Bicycle Crank Axle Coupling Reducing Stress Concentration
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Solution Overview
Problem
Bicycle crank assemblies face stress concentration issues during pedaling due to the spline type connection between the crank arm and axle, leading to potential damage or deformation.
Innovation Solution
The bicycle crank assembly incorporates a unique axle coupling structure featuring full-length splines and short splines with truncated ends, creating recessed areas that reduce stress concentrations by strategically positioning these features along the axial direction of the crank axle receiving opening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a spline type connection is used to couple the crank axle to the crank arm, then the connection strength is improved, but stress concentration occurs during pedaling
Solution Approach 1:
The axle coupling structure is divided into multiple splines (at least three splines) arranged around the crank axle receiving opening. Each spline acts as an independent load-bearing element, distributing the pedaling force across multiple contact points rather than concentrating stress at a single interface, thus reducing stress concentration while maintaining connection strength
Solution Approach 2:
The splines are positioned at specific locations within the crank arm material. The material distribution is optimized locally at the spline positions to handle shear forces, while maintaining overall crank arm integrity. This localized reinforcement reduces stress concentration at the coupling interface without compromising the crank arm's lightweight design
2Weight of moving object
If the crank arm is made lightweight to reduce bicycle weight, then the overall weight is reduced, but the crank arm may deform under repeated pedaling loads
Solution Approach 1:
The crank arm is designed as a hollow tube with internal reinforcement structures. The hollow geometry provides weight savings while the internal structure (including the spline arrangement) provides structural integrity. This segmented approach allows the crank arm to be lightweight yet resistant to deformation under repeated pedaling loads
Solution Approach 2:
The crank arm utilizes composite construction combining hollow tubular geometry with internal reinforcement elements. This composite structure achieves optimal strength-to-weight ratio, preventing deformation under load while maintaining lightweight construction
3Stability of the object's composition
If full length splines are used to extend completely through the crank arm, then the connection rigidity is improved, but stress concentration increases at the end edges
Solution Approach 1:
The splines are designed with varying lengths - at least one spline has a truncated end that does not extend completely through the crank arm thickness. This creates a gradual transition in the coupling interface, reducing stress concentration at the end edges while maintaining sufficient rigidity for power transmission. The local modification at the spline ends prevents stress buildup without compromising overall connection strength
Data Source
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AI summary
A bicycle crank assembly is provided with a crank arm including a front side surface and a back side surface. The crank arm has a crank axle mounting portion with a crank axle receiving opening defined by an axle coupling structure. The axle coupling structure at least includes a plurality of full length splines and at least one short spline. The full length splines extends completely in an axial direction of the crank axle receiving opening from a first axial end edge to a second axial end edge. The short spline extends in the axial direction with a truncated end positioned adjacent one of the first and second axial end edges such that the at least one short spline does not extend completely from the other of the first and second axial end edges to the one of the first and second axial end edges.