Power Smoothing Crank Arm Spring Assembly Torque Control
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Solution Overview
Problem
Existing bicycle crank systems experience torque spikes and valleys during pedaling, leading to reduced drive wheel traction, muscle fatigue, and decreased power output, with existing solutions being costly, incompatible with conventional frames, or unsuitable for various riding conditions.
Innovation Solution
A crank arm design featuring a first member pivoting about a crank axis and a second member rotationally coupled with a spring assembly that biases the second member towards a neutral rotation configuration, storing and releasing energy to smooth the torque curve, thereby reducing torque spikes and valleys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a spring assembly is added to smooth the torque curve, then torque spikes are reduced and power output is improved, but device complexity increases
Solution Approach 1:
The spring assembly is nested within the crank arm structure itself, with the spring housed inside the crank arm body. This integration allows the power smoothing function to be added without requiring separate external components or significant structural modifications to the crank mechanism.
Solution Approach 2:
The spring assembly changes the mechanical parameters of the crank system by introducing elastic deformation capability. The spring constant and pre-load are optimized to provide the desired torque smoothing effect, transforming the rigid crank into a compliant mechanism that can absorb and release energy.
2Power
If variable length crank arm is used to store energy, then torque curve is smoothed, but pedal path becomes undesirable causing stress on rider's joints
Solution Approach 1:
The crank arm is divided into two separate members: a first member that pivots about the crank axis and a second member that is rotationally coupled to the first member and receives the pedal. This segmentation allows the spring assembly to be integrated between the two members, enabling energy storage while maintaining a fixed pedal path.
Solution Approach 2:
The spring assembly acts as an intermediary element between the first and second crank members. It provides the energy storage function through elastic deformation while allowing the pedal interface to maintain its optimal fixed position, thereby avoiding any adverse effects on the rider's joints.
3Power
If oval chain ring is used to decrease torque peaks, then torque curve is improved, but gear shifting becomes more difficult and chain rattling increases
Solution Approach 1:
Instead of modifying the chain ring shape as in conventional oval cranksets, this invention inverts the approach by modifying the crank arm geometry and adding a spring assembly. The crank arms are made non-circular with varying distance from the crank axis to the pedal interface, achieving torque smoothing through crank geometry rather than chain ring shape.
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 power output and speed by up to 2% and reduces rider fatigue and joint stress, while increasing drive wheel traction and compatibility with conventional frames.
Implementation Method 1
a spring assembly configured to bias the second member towards a neutral rotation configuration relative to the first member and to resist rotation of the second member away from the neutral rotation configuration
Implementation Method 2
storing and releasing energy to smooth the torque curve
Data Source
AI summary
A crank arm for a pedal-driven vehicle is described herein. The crank arm includes a first member that pivots about a crank axis of the pedal-driven vehicle and a second member rotationally coupled to the first member and configured to receive a pedal. The crank arm further includes a spring assembly configured to bias the second member towards a neutral rotation configuration relative to the first member and to resist rotation of the second member away from the neutral rotation configuration, wherein a distance between the crank axis and the pedal interface is greater than a distance between the crank axis and the member pivot point when the second member is in the neutral rotation configuration.