Bicycle Front Fork Upper Frame Axial Rib Design
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Solution Overview
Problem
Conventional bicycle front forks, particularly those made of carbon fiber reinforced resin, are prone to damage from stress parallel to the forward and backward directions, and the fork crown is vulnerable to axial stress from the fork tubes, necessitating an enhancement in structure strength.
Innovation Solution
The design incorporates an upright tube with an axial rib and two branch tubes with parallel axial ribs, which enhance structural strength by partitioning the tubes into chambers, allowing for improved stress distribution and connection of fork tubes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional carbon fiber reinforced resin front fork structure is used, then manufacturing simplicity is maintained, but structure strength is insufficient to bear stress from front wheel
Solution Approach 1:
The upright tube is segmented into multiple sections with different wall thicknesses along its length, creating variable structural strength where the upper section has greater thickness to withstand bending moments from the front wheel, while the lower section has reduced thickness. This segmentation allows the fork to achieve high strength where needed without uniformly increasing complexity throughout the entire structure.
Solution Approach 2:
Different sections of the upright tube are given different wall thicknesses to match the local stress distribution - the upper section experiences higher bending stresses and is designed with greater wall thickness, while the lower section experiences less stress and has thinner walls. This local quality variation optimizes strength-to-weight ratio and resolves the contradiction between overall strength and structural simplicity.
2Strength
If uniform wall thickness is used in upright tube, then manufacturing simplicity is maintained, but stress distribution is inadequate under front wheel load
Solution Approach 1:
The wall thickness parameter of the upright tube is varied continuously or in steps along its length, transitioning from greater thickness at the upper section to smaller thickness at the lower section. This parameter change optimizes the stress bearing capacity by matching material distribution to the bending moment diagram, while remaining manufacturable through conventional carbon fiber molding techniques.
3Strength
If greater wall thickness is used throughout upright tube, then structure strength is improved, but weight increases
Solution Approach 1:
The upright tube is divided into sections with different wall thicknesses, allowing concentrated material placement only in the upper high-stress region rather than uniformly throughout. This segmentation achieves the required strength at the critical loading point while minimizing material usage and overall weight of the front fork assembly.
Solution Approach 2:
The wall thickness is locally increased only in the upper section where bending stresses from front wheel contact are maximum, while the lower section maintains thinner walls. This local quality differentiation provides the necessary strength where needed without adding unnecessary weight to the entire fork structure.
Data Source
Figure 1
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AI summary
An upper frame of a front fork (10) for a bicycle includes an upright tube (20) and two branch tubes (30). The upright tube (20) has an axial rib (22). The two branch tubes (30) extend bilaterally from a bottom end of the upright tube (20) and each have an axial rib (32) parallel substantially to a longitudinal direction (A) of the upright tube (20) and a connecting portion (34) located at an end of the branch tube (30) for connection of a fork tube. Thus, the structure strength of the upright tube (20) can be enhanced by the axial rib (22) thereof, and the structure strength of the branch tubes (30) can be enhanced by the axial ribs (32) thereof to bear stress generated from the fork tubes.