Variable-Arm Pedal Crank Mechanism for Lightweight Bicycles
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Solution Overview
Problem
Existing bicycle pedal crank mechanisms are either too complex, prone to jamming, or ineffective in varying lever arm length without compromising pedaling efficiency and are not suitable for lightweight bicycles due to their weight and dimensions.
Innovation Solution
A double variable-arm push lever mechanism with a kinematic guide assembly that allows the lever arm to change length during pedaling, reducing overall dimensions and weight, and ensuring smooth operation by guiding the translational motion of the pedal projections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a telescopic pedal crank is used to vary lever arm length, then the lever arm can be lengthened/shortened during pedalling, but the device becomes heavier and more complex with box-shaped bodies that are prone to jamming
Solution Approach 1:
The patent extracts the problematic box-shaped body and telescopic rod mechanism from the pedal crank design. Instead, it uses a simplified approach where the pedal is directly connected to the crank arm, and the variable lever arm effect is achieved through the natural rotation of the pedal within the crank arm structure, eliminating the need for separate telescopic components.
Solution Approach 2:
The pedal crank mechanism is segmented into distinct functional components: the crank arm, the pedal, and the connection pivot. This segmentation allows each component to perform its specific function independently, with the pedal rotating freely within the crank arm to achieve variable lever arm length without requiring complex integrated structures.
2Adaptability or versatility
If an eccentric axis mechanism is used to lengthen/shorten the lever arm, then the lever arm can be varied by a distance equal to the eccentricity, but the pedal cannot effectively transmit motion to the crank without a kinematic guide assembly
Solution Approach 1:
The pedal is designed to rotate freely within the crank arm structure, using its own rotational motion to achieve the variable lever arm effect. The pedal's rotation within the fixed crank arm naturally creates the eccentric motion pattern without requiring external kinematic guide assemblies or additional actuation mechanisms.
3Device complexity
If a fixed-length lever is used, then the structure is simple and reliable, but the rotation speed cannot be varied without intervening on transmission ratio and thrust force
Solution Approach 1:
The pedal crank mechanism transitions from a static fixed-length lever to a dynamic system where the effective lever arm length varies during rotation. The pedal's rotational freedom within the crank arm creates a dynamic lever arm length that changes with the rotation angle, enabling rotation speed variation without changing the physical structure or transmission ratio.
Data Source
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AI summary
The invention is a mechanism (100) for generating a rotational motion, comprising a central pivot (P) and two push levers or pedal cranks (10). Each pedal crank (10) is constituted by a single rectilinear rod (11) constrained between two heads (12, 13), wherein said first head (12) is rigidly associated with said central pivot (P), and wherein a freely rotating pedal (20) is mounted on said second head (13), which in turn is rigidly associated with said rod (11). Said rod (11) can slide in a through hole (121) present in said first head (12) between a first position of maximum distance (M), in which said second head (13) and thus said pedal (20) are at the maximum distance from said pivot (P), and a second position of minimum distance (m), in which said second head (13) and thus said pedal (20) are at the minimum distance from said pivot (P).