Bicycle Gearshift Actuation Device Extra-Stroke Coupling
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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 between the cable-winding bush and indexing bush featuring a predetermined circumferential clearance, allowing for a gearshifting extra-stroke angle, which ensures the transmission chain engages the next larger toothed wheel by providing an additional stroke beyond the indexing stroke.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coupling with predetermined circumferential clearance is introduced between cable-winding bush and indexing bush, then reliability of upward gearshifting is improved, but device complexity increases
Solution Approach 1:
The coupling between cable-winding bush and indexing bush is designed with predetermined circumferential clearance that provides an extra-stroke angle before indexing engagement. This preliminary movement ensures the chain is pulled far enough to reliably engage the next larger toothed wheel, preventing refused gearshifting before indexing occurs.
Solution Approach 2:
The invention modifies the coupling parameters by introducing a specific circumferential clearance corresponding to a predetermined gearshifting extra-stroke angle. This parameter change allows the cable-winding bush to rotate slightly relative to the indexing bush, providing additional cable pull beyond the standard indexing stroke to ensure reliable chain engagement.
2Reliability
If a gearshifting extra-stroke is provided beyond the indexing stroke, then the transmission chain reliably engages the next larger toothed wheel, but the device structure becomes more complex
Solution Approach 1:
The coupling mechanism provides preliminary movement (extra-stroke) of the cable-winding bush relative to the indexing bush before the indexing engagement occurs. This preliminary action pulls the chain additional distance to ensure it clears the current toothed wheel and reliably engages the next larger one, preventing refused gearshifting.
Solution Approach 2:
The cable-winding bush is nested within or coupled to the indexing bush, with the coupling allowing relative rotation up to the predetermined extra-stroke angle. This nested arrangement provides the extra-stroke function while maintaining a compact structure that doesn't significantly increase overall device complexity.
Data Source
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AI summary
The invention relates to an actuation device (10) for a control cable for a bicycle gearshift, comprising: - a casing (14), configured for fixing to bicycle handlebars, - a cable-winding bush (22), on which the control cable is wound and which is angularly mobile in the casing (14) about a main axis (A) of the device (10), - an indexing bush (26) coaxial to the cable-winding bush (22) and associated with it to removably hold the cable-winding bush (22) in predetermined angular positions, angularly spaced apart each other by predetermined indexing angles (α), - a manoeuvring mechanism (30), operative on the cable-winding bush (22) to rotate it in a first angular direction (R) about the main axis (A) of the device (10), to obtain an upward gearshifting. Between the cable-winding bush (22) and the indexing bush (26) it is provided a coupling (40) with a predetermined circumferential clearance (42) corresponding to a predetermined gearshifting extra-stroke angle (β).