Bicycle Crank Arm Noise Reduction via Damping Element
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Solution Overview
Problem
Racing bicycle right crank arm assemblies with multiple toothed crowns generate annoying noise during operation, particularly in the 'maximum crossover' condition, due to chain contact with pins on the larger toothed crown, which is amplified by solid composite material crank arms acting as a 'sound box'.
Innovation Solution
Incorporating a damping element between the right crank arm and the toothed crown, made from materials like closed cell polyurethane foam, nitrile rubber, or polypropylene, to absorb the axial displacement and friction-induced impulses, thereby reducing noise transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pins are provided on the inner face of the toothed crown having the greater diameter to facilitate gear shifting, then gear shifting is facilitated, but chain contact with the pins produces annoying noise
Solution Approach 1:
A damping element is introduced as an intermediary component between the toothed crown and the crank arm. This damping element absorbs the impulses generated by chain contact with the pins, converting mechanical vibration into heat energy through internal friction. The damping element thus mediates between the noise-generating pins and the crank arm, eliminating the harmful noise while preserving the gear-shifting function of the pins.
Solution Approach 2:
The harmful noise generated by chain contact with the pins is converted into a beneficial damping effect. The damping element is specifically designed to absorb the axial displacement impulses caused by chain-pins interaction, transforming the harmful vibrational energy into heat through material damping. This converts the previously harmful noise-generating mechanism into a controlled energy dissipation process that reduces overall system noise.
2Strength
If a solid composite material crank arm is used, then the crank arm structure is simplified and strength is improved, but the crank arm amplifies noise acting as a sound box
Solution Approach 1:
The damping element serves as an intermediary that decouples the noise transmission path from the strong crank arm structure. By placing the damping element between the toothed crown and the crank arm, it intercepts and absorbs vibrational impulses before they can propagate through the high-strength composite crank arm, preventing the crank arm from acting as a sound box while maintaining its structural integrity.
Solution Approach 2:
The damping element changes the vibrational parameters of the crank arm assembly by introducing energy dissipation mechanisms. The damping material alters the frequency response and vibration amplitude characteristics of the system, converting high-amplitude noise-generating vibrations into low-amplitude damped oscillations, thereby changing the acoustic output of the crank arm structure.
3Object-generated harmful factors
If a damping element is added between the crank arm and toothed crown, then noise is reduced, but device complexity increases
Solution Approach 1:
The damping element is designed to fit within the existing interface space between the toothed crown and the crank arm, utilizing the available axial clearance. This nested arrangement allows the damping element to be accommodated without significantly increasing the overall assembly dimensions or requiring major structural modifications, thus minimizing the increase in device complexity while achieving noise reduction.
Solution Approach 2:
The damping element is implemented as a thin-walled or thin-film structure that provides effective damping with minimal material volume. This thin-film approach allows the damping element to be easily integrated into the existing assembly without adding significant complexity, while still providing sufficient surface area for effective vibration absorption and noise reduction.
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 damping element significantly reduces noise generated by chain contact with the pins, providing a noticeable reduction in operational noise, especially effective in solid composite material crank arms, and also protects the damping element from dirt and wear with a polyvinyl chloride coating.
Implementation Method 1
at least one damping element arranged between the right crank arm and the toothed crown and in abutment against respective faces of the right crank arm and the toothed crown
Implementation Method 2
absorb the axial displacement and friction-induced impulses
Implementation Method 3
protects the damping element from dirt and wear with a polyvinyl chloride coating
Data Source
AI summary
A right crank arm assembly for a bicycle has a right crank arm and at least one toothed crown that is coupled to the right crank arm. At least one damping element is arranged between the right crank arm and the toothed crown to be in abutment against respective faces of the right crank arm and the toothed crown.