Adjustable Elliptical Sprocket Crank Assembly
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Solution Overview
Problem
Conventional bicycle crank assemblies with circular sprockets experience suboptimal power transfer, especially on inclined terrain, and elliptical sprockets also fail to maintain optimal power stroke in such conditions.
Innovation Solution
A crank assembly with a carrier shaft slidably mounted on the crank axle, allowing the elliptical sprocket's start time of the power stroke to be adjusted by sliding the carrier shaft relative to the crank axle, facilitated by a lever and potentially an inclination sensor and controller for terrain adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional circular sprocket is used, then the structure is simple, but the power transfer is suboptimal especially on inclined terrain
Solution Approach 1:
The patent applies the dynamics principle by making the sprocket adjustable from a fixed circular shape to a variable elliptical shape. The carrier shaft can slide along the crank axle to change the elliptical orientation, allowing the sprocket to adapt its geometry dynamically based on terrain conditions. This enables optimal power stroke timing on inclined terrain while maintaining simplicity through a single adjustable mechanism rather than multiple fixed components.
2Productivity
If an elliptical sprocket is used, then power transfer is improved on flat terrain, but power stroke remains suboptimal on inclined terrain
Solution Approach 1:
The patent resolves this contradiction by implementing a dynamic adjustment mechanism. The carrier shaft can slide along the crank axle to change the elliptical orientation of the sprocket. On flat terrain, the sprocket maintains a fixed elliptical shape optimized for horizontal cycling. On inclined terrain, the carrier shaft can be repositioned to adjust the elliptical angle, allowing the sprocket to adapt to the changing terrain conditions and maintain optimal power stroke timing.
Solution Approach 2:
The patent applies parameter changes by modifying the geometric parameters of the elliptical sprocket. Specifically, the orientation angle of the elliptical major axis can be changed by sliding the carrier shaft along the crank axle. This parameter adjustment allows the sprocket to optimize its power stroke characteristics for different terrain conditions, transforming it from a fixed-geometry device to one that can adapt its shape parameters to match operational requirements.
3Adaptability or versatility
If the carrier shaft is made adjustable to change power stroke timing, then adaptability to terrain is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the carrier shaft to serve multiple functions: it supports the elliptical sprocket, enables timing adjustment through sliding motion, and provides a mechanism for changing the elliptical orientation. The same component (carrier shaft) handles both the structural support function and the adjustment function, reducing the need for separate dedicated adjustment mechanisms and thereby limiting the increase in overall device complexity.
Solution Approach 2:
The patent resolves this contradiction through a simple dynamic mechanism where the carrier shaft can slide along the crank axle. This single sliding degree of freedom provides sufficient adjustability to change power stroke timing for different terrain conditions without requiring complex multi-degree-of-freedom adjustment systems. The dynamic capability is achieved through a straightforward linear sliding motion rather than through complicated mechanical linkages or electronic controls.
Data Source
AI summary
A crank assembly for a bicycle includes a crank axle rotatably mounted to a frame of the bicycle, and a carrier shaft slidably mounted on the crank axle and configured to slide in a direction substantially parallel to a central longitudinal axis of the crank axle and relative to the crank axle. The crank assembly also includes an elliptical sprocket mounted on the carrier shaft. The elliptical sprocket rotates to move the bicycle in response to a rotation of the crank axle. A start time of a power stroke of the elliptical sprocket is changed by sliding the carrier shaft relative to the crank axle.