Extendable Bicycle Cranks With Eccentric Telescopic Mechanism
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Solution Overview
Problem
Existing bicycle pedaling mechanisms with variable crank arm lengths, such as those using elliptical trajectories, are unreliable and counterproductive at high cadences, as they deviate from natural pedaling dynamics, leading to inefficient energy transfer.
Innovation Solution
A device with crank arms that extend during forward pedaling and shorten during backward pedaling, utilizing an eccentric mechanism integrated into conventional crank arms, allowing for progressive length adjustment without gears, ensuring comfortable and reliable pedaling by maintaining a circular motion with varying lever arm length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If variable geometry crank mechanisms with elliptical trajectories are used to extend crank arms during driving phase, then pedaling efficiency is improved, but the mechanism complexity and reliability deteriorate due to complex gear systems
Solution Approach 1:
The patent extracts the gear transmission system from the variable crank mechanism, replacing it with a direct telescopic extension structure. The crank arm extends and retracts directly through the telescopic mechanism without requiring intermediate gear conversions, thereby simplifying the overall structure while maintaining the variable geometry function.
Solution Approach 2:
The patent implements a dynamic crank arm length adjustment mechanism where the crank arm telescopes to change its effective length during the pedaling cycle. The crank arm transitions from a fixed length to a variable length structure, allowing the radius to be dynamically adjusted according to the pedaling phase, thereby improving pedaling efficiency without complex gears.
2Force
If elliptical trajectory mechanisms are employed to vary crank arm length, then force application is optimized, but the natural pedaling dynamics are disrupted leading to counterproductive effects at high cadences
Solution Approach 1:
The patent maintains natural pedaling dynamics by allowing the crank arm to rotate freely in a circular trajectory while simultaneously varying its length. The telescopic mechanism adjusts the crank arm radius dynamically during rotation, preserving the natural circular motion of the pedal while optimizing force application through variable lever arm length.
Solution Approach 2:
The patent implements periodic extension and retraction of the crank arm that synchronizes with the pedaling cycle. The crank arm extends during the downward driving phase when force is applied and retracts during the upward return phase, creating a periodic variation in lever arm length that enhances force application without disrupting the natural rhythm of pedaling.
3Productivity
If telescopic crank arms with gear systems are used to achieve variable length, then lever arm optimization is achieved, but reliability deteriorates due to additional moving parts and potential failure points
Solution Approach 1:
The patent removes the gear transmission system entirely from the variable crank mechanism, replacing it with a direct telescopic extension structure. The crank arm extends and retracts directly through the telescopic mechanism without requiring intermediate gear conversions, thereby simplifying the overall structure while maintaining the variable geometry function.
Solution Approach 2:
The telescopic crank mechanism is designed to automatically extend and retract based on the rotational position and forces applied during pedaling. The mechanism uses the pedaling motion itself to drive the extension and retraction, eliminating the need for separate control systems or additional actuating mechanisms, thereby improving reliability.
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 solution provides increased pedaling momentum with progressive extension, maintaining natural pedaling dynamics and reliability by ensuring the pedals remain essentially horizontal, enhancing user comfort and efficiency without the need for complex gear systems.
Implementation Method 1
The pedal (11) rotates within a bearing
Implementation Method 2
an eccentric disk (9) is fixed to the shaft (10), the eccentric shaft (7) of which is coupled to a second crank arm (6)
Implementation Method 3
The movement of the extension existing on the main crank arm is effected by means of a linear bearing
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A bicycle pedal with extendible crank arms wherein both crank arms incorporate an extension (4) which incorporates a bearing for a shaft (10), the corresponding pedal (7) fixed to the outer end thereof, and the inner end is joined axially to an eccentric disk (9), the eccentric shaft (7) of which is coupled to a second crank arm (6) which is coupled at a fixed point (8) to the main crank arm (3), such that rotating the shaft (10) of the pedal causes the movement of the extension (4), extending or shortening the length of the pedaling lever formed by the crank arm (3) and the corresponding extension thereof (4) depending on whether the pedal is in a position of impulsion or retraction, respectively.