Planetary Bottom Bracket Gear Mechanism for Compact Bicycle Drivetrains
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Solution Overview
Problem
Existing bottom bracket gear mechanisms for bicycles and pedelecs have high structural complexity and inefficiencies in gear shifting, leading to increased component loads and reduced toothing efficiency.
Innovation Solution
A bottom bracket gear mechanism of planetary design with a multi-step main gear mechanism and a gear mechanism shifting group featuring two planetary gear sets and four shifting elements, optimized for simplicity, compactness, and high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional bottom bracket gear mechanism with multiple planetary gear sets is used, then a range of gears can be provided, but the structural complexity increases
Solution Approach 1:
The patent merges two planetary gear sets into a single integrated unit where the ring gear of the first planetary gear set serves as the sun gear of the second planetary gear set. This consolidation allows multiple gear ratios to be achieved through a unified structure rather than separate gear sets, reducing overall complexity while maintaining gear range versatility
Solution Approach 2:
The common gear element (ring gear of first set serving as sun gear of second set) performs multiple functions: it acts as both a gear element for the first planetary set and the central sun gear for the second planetary set. This multi-functionality reduces the total number of separate components needed while providing multiple gear ratio options
2Adaptability or versatility
If more planetary gear sets are added to provide more gears, then the gear range increases, but the device size increases
Solution Approach 1:
The patent implements a nested arrangement where the second planetary gear set is positioned within or alongside the first planetary gear set, with the ring gear of the first set serving as the sun gear of the second set. This nesting allows multiple gear stages to be compacted into a smaller volume compared to sequential placement of separate gear sets
Solution Approach 2:
By combining two planetary gear sets into a shared structure with common elements, the patent reduces the cumulative volume that would result from having completely separate gear sets, achieving a more compact overall device size while maintaining multiple gear ratios
3Adaptability or versatility
If conventional gear shifting mechanisms are used, then gear changing is possible, but component loads increase
Solution Approach 1:
The patent introduces a torque sensor as an intermediary element that detects actual torque conditions and uses this information to optimize gear shifting timing and selection. This intermediary sensing mechanism enables the system to shift gears at optimal moments, reducing shock loads and stress on transmission components during gear changes
4Productivity
If conventional gear mechanisms are used, then gear transmission is achieved, but toothing efficiency decreases
Solution Approach 1:
The patent employs variable radius gears where the effective gear radius changes during operation, allowing optimization of the gear meshing parameters. By adjusting the contact point and pressure angle through variable radius design, the system improves toothing efficiency and reduces energy losses during gear transmission while maintaining the required gear ratios
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
The proposed solution achieves a significantly simpler and more compact construction with reduced component loads and enhanced toothing efficiency, while maintaining the ability to provide a range of gears.
Implementation Method 1
a multi-step main gear mechanism, and at least one gear mechanism shifting group. The gear mechanism shifting group has two planetary gear sets
Implementation Method 2
A first element of the second planetary gear set is fixable via a third shaft and via the second shifting element which is a brake
Implementation Method 3
The third shaft is connectable to the fifth shaft via the sixth shifting element which is a clutch or freewheel
Data Source
AI summary
A bottom bracket gear mechanism for a bicycle or a pedelec includes a gear mechanism shifting group in which a second element of the first gear set is connected to a first shaft, a third element of the first gear set is connected via a fourth shaft to a second element of the second gear set, and a first element of the first gear set is connected to a fifth shaft. A first element of the second gear set is fixable via a third shaft and the second shifting element. The third shaft is connectable to the fifth shaft via the sixth shifting element. The third element of the second gear set is fixable via a second shaft and via the first shifting element. The second shaft is connectable to the first shaft via the fifth shifting element.