Bicycle Crank Assembly Axial Fixing Member Design
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Solution Overview
Problem
Direct-mount bicycle crank assemblies often experience radial gaps between components, leading to reduced structural integrity and efficiency in securing the sprocket, which affects bending stiffness and torque transmission.
Innovation Solution
A bicycle crank assembly design featuring a fixing member with a base portion, projection, and threads that engage with the crank arm and axle, providing axial stability and torque transmission through a tubular shape and annular contact surfaces, along with a seal member to prevent contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixing member is used to secure the sprocket to the crank arm, then the sprocket can be firmly fixed, but radial gaps may exist between adjacent parts reducing bending stiffness
Solution Approach 1:
The invention addresses radial gaps by introducing axial contact through the contact part on the inner periphery of the base portion. This shifts the contact dimension from radial to axial, eliminating gaps in the axial direction while maintaining radial clearance for proper assembly and thermal expansion.
Solution Approach 2:
The contact part acts as an intermediary element between the fixing member and the crank arm/crank axle. It provides a dedicated contact surface that transmits axial forces and eliminates gaps without interfering with the radial positioning or thread engagement.
2Ease of operation
If multiple separate parts are used for the fixing member, then assembly may be complex, but using a single integrated base portion simplifies mounting
Solution Approach 1:
The invention merges the base portion into a single integrated component that incorporates the contact part on its inner periphery. This consolidation reduces the total number of parts and simplifies assembly while maintaining the gap-elimination function through the integrated contact surface.
3Strength
If the base portion is made solid, then manufacturing is simple, but making it tubular increases rigidity of the fixing member
Solution Approach 1:
The tubular configuration changes the cross-sectional geometry from solid to hollow, creating a moment of inertia that increases bending rigidity. This dimensional change in the cross-section provides structural strength while reducing material usage and facilitating assembly through the crank arm.
Data Source
AI summary
A bicycle crank assembly includes a fixing member for fixing a sprocket to a crank arm. The fixing member includes a radially-extending projection, to prevent the sprocket from moving relative to the crank axle in an axial direction, and an axially-extending base portion, which is secured to the crank arm. A contact part is provided on an inner periphery of the base portion and contacts the crank axle or is provided on the crank axle and contacts the base portion. The contact part permits force to be transmitted between the crank axle and the fixing member to limit flexing of the crank axle assembly.