Bicycle Crank Assembly With Adjustable Sprocket Power Stroke
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Solution Overview
Problem
Conventional bicycle crank assemblies do not maintain optimal power transfer when riding on inclined terrain, leading to suboptimal power stroke and increased rider fatigue.
Innovation Solution
A crank assembly with a carrier shaft and actuator system that adjusts the start time of the power stroke based on terrain inclination and direction, using sensors and an electric motor to slide the sprocket relative to the crank axle, allowing for optimal power delivery and maintaining pedaling cadence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an oval or elliptical sprocket is used to improve power transfer, then power transfer is improved on flat terrain, but power stroke becomes suboptimal on inclined terrain
Solution Approach 1:
The patent applies dynamics by making the sprocket orientation adjustable rather than fixed. The carrier shaft can rotate relative to the crank axle, allowing the sprocket's major axis to be dynamically reoriented. This enables the power stroke to remain optimal whether the bicycle is on flat terrain or inclined terrain, resolving the contradiction between optimized power transfer and adaptability to different terrains.
2Power
If the power stroke timing is adjusted to maintain optimal power transfer on inclined terrain, then power delivery is improved, but device complexity increases
Solution Approach 1:
The patent merges the functions of power transmission and orientation adjustment into a single integrated mechanism. The carrier shaft simultaneously carries the sprocket and provides the rotation capability. The actuator system combines the electric motor, drive gear, and carrier shaft rotation into a unified mechanism that adjusts sprocket orientation, reducing overall system complexity while maintaining optimal power delivery.
Solution Approach 2:
The system uses sensors to detect terrain inclination and automatically actuates the carrier shaft rotation to maintain optimal power stroke timing. This self-adjusting capability eliminates the need for manual intervention and reduces the complexity of control mechanisms while ensuring consistent power delivery across varying terrain conditions.
3Device complexity
If a fixed sprocket orientation is used, then device complexity is reduced, but power stroke optimization is lost on inclined terrain
Solution Approach 1:
The patent transforms the fixed sprocket orientation into a dynamic, adjustable orientation. The carrier shaft's ability to rotate relative to the crank axle allows the sprocket to adapt its orientation based on terrain inclination. This dynamic capability maintains power stroke efficiency on inclined terrain while adding only moderate complexity through the carrier shaft and actuator mechanisms.
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
This solution provides consistent power delivery and reduced rider fatigue by adjusting the power stroke timing to align with gravitational forces, regardless of terrain changes, and allows for the use of asymmetric elliptical sprockets without affecting pedaling cadence.
Implementation Method 1
The actuator includes an electric motor, a screw adapted to be rotated by the electric motor, and a lever operatively coupled to the screw and engaged with the carrier shaft
Data Source
AI summary
A crank assembly for a bicycle includes a crank axle, crank arms mounted to the crank axle to rotate the crank axle, a carrier shaft slidably mounted on the crank axle and configured to slide relative to the crank axle, and a sprocket mounted on the carrier shaft. A position sensor determines a relative position of a diametric axis of the sprocket relative to a central longitudinal axis of the crank arm at an end of a power stroke. Further, an actuator is operatively coupled to the carrier shaft to slide the carrier shaft, and a controller is configured to actuate the actuator to slide the carrier shaft relative to the crank axle based on input from the position sensor to change a start time of the power stroke of the sprocket.