Bicycle Derailleur Non-Circular Link Pin Torque Transmission
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Solution Overview
Problem
Existing bicycle derailleurs face challenges in efficiently and reliably shifting chains between sprockets due to limitations in the mechanical linkage and motor unit design, leading to inefficiencies and potential damage from torque transmission.
Innovation Solution
A bicycle derailleur design featuring a base member, linkage structure, and motor unit with a rotatable link pin and coupling parts of non-perfect circular profiles, including polygonal shapes and flat surfaces, to transmit rotational force effectively and securely, while minimizing gear complexity and maximizing flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional circular coupling part is used to transmit rotational force, then the structure is simple, but the transmission reliability is insufficient under high torque conditions
Solution Approach 1:
The coupling part employs an asymmetric non-circular profile (such as polygonal shapes like hexagons or octagons) instead of a traditional circular cross-section. This asymmetric geometry provides multiple flat surfaces that engage with corresponding surfaces on mating components, creating multiple contact points that distribute torque more effectively and prevent relative rotation under load, thereby significantly improving transmission reliability while maintaining reasonable structural complexity
Solution Approach 2:
The coupling part incorporates curved or rounded edges on its non-circular profile, transitioning between flat surfaces with rounded transitions. This curvature design reduces stress concentration at sharp corners, facilitates smoother engagement and disengagement, and maintains rotational movement while ensuring reliable torque transmission through the combination of flat contact surfaces and rounded transition zones
2Strength
If multiple gears are used in the motor unit to transmit rotational force, then the torque transmission is robust, but the gear structure becomes complex and prone to wear
Solution Approach 1:
The design extracts and eliminates unnecessary intermediate gears from the torque transmission path. By using the non-circular link pin coupling directly to transmit torque from the motor output to the linkage structure, the patent removes redundant gear stages, reducing structural complexity, minimizing wear points, and maintaining robust torque transmission capability through the direct mechanical coupling of the asymmetric profiles
Solution Approach 2:
The coupling part integrates multiple functions into a single component: it serves as both the torque transmission element and the rotational coupling mechanism. The non-circular profile combines torque transmission, rotational constraint, and positional encoding functions, eliminating the need for separate gears, couplings, and sensors, thereby reducing overall gear structure complexity while maintaining strength
3Measurement precision
If a complex linkage structure is used to control chain shifting, then the shifting precision is improved, but the mechanical wear and maintenance requirements increase
Solution Approach 1:
The non-circular link pin coupling serves multiple functions simultaneously: it transmits torque, maintains precise rotational positioning, guides the linkage movement, and provides mechanical encoding of the shifting position. This multi-functionality eliminates the need for separate precision positioning mechanisms, reducing the number of moving parts subject to wear while maintaining high chain shifting precision through the geometric constraints of the asymmetric profile
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
The design enhances the reliability and efficiency of chain shifting by ensuring precise and robust transmission of rotational force, reducing wear and tear, and simplifying the construction of the gear structure, thereby protecting the motor from excessive torque.
Implementation Method 1
The motor unit is configured to apply rotational force to the first link pin to rotate the first link pin relative to the base member about the first pivot axis
Implementation Method 2
The first coupling part has a first profile other than a perfect circle as viewed along the first pivot axis. The second coupling part has a second profile other than a perfect circle as viewed along the first pivot axis
Data Source
AI summary
A bicycle derailleur comprises a base member, a linkage structure, and a motor unit. The linkage structure includes a first link pin rotatably mounted to the base member about a first pivot axis. The motor unit is configured to apply rotational force to the first link pin to rotate the first link pin relative to the base member about the first pivot axis.