Bicycle Power-Saving Crank with Offset Outer Arm
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing bicycle driving structure, particularly the crank mechanism, faces inefficiencies in force transmission during the upstroke phase of pedaling, especially for riders using regular shoes without clipless pedals.
Innovation Solution
The bicycle power-saving crank incorporates a base arm and an outer arm, where the outer arm is offset relative to the base arm, increasing the lever arm length and shifting the dead spot position forward, enhancing force transmission and pedaling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the crank length is increased to improve force transmission during upstroke, then the lever arm length increases and power transmission improves, but the device complexity increases due to additional components
Solution Approach 1:
The crank is divided into two functional segments: a base arm connected to the chainwheel and an outer arm connected to the pedal. This segmentation allows each arm to have optimized functions - the base arm provides structural support while the outer arm extends the lever arm for improved force transmission during upstroke phase.
Solution Approach 2:
The outer arm is positioned offset outward in the travel direction relative to the base arm, creating a two-dimensional spatial arrangement. This dimensional change increases the effective lever arm length without proportionally increasing overall crank complexity, as the offset positioning allows the outer arm to engage the pedal at an optimized angle.
2Productivity
If the outer arm trajectory is offset outward to shift dead spot position and improve force transmission, then pedaling efficiency improves, but the crank structure becomes more complex
Solution Approach 1:
The outer arm trajectory is deliberately offset asymmetrically outward in the travel direction relative to the base arm trajectory. This asymmetric positioning shifts the dead spot position forward in the pedaling cycle, allowing effective force application during the upstroke phase when conventional symmetric cranks are least effective.
Solution Approach 2:
The offset trajectory positioning is designed to anticipate and prepare for the upstroke phase by shifting the dead spot position forward. This preliminary geometric arrangement ensures that the pedal is already in a favorable position for force application before the upstroke begins, improving overall pedaling efficiency.
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 design achieves a potential power savings of 50% by increasing the lever arm length and improving force transmission, especially during the upstroke phase, resulting in improved pedaling performance and energy savings.
Implementation Method 1
Through the addition of the outer arm, an additional length results in an increased lever arm length, achieving power saving.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A bicycle power-saving crank includes: a base arm, positioned on an outside of a chainwheel and connected at one end to the chainwheel, wherein the base arm is rotatable synchronously with the chainwheel; a base sprocket, fixed to the base arm and facing in the chainwheel; an outer sprocket, rotatably connected to the other end of the base arm via an outer spindle; a transmission component, rotatably connected to the base sprocket and the outer sprocket; and an outer arm, having one end rotatably connected to the outer spindle and rotatable synchronously with the outer sprocket and the other end rotatably connected to a pedal. Through the addition of the outer arm, an additional length results in an increased lever arm length, achieving power saving.