Bicycle Eccentric Bottom Bracket for Chain Tension Adjustment
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Solution Overview
Problem
Existing methods for chain tensioning on bicycles, such as horizontal rear dropouts, can lead to slippage and misalignment issues, particularly when trying to align disk brakes, and do not effectively maintain chain tension.
Innovation Solution
An eccentric bottom bracket assembly that includes two members with flanges to secure the bottom bracket in place, allowing rotation to adjust the distance between the crank and hub sprockets, thereby adjusting chain tension without requiring special frame modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a horizontal rear dropout is used to adjust chain tension, then the distance between sprockets can be changed, but the axle may slip and the wheel may become misaligned
Solution Approach 1:
The bottom bracket is divided into two separate members that can rotate independently within the bottom bracket shell. This segmentation allows the crank bearing assembly to be positioned at different distances from the hub sprocket, enabling chain tension adjustment without moving the rear axle or wheel, thus preventing slippage and misalignment issues.
Solution Approach 2:
The bottom bracket members are designed to rotate dynamically within the bottom bracket shell, allowing the crank bearing assembly to move between different positions. This dynamic adjustment mechanism enables chain tension modification while maintaining fixed wheel and brake caliper positions, eliminating the alignment problems associated with horizontal rear dropouts.
2Ease of operation
If the rear axle position is changed within the rear dropout to adjust chain tension, then chain tightness can be modified, but disk brake alignment becomes difficult
Solution Approach 1:
By segmenting the bottom bracket into two rotatable members, the system separates the chain tension adjustment function from the wheel and brake alignment functions. The crank bearing assembly can be repositioned to adjust chain tension while the rear axle and wheel remain fixed in the dropout, keeping the disk brake aligned with the brake caliper.
Solution Approach 2:
The rotatable bottom bracket members act as intermediaries between the crank bearing assembly and the fixed frame. They transmit the adjustment motion to change chain tension while isolating the wheel and brake system from this motion, thereby maintaining brake alignment without requiring manual realignment after tension adjustment.
3Reliability
If flanges are added to prevent member sliding through the bottom bracket shell, then the bottom bracket is secured in place, but the device complexity increases
Solution Approach 1:
The bottom bracket is segmented into two members, each with its own flange. This segmentation allows each member to be independently secured to the bottom bracket shell, providing reliable attachment while keeping each individual member relatively simple in structure.
Solution Approach 2:
Instead of creating a complex locking mechanism or using set screws to prevent sliding, the design inverts the approach by using simple flanges that press against the sides of the bottom bracket shell. The flanges provide security through their position and the friction they create, eliminating the need for additional fastening components.
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
Provides a reliable and adjustable chain tensioning system that prevents slippage and misalignment, ensuring proper brake alignment and chain tightness across a range of orientations.
Implementation Method 1
the flanges press against the sides of the bottom bracket shell, holding the eccentric bottom bracket together and securing it in place
Implementation Method 2
An eccentric bottom bracket and an associated method for adjusting the tension of a bicycle chain are provided. The eccentric bottom bracket includes two members, each having a body, a flange, and an eccentric opening for a crank bearing assembly
Data Source
AI summary
An eccentric bottom bracket for a bicycle. The eccentric bottom bracket includes opposing first and second members. The first member and the second member each include a body and a flange. Each body is sized and shaped to penetrate an opening of a bottom bracket shell of a bicycle. Each flange is sized and shaped to prevent complete admittance of the member into the bottom bracket shell. Each body also has a bearing guide with an axis that is parallel to but offset from a center axis of the bottom bracket shell when that body is fit into the bottom bracket shell. The eccentric bottom bracket also includes a tightening assembly for selectively applying a compressive force between the body of the first member and the body of the second member. The compressive force secures the first member and the second member to the bottom bracket shell.