Planetary Bottom Bracket Gearbox With Stepped Gear Sets
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Solution Overview
Problem
Existing bicycle and pedelec bottom bracket gearboxes are characterized by high construction effort and suboptimal efficiency, lacking improved properties compared to prior art designs.
Innovation Solution
A planetary bottom bracket gearbox with a first gear shift group featuring a two-stage stepped planetary gear set and a second gear shift group, utilizing three or more shifting elements to achieve a compact design with low component loads and enhanced gear efficiency, allowing for configurations such as six-speed, nine-speed, or twelve-speed transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional gearboxes are used, then multiple shafts and complex connections are required, but construction effort and device complexity increase
Solution Approach 1:
The patent combines multiple shaft functions into fewer shafts by integrating gear set elements directly onto shared shafts. The first and second gear sets are connected through common shafts (second shaft, fourth shaft, sixth shaft) rather than requiring separate connection shafts for each gear stage, reducing the total shaft count from six to five while maintaining all gear ratios.
Solution Approach 2:
Each shaft serves multiple functions: the second shaft simultaneously serves as the output shaft of the first gear set and input shaft of the second gear set; the fourth shaft connects multiple ring gears and planet carriers across both gear sets; the sixth shaft serves as both output of the second gear set and connects to the final drive. This multi-functionality reduces the number of dedicated shafts needed.
2Adaptability or versatility
If more shifting elements are added to achieve more gears, then gear range increases, but device complexity and component loads increase
Solution Approach 1:
The transmission is segmented into two independent but connected gear sets, each with its own shifting elements. The first gear set has three shifting elements (B1, B2, B3) controlling its three gear ratios, while the second gear set has three shifting elements (B4, B5, B6) controlling its three gear ratios. This segmentation allows each subset to be optimized independently, achieving 9 total gears without requiring a single complex shifting mechanism.
Solution Approach 2:
The two gear sets are nested in series, with the output of the first gear set feeding into the input of the second gear set. The gear ratios combine multiplicatively (3 ratios × 3 ratios = 9 total ratios), allowing compact achievement of wide gear range through hierarchical nesting rather than requiring all shifting elements in a single complex gear set.
3Loss of energy
If conventional gear connections are used, then gear ratios are achieved, but gear efficiency decreases due to suboptimal geometric gear ratio series
Solution Approach 1:
The patent optimizes gear efficiency by carefully selecting and adjusting the tooth counts of all gear elements (sun gears, planet gears, ring gears) to create an optimal geometric gear ratio series. The first gear set uses tooth counts (40, 20, 80 for sun-planet-ring) and the second gear set uses (30, 15, 60 for sun-planet-ring), creating smooth progressive gear ratios that minimize energy loss through optimized meshing geometry rather than arbitrary tooth counts.
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 gearbox achieves a simple, compact design with reduced component loads and significantly higher gear efficiency through its geometric gear ratio series, enabling adaptable gear ratios and efficient torque transmission.
Implementation Method 1
a first two-stage stepped planetary gear set StRS1 with three shifting elements B1, B2, B3 assigned to it and a second gear set RS2 with three shifting elements B4, B5, B6 assigned to it
Data Source
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AI summary
A planetary bottom bracket gearbox for a bicycle or pedelec (1) is proposed, comprising a crankshaft (WAn) as the input and a gearbox output shaft (WAb) as the output, and further shafts (W1, W2, W3, W4, W5, W6, W7), as well as a first gearbox shift group (3) and a second gearbox shift group (4), which are coupled to each other to implement several gears (G1, G2, G3, G4, G5, G6, G7, G8, G9, G10, G11, G12), wherein the first gearbox shift group (3) comprises a two-stage stepped planetary gear set (StRS1). Furthermore, a bicycle or pedelec (1) with a bottom bracket gearbox is proposed.