable-winding bush to rotate it in a first angular direction about the main axis of the device, to obtain an upward gearshifting; and, a predetermined circumferential clearance corresponding to a predetermined gearshifting extra-stroke angle is provided between the cable-winding bush and the indexing bush.