Bottom Bracket Planetary Gearbox With Nested Coaxial Gear Sets
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Solution Overview
Problem
Existing bottom bracket gearboxes for bicycles and pedelecs require a large amount of installation space due to the use of multiple planetary gear sets and shift elements, leading to inefficiencies and increased component loads.
Innovation Solution
A bottom bracket gearbox design utilizing three coaxial planetary gear sets and five shift elements, including interlocking brakes and freewheel units, to achieve a compact and efficient gear shifting mechanism with a geometric transmission ratio range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple planetary gear sets and shift elements are used to achieve more gears, then the gear range is improved, but the installation space increases
Solution Approach 1:
The patent combines multiple planetary gear sets (first, second, and third planetary gear sets) into a single integrated bottom bracket gearbox assembly, where the gear sets share common structural elements and spatial arrangement. This merging approach allows the system to achieve a wide gear range through multiple planetary stages while maintaining a compact overall footprint that would be smaller than separate gear sets arranged in series
Solution Approach 2:
The patent employs a nested configuration where planetary gears are arranged concentrically around the crank axle, with multiple planetary gear sets positioned at different radial distances but sharing the same axial space. The shift elements are integrated within the planetary gear structure itself, nesting the shifting mechanism within the existing gear train rather than adding separate external components
2Adaptability or versatility
If more planetary gear sets are added to increase gear options, then the gear variety is improved, but the component complexity increases
Solution Approach 1:
The shift elements in the patent are designed to perform multiple functions: they simultaneously engage different planetary gear sets, control the connection between crank axle and planetary gears, and enable various gear ratio selections. This multi-functionality reduces the number of dedicated components needed, as each shift element can control multiple gear engagement states across different planetary stages
Solution Approach 2:
The patent divides the gearbox into modular planetary gear sets (first, second, and third planetary gear sets) that can be independently analyzed and manufactured, yet function together as an integrated system. Each planetary gear set can be designed with standardized components that are segmented for easier assembly and maintenance, reducing overall system complexity
3Adaptability or versatility
If more shift elements are used to implement additional gears, then the gear options are improved, but the component load increases
Solution Approach 1:
Multiple shift elements are combined into a unified shifting mechanism that controls engagement across all planetary gear sets simultaneously. Rather than having separate actuation systems for each gear change, the shift elements work together as an integrated system, distributing the mechanical load across multiple engagement points and reducing the force requirement at any single component
Data Source
AI summary
A bottom bracket planetary gearbox for a bicycle or a pedelec includes a crank axle, a gearbox output shaft, four additional shafts, five shift elements, and three planetary gear sets. The planetary gear sets are coaxial with the crank axle. The shift elements are engageable to implement at least six gears.